Free ARRT MRI Practice Test

Answer: C. MR Conditional means the item has demonstrated safety only under the defined conditions in its labeling. Those conditions can include static field strength, spatial field gradient, gradient-field limits, SAR or B1+rms limits, coil restrictions, positioning, and device-programming requirements. “MR Safe” means no known hazards in any MR environment; “MR Unsafe” means unacceptable risk. Identify the exact device and follow its current labeling before scanning.

Review next: MR Safe, MR Conditional, and MR Unsafe labeling, and how to read device conditions.

Sources: 17; 1

Answer: C. Slew rate = peak amplitude ÷ rise time. Convert first: 40 mT/m = 0.040 T/m and 0.2 ms = 0.0002 s, so 0.040 ÷ 0.0002 = 200 T/m/s. The other choices come from unit slips. Higher slew rates allow shorter TR, TE, and echo spacing, but faster gradient switching also raises the likelihood of peripheral nerve stimulation.

Review next: Gradient specifications: amplitude, rise time, slew rate, and duty cycle.

Sources: 20; 12; 1

Answer: D. A 1 mm (or finer) isotropic 3D T1 can be reformatted in any plane without losing resolution, which supports assessment of anatomy, volume, cortical thickness, gray–white contrast, heterotopia, and sulcation, all key for subtle malformations of cortical development. CSF suppression is FLAIR's job, flow measurement is phase contrast's, and 3D T1 supplements rather than replaces T2-weighted and FLAIR imaging.

Review next: Seizure protocol: 3D isotropic T1 and reformatting.

Sources: 55; 1

Answer: C. Larmor equation: f = γ × B0 = 42.58 MHz/T × 3.0 T = 127.74 MHz. 63.87 MHz is the frequency at 1.5 T, 42.58 MHz corresponds to 1.0 T, and 255.48 MHz would be 6.0 T. Frequency scales linearly with field strength: double the field, double the frequency.

Review next: The Larmor equation and resonant frequencies at 1.5 T and 3.0 T.

Sources: 18; 1

Answer: D. Longer trains acquire more k-space lines per TR, so the scan gets shorter, but lines acquired late in the train have decayed more. When those late, weaker echoes fill high-spatial-frequency (edge) data, sharpness suffers; this is T2 blurring. Contrast stays about the same if effective TE is unchanged, and ETL doesn't by itself change chemical shift.

Review next: Echo train length, T2 blurring, and scan time.

Sources: 30; 1

Answer: B. MRCP uses bile and pancreatic fluid as natural contrast. Heavily T2-weighted sequences, such as HASTE or a respiratory-triggered 3D fast spin echo, make long-T2 fluid bright while surrounding tissue with shorter T2 is dark. Patients typically fast about 4 hours to reduce gastroduodenal secretions and bowel motion and to distend the gallbladder. The technique doesn't depend on gadolinium, inflow, or diffusion weighting.

Review next: MRCP: heavily T2-weighted technique and patient prep.

Sources: 48; 1

Answer: C. The sampling frequency must be at least twice the highest frequency present: 2 × 16 kHz = 32 kHz. Sampling more slowly causes high frequencies to be misrepresented as lower ones, which is aliasing. Sampling at 64 kHz also works, but it isn't the minimum.

Review next: The Nyquist theorem and sampling rate.

Sources: 25; 1

Answer: D. In spoiled GRE, T1 weighting is favored by a short TR, a relatively large flip angle, and a short TE. Small flip angles favor proton density weighting, and lengthening TE adds T2* weighting. Gradient echo has no 180° refocusing pulse, so it reflects T2* rather than true T2.

Review next: Spoiled GRE contrast: flip angle, TR, and TE.

Sources: 35; 21; 1

Answer: A. Central k-space holds the low spatial frequencies that set overall signal, contrast, and the coarse shape of anatomy. The periphery holds high spatial frequencies that encode edges and fine detail, which is spatial resolution. That's why fast spin echo contrast follows the echo that fills the center (effective TE), and why contrast-enhanced MRA times the center of k-space to peak arterial enhancement.

