Triple-sensitivity X-ray computed tomography using analog and digital amplifiers

To reconstruct three-energy tomograms simultaneously, we constructed a triple-sensitivity X-ray computed tomography (TS-CT) scanner to observe gradual variations in image contrast. The TS-CT scanner is a first-generation type using a room-temperature cadmium telluride (CdTe) detector with one analog and two digital amplifiers. Using a line beam,CT is performed by repeating the translation using the CdTe detector and rotation using a turntable. The CdTe detector,with a specific gravity of 5.85, is highly sensitive to X rays and detects photons penetrating an object using a 0.25-mm diameter lead pinhole for improving the spatial resolution. Without photon counting, the currents flowing through the CdTe diode are converted into voltages using a current-to-voltage amplifier and amplified by a voltage-to-voltage amplifier. The effective photon energy increased with increasing digital amplification factor at a constant maximum output of 5.06 V owing to the beam hardening by the object. In the TS-CT, the tube voltage and current were regulated as 100 kV and 1.0 mA, respectively. The spatial resolutions and scanning time for CT were approximately 0.25×0.25 mm2 and 19.6 min,respectively. Using gadolinium contrast media, the image contrast of the media varied substantially according to changes in the digital amplification factor, and blood vessels were observed at a high contrast. The digital amplifier could be used instead of a real analog amplifier at low amplification factors below 3.0.