Zero-Dark-Counting Brief Measurement of X-ray Spectra Using a Lutetium-Oxyorthosilicate Multipixel-Photon Detector Driven in Pre-Geiger Mode

Brief measurement of X-ray spectra using a detector, consisting of a lutetium oxyorthosilicate (LSO) crystal and a multipixel photon counter (MPPC) is described. X-ray photons are detected using the LSO crystal and a 0.5-mm-diam 3.0-mm-thick lead pinhole, and scintillation photons produced in the crystal are detected using the MPPC. The photocurrents flowing through the MPPC are converted into voltages and amplified using a stable high-speed current-voltage amplifier, and the output event pulses from the amplifier are sent to a multichannel analyzer to perform pulse-height analysis. Without the counts of  photons from the LSO crystal, the dark count rate was reduced to 0 count per second by reducing the MPPC bias voltage to 65.11 V in the pre-Geiger mode. The photon energy was determined by two-point calibration using K-fluorescent energies of iodine and lead, and the energy resolutions was below 30% at 74.2 keV. Using the LSO-MPPC detector, both the maximum-photon and the peak-count energies increased with increasing tube voltage, and the maximum count rate was 31 kilocounts per second at a tube voltage of 100 kV and a current of 0.16 mA. Dual-energy computed tomography was accomplished using gadolinium contrast media.