image basics

Question 1

Assuming all other parameters are the same, an echo time of ___________ ms provides the best Signal-to-Noise Ratio.

Answer 1

15

Question 2

Fat has a _______ T1 relaxation time and a ________ T2 relaxation time.

Answer 2

short; short

Question 3

Water has a __________ T1 relaxation time and a ________ T2 relaxation time

Answer 3

long; long

Question 4

If the repetition time is doubled, the scan time will:

Answer 4

Double

Question 5

Which of the following is NOT affected by changing the slice thickness?

Answer 5

The T1 contrast

Question 6

Which of the following would NOT compensate for the change in signal-to-noise as a result of decreasing the FOV?

Answer 6

Reducing the number of excitations

Question 7

Reducing the phase matrix from 256 to 192 will:

A. Increase the signal-to-noise ratio
B. Decrease imaging time
C. Decrease spatial resolution
D. All of the above

Answer 7

All of the above

Question 8

SNR increases with all the following adjustments, EXCEPT

Answer 8

Decreasing pixel size

Question 9

: Another name for a picture element is a:

Answer 9

Pixel

Question 10

What formula is used to calculate the size of the pixel?

Answer 10

FOV ÷ matrix

Question 11

Which parameter will provide the better spatial resolution?

A. 4mm slice thickness; 256 x 192 matrix
B. 4mm slice thickness; 256 x 256 matrix
C. 6mm slice thickness; 256 x 192 matrix
D. 6mm slice thickness; 256 x 256 matrix

Answer 11

4mm slice thickness; 256 x 256 matrix

Question 12

If a sequence with a matrix of 256 x 512 is adjusted to 512 x 512,

Answer 12

The SNR will decrease and the scan time will increase

Question 13

: In a fast spin echo sequence with a 28 cm FOV, 256 x 512 matrix, TR 2200, 90 TE, 5mm slice thickness, 8 ETL and 3 NEX, the scan time would be

Answer 13

3 minutes 31 seconds

Question 14

Decreasing the TR will:

A. Lower SNR
B. Reduce scan time
C. Increase SNR
D. Both A and B

Answer 14

Both A and B

Question 15

With regards to k-space, the data containing high resolution are located along:

Answer 15

The outer lines

Question 16

With regards to k-space, the data containing signal and contrast information are located along:

Answer 16

The central lines

Question 17

As the number of excitations (NEX) is increased from 1 to 3, which of the following does NOT occur?

Answer 17

The pixel size is increased

Question 18

Reducing the FOV (field of view) only will result in

Answer 18

Decreased signal-to-noise

Question 19

The scan time of a fast spin echo sequence utilizing a TR of 3500ms, a TE of 90ms, a 256x256 matrix, 1NSA, a 220mm FOV and an echo train length of 5 is ______ minutes, approximately.

Answer 19

3

Question 20

Assuming all other parameters are the same, a ___________ ms TR provides the best signal-to-noise ratio.

Answer 20

800

Question 21

The smallest object that can be resolved in an image acquired with a 20cm FOV and a 224 x 224 matrix is _________ mm.

Answer 21

0.89

Question 22

With a recFOV that is twice as tall as it is wide, and the phase direction oriented along the smaller “width” dimension of the FOV, which of the following relationships between the frequency and phase steps yields square pixels?

Answer 22

Phase steps must be half the number of frequency steps

Question 23

What would the scan time be in a 3D volume acquisition as follows: TR 32 ms, TE 4 ms, Flip Angle 15°, FOV 18cm, 2mm slice thickness, 96 slices, 192 x 256 matrix?

Answer 23

9 min 50 sec
3D scan time formula: TR x Phase Matrix x NEX x # slices

Question 24

Choose the correct slice thickness to create an isotropic voxel for the following: TR 2000, TE 90, Matrix 256 x 256, FOV 32cm

Answer 24

1.25 mm

Question 25

The pixel size of the images which result from a 3D acquisition using a 240mm FOV, a 272 x 272 matrix, 32 slices and a volume of 64 mm is:

Answer 25

: 0.88 x 0.88 mm FOV ÷ Matrix = pixel size..... 240 ÷ 272 = 0.88mm

Question 26

An increase in TR will produce all of the following EXCEPT

Answer 26

Decrease the number of available slices

Question 27

A set of specifically timed instructions to the magnet is known as

Answer 27

A pulse sequence

Question 28

All of the following affect acquisition time EXCEPT:

