MRI Safety and Screening Quiz

MR Safety and Screening Quiz

OVERVIEW

  1. 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?
    1. 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.
    2. Use a hand-held ferromagnetic metal detector to exclude a dangerous implant or foreign body
    3. Obtain x-rays of the head & neck, chest, and abdomen/pelvis as a screening procedure
    4. Refuse to do the MRI until a full medical history can be obtained.

    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. Link to Q&A discussion

  2. Which of the following is considered an “active” implant?
    1. Implanted infusion pump
    2. Magnetic dentures
    3. Cerebrospinal fluid shunt with a programmable valve
    4. Swan-Ganz catheter

    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. Link to Q&A discussion

  3. Which of the following is not currently acceptable terminology for the safety of a device in MRI?
    1. MR Unsafe
    2. MR Conditional
    3. MR Compatible
    4. MR Safe

    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. Link to Q&A discussion

  4. Concerning safety labeling of devices, which of the following statements is true?
    1. A large silicone implant cannot be rated as MR Safe if it contains a single tiny non-ferromagnetic clip deep inside it.
    2. An MR Conditional device is safe to scan provided the majority of specified conditions are followed.
    3. Any implant containing a permanent magnet is MR Unsafe.
    4. If an implant does not undergo movement or heating under rigorous ASTM testing, it can be rated MR Safe.

    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. Link to Q&A discussion

  5. Concerning projectile incidents in MRI, which of the following is true?
    1. Worldwide at least a dozen people have died from projectile accidents since the beginnings of MRI.
    2. All reported deaths have involved ferromagnetic oxygen cylinders.
    3. Most reported projectile incidents involve small objects.
    4. An object made of non-ferromagnetic materials can still become a dangerous projectile.

    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. Link to Q&A discussion

  6. Which of the following statements about metal detectors in the MR setting is false?
    1. Metal detectors in MRI are very similar to those used for airport screening.
    2. The Joint Commission now requires all new and renovated MR suites to be equipped with ferromagnetic metal detectors.
    3. MR metal detectors cannot reliably detect deeply implanted ferromagnetic materials.
    4. Alarm fatigue can be a problem at sites using MR metal detectors.

    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

  7. Concerning MR imaging in the pregnant patient, which statement is false?
    1. Because of unknown risks to the fetus, MR should only be performed when the life of the mother or fetus is immediately threatened.
    2. The administration of gadolinium contrast should be avoided if at all possible.
    3. Low-SAR sequences are preferred to avoid heating fetal tissue.
    4. Quiet gradient sequences are preferred to avoid fetal exposure to loud noise after the first trimester.

    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. Link to Q&A discussion

  8. Which of the following commonly encountered postoperative items should be further scrutinized as a potential MR safety hazard:
    1. Skin staples
    2. IV catheter and tubing
    3. EKG pads
    4. Penrose drain

    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. Link to Q&A discussion

  9. For which patients is temperature monitoring during MRI not required?
    1. Healthy teenagers
    2. Healthy infants
    3. Anesthetized patients
    4. Elderly patients

    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. Link to Q&A discussion

  10. The most reliable device to measure body temperature during MRI is
    1. A rectal fiberoptic probe
    2. An esophageal fiberoptic probe
    3. A foley catheter thermistor
    4. An LCD skin detector placed in the axilla

    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. Link to Q&A discussion

  11. In which of the following orbital locations would the presence of small piece of metal not be a contraindication to MRI?
    1. Floating in the vitreous humor
    2. In the retroconal space
    3. In the lacrimal gland
    4. On the conjunctiva

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

  12. Considering the use of orbital CT to screen for metallic foreign bodies prior to MRI, which of the following is false?
    1. Orbital CT should be performed routinely on all machinists, pipe fitters, foundry workers, or anyone with similar occupational exposure to metal fragments.
    2. Plain films of the orbits are an acceptable alternative to CT.
    3. Low-dose CT techniques should be employed.
    4. CT may detect metal fragments too small to be of clinical concern for MRI.

    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. Link to Q&A discussion

  13. Concerning bullets and ballistic fragments, which statement is true?
    1. A hand-held ferromagnetic metal detector can reliably determine whether a bullet is made of lead or steel.
    2. Dual energy CT can reliably determine whether a bullet is made of lead or steel.
    3. For the last 25 years in the USA, steel-jacketed rifle bullets have been illegal to sell or possess.
    4. Deformity of a bullet fragment or a debris trail seen on x-ray suggests the projectile is not made of steel.

