Free ARRT MRI Exam Flashcards

Estimated glomerular filtration rate (eGFR). Reported NSF cases cluster in patients with eGFR below 30 mL/min/1.73 m2, on dialysis, or in acute kidney injury. The ACR Manual on Contrast Media places most agents used today in Group II, which has very few unconfounded NSF cases.

Correct patient, correct procedure, and correct site or side, verified with at least two patient identifiers checked against the order and the clinical indication. ARRT added the time-out and communication of critical findings to the MRI Patient Care category effective February 1, 2025.

A local reaction is extravasation or phlebitis at the IV site: stop the injection, elevate the limb, apply a cold pack, watch for compartment signs, and document. A systemic reaction is allergic-like, from hives to anaphylaxis: call for help, protect the airway, and expect epinephrine for a severe reaction.

Feet-first or prone entry when the anatomy allows, a mirror or prism, a blindfold, cool airflow, a support person in the room, and running the shortest sequences first. Keep continuous verbal contact and give the patient a squeeze bulb that reaches staff outside the room.

Zone I is unrestricted public space and Zone II is the supervised screening interface where patients are greeted and screened. Zone III is restricted to screened, MR-trained personnel behind a physical lock or badge control, and Zone IV is the magnet room itself, entered only through Zone III and marked with a lighted sign warning that the magnet is always on.

Translational (projectile) force peaks where the spatial gradient of the static field is steepest, typically just inside the bore opening rather than at isocenter. The 5 gauss (0.5 mT) line marks the boundary that must be kept restricted from the general public.

MR Safe (green square) poses no known hazard in any MR environment; MR Conditional (yellow triangle) is safe only within labeled limits such as field strength, spatial gradient, SAR, and scan duration; MR Unsafe (red circle with a slash) must never enter Zone IV. Verify device make, model, and labeling before scanning.

RF energy deposited as heat, measured as specific absorption rate, plus conductive loops formed by crossed limbs, skin-to-skin contact, or looped cables. Pad between skin surfaces and the bore wall, uncross arms and legs, and remove unused coils and cables. FDA treats whole-body SAR above 4 W/kg over 15 minutes as significant risk.

Acoustic noise, produced when Lorentz forces vibrate the gradient coils, and peripheral nerve stimulation driven by the rate of field change (dB/dt). Hearing protection should be used for every patient, and FDA flags A-weighted noise above 99 dBA measured with hearing protection in place as significant risk.

Precessional frequency equals the gyromagnetic ratio times the field strength. Hydrogen's gyromagnetic ratio is 42.58 MHz/T, giving about 63.87 MHz at 1.5 T and 127.74 MHz at 3 T. Only spins precessing at that frequency absorb energy from the transmitted RF pulse.

T1 is the time for longitudinal magnetization to recover 63 percent of its original value as spins release energy to the surrounding lattice. T2 is the time for transverse magnetization to fall to 37 percent of its starting value as spins exchange energy with each other and lose phase coherence.

T2* decay adds dephasing from static field inhomogeneity and local susceptibility to true spin-spin relaxation. A 180-degree refocusing pulse reverses the inhomogeneity component, so spin echo sequences show T2 contrast while gradient echo sequences, which lack that pulse, show T2*.

Ferromagnetic and paramagnetic materials warp the local field, dephasing spins and mismapping signal. Reduce it by choosing spin echo or fast spin echo over gradient echo and EPI, shortening the TE, widening the receive bandwidth, and using thinner slices and smaller voxels.

Coils sit in liquid helium near 4 K, where they conduct with no resistance. A quench boils that helium off suddenly; the gas displaces oxygen, so evacuate patient and staff immediately, do not re-enter, and wait until the vent path and oxygen monitor confirm the room is safe.

The slice-select gradient runs during the RF pulse so only one slice reaches resonance. The phase-encoding gradient is pulsed between excitation and readout to impose a phase shift along one axis. The frequency or readout gradient runs while the echo is sampled.

Central lines carry low spatial frequencies and supply overall signal and contrast. Peripheral lines carry high spatial frequencies and supply edge detail and spatial resolution. Each phase-encoding step fills a line of k-space, not a strip of the picture.

