Practice Test GeeksMRI - Magnetic Resonance Imaging Practice Test
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Physics 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.

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  1. What is the primary source of acoustic noise in an MRI scanner?

    Answer: Rapid switching of gradient coils within the static magnetic field

    Lorentz forces act on gradient coil conductors carrying rapidly switched currents within B0, causing coil vibration and the characteristic loud knocking noise.

  2. Which type of MRI coil provides the best SNR for imaging a small, superficial structure?

    Answer: Small surface coil placed directly over the region of interest

    A small surface coil placed close to the target anatomy maximizes signal reception from that area while minimizing noise from surrounding regions.

  3. In MRI safety, what is the specific absorption rate (SAR)?

    Answer: The rate of RF energy absorbed per unit mass of tissue, measured in W/kg

    SAR measures RF power deposition in tissue; regulatory limits exist to prevent tissue heating, especially important at higher field strengths and with certain sequences.

  4. Which MRI pulse sequence is most commonly used to perform MR angiography without contrast injection?

    Answer: Time-of-flight (TOF) angiography

    TOF MRA relies on flow-related enhancement: unsaturated blood flowing into a saturated imaging slice produces high signal relative to stationary tissue.

  5. What is the relationship between magnetic field strength (B0) and the Larmor frequency?

    Answer: Larmor frequency is directly proportional to B0 (ω₀ = γ·B0)

    The Larmor equation states ω₀ = γ·B0, so doubling the field strength doubles the resonance frequency (e.g., 63 MHz at 1.5T, 128 MHz at 3T for hydrogen).

  6. Fast spin echo (FSE/TSE) sequences reduce scan time compared to conventional spin echo by:

    Answer: Acquiring multiple phase-encoding lines after each 90° excitation (echo train)

    FSE uses a train of 180° pulses after each excitation to fill multiple k-space lines per TR, reducing total scan time by a factor equal to the echo train length.

  7. Magnetization transfer contrast (MTC) in MRI works by:

    Answer: Saturating bound protons in macromolecules, which reduces free water signal through exchange

    Off-resonance RF pulses saturate the broad resonance of bound macromolecular protons; this saturation is transferred to free water protons via chemical exchange, reducing their signal.