    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. Link to Q&A discussion

  14. In assessing a patient with a presumed ferromagnetic bullet or shrapnel, which factor is the most important in assessing risk of performing an MRI?
    1. Location of the fragment
    2. Shape of the fragment
    3. Length of time since implantation
    4. Whether it was acquired in a military setting

    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. Link to Q&A discussion

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STATIC FIELDS

  1. Which of the following statements about ferromagnetism is false?
    1. By definition all ferromagnetic materials must contain at least some iron.
    2. Ferromagnetism results when electron spins in magnetic domains align.
    3. As a ferromagnetic substance becomes magnetized, the magnetic domains change in size and shape.
    4. Hard ferromagnetic materials retain appreciable magnetization when removed from an external magnetic field.

    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. Link to Q&A discussion

  2. Which of the following metals is not considered ferromagnetic?
    1. Nickel
    2. Cobalt
    3. Chromium
    4. Magnesium

    Manganese, but not magnesium (d), is ferromagnetic. Link to Q&A discussion

  3. Concerning stainless steels, which of the following is false?
    1. 400 series stainless steels are ferromagnetic, while 300 series are non-magnetic.
    2. Austenitic stainless steels are ferromagnetic, while martensitic stainless steels are non-magnetic.
    3. Since 1990 the FDA has required all steel implants to be made of non-ferromagnetic stainless steel.
    4. Even non-ferromagnetic stainless steel can develop ferromagnetic properties if bent or stretched during machine working.

    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. Link to Q&A discussion

  4. Concerning magnetic saturation, which statement is false?
    1. Nearly all iron alloys saturate in the range of 1-2 Tesla.
    2. All ferromagnetic materials become saturated in a 3.0T field.
    3. It is impossible to create a permanent iron magnet having a field greater than 2.5 Tesla.
    4. The maximum strength of a permanent magnet is independent of its saturation point.

    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

  5. An implant made of which of the following materials could pose a safety risk because of ferromagnetic properties:
    1. Platinum
    2. Nitinol (Ni-Titanium alloy)
    3. Silicon steel
    4. Gold

    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) Link to Q&A discussion

  6. Which of the following rare earth elements is commonly used to make room temperature permanent magnets?
    1. Neodymium
    2. Magnetodynium
    3. Holmium
    4. Dysprosium

    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! Link to Q&A discussion

  7. Which metal or alloy in the list below would be expected to produce the largest susceptibility artifact on gradient-echo imaging?
    1. Lead
    2. Copper
    3. Aluminum
    4. Nitinol (Ni-Ti alloy)

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

  8. Concerning the hysteresis curve for a ferromagnetic material, which of the following is true?
    1. The curves for a material changes after its first time exposure to an external field.
    2. Coercivity is the magnetization that remains once the external field has been removed
    3. Reversing the direction of the magnetic field cannot reverse the magnetization.
    4. The hysteresis curves for a hard ferromagnetic material have small coercivities.

    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). Link to Q&A discussion

  9. Concerning demagnetizing fields, which statement is false?
    1. The demagnetizing fields for diamagnetic and paramagnetic materials are so small that they may effectively be disregarded.
    2. The demagnetizing field (D) points in the opposite direction to the magnetization (M)
    3. The demagnetizing field (D) points in the opposite direction to the external field (Bo)
    4. The demagnetizing field (D) increases the net magnetic field inside an object.

    Answer d is false. The demagnetizing field, by opposing M and B, decreases the net magnetic field inside an object. Link to Q&A discussion

  10. Concerning the effects of demagnetizing fields, which statement is false?
    1. Demagnetizing fields increase the apparent magnetic susceptibility of weakly ferromagnetic objects.
    2. The apparent susceptibility of an object made of a strongly ferromagnetic material primarily depends on its shape, not its specific composition.
    3. Demagnetizing fields in ferromagnetic materials reduce the size of the external field needed to achieve magnetic saturation.
    4. Demagnetizing factors are dimensionless numbers between 0 and 1.

