A low cost data acquisition system for small field of view gamma cameras

Abstract

We have developed a low cost data acquisition system to be used as the backend electronics for one of two small field-of-view gamma cameras. Both cameras are small field-of-view camera designs; however the objectives of each are very different. One design is that of an affordable PMT-based gamma camera, while the other is an MRI compatible APD- based camera.The data acquisition system is built around the robust Freescale 56F807 16-bit digital signal controller for a cost of about $15 per channel. The raw events are preprocessed using the Cremat charge sensitive preamplifier and a Cremat Gaussian shaping amplifier. Shaped pulses are held and triggered using an analog devices monolithic peak detector (PKD01). The DSP runs two dual, four-input ADCs capable of 12-bit resolution across a 3.28-volt range and is capable of performing a 16- channel conversion in 5.3 mus [1]. The total time dead time per 16 samples was measured at 7.5 mus, thus producing a theoretical maximum count rate of over 130,000 cps. The acquisition system was found to have a FWHM energy resolution of 1.1% when converting pulses of 2-volt peaks generated by a reference pulser coupled to the pulse shaper. The non-paralyzable, single channel acquisition system effectively collects events with minimal dead- time. Future work on this system will include the addition of 12 more channels to the system in order resolve two dimensional position information for both the PMT-based system and the APD-based system with a 4 x 4 detector array.