Question: Which cardiac chambers are typically imaged on the short-axis view?

Choices:
- RA and RV
- RA and LA
- LA and LV
- RV and LV

Cardiovascular and MRA Quiz

The short axis view is typically used to show the left and right ventricles.


Question: What structure is optimally displayed on the so-called “candy-cane” view?

Choices:
- Thoracic aorta
- Circumflex artery
- Left main coronary artery
- Right coronary artery

Cardiovascular and MRA Quiz

The candy-cane view is an oblique sagittal section that lays out the ascending, transverse, and descending thoracic aorta and its proximal branches.


Question: Why might one wish to start two IV’s prior to MRI if stress testing is being performed?

Choices:
- The second serves as backup in case the first IV fails.
- The total amount of fluid and medications required during the exam exceed the capacity of a single average-bore IV.
- Gadolinium contrast and adenosine cannot be given through the same line.
- The second IV is needed for blood sampling during the exam.

Cardiovascular and MRA Quiz

Gadolinium and adenosine cannot be given through the same line, so two separate IVs are required. Separate lines are optional if regadenoson or dobutamine are used.


Question: Which of the following foods and medications should be discontinued at least 12-24 hours before a stress MRI?

Choices:
- Nitroglycerin
- Calcium-channel blockers
- Caffeinated beverages
- Quinidine

Cardiovascular and MRA Quiz

Patients should be advised not to consume stimulants such as coffee, tea, caffeinated sodas, energy drinks, and chocolate within 12-24 hours of the scan.  These can interfere with the efficacy of the pharmacological stress testing and interpretation of the examination.


Question: What is the most common EKG change noted when a patient is placed in an MRI?

Choices:
- Reduction of the R-wave
- Inversion of the R-wave
- Elevation of the T-wave
- ST-segment elevation

Cardiovascular and MRA Quiz

Although all the above phenomena can occur, elevation of the T-wave is most frequently observed. This elevation may be so marked that the T-wave actually becomes larger than the QRS-complex.


Question: What is the cause of the EKG changes described above?

Choices:
- Ionic currents induced by thoracic blood flow
- Susceptibility effects
- Stimulation of accessory cardiac conduction pathways
- Induced currents in the EKG leads

Cardiovascular and MRA Quiz

This magnetic field effect on the EKG does not originate in the heart itself, but represents a superimposed voltage within blood in the descending thoracic aorta which has been induced by its flow in the magnetic field.  The induction of a voltage in a conductive fluid flowing through a magnetic field is called the magnetohydrodynamic (MHD) effect.


Question: Which EKG wave is primarily used for cardiac triggering?

Choices:
- P-wave
- Q-wave
- R-wave
- T-wave

Cardiovascular and MRA Quiz

Cardiac gating is typically performed using detection of the R-wave since this is usually the most prominent feature of the EKG. The R-wave coincides with the beginning of ventricular systole.


Question: The R-wave corresponds to what cardiac event?

Choices:
- Beginning of atrial contraction
- Beginning of ventricular systole
- Peak contraction of the ventricle
- Beginning of ventricular diastole

Cardiovascular and MRA Quiz

The R-wave coincides with the beginning of ventricular systole.


Question: If the heart rate is 100 bpm, what is the length of the R-R interval in milliseconds?

Choices:
- 60 ms
- 100 ms
- 600 ms
- 1000 ms

Cardiovascular and MRA Quiz

Over 1 minute = 60 seconds, there are 100 beats marked by R waves.  The R-R interval is therefore 60s /100 = 0.6 s or 600 ms.


Question: In the patient above with a heart rate of 100 bpm, which of the following TR values would not be available for a prospectively gated sequence?

Choices:
- 600 ms
- 900 ms
- 1200 ms
- 1800 ms

Cardiovascular and MRA Quiz

The repetition time (TR) in a prospectively gated sequence cannot be freely set but must be a multiple of the average R-R interval. Thus for a patient with heart rate = 100, the only choices for TR would be 600 ms, 1200 ms, 1800 ms, etc.


Question: Continuing the above example in the patient with HR = 100 bpm, what would be the TR if a gating factor of 4 were chosen?

Choices:
- 125 ms
- 600 ms
- 1200 ms
- 2400 ms

Cardiovascular and MRA Quiz

The R-R multiple chosen is called the gating factor. So, if the average R-R interval were 600 ms, the corresponding TR value would be 600 x 4 = 2400 ms.


Question: In a gated study, the time between the first R-wave and the beginning of data acquisition is known as the

Choices:
- Trigger window
- Acquisition window
- Trigger delay
- Quiescent interval

Cardiovascular and MRA Quiz

Trigger delay is the time interval between the first R-wave and the beginning of data acquisition.


Question: Which of the following is not an advantage of retrospective gating compared to prospective gating?

Choices:
- TR is not restricted to be a multiple of the R-R interval
- Data acquired during arrythmias can be rejected.
- Data acquired during patient motion can be rejected.
- Magnetohydrodynamic distortions in the EKG can be corrected.

Cardiovascular and MRA Quiz


Question: For cardiac imaging navigator pulses are most commonly placed

Choices:
- On the dome of the right hemidiaphragm
- On the dome of the left hemidiaphragm
- On the left ventricle
- On the chest wall

Cardiovascular and MRA Quiz

Navigator pulses are typically applied so as to excite 1-dimensional beams or 2-dimensional planes of tissue. Although navigators may be placed over the heart directly, more commonly they are placed to intersect the right hemidiaphragm at its dome.


Question: Which one of the following statements about double IR sequences for cardiac imaging is true?

Choices:
- The first 180°-pulse is spatially selective, while the second 180°-pulse is non-selective.
- Blood suppression requires outside blood flowing in and displacing blood initially within the slice.
- Both blood and fat signals are suppressed.
- Short TI values are required when the heart rate is slow.

Cardiovascular and MRA Quiz

The first inverting pulse is spatially non-selective, while the second pulse is spatially selective, so (a) is false. Inflow of outside blood is a critical requirement for DIR to function properly, so (b) is true. DIR does not suppress fat, so (c) is false. Finally, long (not short) TI values are required when the heart rate is slow.


Question: An advantage of triple IR over double IR for cardiac imaging is

Choices:
- Suppression of pericardial and mediastinal fat
- Shorter imaging times
- More freedom on choice of TI values
- Improved T1 contrast

Cardiovascular and MRA Quiz

Suppression of fat using a third inverting pulse is the primary advantage for triple IR. It comes with limitations, including longer imaging times, less choice on TI values, and replacement of T1 contrast by T2 contrast.


Question: How many distinct segments are enumerated in the American Heart Association (AHA) standard model for left ventricular anatomy that are displayed on polar/target/bull’s eye plots?

Choices:
- 15
- 17
- 19
- 21

Cardiovascular and MRA Quiz

There are 6 basal, 6 middle and 5 apical segments adding to a total of 17.


Question: Which of the following methods is considered a “dark blood” MRA technique?

Choices:
- Time-of-flight MRA
- Gadolinium-enhanced MRA
- SSFP MRA
- Susceptibility-weighted MRA

Cardiovascular and MRA Quiz

Dark ("black") blood MRA techniques suppress signal from flowing blood while maintaining high signal in the surrounding stationary tissues, thus rendering the vessels black. Of those listed, only susceptibility-weighted MRA is a black blood technique.


Question: Which of the following methods is not a “bright blood” MRA technique?

Choices:
- Phase-contrast MRA
- Double inversion recovery MRA
- Arterial spin-labeled MRA
- Ferumoxytol-enhanced MRA

Cardiovascular and MRA Quiz

Single, double, or even triple 180°-inversion pulses may be used to suppress the signal from blood and other tissues (such as fat or myocardium) based on their respective T1 values. Black blood IR methods are most commonly used for cardiac and vessel wall imaging.


Question: Which of the following is not an advantage of dark-blood compared to bright-blood MRA techniques?

Choices:
- Less overestimation of stenosis
- Better delineation of vessel walls
- Better sensitivity to low-flow states
- Fewer pulsation artifacts

Cardiovascular and MRA Quiz

Dark-blood MRA has some unique advantages compared to bright-blood techniques. Flow separation and turbulence, which cause unwanted signal losses and overestimation of stenoses on bright-blood MRA, paradoxically improve image quality on dark-blood MRA. Because intraluminal signal is suppressed, vessels containing "black blood" do not generate pulsation (ghosting) artifacts. Additionally, the lack of intraluminal signal allows the walls of vessels (or cardiac chambers) to be clearly delineated. For these reasons, dark-blood techniques are predominantly used in cardiac imaging and for evaluation of diseases of the vessel wall (atherosclerotic plaque and dissection). Although an excellent method for imaging high-flow vessels, dark-blood techniques are less sensitive to slower flow states. "Black" blood is difficult to separate from adjacent low-signal non-vascular structures, such as calcifications, cortical bone, and air.


Question: What is the purpose of the so-called “traveling sat” pulses in 2D-TOF MRA?

Choices:
- To reduce venous contamination
- To maximize contrast between stationary tissues and blood
- To minimize signal losses from phase dispersion
- To increase signal from inflowing spins

Cardiovascular and MRA Quiz

These sat pulses are used to suppress venous signal that would normally flow into each slice.


Question: What is the purpose of using moderate-to-large flip angles (30°−60°) in 2D-TOF-MRA sequences?

Choices:
- To reduce venous contamination
- To maximize contrast between stationary tissues and blood
- To minimize signal losses from phase dispersion
- To increase signal from inflowing spins

Cardiovascular and MRA Quiz

Larger flip angles produce more magnetic saturation of stationary tissues within the imaged volume, and thus maximize contrast with inflowing blood.


Question: Concerning optimal parameter selection for TOF MRA sequences, which of the following statements is true?

Choices:
- TR should be very long to insure the greatest degree of inflow enhancement.
- TE should be very long to increase vascular signal from T2 effects.
- Slice orientation should be perpendicular to the direction of flow.
- Flip angle (α) should be very small to increase tissue saturation.

Cardiovascular and MRA Quiz

Only (c) is true. The benefits of very long TR to improve inflow enhancement is offset by increased signal from background tissue.  TE should be short to reduce spin-phase losses. Flip angles should be moderate to large to decrease tissue from static tissues.


Question: Blood in an artery with mean velocity of 50 cm/s flows perpendicularly into a 2-cm-thick slice.  At what value of TR is flow-related enhancement maximized?

Choices:
- 10 ms
- 20 ms
- 30 ms
- 40 ms

Cardiovascular and MRA Quiz

Maximum flow-related enhancement occurs when inflowing blood completely replaces that present in a given slice.  When flow is perpendicular to the slice, maximum enhancement occurs when V  ≥  d / TR, or equivalently, when TR  ≥  d /V.  For d = 2 cm and V = 50 cm/s, this means a TR  ≥ 2/50 s = 0.04 s = 40 ms


Question: Concerning magnetization-transfer enhanced MRA, which statement is false?

Choices:
- It is effective for both time-of-flight and phase-contrast MRA
- It is effective for both non-contrast and contrast-enhanced MRA
- Small vessel detail is improved
- Image acquisition time is slightly prolonged.

Cardiovascular and MRA Quiz

MT-MRA is used only for TOF and contrast-enhanced MRA. It offers no benefit for PC-MRA.


Question: Concerning variable (ramped) pulses, which statement is true?