    All statements are true except a). Demagnetizing fields decrease the apparent magnetic susceptibility of weakly ferromagnetic objects. Link to Q&A discussion

  11. 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.
    1. 0.5 T
    2. 1.0 T
    3. 1.5 T
    4. 3.0 T

    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) Link to Q&A discussion

  12. Which of the following shaped materials would have the largest demagnetizing factor (N) along the direction of the main magnetic field?
    1. A sphere
    2. A flat plate facing the main field
    3. A flat plate parallel to the main field
    4. An elongated cylinder pointing in the direction of the main field

    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. Link to Q&A discussion

  13. Mathematical analysis of predicted magnetic forces on metal objects often uses models based on
    1. Spheres
    2. Long tubes
    3. Ellipsoids
    4. Flat sheets

    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. Link to Q&A discussion

  14. Translational force on an unsaturated metal object brought near a cylindrical bore MR scanner is maximal
    1. When first entering the door of the MR scanner room
    2. At scanner isocenter in the middle of the bore
    3. At scanner isocenter at the edge of the bore
    4. Just inside the edge of the magnet bore opening

    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. Link to Q&A discussion

  15. The torque on an unsaturated metal object brought near a cylindrical bore MR scanner is maximal
    1. When first entering the door of the MR scanner room
    2. At scanner isocenter in the middle of the bore
    3. At scanner isocenter at the edge of the bore
    4. Just inside the edge of the magnet bore opening

    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. Link to Q&A discussion

  16. Where is the force on an unsaturated metal object the smallest?
    1. Only exactly at scanner isocenter
    2. At the majority of places inside the magnet bore where the static field is homogeneous
    3. Just inside the edge of the scanner bore opening
    4. One meter from the scanner bore opening

    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. Link to Q&A discussion

  17. 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?
    1. The torque is maximal when the wrench is held upright and perpendicular to the main magnetic field.
    2. The torque is maximal when the wrench is tilted at 45º toward the field.
    3. The torque is maximal when the wrench is turned to be parallel to the field.
    4. The exact shape or position of the wrench makes no difference on the torque, only its mass.

    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 Link to Q&A discussion

  18. When a metal object becomes magnetically saturated by an external field (B), which of the following is false?
    1. The displacement force is independent of B.
    2. The displacement force is independent of dB/dz.
    3. The torque is independent of B.
    4. The torque is independent of the object’s angulation (θ) with respect to B.

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

  19. 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
    1. Tesla
    2. Tesla/meter
    3. Tesla/meter²
    4. Tesla²/meter

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

  20. For a typical cylindrical MR scanner, the location of the maximum Spatial Gradient Product is
    1. In the middle of the bore at magnet isocenter
    2. Against the wall of the bore at magnet isocenter
    3. In the middle of the bore opening
    4. Along the wall at the bore opening

    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. Link to Q&A discussion

  21. 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?
    1. The ASTM would state that the risk imposed by magnetic force is no greater than that of the earth’s gravity.
    2. The ASTM would declare this object to be MR Conditional.
    3. The ASTM would declare this object to be MR Unsafe.
    4. The ASTM would declare this object to be MR Safe.

    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. Link to Q&A discussion

  22. Concerning the Lorentz force, which of the following is true?
    1. It is the force is experienced by charged particles moving through an electric field.
    2. It is responsible for T-wave changes on an EKG
    3. It is responsible for magnetophosphenes and taste disturbances in 7T scanners.
    4. It is responsible for the stacking up of sickle cell erythrocytes in a magnetic field.

    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. Link to Q&A discussion

  23. Which of the following concerning MR-related dizziness and vertigo is false?
    1. It is much more common at 7T than 3T.
    2. It is likely due to a Lorentz force acting on endolymphic ionic currents.
    3. It is exacerbated by rapid head or table motion.
    4. It is most severe and persistent when the patient’s head reaches magnet isocenter.

    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). Link to Q&A discussion

  24. Concerning magnetophosphenes, which statement is false?
    1. They are much more common at 7T than 3T.
    2. They are caused by electric field stimulation of the optic nerve.
    3. Technologists walking around the scanner may experience them.
    4. They are exacerbated by rapid head or table motion

    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. Link to Q&A discussion

  25. Concerning metallic taste sensations during MRI, which of the following is false?
    1. Their mechanism of generation is similar to that of magnetophosphenes.
    2. They are related to release of ions from metallic dental fillings.
    3. They are much more common at 7T than 3T.
    4. They are much less common than vertigo or magnetophosphenes.

