A high resolution, monolithic crystal, PET/MRI detector with DOI positioning capability.

We report on a high resolution, monolithic crystal PET detector design that provides depth of interaction (DOI) positioning within the crystal and is compatible for operation in a MRI scanner to support multimodal anatomic and functional imaging. Our design utilizes a novel sensor on the entrance surface (SES) design combined with a maximum likelihood positioning algorithm. The sensor will be a two-dimensional array of micro-pixel avalanche photodiodes (MAPD). MAPDs are a new type of solid-state photodetector with Geiger mode operation that can provide signal gain similar to a photomltipiler tube (PMT). In addition, they can be operated in high magnetic fields to support PET/MR imaging. Utilizing a multi-step simulation process, we determined the intrinsic spatial resolution characteristics of a detector using the proposed design. For a 48.8 mm by 48.8 mm by 15 mm LSO crystal detector readout by an 8 by 8 array of 5.8 mm by 5.8 mm MAPD elements the intrinsic spatial resolution is 0.83 mm FWHM in X, 0.92 mm FWHM in Y and 1.83 mm FWHM in Z (i.e., DOI) for normally incident photons. Comparing the results versus using a conventional design with the photosensors on the backside of the crystal, an average improvement of 25% in X, 23% in Y, and 20% in Z is achieved.