Question: Why might a surgical supply manufacturer choose to make halos and external fixation rods out of carbon fiber reinforced polymer?

Choices:
- They are lighter than their metal equivalents.
- They are stronger and more flexible than their metal equivalents.
- They are only weakly conductive.
- They are only weakly ferromagnetic.

MR Safety and Screening Quiz

The primary reason for using these materials is that they are essentially non-conductive. When rods or halo ring and pins are made out of conductive metals such as MR-compatible titanium or other non-ferromagnetic alloys, they may result in thermal burns along pin tracts or where the frame is in contact with the skin. Because external fixation devices lie predominantly outside the body (where the E-field is strongest), conductive currents may be induced in the rods.


Question: A patient with an external fixation frame complains of tingling and discomfort due to vibration of the frame during scanning.  What is the likely cause of this?

Choices:
- Resonant amplification of normal scanner mechanical vibrations
- Vibration of the frame due to gradient-induced eddy currents.
- Vibration of the frame due to RF-induced eddy currents.
- Subconscious to-and-fro movement of the frame by the patient due to peripheral nerve stimulation

MR Safety and Screening Quiz

Even with fully MR-compatible external fixation arrays, an occasional patient may experience tingling or tugging during scanning, necessitating early termination of the scan. In some instances this is due to vibrations in the frame due to gradient-switching-induced eddy currents. While harmless, these vibrations may be misinterpreted by the patient as heating. The phenomenon is more likely to occur when the fixation device is located far from magnet isocenter.


Question: The abbreviation CIED stands for

Choices:
- Cardiac Implanted Electronic Device
- Cardiac Implanted Electrical Defibrillator
- Cardioverting Internal/External Defibrillator
- Cardiac Internal Excitation Device

MR Safety and Screening Quiz

CIED is a commonly used abbreviation in the medical literature to refer to any Cardiac Implanted Electronic Device used to detect and/or treat rhythm distuburbance. CIED’s include both Permanent Pacemakers (PPMs) and Implanted Cardioverter-Defibrillators (ICDs).


Question: Two-lead CIEDs typically terminate in

Choices:
- The right atrium and right ventricle
- The right atrium and left ventricle
- The right ventricle and left ventricle
- The left atrium and left ventricle

MR Safety and Screening Quiz

Most two-lead CIEDs terminate in the right atrium and right ventricle, allowing for dual-chamber sensing and pacing that follows the nature contraction of the heart  Link to Q&A discussion


Question: Concerning Implanted Cardioverter-Defibrillators (ICDs), which statement is false?

Choices:
- ICDs are the preferred CIED for treating ventricular fibrillation.
- ICD’s are the preferred CIED for treating symptomatic bradycardia.
- ICD’s are designed to deliver high-energy shocks.
- Some ICDs do not have shock leads in the heart.

MR Safety and Screening Quiz

ICD’s are designed to treat tachyarrhythmias like ventricular fibrillation, while permanent pacemakers are preferred for treating symptomatic bradyarrhythmias. Subcutaneous ICDs have their shock leads outside the heart.


Question: “Leadless” pacemakers are generally placed in the

Choices:
- Left atrium
- Left ventricle
- Right atrium
- Right ventricle

MR Safety and Screening Quiz

Most leadless pacemakers like the Nanostim™ and Micra™ are placed in the right ventricle. Internal accelerometers allow them to partially sync with right atrial contraction, but essentially they only sense and pace the RV. Because of their small size, they are unable to deliver high-energy shocks for tachyarrythmias.


Question: Which of the following pacemaker scenarios would invoke the greatest MR safety concern?

Choices:
- Scanning a patient with retained epicardial leads
- Scanning a patient with a temporary transvenous pacemaker
- Scanning a patient within 6 weeks of placement
- Scanning a patient with a legacy/non-conditional pacemaker

MR Safety and Screening Quiz

Due to the risk of significant lead heating demonstrated in animal models, scanning a patient with a temporary transvenous pacemaker is considered unsafe.  Scanning a patient with a legacy pacemaker carries a small risk (which can be mitigated by using procedures documented by the Heart Rhythm Society (2017).


Question: What is the principal risk associated with scanning a patient with a subcutaneously implanted loop recorder?

Choices:
- Skin burns over the device
- Permanent malfunction of the device
- Electric, shock-like sensations
- Erasure of previously recorded data

MR Safety and Screening Quiz

Loop recorders are considered MR Conditional at 1.5T and/or 3.0T. Because data may be corrupted or erased by magnetic fields, it is recommended that any desired recorded information be downloaded before the MRI and cleared after the MRI.


Question: Concerning the MR safety of cardiac valves and annuloplasty devices, which statement is true?

Choices:
- Most older metal valves are considered MR Unsafe.
- All valves and annuloplasty devices are considered MR Safe or Conditional up to 3.0 T.
- A mandatory 6 week waiting period is required before scanning for all valves.
- A mandatory 6 week waiting period is required before scanning for any valve or annuloplasty device containing metal.

MR Safety and Screening Quiz

The results of numerous investigations have demonstrated that metal-containing valves do undergo magnetically induced torques, but the magnitude of this effect is much less than the force exerted by the beating heart itself. This is in part because the metals used in modern mechanical valves (titanium, Elgiloy®) are not ferromagnetic. Even very old stainless steel valves are likewise considered of no danger in MRI. Thus at present, most centers consider all implanted heart valves and annuloplasty rings conditionally safe for MR imaging up to 3.0T, and do not require any waiting period after surgery before they can be scanned.


Question: A person with altered mental status is sent from the emergency room for an urgent MRI, but no family, prior scans, or medical history are available. What should you do to ensure reasonable safety for the exam?

Choices:
- Call the ER physician and ask if there are any reasonable alternatives to MRI in light of the absent history, and if not, go ahead and perform the scan as ordered.
- Use a hand-held ferromagnetic metal detector to exclude a dangerous implant or foreign body
- Obtain x-rays of the head & neck, chest, and abdomen/pelvis as a screening procedure
- Refuse to do the MRI until a full medical history can be obtained.

MR Safety and Screening Quiz

In the total absence of medical history, minimum screening prior to MRI should involve x-rays of the head & neck, chest, and abdomen/pelvis which will identify the overwhelming majority of potentially dangerous implants and foreign bodies. So c) is true. Although it is reasonable to ask the ER physician if an alternative imaging exam could be performed instead, it is not sufficient just to carry out the order for the MRI without further safety checks, so a) is false. A hand-held metal detector will not necessarily identify objects deep within the body or those composed of non-ferromagnetic metals, so b) is false. Refusal to do the exam may deny the patient an important and urgent diagnosis that could compromise his health, so d) is also false.


Question: Which of the following is considered an “active” implant?

Choices:
- Implanted infusion pump
- Magnetic dentures
- Cerebrospinal fluid shunt with a programmable valve
- Swan-Ganz catheter

MR Safety and Screening Quiz

Active implants contain their own power source, so a), an implanted infusion pump is the only correct answer since it has a battery.  Magnetic dentures and programmable CSF valves contain permanent magnets, but do not have an intrinsic power source. Swan-Ganz catheters may contain wires and electronic sensors, but are powered externally and hence considered “passive” devices.


Question: Which of the following is not currently acceptable terminology for the safety of a device in MRI?

Choices:
- MR Unsafe
- MR Conditional
- MR Compatible
- MR Safe

MR Safety and Screening Quiz

Although used before 2005, MR Compatible (c) is no longer acceptable terminology according to ASTM Standard F2503-20.  Many devices manufactured and tested before 2005 may still carry the old labeling, however.


Question: Concerning safety labeling of devices, which of the following statements is true?

Choices:
- A large silicone implant cannot be rated as MR Safe if it contains a single tiny non-ferromagnetic clip deep inside it.
- An MR Conditional device is safe to scan provided the majority of specified conditions are followed.
- Any implant containing a permanent magnet is MR Unsafe.
- If an implant does not undergo movement or heating under rigorous ASTM testing, it can be rated MR Safe.

MR Safety and Screening Quiz

To be considered MR Safe, a device must contain no metal components whatsoever. The tiny screw in the silicone implant renders it MR Conditional, so a) is true.  MR Conditional devices must meet all of the conditions specified, so b) is false. Having a permanent magnet inside does not necessarily render a device MR Unsafe (though it may be). Finally, if an implant contains a small amount of metal, even if it does move or heat up under laboratory testing, it cannot be considered MR Safe, only MR Conditional. Hence d) is also false.


Question: Concerning projectile incidents in MRI, which of the following is true?

Choices:
- Worldwide at least a dozen people have died from projectile accidents since the beginnings of MRI.
- All reported deaths have involved ferromagnetic oxygen cylinders.
- Most reported projectile incidents involve small objects.
- An object made of non-ferromagnetic materials can still become a dangerous projectile.

MR Safety and Screening Quiz

Only two documented deaths have been reported from projectile injuries in MRI – a child in New York in 2001 and a man in Mumbai in 2018. Both were hit with ferromagnetic oxygen cylinders. So a) is false and b) is true. Most reported projectile incidents involve large objects (e.g. wheelchairs, carts, IV poles) inadvertently brought into the MR room, so c) is false. Objects made entirely of non-ferromagnetic materials would be only weakly attracted to the magnetic field and would not pose a danger, hence d) is false.


Question: Which of the following statements about metal detectors in the MR setting is false?

Choices:
- Metal detectors in MRI are very similar to those used for airport screening.
- The Joint Commission now requires all new and renovated MR suites to be equipped with ferromagnetic metal detectors.
- MR metal detectors cannot reliably detect deeply implanted ferromagnetic materials.
- Alarm fatigue can be a problem at sites using MR metal detectors.

MR Safety and Screening Quiz

Answer a) is false, while the other statements are true.  Airport detectors are designed to the presence of any metal, whereas MRI detectors are designed to alarm in the presence of ferromagnetic metal only. Link to Q&A discussion


Question: Concerning MR imaging in the pregnant patient, which statement is false?

Choices:
- Because of unknown risks to the fetus, MR should only be performed when the life of the mother or fetus is immediately threatened.
- The administration of gadolinium contrast should be avoided if at all possible.
- Low-SAR sequences are preferred to avoid heating fetal tissue.
- Quiet gradient sequences are preferred to avoid fetal exposure to loud noise after the first trimester.

MR Safety and Screening Quiz

Although the risk of MR to the developing fetus is extremely low, it may not be zero and thus judicious use of MRI is recommended only after discussion with the patient. Most valid indications for MRI are serious but not immediately life-threating (e.g. maternal stroke, fetal anomaly), so choice a) is false. The other choices are true.


Question: Which of the following commonly encountered postoperative items should be further scrutinized as a potential MR safety hazard:

Choices:
- Skin staples
- IV catheter and tubing
- EKG pads
- Penrose drain

MR Safety and Screening Quiz

EKG pads, answer c) should draw the most concern, as those not certified for MRI contain metal and may cause skin burns. Skin staples are made of non-ferromagnetic metal and pose no risk of injury or dislodgment. IV catheters and tubing are safe (provided no metal clamps are attached). Finally, penrose drains contain no metal and are also MR Safe.


Question: For which patients is temperature monitoring during MRI not required?

Choices:
- Healthy teenagers
- Healthy infants
- Anesthetized patients
- Elderly patients

MR Safety and Screening Quiz

Otherwise healthy teenagers and non-elderly adults undergoing routine MRI would be unlikely to experience thermodynamic instability, and not require temperature monitoring. So answer a) is correct. The other listed types of patients are at risk and should be monitored.