    The phenomenon occurs in patients without dental fillings, so answer b) is false. Link to Q&A discussion

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RF FIELDS

  1. Concerning RF-transmit body coils, which of the following is false?
    1. They consist of multiple rungs in a so-called “bird cage” configuration.
    2. In addition to transmission they are commonly used for reception of the RF signal.
    3. They do not extend the full length of the body coil.
    4. They cannot be seen by the patient.

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

  2. RF “hot spots” associated with RF-transmit coils are located
    1. In the middle of the bore at magnet isocenter
    2. Along the walls of the bore at magnet isocenter
    3. Immediately adjacent to the wall at the bore opening
    4. All of the above
    5. None of the above

    RF “hot spots” are located adjacent to the wall of the scanner at locations corresponding to the end of the RF coil rungs. These are typically located about 20-25 cm on either side of isocenter along the scanner walls. The correct answer is e), none of the above. Link to Q&A discussion

  3. Concerning the use of RF-transmit body coils
    1. They are required for clinical spine imaging
    2. They are required for clinical head imaging
    3. They are required for clinical knee imaging
    4. They are required for phosphorus spectroscopy of the calf muscle

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

  4. Radiofrequency fields are part of the electromagnetic spectrum considered to have frequencies lying in the approximate range of
    1. 64 MHz to 128 MHz
    2. 3 kHz to 300 MHz
    3. 3 kHz to 1 GHz
    4. 3 kHz to 300 GHz

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

  5. Concerning the thermal effects of RF-irradiation as used in MRI, which statement is true?
    1. T1 relaxation with energy transfer from nuclei to the lattice makes a significant contribution to tissue heating.
    2. The RF magnetic and electric fields point in opposite directions.
    3. The coexistent electric field (E), not the magnetic field (B1) per se, is responsible for nearly all the RF-thermal effects in MRI.
    4. About half of transmitted RF power is absorbed by nuclei.

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

  6. Which mechanism of RF-induced tissue heating is unlike the others?
    1. Resistive heating
    2. Joule heating
    3. Ohmic heating
    4. Dielectric heating

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

  7. Which mechanism is primarily responsible for making my bowl of soup warm up in the microwave oven?
    1. Resistive heating
    2. Joule heating
    3. Ohmic heating
    4. Dielectric heating

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

  8. The units for specific absorption rate (SAR) are
    1. Watts per kilogram
    2. Watts per second
    3. Joules per kilogram
    4. Joules per second

    SAR is power (watts) deposited in a certain mass of tissue (kg). Answer a) is correct. Link to Q&A discussion

  9. Concerning SAR which of the following is false?
    1. SAR is proportional to tissue electrical conductivity.
    2. SAR decreases with increasing body size.
    3. SAR is proportional to the square of both Bo and B1.
    4. SAR is proportional to the duty cycle.

    Answer b) is false. SAR increases exponentially with increasing body size and is thus a significant concern with large or obese patients. Link to Q&A discussion

  10. What are the units of measurement for the duty cycle?
    1. Seconds
    2. Watts/kg
    3. Percent
    4. Joules/second

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

  11. A 50-kg woman is imaged using a 3-minute pulse sequence having an SAR of 2.0 W/kg. The total RF energy absorbed is
    1. 180 Joules
    2. 300 Joules
    3. 3000 Joules
    4. 18,000 Joules

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

  12. Consider two otherwise identical gradient echo pulse sequences, the first using an RF-flip angle (α) = 15º and the second using α = 30º. The SAR of the second pulse sequence is
    1. Twice as large as the first.
    2. Half as large as the first.
    3. Four times as large as the first.
    4. One fourth as large as the first.

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

  13. Which of the following is not the name of an MRI Operating Mode based on perceived risk to subjects as defined by the International Electrotechnical Commission (IEC)?
    1. Normal
    2. First Level
    3. Second Level
    4. Third Level

    There is no Third Level Operating Mode. Also note that Normal is the lowest level and is not the same as First Level. Link to Q&A discussion

  14. Concerning Operating Modes for MRI as defined by the International Electrotechnical Commission (IEC) which statement is false ?
    1. The same SAR limits apply regardless of whether a volume transmit or local transmit coil is used.
    2. Higher SAR limits are allowed for extremity imaging than trunk imaging.
    3. Other factors (such as static field strength and rates of time-varying gradients) are used in addition to SAR levels when defining the MRI Operating Mode
    4. Second level operation can only be performed under an appropriate ethics/human studies/institutional review board protocol

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

  15. When is it acceptable to change from Normal to First Level Controlled Operating Mode?
    1. Whenever one needs to increase the number of slices for a given TR.
    2. Whenever one needs to perform more rapid imaging in a moving patient.
    3. Whenever deemed necessary and under supervision of a physician.
    4. Whenever the patient’s body weight is unknown and may be underestimated.

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

  16. Which one of the following pulse sequences would have the lowest SAR?
    1. A single-shot echo-planar diffusion scan of the bran
    2. A T2-weighted turbo spin-echo scan of the pelvis
    3. A T1-weighted, fat suppressed spin-echo image of the cervical spine
    4. A 2D time-of-flight MRA of the lower extremities

    The EPI diffusion scan, using predominantly recalled echoes by gradient reversal, would have the lowest SAR of the scans listed. Link to Q&A discussion

  17. Which of the following technical parameter changes alone would not be useful in reducing SAR?
    1. Increase TR
    2. Increase number of slices
    3. Reduce flip angle
    4. Use of hyperechoes

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

  18. Altering the following image acquisition parameters by themselves will have no effect on SAR, except for
    1. Number of signals averaged
    2. Slice width
    3. Receiver bandwidth
    4. Use of parallel imaging
    5. RF pulse shape or duration

    Answer e), changing the RF-pulse shape or duration, has a powerful effect on SAR. Many scanners offer the option of low SAR pulses, including VERSE, that may reduce SAR as much as 25-30%. Link to Q&A discussion

  19. All of the following are trade-offs for the use of low SAR RF-pulses except
    1. More slice cross-talk
    2. Longer minimum TE values
    3. Longer imaging time
    4. Fewer slices for a given TR

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

  20. Which of the following physical mechanisms is not an important factor in RF-induced thermal injury?
    1. Inductive heating
    2. Magnetohydrodynamic effect
    3. Heating of a resonant loop
    4. Antenna effect

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

  21. Which of the following statements about the “antenna effect” is false?
    1. It explains SAR hot spots at the end of a wire or electrode.
    2. It results from standing waves along the length of the wire.
    3. The effect is maximal when the wire measures close to the RF wavelength.
    4. Wires measuring about 26 cm at 1.5T and 13 cm at 3.0T are the most likely to experience this phenomenon.

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

  22. Which of the following would not be an acceptable position for a patient undergoing MRI?
    1. Prone
    2. Hands clasped across lap
    3. Arms straight up
    4. Supine with knees bent at 90º

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

  23. What should be done if an MR patient has a large tattoo?
    1. Nothing; they are totally safe to scan except in rare cases.
    2. Warn the patient about heating and to notify tech immediately if any discomfort.
    3. Allow scanning, but apply an ice pack to the tattoo during the procedure.
    4. Do not scan the patient; large tattoos are contraindicated due to high risk of burns.

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

  24. Concerning transdermal medication patches, which statement is incorrect?
    1. All patches must be removed prior to scanning.
    2. Only metal-backed patches must be removed.
    3. A metal back patch need not be removed if it is not in the region of the transmit RF-coil.
    4. Before removing a patch for MRI, the patient’s physician should be contacted to be sure it is safe for the patient to not receive her patch medication for the duration of the scan.

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

  25. Concerning large patients that may touch the walls of the scanner, which of the following is true?
    1. They may feel uncomfortable and experience claustrophobia, but are in no medical danger.
    2. Ideally a sheet should be placed between the patient and the wall to avoid bacterial contamination of the scanner from the patient’s skin.
    3. Special foam padding provided by the manufacturer should be used to prevent the patient from touching the walls.
    4. It is OK to scan the patient without padding if they are too big.

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

  26. Concerning wires and cables within the bore of the MR scanner, which statement is false?
    1. Skin contact must be avoided by padding or positioning.
    2. The wires should be run down along the sidewall of the MR bore parallel to the main magnetic field.
    3. The wires should not be crossed.
    4. If more than one wire is exiting, it is ideal to leave a little space between them to prevent capacitive coupling.

