MRI MRI Pulse Sequences 2

Question 1

Inversion recovery sequences null a specific tissue when the readout pulse is applied at time TI equal to:

Accepted Answer

0.693 × T1 of the tissue (T1 × ln2)

Answer

The longitudinal magnetization of a tissue crosses zero at TI = T1 × ln(2) ≈ 0.693 × T1; applying the readout at this moment nulls that tissue's signal.

Question 2

The b-value in diffusion-weighted imaging controls the degree of diffusion weighting. Increasing the b-value:

Accepted Answer

Increases diffusion contrast but decreases SNR

Answer

Higher b-values provide greater diffusion contrast by increasing the dephasing of mobile water protons, but at the cost of reduced SNR due to greater signal attenuation from all spins.

Question 3

SSFP (steady-state free precession) sequences such as TrueFISP/FIESTA produce contrast that is proportional to which tissue property ratio?

Accepted Answer

T2/T1

Answer

SSFP signal is proportional to T2/T1 ratio; tissues with high T2/T1 (like blood and fluids) appear very bright, making SSFP ideal for cardiac cine and vascular imaging.

Question 4

Which sequence parameter directly controls the slice thickness in a 2D spin-echo acquisition?

Accepted Answer

Bandwidth of the RF pulse divided by the slice-select gradient amplitude

Answer

Slice thickness = RF pulse bandwidth ÷ slice-select gradient amplitude; thicker slices can be produced by widening the RF bandwidth or reducing the gradient strength.

Question 5

What is the primary advantage of parallel imaging techniques (e.g., GRAPPA, SENSE) in MRI?

Accepted Answer

They reduce scan time or allow higher spatial resolution by using multiple coil elements to under-sample k-space

Answer

Parallel imaging exploits spatial sensitivity differences among phased-array coil elements to reconstruct fully sampled images from under-sampled k-space, reducing scan time by the acceleration factor (R).

MRI - Magnetic Resonance Imaging Practice Test

MRI - Magnetic Resonance Imaging Practice Test

MRI MRI Pulse Sequences 2