SITE PLANNING

  1. Which of the following components of an MR system is typically not located in an adjoining equipment room?
    1. RF-power amplifiers
    2. Gradient amplifiers
    3. Helium pump
    4. Gradient coils

    Gradient coils are an integral part of the MR scanner itself and are not located in a separate equipment room. Link to Q&A discussion

  2. Where is the master computer located that controls the MR scanner and processes data into images?
    1. In the MR scanner room
    2. In the MR scanner control room
    3. In the nearby MR equipment room
    4. At least 25 meters distant from the main scanner to avoid interference

    The master computer is located in the scanner console in the control room immediately adjacent to the magnet room. Because of scanner shielding there is not need for it to be in a remote location (answer d is false). Link to Q&A discussion

  3. The function of the array processor is to
    1. Generate triggers for the array of RF-pulses and gradient waveforms used for imaging
    2. Reconstruct the raw NMR data into images
    3. Calculate RF frequency offsets and gradient strengths for desired slice selection and field-of-view
    4. Activate and/or disable various coil elements in an array

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

  4. Which scanner is the heaviest (and would thus require the most floor support)?
    1. 0.35 T Permanent magnet system
    2. 0.6 T Resistive magnet system
    3. 1.5 T Superconductive system
    4. 3.0 T Superconductive system

    Permanent magnet systems may weigh over 35,000 pounds (16,000 kg), over 3 times more than a superconductive scanner. Link to Q&A discussion

  5. Which scanner is would have the lowest overall siting and operational costs?
    1. 0.35 T Permanent magnet system
    2. 0.6 T Resistive magnet system
    3. 1.5 T Superconductive system
    4. 3.0 T Superconductive system

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

  6. Which component of a superconducting MR scanner does not require specialized cooling to maintain function?
    1. Main coil windings
    2. Gradient coils
    3. Gradient amplifiers
    4. Radiofrequency coils
    5. Radiofrequency amplifiers

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

  7. The B0 field of an MR scanner is strongest and most homogeneous at
    1. At the opening (gantry) of the magnet
    2. At bore level about 1 meter directly in front of the magnet
    3. In the middle of the bore at isocenter
    4. On the outside of the magnet immediately against its wall

    The B0 field is both strongest and most homogenous at magnet isocenter. Link to Q&A discussion

  8. Which scanner would have the largest fringe field?
    1. 0.35 T Permanent magnet system
    2. 0.6 T Resistive magnet system
    3. 1.5 T Superconductive system
    4. 3.0 T Superconductive system

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

  9. If one moves from 1 meter to 2 meters away from a magnet, the fringe field will be reduced by a factor of approximately
    1. √2
    2. 2
    3. 4
    4. 8

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

  10. The fringe fields of cylindrical superconducting magnet are highest
    1. In the x-direction (transverse and horizontal to the axis bore)
    2. In the y-direction (transverse and vertical to the axis bore)
    3. In the z-direction (along the axis bore)
    4. They are equal in all directions

    Fringe fields are significantly higher along the z-axis (the direction of B0). Link to Q&A discussion

  11. The primary purpose for passive magnetic shielding is
    1. To reduce fringe magnetic fields outside the scanner room.
    2. To keep extraneous radiofrequency noise from entering the scanner room.
    3. To constrain the NMR signal to remain within the bore of the magnet for better reception.
    4. To reduce the effects of moving equipment (such as cars and elevators) from distorting the magnetic field.

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

  12. Concerning passive shielding, which statement is true?
    1. It is performed by placing heavy copper plates along the walls of the scanner room.
    2. It is a method to reduce extraneous radiofrequency interference with the MR signal.
    3. It is more commonly required for 7.0T than for 1.5 T installations.
    4. Active shielding technology found in modern scanner design has not changed the need for it.

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

  13. Passive magnetic shielding of the scanner room is typically achieved using sheets or rods made of
    1. Copper
    2. Iron
    3. Aluminum
    4. Lead

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

  14. The fringe magnetic field arising from an MR scanner
    1. Can be eliminated by active shielding.
    2. Can be eliminated by passive shielding.
    3. Can be reduced by radiofrequency shielding.
    4. None of the above.