Question: The most reliable device to measure body temperature during MRI is

Choices:
- A rectal fiberoptic probe
- An esophageal fiberoptic probe
- A foley catheter thermistor
- An LCD skin detector placed in the axilla

MR Safety and Screening Quiz

The best answer is b), a probe with either a fluorotopic or gallium-arsinide (GaAs) detector and fiberoptic cable placed in the distal third of the esophagus.


Question: In which of the following orbital locations would the presence of small piece of metal not be a contraindication to MRI?

Choices:
- Floating in the vitreous humor
- In the retroconal space
- In the lacrimal gland
- On the conjunctiva

MR Safety and Screening Quiz

The lacrimal gland, answer c) is sufficiently far away from vital visual structures to cause injury if magnetically induced displacement occurred.


Question: Considering the use of orbital CT to screen for metallic foreign bodies prior to MRI, which of the following is false?

Choices:
- Orbital CT should be performed routinely on all machinists, pipe fitters, foundry workers, or anyone with similar occupational exposure to metal fragments.
- Plain films of the orbits are an acceptable alternative to CT.
- Low-dose CT techniques should be employed.
- CT may detect metal fragments too small to be of clinical concern for MRI.

MR Safety and Screening Quiz

Simply possible exposure to metal by virtue of their work is, in my opinion, not enough to warrant expensive screening by CT if there is no known history of injury. The actual risk of significant eye injury is exceedingly rare, with less than a half dozen cases reported over 40 years. So answer a) is false. The other statements are all true.


Question: Concerning bullets and ballistic fragments, which statement is true?

Choices:
- A hand-held ferromagnetic metal detector can reliably determine whether a bullet is made of lead or steel.
- Dual energy CT can reliably determine whether a bullet is made of lead or steel.
- For the last 25 years in the USA, steel-jacketed rifle bullets have been illegal to sell or possess.
- Deformity of a bullet fragment or a debris trail seen on x-ray suggests the projectile is not made of steel.

MR Safety and Screening Quiz

Only answer d) is correct, but such findings are not definitive, just strongly suggestive about composition.  The other choices are all false. If the bullet sets off the alarm on a hand-held detector it is ferromagnetic, but a negative result is inconclusive. Likewise, although dual-energy CT and other techniques hold promise, technical issues still exist. Finally, steel-jacketed bullets are illegal in the US for handguns, but not for rifles.


Question: In assessing a patient with a presumed ferromagnetic bullet or shrapnel, which factor is the most important in assessing risk of performing an MRI?

Choices:
- Location of the fragment
- Shape of the fragment
- Length of time since implantation
- Whether it was acquired in a military setting

MR Safety and Screening Quiz

Like real estate, it’s all about location, location, location. Choice a) is the best choice. If the foreign body is embedded in soft tissue like the brain, even with scarring it can still move appreciably when placed in a magnetic field and cause appreciable local tissue damage. Conversely, fragments embedded in firm tissue like muscle, bone, or tendon, are less likely to move. The shape is important, as long jagged pieces are more dangerous than small round ones. And the longer it has been since injury, the more time has passed for development of scarring/fibrosis that would restrict movement in a magnetic field.  But location trumps shape and time in relative importance. Having been acquired in a military setting increases the probability that the fragment is ferromagnetic, but the question states you have already presumed this composition.


Question: Which of the following statements about ferromagnetism is false?

Choices:
- By definition all ferromagnetic materials must contain at least some iron.
- Ferromagnetism results when electron spins in magnetic domains align.
- As a ferromagnetic substance becomes magnetized, the magnetic domains change in size and shape.
- Hard ferromagnetic materials retain appreciable magnetization when removed from an external magnetic field.

MR Safety and Screening Quiz

Notwithstanding the name, ferromagnetic materials do not need to contain iron; they only need to form magnetic domains with the capacity to become magnetized. Nickel, cobalt, chromium, manganese, and several rare earth elements and their alloys are ferromagnetic. Hence a) is false. Statements b), c), and d) are true.


Question: Which of the following metals is not considered ferromagnetic?

Choices:
- Nickel
- Cobalt
- Chromium
- Magnesium

MR Safety and Screening Quiz

Manganese, but not magnesium (d), is ferromagnetic.


Question: Concerning stainless steels, which of the following is false?

Choices:
- 400 series stainless steels are ferromagnetic, while 300 series are non-magnetic.
- Austenitic stainless steels are ferromagnetic, while martensitic stainless steels are non-magnetic.
- Since 1990 the FDA has required all steel implants to be made of non-ferromagnetic stainless steel.
- Even non-ferromagnetic stainless steel can develop ferromagnetic properties if bent or stretched during machine working.

MR Safety and Screening Quiz

Answer a) is true but b) is false because the names have been reversed: martensitic (= 400 series) steels are ferromagnetic, while austenitic (= 300 series) steels are non-magnetic. Both c) and d) are true.


Question: Concerning magnetic saturation, which statement is false?

Choices:
- Nearly all iron alloys saturate in the range of 1-2 Tesla.
- All ferromagnetic materials become saturated in a 3.0T field.
- It is impossible to create a permanent iron magnet having a field greater than 2.5 Tesla.
- The maximum strength of a permanent magnet is independent of its saturation point.

MR Safety and Screening Quiz

Option d) is false. The saturation point limits the maximum attainable strength of a permanent magnet or iron core electromagnet, which in most cases is well below 2 Tesla. Answers a)-c) are true  Link to Q&A discussion


Question: An implant made of which of the following materials could pose a safety risk because of ferromagnetic properties:

Choices:
- Platinum
- Nitinol (Ni-Titanium alloy)
- Silicon steel
- Gold

MR Safety and Screening Quiz

Answer c), silicon steel, is highly ferromagnetic and unsuitable as an implant material. The others are essentially non-magnetic (platinum and Nitinol mildly paramagnetic, gold mildly diamagnetic)


Question: Which of the following rare earth elements is commonly used to make room temperature permanent magnets?

Choices:
- Neodymium
- Magnetodynium
- Holmium
- Dysprosium

MR Safety and Screening Quiz

Neodymium (a) doped with iron and boron is commonly used as a base for room temperature permanent magnets, as is samarium-cobalt. Holmium and dysprosium are highly ferromagnetic below 20 ºK but lose this property at higher temperatures.  Choice b), magnetodynium, is not an element!


Question: Which metal or alloy in the list below would be expected to produce the largest susceptibility artifact on gradient-echo imaging?

Choices:
- Lead
- Copper
- Aluminum
- Nitinol (Ni-Ti alloy)

MR Safety and Screening Quiz

Nitinol, answer d) has the largest magnetic susceptibility due to its nickel content and would produce the largest artifact.


Question: Concerning the hysteresis curve for a ferromagnetic material, which of the following is true?

Choices:
- The curves for a material changes after its first time exposure to an external field.
- Coercivity is the magnetization that remains once the external field has been removed
- Reversing the direction of the magnetic field cannot reverse the magnetization.
- The hysteresis curves for a hard ferromagnetic material have small coercivities.

MR Safety and Screening Quiz

Only a) is true. A “virgin” material (i.e. one never exposed to a large external field) begins with zero or minimal internal magnetization, that grows to a maximum (the saturation value) as the external field is applied. When this field is removed, the magnetization generally does not return to zero but remains at a positive value - the remanence -  not “coercivity” as falsely stated in b).  Reversing the external field can reverse the magnetization as long as it has magnitude greater than the coercivity value (answer c is false). Hard ferromagnetic materials are difficult to demagnetize, with very wide hysteresis curves and hence large coercivities (answer d is false).


Question: Concerning demagnetizing fields, which statement is false?

Choices:
- The demagnetizing fields for diamagnetic and paramagnetic materials are so small that they may effectively be disregarded.
- The demagnetizing field (D) points in the opposite direction to the magnetization (M)
- The demagnetizing field (D) points in the opposite direction to the external field (Bo)
- The demagnetizing field (D) increases the net magnetic field inside an object.

MR Safety and Screening Quiz

Answer d is false. The demagnetizing field, by opposing M and B, decreases the net magnetic field inside an object.


Question: Concerning the effects of demagnetizing fields, which statement is false?

Choices:
- Demagnetizing fields increase the apparent magnetic susceptibility of weakly ferromagnetic objects.
- The apparent susceptibility of an object made of a strongly ferromagnetic material primarily depends on its shape, not its specific composition.
- Demagnetizing fields in ferromagnetic materials reduce the size of the external field needed to achieve magnetic saturation.
- Demagnetizing factors are dimensionless numbers between 0 and 1.

MR Safety and Screening Quiz

All statements are true except a). Demagnetizing fields decrease the apparent magnetic susceptibility of weakly ferromagnetic objects.


Question: A person with a steel BB lodged in his eye approaches a 3.0T MR scanner. Assuming the low-carbon steel of which it is made has a saturation value Bsat = 1.5T and because it is spherical, it has a demagnetization factor (N) of 1/3 in each direction, calculate the fringe external field (Bext) where the BB would become magnetically saturated.

Choices:
- 0.5 T
- 1.0 T
- 1.5 T
- 3.0 T

MR Safety and Screening Quiz

The external field which produces magnetic saturation is given by the equation Bext= N • Bsat. For the case of the BB, Bext= 1/3 • 1.5T = 0.5T (answer a)


Question: Which of the following shaped materials would have the largest demagnetizing factor (N) along the direction of the main magnetic field?

Choices:
- A sphere
- A flat plate facing the main field
- A flat plate parallel to the main field
- An elongated cylinder pointing in the direction of the main field

MR Safety and Screening Quiz

A flat plate oriented en face to the direction of the main field would have virtual poles very close together and hence produce a strong demagnetizing effect. N would therefore be close to 1.0, the maximum possible value for any shaped object, so answer b) is correct.


Question: Mathematical analysis of predicted magnetic forces on metal objects often uses models based on

Choices:
- Spheres
- Long tubes
- Ellipsoids
- Flat sheets

MR Safety and Screening Quiz

Answer c), ellipsoids, is correct. By changing the length, angulation, and diameter parameters, an ellipsoid can be approximately deformed into one of the other shapes. And ellipsoids admit to a closed-form mathematical solution in many cases.


Question: Translational force on an unsaturated metal object brought near a cylindrical bore MR scanner is maximal

Choices:
- When first entering the door of the MR scanner room
- At scanner isocenter in the middle of the bore
- At scanner isocenter at the edge of the bore
- Just inside the edge of the magnet bore opening

MR Safety and Screening Quiz

Translational force is proportional to the local field (B) multiplied by its spatial rate of change (dB/dz), a combined entity known as the spatial gradient product (SGP).  The SGP is strongest near the edges of the magnet bore opening, making this the most powerful place for translational forces (answer d is correct). At the magnet isocenter, however, dB/dz ≈ 0, so surprisingly there is no translational force once the object reaches the center of the magnet.


Question: The torque on an unsaturated metal object brought near a cylindrical bore MR scanner is maximal

Choices:
- When first entering the door of the MR scanner room
- At scanner isocenter in the middle of the bore
- At scanner isocenter at the edge of the bore
- Just inside the edge of the magnet bore opening

MR Safety and Screening Quiz

This is a somewhat of a trick question. The answer is actually d), at a location slightly more posterior to the that of the spatial gradient or spatial gradient product. For an unsaturated object, torque is proportional to the square of the magnetic field (B²). So the torque is maximal where B is greatest. Most people assume this is in the center of the scanner, but for cylindrical magnets the local field is perhaps 10-20% higher just inside the bore opening along the inside walls of the scanner.  The correct answer is therefore d), at a location slightly more posterior to the that of the spatial gradient or spatial gradient product maximal where the magnetic field (B) is strongest.


