Characterization of a λ-ray detector based on square PSPMT array

Abstract

Although gamma cameras have emerged in the sixties, their spatial resolution is still not sufficient to detect small tracer concentration abnormalities. Examinations like mammo- scintigraphy requires high spatial resolution and then the possibility to position the detector as close to the explored organ as possible. Diagnostic accuracy in nuclear medicine imaging can know a notable advancement with the emergence of the new position sensitive photomultiplier tube (PSPMT). This component allows to develop a compact gamma detector which fulfils these requirements. This study investigates the feasibility and the characteristics of a medium field of view high spatial resolution gamma ray detector based on an array of R8520 PSPMT coupled to a pixelated NaI(Tl) crystal array. As first results, a photocathode uniformity variation of 1 to 3 was observed on the whole field of view. Energy resolution obtained is better than 10% FWHM at 140 keV in PSPMT centers. Concerning spatial linearity, it depends on the uniformity of the PSPMT used. Consequently, it will be necessary to develop linearity and energy correction methods. diameter. These results are better than those obtained with classical Anger gamma cameras (3). Due to its small size, it is well adapted to small organs exploration like thyroid and small animals (4). This research led to a technology transfer to ARIES company. The necessity of high spatial resolution mammoscintigraphy (5)-(6)-(7)-(8) for early and reliable detection of the breast cancer leads us to develop a new high performances gamma detector with a larger detection area. A new compact position sensitive photomultiplier tube, R8520-00-C12 (9), has been developed by HAMAMATSU. The interest of this new generation is its very low height (27 mm) which allows to build a very compact and relatively light gamma detector. Their square shape (25.7 mm x 25.7 mm) and their small dead edge (1.85 mm) authorize their juxtaposition in order to obtain a large detection area defined according to the diagnostic application. In this paper we investigate the feasibility and the characteristics of a medium field of view (MOV) high resolution gamma detector based on these PSPMTs and we present the first results concerning uniformity response, energy resolution and spatial linearity.