Principles of MRI

Question 1

RF pulse (radiofrequency pulse):

a. Increase the longitudinal magnetization by moving the protons from the low to the high energy states.
b. Increase the transverse magnetization by aligning the protons in phase.
c. Should have a lower frequency than the precession frequency.
d. resonance is the exchange of energy between the proton and the lattice.
e. stoping the RF pulse increases the transverse magnetization in a process called transverse relaxation.

Answer 1

B Increase the transverse magnetization by aligning the protons in phase.

Question 2

T1 and T2 relaxation constants:

a. T2 is longer than T1.
b. water and liquids (e.g. CSF) have longer T1 and shorter T2.
c. Brain tissue (mostly fats) has shorter T1 and shorter T2.
d. According to the Lamor equation stronger magnetic field leads to higher precession frequency which leads to shorter T1.
e. T1 is affected by inhomogeneities in the external magnetic field and the tissue’s internal magnetic field.

Answer 2

c. Brain tissue (mostly fats) has shorter T1 and shorter T2.

Question 3

In the Spin echo pulse sequence:

a. T2 weighted image has shorter TR, shorter TE
b. T1 weighted image has longer TR, longer TE
c. proton density-weighted image has longer TR, shorter TE.
d. 180 pulse is followed by 90 pulse.
e. Can form only T1 and T2 weighted images.

Answer 3

C proton density-weighted image has longer TR, shorter TE.

Question 4

T1, T2, and proton density-weighted images:

a. In the T1 weighted image the CSF appears darker than the surrounding.
b. In the T2 weighted image the CSF appears darker than the surrounding.
c. In the T1 weighted image the gray matter is lighter than the white matter.
d. The contrast medium (e.g, Gadolinium) is usually used in T2 weighted images.
e. Contrast media lengthen T1 and T2.

Answer 4

A In the T1 weighted image the CSF appears darker than the surrounding.

Question 5

Pulse sequences:

a. Inversion sequence –>T2 weighted image
b. partial saturation recovery sequence –> proton density-weighted image
c. saturation recovery sequence –> T1 weighted-image
d. Inversion sequence: use 90 pulse then 180 pulse.
e. In partial saturation/saturation recovery sequences, only 90 pulses are used.

Answer 5

e. In partial saturation/saturation recovery sequences, only 90 pulses are used.

Question 6

Gradient echo sequences (fast echo sequences):

a. Use 180 pulse to reverse the dephasing of protons instead of a magnetic gradient
b. Signal decays due to T2-effects.
c. The primary cause of these sequences is to increase the TR.
d. Use flip angles (e.g. 30Cْ ) pulses, to increase the longitudinal magnetization and the signal strength.
e. Use 180 pulse

Answer 6

d. Use flip angles (e.g. 30Cْ ) pulses, to increase the longitudinal magnetization and the signal strength.

Question 7

Image formation:

a. The slice selecting gradient is applied after the RF pulse
b. The frequency encoding gradient changes the frequency of protons from head to toe.
c. The frequency encoding gradient is applied temporarily after the RF pulse across the slide and changes the precession frequency of protons in a slice for a moment then they return to have the same precession frequency but out of phase.
d. The slice selecting, the frequency encoding, and the phase encoding magnetic coil gradients encode the spatial information of images in the z, y, and axes.
e. The different frequency and phase-encoded signals are further analyzed by Fourier transformation to reconstruct the image.

Answer 7

D and E

d. The slice selecting, the frequency encoding, and the phase encoding magnetic coil gradients encode the spatial information of images in the z, y, and axes.
e. The different frequency and phase-encoded signals are further analyzed by Fourier transformation to reconstruct the image.