Question: Which scanner would have the largest fringe field?

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

Fringe fields are generally directly related to field strength, so the higher the main field, the greater the fringe. Thus the correct answer is d). Magnet configuration also is important.  Specifically, C-shaped magnets (the typical configuration for permanent scanners) have relatively low fringe fields.


Question: If one moves from 1 meter to 2 meters away from a magnet, the fringe field will be reduced by a factor of approximately

Choices:
- √2
- 2
- 4
- 8

Magnets & Scanners Quiz

In theory the strength of a magnetic fringe field is inversely related to the third power of the distance (1/r³) from the magnet isocenter. Thus moving twice as far away from the magnet, the fringe field should fall by a factor of approximately 1/2³ = 1/8.


Question: The fringe fields of cylindrical superconducting magnet are highest

Choices:
- In the x-direction (transverse and horizontal to the axis bore)
- In the y-direction (transverse and vertical to the axis bore)
- In the z-direction (along the axis bore)
- They are equal in all directions

Magnets & Scanners Quiz

Fringe fields are significantly higher along the z-axis (the direction of B0).


Question: The primary purpose for passive magnetic shielding is

Choices:
- To reduce fringe magnetic fields outside the scanner room.
- To keep extraneous radiofrequency noise from entering the scanner room.
- To constrain the NMR signal to remain within the bore of the magnet for better reception.
- To reduce the effects of moving equipment (such as cars and elevators) from distorting the magnetic field.

Magnets & Scanners Quiz

Passive shielding typically involves placing iron posts or sheets of steel in selected places around scanner floor or wall to minimize fringe field extension outside the scanner room. Passive shielding is generally not necessary with modern self-shielded scanners unless they are closely space or near other sensitive equipment.


Question: Concerning passive shielding, which statement is true?

Choices:
- It is performed by placing heavy copper plates along the walls of the scanner room.
- It is a method to reduce extraneous radiofrequency interference with the MR signal.
- It is more commonly required for 7.0T than for 1.5 T installations.
- Active shielding technology found in modern scanner design has not changed the need for it.

Magnets & Scanners Quiz

Passive shielding is a method to reduce fringe magnetic fields, so a) copper lining of the walls to reduce b) RF-interference are incorrect. It is more needed for higher field strength installations, so c) is true. Active shielding technology in modern scanners has reduced the need for passive methods, so d) is false.


Question: Passive magnetic shielding of the scanner room is typically achieved using sheets or rods made of

Choices:
- Copper
- Iron
- Aluminum
- Lead

Magnets & Scanners Quiz

A ferromagnetic substance such as iron or steel is required to constrain the fringe field lines.


Question: The fringe magnetic field arising from an MR scanner

Choices:
- Can be eliminated by active shielding.
- Can be eliminated by passive shielding.
- Can be reduced by radiofrequency shielding.
- None of the above.

Magnets & Scanners Quiz

Active and passive shielding can reduce, but not eliminate fringe fields. Radiofrequency shielding reduces noise but does not affect fringe fields  Link to Q&A discussion


Question: What is the “5 Gauss Line”?

Choices:
- A place inside the scanner where x- and y-gradients differ in strength by less than 5 Gauss (5 mT).
- The boundary in an MRI center inside of which one’s credit cards will be erased.
- A fringe field line that may pose danger to patients with certain pacemakers
- A fringe field line in the scanner room safe for patients but which MR technologists should avoid crossing.

Magnets & Scanners Quiz

The 5-Gauss Line was established by the US Food and Drug Administration (FDA) as a boundary to which the unsuspecting public should not be exposed. The value was based on the fact that the reed switch in older pacemakers could be flipped by exposure to this level of stray magnetic field, potentially converting a patient’s demand pacemaker into asynchrony mode. It should be recognized that it is not just a line, but a surface that extends outward from the scanner in 3 dimensions. Thus it can extend into the floors above and below the scanner as well as to the sides.


Question: Which statement about ACR Safety Zones 1 and 2 is correct?

Choices:
- Both Zones 1 and 2 lie outside the 5 Gauss line.
- Patient safety screening is required before entering Zone 2
- The general public should not be admitted to Zone 1; it is only for MR patients and their families.
- Patients with pacemakers can at risk if allowed to enter Zone 2.

Magnets & Scanners Quiz

Zone 1 is for the general public. Entry is generally restricted beginning in Zone 2, as this is where safety screening takes place. Both lie outside the 5 Gauss line and are safe for everyone.


Question: Which statement about ACR Safety Zone 3 is false?

Choices:
- Patients should not be admitted to Zone 3 unless they have undergone safety screening.
- Ferromagnetic objects may not be brought into this area.
- The MR operator's console is located in this area.
- Medical personnel should not be admitted to this area unless they have undergone MR safety training.

Magnets & Scanners Quiz

Zone 3 includes areas within the 5-Gauss line, so all patients and family members need to be screened prior to entry. Zone 3 includes the area where the MR operator's console is located. The fringe fields in Zone 3 are sufficiently small that there is no risk for flying ferromagnetic objects to be propelled into the scanner. Nevertheless, there is generally easy direct access from Zone 3 into the scanner room (Zone 4) where dangerous flying objects can occur. Ferromagnetic objects in Zone 3 are discouraged but not forbidden; they certainly should not be brought near the door of the scanner room. For these reasons all medical personnel must be trained/educated in MR safety before being allowed into Zone 3.


Question: Which statement about ACR Safety Zone 4 is true?

Choices:
- Accompanying family members should never be allowed access to Zone 4.
- Zone 4 is synonymous with the room containing the MR scanner.
- Zone 4 is includes the scanner, the operator's console, and equipment room (where gradient amplifiers are located).
- A locked door requiring badge, key, or combination access must be present and remain closed between Zone 3 and Zone 4 except when moving patients.

Magnets & Scanners Quiz

Zone 4 is the scanner room itself, so b) is true and c) is false. Family members may be allowed in the scanner room provided they have been appropriately screened, so a) is false. The door to the scanner room is not locked and is frequently left open when scanning is not in progress (though we recommend having a strap across it to prevent inadvertent entry). Ferromagnetic materials should not be brought into Zone 4 as the risk of them being propelled into the scanner is high.


Question: Why might large trucks on a road 20 meters away from an MR scanner be of potential concern for siting?

Choices:
- Their CB radios operate at the same frequencies as the MR signal.
- The scanner magnetic field can be affected by the dense iron in their chassis as they pass by.
- The physical vibrations they produce can affect image quality.
- At this distance heavy truck traffic should be of no concern at all.

Magnets & Scanners Quiz

Environmental vibrations can significantly affect scanner performance, and sites should undergo vibration testing prior to installation of a scanner. The frequent passage of heavy trucks on a nearby road would be one possible cause. Other vibration sources include nearby air conditioning equipment, motors, and building elevators. RF-interference from CB radios should not be a special problem, as these frequencies would normally be filtered out by standard RF-shielding. At a distance of 20 meters, moving metal should not cause a static field disturbance; however, this could be of concern if the trucks passed as close as 10 meters by.


Question: The loud noise produced by an MR system during a scan is primarily due to

Choices:
- Vibrations of the gradient coils
- Vibrations of the radiofrequency coils
- Vibrations of the main magnet windings
- Vibrations from the chiller and helium pump

Magnets & Scanners Quiz

The noise produced during a scan is primarily due to electromechanical vibrations generated by gradients as they are rapidly turned on and off during a pulse sequence. This is transmitted to other structures in the magnet housing that may also vibrate secondarily and amplify the noise.


Question: Which of the following sequences would likely generate the loudest noise during scanning?

Choices:
- T2-weighted Turbo spin-echo (TSE) imaging of the spine
- Dixon fat-water imaging of the liver
- Echo-planar diffusion tensor imaging of the brain
- MR spectroscopy of the prostate

Magnets & Scanners Quiz

The loudest sequences are those where gradients are switched on and off most rapidly, such as in echo-planar imaging and short TE gradient echo imaging.


Question: Which of the following statements about MR scanner noise is false

Choices:
- Sound levels can reach up to 120 dB for some sequences.
- Although potentially uncomfortable for the patient, there is no real risk to hearing.
- Ear protection is mandatory for all patients undergoing MR imaging.
- New quiet pulse sequences can reduce noise levels to within 10 dB of background.

Magnets & Scanners Quiz

Sound levels indeed can reach 120 dB for some sequences, especially echo-planar ones. This can result in damage to the inner ear and produce hearing loss, so option b) is false. Thus ear protection is mandatory for all patients.


Question: Which of the following methods can reduce scanner noise?

Choices:
- Avoidance of echo-planar sequences
- Use of "soft" gradient pulses with longer rise times
- Use of 3D ultrashort TE sequences
- All of the above

Magnets & Scanners Quiz

These strategies will all produce a reduction of noise levels during scanning.


Question: Newer "quiet" MR sequences with longer gradient ramp times are now available. Which of the following statements about these sequences is true

Choices:
- They can reduce noise levels to within 10 dB of background.
- This strategy can be applied to all pulse sequences.
- They can be employed with no signal-to-noise penalty.
- They do not affect number of slices for a given TR.

Magnets & Scanners Quiz

Newer quiet sequences can reduce noise levels to less than 10 dB of background, so answer a) is true. They can be used on many (but not all) pulse sequences. Because of the increasing rise and fall times there is a shorter sampling window and SNR is reduced. A penalty in the maximum number of slices may also occur at constant bandwidth due to the increased time spent in ramping gradients.


Question: Radiofrequency shielding of the scanner room is most commonly achieved by lining the walls with thin sheets of

Choices:
- Iron
- Aluminum
- Copper
- Lead

Magnets & Scanners Quiz

A thin layer of copper around the entire room is most commonly used in scanner installations. It acts as a Faraday cage and is effective at reducing penetration of extraneous radiofrequencies. However, virtually any conductive metal could be used for this purpose, and both steel and aluminum cages are occasionally used. Link to Q&A discussion


Question: The primary purpose for radiofrequency shielding is

Choices:
- To confine fringe fields to the scanner room itself.
- To constrain the NMR signal to remain within the bore of the magnet for better reception
- To keep extraneous radiofrequency noise from entering the scanner room
- To reduce the effects of moving equipment (such as cars and elevators) from distorting the magnetic field.

Magnets & Scanners Quiz

RF-shielding primarily prevents extraneous radiofrequency noises from outside the scanner room from entering and contaminating the MR signal.


Question: A device that allows a plastic oxygen hose to be passed through the wall of an MR scanner room without disrupting the integrity of the RF-shielding is called a

Choices:
- Penetration panel
- Bandstop filter
- Waveguide
- Faraday cage

Magnets & Scanners Quiz

The correct answer is waveguide (c). This looks like a pipe mounted within the wall and has a design that it blocks/traps radiofrequencies in the Larmor frequency range from passing through. This device is commonly part of the penetration panel, which also includes bandstop filters for wires. The Faraday cage is the entire enclosure around a scanner room to produce RF shielding.


