A new susceptibility-weighted image reconstruction method for the reduction of background phase artifacts. Magnetic Resonance in Medicine

Purpose: To significantly reduce the background phase effects, especially at the air–tissue interface, and to enhance the desirable local structures of veins in susceptibility-weighted imaging. Methods: In the proposed reconstruction method called Magnitude of Complex Filtering, a complex-valued magnetic resonance image is acquired using a flow-compensated high-resolution 3D gradient-echo sequence and the magnitude of the complex-valued image is set to 1 so that the phase information, which contains details of the local susceptibility, is emphasized. Then, the nonlinear filter of the Magnitude of Complex Filtering method is applied to the complex-valued image with a constant magnitude. This filter utilizes the magni-tude of the low-pass and high-pass filtered complex data to selectively reduce the background phase effects while enhancing the local structures. The filter output is then proc-essed to generate a susceptibility-weighted image. Results: Compared with the conventional susceptibility-weighted images generated by a homodyne high-pass filter, the susceptibility-weighted images from the proposed Magni-tude of Complex Filtering method show significant improve-ment; the undesirable artifacts at the air–tissue interface regions and the brain boundaries are significantly reduced, while the contrast of the local structures of veins is enhanced. Conclusion: The Magnitude of Complex Filtering method suc-cessfully reduced most background phase effects without requiring additional processing or scan time. Magn Reso