MRI Question Bank — Free Sampler
30 exam-style single-best-answer questions across MRI physics, safety, anatomy, artifacts, and contrast. FRCR / ABR / ARRT / MRSO style.
The gyromagnetic ratio of the hydrogen proton (~42.58 MHz/T) means the Larmor frequency at 1.5 T is closest to:
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Larmor = 42.58 MHz/T × 1.5 T ≈ 63.9 MHz. At 3 T it is ~127.7 MHz.
Which tissue property predominantly determines contrast on a T1-weighted image?
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T1 weighting uses short TR and short TE, so contrast reflects differing longitudinal recovery. Fat (short T1) is bright; fluid (long T1) is dark.
On a standard spin-echo T2-weighted image, cerebrospinal fluid appears:
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CSF has a long T2, so with a long TE it retains high transverse signal and appears bright on T2-weighted spin echo.
The 180° refocusing pulse in a spin-echo sequence exists to:
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The 180° pulse reverses phase so time-invariant field inhomogeneities cancel at the echo, giving true T2 decay rather than the faster T2* of gradient echo.
Which region of k-space contributes most to overall image contrast?
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The centre of k-space holds low spatial frequencies — bulk signal and contrast; the periphery holds edges/detail. This underlies centric ordering for contrast timing.
Doubling the number of signal averages (NEX) changes SNR by approximately:
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SNR ∝ √NEX. Doubling averages raises SNR only ~41% while doubling scan time — a poor trade compared with other levers.
Compared with 1.5 T, imaging at 3 T generally provides:
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SNR scales ~linearly with B0 (so 3 T roughly doubles it), but SAR rises with B0² and chemical-shift (Hz) and susceptibility effects both increase.
A STIR sequence suppresses fat by:
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STIR uses an inversion pulse with TI ≈ 0.69 × T1_fat (~150–170 ms at 1.5 T) so fat is nulled at readout. Being non-spectral, it tolerates B0 inhomogeneity well.
An acute infarct with restricted diffusion appears:
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Restricted diffusion is bright on high-b DWI and dark on ADC. Lesions bright on DWI but also bright on ADC are “T2 shine-through” — always check the map.
Fat and water are in “opposed phase” at 1.5 T at a TE of approximately:
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The ~220 Hz fat–water difference at 1.5 T gives opposed phase at ~2.2 ms and in-phase at ~4.4 ms. Signal drop on opposed phase indicates intravoxel fat (e.g. adrenal adenoma).
FLAIR imaging is valued because it:
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FLAIR is inversion recovery with a long TI chosen to null CSF, making juxtaventricular and sulcal lesions (MS plaques, subarachnoid blood, gliosis) conspicuous.
Time-of-flight MR angiography generates vessel contrast by:
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TOF uses flow-related enhancement: fresh unsaturated blood entering the slab is bright against RF-suppressed stationary tissue — no contrast agent needed.
In the ACR zoning scheme, the room housing the magnet itself is:
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Zone IV is the scanner room. Zone III is the restricted access-controlled region around it, Zone II the transition/interview area, Zone I freely accessible public space.
The 5-gauss (0.5 mT) line marks the boundary beyond which:
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The 5 G (0.5 mT) line is the conventional static-fringe-field threshold; it must lie within a controlled area because pacemakers and sensitive devices can malfunction beyond it.
Specific absorption rate (SAR) quantifies:
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SAR (W/kg) measures RF energy deposition/heating. It rises with B0², flip angle and RF duty cycle; normal-mode whole-body SAR is limited to 2 W/kg.
Peripheral nerve stimulation during MRI is caused by:
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Fast gradient switching induces electric fields (dB/dt); above threshold this causes a twitching/tingling peripheral nerve stimulation, limiting how fast gradients can be driven.
A magnet “quench” refers to:
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In a quench the superconducting coil warms above its critical temperature and dumps helium as gas. The chief danger is oxygen displacement/asphyxiation — hence the quench pipe and room O₂ monitor.
An implant labelled “MR Conditional” means it is:
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MR Conditional devices are safe only when the labelled conditions are met (e.g. max static field, max spatial field gradient, SAR limits, specified region/time). Deviating voids the safety claim.
A patient reports possible metal in the eye from grinding without goggles. You should:
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An intraocular ferromagnetic fragment can move in the field and injure the retina. Orbital plain films (or documented prior CT) exclude one before scanning.
Thermal burns during MRI most commonly result from:
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RF-induced currents concentrate in conductive loops and points of high resistance. Prevent with cable insulation, no loops, padding skin-to-skin contact, and keeping the patient off the bore wall.
On a T1-weighted brain image, normal white matter appears ____ relative to grey matter:
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Myelin lipid shortens T1, so white matter is brighter than grey on T1 (and darker on T2) — the reverse of CT grey-white contrast.
The interventricular foramen (of Monro) connects:
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Each foramen of Monro links a lateral ventricle to the third ventricle; the third connects to the fourth via the cerebral aqueduct.
The adult conus medullaris typically terminates at about:
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The conus usually ends around L1 (T12–L2 range). Below it the cauda equina runs in the thecal sac — relevant to safe lumbar puncture levels.
The middle hepatic vein lies in the plane separating:
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The middle hepatic vein runs in the principal plane (Cantlie’s line) dividing right and left hemilivers in Couinaud segmentation.
Motion ghosting (repeated smeared copies of anatomy) propagates along the:
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Motion changes signal between phase-encode steps, so ghosts propagate along the phase axis regardless of true motion direction. Swapping phase/frequency moves ghosts off the ROI.
Aliasing (wrap-around/fold-over) occurs when:
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When anatomy extends beyond the FOV in the phase direction, undersampled signal folds to the opposite side. Fixes: enlarge FOV, phase oversampling (“no phase wrap”), saturation bands.
A signal void with a bright rim and geometric distortion around a metal hip prosthesis is due to:
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Differing susceptibilities distort local B0 and dephase spins. Mitigate with SE/FSE over GRE, short TE, high bandwidth, thin slices, STIR over spectral fat-sat, and SEMAC/MAVRIC metal sequences.
Artificially increased tendon signal at ~55° to B0 on short-TE sequences describes:
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At ~55° (the magic angle) dipolar interactions are minimised, lengthening T2 so ordered collagen looks bright on short-TE sequences. It disappears on long-TE T2 — a clue it is not real pathology.
Which gadolinium chelate class has the highest stability and lowest Gd release (ACR Group II)?
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Macrocyclic chelates cage the Gd ion in a rigid ring, giving the greatest stability and lowest NSF risk (ACR Group II). Linear agents (especially non-ionic) are less stable.
The standard weight-based dose for most extracellular gadolinium agents is approximately:
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Most extracellular Gd chelates are dosed at ~0.1 mmol/kg (0.2 mL/kg of a 0.5 M solution). Higher-relaxivity and hepatobiliary agents use different doses.