Question

PHYS/BIOL 464 Medical Imaging Instrumentation MRI HW 7A

1.During the magnetic resonance relaxation process after a 90° pulse:

A, Longitudinal magnetization increases

B. Transverse magnetization increases

C. Proton density increases

2. T1 and T2 values depend on:

A. Voxel size.

B. Direction of magnetic field.

C. Type of tissue.

3.Tissue characteristics which can produce a relative and increased intensity (brightness) contrast in a magnetic resonance image include which of the two following factors (choose two):

A. Short T1 values.

B. Long T1 values.

C. Short T2 values.

D. Long T2 values.

4. The process of averaging is used in MRI for the purpose of:

A. Reducing acquisition time.

B. Reducing image noise.

C. Improving detail.

D. Combining T1 and T2 contrast.

5. The amount of time necessary to acquire an MR image depends on which two factors (choose two):

A. TR

B. TE

C. Field of view

D. Matrix size

6. T1 increases with magnetic field.

A. True

B. False

Answer 1

1.

During the magnetic resonance relaxation process after a 90° pulse:

a. Longitudinal magnetization increases. Yes

b. Transverse magnetization increases. No

c. Proton density increases. No

Discussion: There are two phases to the relaxation process. During the longitudinal phase the magnetization increases and during the transverse phase the magnetization decreases. Most image contrast is created in one of these two phases.

2.

T1 and T2 values depend on:

a. Voxel size. No

b. Direction of magnetic field. No

c. Type of tissue. Yes

and Molecular size. Yes

Discussion: T1 and T2 values are characteristics of specific types of tissue. However, the size of the molecules contained in the tissue (fat versus water) is a major factor which determines the T1 values.

3.Tissue characteristics which can produce a relative and increased intensity (brightness) contrast in a magnetic resonance image include which of the two following factors (choose two):

ans A. Short T1 values. and D. Long T2 values.

4. The process of averaging is used in MRI for the purpose of:

ans. D. Combining T1 and T2 contrast.

5. The amount of time necessary to acquire an MR image depends on which two factors (choose two):

ans, B. TE and C. Field of view

6. T1 increases with magnetic field.

ans (a) True