Imaging of biological samples with silicon pixel detectors

Beta autoradiography is a well-established technique to measure the distribution of macromolecule concentration in biological samples. The potential of silicon pixel detectors for imaging tritium radio-labeled samples has already been demonstrated. In the following, a direct comparison between two general purpose sensors, MIMOSA5 and MEDIPIX2, characterized by complementary technologies and architectures is reported. The MIMOSA5 is a high-granularity monolithic CMOS active pixel detector with full analog output, while the MEDIPIX2 is a hybrid device with moderate granularity and a counting architecture. The comparison is based on two main figures: the effective activity and the dark counting rate. Tests were performed relying on tritium standards for autoradiography, with specific activities comparable to radio-labeled proteins in daily use. Different algorithms were developed and tested to discriminate against stochastic noise and cosmic rays. The results do confirm the advantage of real time granular sensors against films and phosphor imaging screens and set the basis for an optimized, customized development.