Review next: What the center vs. the periphery of k-space contributes.

Sources: 23; 1

Answer: C. Respondeat superior makes an employer liable for an employee's wrongful conduct committed while carrying out job duties, which is exactly this situation. Res ipsa loquitur (“the thing speaks for itself”) lets negligence be inferred from the nature of an injury; it concerns proving negligence, not who answers for it. Implied consent is consent inferred from conduct or an emergency. Beneficence is the ethical duty to act for the patient's good, not a liability rule.

Review next: Legal doctrines in the Patient Care outline: respondeat superior, res ipsa loquitur, negligence, battery.

Sources: 1; 47

Answer: B. A zipper along the phase-encode direction usually means outside RF energy is reaching the receiver: an open or poorly sealed door, damaged RF shielding, or RF-emitting equipment in the room. Close the door, check the shielding, and remove the source; call service if it persists. Gibbs ringing appears as parallel lines at sharp edges, motion ghosts are repeated copies of moving anatomy, and partial volume averaging blurs thin structures within a thick slice.

Review next: RF (zipper) artifacts and RF shielding.

Sources: 27; 1

Answer: A. SNR is proportional to the square root of NEX, so doubling NEX raises SNR by √2, about 1.41, while imaging time is directly proportional to NEX and doubles. To double SNR by averaging alone you'd need four times the NEX, and four times the time.

Review next: NEX: its effect on SNR (square root) and scan time (linear).

Sources: 29; 1

Answer: D. Shimming corrects B0 inhomogeneity from the magnet itself and from nearby steel, either passively with ferromagnetic shim pieces or actively with current-carrying shim coils. Gradient coils deliberately create linear field variations for spatial encoding; the RF coil transmits the B1 field and/or receives signal; the quench vent carries helium gas out of the building during a quench.

Review next: Magnet hardware: shim, gradient, and RF coils and what each does.

Sources: 19; 1

Answer: B. For a cardiac or respiratory arrest in Zone IV, the priority is rapid evacuation to a predetermined magnetically safe location and immediate basic life support. If removal is delayed by more than a few seconds, trained MR personnel should begin needed resuscitation while evacuation continues. MR Unsafe equipment such as a conventional AED or crash cart must not be brought into Zone IV, and quenching is not routinely recommended for a medical code. Follow the facility's MR emergency procedure.

Review next: MR emergency procedures: medical emergencies in Zone IV and quench hazards.

Sources: 14; 1

Answer: C. STIR suppresses any tissue whose T1 is close to fat's at the chosen TI. Gadolinium shortens T1, so enhancing tissue can be nulled and the enhancement you wanted to show disappears. Post-contrast fat suppression therefore usually uses a fat-selective method, such as spectral fat saturation or a Dixon technique. STIR's strength is the opposite situation: it is relatively insensitive to B0 inhomogeneity, so it works near metal and away from isocenter.

Review next: Fat suppression choices: STIR vs. spectral fat saturation vs. Dixon.

Sources: 34; 22; 1

Answer: A. Frequency-selective fat saturation needs a homogeneous B0 and can fail far from isocenter, near metal, or where susceptibility varies, because the local fat frequency shifts away from the saturation pulse. STIR suppresses fat by T1 rather than by frequency, so it is relatively insensitive to B0 inhomogeneity. Since STIR isn't fat-specific, keep it to non-contrast imaging. More NEX raises SNR but doesn't fix uneven suppression, and bandwidth doesn't correct field inhomogeneity.

Review next: Fat suppression off isocenter and near metal.

Sources: 34; 1

Answer: A. When fat and water protons share a voxel, their signals partly cancel on opposed-phase images. Visible signal loss compared with in-phase images therefore supports the presence of microscopic intracellular lipid, a characteristic finding of a lipid-rich adrenal adenoma. Hemorrhage, calcification, and simple fluid do not create the same fat-water cancellation pattern. Quantitative thresholds depend on the measurement method and should not be treated as a universal cutoff in this practice item.

Review next: In-phase and opposed-phase imaging in the abdomen.

