Real-time 3D motion tracking using MR micro-coils for PET imaging

Objectives Artifacts from both voluntary and involuntary head motion are major challenges to brain PET imaging. We investigated the feasibility of using MR micro-coils to track head motion and incorporate the MR-coil measured rigid motion fields in iterative PET reconstruction.

Methods We built MR tracking micro-coils (diameter < 5mm) that incorporate sealed doped water and built a dedicated MR sequence to measure the locations of the coils with 15ms temporal resolution. The micro-coils were attached to the surface of an 18F-filled Hoffman phantom. The rotation/translation complex motion pattern of the phantom was induced by a ventilator. PET list-mode and MR tracking data were acquired simultaneously on a PET-MR scanner. PET images were reconstructed using: 1) nMC: iterative PET reconstruction without motion correction; 2) MC: iterative PET reconstruction with the measured real-time rigid motion fields incorporated into the system matrix. Additionally, static phantom data were acquired and reconstructed as the static reference (SR). The contrast ratios were computed for two regions of interest (ROI).

Results Compared to nMC, the motion induced artifact is dramatically reduced in the images reconstructed with MC. The contrast ratios for the two ROIs were 2.6 and 4.4 for nMC, 4.4 and 5.5 for MC, and 4.8 and 5.2 for SR. The MC yielded similar results to SR.

Conclusions PET image quality can be significantly improved by incorporating the real-time 3D motion fields for arbitrary rigid motion measured by low-cost MR tracking micro-coils.

Research Support NIH: R21-EB012326, R01-CA165221