Question: Where is the force on an unsaturated metal object the smallest?

Choices:
- Only exactly at scanner isocenter
- At the majority of places inside the magnet bore where the static field is homogeneous
- Just inside the edge of the scanner bore opening
- One meter from the scanner bore opening

MR Safety and Screening Quiz

The correct answer is b. Translational force is minimized when the spatial gradient (dB/dz) is minimal. Since modern scanners are highly homogeneous, most sites within the main bore of the magnet have dB/dz = 0 and thus produce no translational forces.


Question: A steel wrench is inadvertently brought into the room housing a self-shielded 1.5 T scanner. Which statement is true about the magnetic torque on the wrench?

Choices:
- The torque is maximal when the wrench is held upright and perpendicular to the main magnetic field.
- The torque is maximal when the wrench is tilted at 45º toward the field.
- The torque is maximal when the wrench is turned to be parallel to the field.
- The exact shape or position of the wrench makes no difference on the torque, only its mass.

MR Safety and Screening Quiz

Answer b) is true. The torque of an unsaturated elongated object depends on sin 2θ, where θ is the angle made with the external field. This is maximal when θ = 45º


Question: When a metal object becomes magnetically saturated by an external field (B), which of the following is false?

Choices:
- The displacement force is independent of B.
- The displacement force is independent of dB/dz.
- The torque is independent of B.
- The torque is independent of the object’s angulation (θ) with respect to B.

MR Safety and Screening Quiz

Only d) is false. Torque remains proportional to sin 2θ but independent of B. Displacement force is independent of both B and dB/dz.


Question: The (Spatial Gradient Product) is defined as the (Static Field Strength) times the (Spatial Gradient of the Static Field) at each point in space.  The units of Spatial Gradient Product are

Choices:
- Tesla
- Tesla/meter
- Tesla/meter²
- Tesla²/meter

MR Safety and Screening Quiz

The static field (T) times the spatial gradient (T/m) gives the units of SGP as T²/m, so answer d) is correct.


Question: For a typical cylindrical MR scanner, the location of the maximum Spatial Gradient Product is

Choices:
- In the middle of the bore at magnet isocenter
- Against the wall of the bore at magnet isocenter
- In the middle of the bore opening
- Along the wall at the bore opening

MR Safety and Screening Quiz

Both the SGP and SG are maximal along the wall of the bore opening and usually quite close together. (Answer d).  This region is would exert the strongest displacement force on a metallic object.


Question: A small metallic object is being tested for translational forces by suspending it from a string at the edge of the scanner bore opening using the ASTM method. The hanging object deflects the string by 40º from the vertical. Which of the following conclusions is incorrect?

Choices:
- The ASTM would state that the risk imposed by magnetic force is no greater than that of the earth’s gravity.
- The ASTM would declare this object to be MR Conditional.
- The ASTM would declare this object to be MR Unsafe.
- The ASTM would declare this object to be MR Safe.

MR Safety and Screening Quiz

Because the object did not deflect more than 45º, the deflection force is less than the device’s weight. So by ASTM criteria any risk imposed by the application of the magnetically-induced deflection force is no greater than any risk imposed by normal daily activity in the Earth’s gravitational field. Thus answer a) is correct. The definitions of MR Safe, Unsafe, and Conditional are based on multiple factors (i.e., heating, torque) beyond that available from this simple displacement test.


Question: Concerning the Lorentz force, which of the following is true?

Choices:
- It is the force is experienced by charged particles moving through an electric field.
- It is responsible for T-wave changes on an EKG
- It is responsible for magnetophosphenes and taste disturbances in 7T scanners.
- It is responsible for the stacking up of sickle cell erythrocytes in a magnetic field.

MR Safety and Screening Quiz

Only b) is true. This describes the magneto-hydrodynamic (MHD) effect, which is a change in recorded EKG voltages due to displacement of positive and negative ions in the descending aorta due to Lorentz forces. The other choices are false. The Lorentz force is due to particles moving through a magnetic (not electric) field. Magnetophophenes and taste disturbances are due to induced currents per the Faraday-Lenz law. The stacking of sickled red blood cells is a type of susceptibility-induced force.


Question: Which of the following concerning MR-related dizziness and vertigo is false?

Choices:
- It is much more common at 7T than 3T.
- It is likely due to a Lorentz force acting on endolymphic ionic currents.
- It is exacerbated by rapid head or table motion.
- It is most severe and persistent when the patient’s head reaches magnet isocenter.

MR Safety and Screening Quiz

Answer d) is false. Dizziness/vertigo is typically most severe when the patient is pulled in or out of the magnet bore through the gantry entrance. Once the patient’s head is at isocenter, the vertiginous symptoms and nystagmus decrease after about a minute (unless the patient wiggles her head).


Question: Concerning magnetophosphenes, which statement is false?

Choices:
- They are much more common at 7T than 3T.
- They are caused by electric field stimulation of the optic nerve.
- Technologists walking around the scanner may experience them.
- They are exacerbated by rapid head or table motion

MR Safety and Screening Quiz

Answer b) is false. Magnetophosphenes are generated by electric fields of very low frequency and magnitude acting on retinal cells directly, not the optic nerve. The other statements are true.


Question: Concerning metallic taste sensations during MRI, which of the following is false?

Choices:
- Their mechanism of generation is similar to that of magnetophosphenes.
- They are related to release of ions from metallic dental fillings.
- They are much more common at 7T than 3T.
- They are much less common than vertigo or magnetophosphenes.

MR Safety and Screening Quiz

The phenomenon occurs in patients without dental fillings, so answer b) is false.


Question: The units for the diffusion coefficient (D) are

Choices:
- mm/sec
- mm²/sec
- mm³/sec
- Dimensionless

Pulse Sequences Quiz

D reflects the flux of particles through a surface during a certain period of time, it therefore has units of area/time (e.g. mm²/sec).


Question: According to the Stokes-Einstein equation, which of the following system changes would increase the diffusion coefficient?  (You should be able to reason this out even if you’ve forgotten the exact equation).

Choices:
- Increasing temperature
- Increasing viscosity of the medium
- Increasing the size of the particles
- All of the above

Pulse Sequences Quiz

Increasing temperature increases the kinetic energy and hence motion of the particles, so D is increased. Bigger particles and ones in more viscous media move more slowly, so D is decreased.


Question: Comparing the diffusion coefficients of water (Dw) and biological tissues (Dt), which statement is most accurate?

Choices:
- Dw < Dt
- Dw and Dt are almost exactly the same
- Dt is typically only 10-50% of Dw
- Dt is typically less that 1% of Dw

Pulse Sequences Quiz

The diffusion constant for pure water at body temperatures is approximately 3.0 x 10−3 mm2/sec. The values of D for biological tissues are only 10-50% as long, perhaps 1.0 x 10−3mm2/sec on the average.


Question: How many elements are there in a first-order diffusion tensor for describing anisotropic materials?

Choices:
- 3
- 6
- 9
- 12

Pulse Sequences Quiz

In anisotropic materials, diffusion cannot be described by a single number, but a [3 x 3] array called the diffusion tensor. The three diagonal elements (Dxx,  Dyy, and (Dzz) of the tensor represent diffusion coefficients measured in the laboratory frame of reference along each of the principal (x-, y- and z-) directions. The six off-diagonal terms (Dxy, Dyz, etc) reflect correlation between random motions corresponding to each pair of principal directions.


Question: Modern diffusion-weighted pulse sequences all trace their origin to the pulsed gradient spin echo (PGSE) technique developed by

Choices:
- Stejskal and Tanner
- Solomon and Blombergen
- Carr and Purcell
- Einstein and Stokes

Pulse Sequences Quiz

The pulsed gradient spin echo (PGSE) technique was developed by chemists Edward Stejskal and John Tanner in the mid-1960's. It consisted of paired diffusion sensitizing gradients flanking either side of a 180º-inversion pulse. Modern variations include addition of a chemically selective fat suppression pulses, use of bipolar gradients, and a second 180º pulse immediately before the image acquisition module.


Question: How can a larger b-value be achieved with paired pulsed diffusion gradients?

Choices:
- By increasing the amplitude of the gradients
- By increasing the duration of the gradients
- By widening the time interval between the two gradients
- All of the above

Pulse Sequences Quiz

The b-value depends on the strength, duration, and spacing of the pulsed diffusion gradients.  A larger b-value is achieved with increasing the gradient amplitude and duration and by widening the interval between gradient pulses.


Question: What is the approximate range of b-values used to produce diffusion-weighted images in standard clinical MRI today?

Choices:
- 0 – 10 s/mm²
- 0 – 100 s/mm²
- 0 – 1,000 s/mm²
- 0 – 10,000 s/mm²

Pulse Sequences Quiz

Most routine clinical DWI currently use b-values between 0 and 1000 or perhaps 0 and 2000, with slightly lower values being used outside the central nervous system.


Question: What are the minimum number of source image gradient directions that must be applied to obtain a diffusion-weighted anatomic image?

Choices:
- 1
- 3
- 9
- 27

Pulse Sequences Quiz

At least three sets of source images must be obtained. These may be along the laboratory x-, y-, and z-axes or in three arbitrary perpendicular orientations. More modern schemes typically obtain source images in 6, 20 or more directions, but three is the minimum.


Question: What is the definition of the “trace” of a 3x3 diffusion tensor matrix?

Choices:
- The largest element
- The sum of all the elements
- The sum of the diagonal elements
- The average of the diagonal elements

Pulse Sequences Quiz

The term "trace" comes from matrix algebra where it means the sum of diagonal elements of such an array. The trace of the diffusion tensor equals (Dxx +  Dyy + Dzz).


Question: If the trace of a 3x3 diffusion tensor matrix corresponding to a single pixel is calculated to be 1.5 x 10–3 s/mm², what is the corresponding apparent diffusion coefficient (ADC)?

Choices:
- 0.5 x 10–3 s/mm²
- 1.5 x 10–3 s/mm²
- 3.0 x 10–3 s/mm²
- 4.5 x 10–3 s/mm²

Pulse Sequences Quiz

The apparent diffusion coefficient (ADC) is considered to be the average value of the trace, or ADC = (Dxx +  Dyy + Dzz) / 3.


Question: Concerning the ADC map, which one of the following statements is true?

Choices:
- A lesion bright on a trace DWI image will be dark on an ADC map.
- Lesions with very long T2 values will appear dark on an ADC map.
- Normal urine will appear dark on a trace DWI image and bright on an ADC map.
- The ADC map is simply the inverse of the trace DWI image.

Pulse Sequences Quiz

The Trace DW image is not a map of diffusion; it is only diffusion-weighted, a fact implicit in its name. Trace DW images possess considerable T2-weighting. As such, lesions with either very long or very short T2 values may "contaminate" the Trace DW images, making them appear "artificially" bright or dark. These important phenomena are known as "T2-shine-through" and "T2-black-out. T2-effects can be mathematically removed from the DW image to create a pure parametric image of apparent diffusion coefficients (the "ADC Map"). The ADC map is not a simple inverse of the DWI trace image.