Sources: 49; 1

Answer: B. ACR MRI accreditation requires an ongoing technologist QC program at least at the minimum frequencies in the ACR MRI Quality Control Manual. Center frequency and transmitter gain or attenuation are among the technologist QC measurements; annual system performance evaluation is the medical physicist/MR scientist's responsibility. A planned quench and gradient-coil replacement are not routine QC tests.

Review next: Quality control: center frequency, transmit gain, and the other weekly tests.

Sources: 53; 1

Answer: B. Digital Imaging and Communications in Medicine (DICOM), recognized as ISO 12052, defines how medical images and their associated information are structured and shared, which lets scanners, PACS, and workstations from different vendors work together. It isn't MRI-only or vendor-specific. The federal privacy rule for health information is HIPAA, which the content outline lists under confidentiality.

Review next: Informatics: DICOM, PACS, and confidentiality.

Sources: 44; 1

Answer: C. Scan time = TR × phase-encoding steps × NEX = 0.5 s × 256 × 2 = 256 s = 4 min 16 s. The frequency matrix doesn't appear in the formula; only phase-encoding steps add time. Halving NEX or the phase steps would give 2 min 8 s, and doubling either would give 8 min 32 s.

Review next: The scan-time formula: TR × phase-encoding steps × NEX.

Sources: 43; 29; 1

Answer: D. VENC is the velocity that produces a 180° phase shift. Faster flow wraps past ±180° and is displayed as flow in the opposite direction, called velocity aliasing: 90 cm/s at a VENC of 60 gives a 270° shift, read as −90°, or about 30 cm/s backward. Raise VENC to just above the expected maximum (a common starting point is 20–25% above). Setting VENC far too high causes the opposite problem: small phase shifts, noisy measurements, and poor depiction of slow flow.

Review next: Velocity encoding (VENC) and velocity aliasing.

Sources: 37; 1

Answer: B. Bandwidth per pixel = 32,000 Hz ÷ 256 = 125 Hz per pixel. Shift = 220 Hz ÷ 125 Hz per pixel ≈ 1.8 pixels, along the frequency-encoding direction. Narrowing the bandwidth per pixel enlarges the shift; widening it shrinks it. At 3.0 T the fat–water difference doubles to about 440 Hz, so the same settings would give about 3.5 pixels.

Review next: Chemical shift artifact: the fat–water frequency difference and bandwidth per pixel.

Sources: 26; 1

Answer: C. VENC should sit just above the fastest velocity expected. CSF moves far more slowly than arterial blood, and a VENC sized for arteries would use only a small part of the available phase range, producing small phase shifts, poor velocity-to-noise, and weak depiction of slow flow. Lowering VENC raises sensitivity, but setting it below the true peak causes aliasing, so it doesn't prevent aliasing. VENC doesn't set scan time.

Review next: CSF flow studies and choosing a VENC.

Sources: 37; 1

Answer: B. Saturation bands act on blood before it flows into the slice, and venous blood enters from the side opposite the arterial inflow. In the neck, carotid blood flows upward from below while jugular blood flows downward from above, so the venous band goes superior to the slab; in multislice 2D TOF it “walks” with each slice at a fixed offset. A band below the slab would saturate the arteries you're trying to show. TOF depicts any unsaturated inflowing blood, so veins appear unless suppressed.

Review next: TOF MRA and where to place saturation bands.

Sources: 38; 1

Answer: A. Short-TE images are the most sensitive for meniscal tears. ACR teaching materials list non-fat-suppressed proton density FSE with a short effective TE (under about 20 ms), T1-weighted, and gradient echo sequences as having high sensitivity and specificity for the menisci. Long-TE sequences are less sensitive for meniscal tears, and phase contrast measures flow.

Review next: Knee MRI: sequences for the menisci.

Sources: 54; 1

Answer: D. On rapid dynamic imaging, a microadenoma typically shows up as an area of lesser enhancement than the surrounding gland. Some microadenomas are clearest on the dynamic series and others on the routine post-contrast images, which is why pituitary protocols acquire both. A flow void is a vascular finding, not an adenoma feature.

