Chapter 8.1

Question 1

Which of the following is true?

a. MRI images rarely have any artefacts
b. Some artefacts are irreversible and cannot be eliminated, but reduced
c. The cause of artefacts is not important
d. Artefacts can be avoided altogether

Answer 1

b. Some artefacts are irreversible and cannot be eliminated, but reduced

Question 2

Which of the following could cause phase mismapping?

a. pulsatile movement of vessels
b. eye movement
c. swallowing
d. all of the above

Answer 2

d. all of the above

Question 3

With phase mismapping:

a. There is no delay between phase encoding and readout
b. The phase encoding gradients have the same amplitude every TR
c. Is caused by anatomy moving along the frequency encoding gradient
d. There are replications of moving anatomy across the image in the phase direction

Answer 3

d. There are replications of moving anatomy across the image in the phase direction

Question 4

The following are ways to reduce phase mismapping except:

a. using phase aliasing
b. swapping phase and frequency
c. using pre-saturation pulses
d. using respiratory compensation techniques

Answer 4

a. using phase aliasing

Question 5

After swapping phase and frequency encoding gradients to reduce motion artifact in a
sagittal cervical spine:

a. the X gradient performs the frequency encoding
b. the Y gradient performs the phase encoding
c. the Z gradient performs the phase encoding
d. both X and Y gradients perform the phase encoding

Answer 5

c. the Z gradient performs the phase encoding

Question 6

When using a respiratory compensation bellows for respiratory gating or triggering:

a. the bellows should be placed below the umbilicus
b. the center of K space is filled during respiratory motion
c. anatomy moving along a steep phase encoding gradient slope produces much ghosting
d. resolution data is placed at the edge of K space during respiration

Answer 6

d. resolution data is placed at the edge of K space during respiration

Question 7

When imaging the heart, cardiac gating:

a. monitors cardiac motion by coordinating the excitation pulse with the R wave
b. uses EKG gating, so each slice is acquired at the same phase of the cardiac cycle
c. should use peripheral gating as it is more accurate than EKG gating
d. a and b

Answer 7

d. a and b

Question 8

The superimposition of signal that occurs when a LARGE FOV is acquired, is known as:

a. wrap around
b. fold over
c. aliasing
d. partial volume averaging

Answer 8

d. partial volume averaging

Question 9

Increasing the NEX:

a. has no effect on reducing motion artefacts
b. decreases the number of times the signal is averaged
c. motion artefact is averaged out of the image
d. b and c

Answer 9

c. motion artefact is averaged out of the image

Question 10

Voluntary motion can be reduced by all of the following except:

a. Immobilizing patient with pads and straps
b. Keeping the patient nervous
c. Sedation of the patient
d. Constantly remind patient to “keep still” over the intercom

Answer 10

b. Keeping the patient nervous

Question 11

Out of phase signal cancellation artefact is characterized by:

a. fat and water being in phase within the same voxel
b. a bright line around the abdominal organs
c. a black line around the abdominal organs
d. a and c

Answer 11

c. a black line around the abdominal organs

Question 12

Which of the following is a remedy for phase wrap:

a. increase the FOV
b. decreasing the FOV
c. using pre-saturation bands on areas outside the FOV that may wrap into image
d. a and c

Answer 12

d. a and c

Question 13

The zipper artefact is caused by:

a. The pants zipper during abdominal and spinal imaging
b. Interleaving
c. Extraneous RF entering room interfering with signal from patient
d. Inhomogeneity in gradient echo sequences

Answer 13

c. Extraneous RF entering room interfering with signal from patient

Question 14

Chemical shift artefact:

a. occurs at the interface of fat and muscle
b. is the difference in precessional frequency between fat and water and it increases with
magnetic field strength
c. would be insignificant

Answer 14

b. is the difference in precessional frequency between fat and water and it increases with

Question 15

The magnetic susceptibility artefact:

a. appears as a hyper-intense (bright) signal
b. is caused by demagnetization
c. is reduced by using a short TE (less dephasing between tissues)
d. is corrected better with gradients than spin echo because the 180 degree rephasing pulses do not compensate for phase differences

Answer 15

c. is reduced by using a short TE (less dephasing between tissues)

Question 16

Aliasing or wrap around is produced:

a. if the data is under-sampled
b. if the data is mapped into pixels outside the FOV rather than inside
c. only along the phase axis
d. only along the frequency axis

Answer 16

a. if the data is under-sampled

Question 17

With cross-excitation:

a. adjacent slices are excited by the RF pulse of neighboring slices
b. cannot be corrected with interleaving
c. cannot be corrected using a suitable slice gap
d. all of the above

Answer 17

a. adjacent slices are excited by the RF pulse of neighboring slices

Question 18

The truncation artefact:

a. occurs at the interface of high and low signals resulting from undersampling of data
b. may be seen as faint lines adjacent to skull-brain interface when scanning the head
c. may be corrected by increasing the number of phase encodings
d. all of the above

