17 Questions
What is the primary cause of zipper artifacts in MRI images?
External RF entering the scanning room
What is the orientation of zipper artifacts caused by RF from radio transmitters?
Perpendicular to the frequency axis of the image
What should be done with system-generated artifacts?
Report them to the service engineer
What can cause streak artifacts in MRI images?
Leaking RF signals
What type of artifact is caused by external RF entering the scanning room?
Zipper artifact
What is the optimal combination for cervical and thoracic imaging?
Combination of 'Gating' and flow compensation
What is the cause of the point artifact in MRI images?
Constant offset of DC voltage in the receiver coil
What is the result of slices not being parallel in multiangle, multislice acquisitions in the lumbar spine?
A band of signal loss crossing horizontally or vertically in the image
What is the term used to describe the ability of a tissue to be magnetized?
Susceptibility
Where are tissue-air interphases related artifacts commonly seen?
Around the paranasal sinuses and the lungs
What is the result of the presence of paramagnetic material like hemoglobin degradation products in MRI images?
Reduction in the quality of the local field
What is the primary cause of chemical shift artifacts?
Different precessional frequencies of protons in water and fat
What is the result of the phase of the signal just outside of the field of view?
Wrap around artifact
What type of artifact occurs when the diameter of the scanned area is greater than the dimensions of the field of view used?
Wrap around or aliasing artifact
What is the primary method to rectify artifacts?
Identifying and understanding the causes of artifacts
What type of artifact can simulate pathology that does not exist?
Any type of artifact
What type of artifact is related to the random fluctuation of intensity due to noise?
Noise artifact
Study Notes
MRI Artifacts
- Combination of 'Gating' and flow compensation is optimal for cervical and thoracic imaging.
Point Artifact
- Appears as a bright spot of increased signal intensity in the center of the image.
- Caused by constant offset of DC voltage in the receiver coil.
Slice Overlap Artifact
- Characterized by loss of signal in an image from multiangle, multislice acquisitions.
- Occurs when slices obtained at different disk spaces are not parallel.
- Causes a band of signal loss crossing horizontally or vertically in the image, usually prominent posteriorly.
Susceptibility Artifacts
- Caused by local variations in susceptibility due to presence of paramagnetic material like hemoglobin degradation products or tissue-air interphases.
- Results in reduction in the quality of the local field.
- Tissue air interphases related artifacts are commonly seen around the paranasal sinuses and the lungs.
- Can be removed by using spin echo sequences.
Zipper Artifacts
- Caused by external RF entering the room at a certain frequency and interfering with the inherently weak signal coming from the patient.
- Can be caused by RF entering the scanning room when the door is open during acquisition of images.
- RF from radio transmitters will cause zipper artifacts that are oriented perpendicular to the frequency axis of the image.
Classification of Artifacts
- Artifacts can be classified into different categories, including:
- Aliasing
- Chemical shift
- Gibbs/truncation
- Magic angle
- Motion
- Point
- Slice overlap
- Susceptibility
- Zipper
- Array processing
- Col selection
- Wrap Around/Aliasing
Wrap Around/Aliasing Artifact
- Appears when the diameter of the scanned area is greater than the dimensions of the field of view used.
- A part of the image is folded on itself.
- Remedies include:
- Increasing FOV
- Filtering the frequency encoded direction
- Oversampling in the phase encoded direction
Chemical Shift Artifacts
- Appear at the interfaces between water and fat because the precessional frequency of protons is slightly different in these two substances.
- Lead to misregistration of the signals.
This quiz covers the causes and removal of susceptibility artifacts in MRI images, as well as zipper artifacts caused by external RF interference and hardware/software problems.
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