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

Functional imaging with positron emission tomography (PET) may be a promisi ng technique in conjunction with x-ray mammography for breast cancer patien t 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, a nd these scanners have relatively large detector elements (> 4 mm), limitin g spatial resolution. Dedicated PET systems for breast imaging aim to overc ome these limitations and improve the overall diagnostic quality of the ima ges by bringing the detectors closer to the area to be imaged, thereby impr oving sensitivity, and by using smaller detector elements to improve the sp atial resolution. We have designed and developed a modular PET detector tha t is composed of a 9x9 array of 3x3x20 mm(3) 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. T hese detectors can be tiled together without gaps to construct large area d etector arrays to form a dedicated PET breast cancer imaging system. Two co mplete detector modules have been built and tested. All detector elements a re clearly visualized upon flood irradiation of the module. The intrinsic s patial 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 t hreshold. These promising results support the feasibility of developing a h igh resolution, high sensitivity dedicated PET scanner for breast cancer ap plications. (C) 2000 American Association of Physicists in Medicine. [S0094 -2405(00)00407-7].