Artifacts Flashcards
DWI susceptibility artifacts in or around strong air tissue interfaces can be minimized by:
Increasing parallel imaging acceleration factor
All of the following artifacts except __________ occur along the phase encoding axis.
Chemical Shift
Motion is seen as a smearing across the image in the:
phase encoding direction
Magnetic susceptibility artifacts are more prominent with:
Gradient echo
A leak in the RF shielding can appear as
A zipper artifact in the frequency direction
A remedy for a Gibbs truncation artifact would be
Increase the number of phase encodings
A FID crushing artifact can be eliminated with the use of:
Increase in NEX and/or enabling Flow Compensation
Chemical shift artifact occurs because:
Fat and water precess at different frequencies
he ___________ to reduce chemical shift artifacts
Receiver bandwidth should be increased
Aliasing occurs because tissue outside the selected FOV is:
Undersampled
The ________ should be _______ to reduce chemical shift artifacts
Receiver bandwidth; increased
Which artifact mimics a syrinx in the spine?
Truncation
________ 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.
Aliasing artifact
In what anatomical region would you expect to see chemical misregistration the least?
Cerebellum
Which artifact occurs because of chemical misregistration?
Chemical shift
Which of the following influences can lead to artifacts?
Magnetic field inhomogeneity,
machine hardware,
the patient
In a sagittal cervical spine MRI, what could be done to compensate for CSF flow artifacts?
Enable gradient moment nulling
Which would yield more chemical shift artifacts?
3T superconducting magnet
Which of the following could lead to poor fat suppression?
Inhomogeneity
A decrease in the voxel volume yields:
A decrease in partial volume averaging
To reduce the appearance of a Gibbs truncation artifact, the
Number of phase encodings must be increased
To minimize cross talk artifact
Increase the interslice gap
Image 84 displays what type of artifact
Magnetic susceptibility
he arrows in Image 85 point to what kind of artifact?
Gibbs truncation
To correct for the artifact(white arrows) in Image 85:
Increase phase matrix
Image 86 is an example of which kind of artifact?
Magnetic susceptibility
Image 87 displays what kind of artifact?
Motion/ghosting in the phase direction
Image 88 displays what kind of artifact?
RF zipper
Image 89 displays what kind of artifact?
Wraparound (aliasing)
To correct for the artifact in Image 89
Utilize oversampling
Enable anti-aliasing option
Image 90 (white arrow) displays what kind of artifact?
Wraparound (aliasing)
To correct for the artifact in Image 90:
Increase FOV
When the TE is lowered:
Susceptibility artifact decreases
The arrows in Image 100 are pointing to which kind of artifact?
Cross talk artifact
The artifact in Image 100 is caused by:
The imperfect shape of RF slice profiles, which leads to an unintended excitation of an adjacent slice or tissue
One can correct for the artifact seen in Image 100 by:
Increasing interslice gap
Interleaved slice order
Acquiring stacks as complete packages
Letter A in Image 101 is pointing to what type of MR artifact?
Chemical shift
The artifact in Image 101 is caused by:
Differing frequencies of fat and water
To reduce an RF zipper artifact:
Close scan room door and ensure adequate door suction
Ensuring adequate door suction in the MR scan room will aid in preventing which artifacts from appearing in an MR image?
RF zipper
The arrows in Image 99 are pointing to what kind of artifact?
Moire
The artifact in Image 99 is caused by
Interference of aliased signals at different phases
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.
4 Tesla; 8 Tesla
To correct for the artifact shown in Image 172, the MRI technologist would
larger Field of View
reduced parallel imaging reduction factor
The red arrows in Image 172 are indicative of which type of MRI artifact?
Parallel Imaging
To correct for the artifact shown in Image 173, the MRI Technologist would:
increase in NSA/NEX
enabling Flow Compensation
The artifact identified by the orange arrows in Image 173 is a _____________ artifact.
FID crushing/ fine line
____________ techniques should be avoided in metal artifact reduction sequences, as they require a gradient echo-based coil calibration sequence prior to implementation.
Parallel imaging
Magnetic resonance imaging (MRI) uses ________ separate magnetic fields to perform the task of routine image acquisition.
three
What is the term used to measure the magnetic field strength in the periphery of the MRI scan room?
Gauss
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.
main static
What is the term used to describe gradient field interactions as visual light flashes, or “seeing stars”?
magnetophosphenes
Which gradient is primarily responsible for performing the function of determining slice thickness, scan plane and orientation of a pulse sequence?
slice select gradient
All of the following are potential risk factors for SAR thermal absorption during an MR pulse sequence EXCEPT:
Hypotension
______________ are caused by local eddy currents due to the increased conductivity of body tissue, and are identified by areas of shading or signal loss.
Dielectric effects
The yellow arrows in Image 201 display what type of MRI artifact?
Dielectric effects
The yellow arrows in Image 202 are pointing to which artifact
magic angle
The yellow arrows in Image 203 identify what artifact?
Annefact
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.
Annefact
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
Magic angle