Question: A common location for RF-leakage into the scanner room is

Choices:
- Around the door
- Along seals of the scanner window
- At the penetration panel
- Along the junction of copper plates in the scanner room’s walls

Magnets & Scanners Quiz

Because of repetitive opening and closing, RF-seals around the door are frequently damaged and a common source of RF-leakage into the room.


Question: What are the units for angular frequency (ω)?

Choices:
- Hertz (Hz)
- Cycles per second (cps)
- Radians per cycle
- Radians per second

Making an Image Quiz

Angular frequency (ω), also known as radial or circular frequency, measures angular displacement per unit time. Its units are therefore degrees (or radians) per second.


Question: Approximately how many degrees are in one radian?

Choices:
- 30.0º
- 45.0º
- 57.3º
- 71.7º

Making an Image Quiz

By definition, 2π radians span the arc of one circle, or 360º. So 1 radian = 360/2π ≈ 57.3º


Question: A 180º-pulse is sometimes expressed using radians as a

Choices:
- π/2-pulse
- π-pulse
- 3π/2-pulse
- 2π-pulse

Making an Image Quiz

A 180º-pulse is half a circle, or a π-pulse.


Question: As gradients are turned on and off, the angular frequency (ω) of a spin changes with time (t), expressed by the function ω(t).   The area under the graph of ω(t) vs t between two time points (A and B) represents

Choices:
- The spin’s accumulated phase shift between A and B
- The spin’s change in frequency between A and B
- The energy acquired by the spin between A and B
- The change in field strength experienced by the spin between A and B

Making an Image Quiz

The area under the ω(t) vs t curve represents the accumulated phase of the spin during a certain interval. From a unit perspective, frequency is measured in radians or degrees per second while time is measured in seconds, so their product [ω(t) x  t] will have units of radians (or degrees).


Question: The MR signal information received by the RF-coil can be classified as

Choices:
- Frequency modulated
- Amplitude modulated
- Phase modulated
- Pulse modulated

Making an Image Quiz

MR signal information, typically encoded over a range of 50-100kHz, arrives at the receiver amplitude-modulated on the RF carrier wave (e.g. at 64 MHz). The first step in signal process is called demodulation, which removes the carrier.


Question: The real and imaginary components during of an MR signal in the I and Q channels of a receiver are measured at a specific time point to be 3.0 and 4.0 au (arbitrary units) respectively. What is the actual magnitude of the signal?

Choices:
- 3.5 au
- 5.0 au
- 7.0 au
- 12.0 au

Making an Image Quiz

The magnitude (M) = [Re² + Im²]½ = [3² + 4²]½  [25]½ = 5.0 au.


Question: Concerning Fourier representation of the MR signal, which of the following statements is false?

Choices:
- The Fourier expansion of a signal can be written in either trigonometric or exponential form.
- To represent any real signal exactly, an infinite number of frequency components must be included in its Fourier representation.
- The Fourier transformation converts a time-based signal into the frequency domain, but the change cannot be reversed.
- The Fourier series representation of an MR image is always cut short (truncated).

Making an Image Quiz

All are true except for (c).  Fourier transformation is the mathematical procedure connecting a time domain signal, s(t), and its frequency domain representation, S(ω). The inverse Fourier transform converts S(ω) back to s(t).


Question: The time domain signal, s(t), that corresponds to a uniform/rectangular band of frequencies in S(ω) is called a

Choices:
- Double exponential
- Sinc function
- Gaussian
- Lorentzian

Making an Image Quiz

The sinc function, sinc(t) = [sin t]/t, Fourier transforms into a uniform band of frequencies, such as those used to define a slice profile in conventional 2D MR imaging  Link to Q&A discussion


Question: Which of the following scientists did not win the Nobel Prize for their work in NMR?

Choices:
- Felix Bloch
- Raymond Damadian
- Paul Lauterbur
- Peter Mansfield

Making an Image Quiz

Raymond Damadian did not win the Nobel Prize for his work and considered it a personal injustice. He placed full-page ads in several large world newspapers urging the Nobel committee to change their minds, which they never did.


Question: Which of the following is not a method for spatial localization of the MR signal?

Choices:
- Frequency encoding
- Phase encoding
- Location of receiver coils
- Amplitude modulation

Making an Image Quiz

Choice (d), amplitude modulation, refers to the shape of transmitted or received RF-pulses but is not by itself a method of spatial localization.


Question: Which of the following statements about frequency encoding is incorrect?

Choices:
- It commonly used for in-plane localization for 2D imaging.
- It is commonly used for slice selection in 3D imaging.
- Each voxel actually contains a range of frequencies, not just a single frequency.
- For most applications a linear frequency encoding gradient is desired.

Making an Image Quiz

All are correct except (b). Frequency encoding is commonly used for slice selection in 2D imaging, but phase encoding is typically used for slice selection in 3D.


Question: What is a typical total receiver bandwidth for a 1.5T MR scanner?

Choices:
- 1 kHz
- 50 kHz
- 250 kHz
- 500 kHz

Making an Image Quiz

Receiver bandwidth is an operator-selectable parameter, chosen by the technologist before the scan begins. Available values for total receiver BW range from about 5-100 kHz with 50kHz being typical.


Question: What is the width of a pixel in the frequency encoding direction if the field-of-view is 25.6 cm and 512 frequency-encoding steps are used?

Choices:
- 0.5 mm
- 1.0 mm
- 2.0 mm
- 5.0 mm

Making an Image Quiz

Pixel width = FOVf ÷ # frequency encode steps = 256 mm ÷ 512 = 0.5 mm.


Question: If 256 complex measurements of a digitized MR signal are sampled in a period of 5.12 ms, what is the dwell time?

Choices:
- 5 μs
- 10 μs
- 20 μs
- 200 μs

Making an Image Quiz

The dwell time is the interval between digitized samples. So if 256 samples were obtained over a 5.12 ms period, the dwell time would be 5.12 ms/256 = 20 μs.


Question: What is the total receiver bandwidth if the interval between digitized samples (dwell time) is 25 μs?

Choices:
- 2,500 Hz
- 25,000 Hz
- 40,000 Hz
- 50,000 Hz

Making an Image Quiz

Total receiver BW is the same as the digitization rate of the MR signal. In equation form, BW = 1/td = 1/(25 μs) = 40,000 Hz.


Question: In clinical MR imaging at 1.5T, what frequency range would be typical for setting the receiver to  “narrow bandwidth”?

Choices:
- 1 – 5 kHz
- 5 – 20 kHz
- 50 – 52 kHz
- 100 – 101 kHz

Making an Image Quiz

A typical range for narrow receiver bandwidth would be choice (b), 5 – 20 kHz.


Question: Which of the following statements about narrow bandwidth is incorrect?

Choices:
- Narrow BW implies reduced sampling time.
- Narrow BW increases signal-to-noise.
- Narrow BW accentuates chemical shift artifacts.
- Narrow BW accentuates susceptibility artifacts.

Making an Image Quiz

Option (a) is false. Bandwidth is inversely proportional to sampling time. A synonym for "narrow bandwidth" is therefore "extended sampling time".


Question: Which of the following statements about transmitter bandwidth is true?

Choices:
- It is automatically determined once receiver bandwidth is specified.
- Transmitter BW per se is not directly adjusted by the technologist when specifying scan parameters.
- Typical values for transmit BW are 50-100 kHz.
- Most modern RF-pulses for 2D slice-select are sinc-shaped.

Making an Image Quiz

The transmit bandwidth is not usually user-adjustable, so choice (b) is true. Typical values are 1000-2000 Hz and are independent of receiver bandwidth. Simple sinc pulses are no longer used for slice select, being supplanted by more sophisticated designs using the SLR algorithm.


Question: Cross-talk can be reduced by all of the following methods except:

Choices:
- Increasing gaps between slices
- Increasing the strength of the slice-select gradient
- Performing slice interleaving
- Improving the RF slice profile

Making an Image Quiz

Increasing the strength of the slice-select gradient will only serve to produce thinner slices, not improve cross-talk.


Question: The earliest commercial version of simultaneous slice excitation (offered by GE in the 1990s) applicable to single-channel RF coils was called

Choices:
- Phase Offset MultiPlanar (POMP)
- MultiBand (MB)
- Simultaneous Multi-Slice (SMS)
- HyperBand (HB)

Making an Image Quiz

The historical precursor to modern MB/SMS methods was POMP (Phase Offset MultiPlanar) imaging. The POMP technique used a composite RF-pulse to simultaneously excite two slices, each of which were phase-encoded over only one-half of the total field-of-view (FOV). Phase alternation allowed the two slices to be separately reconstructed without overlap. Unlike SMS, POMP does not utilize parallel imaging technology and is hence applicable to single-channel RF coils.


Question: Which of the following statements about MultiBand/Simultaneous Multi-Slice imaging is false?

Choices:
- Use of parallel imaging arrays is required.
- Acceleration factors of 2-4 are typical.
- The slices must be widely spaced apart (2-3 cm).
- The technique imposes a significant penalty in terms of signal-to-noise.

Making an Image Quiz

MB uses coil encoding together with either gradient- or RF-encoding to resolve data along the slice-select (z)-axis. Because modern coil arrays typically have only a few coil elements in the z-direction, coil sensitivity differences along that axis are rather poor. Accordingly the simultaneously excited slices must be spaced widely apart (typically at least 25−30 mm). Unlike standard parallel imaging acceleration techniques, MB/SMS acceleration results in little to no penalty in signal-to-noise. (Option d is false). This is because neither the echo train length, number of phase-encoding steps, nor number of k-space samples has been reduced as occurs in conventional parallel imaging acceleration methods.


Question: What is the approximate in-plane pixel dimensions of a 25 x 25 cm FOV image acquired using 192 phase-encoding steps and 512 samples in the frequency direction

Choices:
- 1.3 x 0.5 mm
- 2.6 x 0.5 mm
- 1.3 x 5.0 mm
- 2.6 x 5.0 mm

Making an Image Quiz

The pixel width in the phase encode direction is 250 mm ÷ 192 ≈ 1.3 mm, while that in the frequency encode direction is 250 ÷ 512 ≈ 0.5 mm.


Question: Concerning 2D Fourier Transform imaging, which statement is false

Choices:
- The number of unique echo signals equals the number of phase-encoding steps.
- The phase shifts between successive echoes are multiples of 180º.
- For low-amplitude phase-encodings the MR signal is strong but provides little information about spatial detail.
- For high-amplitude phase-encodings the MR signal is weak and provides little information about image contrast.

Making an Image Quiz

Choice (b) is false. The phase shifts between the rows are not simple multiples of 180°, but vary from echo to echo depending on the size of the phase-encoding step. The number of echo signals acquired equals the number of phase encode steps, which is usually 192 or 256.  For low order phase-encodings, the MR signal is strong. The frequency projection approximates the general shape of the object but lacks edge definition.  The higher order phase encode steps have smaller MR signals but provide more information about spatial detail, such as the location of edges.


Question: Why is the phase-encode direction often chosen along the shortest anatomic dimension?

Choices:
- This reduces wrap-around artifact.
- This reduces flow-related artifact.
- This reduces artifacts from gross patient motion.
- It is a requirement for parallel imaging.

