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.

I. Introduction

Compact high-resolution gamma cameras are very useful in applications like small animal pinhole single photon emission computed tomography (SPECT) imaging. With small detectors one can place many pinhole cameras around the object of investigation, resulting in a high counting sensitivity [1]–[9]. Other applications of compact gamma cameras include planar gamma camera imaging [10]–[12], radiation monitoring (e.g., [13]), tumor surgery [14], and autoradiography [15].