MRI Pulse Sequences Flashcards

Increasing the echo train length (ETL) in a fast spin echo sequence while other parameters stay the same will:

Answer: Shorten scan time but increase image blurring and decrease the number of slices per TR

A longer ETL fills more k-space lines per TR, reducing scan time but adding T2 blurring and taking more time per slice in each TR.

Fat and water are imaged with a two-point Dixon technique at 1.5 T. Which pair of TEs is most appropriate for opposed-phase and in-phase images?

Answer: 2.2 ms and 4.4 ms

At 1.5 T, fat and water are about 220 Hz apart, so they are opposed-phase near 2.2 ms and in-phase near 4.4 ms.

A double inversion recovery preparation is commonly used in cardiac MRI to:

Answer: Produce black-blood images by nulling the signal from flowing blood

A non-selective inversion followed by slice-selective re-inversion nulls blood that flows into the slice, giving black-blood images of the myocardium.

Which sequence is fastest, acquiring all of k-space after one excitation, but is most prone to susceptibility distortion and N/2 ghosting?

Answer: Single-shot echo planar imaging (EPI)

Single-shot EPI fills k-space with a rapidly oscillating readout gradient, which makes it fast but sensitive to field inhomogeneity and phase errors.

In a patient with an acute ischemic stroke, the infarcted region typically appears:

Answer: Bright on DWI and dark on the ADC map

Cytotoxic edema restricts water diffusion, causing high DWI signal and a low apparent diffusion coefficient.

Which sequence is a 3D T1-weighted gradient echo with an inversion recovery preparation pulse, widely used for volumetric brain imaging?

Answer: MPRAGE

MPRAGE (magnetization-prepared rapid gradient echo) uses an inversion pulse before a fast 3D GRE readout to give strong gray-white T1 contrast.

Dynamic susceptibility contrast (DSC) perfusion imaging of the brain relies on which effect during the first pass of a gadolinium bolus?

Answer: Transient T2* signal loss on rapid gradient echo EPI images

Concentrated gadolinium in the capillaries creates local susceptibility gradients, causing a temporary T2* signal drop that is tracked over time.