Making an Image Quiz

Wrap-around (also called aliasing) occurs when the size of the body part imaged exceeds the defined field-of-view (FOV) in the phase-encode direction. This causes anatomy outside the FOV to be folded in over the main part of the image. To avoid wrap-around the phase-encoding direction is usually chosen to be along the shortest anatomic dimension. Flow-related and other motion artifacts may be moved around by changing the phase-encode direction, but the best direction is based on the location and types of these artifacts, which may or may not be best along the shortest dimension.  For parallel imaging there may be some restrictions on possible phase-encode directions allowed, but setting phase-encode along the shortest axis is not necessarily required.


Question: Which steps in setting up an MR scan are in the proper chronological order?

Choices:
- Set landmark → Perform prescan → Acquire localizer → Position slices
- Acquire localizer → Position slices → Set landmark → Perform prescan
- Set landmark → Acquire localizer → Position slices → Perform prescan
- Perform prescan → Acquire localizer → Set landmark → Position slices

Making an Image Quiz


Question: Which process in the list below is not a part of automatic prescan?

Choices:
- Specific Absorption Rate (SAR) estimation
- Quick shimming
- Center frequency adjustment
- Transmitter gain adjustment

Making an Image Quiz

Specific Absorption Rate (SAR) is estimated by the scanner based on the patient’s body weight, pulse sequence, and pulse sequence parameters selected. This occurs before automatic prescan, allowing the operator to adjust parameters to keep SAR within established limits. Automatic prescan is essentially the last step before the actual scan begins.


Question: In which of the following situations is manual shimming (in addition to prescan quick shimming) nearly always required?

Choices:
- Diffusion-weighted imaging
- MR Spectroscopy
- Fast-spin echo imaging
- Dixon fat-water imaging

Making an Image Quiz

Very detailed high-order shimming is mandatory for spectroscopy. Although spectroscopy shimming can be automated, the settings always require review and often tweaking by the MR technologist.


Question: In which of the following situations is center frequency adjustment most critical?

Choices:
- When using spatial saturation pulses
- When using flow saturation pulses
- When using arterial spin labeling pulses
- When using fat saturation pulses

Making an Image Quiz

The center frequency may be set on water protons, fat protons, or some average of the two.  Accurate center frequency setting is particularly important when spectral fat saturation pulses are employed to make sure the fat peak is adequately suppressed.


Question: What artifact will occur if the receiver attenuator value is set too low during prescan?

Choices:
- Data clipping
- Wrap around
- Ghosts
- Diffuse noise

Making an Image Quiz

If the attenuator value is set too low (i.e., receiver gain is set too high), then the signal will overload the analog-to-digital converter, and data clipping will occur. Since the largest peaks of the MR signal typically are the low order phase-encode steps at the center of k-space, data clipping interferes with image contrast. The result is an image with an "eerie" appearance


Question: What is the purpose of dummy cycles during prescan?

Choices:
- To adjust RF-voltage to achieve a perfect 90º-pulse
- To allow warm-up of the transmit and receive circuitry
- To optimally match coil impedance with that of the patient
- To allow steady state longitudinal and transverse magnetization to be established

Making an Image Quiz

Once RF-excitation begins, the longitudinal and transverse magnetizations need time to reach their steady-state values. During prescan the scanner plays out several cycles of the sequence without recording a signal. These are called dummy cycles, disabled, or discarded acquisitions (DDA). The precise number of dummy cycles depends on the TR and the sequence chosen. Only once the system is near equilibrium does data collection begin.


Question: To sell an MR scanner in the United States, a company must receive what kind of premarket clearance from the Food and Drug Administration?

Choices:
- 401(k)
- 501(k)
- 1099
- 457(b)

Making an Image Quiz

In the United States the Food and Drug Administration (FDA) has statutory authority to regulate the sale and use of MRI equipment. MRI scanners are considered Class II devices, meaning that they have the potential for human harm and require pre-market 501(k) clearance prior to marketing. The FDA has issued guidance documents with non-binding (but strongly suggested) criteria — including those related to hardware, software, performance, site planning, and safety — to attain this premarket approval. The other numbers are all IRS forms and investment accounts unrelated to MRI Link to Q&A discussion


Question: Which of the following organizations does not offer MRI accreditation in the United States?

Choices:
- American College of Radiology (ACR)
- Centers for Medicare & Medicaid Services (CMS)
- RadSite
- The Joint Commission (TJC)

Making an Image Quiz

In the US there are four MRI accrediting organizations that are currently sanctioned by the Centers for Medicare & Medicaid Services (CMS) – the American College of Radiology (ACR), the Intersocietal Accreditation Commission (IAC), The Joint Commission (TJC), and RadSite.


Question: Which of the following quality control measurements must be performed at least weekly on an MR scanner?

Choices:
- Center frequency
- Magnetic field homogeneity
- Slice thickness accuracy
- Monitor resolution

Making an Image Quiz

Daily QC activities include visual inspection of all scanner hardware, the function of safety and communication devices, and general assessment of image quality including identification of artifacts. On at least a weekly basis, a special MR phantom is placed in the scanner and various measurements are made and recorded.  Such measurements include landmark accuracy (table position), center frequency, image uniformity, transmitter gain or attenuation, geometric distortion, spatial resolution, artifact evaluation, and signal-to-noise ratio. Other more sophisticated testing should be performed semiannually or yearly by a medical physicist.


Question: The most common cause of geometric errors is

Choices:
- Warping of the MR phantom
- Abnormal RF-coil impedance
- Miscalibration of one or more imaging gradients
- Center frequency drift

Making an Image Quiz

The most common cause of geometric errors is miscalibration of one or more imaging gradients. Gradients tend to drift over time and require periodic re-calibration by service engineers. Occasionally the problem is caused by Bo inhomogeneity due to improper shim adjustments or an occult ferromagnetic object lodged in the scanner bore.


Question: Detailed procedures and standards for the two most commonly used methods of measuring signal-to-noise in a phantom come from which organization?

Choices:
- The National Electrical Manufacturers Association (NEMA)
- The International Electrotechnical Commission (IEC)
- The International Commission on Non-Ionizing Radiation Protection (ICNIRP)
- The American Society for Testing and Materials (ASTM International)

Making an Image Quiz

The National Electrical Manufacturers Association (NEMA) provides detailed methods and standards for evaluating all types of electrical devices. Those relating specifically to MRI quality include how to measure signal-to-noise (MS 1, 6, & 9), geometric distortion (MS 2 & 12), and uniformity (MS 3).


Question: When complex-valued MR signal data is converted into a magnitude image, the noise statistics are best described using a

Choices:
- Gaussian (normal) distribution
- Poisson distribution
- Gamma distribution
- Rician distribution

Making an Image Quiz

Because region-of-interest (ROI) measurements are typically made on magnitude-reconstructed images, some correction to the statistics must take place. Recall that "raw" MR data is a complex number with real and imaginary parts. When converted to a magnitude only image, the pixel values corresponding to noise are no longer Gaussian, but skewed into a so-called Rician distribution.


Question: The section of an MR phantom consisting of closely spaced lines or holes containing material with strong difference in signal intensity from the background is used to measure

Choices:
- Low-contrast object detectability
- Geometric distortion
- High-contrast spatial resolution
- Image uniformity

Making an Image Quiz

The high-contrast portion of MR phantoms contains closely spaced lines, edges, or holes containing material with strong differences in signal intensity from background. Low-contrast resolution refers to the ability to identify small holes in the phantom with only slightly different relaxation times from background.


Question: The section of an MR phantom consisting of triangular ramps or wedges oriented at a known angle is used to measure

Choices:
- Slice thickness
- Slice position
- Linear accuracy
- Low-contrast resolution

Making an Image Quiz

The most common method to estimate slice thickness is to use a phantom containing triangular ramps or wedges whose surfaces are oriented at a known angle (θ) to the plane of the slice. When a slice passes through the ramp, it produces a stretched "shadow" image whose full width half maximum (FWHM) can be estimated.


Question: The element gadolinium is part of which periodic table group?

Choices:
- Lanthanides
- Actinides
- Alkaline-earth metals
- Transition metals

MR Contrast Agents and Blood Quiz

Gadolinium, element number 64, is located in the exact middle of the lanthanide series of rare-earth elements.


Question: The paramagnetic properties of gadolinium that make it suitable for a contrast agent derive from its

Choices:
- Odd number of protons
- Odd number of protons and neutrons together
- Unpaired inner shell electrons
- Paired electrons in bonding orbitals

MR Contrast Agents and Blood Quiz

Although all elements with odd numbers of nucleons possess nuclear paramagnetism, (responsible for the NMR phenomenon), this is extremely weak except in the immediate vicinity of the nucleus. Because electrons have the same spin (½) but a much smaller size than protons, their gyromagnetic ratios are 657 times larger, giving them powerful magnetic moments. It is unpaired inner shell electrons that give gadolinium its paramagnetic properties.


Question: In its 4f shell, gadolinium has

Choices:
- 4 unpaired electrons
- 7 unpaired electrons
- 4 paired and 3 unpaired electrons
- 7 paired electrons

MR Contrast Agents and Blood Quiz

The 4f electron shell has seven available positions, each of which may potentially be occupied by a lone electron or an electron pair. According to Hund’s rule of maximum multiplicity, electrons will occupy each position singly before filling them in pairs. Gadolinium has seven electrons available to fill the 4f shell, and they are all unpaired.


Question: How many of gadolinium’s unpaired 4f shell electrons participate in bonding/chelation when made into a contrast agent?

Choices:
- 0
- 1
- 4
- 7

MR Contrast Agents and Blood Quiz

None of gadolinium’s 4f shell electrons are directly involved in bonding, thus retaining its powerful paramagnetic properties when formulated as a contrast agent.


Question: If gadolinium is chelated with a very large molecule (like albumin), what happens to its T1 relaxation time?

Choices:
- It remains unchanged
- It shortens
- It lengthens
- It becomes shorter than T2

MR Contrast Agents and Blood Quiz

Smaller aqueous contrast agents (like Gd-DTPA) tumble too quickly to be highly efficient at T1 relaxation. If the contrast agent attaches to a very large molecule (such as albumin), its motion slows to a range much closer to the Larmor frequency and its T1 relaxation time shortens dramatically. Note that choice (d) is impossible, as T1 is always greater than or equal to T2.


Question: Which of the following statements about inner sphere and outer sphere relaxation effects is false?

Choices:
- On a molecule-by-molecule basis, inner sphere relaxation is much more powerful than outer sphere relaxation.
- Inner sphere relaxation requires very close approach of a water molecules to the gadolinium metallic center.
- Although weaker on a per molecule basis, outer sphere effects are important because they involve larger numbers of water molecules.
- Most gadolinium contrast agents have multiple coordination sites available for inner sphere relaxation to take place.

MR Contrast Agents and Blood Quiz

A consequence of its electron structure is that the Gd+3 ion typically exhibits nine coordination sites for bonding and chemical interactions. In all MR contrast agents now commercially available, a ligand group occupies eight of these sites while the ninth is available for transient bonding by a solvent water molecule for an inner sphere effect to occur. So choice (d) is false.