Question: Which of the following is incorrect concerning exponential ADC maps?

Choices:
- eADC maps have a gray scale that parallels that seen in the trace DW images.
- eADC maps are simply the trace DW image divided by the b0 image.
- eADC maps have more noise than trace DW images.
- eADC maps still have the problem of “T2-shine-through”.

Pulse Sequences Quiz

The eADC map is simply the trace DW image divided by the b0 image for each point.


Question: A cerebral hematoma 36-hours-old appears dark on both the b0 and trace DW images.

Choices:
- Diffusion is not restricted in the hematoma.
- This is an example of “T2-shine-through”.
- This is an example of “T2-blackout”.
- This is an example of diffusion anisotropy.

Pulse Sequences Quiz

This case illustrates the “T2-blackout” phenomenon, where severe T2* shortening (here due to paramagnetic deoxyhemoglobin in the hematoma) spills over and “contaminates” the trace DW images. Diffusion is actually restricted in the hematoma (think of all the clumped red blood cells and fibrin), but appears (falsely) dark on the DW image.


Question: Which one of the following mechanisms does not explain restricted diffusion in an acute cerebral infarction?

Choices:
- Increased intracellular water (cytotoxic edema)
- Decreased intracellular and extracellular viscosity.
- Reduction in extracellular space.
- Fragmentation of cellular components.

Pulse Sequences Quiz

All are correct except for (b). As cellular components fragment and proteins unravel, viscosity increases (not decreases). Increased viscosity restricts diffusion because it inhibits the movement of water molecules through the diseased tissue.


Question: Which of the following tumors would not be expected to demonstrate restricted diffusion?

Choices:
- Splenic lymphoma
- Cerebellar medulloblastoma
- Pancreatic serous cystadenoma
- Ewing’s sarcoma (PNET) of the pelvis

Pulse Sequences Quiz

Highly cellular neoplasms with densely packed cells and relatively little extracellular space often demonstrate restricted diffusion. Examples include lymphomas, medulloblastomas, primitive neuroectodermal tumors (PNETs) and highly malignant gliomas. A cystic tumor (like option c would not be expected to restrict diffusion.


Question: How many measurements does it take to determine the unique diffusion tensor elements in the prior question?

Choices:
- 5
- 6
- 7
- 9

Pulse Sequences Quiz

Six measurements need to be taken with the diffusion sensitizing gradients applied, plus one b0 measurement, giving a total of 7.


Question: Concerning the diffusion ellipsoid, which statement is false?

Choices:
- The directions of its major and minor axes are described by eigenvectors.
- The radii of its major and minor axes are eigenvalues.
- The eigenvalues are proportional to Einstein’s root mean square diffusion displacement in each direction.
- The diffusion tensor matrix for the diffusion ellipsoid has 6 unique elements.

Pulse Sequences Quiz

A significant benefit to using the diffusion ellipsoid is that in this frame of reference, the off-diagonal elements of the diffusion tensor disappear. The set of eigenvalues define a matrix with only unique 3 diagonal elements (λ1, λ2, and λ3) with the off-diagonal elements all zeroes. Link to Q&A discussion


Question: Concerning fractional anisotropy (FA), which statement is incorrect?

Choices:
- FA varies from −1 to +1.
- FA is an index for the amount of diffusion asymmetry within a voxel.
- FA = 0 for a voxel with perfect isotropic diffusion.
- On an FA map, brighter areas are more anisotropic than darker areas.

Pulse Sequences Quiz

The value of FA varies between 0 and +1 (option a is incorrect). For perfect isotropic diffusion, λ1 = λ2 = λ3, the diffusion ellipsoid is a sphere, and FA = 0. With progressive diffusion anisotropy, the eigenvalues become more unequal, the ellipsoid becomes more elongated, and the FA → 1. The FA map is a gray-scale display of FA values across the image. Brighter areas are more anisotropic than darker areas.


Question: Concerning whole-body DWI, which statement is false?

Choices:
- Imaging is obtained in multiple blocks or stations, then digitally stitched together.
- Views of the chest and abdomen must be obtained during breath holding to reduce motion artifact.
- Standard image display is in a black-background mode to resemble PET-CT.
- Each DWI sequence is preceded by a STIR-like inversion pulse for fat suppression.

Pulse Sequences Quiz

Whole-body DWI does not require breath holding. Even though the organs of the abdomen and chest move during image acquisition, they do so "coherently". Their physical displacements are cyclic and while this motion produces some spatial blurring it does not significantly affect the magnitude of the DW signal.


Question: All of the following are advantages of readout-segmented DWI over single-shot DWI, except

Choices:
- Increased signal-to-noise
- Decreased imaging time
- Decreased susceptibility artifacts
- Reduced spatial blurring

Pulse Sequences Quiz

Depending on the number of “shots” readout segmented DWI can take 3-5 times longer than single-shot DWI, so option (b) is false.


Question: The key technological development underlying modern small field-of-view DWI methods (like ZOOMit and FOCUS) is

Choices:
- Use of 2D spatially-selective composite RF pulses
- Use of outer volume saturation pulses
- Use of stimulated echo inner volume pulses
- Use of extremely strong, continuously applied gradients

Pulse Sequences Quiz

Newer small FOV DWI sequences employ a special 2D RF excitation pulse that is spatially selective in both the slice select and phase-encoding directions. The 2D RF "pulse" is a composite of approximately 25 closely spaced "sub-pulses" extending over a time frame of about 15 ms. This RF excitation is played out simultaneously with a fast (oscillatory) gradient along the phase-encode axis and a slow ("blipped") gradient along slice-select.


Question: Which of the following statements about intravoxel incoherent motion (IVIM) is true?

Choices:
- IVIM effects are most easily recognized when high b-values are used.
- IVIM describes signal losses due to both diffusion and microscopic perfusion.
- IVIM perfusion effects mitigate the signal losses caused by diffusion alone.
- Le Bihan’s IVIM model allows estimation of capillary blood flow.

Pulse Sequences Quiz

The correct statement is (b): IVIM describes signal losses due to both diffusion and microscopic perfusion. If the gradients are relatively strong, IVIM-induced signal losses are primarily due to diffusion — the Brownian motion of water molecules in and around cells. When weaker gradients are used, however, a second IVIM mechanism also contributes to signal loss — microcirculation of blood in the capillary network. Le Bihan’s IVIM model allows estimation of the perfusion fraction (the percent of a voxel volume occupied by capillaries), but not the blood flow through them.


Question: Which of the following statements about diffusion kurtosis is false?

Choices:
- Diffusion kurtosis measures the non-Gaussian movement of water molecules.
- Kurtosis effects are more noticeable when long echo times are used.
- Kurtosis effects are more noticeable when low b-values are used.
- The mean kurtosis (K) of a pure fluid is zero.

Pulse Sequences Quiz

Standard diffusion weighted imaging (DWI) methods have incorporated Einstein's original concept that the diffusion water molecules follows a Gaussian (normal) distribution. Non-Gaussian behavior becomes more noticeable when stronger gradients (higher b-values) and longer echo times are used.  By definition, a Gaussian distribution has K = 0, which would be the case with a pure fluid.


Question: What is the main type of fat within the body which contributes most to the signal recorded on MRI?

Choices:
- Triglycerides
- Free fatty acids
- Cholesterol
- Phospholipids

Pulse Sequences Quiz

The bulk of the MR signal in fatty human tissues arises from triglycerides, with lesser contributions from free fatty acids and cholesterol (when esterified or in a semi-solid or liquid state).


Question: At a given field strength, how do the nuclear precession frequencies of ¹H protons differ between fat and water?

Choices:
- Fat and water protons precess at the same frequency
- Fat protons precess faster than water protons.
- Fat protons precess slower than water protons.
- Fat protons may precess either faster or slower depending on their location along the triglyceride side chains.

Pulse Sequences Quiz

The H protons of triglycerides are nestled within long carbon chains, shielded by electron clouds and protected from the full force of the externally applied magnetic field. In water, by comparison, the electronegative O atom pulls protective electron clouds away from the H nuclei, exposing them to the full force of the external magnetic field. Thus water protons resonate faster than fat protons.


Question: A chemical shift of 3.5 ppm written in decimal form is

Choices:
- 0,00000035
- 0,0000035
- 0,000035
- 0,00035

Pulse Sequences Quiz

The abbreviation ppm stands for “parts per million” and is equivalent to multiplying the base value by 10−6. So 3.5 ppm = 3.5 x 10−6 = 0.0000035 (answer b).


Question: If the water-fat chemical shift is 3.5 ppm, calculate the fat-water frequency difference for a 7T scanner operating at 200 MHz.

Choices:
- 220 Hz
- 440 Hz
- 700 Hz
- 900 Hz

Pulse Sequences Quiz


Question: If the water-fat chemical shift is 3.5 ppm, calculate the water-fat frequency difference for a portable 0.064T scanner operating at 150 kHz.

Choices:
- 0.5 Hz
- 5 Hz
- 50 Hz
- 500 Hz

Pulse Sequences Quiz

Δf = (150 kHz)(3.5 ppm) = (150 x 103 Hz)(3.5 x10−6) ≈ 0.5 Hz. This very low frequency separation means that water-fat artifacts will be minimal at this field strength, and also that spectral fat suppression methods cannot be used.  Link to Q&A discussion


Question: At 1.5 T water and fat go in and out of phase about every 2.2 msec. How fast would they go in and out of phase at 3.0T?

Choices:
- Every 1.1 msec
- Every 2.2 msec
- Every 3.3 msec
- Every 4.4 msec

Pulse Sequences Quiz

The period of this phase cycling is 1/Δf, where Δf is the frequency offset between the spins. So if the field is doubled, the frequency offset is twice as large, and the phase cycling period is half as large, so (a) 1.1 msec is the correct answer.


Question: An adrenal mass that is of intermediate signal intensity on an in-phase image and low signal on an out-of-phase image is most likely an

Choices:
- Adrenal carcinoma
- Adrenal adenoma
- Adrenal metastasis
- Adrenal pheochromocytoma

Pulse Sequences Quiz

Adrenal adenomas, the most common tumor of the adrenal gland, often contain microscopic lipid droplets. Voxels containing both lipid and water result in signal cancellation with low signal on out-of-phase GRE images.


Question: Which of the following is not one of the four standard images produced by most commercial Dixon-type sequences?

Choices:
- Chemical shift
- Water
- Fat
- In-phase

Pulse Sequences Quiz

Choice (a), chemical shift, is not a standard image generated by a Dixon sequence. The other four are.


Question: Concerning CHESS/Fat-Sat pulses, which one of the following statements is incorrect?

Choices:
- They reduce the number of available slices for a given TR.
- They cause tissue heating.
- They include a spectrally tuned RF-pulse followed by spoiler gradients along one or more axes.
- They are the preferred method for fat suppression at 0.3T and below.

Pulse Sequences Quiz

All are correct except choice (d). The effectiveness of a Fat-Sat pulse depends primarily on field strength and field homogeneity. At fields below 0.3T the water and fat peaks are so close together (in Hz) that it is difficult to cleanly suppress one or the other with a chemically selective pulse. At low fields another method of fat suppression (typically STIR or Dixon) must therefore be used.


Question: Which of the following flip angle patterns would not be considered to define a composite binomial pulse for water excitation?

