Detector characteristics of CCDs for high resolution gamma ray imaging

We are developing a high resolution gamma ray imager for use in Nuclear Medicine at energies up to /spl sim/150 keV. The imager is based upon a charge coupled device (CCD) coated with a polycrystalline scintillator to improve the detection efficiency. Three CCDs from E2V Ltd, bearing 100 /spl mu/m, 300 /spl mu/m and 500 /spl mu/m layers of Gd/sub 2/O/sub 2/S(Tb) (GADOX) have been tested. These CCDs have a pixel size of 44 /spl mu/m. The modulation transfer function (MTF) and relative detection efficiency of the CCDs have been measured using a /sup 241/Am (59.5 keV) source. The MTFs were estimated using the edge spread response function (ESRF) to derive the line spread function (LSF). The measurements show that significant improvements in detector efficiency, together with minimal loss of spatial resolution, follow from the use of a CCD with a 500 /spl mu/m thick GADOX scintillator rather than the standard 100 /spl mu/m scintillator thickness. The 500 /spl mu/m GADOX coated CCD thus has highly promising characteristics for use in a small, high resolution gamma ray imager.