Question: The T1- and T2-relaxivities of a contrast agent are given in what units?

Choices:
- L/mmol-s
- mmol/s
- L/mmol
- unitless

MR Contrast Agents and Blood Quiz

The relaxivity of an MR contrast agent reflects how the relaxation rates of a solution change as a function of concentration [C]. Since a contrast agent may affect the two relaxation rates (1/T1 and 1/T2) individually, there are two corresponding relaxivities, denoted r1 and r2.  By definition, 1/ΔT1 = r1 [C] and 1/ΔT2 = r2 [C]. Since ΔT1 and ΔT2 are given in seconds and [C] is measured in millimoles per liter, r1 and r2 have units of L/mmol-s.


Question: In which of the following scenarios would the T2-shortening effects of gadolinium not be expected to be seen?

Choices:
- MR of the bladder
- MR arthography
- Late enhancement phase cardiac MRI
- MR venography

MR Contrast Agents and Blood Quiz

In routine MR imaging, the mild T2-shortening effects of low doses of gadolinium (which decrease signal intensity) are usually overwhelmed by the more dominant T1-shortening effects (which increase signal intensity) and are therefore not normally observed. When high concentrations of contrast are present, low-T2 effects may predominate. This is seen routinely in MRI of the urinary tract, occasionally in MR arthrograms and venograms (where high concentrations of gadolinium are injected directly into joints or vessels); and in the "first pass" of gadolinium contrast through the vascular system on dynamic contrast enhanced (DCE) studies or time-resolved MR angiography. It would not be seen in late phase imaging of the myocardium.


Question: Concerning gadolinium enhancement as a function of field strength, which statement is true?

Choices:
- All currently used contrast agents demonstrate a slight increase in T1-relaxivity with increasing field strength.
- Contrast agents with lower T1 relaxivities (r1) values produce stronger  enhancement.
- The same dose of contrast will typically generate more enhancement at 1.5T than 0.5T.
- Lower doses of contrast agents are needed at low-field compared to high-field.

MR Contrast Agents and Blood Quiz

Only (c) is true. Because tissue T1 values increase while contrast agent relaxivities are about the same or decrease only slightly with increasing field strength, the net effect is an increase in relative contrast enhancement as field strength increases Link to Q&A discussion


Question: Why do magnetization-transfer preparation pulses increase the visibility of gadolinium enhancement?

Choices:
- They do not. This is a myth.
- They suppress the signal from background tissues.
- They shorten tissue T1.
- They interfere with gadolinium-water inner sphere relaxation.

MR Contrast Agents and Blood Quiz

Because gadolinium (Gd) enhancement is caused by a water-Gd ion interaction (not macromolecular cross-relaxation), MT pulses suppress the signal from background tissues and render Gd-enhanced areas more conspicuous.


Question: The first commercially marketed gadolinium-based MR contrast agent was

Choices:
- Dotarem®
- Magnevist®
- MultiHance®
- Omniscan®

MR Contrast Agents and Blood Quiz

Magnevist®, marketed by Berlex Imaging (and subsequently acquired by Bayer), first received FDA approval in 1988.


Question: Which of the following agents is macrocyclic?

Choices:
- Dotarem®
- Magnevist®
- MultiHance®
- Omniscan®

MR Contrast Agents and Blood Quiz

Dotarem®, along with ProHance® and Gadavist®, are all macrocyclic. The others are linear in structure.


Question: Concerning gadoxetic acid constrast (Eovist®/Primovist®), which statement is false?

Choices:
- Transient dyspnea after injection occurs in about 10% of patients.
- At least 90% of the administered dose is taken up by hepatocytes.
- Elimination is by both biliary excretion and glomerular filtration.
- Hepatic uptake and enhancement is decreased when bilirubin levels are elevated.

MR Contrast Agents and Blood Quiz

Only about half of the administered dose is taken up by hepatocytes. The remainder behaves as other nonspecific extracelleular gadolinium contrast agents.


Question: Although no longer in production, what was unique about the liver contrast agent Teslascan™ sold in the 1990s and early 2000s?

Choices:
- It was based on manganese.
- It was based on iron.
- It was based on copper.
- It was based on magnesium.

MR Contrast Agents and Blood Quiz

To date the only manganese-based contrast agent ever approved for worldwide sales and clinical use was mangafodipir trisodium (Mn-DPDP), marketed in the 1990's under the tradename Teslascan™. Due to low sales, poor clinical performance, and concerns over toxicity, Teslascan™ was withdrawn from the US market in 2003 and from the EU in 2010.


Question: And speaking of MR contrast agents no longer in production, what was unique about Ablavar®?

Choices:
- It was based on manganese.
- It was based on iron oxide.
- It attached to albumin and served as a blood pool agent.
- It was taken up by the reticuloendothelial system.

MR Contrast Agents and Blood Quiz

Withdrawn as a product in 2017 by its manufacturer due to poor sales, Ablavar® had been designed specifically for vascular imaging. The drug underwent reversible bonding to plasma proteins (principally albumin) when injected into the blood, allowing it to be confined intravascularly for several hours.


Question: Concerning superparamagnetic iron oxides (SPIOs) and ultra-small superparamagnetic iron oxides (US-SPIOs), which statement is false?

Choices:
- US-SPIOs may be injected intravascularly, intradermally, or subcutaneously.
- The larger SPIOs are especially useful for lymph node imaging.
- Their T1 and T2 relaxivities are 10-20 x greater than gadolinium contrast agents.
- Their accumulation in the liver, spleen, and bone marrow can be mistaken for hemochromatosis.

MR Contrast Agents and Blood Quiz

Option (b) is false. The largest of these SPIO nanoparticles (50-100 nm) undergo rapid uptake by the liver. Smaller US-SPIO particles (5-50 nm), remain in the circulation and are cleared by lymphatics, draining into lymph nodes where they are captured and retained by macrophages/histiocytes (and potentially other sinus-lining endothelial cells).


Question: Concerning ferumoxytol (Feraheme®/Rienso®) which statement is false?

Choices:
- It is now sold and marketed worldwide as an MR contrast agent.
- It has a long intravascular half-life after intravenous injection, behaving as a blood pool agent.
- It reduces both T1 and T2 relaxation times of the tissues wherein it accumulates.
- It must be given diluted and by slow intravenous injection.

MR Contrast Agents and Blood Quiz

Although ferumoxytol was originally developed as an MR contrast agent, it was instead marketed and approved for intravenous treatment of iron-deficiency anemia associated with chronic renal disease. It has not yet received indications for use as an MR contrast agent. It’s use in this form is considered “off label”.


Question: Concerning bowel contrast materials, a large volume, water-based solution like VoLumen® would be classified as what type of contrast agent?

Choices:
- Positive
- Negative
- Biphasic
- Neutral

MR Contrast Agents and Blood Quiz

Biphasic contrast agents are all water-based, appearing dark on T1-weighted and bright on T2-weighted images. Biphasic enteric contrast agents like VoLumen® contain nonabsorbable additives (resins, polyethylene glycol, mannitol, sorbitol, or other sugar alcohols) that help draw in and retain intraluminal water.


Question: Concerning bowel contrast materials, a suspension of magnetite-based particles like GastroMARK® (ferumoxsil) would be classified as what type of contrast agent?

Choices:
- Positive
- Negative
- Biphasic
- Neutral

MR Contrast Agents and Blood Quiz

Negative contrast agents are designed to make the intraluminal contents dark, especially on T2-weighted images. GastroMARK® causes a remarkable drop in signal within the bowel lumen on both T1 and T2-weighted images. The darkening on T1-weighted images allows visualization of mucosal enhancement.


Question: Compared to non-ionic iodine-based contrast agents, the frequency of acute adverse reactions to gadolinium-based contrast agents is

Choices:
- About the same
- Slightly less
- Slightly more
- Much more

MR Contrast Agents and Blood Quiz

Compared to many other drugs gadolinium contrast agents possess a very low incidence (<2.5%) of acute adverse reactions, mostly minor. Such rates are not too much higher than those occurring during placebo injection of saline and are about one-third as common as reaction rates recorded with nonionic iodine-based contrast media.


Question: Considering gadolinium-based contrast agents as a whole, what is the approximate rate of severe allergic reaction (e.g., facial edema, bronchospasm, hypotension, arrhythmias, widespread uticaria) expected?

Choices:
- 1 in 500 patients
- 1 in 5000 patients
- 1 in 50,000 patients
- 1 in 500,000 patients

MR Contrast Agents and Blood Quiz

Moderately severe hypersensitivity reactions (including bronchospasm, laryngospasm, facial edema, tachycardia, arrhythmias, or widespread urticaria) occur in about 1 in 5000 cases.


Question: Considering gadolinium-based contrast agents as a whole, what is the approximate risk of death from a severe allergic reaction?

Choices:
- 1 in 4,000 patients
- 1 in 40,000 patients
- 1 in 400,000 patients
- 1 in 4,000,000 patients

MR Contrast Agents and Blood Quiz

Worldwide, a number of severe anaphylactoid reactions to gadolinium-based MR contrast agents, including death, have been reported. The incidence of severe reactions is about 1 in 20,000 and the risk of death about 1 in 400,000.


Question: Which one of the following rare reactions to gadolinium has not been reported?

Choices:
- Rhabdomyolysis
- Pancreatitis
- Encephalopathy
- Acute renal failure

MR Contrast Agents and Blood Quiz

To my knowledge, acute rhabdomyolysis has never occurred following gadolinium administration. The other three have been rarely reported.


Question: Comparing “true” anaphylaxis and “anaphylactoid” reactions to gadolinium contrast, which statement is correct?

Choices:
- They can be distinguished based on their clinical presentation.
- Both are IgE-mediated.
- Both cause release of vasoactive amines and inflammatory mediators from mast cells.
- Both are dose-related.

MR Contrast Agents and Blood Quiz

True anaphylaxis is an IgE-mediated type 1 hypersensitivity reaction and is not dose-related. Anaphylactoid reactions have an identical clinical pattern to "true" anaphylaxis but are not IgE-mediated. The two cannot be distinguished clinically. Both cause the same effect on basophils and mast cells to release histamine and other contents.


Question: Which of the following statements about the clinical features of nephrogenic systemic fibrosis (NSF) is incorrect?

Choices:
- Nearly all reported cases have been in patients with severe renal disease or insufficiency.
- Skin thickening and joint contractures are characteristic.
- Involvement of the liver, lungs, muscles and heart also occurs.
- Although painful and disfiguring, the disease is seldom fatal.

MR Contrast Agents and Blood Quiz

Nephrogenic systemic fibrosis (NSF) is a rare, progressive, usually fatal disease characterized by skin thickening, painful joint contractures, and fibrosis of multiple organs including the lungs, liver, muscles, and heart. Nearly all documented cases have occurred in patients with chronic severe renal insufficiency who have received gadolinium contrast.


Question: Which one of the following gadolinium-based contrast agents is less likely than the others to be associated with NSF?

