Th - Basics of MRI and realtime MRI

Question 1

What is T1?

Answer 1

T1 relaxation process is recovery of longitudinal magnetization Mz.
T1 = time to recover to 63%

Question 2

What does a short T1 mean?

Answer 2

Short T1 means: Fast recovery of magnetization Mz (T1 is a tissue property).

Question 3

What is T2?

Answer 3

T2 relaxation is the decay of net transverse magnetization due to dephasing.
T2 = time to decay to 37%

Question 4

What is TR?

Answer 4

Repetition time TR is time between 2 radio-frequency excitation pulses (TR is a machine parameter)

Question 5

What happens with TR when you set it short?

Answer 5

The image is T1 weighted

Question 6

Tissue with short T2: fast dephasing resultant Mxy has fast decay: (light/dark)

Answer 6

Dark

Question 7

Tissue with long T2: slow dephasing resultant Mxy has slow decay: (light/dark)

Answer 7

Light

Question 8

What does ‘bright’ mean on a T2 weighted image?
(3)

Answer 8

Prolonged T2, oedema, inflammation

Question 9

What are the advantages of MRI imaging for image guided radiotherapy (compared with CT) (explain comlpicated) (2)

Answer 9

MRI gives soft tissue contrast, and provides a delineation between the tumor-target, and the healthy surrounding tissues to be spared.
MRI can image a moving target in real-time, in the plane where motion is. e.g. in the sagittal plane, for all tumors moving with respiration (application: e.g. lung tumors)