Choices:
- They are useful in both 2D and 3D TOF MRA.
- Their flip angles are designed to decrease linearly along the direction of flow.
- They are designed to produce greater saturation of stationary tissues deep in the slab.
- They are designed to increase the absolute signal of flowing blood deep in the slab.

Cardiovascular and MRA Quiz

Variable (ramped) RF pulses address the progressive loss of MRA signal from vessels extending deep into a 3D-TOF slab. (They are not used for 2D TOF). The flip angle is designed to increase along the direction of flow, producing greater saturation of stationary tissues deep in the slab. (Answer c is correct).  They also suppress blood slightly, but not as much as stationary tissues.


Question: A common artifact seen with MOTSA MRA is called

Choices:
- The venetian blind artifact
- The stair-step artifact
- The velocity aliasing artifact
- The ringing (Maki) artifact

Cardiovascular and MRA Quiz

Because each MOTSA slab is acquired at separate times, exact registration of position and signal intensity of adjacent slabs may not be possible. This gives rise to the so-called venetian blind artifacts characteristic of this technique.


Question: A common artifact seen with 2D-TOF MRA is called

Choices:
- The venetian blind artifact
- The stair-step artifact
- The velocity aliasing artifact
- The ringing (Maki) artifact

Cardiovascular and MRA Quiz

The stair-step artifact is common on 2D-TOF MRA because patient motion between slices.


Question: In subclavian steal syndrome, the blood flow in one of the two vertebral arteries becomes reversed.  What will be the appearance of this reversed flow vertebral artery on a 2D-TOF MRA of the neck?

Choices:
- Its appearance will be identical to the contralateral (normally flowing) vertebral artery.
- It will appear paradoxically brighter than contralateral vertebral artery.
- It will appear slightly less bright than the contralateral vertebral artery.
- It will be non-visualized, suggesting an occlusion.

Cardiovascular and MRA Quiz

2D-TOF sequences utilize traveling saturation pulses upstream from the imaged slice to eliminate venous contamination.  In the neck, these pulses effectively eliminate signal in the jugular and other deep veins, but will also eliminate signals from arterial flows whose directions have been reversed. So (d) is the correct answer.


Question: Why might a phase-contrast (PC) MRA of the head be preferred over a TOF MRA in a patient with cerebral hemorrhage?

Choices:
- The spatial resolution of PC MRA is much higher.
- PC MRA has been shown to be more accurate in the detection of aneurysms.
- T1-shine through of a hematoma does not affect PC MRA but may obscure TOF MRA.
- The acquisition time of PC MRA is much shorter than equivalent TOF techniques.

Cardiovascular and MRA Quiz

TOF MR angiographic images are displayed using a maximum intensity projection (MIP) algorithm. In addition to bright blood vessels, any other material with high signal intensity will "shine through" and "contaminate" the MIP image. Since underlying TOF MRA pulse sequences are T1-weighted, short T1 materials (hematoma, gadolinium, and fat) are primarily responsible for this phenomenon.  PC MRA, however, relies on phase shift differences due to motion, and does not suffer from shine-though.


Question: The underlying mechanism of phase-contrast MRA is based on

Choices:
- Bipolar flow-encoding gradients
- Unipolar flow-encoding gradients
- RF-phase cycling between excitations
- Use of a linear gradient with constant slope along the phase-encoding axis

Cardiovascular and MRA Quiz

PC MRA utilizes bipolar gradients, applied along one or more directions along which flow information is desired.  A stationary spin subjected to such a gradient pair will experience no net phase shift, but a moving spin will have a net phase shift proportional to its velocity.


Question: The units of the VENC (velocity-encoding) parameter for PC MRA are

Choices:
- dimensionless
- cm/s
- cm²/s
- cm/s²

Cardiovascular and MRA Quiz

VENC is a velocity, so the correct answer is (b), cm/s.


Question: If the VENC in a PC MRA is set at 60 cm/s, the strength and duration of the bipolar gradients are adjusted so that blood flowing at 60 cm/s has a phase shift of

Choices:
- +60º
- +90º
- +180º
- +360º

Cardiovascular and MRA Quiz

For a given VENC, the bipolar gradients are adjusted so blood velocities at this level are assigned a +180º phase shift.


Question: If the VENC is set to 50 cm/s, and the actual forward flow blood velocity is 75 cm/s, what velocity will be displayed on the PC MRA?

Choices:
- +50 cm/s
- +75 cm/s
- +25 cm/s
- −25 cm/s

Cardiovascular and MRA Quiz

If the chosen value of VENC is 50 cm/sec, the bipolar gradient is adjusted so that flows of +25 and +50 cm/sec are assigned a phases of +90° and +180° respectively. If the actual velocity is +75 cm/sec, this flow will be mapped to +270°, a value that cannot be distinguished from a phase shift of −90°. Instead of representing the +75-cm/sec flow as its actual velocity, the computer will assign it a flow of 25 cm/sec in the opposite direction!


Question: A PC MRA using bipolar gradients whose VENCs are properly set determines that velocities in the three cardinal directions are vx = −52 cm/s,  vy = +24 cm/s, and vz = +72 cm/s.  When displayed as a magnitude (speed) image, the brightness of each voxel is proportional to

Choices:
- 148 cm/s
- 92 cm/s
- 72 cm/s
- 44 cm/s

Cardiovascular and MRA Quiz


Question: Concerning the accuracy of PC-MRA velocity measurements compared to Doppler in medium to large vessels, the two measurements generally lie within what percentage of each other?

Choices:
- Less than 1%
- About 5%
- 15% - 25%
- More than 25%

Cardiovascular and MRA Quiz

The two measurements are generally within about 5% of each other.


Question: Which of the following situations would velocity measurements by PC MRA be the most accurate?

Choices:
- Imaging plane perpendicular to the direction of flow
- Pixel size close to the vessel diameter
- Turbulent flow
- Sampling of great vessel flows using 8 frames per cardiac cycle.

Cardiovascular and MRA Quiz

Measurement of flow velocities is most accurate when the vessel is perpendicular to the plane of imaging. When the pixel size exceeds one-third of the vessel diameter, significant partial volume effects may occur with underestimation of flow and peak velocities.  When velocities change suddenly in magnitude, direction, or both, as they do in turbulence, accuracy of flow measurements declines. If the data sampling rate throughout the cardiac cycle is too low, flow may not be measured at its peak value. For imaging the great vessels at least 16 frames per cardiac cycle should be sampled


Question: Which statement about Gated 3D-FSE MRA techniques is incorrect?

Choices:
- They can be gated either to the EKG or peripheral pulse.
- Co-registered images are obtained in diastole and systole.
- Diastolic and systolic images are added together to produce the angiogram.
- Image contrast is based on the long T2 of blood.

Cardiovascular and MRA Quiz

The sequence is cardiac gated either to the EKG or peripheral pulse. Co-registered images are obtained in diastole and systole.  During diastole, the signal in both arteries and veins is high reflecting the long T2 of blood. During systole, venous signal remains high but arterial signal drops due to flow-related signal loss. Subtraction (not addition) of the systolic from the diastolic images results in a pure arterial image.


Question: Which of the following is not a disadvantage of 3D-FSE MRA?

Choices:
- Required use of gadolinium contrast.
- Overestimation of stenoses
- Vascular pulsation artifacts
- Sensitivity to cardiac arrythmias

Cardiovascular and MRA Quiz

Option (a) is false. The main advantage of 3D-FSE MRA is that it does not require contrast, a property that may be important in patients with renal insufficiency (where receiving gadolinium might place them at risk for nerphogenic systemic fibrosis).


Question: Intravascular contrast in balanced steady-state free precssion (b-SSFP) MRA is primarily related to which property of blood?

Choices:
- High spin-density
- Long T1
- Long T2
- High T2/T1 ratio

Cardiovascular and MRA Quiz

b-SSFP MRA exploits the differences between the relatively high T2/T1 ratio of blood compared to most other tissues.


Question: What is the main reason b-SSFP MRA sequences are not routinely used in intracranial imaging?

Choices:
- Its spatial resolution is insufficient to resolve the major intracranial vessels.
- The signal from intracranial vessels is obscured by high signal from nearby CSF.
- Intracranial vessels typically demonstrate turbulent flow which disrupts the SSFP.
- Susceptibility artifacts from the skull base produce troublesome zebra-stripe artifacts over most of the brain.

Cardiovascular and MRA Quiz

Like blood, CSF has a high T2/T1 ratio and so will appear bright on SSFP MRA sequences.  Since the arteries at the base of the brain are literally “bathed” in CSF, this is the main reason the sequences are not commonly used intracranially.


Question: The purposes of the inversion pulse(s) used in inflow-enhanced, IR-prepped 3D-SSFP MRA include all of the following except

Choices:
- Nulling of signal from water-containing background tissue.
- Nulling of signal from fat
- Nulling of signal from venous blood
- Hyperpolarization of incoming arterial spins.

Cardiovascular and MRA Quiz

The inversion pulses allow arterial inflow to be relatively accentuated due to background and venous suppression, not because of hyperpolarization.


Question: Which of the following statements about the Quiescent-Interval Single-Shot (QISS) MRA is incorrect?

Choices:
- It does not require cardiac gating.
- It does not utilize gadolinium contrast.
- It is primarily used for extremity MRA
- Unsaturated blood enters the imaged slice during the quiescent interval (QI)

Cardiovascular and MRA Quiz

QISS is a cardiac-gated, non-contrast inflow technique bearing some similarities to 2D time-of-flight (TOF) and inflow-enhanced SSFP MRA. It is especially designed for peripheral MRA. Fresh (fully magnetized/unsaturated) enters the slice during the quiescent interval, with arterial signal generated by a balanced-SSFP sequence.


Question: Which of the following statements about contrast-enhanced (CE)-MRA is false?

Choices:
- If scanning is performed too early after injection, inadequate vascular visualization may result.
- Scanning performed too late after injection may result in venous contamination.
- If you incorrectly time the bolus on the first acquisition, you can wait 10 minutes and repeat the injection.
- Signal generation is typically performed using a 3D T1-weighted spoiled gradient echo sequence with short TR and TE.

Cardiovascular and MRA Quiz

Ideally, CE-MRA should be performed when the contrast agent arrives in the vessel at or near its peak concentration. To early and you don’t see the vessel; too late and you may get venous contamination.  You only get one chance to get it right and cannot repeat the sequence until the next day or two when the gadolinium clears out of the system.


Question: What is fluoroscopic triggering for MRA?

Choices:
- A method that uses information from an x-ray fluoroscope to assist in timing of the gadolinium bolus.
- A method to estimate timing of arrival of a small (1-2 ml) test bolus of gadolinium.
- A 3D-phase contrast method to estimate the distribution of contrast throughout the entire imaging volume.
- A method providing a “fluoroscopic-like” MR image during transit of a full contrast bolus at which time the MRA acquisition can begin.

Cardiovascular and MRA Quiz

In fluoroscopic triggering the full bolus of contrast (~20 mL) is administered while a fluoroscopic-like picture of the artery of interest is acquired using a rapid 2D gradient-echo technique. The technologist can then initiate MRA acquisition or the triggering can be done automatically.


Question: The preferred k-space sampling method used for most 3D-CE-MRA sequences is called

Choices:
- Elliptical-centric ordering
- Linear ordering
- Sequential ordering
- Stochastic ordering

Cardiovascular and MRA Quiz

Elliptical-centric ordering is now the preferred k-space sampling method used for most CE-MRA examinations. Linear methods may still be used on older equipment and for MRA of the distal extremities where arrival of the contrast bolus may be prolonged or its exact timing difficult to predict.