Choices:
- Magnevist®
- Dotarem®
- OpitMARK™
- Omniscan™

MR Contrast Agents and Blood Quiz

Except for the macrocyclic agent Dotarem®, the other three agents are all linear in structure and have been associated with the greatest number of reported cases of NSF. These have been classified by the ACR as Group I agents, and are no longer advertised in the US and have been withdrawn from the market in many other countries.


Question: Which gadolinium-based contrast agents has to date not been associated with any nonconfounded cases of NSF?

Choices:
- Dotarem®
- ProHance®
- MultiHance®
- Eovist®

MR Contrast Agents and Blood Quiz

No cases of NSF have been reported with the newest gadolinium agent, Eovist® (gadoxetate). However, Eovist® is primarily intended for hepatic imaging and thus there is only limited worldwide experience with it compared to the more general purpose agents. Furthermore, Eovist® (and any future new contrast agents) are being given in an “NSF-conscious” era, where high doses of gadolinium are avoided and careful scrutiny of renal function is undertaken prior to contrast administration.


Question: Below what level of glomerular filtration rate (GFR) does the American Kidney Foundation consider Stage 3 (moderately reduced function) kidney disease?

Choices:
- 90 mL/min/1.73 m²
- 60 mL/min/1.73 m²
- 30 mL/min/1.73 m²
- 15 mL/min/1.73 m²

MR Contrast Agents and Blood Quiz

Stage 3 chronic kidney disease is generally diagnosed for GFRs in the range of 30-60 mL/min/1.73 m². This is about half the normal kidney function level of 90 mL/min/1.73 m².


Question: Which one of the following statements about the use of gadolinium in neonates and infants is false?

Choices:
- The half-life of gadolinium contrast in a normal newborn is at least 4 times longer than in an adult.
- The per kilogram dose of contrast should be lower than that in adults.
- Neonates have a lower renal excretion rate of gadolinium contrast than adults.
- No cases of NSF in neonates or infants have been reported.

MR Contrast Agents and Blood Quiz

Renal excretion rates aside, neonates have twice the volume of extracellular fluid than adults have in proportion to their body weights. Therefore, neonates and young infants who receive gadolinium contrast on a dose-per-kilogram basis will have blood gadolinium concentrations of only one-half that in adults after equilibration. This fact argues against using a lower dose per kilogram in infants than in adults, even though the serum half-life is prolonged.  Clinical experience by our group and others has demonstrated that the adult dose of gadolinium contrast (0.1 mmol/kg for most extracellular agents) is also appropriate in infants and children.


Question: Concerning the administration of gadolinium contrast to lactating women, which statement is false?

Choices:
- Peak excretion into breast milk occurs at about 50 minutes after injection.
- Only a tiny fraction (0.01%-0.04%) of the administered dose is excreted in breast milk.
- Only 1% of orally ingested contrast gadolinium contrast is absorbed by the infant.
- Current scientific evidence shows that breast feeding must be avoided for at least 24 hrs.

MR Contrast Agents and Blood Quiz

Because (b) and (c) are true, the dose entering the infant's circulation is extremely small (1/1,000,000 of the maternal dose) and the potential toxic effects are thought to be miniscule. Only out of an abundance of safety, many centers recommend (but do not require) suspending breast feeding for 24 hours after a gadolinium-enhanced MR study.


Question: Concerning the administration of gadolinium contrast during pregnancy, which statement is false?

Choices:
- An increased number of congenital malformations have been observed in infants of mothers receiving gadolinium contrast during pregnancy.
- Gadolinium contrast easily passes through the placenta and into the fetal circulation.
- Gadolinium contrast absorbed by the fetus is excreted into the urine and subsequently into the amniotic fluid.
- Some gadolinium contrast in the amniotic fluid will be swallowed and resorbed through the fetal GI tract.

MR Contrast Agents and Blood Quiz

In the only controlled human study to date of MRI and gadolinium exposure in pregnancy, a slightly higher incidence of stillbirths and early neonatal deaths (but not congenital malformations) was observed in the gadolinium-exposed group.  More worrisome, however, was an increased number of rheumatologic, inflammatory, and infiltrative skin conditions, including some resembling nephrogenic systemic fibrosis (NSF).


Question: Which of the following statements concerning gadolinium deposition in the brain is false?

Choices:
- Accumulation occurs primarily in the basal ganglia, brainstem, and dentate nuclei.
- Several exposures are usually necessary before visible changes are seen.
- Changes are most visible on T2*-weighted images.
- The incidence of accumulation is less with macrocyclic contrast agents than linear ones.

MR Contrast Agents and Blood Quiz

All are true except (b). High signal due to accumulated gadolinium is noted on T1-weighted images.


Question: Concerning “gadolinium deposition disease” which statement is false?

Choices:
- The FDA has determined there is no convincing current evidence for this diagnosis.
- One important piece of clinical evidence for it is the increased incidence of Parkinson’s disease in patients receiving gadolinium contrast.
- No tissue injury or morphologic changes in gadolinium-accumulating brain areas can be detected by microscopy.
- Celebrity Chuck Norris withdrew his lawsuit against Bracco where he claimed they “poisoned” his wife with gadolinium.

MR Contrast Agents and Blood Quiz

The incidence of Parkinson’s disease is not increased in patients who received gadolinium contrast.


Question: How many iron atoms are in a hemoglobin molecule?

Choices:
- 1
- 2
- 3
- 4

MR Contrast Agents and Blood Quiz

Hemoglobin is comprised of four subunits, each containing a heme group with an iron (Fe) atom nestled at its center.


Question: How many sites on each heme group are available for binding oxygen or another small molecule?

Choices:
- 1
- 2
- 3
- 4

MR Contrast Agents and Blood Quiz

The Fe center of each heme group has 6 potential coordination sites, four of which are occupied by porphyrin nitrogens (N). The fifth coordination site (below the plane of the ring) covalently bonds with a histidine (His) residue from the F8 position of its respective globin chain. This leaves one free coordination site to which oxygen and other small molecules may transiently bind.


Question: Which one of the hemoglobin derivatives listed below is diamagnetic?

Choices:
- Oxyhemoglobin
- Deoxyhemoglobin
- Methemoglobin
- Ferritin

MR Contrast Agents and Blood Quiz

Oxyhemoglobin has no unpaired electrons and is therefore diamagnetic.


Question: In arterial blood from a healthy patient, what is the expected proportion of deoxyhemoglobin?

Choices:
- 0 %
- Less than 5%
- 10 – 20 %
- Greater than 25 %

MR Contrast Agents and Blood Quiz

In arterial blood, the fraction of oxyhemoglobin is about 95%, while deoxyhemoglobin constitutes less than 5% (but not zero). A tiny amount of methemoglobin (<< 1%) may also be detected.


Question: In venous blood from a healthy patient, what is the expected proportion of deoxyhemoglobin?

Choices:
- 0 %
- Less than 5%
- 10 – 20 %
- Greater than 25 %

MR Contrast Agents and Blood Quiz

In venous blood, oxy-Hb still predominates, though in a smaller ratio (venous oxy:deoxy ≈ 70:30.)


Question: Which of the following effects on the MR signal does not result from local increased hematocrit during blood clotting?

Choices:
- Decreased free water content, reducing T1, T2, and spin density.
- Decreased extracellular space, restricting diffusion.
- Increased concentration of phospholipids in red blood cell membranes, shortening T1.
- Increased concentration of hemoglobin, potentiating T2/T2* effects as transition to deoxy-hemoglobin occurs.

MR Contrast Agents and Blood Quiz

All are true except (c). Phospholipid cell membranes have ultrashort T2 values and do not generate a fatty signal on MRI.


Question: Which of the following imaging findings at 1.5T would not be expected to be seen in a hyperacute (< 12 hrs old) cerebral hematoma?

Choices:
- Restricted diffusion
- T1 signal isointense to brain
- T2 signal moderately hypointense to brain
- At least a rim of hypointensity on GRE/SWI images

MR Contrast Agents and Blood Quiz

In a hyperacute hematoma, oxyhemoglobin still predominates, except perhaps at the periphery, and the imaging findings suggest a relatively high-water content lesion that is moderately hyperintense on T2-weighted images.


Question: Which of the following imaging findings at 1.5T would not be expected to be seen in an acute (12–48 hrs old) cerebral hematoma?

Choices:
- Restricted diffusion
- T1 signal hyperintense to brain
- T2 signal markedly hypointense to brain
- GRE/SWI images hypointense to brain

MR Contrast Agents and Blood Quiz

This phase of hematoma formation is dominated by intracellular deoxyhemoglobin, which shortens T2/T2* significantly. The hematoma becomes markedly hypointense on T2-weighted images.


Question: Which of the following imaging findings at 1.5T would not be expected to be seen in an early subacute (2 days – 1 week old) cerebral hematoma?

Choices:
- Restricted diffusion
- T1 signal hyperintense to brain
- T2 signal hyperintense to brain
- GRE/SWI images hypointense to brain

MR Contrast Agents and Blood Quiz

This is the phase of hematoma formation where intracellular methemoglobin predominates. This hemoglobin derivative is highly paramagnetic. Because it is still contained within red blood cells, T2/T2* shortening effects still occur, so T2 signal is low, not high. Access of water molecules close to the iron center due to a conformational change in the globin moiety result in T1 shortening and a bright T1 signal.


Question: Which of the following imaging findings at 1.5T would not be expected to be seen in a late subacute (1 week – 2 months old) cerebral hematoma?

Choices:
- Minimal to no restricted diffusion
- T1 signal hypointense to brain
- T2 signal hyperintense to brain
- GRE/SWI images show central hyperintensity

MR Contrast Agents and Blood Quiz

This phase of hematoma formation is dominated by extracellular methemoglobin, released from red blood cells that have ruptured. Methemoglobin is no longer concentrated into multiple intracellular compartments, but becomes uniformly dispersed throughout the hematoma cavity that is now bright on both T1- and T2-weighted images.


Question: Which of the following imaging findings at 1.5T would not be expected to be seen in the center of a chronic (> 2 months old) cerebral hematoma?

Choices:
- Minimal to no restricted diffusion
- T1 signal hypointense to brain
- T2 signal hyperintense to brain
- GRE/SWI central hypointensity to brain

MR Contrast Agents and Blood Quiz

The imaging characteristics of the center of a chronic hematoma reflects its high water content. As such this region is typically hyperintense to brain on T2-weighted images and hypointense on T1-weighted images with no or minimally restricted diffusion. GRE/SWI signal centrally is also high, but may be dark along the rim of the hematoma cavity due to ferritin/hemosiderin deposition.


Question: Which of the following statements about ferritin is incorrect?

Choices:
- It is the principal iron storage molecule found in animal cells.
- It consists of a hollow protein shell into which iron atoms are packed.
- A typical ferritin molecule contains about 2000 iron atoms.
- It is ferromagnetic.

MR Contrast Agents and Blood Quiz

The ferritin core acts as a solid piece of metal with a single magnetic domain, exhibiting superparamagnetism. Ferromagnetic materials, by contrast, consist of multiple erritinhemosiderin.html domains and retain some residual magnetization after an external magnetic field is removed.


