MRI MRI Pulse Sequences

Question 1

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

Accepted Answer

Long TR, long TE

Answer

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

Question 2

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

Accepted Answer

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

Answer

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.

Question 3

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

Accepted Answer

Spoiled gradient echo (SPGR/FLASH)

Answer

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.

Question 4

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

Accepted Answer

Short-T1 Inversion Recovery — nulls fat signal

Answer

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.

Question 5

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

Accepted Answer

High signal on DWI, low ADC

Answer

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).

MRI - Magnetic Resonance Imaging Practice Test

MRI - Magnetic Resonance Imaging Practice Test

MRI MRI Pulse Sequences