Question: What type of k-space sampling is used in modern time-resolved MRA sequences like TRICKS and TWIST?

Choices:
- Zig-zag
- Cartesian
- Radial
- Spiral

Cardiovascular and MRA Quiz

Modern time-resolved MRA techniques typically use radial sampling schemes, acquiring 3D k-space in segmented round or oval "cylinders".


Question: Which technical component is not a feature used in modern time-resolved MRA sequences like TRICKS and TWIST?

Choices:
- 3D-SSFP acquisition
- Both phase- and read-conjugate symmetry
- Elliptical-centric ordering
- Parallel imaging

Cardiovascular and MRA Quiz

Option (a) is incorrect. Time-resolved MRA methods have at their core a 3D-spoiled GRE sequence with thin slices, very short TRs and TEs, low flip angles, use of both read- and phase-conjugate symmetry, parallel imaging acquisition, and zero-interpolation filling in the slice direction.


Question: What causes the subclavian artery “pseudo-stenosis” artifact on CE-MRA?

Choices:
- Compression of the subclavian artery by the subclavian vein
- Susceptibility effects due to residual gadolinium in the subclavian vein
- Turbulence at its junction with the axillary artery
- Reflux due to retrograde flow from the vertebral artery into the subclavian artery

Cardiovascular and MRA Quiz

A focal irregularity in the subclavian artery mimicking stenosis may occur ipsilateral to the side of contrast injection. This is a susceptibility (T2*) effect due to residual gadolinium in the adjacent subclavian vein, more commonly seen on the left side than right.


Question: What is the cause of the ringing (Maki) artifact on CE-MRA?

Choices:
- Gibbs (truncation) phenomenon
- Central region of k-space scanned before arrival of the contrast bolus
- Central region of k-space scanned too long after arrival of contrast bolus
- Vascular pulsation

Cardiovascular and MRA Quiz

If the central region of k-space is scanned before arrival of the contrast bolus, the vessel will appear dark in the middle, with only its edges demonstrating enhancement.  Scanning too early produces this artifact originally described by Maki et al.


Question: Bulk blood flow (Q) through a certain point in the vascular tree within a given period of time is measured in what units?

Choices:
- cm/s
- cm/s²
- cm²/s
- cm³/s

Cardiovascular and MRA Quiz

Bulk flow is a volume per unit time and is expressed in units of cm³/s.


Question: What is the approximate bulk blood flow (Q) passing through a 2 cm diameter artery where the average velocity is 50 cm/s?

Choices:
- 25 cm³/s
- 50 cm³/s
- 100 cm³/s
- 160 cm³/s

Cardiovascular and MRA Quiz

The cross-sectional area (A) of the vessel is πr² = π (1 cm)² = 3.14 cm². So the bulk blood flow (Q) = V x A = 50 cm/sec x 3.14 cm² = 157 cm³/s.


Question: In what part of a vessel is the blood flow the slowest?

Choices:
- Adjacent to the wall of the vessel
- In the center of the vessel
- Half-way between the wall and center
- The blood flow is the same across the entire vessel.

Cardiovascular and MRA Quiz

Near the vessel wall where fluidic shearing and frictional forces are greatest, the blood flow will be nearly zero. Centrally within the lumen, blood flow will be most rapid.


Question: Which blood vessel normally demonstrates a prominent reversal of flow during the cardiac cycle?

Choices:
- Vertebral artery
- Ascending thoracic aorta
- Middle cerebral artery
- Renal artery

Cardiovascular and MRA Quiz

The thoracic aorta has prominent reversal of flow during diastole as the coronary circulation is filled. The brain and kidneys have low vascular resistance; thus, carotid and renal arterial vessels demonstrate high forward flows even during diastole.


Question: Which blood vessel has the greatest peak velocity?

Choices:
- Thoracic aorta
- Abdominal aorta
- Carotid artery
- Renal artery

Cardiovascular and MRA Quiz

The ascending aorta has the highest average peak velocities of the major vessels; typical values are 150-175 cm/sec. Flow in the distal aorta and iliac vessels slows to the 100-150 range, whereas peak velocities in the proximal carotid, brachial, and superficial femoral arteries are about 80-110 cm/sec.


Question: What happens to peak velocities as a vessel goes becomes increasingly stenotic?

Choices:
- They decrease.
- They increase.
- They remain the same.
- They increase initially then decrease.

Cardiovascular and MRA Quiz

As vessels become increasingly stenotic their peak velocities initially increase (due to the Bernoulli effect). In extremely high-grade stenosis, however, vascular resistance becomes so high that the flow rates and velocities fall just before total occlusion is reached.


Question: In ideal laminar flow the distribution of velocities in cross-section across a vessel should be

Choices:
- Linear
- Constant
- Parabolic
- Hyperbolic

Cardiovascular and MRA Quiz

Laminar flow refers to a predictable distribution of flow velocities in layers (lamina) that parallel the vessel wall.  Theoretically, the distribution of velocities in a perfectly straight, nonbranching vessel with nonpulsatile flow should be parabolic in cross-section.


Question: In which anatomic situation would you not expect to find vortex flow?

Choices:
- Distal to a carotid artery stenosis
- In the proximal (ascending) aorta
- In the distal thoracic aorta
- In an abdominal aortic aneurysm

Cardiovascular and MRA Quiz

Vortex flow refers to localized swirling or stagnant blood flow that has separated from the central streamlines within a vessel. Such vortices, also called flow eddies, frequently occur at vascular bifurcations and distal to areas of stenosis. Vortex flow is prominent in the ascending aorta, as jets of blood are expelled and swirl around during each cardiac contraction. They are less likely in the distal thoracic aorta, so the correct answer is (c).


Question: Which statement about the Reynolds number (Re) in ideal fluids is true?

Choices:
- Values of Re < 2000 predict turbulent flow.
- Values of Re > 2500 predict laminar flow.
- Re is a velocity with units of cm/sec.
- Re is a dimensionless parameter.

Cardiovascular and MRA Quiz

The Reynolds number (Re) is a dimensionless parameter used to predict flow characteristics in ideal fluids. (Answer d is correct). Values of Re less than 2000 predict that flow will be laminar, whereas values greater than 2500 usually indicate that flow will be turbulent.


Question: In which situation would you be more likely to see turbulent flow?

Choices:
- In a vessel with a small diameter
- In a vessel with rapid blood velocities
- In a vessel with elevated blood viscosity
- In the stump of a newly occluded vessel

Cardiovascular and MRA Quiz

The probability of turbulent flow is proportional to the Reynolds number (Re), being directly proportional to blood velocity and vessel diameter, and inversely proportional to blood viscosity. So choice (b) is correct.


Question: Which one of the following flow-related phenomena is considered a time-of-flight (TOF) effect?

Choices:
- High intravascular signal in an entry slice.
- Signal loss due to in-plane flow within an imaging gradient.
- Signal loss due to turbulent flow in an aneurysm.
- High signal in a vessel due to gradient moment nulling.

Cardiovascular and MRA Quiz

Time-of-flight (TOF) effects refer to signal variations resulting from the motion of protons flowing into or out of an imaging volume during a given pulse sequence. High intravascular signal in an entry slice (choice a) is a type of TOF known as flow-related enhancement. The other choices are all spin-phase effects.


Question: Which statement concerning high-velocity signal loss (“washout”) is incorrect?

Choices:
- High-velocity signal loss is considered a time-of-flight effect.
- It is typically seen in arteries and larger veins flowing perpendicular to the plane of imaging.
- It is seen primarily in gradient echo imaging sequences.
- It can occur anywhere in the imaging slab and is not confined to the end slices.

Cardiovascular and MRA Quiz

Answer (c) is incorrect. High-velocity signal loss is typically seen on spin-echo sequences where flowing blood must receive both 90° and 180° pulses to generate a signal.  Gradient echo sequences use single RF-pulses with gradient refocusing.


Question: The total phase gained by a proton moving for time (t) at constant velocity (v) through a constant gradient of strength (G) is proportional to

Choices:
- t
- t²
- v²
- G²

Cardiovascular and MRA Quiz

The phase shift experienced by a moving spin will be proportional to its velocity, the strength of the applied gradient, and the square of the length of time it moves within that gradient.


Question: A radiologist interpreting a head MRI in a patient with suspected stroke dictates: “A flow-void is noted in the basilar artery.” What does this mean?

Choices:
- No blood flow is present in the basilar artery.
- Some flow in the basilar artery may be present, but it is very weak.
- The basilar artery contains flowing blood.
- A thrombus is present in the basilar artery.

Cardiovascular and MRA Quiz

“Flow void” is a widely used term referring to low signal in vessels that contain vigorously flowing blood, and is due to a combination of time-of-flight and spin-phase effects. Although most specialists are familiar with this term, it has the potential for confusion among less sophisticated members of the health care team, who may falsely interpret it to mean absence of flow.


Question: Which of the following statements is not a reason gradient echo sequences can be used to preserve or accentuate signal from flowing blood?

Choices:
- Gradient refocusing of spins is slice-selective.
- Relatively short echo times possible with GRE minimize T2* dephasing.
- Sequential mode acquisition with GRE  makes every slice an “entry slice” with flow-related enhancement.
- Moderate-to-large flip angles with GRE saturate stationary tissue and accentuate T2/T1 contrast of blood.

Cardiovascular and MRA Quiz

All are true except (a). In routine SE imaging, at least part of the reason for flow-related signal loss is that spins move out of the section between the 90°- and 180°-(refocusing)-pulses.  In GRE imaging the refocusing is done by means of a gradient reversal that is not slice-selective.  This nonselective refocusing does not result in hyperintensity of incoming spins, however; it merely prevents them from experiencing TOF signal losses.


Question: Which of the following is not a limitation of the flow compensation (gradient-moment nulling) technique?

Choices:
- Increased minimum TE
- Increased energy deposition (SAR)
- Inability to correct for nonconstant velocities or acceleration
- Increased stress on gradients

Cardiovascular and MRA Quiz

All are true except (b). No extra RF pulses are used, just additional gradient lobes, so no additional energy is deposited by GMN.


Question: In which situation would refocused misregistered flow signal most likely to be observed?

Choices:
- In a vessel running parallel to the phase-encode axis.
- In a vessel running perpendicular to the phase-encode axis.
- In sequences with very short TE values.
- In sequences where flow compensation (gradient-moment nulling) is used.

Cardiovascular and MRA Quiz

Flow misregistration is most commonly seen for in-plane vessels running obliquely to the frequency and phase-encoding axes with long TE’s and the use of gradient-moment nulling.


Question: A point in k-space corresponds to

Choices:
- The amount of a particular spatial frequency in the entire imaged object
- The amount of a particular spatial frequency at a particular point in the imaged object
- The magnitude and phase of the signal arising from a particular point in the imaged object
- The spin density of the signal arising from the entire imaged object.

K-space and Rapid Imaging Quiz

K-space is an array of numbers representing spatial frequencies in the MR image. The individual points (kx,ky) in k-space do not correspond one-to-one with individual pixels (x,y) in the image. Each k-space point contains spatial frequency and phase information about every pixel in the final image.


Question: Which of the following statements about k-space is false?