Choices:
- 1:1
- 0,04237268519
- 0,04306712963
- 1:3:3:1

Pulse Sequences Quiz

Binomial pulses are typically used for selective water excitation as a means of fat suppression. Binomial pulses have flip angles that follow the pattern of coefficients of the binomial expansion of (a+b)n: 1-1, 1-2-1, 1-3-3-1, etc. Thus, a 90º-pulse could be constructed as a [45º-45º] pair, a [22.5º-45º-22.5º] triplet, or a [11.25º-33.75º-33.75º-11.25º] quadruplet. So choice (b), 1:1:1 is not a binomial pulse.


Question: Limitations of the STIR technique for fat suppression include all except

Choices:
- Inability to use it to detect gadolinium enhancement.
- Suppression of other short T1 materials besides fat (eg, protein, blood).
- Tissue heating from multiple 180º pulses.
- Decreased visualization of long T1/long T2 lesions due to competitive signal effects.

Pulse Sequences Quiz

All are valid limitations except for (d), which is incorrect. In routine SE imaging lesions with prolonged T1 and T2 have competitive effects on signal intensity (↑T1 reduces signal while ↑T2 increases signal). In STIR imaging the effects of ↑T1 and ↑T2 are additive, allowing for improved visualization of some lesions, such as multiple sclerosis plaques.


Question: The Spectral Presaturation with Inversion Recovery (SPIR) technique can be thought of as a hybrid combining fat suppression features of

Choices:
- Spectral Fat Sat (CHESS) + STIR
- Dixon Technique + STIR
- Spectral Fat Sat (CHESS) + Selective Water excitation
- Dixon Technique + Selective Water excitation

Pulse Sequences Quiz

SPIR is a hybrid technique that combines a fat-selective RF-pulse and spoiler gradient (similar to CHESS) together with nulling of the residual longitudinal fat magnetization through an inversion delay mechanism (similar to STIR). These spin manipulations purely involve fat; the water resonance is unaffected. After a suitable inversion time to null residual fat signal, any pulse sequence can be used to image the remaining water.


Question: Which of the following statements comparing SPAIR (SPectral Attenuated Inversion Recovery) and SPIR (Spectral Presaturation with Inversion Recovery) is incorrect?

Choices:
- SPAIR uses adiabatic pulses while SPIR does not.
- SPAIR uses an inversion pulse of 180º, while SPIR uses pulses in the 100º -120º range
- SPAIR deposits less RF energy into tissue than does SPIR.
- The inversion time is longer for SPAIR than SPIR.

Pulse Sequences Quiz

Both SPAIR and SPIR can be thought of as CHESS-STIR hybrids. SPAIR uses 180º adiabatic pulses while SPIR uses non-adiabatic pulses in the 100º -120º range. Accordingly-SPAIR pulses deposit more RF-energy in tissue than the smaller flip angle SPIR or CHESS pulses. The inversion time is longer in SPAIR than SPIR, so there is a greater penalty in terms of imaging time and reduced number of slices for a given TR.


Question: Which of the following statements about adiabatic RF-pulses is false?

Choices:
- They are both amplitude- and frequency-modulated.
- Their transmitted frequency changes simultaneously with amplitude as the pulse evolves.
- They are less sensitive to B1 inhomogeneities that other pulses.
- They are commonly used in low-field applications.

Pulse Sequences Quiz

Only (d) is false. Like other non-adiabatic but spectrally selective pulses (CHESS, STIR) they can only be used at higher, rather homogeneous fields where there is a clean separation of water and fat resonances Link to Q&A discussion


Question: Which of the following is not an advantage of gradient echo imaging over spin-echo imaging?

Choices:
- Shorter TEs
- Shorter TRs
- Reduced flow artifacts
- Reduced susceptibility artifacts

Pulse Sequences Quiz

Phase shifts resulting from magnetic field inhomogeneities, static tissue susceptibility gradients, or chemical shifts are not cancelled at the center of the GRE as they are in SE sequences.  Image contrast is therefore dictated not by true T2-relaxation, but by these other factors which constitute T2*. GRE sequences are therefore more frequently troubled by susceptibility and chemical shift artifacts and do not function well on scanners whose magnetic fields lack homogeneity Link to Q&A discussion


Question: Concerning multi-echo GRE, which statement is true?

Choices:
- The peak value of successive echoes is determined by the T2 decay of the tissue imaged.
- The peak value of successive echoes echo is determined by the T1 value of the tissue imaged.
- One common application is for fat-water imaging.
- Each successive echo must be preceded by its own RF-pulse.

Pulse Sequences Quiz

The peak value of successive echoes is determined by the T2* decay (not T2 decay) of the tissue imaged (options a and b are false). One common application of multi-echo GRE is for acquiring fat-water "in-phase" and "out-of-phase" images using two different TE's (options c is true). Only one RF pulse is used for the entire chain of echoes (option d is false).


Question: Which is not a technique for gradient echo spoiling?

Choices:
- Use of very short TR
- Use of 2D multislice mode
- Use of a variable spoiler gradient
- Semirandom phase change of the RF-carrier wave

Pulse Sequences Quiz

All are valid spoiling methods except choice (a). Long TR values produce “natural” spoiling, not short TRs.  When TR>>T2*, the transverse magnetization will naturally decay to zero by the end of the cycle.  Thus any gradient echo sequence using TR values of several hundred milliseconds will no longer have appreciable transverse coherences and be “spoiled”.


Question: A spoiled GRE sequence with TR = 10, TE = 3, and α = 50º would be considered primarily

Choices:
- T1-weighted
- T2-weighted
- T2*-weighted
- Proton-density-weighted

Pulse Sequences Quiz

Short TR and large α accentuate T1-weighted imaging.


Question: A spoiled GRE sequence with TR = 1000, TE = 30, and α = 5º would be considered primarily

Choices:
- T1-weighted
- T2-weighted
- T2*-weighted
- Proton-density-weighted

Pulse Sequences Quiz

Long TR and small α minimize T1 weighting, while long TE accentuates T2* weighting.


Question: A spoiled GRE sequence with TR = 1000, TE = 2, and α = 5º would be considered primarily

Choices:
- T1-weighted
- T2-weighted
- T2*-weighted
- Proton-density-weighted

Pulse Sequences Quiz

Long TR and small α minimize T1 weighting, while short TE minimizes T2* weighting. This leaves the image more proton-density weighted than the other examples.


Question: In a spoiled GRE sequence, a low flip angle (α)

Choices:
- Minimizes T1 weighting
- Accentuates T1 weighting
- Minimizes T2* weighting
- Minimizes proton density weighting

Pulse Sequences Quiz

Flip angle (α) controls T1-weighting. A small flip angle minimizes T1-weighting because the longitudinal magnetizations of various tissues are not differentiated much by such a small angular displacement. Hence at small flip angles, [H] and T2* effects predominate. Conversely, as α → 90º, T1-weighting increases.


Question: In a spoiled GRE sequence, a long TE

Choices:
- Maximizes T2 weighting
- Maximizes T2* weighting
- Minimizes T2 weighting
- Minimizes T2* weighting

Pulse Sequences Quiz

T2*-weighting increases as TE is prolonged. This is because a longer TE allows more time for dephasing before echo formation.


Question: Which of the following SSFP pulse sequences is considered “balanced”?

Choices:
- TrueFISP/FIESTA
- FISP/GRASS/FFE
- DESS/MENSA
- PSIF/T2-FFE

Pulse Sequences Quiz

Sequences such as TrueFISP (Siemens) and FIESTA (GE) sample both FID-like and Echo-like SSFP signals and are considered “balanced”.


Question: Which of the following is not a condition for a SSFP signal to exist?

Choices:
- TR must be longer than T2.
- Phase shifts caused by gradients must be constant from cycle to cycle.
- Field inhomogeneities must be static.
- Spins must be stationary or motion-compensated.

Pulse Sequences Quiz

Choice (a) is incorrect. TR must be significantly shorter (not longer) than T2, or else natural decay processes will destroy the transverse coherence.


Question: Concerning “coherent” gradient echo sequences like GRASS/FISP, which statement is false?

Choices:
- If TR is long compared to T2*, the contrast resembles that of a spoiled GRE sequence.
- TE controls T2* weighting.
- Small flip angles (α) produce T1-weighted images.
- Large flip angles produce images that are weighted by T2/T1.

Pulse Sequences Quiz

Choice (c) is incorrect. A small flip angle minimizes T1-weighting because the longitudinal magnetizations of various tissues are not differentiated much by such a small angular displacement. Hence at small flip angles, [H] and T2* effects predominate.


Question: An important tissue weighting present in balanced SSFP sequences like True FISP and FIESTA is

Choices:
- T1
- T2*
- T1 + T2
- T2/T1

Pulse Sequences Quiz

True FISP sequences behave more like spin echo than gradient echo sequences in that they do not have T2*-dependence. Also, since TR is nearly always much, much shorter than T1 or T2, the signal intensity is related to the ratio T2/T1.


Question: Excluding fluids (like urine, blood, and CSF), which of the following tissues is the brightest on balanced SSFP sequences like True FISP and FIESTA?

Choices:
- Fat
- Myocardium
- Liver
- Brain

Pulse Sequences Quiz

Fat is the second brightest tissue on balanced SSFP images after pure fluids.


Question: What is the explanation for the brightness of fluid and the tissue identified in the prior question?

Choices:
- The T2 values are long.
- The T2* values are long.
- The T2/T1 ratios are large.
- The T1+T2 values are large.

Pulse Sequences Quiz

Balanced SSFP sequences have the special property that their contrast is dependent not on just T1 or T2, but the ratio T2/T1. For most solid tissues, T1>>T2 so the T2/T1 ratio is small (< 0.10). The exceptions are fat (T2/T1 ≈ 0.30, due to its short T1) and fluids (T2/T1 ≈ 0.70, due to the fact that T1 and T2 are approximately equal).


Question: Which of the following statements about DESS (dual-echo steady state) is false?

Choices:
- Its main use is in musculoskeletal imaging.
- It is insensitive to motion.
- FID-like and Echo-like signal components are recorded separately during a single TR interval.
- Fluids are very bright while trabecular bone is very dark.

Pulse Sequences Quiz

By means of a prolonged and unbalanced readout gradient, DESS generates the FID-like and Echo-like signals from the steady-state free precession individually. It then combines the signals on a pixel-by-pixel basis. DESS is very sensitive to motion, so option (b) is false.


Question: Which of the following statements about the GRASE (Gradient and Spin Echo) pulse sequence is true?

Choices:
- It is a widely used sequence for routine head imaging.
- Its tissue energy deposition (specific absorption rate) is higher than with conventional spin echo sequences.
- It is superior to conventional spin echo (CSE) or fast spin echo (FSE) for detecting calcifications and hemorrhages.
- It is primarily used to generate T1-weighted images.

Pulse Sequences Quiz

GRASE is a hybrid technique supposedly combines the best features of CSE and GRE imaging. The GRE contribution makes it useful for detecting calcification of blood (although less so than a pure GRE sequence). Its SAR is lower than a comparable fast spin-echo sequence because there are fewer RF-pulses. GRASE has never achieved much popularity as an imaging method.


Question: The SI unit for magnetic susceptibility (χ)

Choices:
- Tesla
- Oersted
- Ampere-meter
- Dimensionless

Pulse Sequences Quiz

Magnetic susceptibility,  denoted by the Greek letter chi (χ), is defined as the magnitude of the internal polarization (J) divided by the strength of the external field (B). Since it is the ratio of two magnetic fields, susceptibility is a dimensionless number.


