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A feasibility study of the 3D fluorescent image reconstruction for the simultaneous PET and fluorescent CT imaging system using depth of interaction PET detector

The simultaneous imaging system of PET and Fluorescent CT is being developed in the National Institute of Radiological Science in Japan. For the simultaneous system, we are considering using the DOI-PET detectors as simultaneous detectors of the gamma ray for PET and NIR light for fluorescence by changing the upper reflectors to the dichroic mirrors. Here, DOI-PET detector has very low spatial resolution to the NIR light compared to basically used CCD cameras. However, since the NIR light is scattered by biological tissues, it can be possible to reconstruct valuable image from the data which acquired from low resolution devices. In this study, we show feasibility for the Fluorescent CT imaging using the DOI-PET detector by computer simulations. In the simulations, we used a cubic phantom and square shaped detector geometry and a diffusion equation to approximate the light propagation. The system matrices of the Fluorescent CT geometries having different detector resolutions are calculated and we evaluated the singular values of the matrices. Using the system matrices, we simulated the image reconstruction from observed data which is generated by simulation and noise added. As a result, it is confirmed the reconstructed image from low resolution detectors is as same level as one from higher resolution detectors.