Choices:
- The kx and ky axes of k-space generally correspond to the horizontal (x-) and vertical (y-) axes of the image.
- Each point in k-space contains spatial frequency and phase information about every pixel in the final image.
- Each pixel in the image maps to every point in k-space.
- Points near the center of k-space correspond to points in the center of the image.

K-space and Rapid Imaging Quiz

Each point in k-space contains spatial frequency and phase information about every pixel in the final image. So choice (d) is false.


Question: Which of the following statements about k-space is true?

Choices:
- The center of k-space provides information about the edges and details of the imaged object.
- The periphery of k-space provides information about the general shape and contour of the object.
- The raw data at the exact center of k-space always has a larger magnitude than any other point.
- k-space must be filled with data in a specific order.

K-space and Rapid Imaging Quiz

Only (c) is true. There are two reasons the central area of k-space has the largest magnitude. First, the central row (ky = 0) is acquired with no phase-encoding gradient (and hence no destructive wave interference caused by phase-encoding steps). Secondly, the central column of k-space (kx  = 0) coincides with the peak of the MR echo.


Question: In routine anatomic MR images, what points in k-space have the lowest amplitudes?

Choices:
- The four corners
- The center
- The middle of the top and bottom edges
- The middle of the left and right edges

K-space and Rapid Imaging Quiz

Signals from the four corners have the highest spatial frequencies in both directions and correspond to data locations where the MR signals are weakest. For time-savings in spiral imaging, the four corners are often excluded from data sampling with only minimal loss of resolution noted.


Question: The “k” of k-space refers to “wavenumber”, an index for spatial frequency, which is the number of waves or cycles per unit distance. An acceptable unit for “k” could therefore be

Choices:
- Cycles per second
- mm−1
- cm/sec
- Line pairs

K-space and Rapid Imaging Quiz

The wavenumber (k) is simply the reciprocal of the wavelength. Since the wavelength is measured in units of distance, the units for wavenumber are (1/distance), such as 1/mm = mm−1. Other acceptable units would include line pairs per mm and cycles per mm.


Question: Which statement about the location of spatial frequencies in k-space is true?

Choices:
- A point along the kx axis corresponds to horizontal stripes in the image
- A point along the ky axis corresponds to vertical stripes in the image
- A point at a 45º angle from the the kx axis corresponds to stripes at 45º in the image
- If the imaged object is small relative to the field-of-view, its k-space frequency representation will be mostly confined to the center.

K-space and Rapid Imaging Quiz

Option (c) is true. Options (a) and (b) are reversed. Concerning incorrect choice (d), the physical size of the object imaged and its frequency expanse in k-space are inversely related. In other words, small objects have ripples far out into the periphery of k-space, while larger objects have their spectral energies more concentrated at the center.


Question: Consider a conventional 2DFT spin-echo pulse sequence with frequency encoding along the x-axis and phase-encoding along the y-axis. Which statement is false?

Choices:
- For a given phase-encode step (ky), digitized data from the early part of the echo is placed at the far left side of k-space (negative kx values).
- For a given phase-encode step (ky), digitized data from the early part of the echo is placed at the far right side of k-space (positive kx values).
- For a given phase-encode step (ky), digitized data from the peak of the echo is placed at the the point (kx=0, ky=0).
- For a given phase-encode step (ky), digitized data from the peak of the echo is placed at the the point (kx=0, ky).

K-space and Rapid Imaging Quiz

Option (c) is false, while option (d) is true.


Question: Concerning the filling of k-space by a conventional 2DFT spin-echo pulse sequence with frequency encoding along the x-axis and phase-encoding along the y-axis, which statement is false?

Choices:
- The central point of k-space (kx=0, ky=0) corresponds to the constant term in the Fourier representation of the image.
- Except for the central row (ky=0), each row of k-space is acquired with the same constant value of the phase-encoding gradient.
- The central row (ky=0) of k-space is acquired with no phase-encoding gradient.
- The central column of k-space (kx=0) coincides with the peak of the MR echo for each phase-encoding step.

K-space and Rapid Imaging Quiz

Option (b) is false. In 2DFT spin-echo imaging, the phase encoding gradient is stepped in magnitude from cycle to cycle, not held constant. The other statements are correct.


Question: The row-by-row filling of k-space by a conventional 2DFT spin-echo pulse sequence is often referred to as what trajectory?

Choices:
- Cartesian
- Radial
- Zig-Zag
- Blipped

K-space and Rapid Imaging Quiz

Traditionally the Cartesian (row-by-row) method was used nearly exclusively for all pulse sequences, but today many different patterns are widely encountered.


Question: The non-uniform raw data from a radial or spiral acquisition must be placed into a rectangular (Cartesian) matrix format for efficient computations. This process is referred to as

Choices:
- Morphing
- Gridding
- Pigeon-holing
- Compressing

K-space and Rapid Imaging Quiz

“Gridding“ is the commonly used term for this process. Although various methods exist, the typical gridding algorithm first involves multiplication of original data with a set of density compensation weights and convolution with a gridding kernel. The resultant data is then interpolated and placed into the uniformly spaced matrix (the "grid") where a discrete Fourier transform is performed. Finally, the field-of-view is trimmed and the transformed data multiplied by an apodization correction function.


Question: How many phase cycles are needed to uniquely differentiate each pixel along a certain direction in an image?

Choices:
- 0,5
- 1
- 1
- 2

K-space and Rapid Imaging Quiz

One full phase cycle is needed to uniquely differentiate each pixel. If there are N pixels of width (Δw) spanning the field-of-view (FOV), then N phase cycles are needed.


Question: If the data sampling rate is halved in the frequency-encode direction (x), what happens to the spacing (Δkx) between points in k-space?

Choices:
- It remains unchanged.
- It is halved.
- It is doubled.
- It is quadrupled.

K-space and Rapid Imaging Quiz

This is equivalent to sampling every other kx value, so compared to the original pattern, the spacing Δkx) will double  Link to Q&A discussion


Question: If the data sampling rate is halved in the frequency encode direction (x), what happens to the field of view in that direction?

Choices:
- It remains unchanged.
- It is halved.
- It is doubled.
- It is quadrupled.

K-space and Rapid Imaging Quiz

We use the formula Δk = 1/FOV. So doubling Δk means the FOV is halved.


Question: If the data sampling rate is halved in the frequency encode direction (x), what happens to the pixel size in that direction?

Choices:
- It remains unchanged.
- It is halved.
- It is doubled.
- It is quadrupled.

K-space and Rapid Imaging Quiz

The pixel width Δw = 1/ kFOV. As long as the kFOV = 2kmax is unchanged, the pixel width will remain unchanged also.


Question: Supposed the data sampling rate in the frequency encode direction (x) is unchanged, but the sampling time is reduced so that only the central ⅓ of k-space is sampled. What happens to the pixel width and FOV in that direction?

Choices:
- The pixel size is tripled and the FOV is unchanged.
- The pixel size is unchanged and the FOV is tripled.
- Both the pixel size and FOV are reduced by ⅓.
- Both the pixel size and FOV are tripled.

K-space and Rapid Imaging Quiz

Because the data sampling rate is unchanged, Δkx is unchanged and the points are spaced out as before. So since Δk = 1/FOV, the FOVx is unchanged. By sampling only the center ⅓ of k-space, the kFOV is now only ⅓ as large. And since pixel width Δw = 1/ kFOV, this means the pixel width has tripled. Hence answer (a) is correct.


Question: Suppose that the frequency encoding portion of the 2D spin warp imaging was left alone, but the number of phase-encoding steps was cut in half (while leaving the maximum and minimum amplitudes of the phase-encoding gradient unchanged). What happens to the spacing (Δky) between points in the phase-encode direction (y)?

Choices:
- It remains unchanged.
- It is halved.
- It is doubled.
- It is quadrupled.

K-space and Rapid Imaging Quiz

Cutting the number of phase encode steps (Ny) in half in this scenario doubles the increment between successive steps, so Δky is doubled.


Question: In the question above, what does the phrase “while leaving the maximum and minimum amplitudes of the phase-encoding gradient unchanged” mean in terms of kFOV in the y-direction?

Choices:
- It remains unchanged.
- It is halved.
- It is doubled.
- It is quadrupled.

K-space and Rapid Imaging Quiz

The phrase basically stipulates that kFOV is unchanged.


Question: Continuing on with the same scenario as in questions 17 and 18, what happens to the pixel width and the phase FOV?

Choices:
- The pixel size is doubled and the FOV is unchanged.
- The pixel size is unchanged and the FOV is doubled.
- Both the pixel size and FOV are halved.
- The pixel size is unchanged and the FOV is halved.

K-space and Rapid Imaging Quiz

The scenario in these last three questions is to create a rectangular field of view with a 1:2 frequency:phase ratio.  Because Δky is doubled, the FOVy is halved. Furthermore, because both the FOVy and Ny have been reduced by one-half, pixel size in the phase-encode direction (FOVy/ Ny) and overall spatial resolution of the image are also unchanged.


Question: Concerning obtaining a rectangular field of view by reducing the number of phase encoding steps as described above, which of the following statements is false?

Choices:
- This option is most beneficial when imaging the spine and extremities.
- Spatial resolution is unchanged.
- Signal to noise ratio is unchanged.
- Wrap-around artifacts in the phase-encode direction are more likely to occur.

K-space and Rapid Imaging Quiz

Option (c) is false. Because fewer phase-encoding steps and hence fewer echo signals are acquired, the signal-to-noise ratio (SNR) is proportionately lower compared to full FOV imaging.


Question: Provided no phase errors occur during data collection, what type of symmetry does k-space exhibit?

Choices:
- x-axis symmetry
- y-axis symmetry
- z-axis symmetry
- conjugate symmetry

K-space and Rapid Imaging Quiz

Provided no phase errors occur during data collection, k-space possesses a peculiar mirrored property known as conjugate (or Hermitian) symmetry.


Question: Which statement concerning phase-conjugate symmetry (partial Fourier) imaging is false?

Choices:
- Over 50% savings in imaging time can be achieved by the use of this technique.
- More than half of the phase-encoding lines must be sampled to correct for phase errors.
- Spatial resolution is preserved.
- For half-Fourier imaging, signal-to-noise is reduced by about 30%.

K-space and Rapid Imaging Quiz

Phase-conjugate symmetry techniques use data from the top half of k-space to estimate data in the lower half of k-space. In theory, phase-conjugate symmetry allows one to acquire data using only half the normal number of phase-encoding steps, thus potentially reducing imaging time by up to one-half. However, to correct for phase errors, more than half of the phase-encoding lines must be sampled, so the actual time savings is less than 50%.


Question: Which statement concerning read-conjugate symmetry imaging is false?

Choices:
- There is no direct time savings.
- Flow and motion artifacts along the frequency-encode direction are reduced.
- Only the first part of the echo is sampled.
- The technique allows for shorter TE values.

K-space and Rapid Imaging Quiz

The direction of read-conjugate symmetry is along the readout (frequency-encode) axis. Only the last part of the echo is sampled, so choice (c) is false. The other statements are true.


Question: Which of the following statements about zero filling is false?

Choices:
- It may be used either for 2D or 3D imaging
- It is used to expand the imaging matrix in the frequency-encoded direction
- It improves the apparent spatial resolution of the image.
- After the first doubling of matrix size with zeros, no added benefit is realized.

