Monte Carlo Simulation Study of a Dual-Plate PET Camera Dedicated to Breast Cancer Imaging Jin Zhang, Member, IEEE, Peter D. Olcott, Member, IEEE, Angela M. K. Foudray, Student Member, IEEE, Garry Chinn, Member, IEEE, and Craig S. Levin, Member, IEEE Abstract– We studied the performance of a dual-plate positron emission tomography (PET) camera dedicated to breast cancer imaging using Monte Carlo simulation based on GATE open code software. The PET camera under development has two 10x15cm 2 plates that are constructed from arrays of 1x1x3mm 3 LSO crystals coupled to novel silicon-based ultra-thin (<300 μm) position-sensitive avalanche photodiodes (PSAPD). With the photodetector configured “edge-on”, incoming photons see effectively 2-cm-thick of LSO with directly measured 3-mm photon depth-of-interaction. Simulations predict that this camera will have >10% sensitivity, and detector measurements show ~ 1 mm 3 intrinsic spatial resolution, < 12% energy resolution, and ~2 ns coincidence time resolution. With a breast phantom including breast, heart and torso activity (concentration ratio of 1:10:1, respectively), count performance was studied under varying time and energy windows. We also studied visualization of hot spheres within the breast for 1x1x3mm 3 , 2x2x10mm 3 , 3x3x30mm 3 and 4x4x20mm 3 crystal resolutions at different plate separations. Images were reconstructed by focal plane tomography and 3D OS-EM with attenuation and solid angle corrections applied. With an activity concentration ratio of tumor:breast:heart:torso of 10:1:10:1, only the dual-plate PET camera comprising 1x1x3mm 3 crystals can resolve 2.5-mm tumor spheres with an average peak-to-valley ratio of 1.3 in only 30 seconds of acquisition time. I. INTRODUCTION ositron emission tomography (PET) is used for cancer imaging. However, for some dedicated applications such as breast cancer imaging, the traditional full-body PET system has several shortcomings in detection, diagnosis, and staging. In addition to a need for more suitable tracers, there is a need to optimize geometry for breast cancer imaging, reduce the relatively high cost of scanning, and to improve spatial and energy resolution. Scientists and engineers have developed a number of new, portable designs for PET cameras dedicated to breast cancer imaging in the last several years [1-5]. These designs are generally based on position sensitive photomultiplier tubes (PMT) and relatively large lutetium based scintillation crystals. For example, LSO crystal sizes of 3×3×20 mm 3 [4] and 3.1×3.1×10 mm 3 [5] have been studied with dedicated PET cameras. These camera systems have demonstrated limited spatial resolution of about 3.8 mm [4] and 2.3 mm [5] at the center. To improve performance, we are developing a dedicated breast cancer imaging PET camera based on smaller LSO crystals to achieve around 1 mm spatial resolution with high (>10%) sensitivity at the center of the field of view (FOV) and directly measured photon interaction depth capability. The camera will have a dual-panel, portable geometry and uses a novel thin (<300 μm) semiconductor- based position sensitive avalanche photodiode (PSAPD) from RMD Inc., Watertown, MA. The detector modules of this camera utilize the PSAPDs coupled to 3x8 arrays of 1×1×3 mm 3 LSO crystals, which gives 3 mm direct photon depth-of- interaction (DOI) resolution. Preliminary experimental results with standard PSAPD packaged on ceramic substrate have been reported [6]. We have also studied the new thin PSAPD performance [7] that will be used for the PET camera construction. This PET camera, with a FOV of 15x10 mm 2 with variable plate separation, is expected to achieve >10% sensitivity at the center of FOV, and ~1 mm 3 intrinsic spatial resolution, <12% energy resolution at 511 keV, and about 2 ns coincidence time resolution. These performance parameters were achieved using the new thin PSAPD devices [7]. Manuscript received November 4, 2005. This work was supported in part by R21 CA098691 from NIH-NCI. J. Zhang was with the Department of Radiology, Stanford University, Stanford, CA. He is now with PerkinElmer Optoelectronics, 2175 Mission College Blvd., Santa Clara, CA 95054, email: jin.zhang@perkinelmer.com. A.M.K. Foudray is with the Department of Radiology, Stanford University and the Department of Physics, University of California, San Diego, La Jolla, CA, USA (email: afoudray@stanford.edu). P. Olcott is with the Department of Radiology, Stanford University, Stanford, CA. 94305-5344, USA (email: pdo@stanford.edu). G. Chinn is with the Department of Radiology, Stanford University, Stanford, CA. 94305-5344, USA (email: gchinn@stanford.edu). C.S. Levin is with the Department of Radiology, Stanford University, Stanford, CA. 94305-5344, USA (email: cslevin@stanford.edu). In this paper, we present our Monte Carlo simulation results on sensitivity, count rate, and imaging properties of the dual- panel PET camera based on the <300-micron-thick PSAPD. We will also compare the imaging performance based on different LSO crystal size. Crystals with sizes of 2x2x10 mm 3 , 3x3x30 mm 3 with DOI of 10 mm, and 4x4x20 mm 3 have been simulated with the same dual-panel structure. Lesion visualization and contrast resolution of these LSO-PSAPD PET cameras have been compared. Focal plane tomography (FPT) and maximum-likelihood iterative method were used for the image reconstruction. II. MATERIALS AND METHODS We used GATE (Geant4 Application in Tomographic Emission) open source software to perform Monte Carlo simulations of the dual-plate PET camera shown in Fig. 1(a). This camera is constructed with the novel thin PSAPD coupled with 1x1x3 mm 3 LSO crystals shown in Fig. 1(b) and P 0-7803-9221-3/05/$20.00 ©2005 IEEE 2005 IEEE Nuclear Science Symposium Conference Record M03-190 1667 Authorized licensed use limited to: Stanford University. Downloaded on May 25,2010 at 17:44:09 UTC from IEEE Xplore. Restrictions apply.