Anatomy outside the field of view along the phase-encoding axis is mismapped onto the opposite side of the image. Fix it with phase oversampling (no phase wrap), a larger field of view, saturation bands over the offending tissue, or by swapping the phase and frequency directions.

Fat and water protons resonate about 3.5 ppm apart, roughly 220 Hz at 1.5 T and 440 Hz at 3 T, so fat is mismapped along the frequency-encoding axis and dark or bright rims appear at fat-water borders. Widening the receive bandwidth shrinks the shift; fat suppression removes the fat signal entirely.

Slice thickness, spatial resolution, contrast resolution, signal-to-noise ratio, center frequency, transmit gain, and geometric accuracy, plus physical inspection of coils, cables, and RF door seals. A drifting center frequency or a failing door seal usually shows up first as new artifacts.

T1 weighting uses a short TR with a short TE. T2 weighting uses a long TR with a long TE. Proton density weighting uses a long TR with a short TE, which suppresses both T1 and T2 effects and leaves spin concentration as the main source of contrast.

Signal-to-noise ratio rises by the square root of 2, about 41 percent, while scan time doubles. Averaging also blurs random motion into the background, which is why it is sometimes chosen for a restless patient despite the time cost.

Signal-to-noise ratio tracks voxel volume, so a thicker slice, larger field of view, or coarser matrix all raise signal while lowering resolution. Halving slice thickness roughly halves the signal available from each voxel, which usually has to be bought back with averages or bandwidth.

A narrow bandwidth samples less noise and raises signal-to-noise ratio, but it lengthens the minimum TE, worsens chemical shift misregistration, and reduces how many slices fit in a given TR.

Scan time equals TR times the number of phase-encoding steps times the number of signal averages. Shorten it by cutting phase steps with a rectangular field of view or coarser phase matrix, by adding an echo train (divide by echo train length), or by parallel imaging, which undersamples phase steps at a cost in signal-to-noise ratio.

Both are inversion recovery: STIR uses a short TI of roughly 150 to 170 ms at 1.5 T to null fat, while FLAIR uses a long TI of roughly 2000 to 2500 ms to null CSF. Because STIR nulls by T1 value, it can also suppress enhancing tissue whose T1 has been shortened by gadolinium.

A low flip angle leaves most magnetization longitudinal, which reduces T1 weighting and favors proton density or T2* contrast even at a short TR. A high flip angle with a short TR produces T1 weighting. Flip angle also drives SAR, which climbs with the square of the angle.

The b-value sets diffusion sensitivity through gradient strength, duration, and spacing, so a higher b means stronger weighting and less signal. Tissue that is bright on high-b diffusion images and dark on the ADC map has truly restricted diffusion; bright on both indicates T2 shine-through.

Chemical saturation pulses at the fat resonant frequency and needs a homogeneous field. STIR nulls by T1 and stays reliable off isocenter or across a large field of view but gives lower signal-to-noise ratio. Dixon acquires in-phase and opposed-phase data and reconstructs separate water and fat images from one acquisition.

A train of 180-degree refocusing pulses fills several k-space lines per TR, cutting scan time by roughly the echo train length. The costs are higher SAR from the extra RF pulses, blurring from the spread of effective TEs, and fat that stays bright on T2-weighted images.

Spoiling destroys leftover transverse magnetization each TR, leaving T1-weighted images used for dynamic contrast work. Balanced SSFP preserves it, so contrast follows the T2/T1 ratio and fluid and vessels appear bright, at the price of dark banding wherever the field is inhomogeneous.

After one excitation, rapidly oscillating readout gradients fill many or all k-space lines in a fraction of a second, which is what makes diffusion, perfusion, and functional imaging practical. The long readout leaves it very sensitive to susceptibility, so images distort near air-bone interfaces.

Time-of-flight saturates stationary tissue with rapid RF pulses so unsaturated inflowing blood appears bright, which means slow or in-plane flow can be lost. Phase contrast encodes velocity with bipolar gradients and needs a VENC set near the expected peak velocity; too low a VENC aliases the flow.

The transform converts sampled frequency and phase data held in k-space into the displayed image. Centric ordering acquires the central contrast-determining lines first, which is why it pairs with contrast-enhanced angiography timing and breath-holds; keyhole techniques refresh only that center on later frames.