K-space and Rapid Imaging Quiz

Zero-filling is routinely used to expand the image matrix size in the phase-encoded direction, which may be either within-plane (2D) or through-plane/slab select (3D). Zero filling acts as method to interpolate the signals from neighboring voxels, giving the image a smoother and less "pixel-ly" appearance.


Question: Which of the following statements about parallel imaging is false?

Choices:
- It can be used with virtually all pulse sequences.
- It requires multiple receiver coils.
- It can be performed in any direction.
- Its primary purpose is to reduce the number of required phase-encoding steps.

K-space and Rapid Imaging Quiz

The allowed direction(s) in which PI can be performed depends on the arrangement of coils in the array. Specifically, the coils must should have different sensitivity profiles along the direction chosen for PI. PI cannot not be used with just a single surface, head, knee, or large body coil having only one pair of quadrature output channels.


Question: Which of the following is not a disadvantage of parallel imaging?

Choices:
- Increased susceptibility artifacts.
- Increased aliasing artifacts.
- Coil calibration artifacts.
- Increased noise in a non-uniform fashion with reduced SNR.

K-space and Rapid Imaging Quiz

Phase-related distortions in the MR signal due to susceptibility are reduced (not increased) by the PI acquisition and reconstruction process. This is especially advantageous in echo-planar sequences.


Question: Comparing image domain PI techniques (like SENSE/ASSET) and k-space PI techniques like (GRAPPA/ARC), which statement is false?

Choices:
- For high R(acceleration)-values, image domain PI techniques provide slightly higher SNR.
- Image domain PI performs better in heterogeneous body regions (like the chest)
- K-space PI techniques display less aliasing and are more useful when small FOVs are needed.
- K-space PI techniques are more effective at minimizing susceptibility distortions.

K-space and Rapid Imaging Quiz

Image domain PI techniques like SENSE/ASSET perform poorly in heterogenous body regions. This is because accurate coil sensitivity maps may difficult to obtain.  The lungs are a prime example.


Question: What is the proper order of steps in acquiring an image-domain PI image (like SENSE/ASSET)? Abbreviations: A = Acquire partial k-space data; G = Generate coil sensitivity maps; R = Reconstruct individual coil images; U = Unfold/combine partial FOV images.

Choices:
- A — G — R — U
- G — A — U — R
- G — A — R — U
- A — G — U — R

K-space and Rapid Imaging Quiz

The proper order is Generate/Acquire/Reconstruct/Unfold (c).


Question: What is the proper order of steps in acquiring an k-space PI image (like GRAPPA/ARC)? Abbreviations: A = Acquire partial k-space data; C = Combine data into magnitude image; E = Estimate missing k-space lines; G = generate individual coil images

Choices:
- A — C — E — G
- A — E — G — C
- E — A — G — C
- E — A — C — G

K-space and Rapid Imaging Quiz

The proper order is Acquire/Estimate/Generate/Combine (b).


Question: Which of the following statements about CAIPIRINHA sequence is false?

Choices:
- It can be classified as an image-domain PI technique.
- Acceleration factors (R) of 4 are typical.
- It is most commonly used for 3D dynamic liver imaging.
- It uses shifting k-space sampling patterns to reduce pixel aliasing and overlap.

K-space and Rapid Imaging Quiz

CAIPIRINHA is clearly a k-space (not image domain) PI technique, as it depends on k-space data sampling and manipulation prior to reconstruction.


Question: What happens to the imaging time in a PI study as the acceleration factor (R) is increased from 2 to 8?

Choices:
- It decreases by a factor of 4
- It decreases by a factor of 2
- It decreases by a factor of √2
- It decreases by a factor of 1/√2

K-space and Rapid Imaging Quiz

Imaging time is inversely related to R, so if R quadruples (from 2 to 8), the imaging time is reduced by a factor of 4 Link to Q&A discussion


Question: What happens to the signal-to-noise ratio (SNR) in a PI study as the acceleration factor (R) is increased from 2 to 8?

Choices:
- It decreases by a factor of 4
- It decreases by a factor of 2
- It decreases by a factor of √2
- It decreases by a factor of 1/√2

K-space and Rapid Imaging Quiz

SNR is inversely related to √R, so if R quadruples (from 2 to 8), the SNR is reduced by a factor of √4 = 2.


Question: Which statement about the g-factor is false?

Choices:
- It depends on the number and location of coils.
- It depends on the direction of phase-encoding
- It varies by location across the image.
- Typical values range from about 10 to 100.

K-space and Rapid Imaging Quiz

The g-factor depends on 1) number and location of surface coils, 2) coil loading, 3) plane of imaging, 4) direction of phase-encoding within the scan plane, and 5) voxel location within the imaged region. With typical coil designs in common use, g-factors ranging from 1.0 to 2.0 across the imaging volume are commonly measured.


Question: The g-factor in the middle of a homogenous phantom imaged with PI is 2.0 while that near its periphery is 1.0. How do the SNR of the center and periphery compare?

Choices:
- SNR (center) is one-half as large as SNR (periphery).
- SNR (center) is equal to SNR (periphery).
- SNR (center) is twice as large as SNR (periphery).
- SNR (center) is four times as large as SNR (periphery).

K-space and Rapid Imaging Quiz

SNR is inversely related to the g-factor, so if the g-factor doubles, the SNR is only ½ as large.


Question: Artifacts specific to parallel imaging include all of the following except

Choices:
- Coil sensitivity artifacts
- Fold-over (SENSE) ghosts
- Chemical shift
- Spatially dependent noise

K-space and Rapid Imaging Quiz

Chemical shift artifacts are unaffected by the PI reconstruction process and are thus not unique.


Question: Fast/Turbo Spin-Echo Imaging methods are commercial applications of which original technique?

Choices:
- RARE
- MEDIUM
- ROAST
- SMASH

K-space and Rapid Imaging Quiz

Fast spin echo (FSE) imaging, also known as Turbo spin echo (TSE) imaging, are commercial implementations of the RARE (Rapid Acquisition with Relaxation Enhancement) technique originally described by Hennig et al in 1986.


Question: Which notation best describes the FSE/TSE technique?

Choices:
- 90º−180º−echo−90º−180º−echo−90º−180º−echo−…..
- 90º−180º−echo−180º−echo−180º−echo−180º−echo−…..
- 90º−180º−echo−echo−echo−echo−…..
- 90º−180º−echo−90º−echo−180º−echo−90º−echo−180º−echo−…..

K-space and Rapid Imaging Quiz

The FSE/TSE pulse sequence uses a series of 180º-refocusing pulses after a single 90º-pulse to generate a train of echoes.


Question: Advantages of FSE/TSE over conventional spin-echo imaging include all except

Choices:
- Decreased tissue energy deposition
- Reduced susceptibility artifacts
- Reduced imaging time
- Increased resolution or signal-to-noise in same imaging time

K-space and Rapid Imaging Quiz

FSE/TSE offers significant reduction of imaging time by scanning multiple lines of k-space nearly simultaneously. This savings may be used to lengthen TR, allowing more time for recovery of longitudinal magnetization and hence improved signal-to-noise. A higher number of phase-encoding steps may be used, allowing improvement in spatial resolution. Susceptibility-induced signal losses are reduced. However, the multiple 180º deposit considerable energy in tissue, leading to high specific absorption rates (SARs).


Question: What is the main conceptual structural difference between FSE/TSE and Multi-echo Conventional Spin Echo (multi-CSE) sequences?

Choices:
- The number of 90º-pulses within a TR interval
- The pattern of 90º- and 180º-RF pulses within a TR interval
- The pattern of phase-encoding gradients within a TR interval
- The pattern of frequency-encoding gradients within a TR interval

K-space and Rapid Imaging Quiz

The FSE/TSE technique changes the phase-encoding gradient for each of these echoes (a multi-CSE sequence collects all echoes in a train with the same phase encoding).


Question: What is the effective echo time (TEeff)?

Choices:
- The time between the 90º-pulse and first echo
- The time between the 90º-pulse and last echo
- The time between successive echoes in the train
- The time between the 90º-pulse and echo obtained at the center of k-space

K-space and Rapid Imaging Quiz

The effective echo time (TEeff) is the time at which the central line of k-space (ky = 0) is being filled.


Question: What is the echo spacing (ESP)?

Choices:
- The time between the 90º-pulse and first 180º-pulse
- The time between the 90º-pulse and last echo
- The time between successive echoes in the train
- The time between the 90º-pulse and echo obtained at the center of k-space

K-space and Rapid Imaging Quiz

The echo spacing is the time between any two successive echoes.


Question: What is the echo train length (ETL) or turbo factor (TF)?

Choices:
- The number of echoes in a TR interval
- The time between echoes in a TR interval
- The number of RF pulses in a TR interval
- The number of RF pulses required to reach the center of k-space

K-space and Rapid Imaging Quiz

ETL or TF is simply the number of echoes in a FSE train between successive 90º-pulses. Imaging time is reduced proportionally by this factor.


Question: If a conventional spin-echo sequence with a certain TR/TE/spatial resolution takes 8 minutes to perform, an otherwise identical FSE sequence with an echo train length (turbo factor) of 8 would take how long?

Choices:
- 1 minute
- 2 minutes
- 4 minutes
- 8 minutes

K-space and Rapid Imaging Quiz

With an ETL/TF = 8, 8 lines of k-space are transversed for each TR interval, reducing imaging time by a factor of 1/8.


Question: What image changes would not occur with increasing echo train length (ETL) or turbo factor (TF)?

Choices:
- Greater T2-weighting
- Increased signal-to-noise
- Spatial blurring
- Higher signal from fat

K-space and Rapid Imaging Quiz

Longer ETL's are associated with a decrease in overall signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) because the later echoes in the train are smaller in amplitude.


Question: What image changes would not be seen with increasing echo spacing (ESP)?

Choices:
- Increased motion artifacts
- Increased susceptibility artifacts
- Increased edge-related artifacts
- Increased signal-to-noise

K-space and Rapid Imaging Quiz

Increasing echo spacing (ESP) permits the use of longer TE's but adversely impacts SNR and CNR.  Motion, susceptibility, and edge-related artifacts increase.  In general, increased ESP has predominantly deleterious consequences on image quality; the shortest permitted ESP should therefore be chosen in most applications Link to Q&A discussion


Question: What is the reason fat looks brighter on FSE/TSE than on Conventional SE images?

Choices:
- FSE/TSE have more intrinsic T1-weighting
- Multiple FSE/TSE 180º-pulses disrupt J-coupling in fat molecules
- Rapid phase-encode gradient switching inf FSE/TSE disrupts diffusion of fatty acids
- It’s just a visual illusion; the absolute fat signal is unchanged.

K-space and Rapid Imaging Quiz

Although several factors may contribute to the FSE "bright fat" phenomenon, the dominant mechanism is thought to be T2 prolongation secondary to disruption of J-coupling interactions that take normally place between adjacent fat protons.


Question: Comparing FSE/TSE and CSE, which statement is false?

Choices:
- FSE/TSE shows increased sensitivity to susceptibility changes.
- FSE/TSE demonstrates increased magnetization transfer effects.
- FSE/TSE demonstrates spatial blurring
- FSE/TSE demonstrates pseudo-edge enhancement

K-space and Rapid Imaging Quiz

FSE/TSE sequences are less sensitive to susceptibility changes, as the 180°-refocusing pulses occurring at very short intervals allow relatively little time for susceptibility-induced dephasing.