Question: Concerning ferritin and hemosiderin, which statement is true?

Choices:
- The iron in hemosiderin is insoluble; the iron in ferritin is soluble.
- Both are visible by light microscopy.
- Ferritin is paramagnetic, but hemosiderin is ferromagnetic.
- Both hemosiderin and ferritin have a fixed structure and composition.

MR Contrast Agents and Blood Quiz

Only (a) is true. Ferritin is much smaller than hemosiderin and can only be visualized at electron microscopy. Both are paramagnetic. Ferritin has a fixed structure and composition; hemosiderin is an amorphous conglomeration of ferritin particles, proteins, and lipids.


Question: Which of the following processes does not affect the appearance of subarachnoid hemorrhage (SAH) as compared to intraparenchymal brain hemorrhage?

Choices:
- SAH clots are small.
- SAH clots are readily dispersed.
- SAH mixes with cerebrospinal fluid.
- Ambient oxygen levels in the subarachnoid space are low, resulting in faster aging of the hematoma.

MR Contrast Agents and Blood Quiz

Only (d) is false.  Ambient oxygen levels in the subarachnoid space are high, resulting in slower aging of the hematoma. For example, methemoglobin formation is rare until at least 1 week after ictus.


Question: Concerning CT and MRI of subarachnoid hemorrhage (SAH), which statement is false?

Choices:
- Acute SAH is better seen on CT than on MRI.
- The best MR sequence for identifying acute SAH is T1-FLAIR.
- Subacute SAH may be better seen on MRI than CT.
- Evidence for remote SAH is much better seen on MRI than CT.

MR Contrast Agents and Blood Quiz

Option (b) is false. The best sequences for identifying SAH on MRI are T2-FLAIR, GRE/SWI, and DWI.


Question: Which of the following statements concerning the appearance of hemorrhage at very low fields (<0.15 T) is true?

Choices:
- Intracellular deoxyhemoglobin is noticeably dark on T2-weighted images.
- Intracellular methemoglobin is noticeably dark on T2-weighted images.
- Extracellular methemoglobin is bright on T1-weighted images.
- The center of a hyperacute hematoma is dark on T1-weighted images.

MR Contrast Agents and Blood Quiz

Only (c) is true. Neither intracellular deoxy- and met-Hb are dark on T2 weighted images as they are at high fields. This is because the dephasing is due to susceptibility which scales with the square of the magnetic field. The center of an acute clot is bright on T1-weighted images due to hemoconcentration and protein effect.


Question: How many sets of gradient coils does the typical MRI scanner use?

Choices:
- 1
- 2
- 3
- 4

MR Safety and Screening Quiz

The typical MR scanner uses 3 sets of paired gradient coils, one set for each of the x-, y-, and z-directions  Link to Q&A discussion


Question: The magnetic field strength of imaging gradients

Choices:
- Is much less than that of the main field (Bo)
- Is slightly less than that of the main field (Bo)
- Is the same as that of the main field (Bo)
- Is slightly greater than that of the main field (Bo)

MR Safety and Screening Quiz

The strength of the magnetic fields generated by gradients are less than 3% of the main magnetic field (Bo), so their static effects are of no concern. Rather, it is the time rate of change of these gradient fields (dB/dt) that poses potential safety issues for MR imaging.


Question: Which of the following physical effects is not the result of gradient activity?

Choices:
- Acoustic noise
- Vertigo
- Peripheral nerve stimulation
- Metal implant heating

MR Safety and Screening Quiz

Vertigo is primarily an effect due to subject movement in the static magnetic field (Bo). The other choices result from gradients.


Question: Concerning acoustic noise due to gradients, which statement is false?

Choices:
- It is due to vibration of the gradient coils due to rapidly switched electrical currents.
- Acoustic noise in MRI may be temporarily uncomfortable, but it poses no real risk to hearing.
- Echo-planar sequences are especially loud.
- All patients and accompanying family members should be required to use ear protection.

MR Safety and Screening Quiz

Levels of acoustic noise in an MR scanner may reach 130 dB(A), producing both temporary and permanent threshold shifts (loss of hearing). Children are especially susceptible.


Question: Concerning gradient-related electromagnetic fields in patients, which statement is false?

Choices:
- It is the coexistent electric field, rather than the gradient magnetic field, which causes peripheral nerve stimulation.
- Peak electric field values occur during the ramp up and ramp down periods of the gradients.
- Electric fields in a patient are concentrated superficially and at bone/fat/muscle junctions.
- The strongest gradient effects typically occur at magnet isocenter in the middle of the imaged field-of-view.

MR Safety and Screening Quiz

Answer d) is false. The centers of the paired gradient coils are located on either side of isocenter, and the strongest gradient effects typically occur toward the ends of the scanner and outside the imaged field-of-view.


Question: Concerning the strength-duration curve for nerve depolarization, which one of the following is true?

Choices:
- The strength-duration curve plots the threshold for electrical stimulation as a function of stimulus strength and duration.
- The shape of the strength-duration curve is approximately linear.
- The rheobase is the minimum time required to stimulate a nerve regardless of stimulus strength.
- The chronaxie is the minimum voltage required to stimulate a nerve at any duration.

MR Safety and Screening Quiz

Only a) is true. The shape of the strength-duration curve is not linear, but has a hyperbolic/exponential shape. The rheobase represents the minimum stimulus required for excitation, while the chronaxie is the required time for a depolarizing stimulus applied at twice the rheobase value.


Question: Which implant would be least likely to demonstrate gradient-induced heating?

Choices:
- Total hip prosthesis
- Deep brain stimulator electrode
- Cardiac pulse generator
- Implanted infusion pump

MR Safety and Screening Quiz

Because gradient switching frequencies are 100,000 times lower than RF frequencies, induced electrical currents are not confined to the "skin" of the implant, but circulate throughout it. Gradient-induced heating occurs in implants with large cross sections having low-resistance closed current loops (such as hip prostheses, pulse generators, and infusion pumps). A deep brain stimulator electrode would heat due to the RF antenna effect, not gradient action.


Question: Concerning gradient-induced heating, which of the following is incorrect?

Choices:
- Gradient heating is typically more important the RF heating in causing tissue injury.
- Changing gradients heat the implant itself.
- Gradient heating is more likely with fast, high slew rate sequencies like echo-planar imaging.
- Gradient heating affects bulky implants with large transverse cross-sections.

MR Safety and Screening Quiz

Gradient heating is much less important than RF heating, and to my knowledge, no serious injuries have been reported from it. Gradient heating involves the implant itself, with secondary heating of the soft tissues, while RF heats the peri-implant tissues directly Link to Q&A discussion


Question: Concerning RF-transmit body coils, which of the following is false?

Choices:
- They consist of multiple rungs in a so-called “bird cage” configuration.
- In addition to transmission they are commonly used for reception of the RF signal.
- They do not extend the full length of the body coil.
- They cannot be seen by the patient.

MR Safety and Screening Quiz

RF body coils are essentially used only for RF transmission, not reception of the MR signal. (Answer b is false). Local receive coils placed near or on the patient are used for this purpose. The other statements are true.


Question: Concerning the use of RF-transmit body coils

Choices:
- They are required for clinical spine imaging
- They are required for clinical head imaging
- They are required for clinical knee imaging
- They are required for phosphorus spectroscopy of the calf muscle

MR Safety and Screening Quiz

Only answer a) is true.  For clinical head and knee imaging, as well as phosphorus spectroscopy, local transmit-receive RF-coils may be employed, and if so, the body RF coil is not activated.


Question: Radiofrequency fields are part of the electromagnetic spectrum considered to have frequencies lying in the approximate range of

Choices:
- 64 MHz to 128 MHz
- 3 kHz to 300 MHz
- 3 kHz to 1 GHz
- 3 kHz to 300 GHz

MR Safety and Screening Quiz

Although many definitions for the frequency limits for RF exist, most extend from the kHz to the hundreds of GHz range, so answer d) is the best choice


Question: Concerning the thermal effects of RF-irradiation as used in MRI, which statement is true?

Choices:
- T1 relaxation with energy transfer from nuclei to the lattice makes a significant contribution to tissue heating.
- The RF magnetic and electric fields point in opposite directions.
- The coexistent electric field (E), not the magnetic field (B1) per se, is responsible for nearly all the RF-thermal effects in MRI.
- About half of transmitted RF power is absorbed by nuclei.

MR Safety and Screening Quiz

Only a small fraction of RF power, 2% or less, is absorbed by nuclei, and thus T1 relaxation releasing this energy makes no significant contribution to heating. Time-dependent E and B1 fields always coexist, and it is the electric field that drives tissue currents and produces heating. (Answer c is correct). By the Faraday-Maxwell equation, the E field “curls around” the changing B1 field in a perpendicular fashion.


Question: Which mechanism of RF-induced tissue heating is unlike the others?

Choices:
- Resistive heating
- Joule heating
- Ohmic heating
- Dielectric heating

MR Safety and Screening Quiz

The correct answer, (d) Dielectric heating, is caused by reorientation of polar molecules, especially water, with the rapidly changing RF electric field.  The first three choices (a), (b), and (c) are all synonyms and represent heating caused by the movement of ionic molecules accelerated by changes in the RF electric field.


Question: Which mechanism is primarily responsible for making my bowl of soup warm up in the microwave oven?

Choices:
- Resistive heating
- Joule heating
- Ohmic heating
- Dielectric heating

MR Safety and Screening Quiz

The correct answer again is (d) Dielectric heating.  Microwaves act to realign polar molecules, which collide with others, dispersing their kinetic energy as heat. Joule, Resistive, or Ohmic heating (all are synonyms) produce thermal effects by movement of ions and are more important at frequencies lower than microwaves.


Question: The units for specific absorption rate (SAR) are

Choices:
- Watts per kilogram
- Watts per second
- Joules per kilogram
- Joules per second

MR Safety and Screening Quiz

SAR is power (watts) deposited in a certain mass of tissue (kg). Answer a) is correct.


Question: Concerning SAR which of the following is false?

Choices:
- SAR is proportional to tissue electrical conductivity.
- SAR decreases with increasing body size.
- SAR is proportional to the square of both Bo and B1.
- SAR is proportional to the duty cycle.

MR Safety and Screening Quiz

Answer b) is false. SAR increases exponentially with increasing body size and is thus a significant concern with large or obese patients.


Question: What are the units of measurement for the duty cycle?

Choices:
- Seconds
- Watts/kg
- Percent
- Joules/second

MR Safety and Screening Quiz

Duty cycle is the fraction of time in a pulse sequence that RF is being transmitted, so it is measured in percent (%).  Link to Q&A discussion


Question: A 50-kg woman is imaged using a 3-minute pulse sequence having an SAR of 2.0 W/kg.  The total RF energy absorbed is

Choices:
- 180 Joules
- 300 Joules
- 3000 Joules
- 18,000 Joules

MR Safety and Screening Quiz

To solve this you have to convert minutes to seconds and recognize that 1 Watt = 1 Joule per second. Total energy = mass x time x SAR = (50 kg) x (180 s) x 2 (W/kg) = 18,000 J.


