Optimization of the acquisition parameters for a SPET system dedicated to breast imaging Nico Lanconelli, Renato Campanini, Emiro Iampieri, Roberto Pani, Member, IEEE, Maria Nerina Cinti, Paolo Bennati, Nicola Belcari, Manuela Camarda, Luigi Spontoni, Sara Vecchio, Paolo Randaccio, Paolo Russo, Member, IEEE, and Alberto Del Guerra, Senior Member, IEEE Abstract–This work is developed within the framework of a larger project, which aims to develop a multimodal CT-SPET system dedicated to breast imaging. The goal of this paper is to optimize the choice of the various parameters involved in the design of a SPET system dedicated to breast imaging. In particular, we simulated different collimators, different tumor to background (T/B) ratios for two different spherical tumors with diameters of 5 mm and 8 mm. The performance of the explored cameras were analyzed in terms of SNR and image contrast (IC) values, calculated on the reconstructed images. In addition, we investigated the visibility limits of the system, by modifying the tumor size, the T/B value, and the diameter of the breast phantom (8 cm, 10 cm, and 13 cm). As a general tendency, we found out that a high-resolution camera is preferable, in terms of image contrast. On the other hand, the General Purpose collimator seems to give a smoother image, giving rise to SNR values comparable to those obtained with the High-Resolution collimator, even with a reduced contrast. High-sensitivity collimators seem to give a worse response on the reconstructed images. The 8 mm tumor is clearly visible for all the simulated conditions, even if it could be very close to the visibility limit for the High-Sensitivity collimator. The 5 mm tumor is close to the visibility limit for General Purpose and High-Resolution collimators, for a T/B ratio equal to 10:1 and is not visible with High-Sensitivity collimator. The smaller tumor is almost obscured by the background with the thickest breast (13 cm diameter). I. INTRODUCTION he use of Monte Carlo simulation techniques is widespread in the development of Nuclear Medicine apparatus. In particular, simulations can be very useful for optimizing the design of the camera in SPET studies. Simulations provide an effective way to test several acquisition conditions, before performing experimental measurements. This work is developed within the framework of a larger project, which Manuscript received November 17, 2006. This work is developed within the framework of the PRIN2004 Italian project: “New Techniques for Breast Cancer Imaging”. N. Lanconelli, R. Campanini, and E. Iampieri are with the University of Bologna, and INFN-Bologna, Viale Berti-Pichat 6/2, I-40127 Bologna, Italy (e-mail: nico.lanconelli @bo.infn.it). R. Pani, M.N. Cinti, and P. Bennati are with Dipartimento di Medicina Sperimentale, Università La Sapienza, Rome, Italy. P. Randaccio is with Dipartimento di Fisica, Università di Cagliari, Cagliari, Italy. P. Russo is with Dipartimento di Scienze Fisiche, Università Federico II, Naples, Italy. N. Belcari, M. Camarda, L. Spontoni, S. Vecchio, and A. Del Guerra are with Dipartimento di Fisica, Università di Pisa, Pisa, Italy. aims to develop a multimodal CT-SPET system dedicated to breast imaging. The goal of this paper is to optimize the choice of the various parameters involved in the design of a SPET system dedicated to breast imaging. In particular, we simulated different collimators, different tumor to background (T/B) ratios for two different spherical tumors. The performance of the explored cameras are analyzed in terms of SNR and image contrast (IC) values, calculated on the reconstructed images. In addition, we investigated the visibility limits of the system, by modifying the tumor size, the T/B value, and the diameter of the breast phantom. II. METHODS For simulating the entire system (detector and breast phantom), we used EGSnrc, the latest version of the Monte Carlo EGS code family. Simulations included all the physical processes available with EGS, such as Compton and Rayleigh scattering and photoelectric absorption with emission of either fluorescence photons or Auger electrons. We fixed the lower cut-off energy at 5 keV for photons; on the contrary, we neglected electron transport by assuming that an electron deposits all its energy in its point of interaction. In order to further reduce the computational time, we adopted a modular geometric description for the collimator and the pixellated detector [1]. This code has already been validated for simulating various systems dedicated to breast imaging [2,3]. The simulated breast phantom consisted of a varying diameter cylinder (with 8 cm, 10 cm, and 13 cm diameter) made of breast-equivalent tissue. In order to emulate a clinical examination, we calculated the number of simulated photons for a total imaging time of 20 min and a background activity of 100 nCi/cc. We simulated two different spherical tumors (5 mm and 8 mm diameter), located at the center of the cylindrical phantom (6.5 cm from the collimator). We simulated different T/B values (5:1, 10:1; and 15:1). The simulated camera included a lead parallel collimator with hexagonal holes in hexagonal lattice, and a NaI(Tl) pixellated detector. We simulated three different collimators: a High Sensitivity (HS), a High Resolution (HR) and a General Purpose (GP) parallel collimator. The main features of these collimators are described in Table 1. T 2006 IEEE Nuclear Science Symposium Conference Record M14-18 1-4244-0561-0/06/$20.00 ©2006 IEEE. 2959 Authorized licensed use limited to: UNIVERSITA PISA S ANNA. Downloaded on November 21, 2008 at 03:34 from IEEE Xplore. Restrictions apply.