Gallium arsenide pixel detectors for medical imaging

Gallium arsenide pixel detectors processed on a 200 mu m Semi-Insulating (SI) Hitachi substrate were bump-bended to the Omega3 electronics developed at CERN for high energy physics [1]. The pixel dimensions are 50 mu m x 500 mu m for a total of 2048 cells and an active area of similar to 0.5 cm(2). Our aim is to use this system for medical imaging. We report the results obtained after irradiation of the detector with different X-ray sources on phantoms with different contrasts. The system showed good sensitivity to X-rays from Am-241 (60 keV) and Cd-109 (22.1 keV). It is also sensitive to p-particles from Sr-90 as well as from P-32 which is used as a tracer for autoradiography applications. The inherent high absorption efficiency of GaAs associated with the self-triggering capabilities of the pixel readout system reduced considerably the acquisition time compared with traditional systems based on silicon or emulsions. The present configuration is not optimised for X-ray imaging. The reduction of the pixel dimensions to 200 mu m x 200 mu m together with the integration of a counter in the pixel electronics would make the detector competitive for applications like mammography or dental radiology. For certain applications in biochemistry, such as DNA sequencing, where good spatial resolution is required only in one direction, the present setup should allow the best spatial resolution available up to now with respect to other digital autoradiographic systems. DNA sequencing tests are now under way