Off-resonance suppression for multispectral MR imaging near metallic implants

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging (MRI)
• Image Processing

Background:

• Metal artifacts significantly degrade MRI quality, complicating diagnosis.
• Existing metal artifact reduction techniques like view angle tilting (VAT) and multispectral imaging (MSI) (SEMAC, MAVRIC) increase scan times.
• Through-plane aliasing is a challenge in MSI, particularly with larger anatomical regions or complex spectral content.

Purpose of the Study:

• To investigate the efficacy of off-resonance suppression (ORS) in multispectral imaging (MSI) for metal artifact reduction.
• To achieve clinically feasible MRI scan times without through-plane aliasing.
• To evaluate ORS-enhanced SEMAC (ORS-SEMAC) and MAVRIC (ORS-MAVRIC) for improved metal artifact correction.

Main Methods:

• Off-resonance suppression (ORS) was implemented in MSI techniques (SEMAC, MAVRIC) using differential gradient amplitudes for excitation and refocusing.
• ORS provides spatial-spectral selectivity, enabling reduced scan-time and flexible orientation.
• Comparisons were conducted using phantom and volunteer experiments, evaluating ORS-MSI against standard MSI.

Main Results:

• ORS-SEMAC and ORS-MAVRIC required fewer through-plane phase encoding steps than conventional MSI.
• Standard SEMAC and MAVRIC exhibited through-plane aliasing.
• ORS-SEMAC and ORS-MAVRIC successfully produced alias-free images within the same scan times as their non-ORS counterparts.

Conclusions:

• Off-resonance suppression (ORS) is effective for metal artifact reduction in MSI.
• ORS enables precise spatial-spectral region selection, crucial for artifact mitigation.
• This approach facilitates metal artifact reduction in MRI within clinically acceptable scan times, avoiding slice aliasing.