Calibration and characterization of the LBNL positron emission mammography camera

This research project is about developing a novel positron emission tomographic (PET) camera that is specially designed for breast cancer detection. The camera is designed to increase system sensitivity and uniformity of spatial resolution. PET cameras have a potential of imaging breast cancers in the early stage and determining nodal involvement with less than 10% false negative or false positive rates. To optimize the system sensitivity, the camera uses long scintillation crystals to increase the detectability of the annihilation gamma photons and is oriented in a rectangular geometry to be in close proximity to the breast for higher solid angle coverage. However, the long scintillation crystals and the rectangular geometry worsen the penetration effect, which deteriorates the image quality because of the parallax error from the incorrect assignments of the lines of response (LOR). To address this problem, a novel PET detector module with depth of interaction measurement capability developed by others was incorporated in the design. This capability of measuring depth of interaction on an event-to-event basis corrects the ill-assigned LOP, restoring the image quality. Each LBNL positron emission mammography (PEM) detector module consists of an 8 x 8 array of 3 x 3 x 30 mm3 Lutetium Oxyorthosilicate (LSO) crystals coupled on one end to a single photomultiplier tube (PMT) and on the other end to an 8 x 8 silicon photodiode array (PD). The PMT provides accurate timing, the PD identifies the crystal of interaction, the sum of the PMT and PD signals (PD+PMT) provides the total energy, and the ratio Gamma = PD/(PD+PMT) determines the depth of interaction.; This research project has three parts: (1) the integration of the electronic system of the LBNL PEM camera between the hardware, firmware, and software; (2) the development of the in situ calibration and optimization algorithms for the novel LBNL PEM detector modules; and (3) the measurements of the camera performance.; At the time the LBNL PEM camera was designed, it included many innovations: (1) the first use of the combination of a photodiode array and a custom IC with low-noise charge sensitive amplifiers in a PET detector; (2) the first PET detector modules using light sharing for the DOI measurement; (3) the first PET system with realtime DOI measurements; and (4) the first PET system in a stationary rectangular geometry. To incorporate these innovations, several challenges have been overcome to complete a fully working camera.; For the performance measurements, the camera was set up as four detector banks to cover a rectangular patient port that is 8.2 x 6 cm2 with a 5 cm axial extent using 24 detector modules. The performance of the camera was evaluated by imaging various phantoms. The peak sensitivity of the camera was 1.83 kcps/muCi at the center of the FOV using a 6 ns coincidence timing window and a 300--750 keV energy window. With the same setup, The Noise equivalent count rate (NECR) peaks at 33.5 kcps for the mouse-like phantom with an activity concentration of 9.5 muCi/cc and at 18.1 kcps for the rat-like phantom with an activity concentration of 2.2 muCi/cc. For the breast-like phantom, a peak NECR was achieved at 13.5 kcps with an activity concentration of 2.1 muCi/cc. The image quality of the camera was evaluated by imaging a miniature Derenzo phantom. Even though the phantom was imaged with hot spots in close proximity to the detector banks, no radial elongation effect was observed due to the camera's capability of measuring DOI on an event-to-event basis. The phantom region with hot spots that have 2.4 mm edge-to-edge separation is clearly resolved. (Abstract shortened by UMI.)...