Review next: Pituitary protocol: dynamic contrast imaging.

Sources: 56; 1

Answer: A. Direct MR arthrography distends the joint with an intra-articular dilute gadolinium-containing solution placed under image guidance. T1-weighted fat-suppressed imaging makes the contrast-filled joint bright while suppressing fat, helping outline labral and chondrolabral abnormalities. The exact mixture and injection technique are protocol-dependent, so this item does not assume one universal dilution. Intravenous gadolinium is the indirect technique, and STIR is generally avoided after gadolinium because it can suppress enhancing short-T1 tissue.

Review next: Direct MR arthrography: contrast and sequences.

Sources: 59; 34; 1

Answer: C. The ADC map displays diffusivity directly. Restricted diffusion means a low ADC, so the area is dark, the reverse of its bright appearance on trace DWI. Checking the ADC map is how you separate true restriction from T2 shine-through, which is bright on DWI but not dark on ADC.

Review next: DWI and ADC maps: how restricted diffusion looks on each.

Sources: 40; 1

Answer: D. Wrap-around (aliasing) occurs when anatomy outside the phase FOV is mapped back into the image. Phase oversampling acquires extra phase-encoding steps beyond the displayed FOV and discards them during reconstruction, which largely eliminates the wrap without changing displayed FOV or resolution, usually at some cost in scan time. Shrinking the FOV makes wrap worse, and NEX and bandwidth don't change the phase FOV. Other remedies: enlarge the phase FOV, swap phase and frequency directions, saturate tissue outside the FOV, or use a surface coil that sees less distant tissue.

Review next: Aliasing (wrap-around): causes and every remedy.

Sources: 24; 1

Answer: C. Parallel imaging skips phase-encoding lines and uses coil sensitivity information to reconstruct the image, cutting time by roughly R. SNR falls by √R (about 0.71 for R = 2) because fewer samples are taken, and further by the geometry factor (g-factor), which depends on coil arrangement and can make noise uneven across the image. Higher R and poorly placed coils increase the penalty.

Review next: Parallel imaging: acceleration factor, SNR loss, and g-factor.

Sources: 36; 1

Answer: C. Gadoxetate is taken up by functioning hepatocytes and excreted into bile, and most published protocols acquire the hepatobiliary phase about 20 minutes after injection. One study found adequate hepatocyte-phase enhancement in 80% of patients by 15 minutes and 93% by 20 minutes. Uptake depends on liver function, so cirrhosis can delay or weaken it. The earlier timings belong to the dynamic vascular phases.

Review next: Liver MRI with hepatobiliary agents: phase timing.

Sources: 51; 1

Answer: B. CDC recommends Airborne Precautions for known or suspected infectious pulmonary tuberculosis. Healthcare personnel entering the patient's room use a fit-tested NIOSH-approved N95 or higher-level respirator; the patient should wear a mask during medically necessary transport. Standard Precautions still apply, but they are not sufficient by themselves for suspected airborne TB. The MRI department must coordinate transport and room handling with the facility's infection-control policy.

Review next: CDC transmission-based precautions: contact, droplet, and airborne, and the PPE for each.

Sources: 45; 1

Answer: A. Meniscal signal that reaches the articular surface on at least two images indicates a definite tear; surface contact on only one image is treated as a possible tear. Internal signal that doesn't reach the surface doesn't meet this rule, and the other choices aren't tear criteria. Knowing the rule helps you prescribe thin, contiguous slices that cover the whole meniscus.

Review next: Meniscal tear criteria and slice coverage.

Sources: 54; 1

Answer: A. Trace DWI images are both diffusion-weighted and T2-weighted, so a lesion with a very long T2 can look bright even when diffusion isn't restricted. The ADC map settles it: true restriction is dark on ADC, but this lesion is bright on ADC, pointing to increased diffusivity and T2 shine-through. Susceptibility artifact causes signal loss and distortion, and chemical shift causes fat–water misregistration; neither fits.

Review next: T2 shine-through vs. true restricted diffusion.