Question: Consider two otherwise identical gradient echo pulse sequences, the first using an RF-flip angle (α) = 15º and the second using α = 30º.  The SAR of the second pulse sequence is

Choices:
- Twice as large as the first.
- Half as large as the first.
- Four times as large as the first.
- One fourth as large as the first.

MR Safety and Screening Quiz

For uniform rectangular RF pulses, the SAR is approximately proportional to the square of the RF-flip angle (α), so doubling the flip angle quadruples the SAR.


Question: Which of the following is not the name of an MRI Operating Mode based on perceived risk to subjects as defined by the International Electrotechnical Commission (IEC)?

Choices:
- Normal
- First Level
- Second Level
- Third Level

MR Safety and Screening Quiz

There is no Third Level Operating Mode. Also note that Normal is the lowest level and is not the same as First Level.


Question: Concerning Operating Modes for MRI as defined by the International Electrotechnical Commission (IEC) which statement is false ?

Choices:
- The same SAR limits apply regardless of whether a volume transmit or local transmit coil is used.
- Higher SAR limits are allowed for extremity imaging than trunk imaging.
- Other factors (such as static field strength and rates of time-varying gradients) are used in addition to SAR levels when defining the MRI Operating Mode
- Second level operation can only be performed under an appropriate ethics/human studies/institutional review board protocol

MR Safety and Screening Quiz

Different limits apply depending on the type of transmit coil (volume vs local) as well as area imaged, so a) is false.  The other statements are true.


Question: When is it acceptable to change from Normal to First Level Controlled Operating Mode?

Choices:
- Whenever one needs to increase the number of slices for a given TR.
- Whenever one needs to perform more rapid imaging in a moving patient.
- Whenever deemed necessary and under supervision of a physician.
- Whenever the patient’s body weight is unknown and may be underestimated.

MR Safety and Screening Quiz

Answer c) is correct. First Level Controlled Operating Mode requires physician supervision and explicit recognition by the MR tech or operator to confirm awareness of potential risks. The other choices are possible reasons one might wish to upgrade the operating mode, but cannot be done without physician assessment and supervision.


Question: Which one of the following pulse sequences would have the lowest SAR?

Choices:
- A single-shot echo-planar diffusion scan of the bran
- A T2-weighted turbo spin-echo scan of the pelvis
- A T1-weighted, fat suppressed spin-echo image of the cervical spine
- A 2D time-of-flight MRA of the lower extremities

MR Safety and Screening Quiz

The EPI diffusion scan, using predominantly recalled echoes by gradient reversal, would have the lowest SAR of the scans listed.


Question: Which of the following technical parameter changes alone would not be useful in reducing SAR?

Choices:
- Increase TR
- Increase number of slices
- Reduce flip angle
- Use of hyperechoes

MR Safety and Screening Quiz

Option b), increasing the number of slices for a given TR would actually increase SAR, not decrease it. The other answers are true.


Question: All of the following are trade-offs for the use of low SAR RF-pulses except

Choices:
- More slice cross-talk
- Longer minimum TE values
- Longer imaging time
- Fewer slices for a given TR

MR Safety and Screening Quiz

Low SAR pulses are played out at lower amplitude but longer duration than normal RF pulses. This means they operate with lower transmit bandwidths and thus have better slice profiles. So slice cross-talk is reduced, not increased (option a is false). The longer duration low SAR pulses impair minimum TE and TR values, interecho spacing for TSE sequences, and hence may increase imaging time.


Question: Which of the following physical mechanisms is not an important factor in RF-induced thermal injury?

Choices:
- Inductive heating
- Magnetohydrodynamic effect
- Heating of a resonant loop
- Antenna effect

MR Safety and Screening Quiz

The magnetohydrodynamic effect is a current generated by ions in blood moving though a magnetic field. Although it may be responsible for altering the appearance of the EKG, it has no direct harmful physical effects such as thermal injury.


Question: Which of the following statements about the “antenna effect” is false?

Choices:
- It explains SAR hot spots at the end of a wire or electrode.
- It results from standing waves along the length of the wire.
- The effect is maximal when the wire measures close to the RF wavelength.
- Wires measuring about 26 cm at 1.5T and 13 cm at 3.0T are the most likely to experience this phenomenon.

MR Safety and Screening Quiz

Answer c) is false. The antenna effect is maximal when the length of the wire is one-half of the RF wavelength.  The wavelength actually varies depending on the tissue, but for water-containing tissues the 26 cm and 13 cm values are a reasonable starting point.


Question: Which of the following would not be an acceptable position for a patient undergoing MRI?

Choices:
- Prone
- Hands clasped across lap
- Arms straight up
- Supine with knees bent at 90º

MR Safety and Screening Quiz

Skin-to-skin contact must be avoided to prevent induced current loops and possible burns during MRI. So crossing arms or legs and holding hands (answer b) should not be permitted  Link to Q&A discussion


Question: What should be done if an MR patient has a large tattoo?

Choices:
- Nothing; they are totally safe to scan except in rare cases.
- Warn the patient about heating and to notify tech immediately if any discomfort.
- Allow scanning, but apply an ice pack to the tattoo during the procedure.
- Do not scan the patient; large tattoos are contraindicated due to high risk of burns.

MR Safety and Screening Quiz

We recommend strategy in answer b), to warn the patient to be aware of any discomfort and that burns can occasionally occur. Although some centers have recommended applying an ice pack, this seems unproven and unnecessary.


Question: Concerning transdermal medication patches, which statement is incorrect?

Choices:
- All patches must be removed prior to scanning.
- Only metal-backed patches must be removed.
- A metal back patch need not be removed if it is not in the region of the transmit RF-coil.
- Before removing a patch for MRI, the patient’s physician should be contacted to be sure it is safe for the patient to not receive her patch medication for the duration of the scan.

MR Safety and Screening Quiz

Only metal-backed patches within the RF field need to be removed, so statement a) is false. Those made of cloth or paper pose no danger.


Question: Concerning large patients that may touch the walls of the scanner, which of the following is true?

Choices:
- They may feel uncomfortable and experience claustrophobia, but are in no medical danger.
- Ideally a sheet should be placed between the patient and the wall to avoid bacterial contamination of the scanner from the patient’s skin.
- Special foam padding provided by the manufacturer should be used to prevent the patient from touching the walls.
- It is OK to scan the patient without padding if they are too big.

MR Safety and Screening Quiz

Both cutaneous and deep burns can occur if the patient touches the inner wall of the MRI scanner. In this location local RF fields are the highest and there can be capacitive coupling with the RF coil (that is just a few cm away). Specialized foam padding should always be used (answer c is correct). Thin sheets or blankets or nothing is not acceptable.


Question: Concerning wires and cables within the bore of the MR scanner, which statement is false?

Choices:
- Skin contact must be avoided by padding or positioning.
- The wires should be run down along the sidewall of the MR bore parallel to the main magnetic field.
- The wires should not be crossed.
- If more than one wire is exiting, it is ideal to leave a little space between them to prevent capacitive coupling.

MR Safety and Screening Quiz

Option b) is false. Wires should ideally be run down the center of the MR system out between the patient's legs. Wires located close to the walls of the scanner would be close to the RF coil and be at risk for induced currents.


Question: Concerning Specific Energy Dose (SED) and Specific Absorption Rate (SAR), which statement is true?

Choices:
- They are essentially the same, except for a conversion factor to correct for units of measurement.
- The units for SED are Joules/kg.
- Both represent rates of energy absorption by the body during an MRI scan.
- If every sequence in a scanning protocol has SAR values that lie safely within regulatory limits, the SED cannot be excessive.

MR Safety and Screening Quiz

SED and SAR are different. SAR is the rate of energy absorption, measured in W/kg. SED is not a rate, but the total energy absorbed by the body during an entire MRI scan, measured in Joules/kg (answer b is true). It is possible, for example, for each sequence in an MRI scanning protocol to lie safely within regulatory SAR limits, yet total energy deposition in the patient over the course of the entire exam to be excessive. Some MR manufacturers now compute and report both SAR and SED, and limit scanning in a full exam if the accumulated SED is too high.


Question: A 50-kg woman undergoes an MR protocol that consists of two sequences: Sequence 1, lasting 2 minutes, with SAR = 1 W/kg; followed by Sequence 2, lasting 4 minutes, with SAR = 2 W/kg.  The SED for the entire protocol is calculated to be

Choices:
- 10 J/kg
- 100 J/kg
- 600 J/kg
- 800 J/kg

MR Safety and Screening Quiz

Using the defining formula SED = SAR x acquisition time, remembering that minutes must be converted to seconds, and that 1 Watt = 1 Joule/sec, we calculate for Sequence 1: SED1 = (1 W/kg) x (120 s) = 120 J/kg and for Sequence 2: SED2 = (2 W/kg) x (240 s) = 480 J/kg.  So the total SED is 120 + 480 = 600 J/kg (answer c).


Question: All of the following statements about the B1+ field and  B1+rms are true except for

Choices:
- The B1+ field rotates in the opposite direction to nuclear precession.
- SAR is directly proportional to [B1+rms]²
- SAR is directly proportional to [Bo]², but B1+rms is independent of Bo.
- The strength of the B1+ field scales linearly with the voltage supplied to the transmitter.

MR Safety and Screening Quiz

The B1+ field rotates in the same direction as nuclear precession, so option a) is false. B1+ is the component of B1 responsible for tipping of the net magnetization. It can be computed directly by measuring the relative voltage driving the RF-transmitter, and so depends less on the patient or main magnetic field.


Question: Concerning occupational exposure to MRI in the clinical environment, which one of the following statements is true?

Choices:
- Consistent regulatory limits for occupational exposure to magnetic fields exist throughout Europe and the Americas.
- MRI staff working around scanners with fields of 7T or higher commonly experience nausea, dizziness, unsteadiness, and/or see flashes of light.
- There is nothing that can be done to reduce these short-term sensory effects.
- Pregnant MR technologists are at increased risk for miscarriages or premature births.

MR Safety and Screening Quiz

Short-term sensory changes (including nausea, vertigo, and/or magnetophosphenes) are experienced by about one-fourth of MR staff working around 7T scanners. (Answer b is true.) These effects can be mitigated by moving slowly around the scanner and avoiding the scanner bore entrance. Unfortunately, national and international regulations about EM field exposure are varied and often contradictory.  Pregnant MR technologists and other healthcare workers in the MRI environment do not seem to have increased risk for miscarriages or other birth-related problems.


Question: Do cell phones cause cancer?

Choices:
- Definitely yes
- Definitely no
- Probably no, but some data suggests a potential small effect.
- Probably yes, but some data suggests no effect.

MR Safety and Screening Quiz

Cell phone use has been claimed to be associated with gliomas, meningiomas, and vestibular schwannomas.  Much of the literature in support of these claims is clearly flawed, and at least two large studies have found no statistically significant effects. There are, however, a few studies suggesting a small effect, perhaps most strongly for vestibular schwannomas and meningiomas. My answer is therefore c), though you might have your own opinions on this one.


Question: Why did early regulators establish the 5-gauss line as a safety limit for exposure of the general public around MRI facilities?

