Metal artifact reduction sequence
Citation, DOI & article data
A metal artifact reduction sequence (MARS) is intended to reduce the size and intensity of susceptibility artifacts resulting from magnetic field distortion.
A variety of techniques are used for reducing metal artifacts at MRI, both for addressing artifacts due to the presence of metal in the image plane (in-plane artifacts) and for artifacts due to metal in an adjacent plane (through-plane artifacts).
In-plane artifact reduction
A number of simple changes to the scan protocol can greatly reduce artifacts. Examples are 1:
- lower magnetic field strength: 1.5 T rather than 3 T
- increase bandwidth during slice selection and readout
- increase matrix: 512 pixel
- maintain good signal to noise ratio by increasing number of excitations (NEX)
- spin echo instead of gradient echo where possible
- STIR for fat suppression (spectral frequency selective fat suppression performs better in a homogeneous field)
- shorter echo spacing
- smaller water-fat shift
- thinner slices
- view-angle-tilting (VAT)
Through-plane artifact reduction
Multiacquisition variable-resonance image combination (MAVRIC) is a specialized sequence designed by GE to minimize metallic artifact around metallic prostheses 3. It relies on 3D FSE sequences, using multiple different overlapping volumes at different frequency offsets.
Another technique developed by Siemens used for addressing through-plane metal artifacts is Slice-Encoding for Metal Artifact Correction (SEMAC), where an additional slice-encoding gradient is added to a standard fast-spin echo sequence 4. The combination of the MAVRIC and SEMAC technique is known as MAVRIC-SL 5.
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