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

  27. Concerning Specific Energy Dose (SED) and Specific Absorption Rate (SAR), which statement is true?
    1. They are essentially the same, except for a conversion factor to correct for units of measurement.
    2. The units for SED are Joules/kg.
    3. Both represent rates of energy absorption by the body during an MRI scan.
    4. If every sequence in a scanning protocol has SAR values that lie safely within regulatory limits, the SED cannot be excessive.

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

  28. A 50-kg woman undergoes an MR protocol that consists of two sequences: Sequence 1, lasting 2 minutes, with SAR = 1 W/kg; followed by Sequence 2, lasting 4 minutes, with SAR = 2 W/kg. The SED for the entire protocol is calculated to be
    1. 10 J/kg
    2. 100 J/kg
    3. 600 J/kg
    4. 800 J/kg

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

  29. All of the following statements about the B1+ field and B1+rms are true except for
    1. The B1+ field rotates in the opposite direction to nuclear precession.
    2. SAR is directly proportional to [B1+rms]²
    3. SAR is directly proportional to [Bo]², but B1+rms is independent of Bo.
    4. The strength of the B1+ field scales linearly with the voltage supplied to the transmitter.

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

  30. Concerning occupational exposure to MRI in the clinical environment, which one of the following statements is true?
    1. Consistent regulatory limits for occupational exposure to magnetic fields exist throughout Europe and the Americas.
    2. MRI staff working around scanners with fields of 7T or higher commonly experience nausea, dizziness, unsteadiness, and/or see flashes of light.
    3. There is nothing that can be done to reduce these short-term sensory effects.
    4. Pregnant MR technologists are at increased risk for miscarriages or premature births.

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

  31. Do cell phones cause cancer?
    1. Definitely yes
    2. Definitely no
    3. Probably no, but some data suggests a potential small effect.
    4. Probably yes, but some data suggests no effect.

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

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GRADIENT FIELDS

  1. How many sets of gradient coils does the typical MRI scanner use?
    1. 1
    2. 2
    3. 3
    4. 4

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

  2. The magnetic field strength of imaging gradients
    1. Is much less than that of the main field (Bo)
    2. Is slightly less than that of the main field (Bo)
    3. Is the same as that of the main field (Bo)
    4. Is slightly greater than that of the main field (Bo)

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

  3. Which of the following physical effects is not the result of gradient activity?
    1. Acoustic noise
    2. Vertigo
    3. Peripheral nerve stimulation
    4. Metal implant heating

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

  4. Concerning acoustic noise due to gradients, which statement is false?
    1. It is due to vibration of the gradient coils due to rapidly switched electrical currents.
    2. Acoustic noise in MRI may be temporarily uncomfortable, but it poses no real risk to hearing.
    3. Echo-planar sequences are especially loud.
    4. All patients and accompanying family members should be required to use ear protection.

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

  5. Concerning gradient-related electromagnetic fields in patients, which statement is false?
    1. It is the coexistent electric field, rather than the gradient magnetic field, which causes peripheral nerve stimulation.
    2. Peak electric field values occur during the ramp up and ramp down periods of the gradients.
    3. Electric fields in a patient are concentrated superficially and at bone/fat/muscle junctions.
    4. The strongest gradient effects typically occur at magnet isocenter in the middle of the imaged field-of-view.

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

  6. Concerning the strength-duration curve for nerve depolarization, which one of the following is true?
    1. The strength-duration curve plots the threshold for electrical stimulation as a function of stimulus strength and duration.
    2. The shape of the strength-duration curve is approximately linear.
    3. The rheobase is the minimum time required to stimulate a nerve regardless of stimulus strength.
    4. The chronaxie is the minimum voltage required to stimulate a nerve at any duration.

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

  7. Which of the following statements concerning nerve and muscle stimulation by MR gradients is false?
    1. Larger axons are more easily depolarized than smaller ones.
    2. Nerves having twists and kinks are more easily depolarized than straighter nerves.
    3. Deeply located nerves are more easily depolarized than superficial ones. .
    4. The threshold for cardiac stimulation is many times higher than that of peripheral nerves.

