Preliminary study of a DOI-PET detector with optical imaging capability

Positron emission tomography (PET) and optical imaging are two major techniques for molecular imaging. The PET scanner which enables simultaneous detection of optical imaging will be a powerful tool in molecular imaging. Here, we propose a new detector that detects both signals: annihilation photons for PET and photons for optical imaging. It is based on a four layered depth-of-interaction (DOI) PET detector. Since the detector must be set at a close distance to an object for optical imaging, the DOI information becomes important to obtain uniform spatial resolution in PET imaging over the field-of-view. The proposed PET/optical imaging detector consists of a scintillation crystal block and a position sensitive photo multiplier tube (PS-PMT). While the bottom of the crystal block is optically coupled to the PS-PMT, four side surfaces of the crystal block are covered with reflectors. A dichroic mirror is placed on the top of the crystal block. The dichroic mirror allows fluorescence photons (longer wavelength than 600 nm) to pass through while it reflects scintillation photons (wavelength around 450 nm) generated within the crystal block. Owing to the dichroic mirror, both scintillation photons originating inside the crystal block and fluorescence photons coming from outside the block can be detected by the same PS-PMT. To evaluate of the DOI-PET/ optical detector, we first measured the influence of the dichroic mirror. The results show that the dichroic mirror maintains DOI-PET detector performance without significant loss of fluorescence photons for optical imaging.