Image‐quality improvement in pileup‐less cadmium‐telluride X‐ray computed tomography using a frequency‐voltage converter and its application to iodine imaging

抄録

To perform investigation of image‐quality improvement in photon‐counting energy‐dispersive X‐ray computed tomography（ED‐CT）under low count rates, we have developed an ED‐CT system using a frequency‐voltage converter（FVC）and a cadmium telluride detector. The FVC is used to improve the image granulation by compensating for the photon‐count fluctuation. In the ED‐CT, the photon energy range is regulated using a multichannel analyzer（MCA）by determining both the maximum and minimum energies. The FVC consists of a microcomputer, an integrator, and an operational amplifier. When 0.2‐μs‐width event logical pulses from the MCA are sent to the microcomputer, 5‐μs‐width 5.0‐V‐height logical pulses are produced from the microcomputer and sent to the integrator to produce the time‐average voltage which is proportional to the count rate. The integrator output is then amplified by the amplifier, and the FVC output is input to an analog‐digital converter. Pileup‐less CT was accomplished by repeated linear scans and rotation of the object at a tube voltage of 70 kV and a count rate of 1.9 kilo‐counts per second or below. We also performed the iodine K‐edge CT and the energy subtraction.