    Answer c) is false. Because electrical fields in MRI are more superficially concentrated in the body of the patient, superficial nerves are more likely to be stimulated than deep ones. Link to Q&A discussion

  8. Which implant would be least likely to demonstrate gradient-induced heating?
    1. Total hip prosthesis
    2. Deep brain stimulator electrode
    3. Cardiac pulse generator
    4. Implanted infusion pump

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

  9. Concerning gradient-induced heating, which of the following is incorrect?
    1. Gradient heating is typically more important the RF heating in causing tissue injury.
    2. Changing gradients heat the implant itself.
    3. Gradient heating is more likely with fast, high slew rate sequencies like echo-planar imaging.
    4. Gradient heating affects bulky implants with large transverse cross-sections.

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

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MR SAFETY OF IMPLANTED DEVICES

  1. Why did early regulators establish the 5-gauss line as a safety limit for exposure of the general public around MRI facilities?
    1. It is the field strength where a ferromagnetic cerebral aneurysm clip begins to move.
    2. It is the field strength where a paper clip or other equivalent small metal object will fly into the scanner.
    3. It is the field strength where 1970’s era pacemakers might begin to malfunction.
    4. It is approximately 10 times the earth’s magnetic field.

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

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

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

  3. A patient with a recently placed programmable shunt placed is referred for head MRI. What do you do?
    1. Do not scan the patient. A programmable shunt is an absolute contraindication to MRI.
    2. Confirming that the shunt is MR Conditional at up to 3.0T, scan the patient and send him home.
    3. Send the patient to neurosurgery clinic immediately after the scan to have his valve pressure checked.
    4. Tell the patient to make an appointment with his neurosurgeon within the next week to have his valve pressure checked.

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

  4. Concerning precautions that need to be followed for MR conditional intracranial pressure monitoring systems, which statement is false?
    1. Obey the usual restrictions on field strength, spatial gradient field, slew rate, and SAR.
    2. Verify the sensor is working properly prior to MRI.
    3. Disconnect all removable cables and wires from the device.
    4. Make sure non-removable wires are arranged in a straight line along the bore of the scanner and away from the patient’s head.

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

  5. Which one of the following is the most significant safety concern with the scanning of a patient with a deep brain stimulation system?
    1. Permanent damage to the implanted pulse generator
    2. Thermal burn at the electrode tip
    3. Cutaneous burns along ascending wires in the neck
    4. Induction of seizures

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

  6. Why is it recommended that eye makeup be removed prior to MRI?
    1. This is a myth; eye makeup doesn’t have to be removed.
    2. It can cause significant image artifacts around the orbit.
    3. Severe burns can occur on the eyelids.
    4. Corneal injury and blindness can occur.

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

  7. Which of the following orbital implants should elicit the most concern from an MR safety perspective?
    1. Artificial intraocular lenses
    2. Contact lenses
    3. Scleral band
    4. Retinal tacks

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

  8. What is the major safety concern for MR imaging of cochlear implants?
    1. Movement/dislodgement of the internal magnet
    2. RF-induced heating at the tip of the cochlear electrode due to the “antenna effect”
    3. Electronic shorting/malfunction of the electronic stimulator
    4. Scalp burns adjacent to the subcutaneous receiver coil

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

  9. Which of the following dental implants would pose the biggest safety concern in MRI?
    1. Metal crowns and bridges
    2. Amalgam fillings
    3. Braces
    4. Magnetic dentures

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

  10. Which upper airway device should be viewed as a potential safety concern in the MR environment?
    1. Non-cuffed endotracheal tube
    2. Endotracheal tube with spring-loaded pilot balloon valve
    3. Reinforced endotracheal tube
    4. Laryngeal mask airway

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

  11. What is the major MR safety concern about breast tissue expanders?
    1. Loss of saline due to magnetic effects on the valve mechanism
    2. Dislodgment of the MAGNA-SITE® port
    3. Cutaneous burns over the port
    4. Melting of the silicone capsule adjacent to the port

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

  12. What should be done if a patient with an inferior vena cava (IVC) filter needs a scan?
    1. He’s out of luck; nearly all of these are MR Unsafe.
    2. The patient can be scanned, but no sooner than 6 weeks after implantation.
    3. The patient can be scanned but should be warned there is a high risk that the filter may migrate.
    4. The patient can be safely scanned provided MR Conditions are followed.