Sources: 40; 1

Answer: D. Gradient echo sequences have no 180° refocusing pulse, so dephasing from local susceptibility differences, such as iron in blood products, isn't reversed. Those areas lose signal and “bloom,” which makes T2*-weighted GRE and SWI the most sensitive choices. Spin echo and fast spin echo refocus static susceptibility effects, so small deposits are easy to miss. STIR is a fat-suppression technique, not a susceptibility-sensitive one.

Review next: Magnetic susceptibility and why GRE and SWI show blood products.

Sources: 21; 1

Answer: B. Clasped hands, crossed legs, or touching thighs can form a conductive loop that concentrates RF-induced current at a small contact point and causes a burn, with no metal involved. Use MR-specific foam padding to separate body parts and to keep skin off the bore and coil cables. Hospital bedding shouldn't go on the MR table; use MR-provided linens. Slice count doesn't affect the loop, and acoustic noise is a separate gradient issue.

Review next: RF heating: conductive loops, proximity burns, and padding.

Sources: 16; 12; 1

Answer: D. A saturation band suppresses signal from moving tissue before readout, so it can't propagate as artifact across the canal. Placing it over the anterior neck is the standard way to reduce swallowing artifact over the cervical spine; coaching the patient not to swallow during each acquisition helps too. Thicker slices, a shorter TR, or a larger FOV don't remove the moving signal source.

Review next: Cervical spine motion control: saturation bands.

Sources: 38; 1

Answer: A. Consensus MS brain protocols include sagittal T2-FLAIR (often 3D, with reformats), axial T2, and post-contrast T1. FLAIR is more sensitive than T2 for periventricular and juxtacortical plaques, and lesions radiating perpendicular to the ventricles (Dawson fingers) are best seen on parasagittal images. Non-contrast T1 and T2* GRE aren't core lesion-detection sequences, and cervical spine STIR belongs to a separate spine exam.

Review next: Brain MRI for MS: core sequences and imaging planes.

Sources: 57; 58; 1

Answer: B. FLAIR (fluid-attenuated inversion recovery) uses a long TI, on the order of 2,500 ms in typical examples, to null free water such as CSF, so periventricular and cortical lesions stand out on T2-weighted images. A TI near 180 ms is STIR, which nulls fat, and about 650 ms would null gray matter at 1.5 T. Exact TIs vary with TR and field strength.

Review next: Inversion recovery sequences: STIR and FLAIR.

Sources: 33; 32; 1

Answer: C. Epilepsy protocols use a thin, high in-plane-resolution coronal T2 angled perpendicular to the long axis of the hippocampus, so each slice cuts across the hippocampus and its internal structure can be compared side to side, as in suspected mesial temporal sclerosis. AC–PC alignment is used for the axial plane. Slices parallel to the hippocampal axis would run along it instead of across it.

Review next: Brain MRI for seizure: hippocampal angulation.

Sources: 55; 1

Answer: C. Gadolinium is paramagnetic and shortens both T1 and T2, but at clinical doses the dominant visible effect is T1 shortening: tissue recovers more longitudinal magnetization between excitations and appears brighter on T1-weighted images. It doesn't add protons or lengthen T2, and the gadolinium ion isn't imaged directly; we see its effect on nearby water protons. At high concentrations, T2 and T2* shortening can cause signal loss instead.

Review next: How gadolinium changes T1 and T2.

Sources: 22; 1

Answer: D. A superior saturation pulse saturates blood before it flows down the aorta into the imaged slices, which reduces aortic signal and removes the flow artifact it causes. A slice gap, longer TE, or smaller FOV doesn't remove the moving signal source, and a smaller FOV can add wrap-around.

Review next: Flow artifact control in the abdomen: superior saturation pulses.

Sources: 38; 24; 1

Answer: A. Short TR emphasizes differences in T1 recovery, and short TE minimizes T2 effects, giving T1 weighting. Long TR with short TE minimizes both effects and gives proton density weighting; long TR with long TE gives T2 weighting. Short TR with long TE isn't a combination used in practice.

Review next: TR and TE choices for T1, T2, and PD weighting.