Choices:
- It is the field strength where a ferromagnetic cerebral aneurysm clip begins to move.
- It is the field strength where a paper clip or other equivalent small metal object will fly into the scanner.
- It is the field strength where 1970’s era pacemakers might begin to malfunction.
- It is approximately 10 times the earth’s magnetic field.

MR Safety and Screening Quiz

Different origin stories exist for the 5-guass line, but there is general agreement that it was based on the field strength at which certain 1970’s era pacemakers began to malfunction. The observed malfunction was likely due to closure of the internal reed switch, a magnetically sensitive component which changes the operating mode of the pacemaker. The 5-gauss limit as a safety line was officially recommended by the FDA in 1983.


Question: Concerning the safety of cerebral aneurysm clips in the MR environment, which statement is incorrect?

Choices:
- If an aneurysm clip is safe by testing at 3.0T, it will be safe at 7.0T.
- Ferromagnetic aneurysm clips have not been manufactured since the mid-1980’s.
- A patient with a commercially produced aneurysm clip implanted within the last 20 years is safe to scan at 3.0T.
- Always review the operative note or patient’s implant card prior to scanning to ensure MR safety, especially in the 7.0T environment.

MR Safety and Screening Quiz

Notwithstanding the great reticence of scanning patients with aneurysm clips, the risk in the modern era is miniscule, as ferromagnetic clips have not been produced since the 1980’s. All modern aneurysm clips are composed of titanium titanium-alloys, MP35N (nickel/chromium/cobalt), Elgiloy/Phynox (cobalt/nickel/iron) or other non- or at most minimally ferromagnetic properties. Thus virtually any cerebral aneurysm clip implanted in the last 25 years will be MR compatible at least up to 3.0T. However, a few clips that are safe at 3.0T, especially those made of Elgiloy or stainless steel, have exhibited very strong torques at ultra high fields, so it cannot be assumed that safety at 3.0T implies safety at 7.0T.


Question: A patient with a recently placed programmable shunt placed is referred for head MRI. What do you do?

Choices:
- Do not scan the patient. A programmable shunt is an absolute contraindication to MRI.
- Confirming that the shunt is MR Conditional at up to 3.0T, scan the patient and send him home.
- Send the patient to neurosurgery clinic immediately after the scan to have his valve pressure checked.
- Tell the patient to make an appointment with his neurosurgeon within the next week to have his valve pressure checked.

MR Safety and Screening Quiz

All currently manufactured programmable shunt systems are considered MR Conditional up to 3.0T. The main risk of MRI is unintentional resetting of the valve pressure. This occurs in up to 40% of patients with Codman-Hakim® valves and even up to 10% of valves marketed as "MR immune". Within 4 hours after exposure to MRI, all patients must have their shunt pressures interrogated and potentially reprogrammed to the original settings.


Question: Concerning precautions that need to be followed for MR conditional intracranial pressure monitoring systems, which statement is false?

Choices:
- Obey the usual restrictions on field strength, spatial gradient field, slew rate, and SAR.
- Verify the sensor is working properly prior to MRI.
- Disconnect all removable cables and wires from the device.
- Make sure non-removable wires are arranged in a straight line along the bore of the scanner and away from the patient’s head.

MR Safety and Screening Quiz

Statement d) is false. To prevent excessive RF-heating of the sensor tip, the non-removable wires and wire-containing tubing must not lie in a straight-line but be specially positioned in a coil-like configuration of several small loops on or near the patient's head. Sophysa even provides a special holder to wrap and secure the wires of their ICP sensor.


Question: Which one of the following is the most significant safety concern with the scanning of a patient with a deep brain stimulation system?

Choices:
- Permanent damage to the implanted pulse generator
- Thermal burn at the electrode tip
- Cutaneous burns along ascending wires in the neck
- Induction of seizures

MR Safety and Screening Quiz

The primary MR safety concern for DBS systems is heating at the electrode tip due to induced currents and the antenna effect. Antennas capture electromagnetic waves and develop standing-wave patterns of voltage and current that are concentrated near their tips. Three clinical cases have been reported in association with MRI, including one leaving permanent neurologic deficits.


Question: Why is it recommended that eye makeup be removed prior to MRI?

Choices:
- This is a myth; eye makeup doesn’t have to be removed.
- It can cause significant image artifacts around the orbit.
- Severe burns can occur on the eyelids.
- Corneal injury and blindness can occur.

MR Safety and Screening Quiz

All eye make-up, especially mascara, should be removed prior to imaging.  Such cosmetics often contain iron oxides that create a local artifact and may even result in eye irritation during MR imaging. No serious injuries have been reported.


Question: Which of the following orbital implants should elicit the most concern from an MR safety perspective?

Choices:
- Artificial intraocular lenses
- Contact lenses
- Scleral band
- Retinal tacks

MR Safety and Screening Quiz

Although uncommonly used today, some retinal tacks (used for repair of complex detachments) are considered MR unsafe or MR conditional. The other items on the list should present no safety concerns.


Question: What is the major safety concern for MR imaging of cochlear implants?

Choices:
- Movement/dislodgement of the internal magnet
- RF-induced heating at the tip of the cochlear electrode due to the “antenna effect”
- Electronic shorting/malfunction of the electronic stimulator
- Scalp burns adjacent to the subcutaneous receiver coil

MR Safety and Screening Quiz

Pain from magnet movement occurs in a substantial fraction of patients. It may be minimized by wrapping the head with a tight-fitting elastic bandage prior to entering the scanner. In some cases the internal magnet must be removed and replaced as a condition of scanning. In some cases the magnet may be completely dislodged from its base. The antenna effect is not a concern due to the short length of the wire/electrode.


Question: Which of the following dental implants would pose the biggest safety concern in MRI?

Choices:
- Metal crowns and bridges
- Amalgam fillings
- Braces
- Magnetic dentures

MR Safety and Screening Quiz

Conventional (all porcelain/acryllic dentures) are of no concern, but magnetic dentures contain permanent magnets embedded in their periphery that will be attracted to the main magnetic field.  These should be removed prior to scanning. Metal crowns, bridges, and especially braces will create substantial artifacts, but only rare reports of problems during MRI have been reported.


Question: Which upper airway device should be viewed as a potential safety concern in the MR environment?

Choices:
- Non-cuffed endotracheal tube
- Endotracheal tube with spring-loaded pilot balloon valve
- Reinforced endotracheal tube
- Laryngeal mask airway

MR Safety and Screening Quiz

The only upper airway devices of potential concern would be reinforced endotracheal tubes that contain a metal coil (usually stainless steel) spirally wound in the wall of the tube to prevent kinking. Many are considered to be MR Unsafe.


Question: What is the major MR safety concern about breast tissue expanders?

Choices:
- Loss of saline due to magnetic effects on the valve mechanism
- Dislodgment of the MAGNA-SITE®  port
- Cutaneous burns over the port
- Melting of the silicone capsule adjacent to the port

MR Safety and Screening Quiz

Most breast tissue expanders use a MAGNA-SITE®  port for injection. This contains a central permanent magnet for localization purposes that may become dislodged in the MR field. Pain and localized heating have been reported, but no burns. Most manufacturers have declared their tissue expander systems to be MR Unsafe.


Question: What should be done if a patient with an inferior vena cava (IVC) filter needs a scan?

Choices:
- He’s out of luck; nearly all of these are MR Unsafe.
- The patient can be scanned, but no sooner than 6 weeks after implantation.
- The patient can be scanned but should be warned there is a high risk that the filter may migrate.
- The patient can be safely scanned provided MR Conditions are followed.

MR Safety and Screening Quiz

All currently manufactured IVC filters are considered MR Conditional at 1.5T and 3.0T. The spontaneous migration rate for properly implanted IVC filters is on the order of 1%, and there is no evidence MRI affects this rate. There is no good reason to wait 6 weeks before MRI.


Question: During the last decade in the United States, the leading cause of MRI-related deaths has been

Choices:
- Infusion pump malfunction
- Projectiles
- Pacemaker malfunction
- Burns

MR Safety and Screening Quiz

Surprisingly to many, the answer is infusion pump malfunction. At least a half-dozen such cases were reported in the USA alone, a situation so significant that the Food and Drug Administration (FDA) issued a special safety communication in 2017 to address this issue.


Question: Life-threatening effects of the magnetic field on implanted infusion pumps include all except

Choices:
- Deep peri-implant burns due to RF- and/or Gradient-induced eddy currents
- Increased or decreased rate of drug delivery
- Cessation of pump operation while scanning with delayed restart
- Permanent device failure due to demagnetization of the pump magnet

MR Safety and Screening Quiz

Although some heating around infusion pumps, like other metal implants, may occur, severe burns have not been reported and this is not a major concern. The other items (b) – (d) do constitute significant risks for the device.


Question: Which of the following intravascular devices should be considered MR Unsafe?

Choices:
- Aortic stent graft
- Drug-eluting coronary stent
- Swan-Ganz thermodilution catheter
- Vascular closure device

MR Safety and Screening Quiz

In a famous index case from 1988, a portion of a Swan-Ganz catheter outside the patient "melted" during MRI.  Since then, Swan-Ganz catheters have been considered MR Unsafe.  Link to Q&A discussion


Question: Failure of drug delivery by an implanted infusion pump affected by a magnetic field is particularly dangerous for which drug?

Choices:
- Bupivacaine
- Morphine
- Baclofen
- Floxuridine (5-FUdR)

MR Safety and Screening Quiz

Intrathecal baclofen via constant infusion is used to treat pain and spasticity. If the infusion is suddenly stopped, a life-threatening baclofen withdrawal reaction may occur.  Temporary disruption of administration of the other drugs would not likely be dangerous.


Question: Concerning the following bariatric devices, which should raise the greatest MR safety concerns?

Choices:
- Adjustable gastric bands
- Gastric balloons
- Gastric electrical stimulators
- External gastric drainage devices

MR Safety and Screening Quiz

Gastric electrical stimulators (GES), sometimes called “gastric pacemakers” consist of a subcutaneously implanted pulse generator with leads that attach to the stomach musculature or distal vagal nerves. All currently produced GES devices are considered MR Unsafe. The other bariatric items are made predominantly of plastic and silicone and are either MR Safe or (minimally) MR Conditional.


Question: Which of the following contraceptive devices is considered MR Unsafe?

Choices:
- Copper 7 IUD
- Chinese stainless steel ring IUD
- Filshie tubal ligation clips
- Essure® tubal occlusion devices

MR Safety and Screening Quiz

All the devices listed above are considered MR Conditional except for the Chinese stainless steel ring IUD that is MR Unsafe.  These were distributed exclusively in China between 1988 and 2000. But because millions of such IUDs were implanted, a reasonable possibility exists that a middle-aged or older Chinese woman might still have one in place.


Question: Which metal is not commonly used for modern orthopedic implants?

Choices:
- 410 stainless steel
- 316L stainless steel
- Cobalt-chromium alloy
- Pure commercial titanium

MR Safety and Screening Quiz

All of the listed metals are used in orthopedic implants except for the 400 series of stainless steels which are ferromagnetic.