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MRI Pulse Sequences Flashcards

6 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. In a spin-echo sequence, which combination of TR and TE produces a T2-weighted image?

    Answer: Long TR, long TE

    T2-weighting requires long TR (to minimize T1 contrast by allowing full recovery) and long TE (to allow T2 differences between tissues to accumulate).

  2. Fast spin-echo (FSE/TSE) sequences acquire multiple lines of k-space per TR using which approach?

    Answer: A single 90° pulse followed by multiple 180° refocusing pulses (echo train)

    FSE uses an echo train (RARE principle): after a 90° excitation, a series of 180° pulses generates multiple spin echoes, each phase-encoded differently, filling multiple k-space lines per TR.

  3. Which gradient-echo sequence uses a very short TR and a spoiler gradient to eliminate residual transverse magnetization before the next RF pulse?

    Answer: Spoiled gradient echo (SPGR/FLASH)

    Spoiled GRE sequences (SPGR, FLASH) use RF or gradient spoiling to destroy residual transverse magnetization between pulses, producing T1-weighted images with high SNR efficiency.

  4. What does the acronym STIR stand for, and what tissue does it primarily null?

    Answer: Short-T1 Inversion Recovery — nulls fat signal

    STIR (Short-T1 Inversion Recovery) applies an inversion pulse with a TI timed to null fat signal (TI ≈ 150 ms at 1.5T), providing robust fat suppression independent of B0 homogeneity.

  5. Diffusion-weighted imaging (DWI) measures the random Brownian motion of water molecules. Restricted diffusion (e.g., in acute stroke) appears as:

    Answer: High signal on DWI, low ADC

    In acute ischemia, cytotoxic edema restricts water movement; restricted diffusion shows high signal on DWI (b=1000) and low signal on ADC map (low diffusivity).

  6. Which MRI sequence is used to visualize flowing blood as bright signal ('bright blood') without contrast injection by exploiting the inflow of unsaturated spins into the imaging slice?

    Answer: Time-of-flight (TOF) MRA

    TOF MRA uses gradient echo with short TR to saturate stationary tissue; fresh unsaturated blood flowing into the slice appears bright due to the inflow enhancement effect.