Measurements on a novel 4-side buttable photon counting ASIC with integrating charge sharing correction

Photon counting detectors offer some unique features for x-ray imaging. If designed correctly, photon counting detectors have no readout noise and no dark counts. This is an important feature in for example low dose CT imaging where the total dose is distributed over a large number of projections from different angles. In addition to this it is also possible to incorporate pulse height discrimination of each photon event, thus enabling the recording of images from multiple energy intervals in a single exposure. We demonstrate the performance of a newly developed fast photon counting detector with six energy thresholds and 150µm pixel size that can be read out with up to 10000fps. It is a four side buttable device that is bump bonded to a CdTe converter. The very high conversion efficiency of CdTe makes the detector suitable for a wide range of applications requiring high spatial resolution at low doses. The efficiency of the detector is maintained all the way out to the edge of the chip which opens the possibility to build larger detectors still fulfilling medical requirements. The novel detector incorporates a charge sharing correction feature and the effect of this function is demonstrated using the DQE measurements as well as with spectrum reconstruction from Cd109 and Am241 radioactive sources. We show that this charge sharing correction feature affects the properties of NPS and MTF, and the energy resolution is greatly enhanced. Measurements are also compared to a simulation model for the detector system.