1.
A basic MR phantom can be used to test all of the following EXCEPT?
A) Contrast resolution
B) Location of the five gauss line
C) RF uniformity
D) Slice thickness
E) Spatial resolution
Answer:
B) Location of the five gauss line
2.
Which is the most prevalent bioeffect observed with 1.5T MR systems?
A) Acoustic noise level
B) Enzyme kinetic changes
C) Gradient field tissue heating
D) RF energy deposition
E) Visual phosphenes
Answer:
A) Acoustic noise level
3.
Why does the voxel signal decrease with super-paramagnetic iron oxide concentration?
A) Decreased effective T1
B) Decreased effective T2
C) Increased effective T1
D) Increased effective T2
E) Increased T2*
Answer:
B) Decreased effective T2
2. Superparamagnetic Iron Particles
The iron (Fe) oxide particles used in MR imaging are coated with a carbohydrate for stability. These particles demonstrate a stronger paramagnetic character than Gd. Thus, they are labeled ‘super-paramagnetic’ and known as Super-Paramagnetic Iron Oxide (SPIO). Distributed in the circulation, the SPIO is taken up preferentially by Kupffer cells in the liver and spleen. The large magnetic field from these particles is such that the proton-dephasing rate is markedly enhanced, shortening T2 greatly, causing the measured signal of a T2-weighted spin-echo sequence to decrease almost by 100% at the optimum Fe concentration of approximately 10 μmol/kg body weight. As SPIO is taken up by normal tissues, abnormalities are relatively enhanced.
4.
Regarding eliminating projectile hazards from the MR suite , which is NOT a correct method to employ?
A) Any MR safe or tested MR conditional object is allowed in Zones III or IV.
B) Items with a green square surrounding the green letters “MR” may be safely taken into any Zone.
C) Metallic items with the triangular yellow ‘MR conditional’ label may only be safely taken into Zone IV when approved by the MRI Safety website [www.mrisafety.com]
D) Never assume device MR compatibility or safety information if not clearly documented.
E) Test all objects of unknown composition with a strong hand-held magnet.
Answer:
A) Any MR safe or tested MR conditional object is allowed in Zones III or IV. (see option C)
5.
If MR safety data are not prospectively available for a given metallic device and negligible attractive forces are observed with a handheld magnet (1,000 gauss), which label should be attached to the device?
A) Round green “MR safe” label.
B) Square green “MR conditional” label.
C) Square red “not MR safe” label.
D) Triangular yellow “MR conditional” label.
Items with no or negligible ferromagnetic forces (as demonstrated with the strong handheld magnet mentioned above) are labeled with the triangular yellow ‘MR conditional’ label until the composition of the item is known to be non-metallic.
6.
Regarding SAR, all of the following statements are true EXCEPT
A) SAR increases linearly with magnetic field strength
B) SAR increases with the square of the pulse flip angle
C) Lengthening TR reduces SAR
D) SAR measures the power deposited per kilogram tissue
E) SAR is the acronym for the specific absorption rate
Answer:
A) SAR increases linearly with magnetic field strength
Factors Affecting SAR
• As SAR increases with the square of the magnetic field strength, SAR limits can be easily surpassed with high field (≥ 3T) systems. Nothing can be done regarding lowering this except scanning with a lower field system.
• SAR increases with the square of the flip angle. This helps for fast imaging sequences where the flip angle is typically low (10-40 degrees), but usually for these sequences the repetiotion time (TR) is also low, thus the energy deposition as a function of time (power) may be still be large.
• Some systems to reduce SAR will suggest the lengthening of TR, which increases the overall time in which the energy is deposited, thus reducing deposited power.
• SAR increases with the number of RF pulses per cycle (TR), for example, high echo train length spin echo sequences.
• SAR increases with patient size, in order to deposit signal throughout a larger interrogated volume.
7.
Concerning MR of cardiac pacemakers and implantable cardioverter defibrillators (ICDs), which of the following statements is TRUE?
A) Some ICDs have been labeled by the FDA as safe for low-field MR but not for high-field MR.
B) No deaths have been reported as a result of scanning patients with ICDs, only as a result of scanning patients with pacemakers.
C) The presence of a pacemaker or an ICD is an absolute contraindication to MR.
D) Life-threatening arrhythmias and serious device malfunction may occur.
Answer:
D) Life-threatening arrhythmias and serious device malfunction may occur.
Cardiac Pacemakers or Implantable Cardioverter Defibrillators
There is only one FDA approved heart pacemaker designed to be used safely during certain MR exams, the Revo MRI SureScan Pacing System. Other than this device, it is recommended that patients with cardiac pacemakers or implantable cardioverter fibrillators (ICDs) not be imaged with MR. Although the majority of deliberate scans of device patients have proceeded without mishap, when precautions were taken, deaths have occurred under poorly and incompletely characterized circumstances when device patients underwent MR. Special precautions and advice for imaging patients with these devices is given in the ACR Guidance Document for Safe MR Practices: 2007.
8.
ACR guidelines divide an MR site into four conceptual zones with progressive restriction of access. Which is the highest zone into which ferromagnetic objects and equipment may be safely taken?
A) Zone I
B) Zone II
C) Zone III
D) Zone IV
Answer:
B) Zone II
Thus, ferromagnetic objects should be restricted from entering Zone III.
9.
Regarding RF heating, which one of the following is NOT true?
