Question 1

A pulse sequence that demonstrates the least amount of magnetic susceptibility artifact:

Accepted Answer

Both spin echo and fast spin echo sequences.

We do not see magnetic susceptibility artifact in images which are collected using a 180° RF pulse to form the echo.

Question 2

Magnetic susceptibility, is a measure of the tendency of a material to become magnetized.

Accepted Answer

The artifact results in tissues with differing magnetic susceptibilities having different resident frequencies.

For this reason, it is a dephasing mechanism

Question 3

In which of the following directions may Aliasing occur with a 3-D volume acquisition:

Slice select direction, read out direction, phase encoding direction.

Accepted Answer

Occurs in 3D and 2D imaging when anatomy extends past the selected FOV.

In 3D imaging, it can also occur along the volume in the  slice direction. Signal maybe missmapped from the outer edges

Question 4

Scan time with no frequency wrap option applied is the same as the scan time if the no frequency wrap option is not applied

Accepted Answer

Sampling additional frequencies does not affect scan time. 

It is a "free" way of eliminating wraparound in the frequency encoding direction.

Question 5

We only correct for wraparound in the phase direction when necessary:

Additional phases increases scan time.

Accepted Answer

If a no phase wrap option is available, it may make other changes to the scan protocol (halving NSA) so that scan time is not effected.

Question 6

Spoiled gradient echo pulse sequences display effects of magnetic susceptibility

Accepted Answer

Any pulse sequence which does not utilize the 180° RF pulse to rephase the magnetization in the traverse plane may demonstrate the effects of magnetic susceptibility

Question 7

How can fat suppression act as a motion reduction technique?

Accepted Answer

Fat suppression reduces the signal from fatty tissues, and with a darker signal, the tissues will generate less motion artifact.

Question 8

Fat suppression is a technique which uses a spectrally selective saturation region to eliminate the signal from fat:

Accepted Answer

These fatty tissues, now rendered low in signal intensity, will generate less of a motion artifact.

Question 9

Metal artifacts in MR images appear as a local distortion of the signal in the image, for nonferrous metals.

Or is it severe distortion of the signal in the image in the case of Ferris metals

Accepted Answer

This can occur if the metal is within the selected FOV, or even if the metal is very near the selected FOV

Question 10

Transverse image through kidneys example:

The kidneys are a water-based tissue with little fat. They are however, surrounded by peri-renal fat.

Accepted Answer

Presenting an ideal location in the body for chemical shift artifact to occur.

There is shift of the kidneys relative to the peri-renal fat, along the frequency encoding direction of the image

Question 11

Chemical shift artifact results from a shift in the frequencies of fat-based protons relative to water-based protons.

Can be minimized by increasing the receiver bandwidth such that each pixel corresponds to a wider range of frequencies;

Accepted Answer

In this way, a given chemical shift will translate to fewer pixels of shift.

Note, reducing the matrix will not reduce chemical shift artifact. In fact, it will increase pixel size, and shift translated.

Question 12

Several ways to reduce the severity of flow related artifacts:

Utilizing gradient moment nulling to properly rephase the signal from flowing protons.

Saturation pulses to saturate the protons of  inflowing blood.

Accepted Answer

Physiological triggering and gating schemes.

Note, the use of a narrow receiver bandwidth will improve the SNR of the image and can make flow artifacts more pronounce.

Question 13

The dephasing effects of magnetic susceptibility are re-phased with a 180° RF pulse.

Therefore we do not see magnetic susceptibility artifacts in images which are collected using a 180° RF pulse to form the echo

Accepted Answer

It describes the tendency of a material to become magnetized

Question 14

Chemical shift artifact appear as a shift, or miss mapping, of signal along the frequency direction of the image.

Fat-based tissue shifts away from the water-based tissue, there is a signal void, thus, a dark pixel intensity

Accepted Answer

Where the fat-based tissues shift towards the water-based tissue, there is an addition of signal from overlapping tissue, and a bright pixel intensity results.

Question 15

The dark pixel intensity that results from a chemical shift artifact arises from:

Accepted Answer

A signal void which is caused by a signal miss-mapping along the frequency encoding direction of the image

Question 16

Signal fall off artifact

Accepted Answer

System related, occurs when using surface coils

Question 17

Aliasing artifact on volume images:

Some systems have automatic features to eliminate this artifact in the slice direction that automatically collects more slices the needed and then discard the extra slices containing the artifacts.

Accepted Answer

Ex: volume sagittal slice image, applied both no phase & the no frequency wrap option. slice. Wrap still occurs in volume/slice direction.

both no frequency/no phase wrap option selected: no wraparound at top, bottom, left or right side to the image

Question 18

Applying a no frequency wrap option will eliminate wraparound artifact from the top and bottom of a coronal knee image.

Application of no frequency wrap option will effectively eliminate the wraparound from the top and bottom of a coronal on the image

Accepted Answer

In coronal and sagittal imaging, increasing FOV is not an affective option for eliminating wraparound

 because there'll always be anatomy extending outside the FOV, along the long axis of the body

Question 19

We can eliminate aliasing artifact in the frequency encoding direction by:

Accepted Answer

Using the no frequency wrap option with no scan time penalty

Question 20

RF artifacts appear as a line orientated perpendicular to the frequency encoding direction of the image.

Aliasing artifact appears as miss mapping of signal from one side of the image to the opposite side.

Accepted Answer

Truncation artifact appears as a ringing of high contrast Borders in the image.

Metal artifact includes local distortion of the image and areas of signal void with associated bright signals

Question 21

Metal artifacts cannot be removed from the image without removing the offending metal from the patient.

There are no other ways to eliminate them, they however do increase in severity with gradient echo pulse sequences

Accepted Answer

Because gradient echo sequences do not utilize the 180° pulse to rephase the echo.

Therefore they're more susceptible to anything that causes local distortion in the magnetic field

Question 22

Three ways to eliminate aliasing artifact:

Increasing FOV, Saturation pulse, and utilizing no wrap option

Accepted Answer

No wrap option: 

sampling more frequencies or phases allows us to determine those signals emanating from outside FOV for elimination.

Question 23

Chemical shift artifact:

Results from how the resident frequencies form fat base protons and water-based protons differ.

Translating into positional differences in the image along the frequency encoding direction

Accepted Answer

We can minimize this shift in the image by utilizing a wider receiver bandwidth.

This way each pixel will represent a wider range of frequencies, and the chemical shift will translate into fewer pixels of shift

Question 24

Chemical shift artifact occurs at the interface of two tissues who's protons experience different resident frequencies

Accepted Answer

Magnetic susceptibility artifact occurs at the interface of two tissues that experience different magnetic susceptibilities

Question 25

Result of reducing slice thickness to reduce partial Voluming effects:

Decreased SNR, increased spatial resolution, decreased anatomical coverage with the same number of slices.

Accepted Answer

A thinner slice yields improve spatial resolution along a slice spacial direction.

Thinner slices will decrease the SNR, since fewer protons are contributing to the signal on each voxel.

Question 26

True regarding Truncation artifacts:

And apparent when a high contrast border falls within a single pixel, reduce by applying a raw data filter, reduced by using a high value for the image matrix:

Accepted Answer

Utilizing a raw data filter to minimize the chopping off of the side lobes of the echo.

Utilizing a larger matrix will reduce the likelihood of the sharp contrast border falling within one pixel, since the pixels are now smaller.

Question 27

Chemical shift artifact will appear in the:

Accepted Answer

Frequency encoding direction

12 ARTIFACTS

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