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

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.