Development of Registration and Fusion Methods for the Jonasson Medical Imaging Center MiniPET-microCT

Abstract: Multimodal image registration is essential when combining functional and structural imaging modalities. Among the most common combinations, numerous methods have been developed for co-registration of CT and PET, typically validated on human size scanners. However, only a few registration studies have been performed for the combination of small animal miniPET and microCT imaging. The Jonasson Center for Medical Imaging at KTH possesses an integrated miniPET/ microCT for pre-clinical research purposes. The motivation for this work is the need for the development of fusion method(s) for combining the data of these two modalities. In this work, a novel pipeline registration method, employing image processing and Mutual Information (MI) is proposed and implemented. The method starts with a pre-alignment step before acquisition of the miniPET/microCT volumes, followed by scaling, binarization and processing of the two volumes and finally, a registration procedure by Maximization of Mutual Information (MIM) as a voxel-based similarity metric. A established intrinsic landmarks based method is also implemented for comparison. For the validation of the methods, volumes acquired by in-house designed 3D printed Polyethylene (PE) phantoms, filled with multiple concentrations of FDG were used. The misalignment between corresponding points volumes after registration, is analyzed and compared in terms of absolute spatial distance. The proposed method based on 3D processed volumes outperformed the Landmarks based registration method, showing average misalignments of 0.5 mm. The registered volumes were also successfully visualized together using Alpha blending. By so, an automatic fusion method for miniPET/microCT has thus been implemented, presented and evaluated, raising prospects for multimodal imaging research at the Jonasson Center for Medical Imaging.