MRI MRI Sequences and Protocols 1 — Questions and Answers
Question 1: In a spin echo (SE) sequence, increasing the repetition time (TR) while keeping TE short primarily results in:
- Increased T2 weighting
- Increased T1 weighting
- Decreased T1 weighting (more proton density/T2-like contrast) (Correct answer)
- Increased SNR only with no contrast change
Correct 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.
Question 2: FLAIR (Fluid-Attenuated Inversion Recovery) suppresses which signal and is most useful for detecting:
- Fat signal; bone marrow edema
- CSF signal; periventricular and cortical lesions (Correct answer)
- Blood signal; hemorrhage
- Muscle signal; soft tissue tumors
Correct 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.
Question 3: Which MRI sequence is most commonly used for evaluating liver lesions using T2 contrast with heavy T2 weighting for the bile ducts?
- T1 in-phase/opposed-phase
- MRCP (heavily T2-weighted 3D or thick-slab) (Correct answer)
- DWI b1000
- STIR of the abdomen
Correct 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.
Question 4: Gradient echo (GRE) sequences differ from spin echo sequences primarily because GRE:
- Uses a 180° refocusing pulse to eliminate field inhomogeneity effects
- Uses a gradient reversal to form an echo, making it sensitive to magnetic susceptibility (T2*) (Correct answer)
- Always requires longer scan times
- Cannot be used for dynamic contrast imaging
Correct 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.
Question 5: Which parameter directly controls the degree of T2 weighting in a spin echo sequence?
- TR (repetition time)
- TE (echo time) (Correct answer)
- Flip angle
- Bandwidth
Correct answer: TE (echo time)
TE determines how long transverse magnetization decays before sampling; a longer TE allows more T2 decay, increasing T2 contrast.
Question 6: Magnetization transfer contrast (MTC) in MRI is based on the exchange of magnetization between which two proton pools?
- Free water protons and bound macromolecular protons (Correct answer)
- Fat protons and water protons
- Intracellular and extracellular water
- Arterial and venous blood
Correct 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.
MRI MRI Sequences and Protocols 1
In a spin echo (SE) sequence, increasing the repetition time (TR) while keeping TE short primarily results in: