ARRT MRI flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Normal GFR threshold

GFR below 30 mL/min/1.73 m² is severe renal impairment; group I gadolinium is contraindicated and group II agents are used only at lowest dose with caution.

NSF risk agents

Nephrogenic systemic fibrosis is associated with linear gadolinium agents in severe renal failure; macrocyclic group II agents have the lowest dissociation and risk.

Metformin and gadolinium

For gadolinium, metformin generally may be continued; withholding 48 hours applies mainly after iodinated contrast in eGFR below 30 or AKI.

Extravasation first steps

Stop injection, remove IV, elevate extremity, apply cold compress, document volume and site, and monitor for compartment syndrome.

Anaphylactoid contrast reaction

Stop injection, call for help, assess airway, give oxygen, and administer IM epinephrine for bronchospasm or hypotension.

Pregnancy MRI contrast

Iodinated and gadolinium contrast cross the placenta; MRI without contrast is preferred, and gadolinium is given only when essential.

MRI metal screening

Ask about pacemakers, aneurysm clips, cochlear implants, ocular metal, shrapnel, and tattoos; verify implant labeling before entering the magnet room.

Sedation monitoring

During sedation, continuously monitor SpO2 and HR, record BP every 5 minutes, and observe respiration and level of consciousness.

T1 weighting parameters

Short TR under about 800 ms and short TE under about 30 ms produce T1 contrast; fat is bright and fluid is dark.

T2 weighting parameters

Long TR over about 2000 ms and long TE over about 80 ms produce T2 contrast; fluid is bright and fat remains bright.

STIR fluid sensitivity

STIR uses inversion recovery with TI about 150 ms at 1.5 T to null fat, making fluid and edema bright.

FLAIR CSF suppression

FLAIR applies a long inversion time near 2000 ms to null CSF, improving detection of periventricular and cortical lesions.

MRCP technique

MRCP uses heavily T2-weighted thick-slab or 3D respiratory-triggered sequences so stationary fluid in bile and pancreatic ducts is bright.

TOF MRA principle

Time-of-flight MRA relies on flow-related enhancement of unsaturated blood entering the slice; no gadolinium is required.

Chemical shift artifact

Fat and water protons precess at different frequencies; at the fat-water interface, misregistration occurs along the frequency-encoding direction.

Aliasing correction

Wrap-around artifact occurs when anatomy exceeds FOV; increase FOV, use saturation bands, or apply oversampling along the phase-encoding direction.

Larmor equation

Precessional frequency equals gyromagnetic ratio times field strength; for hydrogen-1, 42.58 MHz per tesla, giving 63.9 MHz at 1.5 T.

T1 relaxation time

T1 is the time for longitudinal magnetization to recover to 63 percent of its final value after a 90-degree radiofrequency pulse.

T2 relaxation time

T2 is the time for transverse magnetization to decay to 37 percent of its initial value; T2 star adds static field inhomogeneity.

Ernst angle formula

The Ernst angle maximizes signal for a given TR and T1 and is calculated as cosine theta equals e to the minus TR over T1.

k-space center

Central k-space lines encode image contrast and SNR; peripheral lines encode spatial resolution and edge detail.

SNR voxel relation

Signal-to-noise ratio is proportional to voxel volume times the square root of excitations; larger voxels or more averages increase SNR.

Receive bandwidth effect

Increasing receive bandwidth lowers SNR but shortens minimum TE and reduces chemical shift and susceptibility artifact.

SAR determinants

Specific absorption rate rises with field strength squared, flip angle squared, and RF duty cycle; fast spin echo sequences deposit more energy.

Inversion time nulling

To null a tissue, set inversion time to its T1 times the natural logarithm of 2, approximately 0.693 times T1.

Gradient slew rate

Slew rate is the rate of gradient amplitude change; higher slew rates permit faster encoding but increase peripheral nerve stimulation risk.

Five gauss line

The 5 gauss line marks the boundary where the static field may affect implanted devices and loose ferromagnetic objects; it is posted and restricted.

MRI zones

Zone I is public, zone II is screened, zone III is restricted, and zone IV is the magnet room with the strongest field.

RF burn prevention

Avoid skin-to-skin contact loops, keep cables off the patient, and use padding; RF currents can cause burns even without heating the whole body.

Acoustic noise protection

MRI gradients produce noise that can exceed 99 decibels; earplugs or headphones are required for patients and staff in the magnet room.

Cryogen quench

A quench releases helium gas, displacing oxygen; evacuate the room, open doors, and do not reenter until oxygen levels are safe.

MR conditional implant

An MR conditional device is safe only under specified field strength, SAR, and coil conditions; verify the exact labeling before scanning.