Question: Which pulse would be considered a driven-equilibrium pulse if played at the end of an MR sequence?

Choices:
- +90º
- +180º
- −90º
- −180º

K-space and Rapid Imaging Quiz

Driven equilibrium (DE), also known as fast recovery, is technique in which a −90º "flip-back" pulse is used to help restore longitudinal magnetization at the end of an MR sequence.


Question: Comparing the tissue energy deposition of RF-pulses, which is true?

Choices:
- Both 90º- and 180º-pulses deposit approximately the same energy
- A 180º-pulse deposits twice the energy as a 90º-pulse.
- A 180º-pulse deposits half the energy as a 90º-pulse.
- A 180º-pulse deposits four times the energy as a 90º-pulse.

K-space and Rapid Imaging Quiz

Energy deposition from an RF-pulse is proportional to the square of the flip angle (α²). Thus, a 180°-pulse deposits 4x the energy of a 90°-pulse.


Question: Which pulse sequence feature is not commonly implemented as described in 3D-FSE sequences like CUBE/SPACE/VISTA?

Choices:
- Very short TE’s (2-4 ms)
- Medium length echo trains (Turbo factors 8-16)
- Reduced flip angles
- Partial Fourier imaging with zero-interpolation filling.

K-space and Rapid Imaging Quiz

3D-FSE sequences use extremely long echo trains, with perhaps 100-200 echoes. Other features include non-selective RF pulses, parallel imaging, and optimized k-space trajectories.


Question: Why is a zig-zag k-space trajectory commonly used for echo planar imaging instead of a consistent Cartesian (left to right) trajectory as in spin-echo imaging?

Choices:
- It offers better spatial resolution.
- It has fewer artifacts.
- It is faster to perform.
- It is done in the phase-encode direction rather than frequency-encode direction.

K-space and Rapid Imaging Quiz

The zig-zag trajectory is popular because it is easy to program and faster, as it doesn’t require rewinding the readout gradient back to −kmax after each echo. The spatial resolution is the same, and the zig-zag is prone to more artifacts, like Nyquist N/2 ghosts.


Question: All of the following statements about single-shot FSE (HASTE) are true except

Choices:
- Gradient echo signal generation is used for speed.
- The total number of echoes may exceed 200.
- Phase-conjugate symmetry is exploited to limit phase-encode steps.
- Common applications include MR cholangiography and MR myelography.

K-space and Rapid Imaging Quiz

Implicit in its name SS-FSE/HASTE is a fast-spin echo technique, meaning that spin-echoes, not gradient echoes are recorded.


Question: When the current flowing through a wire reverses direction, the magnetic field around the wire

Choices:
- Does not change
- Increases
- Disappears
- Reverses direction

Magnets & Scanners Quiz

Ampère’s Law states that a current (i) in a wire induces a magnetic field (B) around the wire. if the direction of current flow reverses, the direction of the field does also, so d) is correct. The magnitude of the field depends on the magnitude of the current, so b) and c) are false. Link to Q&A discussion


Question: The bulk magnetic properties of matter derive primarily from

Choices:
- Protons
- Neutrons
- Electrons
- Whole nuclei

Magnets & Scanners Quiz

The combination of intrinsic electron spin and electron orbital angular momentum is primarily responsible for the bulk magnetic properties of matter. Protons, neutrons, and whole nuclei possess spin but the size of the magnetic effect is relatively small and limited to juxta-nuclear region of the atom only.  Link to Q&A discussion


Question: If the current in a wire doubles, the induced magnetic field

Choices:
- Doubles
- Quadruples
- Remains the same
- Is reduced by half

Magnets & Scanners Quiz

Ampère’s Law states that a current (i) in a wire induces a magnetic field (B) around the wire proportional to that current. If the current doubles, the magnitude of B also doubles. Link to Q&A discussion


Question: The direction of magnetic field lines surrounding a wire can be determined using

Choices:
- The right-hand rule
- The left-hand rule
- Faraday's Law
- Lenz' Law

Magnets & Scanners Quiz

Fleming developed the right hand rule in which if you grasp a wire carrying current with the right hand and point your thumb in the direction of the current, your fingers will curl around the wire in the direction of the induced magnetic field. Link to Q&A discussion


Question: The voltage induced across a stationary conductor in an external static magnetic field

Choices:
- Depends on the angle of the conductor with the magnetic field
- Increases with time
- Is zero
- Depends on the strength of the magnetic field

Magnets & Scanners Quiz

This is an example of the Faraday-Lenz Law, where the induced voltage is directly proportional to the rate of change of the magnetic field (dB/dt). In this case both the conductor and magnetic field are static, so dB/dt = 0 an the induced voltage is zero. Link to Q&A discussion


Question: Concerning the relationship between electricity and magnetism, which of the following statements is false?

Choices:
- A constant current in a wire induces a constant magnetic field around the wire.
- A changing current in a wire induces a changing magnetic field around the wire.
- A constant magnetic field induces voltage in a nearby stationary wire.
- A changing magnetic field induces voltage in a nearby wire.

Magnets & Scanners Quiz

Ampère’s Law states that a current (i) in a wire induces a magnetic field (B) around the wire. If the current is constant, the magnetic field is constant, but if the current fluctuates, so will the magnetic field. Thus (a) and (b) are true.


Question: Which question about the Tesla (T) is correct?

Choices:
- It is the official unit for magnetic induction field strength in the cgs system.
- 1 Tesla = 1,000 Gauss (G)
- 1 G = 1 mT
- It is one of the coolest cars on the road

Magnets & Scanners Quiz

The Tesla is the unit for magnetic induction field strength in the International System of Units (SI), formerly known as the mks (meter-kilogram-second) system. Gauss is the equivalent unit in the cgs (centimeter-gram-second) system, so a) is false. 1 Tesla = 10,000 G, and 1 G = 0.1 mT, so both b) and c) are false. This leaves option d) as the correct answer, which everyone knows anyway! Link to Q&A discussion


Question: Concerning magnetic field strengths, which statement is true?

Choices:
- The earth's magnetic field is about 0.5 G.
- A junkyard electromagnet that picks up cars is much stronger than the main field of most MR scanners.
- Research MR scanners for humans now exist with field strengths exceeding 20 T.
- Higher field strength scanners have wider bores than lower field strength scanners to accommodate the extra flux lines

Magnets & Scanners Quiz

The earth’s magnetic field at the equator is about 0.5 G, so a) is the correct answer. Junkyard electromagnets generally have field strengths of about 1T, limited by the flux density of steel, so they are much weaker than most MR scanners, and thus b) is false. The largest current human scanners are 11.7T, so c) is false. Higher field strength scanners have smaller bores, not larger ones, so d) is false. Link to Q&A discussion


Question: Which of the following materials is paramagnetic?

Choices:
- Water
- Fat
- Bone
- Air

Magnets & Scanners Quiz

Most biological tissues (including water, fat, and bone) are weakly diamagnetic. Molecular O2 is paramagnetic, overwhelming the weak diamagnetism of the other components of air N2 and CO2. Link to Q&A discussion


Question: A material that is weakly repulsed by a magnetic field is known as

Choices:
- Paramagnetic
- Diamagnetic
- Superparamagnetic
- Ferromagnetic

Magnets & Scanners Quiz

Diamagnetic materials generate an internal polarization (J) that opposes the externally applied field, so b) is correct. The polarization of the other classes of materials is in the direction of the field and are attracted by the field. Link to Q&A discussion


Question: Susceptibility (χ) is negative for materials that are

Choices:
- Paramagnetic
- Superparamagnetic
- Diamagnetic
- Ferromagnetic

Magnets & Scanners Quiz

Susceptibility (χ) is negative when the internal polarization (J) points opposite to the main magnetic field (B). By definition, only diamagnetic materials have negative susceptibilities. Link to Q&A discussion


Question: Ferromagnetic materials form magnetic ________ when arrays of electron spins become linked via quantum exchange interaction.

Choices:
- Flux lines
- Poles
- Vectors
- Domains

Magnets & Scanners Quiz

Exchange interaction is a quantum effect in which unpaired electrons link together to form individual magnetic domains which behave as individual small "magnets". Link to Q&A discussion


Question: Comparing superparamagnetic and ferromagnetic materials, which statement is false?

Choices:
- Ferromagnetism is usually more powerful than superparamagnetism.
- Ferromagnetism persists when the magnetizing field is removed.
- Superparamagnetism persists once the external field is removed.
- Superparamagnetism can be thought of as a single-domain particle.

Magnets & Scanners Quiz

Ferromagnetic materials retain memory (remenance) of prior magnetization, while superparamagnetic particles are single domain but whose magnetization disappears once the the magnetizing field is removed. Link to Q&A discussion


Question: The most common design configuration for clinical MR scanners is

Choices:
- Open bore superconducting
- Closed bore superconducting
- Open bore permanent
- Dipolar electromagnet

Magnets & Scanners Quiz

Over 90% of MR scanners sold today are of the closed bore (cylindrical) superconducting type. The second most common is open bore permanent.


Question: The highest field strength permitted for adults in routine clinical practice by the United States Food and Drug Administration (FDA) is

Choices:
- 3.0 Tesla
- 7.0 Tesla
- 8.0 Tesla
- 11.7 Tesla

Magnets & Scanners Quiz

The current FDA limit for clinical MR scanners is 8.0 T for adults and children older than 1 month; it is 4.0 T for children younger than 1 month. The highest field strength clinical scanner commercially manufactured are 7.0 T, although human-sized research scanners of up to 11.7 T exist. Link to Q&A discussion


Question: The first company to produce a clinical whole-body MRI scanner for commercial use was

Choices:
- GE
- Fonar
- Siemens
- Technicare

Magnets & Scanners Quiz

Raymond Damadian formed the first company FONAR to manufacture MR scanners for clinical use in 1982.


Question: The direction of the main magnetic field (Bo) in a cylindrical closed bore scanner is

Choices:
- Longitudinal (along the main axis) of the cylinder
- Horizontal (cross-wise to the cylinder and parallel to the floor)
- Vertical (cross-wise to the cylinder and perpendicular to the floor)
- Can be at any angle depending on which gradients are turned on

Magnets & Scanners Quiz

The main magnetic field of cylindrical scanners is along the long axis of the cylinder (solenoid). Answer d) is patently false as gradients do not alter the direction of the (Bo) field.


Question: Which of the following is not an advantage of low- and intermediate-field (< 1.0 T) MR scanners?

Choices:
- Lower price
- Lower fringe field
- Improved detection of gadolinium enhancement
- Lower energy deposition in tissues

Magnets & Scanners Quiz

Gadolinium enhancement relative to tissues is reduced at lower fields, a disadvantage.


Question: Which of the following is not an advantage of high-field (≥ 1.0 T) MR scanners?

Choices:
- Higher signal-to-noise
- Better detection of calcifications and hemorrhage
- Smaller artifacts around metallic implants
- Better magnetic field homogeneity

Magnets & Scanners Quiz

Susceptibility artifacts around metal objects are worse at high fields than at lower fields.


Question: Quoted specifications for four different magnets are given below. Which one has the best homogeneity?