Sources: 31; 1

Answer: B. STIR nulls fat by reading out when fat's recovering longitudinal magnetization crosses zero, about 0.69 × the T1 of fat when TR is long, which is roughly 180 ms at 1.5 T. About 650 ms would null gray matter at 1.5 T, and about 2,500 ms is in the range used for FLAIR to null CSF. Null times move upward at 3.0 T.

Review next: Inversion times that null fat, gray matter, and CSF.

Sources: 32; 33; 1

Answer: A. Translational force depends on both the static magnetic field and its spatial field gradient, so it is greatest where their relevant product is greatest. For many cylindrical systems this occurs near a bore opening, where the field changes rapidly, but the exact location is magnet-specific and must be taken from the manufacturer's spatial-gradient information. Torque is a different effect and tends to track field strength rather than the spatial gradient alone.

Review next: Translational force vs. torque, and the spatial gradient of the static field.

Sources: 14; 1

Answer: D. A fomite is an inanimate object, such as a coil, positioning sponge, or bedding, that carries an infectious agent from one host to another. CDC classifies this as indirect, vehicleborne transmission. Direct contact requires person-to-person contact; vectorborne transmission uses a living carrier such as a mosquito or tick; airborne transmission uses droplet nuclei or dust suspended in air. The fix is disinfecting equipment between patients.

Review next: The chain of infection and direct vs. indirect (vehicleborne, vectorborne, airborne) transmission.

Sources: 46; 1

Answer: B. The 180° pulse reverses phase spread caused by static, time-independent frequency differences (magnet inhomogeneity, static susceptibility gradients, chemical shift), so those spins rephase at TE. It can't undo true T2 decay, which comes from random, time-varying field fluctuations between spins; the spin–spin and molecular-motion options both describe that. T1 recovery is longitudinal and isn't what the refocusing pulse addresses. This is why spin echo images reflect T2 while gradient echo images reflect T2*.

Review next: T2 vs. T2* decay and what the 180° refocusing pulse does.

Sources: 21; 1

Answer: D. FSE contrast is set mainly by the echo that fills central k-space, the effective TE. Changing ETL alone doesn't change contrast if effective TE stays the same, although longer trains shorten scan time and increase blurring. Slice number affects coverage and timing, and receiver bandwidth changes chemical shift displacement, not T2 weighting.

Review next: Effective TE and how FSE contrast is set.

Sources: 30; 23; 26; 1

Answer: D. Tightly ordered collagen fibers, such as tendon, can show artificially increased signal on short-TE sequences when they lie at about 55° (54.7°) to B0. In tendons the effect usually fades once TE exceeds about 40 ms, so signal that disappears on long-TE images is consistent with magic angle rather than pathology; a true tear would stay abnormal on T2-weighted images. Chemical shift and partial volume don't depend on fiber orientation.

Review next: The magic angle effect and TE.

Sources: 42; 1

Answer: B. Central k-space largely determines image contrast. Acquiring it first, at the arterial peak, maximizes arterial signal, while venous enhancement arriving later lands mostly in peripheral k-space, which affects edge detail more than overall signal, so venous contamination drops. Mistiming lowers arterial contrast and can raise venous signal. The view ordering doesn't change total scan time or the dose given.

Review next: Contrast-enhanced MRA timing and centric k-space ordering.

Sources: 39; 23; 1

Answer: A. Fast spin echo acquires several phase-encoding lines per TR, so imaging time is roughly the conventional time divided by ETL: 256 s ÷ 4 = 64 s, about 1 min 4 s. The 17 min 4 s choice multiplies instead of divides. In practice, long echo trains can limit how many slices fit in each TR, which can eat into the savings.

Review next: How echo train length changes FSE scan time.

Sources: 30; 43; 1

Answer: B. In the ACR four-zone model, Zone II is the supervised interface between the freely accessible public area (Zone I) and the more tightly controlled Zones III and IV. Patient preparation and MR screening commonly occur there before a patient enters Zone III. Zone IV is the magnet room itself.

Review next: ACR Zones I–IV and who may enter each.

