Advanced Apps Advanced MR Imaging/Artifacts

Question 1

The HEIGHT of a peak on an MR spectrum correlates to the _________ of a substance that was detected.

Answer 1

Amount

The HEIGHT of a peak on an MR spectrum correlates to the amount of a substance that was detected

Question 2

Which of the following is NOT a metabolite found in a 1H spectrum of normal brain tissue?

Answer 2

Succinylcholine

Succinylcholine is a respiratory suppressant, not a metabolite found in normal brain tissue

Question 3

The final result in a spectroscopy study is:

Answer 3

A spectrum of specific detected metabolites

Spectroscopy (MRS) allows doctors to obtain biochemical information about the chemical components in tissues of the human body in a non-invasive way.

Question 4

Contrast in Diffusion Weighted Imaging (DWI) depends on:

Answer 4

All of the above

Contrast in Diffusion Weighted Imaging (DWI) depends on the degree to which molecular mobility is impaired (water restriction), the sensitivity of the sequence to Brownian motion, and the direction of water diffusion.

Question 5

Common problems in DWI include:

Answer 5

All of the above

Common problems in DWI include sensitivity to magnetic susceptibility when using echo planar readout, bulk patient motion, and low SNR.

Question 6

In DWI sequences, ADC stands for:

Answer 6

Apparent Diffusion Co-efficient

The first successful clinical application of DWI was in imaging the brain following stroke in adults. Areas which were injured during a stroke showed up “darker” on an ADC (apparent diffusion co-efficient) map compared to healthy tissue.

Question 7

The final result in a perfusion study is:

Answer 7

A set of calculated images which indicate various flow characteristics

The final result in a perfusion study is a set of calculated images which indicate various flow characteristics

Question 8

____________ can be described as water molecules moving the same way in every direction.

Answer 8

Isotropic diffusion

Isotropic diffusion: Water molecules move the same way in every direction.

Question 9

____________ can be described as water molecules moving in a preferred direction.

Answer 9

Functional MRI

The imaging technique that employs a very rapid pulse sequence while the patient is at rest or performing a task is known as Functional MRI.

Question 10

The echoes collected from a 256/256 Sagittal Cervical spine have a frequency range 14.1 kHz above and below the central frequency, 1.5Tesla system with 220 Hz chemical shift between fat and water, the vertebral body signal will shift _____ pixels relative to the signal in intervertebral disk.

Answer 10

2.0

28.2 x 1000 = 28200 Hz; 28200 ÷ 256 = 110; 220 ÷ 110 = 2 pixels shift between fat and water

Question 11

What would the pixel shift be in a sequence acquired at 1.5Tesla (220 Hz) with a 224 matrix and a BW of 26.8 kHz?

Answer 11

1.8

26.8(bandwidth in kHz) x 1000 to convert into Hz = 26800
26800 ÷ 224(matrix) = 120 Hz frequency difference per pixel
220(chemical shift) ÷ 120 = 1.8, the fat image will be shifted 1.8 pixels along the frequency/readout axis relative to water

Question 12

DWI susceptibility artifacts in or around strong air tissue interfaces can be minimized by:

Answer 12

Increasing parallel imaging acceleration factor

Increasing parallel imaging factors can decrease susceptibility artifacts around air tissue interfaces, such as temporal bone/auditory canal regions.

Question 13

All of the following artifacts except __________ occur along the phase encoding axis.

Answer 13

Chemical Shift

Chemical shift primarily occurs along the frequency axis.

Question 14

Motion is seen as a smearing across the image in the

Answer 14

phase encoding direction

Question 15

Magnetic susceptibility artifacts are more prominent with:

Answer 15

Gradient echo

Gradient echo is more susceptible to metallic artifacts due to the lack of 180° refocussing pulse that would reduce field inhomogeneities.

Question 16

A leak in the RF shielding can appear as:

Answer 16

A zipper artifact in the frequency direction

Question 17

A remedy for a Gibbs truncation artifact would be:

Answer 17

Increase the number of phase encodings

To correct for Gibbs truncation artifact, increase the number of phase encodings or reduce the FOV (while maintaining matrix)

Question 18

A FID crushing artifact can be eliminated with the use of:

Answer 18

A and/or C

Increase in NEX and/or enabling Flow Compensation can correct for FID artifacts

Question 19

Chemical shift artifact occurs because:

Answer 19

Fat and water precess at different frequencies

Question 20

The ___________ to reduce chemical shift artifacts.

Answer 20

Receiver bandwidth should be increased

Question 21

Aliasing occurs because tissue outside the selected FOV is:

Answer 21

Undersampled

Aliasing (wrap-around artifact) occurs when tissue outside the FOV (in the phase direction) is undersampled.