Choices:
- <1 ppm over a 40 cm DSV
- <1 ppm over a 20 cm DSV
- >1 ppm over a 40 cm DSV
- >1 ppm over a 20 cm DSV

Magnets & Scanners Quiz

Homogeneity specifications are typically quoted as magnetic field deviation in parts per million (ppm) over a defined spherical volume (DSV). So a magnet with the smallest ppm over the largest DSV would be the most homogeneous — answer a). Link to Q&A discussion


Question: Which of the following statements about passive shimming is true?

Choices:
- Its primary purpose is to correct for field distortions produced by a patient's body.
- Ferromagnetic materials cannot be used for passive shimming.
- Passive shimming is affected by room temperature.
- Once the field is calibrated and magnetic homogeneity achieved, the passive shim materials can be removed.

Magnets & Scanners Quiz

Passive shimming involves the placement of ferromagnetic elements (typically plates or rods to correct for static field inhomogeneities in an empty magnet, not one containing a patient. Thus a) and b) are both false. The shim elements are made of metal and hence the quality of shimming depends upon scanner and room temperature, so answer c) is true.  The shim elements are not removed, but remain in the magnet after shimming is completed, so d) is false. Link to Q&A discussion


Question: Which of the following statements about superconductivity is correct?

Choices:
- All elements can become superconducting if the temperature is low enough.
- Only metals can become superconductors.
- The magnetic field is zero inside the center of a superconducting wire.
- The resistance of a wire linearly decreases toward zero as the temperature falls below the transition temperature (TC).

Magnets & Scanners Quiz

Only about half of the known elements can become superconductive at low temperatures, so a) is incorrect. Most of these are metals or metal alloys, but some non-metal ceramics may also possess superconductivity. The onset of superconductivity is immediate, with resistance dropping to zero once the transition temperature is crossed; thus answer d) is false. The correct answer is c), which describes the Meissner effect, the complete expulsion of all magnetic fields from the interior of the superconductor with creation of a state of perfect diamagnetism.


Question: The superconducting component in the main windings of nearly all clinical MR scanners is an alloy of

Choices:
- Niobium (Nb) and Titanium (Ti)
- Niobium (Nb) and Copper (Cu)
- Nickel (Ni) and Titanium (Ti)
- Nickel (Ni) and Copper (Cu)

Magnets & Scanners Quiz

The main windings of nearly all clinical superconducting scanners use Niobium (Nb) - Titanium (Ti) alloy microfilaments embedded in a copper core. The copper core is not superconducting but serves to support the microfilaments and serve as a current shunt in the event of a quench.


Question: The cryostat of a typical superconducting MR scanner contains all of the following except

Choices:
- Liquid helium
- Liquid nitrogen
- Main magnet windings
- superconducting shim coils

Magnets & Scanners Quiz

Although common in the past, modern refrigeration systems have obviated the need for liquid nitrogen, so only liquid helium is present within the cryostat of today's MR scanners.


Question: The temperature of liquid helium is approximately

Choices:
- 4 °K
- 0 °K
- −4 °K
- −400 °C

Magnets & Scanners Quiz

The temperature of liquid helium used to cool the magnet main windings is just a few degrees above absolute zero, about 4 °K. This is several degrees less than the transition temperature needed to maintain superconductivity in the NbTi alloy wires. No temperature equal or below absolute zero (0 °K or −273.15 °C) is possible, so answers b), c) and d) are all false.


Question: MRI facilities often display a sign on the door that says: "Warning! The magnet is always on." This sign would not strictly apply to a

Choices:
- Resistive magnet scanner
- Permanent magnet scanner
- Superconducting magnet scanner
- The sign is applicable to all types of scanners, always.

Magnets & Scanners Quiz

Only FONAR still make still makes a resistive (electromagnet-type) MR scanner for human use, which can be turned off when not in use.  All permanent magnet and superconductive scanners remain at full field strength at all times, however, so the sign applies to nearly all MR facilities. Link to Q&A discussion


Question: Pushing the "big red button" near the door to a room housing an MRI scanner

Choices:
- Immediately opens the door even if scanning is in progress
- Initiates a controlled quench of the magnetic field
- Turns off all electric power to the scanner and room
- Calls emergency providers (911) and sounds an alarm

Magnets & Scanners Quiz

The "big red button" is often labeled "Magnet Stop" or "Emergency Run Down" and when pressed, initiates a controlled quench of the magnetic field. It should be used only in a life-threatening emergency, such as a patient pinned in the scanner by a metal object.


Question: During a magnetic quench, why should patients and employees be evacuated from the scan room?

Choices:
- Even in small quantities gaseous helium causes burning and irritation to the eyes.
- Asphyxiation may occur.
- Severe frostbite would be likely.
- The released helium may catch fire or explode.

Magnets & Scanners Quiz

Helium is odorless and colorless, but can potentially fill the scanner room resulting in asphyxiation. Fortunately, quench pipes typically vent nearly all released helium out of the room so death from a quench has never occurred in a medical setting to my knowledge. Direct contact with liquid helium would cause burns, but a mist of helium gas would not likely cause eye injury or frostbite (although this could occur in theory with high concentrations of gas in the room). Link to Q&A discussion


Question: Magnetic field gradients for imaging are typically measured in units of

Choices:
- Millitesla per meter (mT/m)
- Gauss per second (G/s)
- Tesla (T)
- Tesla per meter per second (T/m-s)

Magnets & Scanners Quiz

A magnetic field gradient is defined as the change in magnetic field measured over a certain distance, so the only appropriate unit is answer a), millitesla per meter= [magnetic field strength]/distance. Gradient strength is also reported in Gauss/cm (G/cm).


Question: For a supine patient, enabling the z-gradient alone to alter the magnetic field within a patient during slice selection would create a(n)

Choices:
- Axial slice
- Coronal slice
- Sagittal slice
- Oblique slice

Magnets & Scanners Quiz

Applying a single gradient causes a frequency variation of protons as a function of position along the direction of the gradient. This change in frequency can be used for spatial encoding. If the gradient is played out during slice selection and again during signal readout, a slice can be selected perpendicular to the gradient directio Link to Q&A discussion


Question: What is the effect of applying the x- and z-gradients simultaneously during slice selection?

Choices:
- The image will be distorted.
- Significant interslice cross-talk will occur.
- An oblique slice will be created.
- The scanner will display a warning that such a combination is not allowed.

Magnets & Scanners Quiz

Applying a single gradient during slice selection creates a slice perpendicular to the axis of the gradient. Applying two (or three) gradients simultaneously produces single (or double) oblique slices respectively.


Question: When the y-gradient is turned on, what happens to the direction of the main (Bo) field?

Choices:
- The Bo field now points slightly to the right.
- The Bo field now points slightly toward the ceiling.
- The Bo field is reversed.
- The Bo field remains pointing in its original (z)-direction.

Magnets & Scanners Quiz

Gradients do NOT generate transverse components that rotate/tip Bo from side-to-side or up-and-down.  They act only to create in-plane "skewing" of the z-components of Bo.


Question: The basic coil configuration used to generate the z-gradient in a cylindrical MR scanner is known as

Choices:
- Maxwell pair.
- Double saddle.
- Golay.
- Fingerprint.

Magnets & Scanners Quiz

Z-gradients are typically produced using two looped coils carrying current in opposite directions, a configuration known as the Maxwell pair. The other coil types listed are used primarily for x- and y-gradients.


Question: Which of the following statements about eddy currents is false?

Choices:
- They create a wide range of image artifacts, including ghosts and blurring.
- They are a manifestation of Faraday's Law of induction.
- They especially affect traditional spin-echo sequences with long TE's.
- They create tissue heating.

Magnets & Scanners Quiz

Eddy currents are produced rapidly changing magnetic fields (especially from the switching of imaging gradients) and are thus a manifestation of Faraday's Law. They are typically seen with rapid gradient echo or echo-planar sequences using short TE's; hence answer c) is false. They are uniformly undesirable, creating various artifacts and tissue heating problems.


Question: Concerning actively shielded gradients, which statement is true?

Choices:
- The are the most effective way to reduce eddy currents in superconducting systems.
- The are the most effective way to reduce eddy currents in superconducting systems.
- Current in these coils runs in a direction opposite to their associated imaging gradients.
- All of the above are true.

Magnets & Scanners Quiz

Active shielded gradients are nearly universally used in superconducting scanners because of their high effectiveness in reducing eddy currents in the magnet itself. They do not affect eddy currents generated in tissues, however.


Question: Which of the following methods is not used to reduce eddy currents:

Choices:
- Actively shielded gradients.
- Self-shielded gradients.
- Active shimming coils.
- Pre-compensation.

Magnets & Scanners Quiz

The terms “Actively shielded” and “self-shielded” gradients are synonymous, and are the most effective way to reduce eddy currents. Pre-compensation distortion of waveforms is also helpful. Active shimming coils are used to make the main magnetic field more homogeneous and have nothing to do with eddy currents or their correction.


Question: Typical values for peak gradient strength in a modern 1.5 T scanner are in the range of

Choices:
- 1-10 mT/m.
- 20-50 mT/m.
- 200-400 mT/m.
- 500-1000 mT/m.

Magnets & Scanners Quiz

Lower field strength permanent magnets have peak gradients in the range of 15-25 mT/m.


Question: The time for a gradient to ramp from zero to its maximum value is known as its

Choices:
- Rise time.
- Gradient time.
- Slew rate.
- Duty cycle.

Magnets & Scanners Quiz


Question: The definition of gradient slew rate is

Choices:
- Peak gradient strength ÷ main field strength (Bo).
- Peak gradient strength ÷ total time the gradient is on.
- Peak gradient strength ÷ Rise time.
- The number of times a gradient is turned on and off per second.

Magnets & Scanners Quiz

Slew rate is defined to be Peak gradient strength ÷ Rise time.


Question: The units for slew rate are given in

Choices:
- Millitesla per meter (mT/m).
- Tesla per meter per second (T/m/s).
- Tesla per second (T/s).
- Milliseconds (ms).

Magnets & Scanners Quiz

Peak gradient strength is typically measured in mT/m and rise time is measured in ms. Their ratio, slew rate, therefore has units T/m/s.


Question: Typical maximum slew rate values quoted for modern 1.5 T scanners are in the range of

Choices:
- 1−2 T/m/s.
- 10−20 T/m/s.
- 100−200 T/m/s.
- 1000−2000 T/m/s.

Magnets & Scanners Quiz

Answer c) is correct. Slew rates much higher than this can be obtained in research scanners but are limited due to the risk of peripheral nerve stimulation by the rapidly switching gradients.


Question: A gradient that ramps from 0 to a peak amplitude of 30 mT/m in 0.25 ms has a slew rate of

Choices:
- 30 T/m/s.
- 60 T/m/s.
- 90 T/m/s.
- 120 T/m/s.

Magnets & Scanners Quiz

Slew rate = [Peak gradient strength] ÷ [Rise time] = [30 mT/m] ÷ [0.25 ms] = 120 T/m/s.


Question: Which gradient specification is generally the most important when assessing how well an MR system is capable of performing rapid, high-resolution imaging?

Choices:
- Peak gradient strength.
- Slew rate.
- Rise time.
- Magnetic field strength.

Magnets & Scanners Quiz

The slew rate incorporates both peak gradient strength and rise time into its definition and is the best single gradient specification to consider. Static magnetic field strength is an important consideration for high-resolution imaging but is not a gradient specification.


Question: How many sets of paired physical gradients are present in an MR scanner?

