WE‐D‐330A‐05: Voxel‐Based MicroCT‐MicroPET Image Registration for Molecular Imaging Study

Purpose: Registration of micro‐PET and micro‐CT images is important for the interpretation of multi‐modality images. Here we develop a voxel‐based image registration method to facilitate the co‐registration of multi‐modality imaging of small animals. Method: Rigid image registration (six degrees of freedom: three translational and three rotational parameters) was developed using an open‐source ITK/VTK platform for coregistering micro‐PET and micro‐CT data. Modules importing/exporting DICOM data (binary mask files of contours and image sets) and the scanner specific proprietary microPET/CT/MRI data were also developed. Automated registration procedures based on the normal cross‐correlation (NCC) metric and mutual information were implemented. To better “see” the bony landmarks in microPET, a strategy for enhancing the bone matrix uptake of radiotracer by adding a tracer amount of 18F during the FDG‐microPET imaging was investigated. The convergence behavior of the voxel‐based registration algorithms was analyzed and the global convergence of the calculation was demonstrated. The accuracy of the developed registration algorithm was assessed by measurements using dual‐modality external fiducial line sources incorporated into the mouse cradle. Results: A voxel‐based registration technique has been established for in vivo molecular imaging study. Application of the technique to a number of mice micro‐PET and micro‐CT registrations indicated that an accuracy of better than 0.2 mm is achievable with the help of 18F injection. Without lighting‐up of the bony structures, however, we found that it is difficult to obtain a registration better than 1mm for regular FDG‐microPET. Computationally, the setup based on the NCC metric performs better in comparison with the mutual information approach. Conclusion: A NCC metric coupled with the use of 18F injection allowed us to obtain sub‐millimeter accuracy in microPET‐microCT registration of mice. The robust registration procedure should be valuable for routine molecular imaging application.