MRI Sequences and Protocols Flashcards

In a spin echo (SE) sequence, increasing the repetition time (TR) while keeping TE short primarily results in:

Answer: Decreased T1 weighting (more proton density/T2-like contrast)

A long TR allows full T1 recovery of all tissues, reducing T1 contrast differences; combined with short TE, this produces proton density weighting.

FLAIR (Fluid-Attenuated Inversion Recovery) suppresses which signal and is most useful for detecting:

Answer: CSF signal; periventricular and cortical lesions

FLAIR uses an inversion pulse timed to null CSF, making periventricular lesions and cortical pathology (MS plaques, subarachnoid hemorrhage) visible against suppressed fluid.

Which MRI sequence is most commonly used for evaluating liver lesions using T2 contrast with heavy T2 weighting for the bile ducts?

Answer: MRCP (heavily T2-weighted 3D or thick-slab)

MRCP uses heavily T2-weighted sequences to make bile and pancreatic fluid appear bright, providing a non-invasive map of the biliary and pancreatic ductal system.

Gradient echo (GRE) sequences differ from spin echo sequences primarily because GRE:

Answer: Uses a gradient reversal to form an echo, making it sensitive to magnetic susceptibility (T2*)

GRE uses gradient reversal without a 180° refocusing pulse, making it sensitive to susceptibility effects (T2*) and allowing faster acquisition.

Which parameter directly controls the degree of T2 weighting in a spin echo sequence?

Answer: TE (echo time)

TE determines how long transverse magnetization decays before sampling; a longer TE allows more T2 decay, increasing T2 contrast.

Magnetization transfer contrast (MTC) in MRI is based on the exchange of magnetization between which two proton pools?

Answer: Free water protons and bound macromolecular protons

MTC involves saturation of bound macromolecular protons, which transfer their saturation to free water protons, reducing signal in tissues with high macromolecular content.