A signal must be sampled at least twice per cycle of its highest frequency to be represented correctly. Sampling below that rate mismaps high frequencies as low ones, which is the mathematical basis of aliasing. Nyquist theorem entered the ARRT MRI blueprint with the February 2025 update.

A maximum intensity projection keeps the brightest voxel along each ray through a 3D data set and is the standard angiographic display, while multiplanar reformation re-slices the same data in another plane. Subtraction removes the precontrast series from the postcontrast one, and ADC mapping calculates diffusion coefficients from two or more b-values.

DICOM is the file and network standard that carries the images together with patient and acquisition data. PACS stores, retrieves, and distributes those studies and links them to the electronic medical record. Access must be role-based and logged to meet HIPAA confidentiality requirements.

Supine and head first in a dedicated head or head-neck coil, with the head immobilized and the landmark at the glabella or nasion. Axial slices are angled along a reproducible line such as the anterior-posterior commissure line so that follow-up studies can be compared directly.

Sagittal and axial FLAIR with slices of about 3 mm. Periventricular plaques radiate perpendicular to the lateral ventricles and corpus callosum, the appearance called Dawson's fingers. Gadolinium is added because enhancing lesions indicate active disease.

A thin-section, high-resolution 3D heavily T2-weighted acquisition through the temporal bones, which silhouettes cranial nerves VII and VIII against bright CSF. Post-contrast T1 imaging is added when a vestibular schwannoma is suspected.

It uses a small field of view with thin coronal and sagittal T1 slices, about 2 to 3 mm, targeted on the sella, plus a dynamic post-contrast series. A microadenoma usually enhances more slowly than the normal gland, so it looks relatively dark on the early dynamic frames.

N-acetylaspartate at 2.0 ppm marks viable neurons, creatine at 3.0 ppm serves as the internal reference, and choline at 3.2 ppm reflects cell membrane turnover. Tumors raise choline and lower NAA. A lactate doublet at 1.3 ppm inverts at an intermediate TE near 135 to 144 ms.

An anterior band placed over the pharynx and great vessels. It suppresses swallowing motion and carotid pulsation that would otherwise ghost across the cord along the phase-encoding direction. Coverage for a cervical study runs from the skull base through about T1 to T2.

Heavily T2-weighted long-TE sequences leave only near-static fluid bright, so bile and pancreatic ducts stand out against dark surrounding tissue. The patient fasts four to six hours, may drink a negative oral agent to null gastric and duodenal fluid, and data are collected with breath-holds or respiratory triggering.

Fat and water precess at slightly different frequencies, so at 1.5 T their signals oppose near a TE of about 2.2 ms and realign near about 4.4 ms. A voxel containing both loses signal on the opposed-phase image, and that drop is the finding that indicates steatosis or a fat-containing lesion.

Prone in a dedicated bilateral breast coil with the breasts pendant and immobilized, imaged before and repeatedly after gadolinium so enhancement kinetics can be plotted. Screening exams are ideally scheduled during days 7 to 14 of the menstrual cycle to limit background parenchymal enhancement.

Whenever cardiac motion or pulsatile flow would blur the target, including cardiac, thoracic aorta, and some spine work. The ECG R wave triggers data collection so every k-space line is acquired at the same point in the cardiac cycle. Peripheral pulse gating substitutes when the ECG trace is unreliable.

Supine with the arm at the side in slight external rotation and the humeral head centered in a dedicated surface coil. Working from the axial images, oblique coronal slices are planned parallel to the supraspinatus tendon and oblique sagittal slices perpendicular to it.

Sagittal slices are angled along the course of the ACL, roughly 10 to 15 degrees, so the ligament is displayed along its length. On 4 to 5 mm peripheral sagittal slices a normal meniscus body appears as a bow tie on two consecutive images; fewer than two bow ties suggests a tear or prior resection, and more than two suggests a discoid meniscus.

Dilute gadolinium, roughly one part contrast to 200 parts saline, is injected into the joint under imaging guidance to distend the capsule. Fat-suppressed T1-weighted images in multiple planes then show bright contrast tracking into labral, ligament, or cartilage defects.

Small bilateral surface coils are placed over each joint and sagittal oblique slices are planned perpendicular to the long axis of the mandibular condyle. Images are acquired in both closed-mouth and open-mouth positions, sometimes as a CINE series, to show whether the disc reduces.