Quasi‐monochromatic X‐ray photon counting using a silicon‐PIN detector and an energy‐selecting device and its application to iodine imaging

Abstract

Quasi‐monochromatic photon counting was performed using a silicon PIN detector and an energy‐selecting device, consisting of two comparators and a microcomputer. The two threshold energies are determined using low and high‐energy comparators, respectively. The microcomputer produces a single logical pulse when only a logical pulse from a low‐energy comparator is input to the microcomputer. Next, the microcomputer never produces the pulse when two pulses from low and high‐energy comparators are input to the microcomputer, simultaneously. The logical pulses from the microcomputer are input to a frequency‐voltage converter（FVC）to convert count rates into voltages; the rate is proportional to the voltage. The output voltage from the FVC is sent to a personal computer through an analog‐digital converter to reconstruct tomograms. The X‐ray projection curves for tomography are obtained by repeated linear scans and rotations of the object at a tube voltage of 70kV and a current of 0.20mA. Iodine（I）K‐edge CT was performed using contrast media and X‐ray photons with a count rate of 1.4 kilocounts per second and energies ranging from 34 to 55keV, since these photons with energies beyond I‐K‐edge energy 33.2keV are absorbed effectively by I atoms.