Answer 18

d. all of the above

Question 19

Cross-talk:

a. is caused by having too large of an inter-slice gap
b. is caused by nuclei dissipating energy to neighboring slices
c. is caused by nuclei gaining energy through spin-spin relaxation
d. has a similar appearance to zipper artifact

Answer 19

b. is caused by nuclei dissipating energy to neighboring slices

Question 20

The shading artefact:

a. produces hypointense signal throughout the imaging volume
b. occurs when using the correct coil size for anatomy to be covered
c. can be caused by inhomogeneities in the main magnetic field
d. all of the above

Answer 20

c. can be caused by inhomogeneities in the main magnetic field

Question 21

The Moiré artefact appears as black and white zebra banding at the edge of the FOV.

a. True
b. False

Answer 21

a. True

Question 22

The magic angle artefact:

a. lies at a 35 degree angle to main field, with a high signal
b. cannot be corrected
c. is seen in tissues that contain collagen
d. both a and c

Answer 22

c. is seen in tissues that contain collagen

Question 23

What is the periodicity of fat and water at 1.5T?

a. 220Hz
b. 4.2ms
c. 147Hz
d. 7ms

Answer 23

b. 4.2ms

Question 24

Frequency wrap:

a. aliasing occurs along phase encoding axis
b. is unaffected by the Nyquist theorem
c. is caused by under-sampling of frequencies present in the echo
d. none of the above

Answer 24

c. is caused by under-sampling of frequencies present in the echo

Question 25

Frequency wrap can be reduced by:

a. increasing the digital sampling frequency
b. increasing the number of phase encodings
c. using frequency filters
d. a and c

Answer 25

d. a and c

Question 26

Out of phase signal cancellation artefact, can be corrected by selecting a TE that matches the
periodicity of fat & water at the field strength.

a. True
b. False

Answer 26

a. True

Question 27

Peripheral gating should be used to reduce phase mismapping when imaging small vessels or
the spinal cord.

a. True
b. False

Answer 27

a. True

Question 28

Swallowing and pulsatile motion of the carotids along the phase axis produces _______ over
the spinal cord.

a. Chemical shift artefact
b. Moire artefact
c. ghosting
d. cross-excitation

Answer 28

c. ghosting

Question 29

Some systems use a method known as respiratory gating or _______ that times the excitation
RF pulse with a certain phase of respiration.
a. popping
b. blending
c. navigating
d. triggering

Answer 29

d. triggering

Question 30

Which gating uses a light sensor attached to the patients finger to detect the pulsation of blood cells through the capillaries?

a. limb
b. side
c. ECG
d. Peripheral

Answer 30

d. Peripheral

Question 31

Aliasing along the frequency encoding axis is known as frequency:

a. encasement
b. wrap
c. compensation
d. pulsing

Answer 31

b. wrap

Question 32

Which artefact produces distortion of the image with large signal voids?

a. truncation
b. out of phase
c. magnetic susceptibility
d. cross-excitation

Answer 32

c. magnetic susceptibility

Question 33

Which artefact appears as a dense line on the image at a specific point?

a. Moire
b. zipper
c. shading
d. magnetic susceptibility

Answer 33

b. zipper

Question 34

34. The superimposition of signal that occurs when a small FOV is acquired, is known as all of the following EXCEPT:
    a. wrap around
    b. fold over
    c. aliasing
    d. partial volume averaging

Answer 34

d. partial volume averaging

Question 35

Motion is seen as a smearing in the:

a. frequency encoding direction
b. phase encoding direction
c. slice selection direction
d. z axis direction

Answer 35

b. phase encoding direction

Question 36

To correct for Gibbs (truncation) artefact, the:

a. the number of phase encodings is increased
b. the number of phase encodings is decreased
c. FOV is increased
d. TE is decreased

Answer 36

a. the number of phase encodings is increased

Question 37

Chemical shift becomes more obvious as the:

a. transmitter bandwidth is increased
b. receiver bandwidth is decreased
c. receiver bandwidth is increased
d. field strength of the magnet decreases

Answer 37

b. receiver bandwidth is decreased

Question 38

Magnetic susceptibility effects are less prominent with:

a. gradient echo sequences
b. spin echo sequences
c. SSFP sequences
d. inversion recovery sequences

Answer 38

b. spin echo sequences

Question 39

Motion artefacts occur due to periodic and/or aperiodic motion. Respiratory motion is an example of:

a. periodic motion
b. aperiodic motion
c. random motion
d. daily motion

Answer 39

a. periodic motion

Question 40

Motion artefacts occur due to periodic and/or aperiodic motion. Peristaltic motion is an
example of:
a. periodic motion
b. aperiodic motion
c. random motion
d. daily motion

Answer 40

b. aperiodic motion