Electronics for a photon-counting gamma camera based on an electron-multiplying CCD

We have developed a compact ultra-high resolution gamma camera (UGC), based on an Electron-multiplying CCD (EMCCD). The EMCCD can be used for photon-counting gamma-camera imaging, since it has an extremely low readout noise even at high readout rates (>1 electron/pixel at 50 images/s or 11.1 Mpixel/s). The high frame rate facilitates the analysis of individual non-overlapping scintillation events with minimal accumulation of dark current noise. In this article we describe the drive- and readout electronics of the EMCCD, and the image processing hardware and software. A digital signal processor (DSP) facilitates realtime frame analysis, comprising photon counting and energy discrimination, and reduces the data stream from 162 kB per frame to eight bytes per detected scintillation event (i.e. for a typical application in multi-pinhole SPECT a data reduction from 28 GByte/hour by a factor of 20,000 to 1.4 MByte/hour). Such a reduced data stream is needed for applications that require the use of a large number of gamma cameras simultaneously. The image processing hardware that we describe allows the images from the EMCCD to be processed in real-time, at a rate of 50 images per second. First gamma camera images with a spatial resolution better than 150 micrometers full width of half maximum (FWHM) are shown