Choices:
- 1
- 2
- 3
- 6

Magnets & Scanners Quiz

Three sets of paired primary gradients are present in all MR scanners, producing field distortions along the three cardinal directions (x, y, and z).   Link to Q&A discussion


Question: Which of the following statements about gradient duty cycle is false

Choices:
- It is commonly measured in percent (%).
- It represents the fraction of time that the gradient works at maximum amplitude.
- Its value depends on the pulse sequence timing parameters and number of slices.
- Its value is independent of the type of pulse sequence (SE, IR, etc).

Magnets & Scanners Quiz

The duty cycle is defined as the percent time a gradient works at maximum amplitude during a pulse sequence. Its value will therefore vary with the pulse sequence and timing parameters, so d) is false.  Link to Q&A discussion


Question: Which of the following statements about the gradient subsystem is true

Choices:
- The gradient coils are located within the cryostat.
- Gradient coils generate considerable heat during operation.
- The gradient coils are cooled by liquid helium.
- Increasing power supplied to a gradient decreases the slope of the gradient.

Magnets & Scanners Quiz

Gradient systems are not superconducting and are not located within the cryostat. They do generate considerable heat and typically require water and air cooling (though not cooling by liquid helium). Increasing power to a gradient increases (rather than decreases) its strength/slope.  Link to Q&A discussion


Question: Which coils are located closest to the patient in an MR scanner?

Choices:
- Gradient coils.
- RF-receiver coils.
- Shim coils.
- Body RF-transmit coils.

Magnets & Scanners Quiz

RF-receiver coils are placed closest to the patient so they may detect the MR signal with highest sensitivity.


Question: In the construction of a superconducting MR magnet, which is the correct order of coils from outermost to innermost?

Choices:
- Main magnet windings, gradient coils, RF coils, shielding coils.
- Gradient coils, shield coils, main magnet windings, RF coils.
- Shielding coils, main magnet windings, gradient coils, RF coils.
- RF coils, shield coils, main magnet windings, gradient coils.

Magnets & Scanners Quiz

Shielding coils are the outermost coils. Their function is to reduce the external fringe fields from the main magnet windings, the next coil encountered. Next come resistive shim coils used to improve magnet homogeneity. Then the gradients, then the RF transmit coils, and finally the RF receiver coils (closest to the patient).


Question: Although most local RF coils are "receive only", some specially designed to operate in "transmit-receive (T/R)" mode. T/R coils commonly offered by MR vendors include all of the following except

Choices:
- Head coils.
- Knee coils.
- Spectroscopy coils.
- Spine coils.

Magnets & Scanners Quiz

Standard spine and body phased surface coil arrays are not offered for transmit/receive dual operation.


Question: A 1.5 T MR scanner has a base operating frequency of approximately 64 MHz. In the electromagnetic spectrum, this is considered to be in the range of

Choices:
- Infrared frequencies.
- Radio frequencies.
- X-ray frequencies.
- Microwave frequencies.

Magnets & Scanners Quiz

MRI operates in the same frequency range as those used for radio and TV transmission.


Question: Use of a single element surface coil placed directly on the patient offers which advantages?

Choices:
- High signal-to-noise.
- Increased depth of penetration.
- Capability for larger fields-of-view.
- All of the above.

Magnets & Scanners Quiz

A single element surface coil offers high signal-to-noise for receiving signals from voxels beneath the coil. The depth of penetration is limited, however, usually to less than 75% of the diameter of the coil. Larger FOV's are not possible, limited again by the size of the coil.


Question: Comparing 10 cm and 20 cm diameter surface coils, which of the following is false?

Choices:
- The sensitive volume of the 20 cm coil is larger.
- The penetration depth of the 20 cm coil is greater.
- The 20 cm coil has higher signal-to-noise for voxels immediately under the coil.
- The 20 cm coil offers a larger field of view.

Magnets & Scanners Quiz

For voxels immediately under the coil, the 10 cm coil would have superior SNR than for the 20 cm one.  The other statements are all true.


Question: Comparing linear and quadrature coils

Choices:
- Quadrature coils offer twice the signal-to-noise.
- Quadrature coils offer four times the signal-to-noise.
- Quadrature coils offer about 40% greater signal-to-noise.
- Quadrature coils are about 40% larger.

Magnets & Scanners Quiz

Quadrature coils can be the same size as linear coils, but offer a signal-to-noise ratio of approximately √2  (≈ 1.41), or about 40% greater than that of linear coils.


Question: A sinusoidal wave can be described by the equation S(t) = A sin (ωt − φ). The constant A represents

Choices:
- Angular frequency.
- Difference in height between positive and negative peaks.
- Half the difference in height between positive and negative peaks.
- Phase shift.

Magnets & Scanners Quiz

A is called the "amplitude" of the sinusoidal wave measured from zero to its maximum positive value. The full excursion between positive and negative peaks is 2A, so "A" is ½ this difference.


Question: An MR scanner employs three different magnetic fields— the main field (B0), gradient fields (G), and radiofrequency field (B1). In terms of relative strength from weakest to strongest, the proper ranking is

Choices:
- B1 < G < B0
- G < B0 < B1
- G < B1 < B0
- B1 < B0 < G

Magnets & Scanners Quiz

The main magnetic field  (B0) is by far the strongest, typically larger than 1 Tesla. Gradient fields are of intermediate strength with values in the mT range. Radiofrequency fields are the smallest, with B1 values on the order of 10−50 μT.


Question: Which of the following is not an advantage of parallel (multi-)transmit RF?

Choices:
- Decreased RF-energy deposition in tissues.
- Reduced shading artifacts.
- Increased standing waves due to dielectric effect.
- More uniform excitation.

Magnets & Scanners Quiz

Parallel transmit RF excitation offers many advantages, particularly as field strength increases, including improved homogeneous excitation and artifact reduction. The incorrect answer a) standing waves due to dielectric effect are decreased, not increased with parallel transmission.


Question: Comparing phased array and parallel array coils, which of the following is true?

Choices:
- Both types of coils offer improved signal-to-noise and increased field-of-view.
- Overlap of coil elements is avoided in both types.
- Phased array coils are also known as switchable arrays.
- Both can be used equally well with parallel imaging acquisition methods.

Magnets & Scanners Quiz

Only answer a) is true. Overlap of coil elements is common design feature of phased array coil systems, but must be avoided in parallel arrays. Although some phased array coils are compatible with parallel imaging applications, most are not. Finally, phased and switchable arrays are not the same, the latter largely being abandoned 20+ years ago.


Question: Parallel imaging systems are composed of coil elements, segments, and channels. The proper transmission hierarchy beginning with the patient and proceeding upward through the processing chain is

Choices:
- Elements → channels → segments
- Elements → segments → channels
- Elements → channels → segments
- Channels → elements → channels

Magnets & Scanners Quiz


Question: Advantages of parallel receiver coil arrays include all of the following except

Choices:
- Increased signal-to-noise.
- Increased field-of-view.
- Ease of design.
- Reduced imaging time.

Magnets & Scanners Quiz

Parallel coil configurations offer all the advantages above, with the exception of ease of design. In fact, it is rather difficult to pack many small coils closely together in these arrays without significant magnetic interactions.


Question: The effective depth of penetration for signal reception from a 20 cm diameter single loop surface coil is approximately

Choices:
- 10−15 cm
- 20−25 cm
- 30−40 cm
- 40−50 cm

Magnets & Scanners Quiz

The penetration depth for reception from a simple loop RF surface coil is typically only about 50-75% of the coil's diameter.  Link to Q&A discussion


Question: Concerning the main transmit RF-body coil, which statement is false?

Choices:
- It is commonly used to receive the MR signal
- It is built into the scanner gantry housing and cannot be seen by the patient
- It is considered a transceiver coil, capable of both RF transmission and reception.
- Its transmission field (B1) is perpendicular to the main magnetic field (B0).

Magnets & Scanners Quiz

The body coil is hidden within the scanner gantry housing. Its primary purpose is to transmit the B1 field which is perpendicular to B0. It is a transceiver coil capable of both RF transmission and reception. However, it is seldom used for reception because better signal-to-noise is obtained using surface coils for this purpose. Hence, answer a) is false.   Link to Q&A discussion


Question: Which of the following components of an MR system is typically not located in an adjoining equipment room?

Choices:
- RF-power amplifiers
- Gradient amplifiers
- Helium pump
- Gradient coils

Magnets & Scanners Quiz

Gradient coils are an integral part of the MR scanner itself and are not located in a separate equipment room.


Question: Where is the master computer located that controls the MR scanner and processes data into images?

Choices:
- In the MR scanner room
- In the MR scanner control room
- In the nearby MR equipment room
- At least 25 meters distant from the main scanner to avoid interference

Magnets & Scanners Quiz

The master computer is located at the scanner console in the control room immediately adjacent to the magnet room. Due to the shielding of the scanner, it does not need to be in a remote location (answer d is false). However, this is now starting to change and some commercial houses are starting to install it in the technical room.


Question: The function of the array processor is to

Choices:
- Generate triggers for the array of RF-pulses and gradient waveforms used for imaging
- Reconstruct the raw NMR data into images
- Calculate RF frequency offsets and gradient strengths for desired slice selection and field-of-view
- Activate and/or disable various coil elements in an array

Magnets & Scanners Quiz

The array processor is a special board within the main computer that operates the MR scanner. It is responsible for performing Fast Fourier Transformation (FFT) of the raw data and constructing the data into images.


Question: Which scanner is the heaviest (and would thus require the most floor support)?

Choices:
- 0.35 T  Permanent magnet system
- 0.6 T Resistive magnet system
- 1.5 T Superconductive system
- 3.0 T Superconductive system

Magnets & Scanners Quiz

Permanent magnet systems may weigh over 35,000 pounds (16,000 kg), over 3 times more than a superconductive scanner.


Question: Which scanner is would have the lowest overall siting and operational costs?

Choices:
- 0.35 T  Permanent magnet system
- 0.6 T Resistive magnet system
- 1.5 T Superconductive system
- 3.0 T Superconductive system

Magnets & Scanners Quiz

Notwithstanding additional siting costs regarding their weight as described in the previous question, permanent magnet scanners do not require cryogens nor a sophisticated chiller system, so their operational costs are extremely low. Their fringe fields are typically very small as well, allowing them to have much smaller room requirements. Resistive electromagnet scanners, by comparison, have high operational costs due to use of electricity and increased environmental cooling requirements. Superconducting scanners are the most expensive to site due to their size, fringe fields, and cooling requirements.


Question: Which component of a superconducting MR scanner does not require specialized cooling to maintain function?

Choices:
- Main coil windings
- Gradient coils
- Gradient amplifiers
- Radiofrequency coils

Magnets & Scanners Quiz

The main coil windings, of course maintained at superconducting temperatures by liquid helium. Both gradient coils and amplifiers get very hot and must be cooled by circulating water/antifreeze exchanged through chiller circuitry. Radiofrequency amplifiers are usually in the same cabinet as gradients and also require air and/or water cooling. The RF transmit coils themselves do get warm but require no separate cooling. The RF receive coils close to the patient do not heat up at all.


Question: The B0 field of an MR scanner is most homogeneous at

Choices:
- At the opening (gantry) of the magnet
- At bore level about 1 meter directly in front of the magnet
- In the middle of the bore at isocenter
- On the outside of the magnet immediately against its wall

Magnets & Scanners Quiz

The B0 field is most homogenous at magnet isocenter.