metal artifact reduction sequence
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 :
- 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 . 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 . The combination of the MAVRIC and SEMAC technique is known as MAVRIC-SL .
See also
Siehe auch:
und weiter:
Assoziationen und Differentialdiagnosen zu Metallartefaktreduktion in der Magnetresonanztomographie:
