Design and evaluation of an LSO PET detector for breast cancer imaging

Functional imaging with positron emission tomography (PET) may be a promising technique in conjunction with x-ray mammography for breast cancer patient management. Conventional whole body PET scanners provide metabolic images of breast cancer patients with several shortcomings related to the general-purpose nature of these systems. In whole body scanners, the detectors are typically 20-30 cm away from the breast or axilla, reducing sensitivity, and these scanners have relatively large detector elements (> 4 mm), limiting spatial resolution. Dedicated PET systems for breast imaging aim to overcome these limitations and improve the overall diagnostic quality of the images by bringing the detectors closer to the area to be imaged, thereby improving sensitivity, and by using smaller detector elements to improve the spatial resolution. We have designed and developed a modular PET detector that is composed of a 9x9 array of 3x3x20 mm3 lutetium oxyorthosilicate (LSO) scintillator crystals coupled to an optical fiber taper, which in turn is coupled to a Hamamatsu R5900-C8 position-sensitive photomultiplier tube. These detectors can be tiled together without gaps to construct large area detector arrays to form a dedicated PET breast cancer imaging system. Two complete detector modules have been built and tested. All detector elements are clearly visualized upon flood irradiation of the module. The intrinsic spatial resolution (full-width at half-maximum) was measured to be 2.26 mm (range 1.8-2.6 mm). The average energy resolution was 19.5% (range 17%-24%) at 511 keV. The coincidence time resolution was measured to be 2.4 ns. The detector efficiency for 511 keV gamma rays was 53% using a 350 keV energy threshold. These promising results support the feasibility of developing a high resolution, high sensitivity dedicated PET scanner for breast cancer applications.