Quantitative evaluation of metal artifact reduction techniques

Purpose: To develop a technique to quantify artifact, and to use it to compare the effectiveness of several approaches to metal artifact reduction. including view angle tilting and increasing the slice select and image bandwidths (BWs), in terms of metal artifact reduction. noise, and blur. Materials and Methods: Nonmetallic replicas of two metal implants (stainless steel and titanium/chromium-cobalt femoral prostheses) were fabricated from wax, and MR images were obtained of each component immersed in water. The differences between the images of each metal prosthesis and its wax counterpart were measured. The contributions from noise and blur were isolated, resulting in a measure of the metal artifact. Several off-resonance artifact reduction techniques were assessed in terms of metal artifact reduction capability. as well as signal to noise ratio and blur. Results: Increasing the image BW from +/-16 kHz to +/-64 kHz was found to reduce the artifact by an average of 60%, while employing view angle tilting (VAT) alone was found to reduce the artifact by an average of 63%. The metal artifact reduction sequence (MARS). which combines several susceptibility artifact reduction techniques, resulted in the least amount of image distortion, reducing the artifact by an average of 79%. Conclusion: The results indicate that while VAT alone (with an image BW of +/-16 kHz) resulted in the smallest amount of total energy and no reduction in the signal-to-noise ratio compared to a conventional spin-echo pulse sequence. MARS resulted in significantly less artifact and dramatically less blur.