Chapter 8.1 Flashcards
Artifacts
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
b. Some artefacts are irreversible and cannot be eliminated, but reduced
Which of the following could cause phase mismapping?
a. pulsatile movement of vessels
b. eye movement
c. swallowing
d. all of the above
d. all of the above
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
d. There are replications of moving anatomy across the image in the phase direction
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
a. using phase aliasing
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
c. the Z gradient performs the phase encoding
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
d. resolution data is placed at the edge of K space during respiration
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
d. a and b
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
d. partial volume averaging
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
c. motion artefact is averaged out of the image
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
b. Keeping the patient nervous
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
c. a black line around the abdominal organs
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
d. a and c
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
c. Extraneous RF entering room interfering with signal from patient
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
b. is the difference in precessional frequency between fat and water and it increases with
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
c. is reduced by using a short TE (less dephasing between tissues)
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
a. if the data is under-sampled
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
a. adjacent slices are excited by the RF pulse of neighboring slices
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
d. all of the above
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
b. is caused by nuclei dissipating energy to neighboring slices
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
c. can be caused by inhomogeneities in the main magnetic field
The Moiré artefact appears as black and white zebra banding at the edge of the FOV.
a. True
b. False
a. True
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
c. is seen in tissues that contain collagen
What is the periodicity of fat and water at 1.5T?
a. 220Hz
b. 4.2ms
c. 147Hz
d. 7ms
b. 4.2ms
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
c. is caused by under-sampling of frequencies present in the echo
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
d. a and c
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
a. True
Peripheral gating should be used to reduce phase mismapping when imaging small vessels or
the spinal cord.
a. True
b. False
a. True
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
c. ghosting
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
d. triggering
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
d. Peripheral
Aliasing along the frequency encoding axis is known as frequency:
a. encasement
b. wrap
c. compensation
d. pulsing
b. wrap
Which artefact produces distortion of the image with large signal voids?
a. truncation
b. out of phase
c. magnetic susceptibility
d. cross-excitation
c. magnetic susceptibility
Which artefact appears as a dense line on the image at a specific point?
a. Moire
b. zipper
c. shading
d. magnetic susceptibility
b. zipper
- 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
d. partial volume averaging
Motion is seen as a smearing in the:
a. frequency encoding direction
b. phase encoding direction
c. slice selection direction
d. z axis direction
b. phase encoding direction
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
a. the number of phase encodings is increased
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
b. receiver bandwidth is decreased
Magnetic susceptibility effects are less prominent with:
a. gradient echo sequences
b. spin echo sequences
c. SSFP sequences
d. inversion recovery sequences
b. spin echo sequences
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
a. periodic motion
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
b. aperiodic motion
