Low-dose low-scattering X-ray computed tomography with high-spatial-energy resolutions using a cooled cadmium telluride detector

Abstract

To improve the image quality of photon-counting energy-dispersive X-ray computed tomography (CT) and to reduce the incident dose for the object, we have developed a low-dose low-scattering CT scanner with high-spatial and -energy resolutions using a cooled cadmium telluride (CdTe) detector. X-ray photons are absorbed by the CdTe crystal, and the event pulses from the shaping amplifier are input to a high-speed triple-energy (TE) counter. In the TE-CT, four 3.0-mm-thick lead (Pb) pinholes are used. The line-beam diameter is roughly reduced using the first 2.0-mm-diam pinhole. Using the second 0.5-mm-diam pinhole, the line-beam diameter is reduced again, and the 0.5-mm-diam line beam is exposed to the object. The scattering photon count was reduced using the third 0.5-mm-diam pinhole, and the only penetrating photons are absorbed by the cooled CdTe crystal through the fourth 0.3-mm-diam pinhole for improving the spatial resolution. K-edge tomograms using iodine (I) and gadolinium (Gd) media were obtained simultaneously at two energy ranges of 33–50 and 50–100 keV, respectively. Utilizing I-K-edge CT, coronary arteries filled with I medium were visible. Next, blood vessels filled with Gd medium were observed at high contrasts using Gd-K-edge CT. The maximum count rate was 30 kilocounts per second (kcps) at a tube current of 0.33 mA, and the minimum count rate after penetrating objects was approximately 2 kcps. The maximum incident dose for the object was approximately 0.3 mGy, and the exposure time for TE-CT was 19.6 min at a total rotation angle of 360°. The energy resolution of the detector was 1.1% at 59.5 keV, and the spatial resolutions had values of 0.3 × 0.3 mm2.