Imaging performance of a DEPFET pixel Bioscope system in Tritium autoradiography

A Bioscope system based on a 64×64-matrix of DEPFET pixels has been developed for real-time digital autoradiography in biomedical applications. It provides very good energy and spatial resolution at the same time. The DEPFET pixel cells consist of p-channel JFETs integrated into the high-ohmic n-silicon substrate. This leads to a very low noise performance at room temperature. Two dedicated ASIC chips have been developed for steering and readout of the pixel matrix. The measured system noise of (69±4)e- at 35∘C is mostly due to sensor leakage current and can be largely reduced by cooling or a faster readout. The spatial resolution is examined by measurements with a laser as well as with a dedicated test chart and is determined to be (6.7±0.7)μm for 6 keV-X-rays and 4.3±0.8μm for 22 keV-X-rays. The measurements are compared to simulation results with different reconstruction algorithms. Due to the thin entrance window at the detector backside and the low noise performance, a detection of low-energy β-emitters such as 3H is possible. Measurements with 3H-labeled biological samples were taken. The ability of the DEPFET pixel Bioscope to separate different radiolabels in the same sample is demonstrated by a measurement with 3H and 14C.