Answer 28

TE

Question 29

All of the following yield a higher signal-to-noise ratio EXCEPT

Answer 29

Increase TE

Question 30

All of the following would aid in reducing scan time EXCEPT:

Answer 30

Reducing TE

Question 31

Each line of k-space is defined by the

Answer 31

Phase encoding gradient

Question 32

High amplitude signals are stored in the

Answer 32

Center portion of k-space

Question 33

Acquiring a bit more than half the phase k-space samples, then interpolating the data with zeroes for the remaining half is a technique known as: A. Half Fourier B. Zero fill C. Fast spin echo D. A and/or B

Answer 33

A and/or B

Question 34

Increasing NSA will

Answer 34

Improve SNR

Question 35

A reduction in FOV will result in: A. Decrease in spatial resolution B. Increase in SNR C. Decrease in SNR D. None of the above E. A and C only

Answer 35

Decrease in SNR

Question 36

Reducing the slice thickness will result in A. An increase in partial volume averaging B. A decrease in SNR C. An increase in SNR D. A & B only E. None of the above

Answer 36

A decrease in SNR

Question 37

The central lines of k-space are associated with _____________ in a fast spin echo sequence.

Answer 37

Contrast information

Question 38

The timing of the RF pulses in an MRI pulse sequence controls:

Answer 38

Image contrast

Question 39

A method of reducing MRI scan time by not filling as many lines of k-space in the phase direction, while maintaining spatial resolution, is known as:

Answer 39

Rectangular FOV

Question 40

The overall signal-to-noise ratio will increase in 3D volume imaging when there is an increase in: A. Number of slices or partitions B. TE C. Phase Matrix D. Field of View E. A and/or D

Answer 40

A and/or D

Question 41

Which of the following pulse sequence parameter combinations would yield an image with the most blurring?

Answer 41

6000TR, 80TE, 256 x 256, 5mm slice thickness, 16 ETL, 4NSA

Question 42

Reducing the number of lines filled in k-space will produce an image: A. With a decrease in spatial resolution B. With an increase in spatial resolution C. With an decrease in overall SNR D. A and C

Answer 42

With a decrease in spatial resolution

Question 43

If the NEX is increased from 2 to 6, the signal-to-noise ratio increase would be

Answer 43

1.7

Question 44

Calculate the voxel volume for the following pulse sequence parameters: TR 450, TE 20, FOV 24cm, 320 x 320 matrix, 3mm slice thickness

Answer 44

1.69mm3 To calculate voxel volume, first determine pixel area. FOV/matrix x FOV/matrix = pixel area. Pixel area x slice thickness = voxel volume. 240/320 x 240/320 = 0.5625 mm2. 0.5625 x 3 = 1.69mm3

Question 45

Calculate the voxel volume for the following pulse sequence: TR 2000, TE 85, FOV 28cm, Matrix 272 x 320, 5mm slice thickness, 3 NSA

Answer 45

4.55 mm3 To calculate voxel volume, first determine pixel area. FOV/matrix x FOV/matrix = pixel area. Pixel area x slice thickness = voxel volume. 280/272 x 280/320 = 0.91 mm2. 0.91 x 5 = 4.55mm3

Question 46

Calculate the pixel area for the following sequence: TR 450, TE 12, FOV 18cm, 224 x 256 matrix, 4 NEX.

Answer 46

0.56 mm2 FOV/matrix x FOV/matrix = pixel area. 180/224 x 180/256 = 0.56 mm2

Question 47

Calculate the pixel area for the following sequence: TR 4000, TE 120, FOV 28cm, 304 x 304 matrix, 2 NEX, ETL 12.

Answer 47

0.85 mm2 FOV/matrix x FOV/matrix = pixel area. 280/304 x 280/304 = 0.85 mm2

Question 48

K-space is typically filled:

Answer 48

: One line at a time

Question 49

\_\_\_\_\_\_\_ is when only half the views of k-space are filled in the frequency axis

Answer 49

Partial or fractional echo

Question 50

As the number of phase encodings is increased from 256 to 512, SNR (signal to noise ratio):

Answer 50

Decreases