Question: Concerning diamagnetism, which statement is false?

Choices:
- The internal magnetization/polarization of a diamagnetic substance opposes the applied field.
- Diamagnetic substances have positive susceptibilities (χ > 0).
- Water, and hence most tissues, are diamagnetic.
- Calcifications are diamagnetic.

Pulse Sequences Quiz

Diamagnetic substances become polarized in a manner that opposes the applied magnetic field. They have negative, not positive, susceptibilities (option b is false). Water, calcifications, and most tissues are diamagnetic.


Question: Concerning paramagnetism, which statement is false?

Choices:
- The internal magnetization/polarization of a paramagnetic substance is in the same direction as the applied field.
- Air is paramagnetic.
- Gadolinium contrast material is paramagnetic.
- Most steels are paramagnetic.

Pulse Sequences Quiz

Paramagnetic substances become polarized in a manner that augments the applied magnetic field. They have positive susceptibilities. Surprisingly, molecular oxygen is mildly paramagnetic, so air is as well. Gadolinium contrast is paramagnetic. Most steels are ferromagnetic, a phenomenon resembling, but many orders of magnitude greater than paramagnetism.


Question: Which of the following 2D gradient echo sequences would be most useful for demonstrating small calcifications or hemorrhages in the brain?

Choices:
- TR = 800, TE = 30, α = 20°
- TR = 2000, TE = 10, α = 70°
- TR = 60, TE = 3, α = 45°
- TR = 800, TE = 10, α = 45°

Pulse Sequences Quiz

Hemorrhage/calcification GRE sequences are characteristically operated in 2D multi-slice mode using relatively long TR's and low flip angles (both minimizing T1 effects) and relatively long TE's (to accentuate T2* dependence). So choice (a) is the best answer.


Question: Concerning susceptibility-weighted imaging (SWI), which of the following is false?

Choices:
- SWI images are typically acquired in 3D rather than 2D mode.
- Magnitude and phase information can be individually viewed or combined.
- SWI imaging is inferior to 3D GRE studies for detecting microhemorrhages and calcifications.
- SWI studies typically include minimum intensity images.

Pulse Sequences Quiz

Multiple studies have shown that SWI imaging is superior to 3D GRE studies for detecting microhemorrhages and calcifications.


Question: Concerning SWI phase map images, which statement is incorrect?

Choices:
- A lesion that is bright on a GE scanner will appear dark on a Siemens scanner.
- Phase map images are displayed using a minimum intensity projection algorithm.
- If a venous sinus appears dark on a phase image, paramagnetic blood products will also be dark.
- The choroid plexus and pineal gland provide a good internal reference for diamagnetic substances.

Pulse Sequences Quiz

Phase map images are rendered in a simple magnitude mode on a slice-by-slice basis, so option (b) is false. The "colors" (black or white) of diamagnetic and paramagnetic substances on SWI phase images are scanner- dependent, so reference to a known tissue (veins for paramagnetic, choroid plexus calcification for diamagnetic) are needed as an internal check.


Question: The MR signal generated by a single RF-pulse is called a

Choices:
- Free induction decay (FID)
- Spin echo (SE)
- Gradient echo (GRE)
- Stimulated echo (STE)

Pulse Sequences Quiz

The FID is produced by a single RF-pulse as the tipped nuclear magnetization precesses around Bo and generates current in the receiver coil via induction (Faraday-Lenz Law).


Question: Concerning the FID, which of the following is true?

Choices:
- It oscillates indefinitely at the resonance frequency
- It decays with time constant T2*
- It increases in amplitude with time constant T1
- It is generated by a perfect 180º pulse

Pulse Sequences Quiz

The FID is a damped sinusoidal oscillation at the resonance frequency that decays with time constant T2*.


Question: If a magnetic field gradient is turned on immediately after an RF pulse, what happens to the MR signal?

Choices:
- It becomes a free induction decay (FID)
- It remains unchanged
- It dies out quickly
- It becomes refocused into a gradient echo (GRE)

Pulse Sequences Quiz

The initial MR signal is already synonymous with the FID (choice a is false). Turning on a gradient during the FID causes it to decay more quickly than it would by T2* processes alone (choice c is correct). A second, later applied gradient with opposite polarity is required to generate a GRE.


Question: Another name for a gradient echo is a

Choices:
- Field echo
- RF echo
- Spin echo
- Stimulated echo

Pulse Sequences Quiz

Less commonly used, field echo (FE) is the correct answer. Some manufacturers, including Philips and Canon, use FE or FFE (fast field echo) to name their gradient echo sequences. Another synonym is gradient-recalled echo (GRE).


Question: What happens if a gradient is turned on after the FID has spontaneously decayed?

Choices:
- A gradient recalled echo is produced.
- A spin echo is produced.
- The FID is partially regenerated.
- Nothing.

Pulse Sequences Quiz

Once the FID has spontaneously decayed by T2* processes, no signal can be recovered by action of a gradient.


Question: The first lobe of a gradient applied during a simple GRE imaging sequence is called the

Choices:
- Readout gradient.
- Dephasing gradient.
- Rephasing gradient.
- Bipolar gradient.

Pulse Sequences Quiz

The first step in a GRE sequence is to dephase the FID, so this lobe is referred to as the “dephasing gradient”.  The dephasing gradient results in accelerated dephasing beyond normal T2* processes with 'squelching/ scrambling' of the FID.


Question: The rephasing gradient refocuses spins that have been dephased by

Choices:
- The dephasing gradient only
- T2 only
- T2* only
- The dephasing gradient, T2, and T2*

Pulse Sequences Quiz

The rephasing gradient only refocuses spins scrambled by the dephasing gradient itself. T2 and T2* processes are unaffected and contribute to continued signal loss  Link to Q&A discussion


Question: Spin echoes were first described by

Choices:
- Felix Bloch
- Edward Purcell
- Isador Rabi
- Erwin Hahn

Pulse Sequences Quiz

Erwin Hahn discovered spin echoes while a graduate student in 1949.


Question: A single spin echo is produced by

Choices:
- A single RF-pulse
- A single RF-pulse plus gradient reversal
- Two RF-pulses
- Three RF-pulses

Pulse Sequences Quiz

A single RF pulse generates a free induction decay (FID), but two successive RF pulses produce a spin echo (SE).


Question: In a spin echo pulse sequence, the time between the middle of the first RF-pulse and the peak of the spin echo is

Choices:
- TR
- TE
- TE/2
- TI

Pulse Sequences Quiz

The time between the middle of the first RF pulse and the peak of the spin echo is called the echo time (TE).


Question: In a spin echo pulse sequence, the time between the first and second RF-pulses is

Choices:
- TR
- TE
- TE/2
- TI

Pulse Sequences Quiz

The spin echo occurs at time TE, which is twice the interpulse spacing. So the correct answer is TE/2 Link to Q&A discussion


Question: Spin-echoes for imaging are often produced using a 90º-pulse followed by a 180º-pulse. What would happen if the second pulse were changed to 90º?

Choices:
- No echo would be produced.
- A normal sized echo would be produced at a time 2 x TE
- An echo half as large would be produced at time TE
- An echo half as large would be produced at time 2 x TE

Pulse Sequences Quiz

A 90º-90º RF pair was what Erwin Hahn originally used, and the resultant echo is often known as a Hahn echo.  A Hahn echo will be formed from any two arbitrary RF pulses at time TE, with magnitude reduced depending on the angles chosen. The maximum SE intensity of a 90°-90° pair is only half as large as that produced by a 90°-180° pair.


Question: Which spin-echo pulse pair would be expected to produce the largest signal?

Choices:
- 90º-90º
- 90º-180º
- 180º-90º
- 180º-180º

Pulse Sequences Quiz

The reason 90°-180° pairs are most commonly used is that this combination produces the maximum possible echo signal. The maximum SE intensity of a 90°-90° pair is only half as large as that produced by a 90°-180° pair. In general, if the first RF-pulse has flip angle α1 and the second has flip angle α2, the maximum signal intensity of the Hahn echo will be smaller than the conventional (90°-180°) echo by a factor of  (sin α1)•(sin² α2/2).


Question: Of these, how many are considered to be “stimulated” echoes?

Choices:
- 1
- 2
- None of them
- All of them

Pulse Sequences Quiz

Only 1 stimulated echo is produced by 3 RF pulses.


Question: A sample placed in a static magnetic field develops an initial longitudinal magnetization Mo. It is then subjected to series of RF-pulses equally spaced apart by time TR. If TR>>T1, what can be said about Mz, the longitudinal magnetization immediately before each subsequent RF-pulse?

Choices:
- It cannot be predicted.
- It is the same as Mo.
- It is larger than Mo.
- It is smaller than Mo.

Pulse Sequences Quiz

If TR is sufficiently long (the usual requirement is TR > 4-5x T1), the longitudinal magnetization will have time to completely recover and be restored to its full initial magnetization Mo at the time of the next RF-pulse.


Question: A sample placed in a static magnetic field develops an initial longitudinal magnetization Mo. It is then subjected to series of RF-pulses equally spaced apart by time TR. If T2* < TR < T1, what can be said about Mz, the longitudinal magnetization immediately before each subsequent RF-pulse?

Choices:
- It cannot be predicted.
- It is the same as Mo.
- It is larger than Mo.
- It is smaller than Mo.

Pulse Sequences Quiz

In this scenario, TR is now the same or shorter than T1. Here the second and subsequent pulses occur before the longitudinal magnetization has returned to its initial value (Mo). After a few pulses a new steady-state longitudinal magnetization (Mss) will be established, where Mss) < Mo.


Question: The above situation (in Question 17) is known as

Choices:
- Partial saturation
- Complete saturation
- Steady-state free precession
- Incomplete magnetic equilibrium

Pulse Sequences Quiz

This phenomenon is called partial saturation, meaning that the spin system has not fully relaxed back to its equilibrium condition.


Question: A sample placed in a static magnetic field develops an initial longitudinal magnetization Mo. It is then subjected to series of RF-pulses equally spaced apart by time TR. If T2* < TR < T1, what can be said about Mxy, the transverse magnetization, midway between subsequent RF-pulses?

Choices:
- It cannot be predicted.
- It is the same as Mo.
- It is smaller than Mo but not zero.
- It is zero.

Pulse Sequences Quiz

The sample is partially saturated, as noted in question #17, reaching a new non-zero steady-state longitudinal magnetization, Mss) < Mo. But because TR > T2*, complete decay of the transverse magnetization occurs midway between each pair of RF-pulses, so the answer is zero (d).


Question: If the initial longitudinal magnetization of a sample is Mo, what is the longitudinal magnetization immediately after a 90º-pulse?

Choices:
- Mo
- −Mo
- ½ Mo
- Zero

Pulse Sequences Quiz

After an ideal 90º-pulse the longitudinal magnetization should be zero.


Question: If the initial longitudinal magnetization of a sample is Mo, what is the transverse magnetization immediately after a 90º-pulse?

Choices:
- Mo
- −Mo
- ½ Mo
- Zero

Pulse Sequences Quiz

After an ideal 90º-pulse all the longitudinal magnetization should be converted to transverse.


