Chapter 5 Questions

Front 1

If the radiologist requires 2mm slices through the pituitary, and 2.4 cm of coverage, how many slices must be selected (assuming no gap)?

Back 1

12

Front 2

If all other sequence parameters remain constant, but the echo time is increased:

Back 2

Number of slices per TR decreases

*TE does not affect the resolution

Front 3

As the number of signal averages is increased from 1 to 3, which of the following does NOT occur?
A. scan time triples
B. three cycles of the TR occur for each phase line in the image matrix
C. the image resolution remains the same
D. the signal to noise ratio is three times better

Back 3

D. the signal to noise ratio is three times better
*Actually for each doubling of signal averages the resulting increase in signal to noise is approximately 40%

*Resoultion is NOT affected by signal averages.

Front 4

Which of the following is a result of reducing the FOV?
1. Anatomical structures appear smaller
2. Increased S/N
3. Improved spatial resolution

Back 4

Improved spatial resolution
*The signal to noise will DECREASE

Front 5

The echoes collected from a 256x256 sagittal lumbar spine image have a frequency range that extends 14.1 kHz above and 14.1 kHz below the central frequency of the echoes. If this exam was performed on a 1.5 Telsa MRI system, where there is approximately 220Hz. Chemical shift between fat and water, the signal in the vertebral bodies will shift ____ pixels relative to the signal in the disks.

Back 5

2
*(Question 5, chapter 5)

Front 6

A certain gradient echo sequence generates an optimal S/N with a repetition time of 250 ms and a flip angle of 45 degrees. If the TR is reduced to 200ms how should the flip angle be changed to recover some of the lost S/N?

Back 6

The flip angle should be decreased (in order to preserve the optimal strength of the echo)

Front 7

Assuming all other parameters are the same, an echo time of ____ ms provides the best S/N.
A. 15
B. 30
C. 70
D. 90

Back 7

15
*The shorter the TE the greater the S/N regardless of all other factors.

Front 8

Which of the following echo train lengths generate a set of images with the greatest S/N assuming all other parameters are the same, and assuming the 1st echo forms at TE=50ms with 10ms between subsequent echoes?
a. 3
b. 5
c. 12
d. 16

Back 8

3
*The shorter the TE the higher the S/N

Front 9

Which of the following echo train lengths generates a set of images in the shortest amount of time assuming all other parameters are the same?
a. 3
b. 5
c. 12
d. 16

Back 9

16
*As echo train length increases scan time porportionally decreases

Front 10

If the TR is doubled, the scan time will:

Back 10

Double

Front 11

Assuming all other parameters are the same, a ____ms echo time provides the strongest T2 contrast.
a. 15
b. 30
c. 90
d. 110

Back 11

110
*The longer the TE the higher the contrast

Front 12

If seventeen 5mm slices are prescribed and a gap of 1mm is chosen, the total anatomical coverage is _____ cm.

Back 12

10.1 cm
*(17 slices x 5 mm/slice) + (16 gaps x 1 mm/gap) = 85mm + 16mm= 101 mm = 10.1 cm.

Front 13

Which of the following pulse sequence parameters is responsible for partial volume averaging?

Back 13

Slice thickness

Front 14

Which of the following would NOT compensate for the change in S/N as a result of decreasing the FOV?

Back 14

A decrease in number of signal averages

*A decrease in the number of signal averages will result in a loss of signal to noise because less signal noise will be averaged out of the recorded echoes.

Front 15

Assuming all other parameters are the same, a ___ms echo time provides the strongest T1 contrast.
a. 1
b. 10
c. 15
d. 90

Back 15

1
*If we want to maximize T1 contrast then we must minimize T2 contrast. TE contributes to T2 contrast.

Front 16

What is wrong with a T2 weighted, fast spin echo image that has a 1.2 sec. TR and an 85 msec TE?
1. The TE will cause the image to have low S/N
2. The TE will cause the image to have very little T2 contrast
3. The TR does not effectively minimize the T1 contrast.

Back 16

3. The TR does not effectively minimize the T1 contrast
*The TR is too short, generally you need a TR of more than 3 seconds to effectively start to eliminate T1 effects.

