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 charge-coupled device (EMCCD) coupled to a columnar CsI(Tl) scintillator. The EMCCD is suitable for photon-counting gamma-camera imaging, since it has an extremely low readout noise, even at high frame rates (<1 electron/pixel at 50 images/s or 11 Mpixel/s). The high frame rate prevents overlapping of scintillation events and reduces the accumulation of dark current noise. In this paper, we describe the drive- and readout electronics of the EMCCD, the image processing hardware and software, and the first ultra-high-resolution gamma-ray images obtained with the UGC. A digital signal processor (DSP) facilitates real-time frame analysis, comprising photon counting and energy discrimination, and reduces the data stream from 162 kB per frame to 8 B per detected scintillation event (i.e., for a typical application in multipinhole single photon emission computed tomography (SPECT) a data reduction from 28 GB/h by a factor of 20 000 to 1.4 MB/h). 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 as good as 60 /spl mu/m full-width of half-maximum (FWHM) are shown. The prototype UGC allows for photon counting without the need for an image intensifier and has energy discriminating capabilities.