Question: If the initial longitudinal magnetization of a sample is Mo, what are the longitudinal (Mz) and transverse (Mz) magnetizations

Choices:
- About 90% of Mo
- About 70% of Mo
- About 50% of Mo
- About 10% of Mo

Pulse Sequences Quiz

From trigonometric identities we see that when a magnetization vector initially aligned with the z-axis is flipped by angle α, the transverse and longitudinal components of magnetization after the flip will be [Mo


Question: The flip angle that maximizes MR signal from a tissue in a GRE sequence without transverse coherences is known as the

Choices:
- Hahn angle
- Bloch angle
- Purcell angle
- Ernst angle

Pulse Sequences Quiz

Named after Richard R. Ernst, who received the Nobel Prize in Chemistry in 1991 for his discovery.


Question: When is the Ernst (optimal flip) angle approximately equal to 90º?

Choices:
- When TR >> T1
- When TR ≈ T1
- When TR << T1
- Never

Pulse Sequences Quiz

The Ernst angle (αE) can be calculated from the equation, αE = arccos (e−TR/T1). It reaches its maximum of 90º only when TR >> T1.


Question: In a spin-echo pulse sequences the 180°-pulse refocuses spins dephased by

Choices:
- Magnetic field inhomogeneities
- Diffusion
- T2 processes
- All of the above

Pulse Sequences Quiz

The 180°-pulse allows refocusing of nonmoving spins whose phases have been scattered by constant field distortions and inhomogeneities. The pulse does not correct for T1 or true T2 effects due to random processes at the atomic/molecular level. It does not correct for phase shifts of spins that move, flow, diffuse or undergo chemical exchange.


Question: Comparing Multi-echo Spin Echo (MSE) and Fast (Turbo) Spin Echo (FSE), which of the following statements is false?

Choices:
- Both MSE and FSE use more than one 180°-pulses during each TR interval.
- MSE uses only one phase-encoding gradient during each TR interval.
- FSE applies the phase-encoding gradient multiple times during each TR interval.
- The echo amplitude decreases with successive 180°-pulses in both MSE and FSE imaging.

Pulse Sequences Quiz

In FSE different phase-encoding gradients are being applied with each 180°-pulse, so the amplitude of the echo may vary depending on the phase-encode step.  In MSE the phase-encoding gradient is turned on only once in each TR interval, so successive echoes become reduced in signal intensity.


Question: Which of the following spin-echo parameter selections would produce a proton-density-weighted image?

Choices:
- TR = 500, TE = 10
- TR = 500, TE = 100
- TR = 5000, TE = 10
- TR = 5000, TE = 100

Pulse Sequences Quiz

Answer c), a long TR and short TE are used to produce a proton-density-weighted image.


Question: A spin-echo sequence using a short TR and long TE produces

Choices:
- A T1-weighted image
- A T2-weigthed image
- A PD-weighed image
- A noisy low contrast image

Pulse Sequences Quiz

The correct answer is d). So this combination is seldom used.


Question: Tissues or lesions with long values of T1 and T2 are typically

Choices:
- Bright on T1-weighted SE images
- Bright on T2-weighted SE images
- Bright on both T1- and T2-weighted SE images
- Dark on both T1- and T2-weighted SE images

Pulse Sequences Quiz

Such lesions are typically bright on T2-weighted images and dark on T1-weighted images.


Question: In the Inversion Recovery (IR) spin-echo pulse sequence, the inversion time (TI) is defined as

Choices:
- The time between the first 180°-pulse and first 90°-pulse
- The time between the first 180°-pulse and the echo
- The time between the two 180°-pulses in each TR interval
- The time between the first 90°-pulse and second 180°-pulse

Pulse Sequences Quiz

Answer a) is the definition of TI.  Link to Q&A discussion


Question: Advantages of IR techniques include

Choices:
- Shorter scan times
- Decrease in flow-related artifacts
- Additive T1 and T2 contrast
- Lower specific absorption rate (SAR)

Pulse Sequences Quiz

In conventional SE imaging combined T1 and T2 effects are generally competitive, meaning that ↑T1 generally results in decreased signal intensity while ↑T2 results in increased intensity.  In IR imaging by the appropriate choice of TR, T1 and T2 effects can be separated and made to be additive.


Question: On a magnitude-reconstructed IR image obtained at 1.5 T, which inversion time would be useful for suppressing fat?

Choices:
- TI = 170
- TI = 450
- TI = 980
- TI = 2000

Pulse Sequences Quiz

For most tissues the null point typically occurs when TI ≈ 0.69 x T1.  For fat with a T1 value at 1.5 T of approximately 250, this corresponds to a TI of approximately 170 ms.


Question: Which of the following statements concerning phase-sensitive inversion recovery (PSIR) is false?

Choices:
- Short T1 tissues always have a signal brighter than long T1 tissues, regardless of TI.
- Background air always appears black.
- Selective nulling of tissues by adjusting TI is not possible as it is for magnitude-reconstructed IR.
- It is useful for assessing pediatric myelination and myocardial contrast enhancement.

Pulse Sequences Quiz

Phase-sensitive IR preserves the information about the polarity of the longitudinal magnetization after the 180°(inverting)-pulse, with more negative values rendered increasingly darker. Background air is generally rendered a middle shade of gray, not black. Short T1 tissues are always brighter than long T1 tissues, but both can be darker than air at short TI’s. Common applications are in pediatric and cardiac imaging.


Question: Concerning the null point value (TInull) for a given tissue in magnitude-reconstructed IR, which statement is false?

Choices:
- TInull increases with increasing field strength.
- TInull increases with increasing T1 value
- For long TR, TInull ≈  0.69 x T2.
- TInull depends on whether the signal is generated by a conventional spin-echo or fast spin-echo sequence.

Pulse Sequences Quiz

For TR>>T1, TInull = T1 • (ln 2) ≈ 0.69 x T1, (not 0.69 x T2, so answer c is false). Because tissue T1 increases with field strength, TInull does also. TInull depends on echo time of the last echo in a FSE sequence.


Question: Which of the following statements about the Short TI Inversion Recovery (STIR) sequence is false?

Choices:
- It is a very useful technique for fat saturation.
- It is a very useful technique for detecting gadolinium enhancement.
- It has additive T1 and T2 effects.
- It is especially useful in lower field permanent magnets with relatively poor homogeneity.

Pulse Sequences Quiz

STIR cannot be used as a fat suppression technique post-gadolinium. STIR does not specifically suppress fat; it only suppresses tissues with T1 values in the range of fat (200-300 ms), so gadolinium enhancement would be suppressed.


Question: Which of the following pulse sequence parameters might be used to create a T1-FLAIR brain image?

Choices:
- TR = 2500, TE = 10, TI = 900
- TR = 2500, TE = 50, TI = 180
- TR = 4000, TE = 80, TI = 1800
- TR = 8000, TE = 100, TI = 2500

Pulse Sequences Quiz

Answer (a) is correct. Answer (b) would be considered a STIR image, while (c) and (d) would be T2-FLAIR images.


Question: Double Inversion Recovery (DIR) sequences for brain imaging utilize two different TI values, which typically suppress

Choices:
- Fat and CSF
- CSF and white matter
- CSF and gray matter
- Gray matter and white matter

Pulse Sequences Quiz

DIR brain imaging is particularly useful for detecting lesions of the white matter and cortex. Typically the first 180°-pulse suppresses CSF and the second suppresses white matter.


Question: Concerning nuclear spin (I), which of the following is true?

Choices:
- Spin is due to rotation of the nucleus about its axis.
- Protons have spin, but neutrons do not.
- Spin can only have integer or half-integer values.
- Another name for spin is "precession".

The NMR Phenomenon Quiz

Spin is a fundamental quantum property of subatomic particles and does not result from their physical rotation. Many subatomic particles besides the proton have spin, including the neutrons and electrons. Spin is quantized and can take on a limited number of discrete values, so c) is true. When placed in an external magnetic field, nuclear spin results in precession, but spin and precession are not the same.


Question: Which of the following spins (I) could a nucleus not possess?

Choices:
- 0
- 45293
- 45355
- 45537

The NMR Phenomenon Quiz

Quantum mechanics restricts nuclear spin to only integer or half-integer (1/2, 3/2, 5/2, etc) values, so I = 3/4 is not permitted.  Link to Q&A discussion


Question: Concerning nuclear spin (I), which of the following statements is false?

Choices:
- A longer but equivalent name for "spin" is "spin angular momentum".
- For hydrogen (¹H) MRI it is common and acceptable to use the terms "nucleus", "spin", and "proton" interchangeably.
- Routine clinical MRI measures signal from hydrogen (¹H) nuclei only.
- The hydrogen (¹H) nucleus contains one proton and one electron.

The NMR Phenomenon Quiz

The hydrogen (¹H) nucleus contains only a single proton surrounded by an electron cloud, so d) is false. The other statements are all true.


Question: Concerning nuclear spin (I), which of the following statements is false?

Choices:
- Protons and neutrons each have spin = ½.
- To determine net nuclear spin (I), you simply add up the number of protons and neutrons and divide by 2.
- Different isotopes of the same element commonly have different nuclear spins.
- Every element has at least one isotope with non-zero spin.

The NMR Phenomenon Quiz

Net nuclear spin (I) does depend on the total number of protons and neutrons, but no simple formula for I exists as interactions between more elementary components (quarks and gluons) must be considered. The other statements — a), c) and d) — are all true.


Question: Concerning nuclear spin (I) and NMR, which of the following statements is false?

Choices:
- All nuclei can undergo NMR except those containing even numbers of both protons and neutrons.
- Every element in the periodic table has at least one isotope that can undergo NMR.
- Across the periodic table nuclear spins (I) with values ranging from 0 to 8 can be found.
- Nuclei with I = 0 readily undergo NMR.

The NMR Phenomenon Quiz

Only nuclei with non-zero spins can undergo NMR, so d) is false. The other statements are all true.


Question: Which of the following statements concerning the magnetic dipole moment is false?

Choices:
- It is a representation of the nucleus modeled as a tiny bar magnet with north and south poles.
- An alternative representation is a vector (μ) arising from a small current loop.
- Like a compass needle, a dipole moment will tend to align with an externally applied magnetic field to assume its lowest energy state.
- The dipole moment will precess when placed in an external magnetic field.

The NMR Phenomenon Quiz

The magnetic dipole moment (μ) will experience a torque causing it to align with an externally applied magnetic field, but will not precess around the field.


Question: Which of the following statements about a magnetic dipole placed in an external magnetic field is false?

Choices:
- The dipole is at its lowest energy state when pointing in a direction opposite the field.
- The torque (twisting force) experienced by the dipole is directly proportional to the strength of the external field.
- The torque (twisting force) experienced by the dipole depends on the angle between the dipole and the external field.
- The energy of the dipole-external field system depends on the angle between the dipole and the external field.

The NMR Phenomenon Quiz

The dipole (μ) experiences a torque (τ) given by the vector cross-product τ =  μ x B0. In terms of scalar magnitudes: ||τ|| = ||μ||  ||B0|| sin θ, where θ is the angle between them. The energy (E) is defined by the dot product, E =  −μ • B0 =  −||μ||  ||B0|| cos θ. The energy is at its maximum (not a minimum), when the dipole points opposite the field (θ = 180°), so answer a) is false, .


Question: The dipole magnetic moment (μ) is directly proportional to nuclear spin (I), connected by a constant called the

Choices:
- Gyromagnetic ratio (γ)
- Planck's constant (h)
- Nuclear susceptibility (χ)
- Chemical shift (δ)

The NMR Phenomenon Quiz

The two are connected by the gyromagnetic ratio (γ), described through the relationship: μ = γI


Question: Which of the following statements about the gyromagnetic ratio (γ) is false?