Front 17

A set of images is acquired with a 150 mm FOV. Keeping all other parameters constant, a second set of images is acquired with a 300 mm FOV, and then magnified so that the anatomical structures in the first and second set of images appear the same size. Which of the following statements is FALSE?
1. the spatial resolution of the second set of images is better than the first set of images
2. the S/N of the second set of images is worse than the first set of images
3. the scan time of the second set of images is twice that of the first set of images.

Back 17

1 and 3

*FOV has no effect on scan time
*The larger the FOV the worse the spatial resolution

Front 18

In order to partially compensate for changes in S/N, how should the TR be adjusted when moving from a 1.5 telsa system to a 0.3 telsa system?
1. the TR should be decreased
2. the TR should be increased
3. the TR has no effect on the S/N

Back 18

The TR should be increased (to produce better signal)

Front 19

Which of the followig is NOT related to the receiver bandwidth?

Back 19

The range of frequencies transmitted to select the slice thickness.
*The reciever bandwidth is determined by the amplitude of the readout gradient which generates a range of precessional frequencies into which the echo is encoded.

Front 20

________ is a method to reduce the MR scan time that also results in a loss of spatial resolution.

Back 20

Reducing the matrix

Front 21

When converting the recommended protocol for fat suppression inversion recovery sequence from a low field MR system to a high field system, the _________ in order to maintain equivalent fat nulling.

Back 21

TI should be increased

Front 22

A pulse sequence is going to have a scan time of 4 minutes. If the technologist then selects to use parallel imaging with a parallel imaging factor of 2 without changing any other parameters, the scan time will now be _______ minutes.

Back 22

2

Front 23

Which of the following statements is FALSE regarding the spatial resolution of an image?a. It may be calculated by dividing the matrix by the FOV.b. it may remain unaffected if both the FOV and matrix are variedc. it is unaffected by an increase in the number of signal averages d. it is a measure of the size of an object which can be detected in the image

Back 23

A. It may be calulated by dividing the matrix by the FOV.*You must divide the FOV by the matrix!

Front 24

A technique used to reduce the MR scan time which requires the use of an array coil is:

Back 24

Parallel imaging

Front 25

Assuming all other parameters are the same, a ______ ms repetition time provides the best S/N.a. 30b. 200c. 300d. 800

Back 25

800*Long TR yeilds high S/N

Front 26

During a spoiled gradient echo pulse sequence with 12 slices, how many gradient echoes are collected during one TR period.

Back 26

12*One echo collected from each slice at a single phase step

Front 27

Which of the following statements is FALSE regarding a low reciever bandwidth?1. it generates lower S/N images2. it should be applied in regions of the body where there are fatty and watery tissues adjacent to one another3. it is selected with a higher readout gradient amplitude

Back 27

1, 2 and 3.

Front 28

Which of the following are TRUE?1. T1 contrast is maximized with short TRs2. Contrast is defined as the difference in magnetizations of two tissues3. T2 contrast is maximized with short TEs.

Back 28

1. T1 contrast is maximized with short TRs*Contrast is not the difference but rather the RATIO of magnetization of two tissues.

Front 29

A fast spin echo sequence with a TR of ____ ms and a TE of ____ ms will yeild a proton density image.

Back 29

2500, 20*Long TR and short TE

Front 30

The smallest object that can be resolved in an image acquired with a 24 cm FOV and a 512x512 matrix is _____ mm.

Back 30

0.47*This can be determined by 1. Image FOV 2. image matrix to find pixel size.

Front 31

Which of the following is the correct scan time for a spin echo sequence with the following parameters: TR=2200ms, TE=20, 90ms matrix= 256x256, 1 excitation, FOV= 230mm?

Back 31

*Scan time is calculated as follows: scan time= TR times (size of the matrix along the phase direction) times (number of signal averages) divided by the echo train length. -In a spin echo the echo train length is 1.

Front 32

When using a rectangular FOV, which is twice as tall as it is wide, and the phase direction of the image is oriented along the smaller dimension of the FOV, which of the following relationships between the frequency and phase steps of the matrix guarantees square pixels?

Back 32

The number of phase steps must be half of the number of frequency steps