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

  13. During the last decade in the United States, the leading cause of MRI-related deaths has been
    1. Infusion pump malfunction
    2. Projectiles
    3. Pacemaker malfunction
    4. Burns

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

  14. Life-threatening effects of the magnetic field on implanted infusion pumps include all except
    1. Deep peri-implant burns due to RF- and/or Gradient-induced eddy currents
    2. Increased or decreased rate of drug delivery
    3. Cessation of pump operation while scanning with delayed restart
    4. Permanent device failure due to demagnetization of the pump magnet

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

  15. Which of the following intravascular devices should be considered MR Unsafe?
    1. Aortic stent graft
    2. Drug-eluting coronary stent
    3. Swan-Ganz thermodilution catheter
    4. Vascular closure device

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

  16. Failure of drug delivery by an implanted infusion pump affected by a magnetic field is particularly dangerous for which drug?
    1. Bupivacaine
    2. Morphine
    3. Baclofen
    4. Floxuridine (5-FUdR)

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

  17. Concerning the following bariatric devices, which should raise the greatest MR safety concerns?
    1. Adjustable gastric bands
    2. Gastric balloons
    3. Gastric electrical stimulators
    4. External gastric drainage devices

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

  18. Which of the following contraceptive devices is considered MR Unsafe?
    1. Copper 7 IUD
    2. Chinese stainless steel ring IUD
    3. Filshie tubal ligation clips
    4. Essure® tubal occlusion devices

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

  19. Which metal is not commonly used for modern orthopedic implants?
    1. 410 stainless steel
    2. 316L stainless steel
    3. Cobalt-chromium alloy
    4. Pure commercial titanium

    All of the listed metals are used in orthopedic implants except for the 400 series of stainless steels which are ferromagnetic. Link to Q&A discussion

  20. Why might a surgical supply manufacturer choose to make halos and external fixation rods out of carbon fiber reinforced polymer?
    1. They are lighter than their metal equivalents.
    2. They are stronger and more flexible than their metal equivalents.
    3. They are only weakly conductive.
    4. They are only weakly ferromagnetic.

    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. Link to Q&A discussion

  21. 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?
    1. Resonant amplification of normal scanner mechanical vibrations
    2. Vibration of the frame due to gradient-induced eddy currents.
    3. Vibration of the frame due to RF-induced eddy currents.
    4. Subconscious to-and-fro movement of the frame by the patient due to peripheral nerve stimulation

    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. Link to Q&A discussion

  22. The abbreviation CIED stands for
    1. Cardiac Implanted Electronic Device
    2. Cardiac Implanted Electrical Defibrillator
    3. Cardioverting Internal/External Defibrillator
    4. Cardiac Internal Excitation Device

    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). Link to Q&A discussion

  23. Two-lead CIEDs typically terminate in
    1. The right atrium and right ventricle
    2. The right atrium and left ventricle
    3. The right ventricle and left ventricle
    4. The left atrium and left ventricle

    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

  24. Concerning Implanted Cardioverter-Defibrillators (ICDs), which statement is false?
    1. ICDs are the preferred CIED for treating ventricular fibrillation.
    2. ICD’s are the preferred CIED for treating symptomatic bradycardia.
    3. ICD’s are designed to deliver high-energy shocks.
    4. Some ICDs do not have shock leads in the heart.

    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. Link to Q&A discussion

  25. “Leadless” pacemakers are generally placed in the
    1. Left atrium
    2. Left ventricle
    3. Right atrium
    4. Right ventricle

    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. Link to Q&A discussion

  26. Which of the following pacemaker scenarios would invoke the greatest MR safety concern?
    1. Scanning a patient with retained epicardial leads
    2. Scanning a patient with a temporary transvenous pacemaker
    3. Scanning a patient within 6 weeks of placement
    4. Scanning a patient with a legacy/non-conditional pacemaker

    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). Link to Q&A discussion

  27. What is the principal risk associated with scanning a patient with a subcutaneously implanted loop recorder?
    1. Skin burns over the device
    2. Permanent malfunction of the device
    3. Electric, shock-like sensations
    4. Erasure of previously recorded data

    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. Link to Q&A discussion

  28. Concerning the MR safety of cardiac valves and annuloplasty devices, which statement is true?
    1. Most older metal valves are considered MR Unsafe.
    2. All valves and annuloplasty devices are considered MR Safe or Conditional up to 3.0 T.
    3. A mandatory 6 week waiting period is required before scanning for all valves.
    4. A mandatory 6 week waiting period is required before scanning for any valve or annuloplasty device containing metal.

    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. Link to Q&A discussion

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