Edge-on illumination photon-counting for medical imaging

In medical X-ray Computed Tomography (CT) a silicon based sensor (300 mu m to 1000 mu m) in face-on configuration does not collect the incoming X-rays effectively because of their high energy (40-140keV). For example, only 2% of the incoming photons at 100keV are stopped by a 500 mu m thick silicon layer. To increase the efficiency, one possibility is to use materials with higher Z (e.g. GaAs, CZT), which have some drawbacks compared to silicon, such as short carrier lifetime or low mobility. Therefore, we investigate whether illuminating silicon edge-on instead of face-on is a solution. Aim of the project is to find and take advantage of the benefits of this new geometry when used for a pixel detector. In particular, we employ a silicon hybrid pixel detector, which is read out by a chip from the Medipix family. Its capabilities to be energy selective will be a notable advantage in energy resolved (spectral) X-ray CT.