Off-resonance suppression for multispectral MR imaging near metallic implants.
OBJECTIVE
Metal artifact reduction in MRI within clinically feasible scan-times without through-plane aliasing.


METHODS
Existing metal artifact reduction techniques include view angle tilting (VAT), which resolves in-plane distortions, and multispectral imaging (MSI) techniques, such as slice encoding for metal artifact correction (SEMAC) and multi-acquisition with variable resonances image combination (MAVRIC), that further reduce image distortions, but significantly increase scan-time. Scan-time depends on anatomy size and anticipated total spectral content of the signal. Signals outside the anticipated spatial region may cause through-plane back-folding. Off-resonance suppression (ORS), using different gradient amplitudes for excitation and refocusing, is proposed to provide well-defined spatial-spectral selectivity in MSI to allow scan-time reduction and flexibility of scan-orientation. Comparisons of MSI techniques with and without ORS were made in phantom and volunteer experiments.


RESULTS
Off-resonance suppressed SEMAC (ORS-SEMAC) and outer-region suppressed MAVRIC (ORS-MAVRIC) required limited through-plane phase encoding steps compared with original MSI. Whereas SEMAC (scan time: 5'46") and MAVRIC (4'12") suffered from through-plane aliasing, ORS-SEMAC and ORS-MAVRIC allowed alias-free imaging in the same scan-times.


CONCLUSIONS
ORS can be used in MSI to limit the selected spatial-spectral region and contribute to metal artifact reduction in clinically feasible scan-times while avoiding slice aliasing.
Medical Physics Department, Reinier de Graaf Groep, Delft, the Netherlands.
J Chiel
JC
den Harder
Technology Development Department, Philips Healthcare, Best, the Netherlands.
Gert H
GH
van Yperen
Imaging Systems Department, Philips Healthcare, Hamburg, Germany.
Ulrike A
UA
Blume
Imaging Division, University Medical Center Utrecht, Utrecht, the Netherlands.
Clemens
C
Bos
D000465:Algorithms; D016477:Artifacts; D006621:Hip Joint / Q000473:pathology* / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008670:Metals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D008670:Metals
MAVRIC; SEMAC; arthroplasty; magnetic resonance imaging; metal implants; multispectral imaging