Question 22

The ________ should be _______ to reduce chemical shift artifacts.

Answer 22

Receiver bandwidth; increased

A higher bandwidth is used for the reduction of chemical shift artifacts (lower bandwidth - more chemical shift - but better signal to noise ratio).

Question 23

Which artifact mimics a syrinx in the spine?

Answer 23

Truncation

Question 24

________ occurs when tissue outside the Field of View is undersampled, causing a misregistration of anatomical location, in the phase direction, but on the opposite side of the anatomical location, also known as wrap-around artifact

Answer 24

Aliasing artifact

Question 25

In what anatomical region would you expect to see chemical misregistration the least?

Answer 25

Cerebellum

Question 26

Which artifact occurs because of chemical misregistration?

Answer 26

Chemical shift

Chemical shift artifacts occur because of chemical misregistration.

Question 27

Which of the following influences can lead to artifacts?

Answer 27

All of the above

Magnetic field inhomogeneity, machine hardware, and the patient can all be influences causing artifacts.

Question 28

In a sagittal cervical spine MRI, what could be done to compensate for CSF flow artifacts?

Answer 28

Enable gradient moment nulling

Gradient moment nulling (or flow compensation) can be used in a cervical spine MRI to minimize CSF flow artifacts.

Question 29

Which would yield more chemical shift artifacts?

Answer 29

3T superconducting magnet

Question 30

Which of the following could lead to poor fat suppression?

Answer 30

Inhomogeneity

Question 31

A decrease in the voxel volume yields

Answer 31

A decrease in partial volume averaging

Question 32

To reduce the appearance of a Gibbs truncation artifact, the:

Answer 32

Number of phase encodings must be increased

Question 33

To minimize cross talk artifact,

Answer 33

Increase the interslice gap

Question 34

To correct the artifact Gibbs truncation

Answer 34

Increase phase matrix

Question 35

When the TE is lowered:

Answer 35

Susceptibility artifact decreases

When the TE is shortened, susceptibility artifacts decrease because shortened TE’s allow less time for dephasing thus reducing signal loss.

Question 36

Crosstalk is cause by:

Answer 36

Differing frequencies of fat and water

Question 37

To reduce an RF zipper artifact:

Answer 37

Close scan room door and ensure adequate door suction

Question 38

Ensuring adequate door suction in the MR scan room will aid in preventing which artifacts from appearing in an MR image?

Answer 38

RF zipper

Question 39

Moire artifact is caused by:

Answer 39

Interference of aliased signals at different phases

Question 40

The Food and Drug Administration (FDA) set static magnetic field clinical use limits of _________ for the entire population and __________ for those over 1 month of age.

Answer 40

4 Tesla; 8 Tesla

Question 41

Fine line or FID crushing artifacts are corrected through

Answer 41

Parallel imaging

Due to the gradient echo-based coil calibration scan required to perform parallel imaging acceleration techniques, this option should be avoided in metal artifact reduction sequences.

Question 42

Magnetic resonance imaging (MRI) uses ________ separate magnetic fields to perform the task of routine image acquisition.

Answer 42

Gauss

Gauss is the term used to measure the magnetic field strength in the periphery of the MRI scan room, whereas Tesla measures magnetic field strength in isocenter

Question 43

The __________ magnetic field poses risks to patients and staff, due to the torpedo effect when a ferromagnetic object becomes magnetized and attracts to the large magnet

Answer 43

main static

The main static magnetic field poses risks to patients and staff, due to the torpedo effect when a ferromagnetic object becomes magnetized and attracts to the large magnet

Question 44

What is the term used to describe gradient field interactions as visual light flashes, or “seeing stars”?

Answer 44

magnetophosphenes

Question 45

Which gradient is primarily responsible for performing the function of determining slice thickness, scan plane and orientation of a pulse sequence?

Answer 45

slice select gradient

The slice select gradient is primarily responsible for performing the function of determining slice thickness, scan plane and orientation of a pulse sequence

Question 46

All of the following are potential risk factors for SAR thermal absorption during an MR pulse sequence EXCEPT:

Answer 46

Dielectric effects

Dielectric effects are caused by local eddy currents due to the increased conductivity of body tissue, and are identified by areas of shading or signal loss.

Question 47

Primarily stemming from active RF coil channels or elements outside the scanning field of view, ______________ artifacts can be corrected by simply de-selecting the element(s) outside the scanning range.

Answer 47

Annefact

Primarily stemming from active RF coil channels or elements outside the scanning field of view, annefact ribbon like artifacts can be corrected by simply de-selecting the element(s) outside the scanning range

Question 48

A _____________ artifact occurs when a tendon or ligament is positioned approximately 55° to the direction of the main magnetic field, and a short TE value pulse sequence is utilized

Answer 48

Magic angle