Choices:
- It can be expressed in units of MHz/Tesla.
- It may have a negative value.
- It is different for each element.
- It is the same for all isotopes of a given element.

The NMR Phenomenon Quiz

The gyromagnetic ratio (γ) is a constant of proportionality between the dipole magnetic moment (μ) and nuclear spin (I). It is commonly expressed in units of MHz/T. Although usually a positive number, it may be negative. A negative value for γ means that the magnetic moment and spin point in opposite directions. The gyromagnetic ratio (γ) is different for every isotope of every element, so answer d) is false.


Question: The ¹H nucleus has a spin (I) = ½. When placed in an external magnetic field, its number of measurable spin states (eigenstates) will be

Choices:
- 0
- ½
- 1
- 2

The NMR Phenomenon Quiz

The number of observable spin states for a nucleus with spin I equals 2I +1. So the ¹H nucleus has 2(½) + 1 = 2 possible spin states.


Question: Besides ¹H, two nuclei commonly studied by NMR spectroscopy are ³¹P and ¹³C. The fact that all three isotopes have identical nuclear spins (I) = ½ means that when placed in an external magnetic field

Choices:
- They will have exactly the same resonant frequencies.
- They will each exhibit two discrete measurable energy states.
- The difference in energy states will be the same for each isotope.
- They will have the same gyromagnetic ratio (γ).

The NMR Phenomenon Quiz

All spin-½ particles will exhibit two discrete energy states when placed in an external magnetic field, so answer b) is true. The isotopes will have different gyromagnetic ratios (γ), different resonant frequencies, and different energy levels, however.


Question: ²³Na is another NMR active isotope used for imaging research. It has a nuclear spin (I) = 3/2. Compared to the ¹H nucleus with I = 1/2, in an external magnetic field

Choices:
- ²³Na will have a higher gyromagnetic ratio (γ) than ¹H.
- ²³Na will have a higher resonance frequency than ¹H.
- ²³Na will manifest 3 discrete energy states.
- ²³Na will manifest 4 discrete energy states.

The NMR Phenomenon Quiz

The number of observable energy states for a nucleus with spin I equals 2I +1. The ²³Na nucleus therefore has 2(3/2) + 1 = 4 possible spin states, so answer d) is correct. The gyromagnetic ratio (γ) and hence resonance frequency do not depend on I.


Question: The famous experiment demonstrating how spin-½ particles can be physically separated into two groups by a magnetic field was performed in 1922 by

Choices:
- Einstein
- Heisenberg
- Stern and Gerlach
- Planck and Dirac

The NMR Phenomenon Quiz

This is a description of the Stern-Gerlach experiment, often provided as tangible proof for the quantization of nuclear angular momentum visible in the macroscopic world.


Question: Which of the following names refers to the highest energy spin state of an ¹H nucleus in a magnetic field?

Choices:
- Spin-up
- Spin-down
- Parallel
- |+½>

The NMR Phenomenon Quiz

The highest energy state occurs when the spin has a direction opposite that of the main magnetic field and is denoted spin-down (correct answer), anti-parallel, or  |−½>.


Question: Why don't all the nuclear spins simply fall to their lowest energy states to minimize total system energy?

Choices:
- They actually do. The above statement is false.
- Such a highly skewed distribution of energy states is prohibited by quantum mechanics.
- Thermal molecular collisions tend to equalize the distribution of nuclei between lower- and higher-energy states.
- The distribution of energy states cannot be known due to the Heisenberg Uncertainty Principle.

The NMR Phenomenon Quiz

The natural tendency for spins to fall to lower energy states is offset by thermal collisions that tend to equalize the two energy levels. The result is a compromise predicted by the Boltzmann distribution.


Question: According to quantum mechanical (QM) theory and experiment, which statement is true?

Choices:
- A spin-½ particle like the proton must exist exclusively in either the spin-up or spin-down state.
- Conclusive evidence for the QM restriction described in part a) is provided by the Stern-Gerlach experiment.
- Scientists have been able to trap and manipulate spins in a superposition between their up- and down-states.
- There is nearly universal agreement among scientists that the Copenhagen Interpretation of QM is correct.

The NMR Phenomenon Quiz

Quantum mechanics does not require a proton to exist exclusively in one of its two primary (eigen)states, only a linear combination of the two. Thus answer a) is false. The Stern Gerlach experiment only shows that when a measurement is made a group of spin-½ particles that one of two results becomes physically manifest. This does not speak to the underlying quantum reality prior to measurement, however, so b) is also false.  Haroche and Weinland, working independently, were awarded the Nobel Prize for Physics in 2012 for their experiments trapping and manipulating spins in superposition states, so c) is true.  The Copenhagen Interpretation of QM, while still the most popular, is far from being universally accepted, so d) is false. Recent polls of quantum physicists found the Many Worlds Interpretation gaining significant ground.  Of course, neither may be correct!


Question: Nuclear precession can be considered the result of a "twisting force" or torque (τ) on a spin's angular momentum as it interacts with an externally applied magnetic field. The orientation of this torque is

Choices:
- Collinear with the spin.
- Collinear with the spin but in the opposite direction.
- Collinear with the magnetic field.
- Perpendicular to both the spin and magnetic field.

The NMR Phenomenon Quiz

The torque (τ) is perpendicular to both the spin angular momentum and the magnetic field. This creates a "twisting force" that can be thought of as "pushing the spin from the side" resulting in nuclear precession rather than alignment with the field. Link to Q&A discussion


Question: Precession may be expressed in either angular (ω0) or cyclic (f0) frequency. The two are are related by the equation

Choices:
- ω0 = 2 π f0
- f0 = 2 π ω0
- ω0 =  π f0
- f0 = π ω0

The NMR Phenomenon Quiz

The correct equation is a). Angular frequency (ω0) is measured in radians per second, where 2 π radians/sec = 360°/sec = 1 cycle (or revolution) per second = 1 Hertz (Hz). Thus the cyclic frequency (f0) must be multiplied by 2 π  to obtain angular frequency (ω0).


Question: The conventional units for angular frequency (ω0) are

Choices:
- Cycles per second (cps)
- Hertz (Hz)
- Radians/sec
- Revolutions per minute (rpm)

The NMR Phenomenon Quiz

The correct answer is c), radians per second. The other options are used to express cyclic frequency (f0).


Question: Which of the following is the correct form of the Larmor equation?

Choices:
- f0 =  γ B0
- f0 =  γ / B0
- f0 =  B0 /  γ
- None of these equations is correct.

The NMR Phenomenon Quiz


Question: What is the approximate gyromagnetic ratio (γ) of the ¹H nucleus?

Choices:
- 10.7 MHz/Tesla
- 42.6 MHz/Tesla
- 64.0 MHz/Tesla
- 128 MHz/Tesla

The NMR Phenomenon Quiz

The correct answer is b), 42.6 MHz/Tesla. I don't think you need to memorize this number, but it can easily be retrieved as I do believe everyone involved with MRI should know that a 1.5T scanner has a resonance frequency of about 64 MHz. Thus γ ≈ 64 MHz ÷ 1.5 Tesla, giving a γ of about 42.6 MHz/T.


Question: If the ¹H resonance frequency in a 1.5T scanner is about 64 MHz, what is the approximate ¹H resonance frequency at 7T?

Choices:
- 128 MHz
- 256 MHz
- 298 MHz
- 426 MHz

The NMR Phenomenon Quiz

Resonance frequency is directly proportional to field strength. So the ¹H resonant frequency at 7.0T can be calculated as 64 MHz x (7.0/1.5) ≈ 298 MHz.  Link to Q&A discussion


Question: Which of the following statements about nuclear precession is true?

Choices:
- Nuclear precession will not begin until a radiofrequency pulse is applied.
- Sustaining nuclear precession requires the continual input of energy from the environment.
- Protons in every drop of water in the ocean and in every snowflake at the north pole are precessing right now.
- It is impossible to obtain MR images using the earth's magnetic field because it is so small.

The NMR Phenomenon Quiz

Nuclear precession occurs spontaneously when protons are placed in any magnetic field.  No energy input is required to start or sustain precession. Precession occurs even in the tiniest magnetic fields, including that of the earth, so answer c) is true. In fact, crude MR images using the earth's magnetic field alone have been obtained.


Question: The slight difference in resonant frequencies noted between ¹H-nuclei in different molecular environments is due to

Choices:
- Different gyromagnetic ratios
- Different local magnetic fields
- Different relaxation times
- Different spin quantum numbers

The NMR Phenomenon Quiz

This question concerns the origin of chemical shift. Variable shielding and deshielding of ¹H-nuclei by molecular electron clouds results in slightly different local magnetic fields that each nucleus experiences. These different local fields alter resonance frequencies slightly.   Link to Q&A discussion


Question: Chemical shifts (δ) are typically reported in units of

Choices:
- Gauss (G)
- Millitesla per meter (mT/m)
- Parts per million (ppm)
- Percent (%)

The NMR Phenomenon Quiz

Chemical shifts are typically reported in ppm, which is independent of field strength. Note that ppm, like %, is dimensionless.  Link to Q&A discussion


Question: The abbreviation "ppm" stands for

Choices:
- Proton paramagnetic moment
- Proton-proton magnetization
- Precession per minute
- Parts per million

The NMR Phenomenon Quiz

The correct answer is d), "parts per million", the commonly used field-independent method to report chemical shifts.


Question: The chemical shift (δ) between water and fat protons measured at 1.5T is approximately 3.5 ppm. What would their chemical shift be at 3.0T?

Choices:
- 1.75 ppm
- 3.5 ppm
- 7.0 ppm
- 10.5 ppm

The NMR Phenomenon Quiz

The chemical shift (δ) in ppm is independent of field strength, so b) is correct.


Question: At 1.5 T the chemical shift between water and fat protons results in a frequency difference of approximately 220 Hz. What would be their frequency difference at 3.0T?

Choices:
- 110 Hz
- 220 Hz
- 440 Hz
- 660 Hz

The NMR Phenomenon Quiz

Field strength is doubled, so Larmor frequency is doubled, and frequency difference due to chemical shift is also doubled. The correct answer is therefore c).


Question: Which of the following statements concerning the net magnetization (M) is false?

Choices:
- M can be considered the vector sum or average millions of individual nuclear spins.
- Using M allows the NMR phenomenon to be analyzed using classical (rather than quantum) physics.
- At equilibrium, M is aligned with the external magnetic field.
- At equilibrium, M precesses around the direction of the external magnetic field.

The NMR Phenomenon Quiz

All statements are true except d). At equilibrium, M is stationary and aligned with the external magnetic field. Application of an RF-pulse is required to tip M out of alignment with B0 at which time it will begin to precess.


Question: In an unmagnetized sample of material far away from strong external magnetic fields, the net magnetization (M)

Choices:
- Is effectively zero in all directions.
- Has a significant non-zero longitudinal component.
- Has significant non-zero transverse components.
- Spontaneously precesses.

The NMR Phenomenon Quiz

In the absence of a strong external magnetic field, individual proton spins are randomly oriented in space and their vector sum is essentially zero in all directions. In reality, however, some small external magnetic field is always present, if only from the earth itself. Thus M is only effectively (but never completely zero) in all directions.