Abstract--We describe the development of a scintillator-coated Charge Coupled Device (CCD) based camera for imaging small volumes of radionuclide uptake in tissues. The High Resolution Gamma Imager (HRGI) is a collimated, scintillator-coated, low cost, high performance imager using low noise CCDs. The HRGI operates in photon counting mode using a peltier cooler to achieve an operating temperature of 0°C. We have measured the spatial resolution and efficiency of a prototype CCD from e2v Technologies Ltd coated with a 500 μm thick Gadox (Gd2O2S(Tb)) layer using 59.5 keV radiation from a 241 Am source and 140 keV gamma-rays from a 99m Tc source. We also describe our first images using 99m Tc phantoms I. INTRODUCTION ommercially available gamma cameras designed for whole body imaging are large and expensive. A standard gamma camera has an intrinsic spatial resolution of ~ 4 mm but a system resolution in the order of ~6 - 10 mm after the necessary collimator is taken into account [1]. There is an increasing demand for small, dedicated gamma cameras that offer higher spatial resolution at reasonable cost. Such cameras would be very useful for imaging sentinel nodes, small organs such as the eye and thyroid and would also find application in radio-guided surgery. Recent reports in the literature reflect the drive towards small, high resolution detectors within the research community [2]-[6]. An earlier report presented measurements on a small un- collimated imager using dental CCDs, operated at room temperature [7]. That report concluded that to realize the goal of a gamma camera for clinical use the following requirements needed to be addressed: J. E. Lees, D. Bassford and G. W. Fraser are with the Space Research Centre, Physics and Astronomy Department, University of Leicester, Leicester, LE1 7RH, UK (telephone +44 116 252 5519, e-mail lee@star.lee.ac.uk) D. Monk and M. Early are with the Department of Medical Physics, Leicester Royal Infirmary, Leicester, LE1 5WW R. J. Ott is with the Institute of Cancer Research & Royal Marsden Hospital Downs Rd, Sutton, Surrey. SM2 5PT UK I. Moody is with e2v Technologies Ltd, 106 Waterhouse Lane, Chelmsford, Essex, CM1 2QU, UK A. C. Perkins and E. Blackshaw are with the Department of Medical Physics, Queens Medical Centre, University of Nottingham, Nottingham, UK * Corresponding author. Tel.: +44 (0)116 252 5519; fax: +44 (0)116 252 2464; e-mail: lee@star.le.ac.uk. • Operation of the CCD in photon-counting mode in order to provide pulse height resolution for scatter rejection and maximum sensitivity for low-activity emitting regions • Reduction of CCD read noise from the ~ 150 electrons rms typical of current dental CCDs to the < 10 electrons representative of CCDs used for direct X-ray detection in astronomy • Cooling of the CCD to reduce the dark current. • Design of a collimator that achieves sub-mm spatial resolution without unduly compromising sensitivity In this paper we report our progress on achieving these requirements and describe our prototype camera: the High Resolution Gamma Imager (HRGI). II. CAMERA DESCIPTION The HRGI operates in photon counting mode and uses a peltier cooler to lower the CCD operating temperature to 0°C reducing the dark current by approximately 10 times from its room temperature value. A Pb collimator is used to allow imaging of extended gamma-ray sources. Figure 1 shows the HRGI enclosed in a protective plastic box. Fig. 1. The High resolution Gamma Imager with the high resolution collimator attached Investigation of scintillator coated CCDs for medical imaging John E. Lees, * David Bassford, George W. Fraser, David Monk, Michael Early, Robert J. Ott, Ian Moody, Elaine Blackshaw and Alan C. Perkins C 0-7803-8701-5/04/$20.00 (C) 2004 IEEE