A) Burns are most likely when the conductors form loops
B) Induced currents cause heating
C) Less than 30% of the MR-related events reported to the FDA are due to burns
D) RF heating must be carefully monitored, especially for 3T systems
E) Tissue heating is the predominant effect of RF exposure
Answer:
C) Less than 30% of the MR-related events reported to the FDA are due to burns
RF Heating of Conductors and Potential Burns
Of reported MR-related events in the FDA’s Manufacturer and User Facility Device Experience Database, 70% are due to burns. The temperature of conductors on the patient’s body during RF stimulation may possibly rise to the point of discomfort and actual burns. This is most likely when the conductors form loops. Induced voltage causes current induction within the loops and with the inherent resistance of the wire, causes heating, hence the temperature rise. In addition, implanted devices (as discussed in Section 3.1.3) may also experience heating effects leading to burns.
10.
Concerning MR of patients with intracranial aneurysm clips, which of the following statements is TRUE?
A) MR is safe for these patients so long as the body part being scanned is not the head.
B) Some nonferromagnetic aneurysm clips are not detectable on routine radiographs of the skull.
C) Aneurysm clips that are composed of titanium or a titanium alloy are always safe in the MR scanner.
D) Insufficient data regarding an individual patient’s aneurysm clip is an absolute contraindication for MR.
Answer:
D) Insufficient data regarding an individual patient’s aneurysm clip is an absolute contraindication for MR.
4. Device and Object Screening
Intracranial Aneurysm Clips
When a patient has been identified as having an intracranial aneurysm clip, the MR exam should not be performed until it can be established with documentation that the clip is either ‘MR safe’ or ‘MR conditional’. Documented titanium clips can be accepted for scanning without other testing. Please see the ACR Guidance Document for Safe MR Practices: 2007 for further information.
11.
Which of the following materials is NOT ferromagnetic?
A) Aluminum
B) Cobalt
C) Iron
D) Nickel
E) Steel
Answer:
A) Aluminum
12.
Means for reducing SAR include all of the following EXCEPT
A) Reducing the echo train length
B) Reducing the flip angle
C) Reducing the number of slices scanned per TR
D) Reducing TR
E) Use of quadrature coils
Answer:
D) Reducing TR
Means of Reducing SAR
• The use of quadrature coils (circularly polarizing or CP) rather than linear coils for transmission of RF, reducing SAR by approximately half,
• Decreasing the flip angle for refocusing pulses (i.e., using 160 degree rather than 180 degree RF pulses for spin echo sequences) – especially for fast spin echo sequences,
• Lengthening TR, thereby reducing the duty cycle,
• Imaging fewer slices per TR or overall sequence,
• Reducing the echo train length (turbo factor) with fast or turbo spin echo sequences, or
• If possible, use of the body (bore) transmit coil should be avoided when other transmit/receive coils may be substituted: e.g., head and knee.
13.
In spin-echo imaging, why does the voxel signal increase with Gadolinium contrast above 0.1 mmol/kg?
A) Decreased effective T1
B) Decreased effective T2
C) Increased effective T1
D) Increased effective T2
E) Increased T2*
Answer:
A) Decreased effective T1
14.
Low contrast detectability in MR measures:
A) geometric distortion, the measured deviation of the acquired image from actual phantom dimensions.
B) how far the sampled echo is misallocated from the presumed k-space data row.
C) that the coil RF sensitivity is nearly constant over the field of view (FOV).
D) the ability of an imaging system to discriminate between small differences in the physical property the imaging system is measuring.
E) the ability of the scanner to adequately resolve minute details in an image.
Answer:
D) the ability of an imaging system to discriminate between small differences in the physical property the imaging system is measuring.
15.
Which one of the following statements regarding MR and special populations is NOT true?
A) It not necessary to screen women of reproductive age for pregnancy prior to imaging.
B) Pediatric patients may require sedation during the MR procedure and adherence to standard of care sedation guidelines are essential.
C) There are no current limits to pregnant healthcare workers working in an around the MR scanner.
D) Those accompanying and remaining with a pediatric patient should be screened to enter Zone IV and offered hearing protection.
E) To ensure that no toys or non-screened comfort items enter Zone IV, it is recommended that all children be gowned before entering Zone IV.
Answer:
C) There are no current limits to pregnant healthcare workers working in an around the MR scanner.
There are no current limits to pregnant healthcare workers working in an around the MR scanner, except they are requested not to remain within Zone IV during actual scanning. Although to date there is no conclusive data for deleterious effects of MR imaging on the fetus, it is deemed prudent to screen women of reproductive age for pregnancy prior to imaging, primarily to establish whether or not a gadolinium-based MR contrast agent (GBMCA) should be administered. GBMCAs cross the placenta into fetal circulation and end up in the amniotic fluid, where due to the duration in the amniotic fluid, the chelated gadolinium may dissociate into potentially toxic gadolinium ions. As the long-term fetal risk with the administration of GBMCAs to the pregnant patient remains unknown and may prove harmful, MR contrast agents should not be administered to pregnant patients unless a well thought out and documented risk-benefit analysis for a specific patient proves otherwise.
To ensure that no toys or non-screened comfort items enter Zone IV, it is recommended that all children be gowned before entering Zone IV. In addition, those accompanying and remaining with the patient should be screened to enter Zone IV and offered hearing protection. Pediatric patients may require sedation during the MR procedure and adherence to standard of care sedation guidelines are essential. Further information regarding sedation can be found in the ACR Guidance Document for Safe MR Practices: 2007.
16.
All of the following affect image ghosting EXCEPT
A) Caused by misalignment of the sampled echo in k-space
B) It is the predominant artifact in MR imaging
C) Quadrature phase ghosting occurs more frequently than motion ghosting
D) The ghost image appears in the phase encoding direction
E) Frequently is a result of patient motion
Answer:
C) Quadrature phase ghosting occurs more frequently than motion ghosting
17.
What produces the noise during an MRI exam?
A) shim coil
B) RF coil
C) gradient coil
D) transmit coil
E) receive coil
Answer:
C) gradient coil