One of solutions to develop an energy resolved X-ray imager with sub-100μm pixel pitch is introduced. It consists of a small readout circuit and a data compressor in pixel. To realize spectroscopic readout circuit, charge counting architecture is adopted. And it equips time independence by removing transient response in analog signal processing and detector independence by controllability of time of signal processing for one pulse. An LSI implementing this system has been developed with 0.18um CMOS process. The pixel pitch is 80um and each pixel has 15 energy thresholds. The behavior of readout X-ray photon’s energy and data compression for photon-counting imaging has been verified by using CdTe detector. Furthermore, supporting other detectors such as TlBr and other energy weighting function than photon-counting are progressing.
X-ray imaging is popular in medical imaging, non-destructive testing and security. Main techniques of X-ray imaging with semiconductor detectors are charge accumulation and photon counting, and the photon counting is expected to identify materials at the same time with taking X-ray photograph by using energy information of X-ray photons. We proposed a direct charge handling method to build a photon counting system with energy information for X-ray imaging. This method operates the charge from the X-ray detector and converts it to encoded digital bit pattern directly without dead time of the front-end circuit. We simulated and built a proposed system to prove operating principals.
Recently, the photon counting X-ray imaging / CT systems have been researched and investigated as a next generation imaging system. CdTe has high attenuation coefficient at hard X-ray (100keV<) for medical imaging system, and photon counting signal processing has very high sensitivity in theoretic. We have demonstrated the photon counting X-ray imaging / CT system by CdTe detectors. The high-contrasted CT images of acryl phantom were taken by this system. In this case, very low power X-ray source (150kV, 1.8uA) was used. CT images could not be reconstructed at low exposure condition less than 9.0uAs in this protocol using traditional CdTe detector, but we could obtain good images by using photon counting CdTe detector even if the very low exposure of 1.8uAs. Photon-counting CT is very powerful technique for low exposure X-ray imaging / CT system.