Knowledge Flashcards
7 cards from real MRI practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Knowledge flashcards as text
What is the Specific Absorption Rate (SAR) a measure of in MRI?
Answer: Rate at which radiofrequency energy is absorbed by the patient's tissue per unit mass
SAR (W/kg) quantifies RF energy deposition in tissue and is a primary safety limit to prevent excessive tissue heating during MRI.
Which MRI sequence is best suited for evaluating articular cartilage because it provides excellent contrast between cartilage, fluid, and bone?
Answer: Proton density fat-saturated (PD FS)
PD fat-saturated sequences highlight cartilage defects as intermediate-signal cartilage contrasts sharply against bright joint fluid and suppressed fat.
What causes the 'zipper' artifact that appears as a line of noise across the MRI image?
Answer: External RF interference entering the scan room through a breach in shielding
A zipper artifact is caused by external RF noise at a specific frequency leaking into the Faraday-shielded room, appearing as a bright line at that frequency position.
In MRI, what does the term 'bandwidth' typically refer to in clinical practice?
Answer: The range of frequencies sampled during readout, affecting SNR and chemical shift
Receiver bandwidth is the range of frequencies digitized during readout; wider bandwidth reduces chemical shift and distortion but decreases SNR.
What is the primary advantage of a 3T MRI scanner compared to a 1.5T scanner?
Answer: Higher SNR that can be traded for faster scans or higher spatial resolution
Field strength doubling theoretically doubles SNR, which can be reinvested in thinner slices, smaller voxels, or reduced scan time.
Which MRI technique uses magnetically labeled water protons as an endogenous tracer to measure cerebral blood flow without contrast injection?
Answer: Arterial Spin Labeling (ASL)
ASL uses RF inversion of arterial water protons proximal to the imaging plane as a flow tracer, enabling non-invasive perfusion measurement.
What is the primary reason gradient coils produce loud acoustic noise during MRI scanning?
Answer: Lorentz forces cause the gradient coil windings to physically vibrate as current rapidly switches
Rapidly switching electrical current in gradient coils within the strong static field produces Lorentz forces that physically deflect the coils, generating loud knocking sounds.