Development of Solid-State Detector for X-ray Computed Tomography

Solid-state detector has recently been used for x-ray Computed Tomography (CT) because it has high light conversion efficiency, quantum efficiency and compact size, compared with Xenon gas detector. In order to reduce radiation dose to the patient in medical x-ray CT, it should be needed to maximize the quantum efficiency and signal-tonoise ratio (SNR) of the detector. In this study, 16-channel detector array consisting of a CdWO4 scintillator, glued onto a p-i-n photodiode has been prepared as a sample CT detector. We investigated overall detector sensitivity with respect to variation of the p-layer thickness because the p-layer mainly restricts the signal-to-noise performance of the detector by increasing the leakage current and decreasing the light photon signal from the scintillator as its thickness increases. From the measurement, we obtained a reasonable dynamic signal response as a function of the incident x-ray magnitude. However, comparing with a reference detector (Analogic cooperation), about 2.5 times lower signal magnitude was achieved even with < 2 μm thickness of the p-layer, which is probably due to the quality of the layer made by the diffusion process.