PET/MRI/VCT: Restoration of Virtual CT from Transmission Scan on PET/MRI Using Joint-Anisotropic Diffusion

CT is a mandatory imaging modality for radiation treatment planning (RTP) while MRI and PET have advantages in tumor delineation and dose prescriptions. To avoid multiple scanning and additional high radiation doses, this paper proposes to integrate low dose transmission scan (TX) into a PET/MRI machine for the synthesis of virtual CT (VCT) for treatment planning. TX is usually extremely noisy with artifact spots and it is necessary to smooth the sinogram to obtain interpretable images. However this results in blurred low resolution images. This study introduces a novel joint-anisotropic diffusion (JAD) method which restores VCT images without loss of resolution using additional anatomical images to regularize the filtering. Through reshaping the anisotropic diffusion tensor using MRI, this method guides the diffusion flux to favor the similarity between VCT and MRI leading to an increase of mutual information. For proof of concept, virtual PET/MRI/VCT system with conventional \(^{68}\)Ga ring source was implemented on GATE and realistic TX data were simulated and tested. The results demonstrate that the new approach improves the geometrical accuracy of VCT and provides a potential application for RTP.