Photon-counting X-ray computed tomography using a YAP(Ce)-PMT detector and beam hardening

摘要

To realize novel photon-counting energy-dispersive X-ray computed tomography (CT), we have developed a low-doseCT scanner using a detector consisting of a cerium-doped yttrium aluminum perovskite [YAP(Ce)] crystal and a smallphotomultiplier tube (PMT). X-ray photons are absorbed by the YAP(Ce) crystal, and negative outputs are produced fromthe PMT. The PMT outputs are amplified by an inverse voltage-to-voltage amplifier, and the event pulses are counted bythe counter with a low threshold energy of 20 keV. First, almost all the photons are counted without the photon-energydependence, since the scintillation-photon number produced by one X-ray photon is proportional to the photon energy.Second, the energy-dispersive imaging is performed using the self-beam hardening by the object. The maximum photoncount of the projection data is determined after the air absorption, and the effective photon energy increases withincreasing digital-amplification factor at the constant maximum count. In the triple-energy CT, the X-ray beam diameterwas 0.5 mm, and the spatial resolutions were approximately 0.3×0.3 mm2. The exposure time for DE-CT was 9.8 min ata total rotation angle of 180°.