Sources: 14; 1

Answer: D. Modern receivers sample the readout more finely than the displayed resolution requires (frequency oversampling) and filter out signal beyond the receiver bandwidth before digitizing it. Together these keep frequency-direction wrap uncommon, though it can still occur if those safeguards fail, so it isn't impossible. Phase-direction wrap is the one that needs active remedies such as phase oversampling.

Review next: Frequency oversampling and anti-alias filtering.

Sources: 25; 24; 1

Answer: C. ACR requires a multiphase T1 series (pre-contrast, early post-contrast, and delayed post-contrast), with the early post-contrast series completed within 4 minutes of the end of the injection; the saline flush isn't counted. A T2-weighted or bright-fluid series is also required. Subtraction images are needed when chemical-shift fat suppression isn't used, but they don't replace correct timing.

Review next: Breast MRI: required series and post-contrast timing.

Sources: 52; 1

Answer: C. eGFR is the standard laboratory estimate used to describe kidney function and is calculated from serum creatinine together with patient variables used by the equation. Current ACR contrast guidance strongly prefers Group II gadolinium-based contrast agents for patients at risk for NSF and emphasizes that acute kidney injury cannot be ruled out by eGFR alone. Hemoglobin, INR, and potassium do not estimate renal filtration. The actual contrast decision follows current facility policy and physician/radiologist judgment.

Review next: Lab values before contrast: BUN, creatinine, eGFR, and what each tells you.

Sources: 41; 1

Answer: B. ACR Group I agents are the agents associated with the greatest number of nephrogenic systemic fibrosis (NSF) cases. Current ACR guidance lists gadodiamide, gadopentetate dimeglumine, and gadoversetamide in Group I. Group II agents are associated with few, if any, unconfounded NSF cases and now include gadobenate dimeglumine, gadobutrol, gadoteric acid, gadoteridol, gadopiclenol, and gadoxetate disodium. “Macrocyclic” describes molecular structure; it is not itself an ACR NSF risk group.

Review next: ACR gadolinium agent groups and NSF risk.

Sources: 41; 1

Answer: A. Phase-contrast imaging encodes velocity as a phase shift scaled to the VENC you choose, so it can quantify flow speed and show direction (and aliases if velocity exceeds VENC). Time-of-flight relies on inflow of unsaturated spins to make vessels bright; it shows where blood flows but doesn't measure velocity. Phase contrast depends on choosing an appropriate VENC, and it needs flow to generate the velocity signal.

Review next: MRA methods: time-of-flight vs. phase contrast.

Sources: 37; 38; 1

Answer: A. SNR is proportional to voxel volume, and halving slice thickness halves the voxel volume, so SNR drops by about half. The square-root relationship (about a 29% loss) applies to NEX, not to voxel size. Thinner slices improve through-plane resolution and reduce partial volume averaging, so you often buy back SNR with more NEX or a better coil.

Review next: Voxel volume and SNR: slice thickness, FOV, and matrix.

Sources: 29; 1

Answer: D. RF power deposition tends to rise substantially at higher field strength because the Larmor frequency is higher; under otherwise comparable pulse conditions, SAR is commonly approximated as increasing with the square of field strength. Moving from 1.5 T to 3.0 T can therefore raise SAR by about fourfold, which is why 3 T protocols may need changes such as lower flip/refocusing angles, longer TR, fewer slices per TR, or other low-SAR strategies. Actual scanner-reported SAR depends on the full pulse sequence, patient model, coil, and system implementation, so the fourfold figure is an approximation for the stated comparison.

Review next: SAR, what raises it, and how 3 T protocols reduce it.

Sources: 12; 1

Answer: A. This is Gibbs (truncation) ringing. Only a finite portion of k-space is sampled, so sharp, high-contrast edges ring, usually most in the phase direction, where fewer samples are taken. Sampling more of k-space (more phase-encoding steps, or a smaller FOV with the same matrix) reduces it; filtering also helps at some cost to sharpness. Slice thickness, NEX, and fat suppression don't address truncation.

Review next: Gibbs (truncation) artifact: cause and compensation.

Sources: 28; 1