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

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

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

  16. Which statement about ACR Safety Zones 1 and 2 is correct?
    1. Both Zones 1 and 2 lie outside the 5 Gauss line.
    2. Patient safety screening is required before entering Zone 2
    3. The general public should not be admitted to Zone 1; it is only for MR patients and their families.
    4. Patients with pacemakers can at risk if allowed to enter Zone 2.

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

  17. Which statement about ACR Safety Zone 3 is false?
    1. Patients should not be admitted to Zone 3 unless they have undergone safety screening.
    2. Ferromagnetic objects may not be brought into this area.
    3. The MR operator's console is located in this area.
    4. Medical personnel should not be admitted to this area unless they have undergone MR safety training.

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

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

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

  19. Why might large trucks on a road 20 meters away from an MR scanner be of potential concern for siting?
    1. Their CB radios operate at the same frequencies as the MR signal.
    2. The scanner magnetic field can be affected by the dense iron in their chassis as they pass by.
    3. The physical vibrations they produce can affect image quality.
    4. At this distance heavy truck traffic should be of no concern at all.

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

  20. The loud noise produced by an MR system during a scan is primarily due to
    1. Vibrations of the gradient coils
    2. Vibrations of the radiofrequency coils
    3. Vibrations of the main magnet windings
    4. Vibrations from the chiller and helium pump

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

  21. Which of the following sequences would likely generate the loudest noise during scanning?
    1. T2-weighted Turbo spin-echo (TSE) imaging of the spine
    2. Dixon fat-water imaging of the liver
    3. Echo-planar diffusion tensor imaging of the brain
    4. MR spectroscopy of the prostate

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

  22. Which of the following statements about MR scanner noise is false
    1. Sound levels can reach up to 120 dB for some sequences.
    2. Although potentially uncomfortable for the patient, there is no real risk to hearing.
    3. Ear protection is mandatory for all patients undergoing MR imaging.
    4. New quiet pulse sequences can reduce noise levels to within 10 dB of background.

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

  23. Which of the following methods can reduce scanner noise?
    1. Avoidance of echo-planar sequences
    2. Use of "soft" gradient pulses with longer rise times
    3. Use of 3D ultrashort TE sequences
    4. All of the above

    These strategies will all produce a reduction of noise levels during scanning. Link to Q&A discussion

  24. Newer "quiet" MR sequences with longer gradient ramp times are now available. Which of the following statements about these sequences is true
    1. They can reduce noise levels to within 10 dB of background.
    2. This strategy can be applied to all pulse sequences.
    3. They can be employed with no signal-to-noise penalty.
    4. They do not affect number of slices for a given TR.

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

  25. Radiofrequency shielding of the scanner room is most commonly achieved by lining the walls with thin sheets of
    1. Iron
    2. Aluminum
    3. Copper
    4. Lead

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

  26. The primary purpose for radiofrequency shielding is
    1. To confine fringe fields to the scanner room itself.
    2. To constrain the NMR signal to remain within the bore of the magnet for better reception
    3. To keep extraneous radiofrequency noise from entering the scanner room
    4. To reduce the effects of moving equipment (such as cars and elevators) from distorting the magnetic field.

    RF-shielding primarily prevents extraneous radiofrequency noises from outside the scanner room from entering and contaminating the MR signal. Link to Q&A discussion

  27. In most clinical MR sites, the principal source RF-interference that needs to be excluded comes from cell phones, TV, and radio transmissions.
    1. True
    2. False

    The most common form of RF interference comes from noise generated from nearby electrical equipment (transformers, motors, pumps) or electronic devices (computers, pulse oximeters, cardiac monitors). Link to Q&A discussion

  28. A device that allows a plastic oxygen hose to be passed through the wall of an MR scanner room without disrupting the integrity of the RF-shielding is called a
    1. Penetration panel
    2. Bandstop filter
    3. Waveguide
    4. Faraday cage

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

  29. A common location for RF-leakage into the scanner room is
    1. Around the door
    2. Along seals of the scanner window
    3. At the penetration panel
    4. Along the junction of copper plates in the scanner room’s walls

    Because of repetitive opening and closing, RF-seals around the door are frequently damaged and a common source of RF-leakage into the room. Link to Q&A discussion

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