We have constructed a triple-energy (TE) X-ray photon counter with a room-temperature cadmium telluride (CdTe) detector and three sets of comparators and microcomputers to obtain three kinds of tomograms at three different X-ray energy ranges simultaneously. X-ray photons are detected using the CdTe detector, and the event pulses produced using amplifier module are sent to three comparators simultaneously to regulate three threshold energies of 15, 33 and 50 keV. Using this counter, the energy ranges are 15-33, 33-50 and 50-100 keV; the maximum energy corresponds to the tube voltage. The photon-energy resolution was 3.5% at 59.5 keV. We performed TE computed tomography (TE-CT) at a tube voltage of 100 kV. Using four lead pinholes, three tomograms were obtained simultaneously. Gadolinium-K-edge CT was carried out utilizing an energy range of 50-100 keV. At a tube voltage of 100 kV and a current of 1.60 mA, the count rate was 59 kilocounts per second (kcps).
To perform low-dose low-scattering X-ray computed tomography (CT), we have constructed a dual-energy (DE) X-ray photon counter with a high-count-rate detector system and energy-range and -region selectors. The detector system consists of a cerium-doped yttrium aluminum perovskite [YAP(Ce)] crystal, a small photomultiplier tube (PMT), and an inverse amplifier for the PMT with a pulse-width extender. In DE-CT, both the X-ray source and the detector module are fixed, and the object on the turntable oscillates on the translation stage. A line beam for DE-CT is formed using a two lead (Pb) pinholes in front of the object. The scattering-photon count from the object is reduced using a Pb pinhole behind the object. To improve the spatial resolution, a 0.5-mm-diam Pb pinhole is attached to the YAP(Ce)-PMT detector. X-ray photons are detected using the detector system, and the event pulses are input to the two energy selectors. In DE-CT, the tube voltage and the maximum current were 100 kV and 0.60 mA, respectively. The energy range and region for soft and gadolinium-K-edge CT are 20-40 and beyond 50 keV (50-100 keV), respectively. The maximum count rate of DE-CT was 84 kilocounts per second, and the exposure time for tomography was 19.6 min at a total rotation angle of 360°.
To obtain three kinds of tomograms at three different X-ray energy ranges simultaneously, we have constructed a triple-energy (TE) X-ray photon counter with a cooled cadmium telluride (CdTe) detector and three sets of comparators and microcomputers. X-ray photons are detected using the CdTe detector, and the event pulses produced using amplifiers are sent to three comparators simultaneously to regulate three threshold energies of 15, 33 and 50 keV. Using this counter, the energy ranges are 15-33, 33-50 and 50-100 keV; the maximum energy corresponds to the tube voltage. We performed TE computed tomography (TE-CT) at a tube voltage of 100 kV. Using four lead pinholes, three tomograms were obtained simultaneously. Iodine-K-edge CT was carried out utilizing an energy range of 33-50 keV. At a tube voltage of 100 kV and a current of 0.11 mA, the count rate was 21 kilocounts per second (kcps).
In the near-infrared-ray computed tomography (NIR-CT) scanner, NIR rays are produced from a light-emitting diode (LED) and detected using a phototransistor (PT) and an infrared filter. The LED-peak wavelength is 850 nm, and 850- nm-peak NIRs are detected using the filtrated PD. The photocurrents flowing through the PT are converted into voltages using an emitter-follower circuit, and the output voltages are sent to a personal computer through an analog-digital converter. The NIR projection curves for tomography are obtained by repeated translations and rotations of the object, and the translating is conducted in both directions of its movement. The 850-nm NIRs easily penetrated living bodies, and the NIR-CT was performed with changes in the sensitivity at relative sensitivities of 1 and 21.
To measure X-ray spectra with high count rates, we developed a detector consisting of a cerium-doped yttrium aluminum perovskite [YAP(Ce)] crystal and a recent multipixel photon counter (MPPC). Scintillation photons are detected using the MPPC, and the photocurrents flowing through the MPPC are converted into voltages and amplified using a high-speed current-voltage (I-V) amplifier. The MPPC bias voltage was set to a value at the pre-Geiger mode to perform zero-dark counting. The event-pulse widths were approximately 200 ns, and the widths were extend to approximately 1 μs. X-ray spectra were measured using a multichannel analyzer (MCA) for pulse-height analysis. The photon energy was roughly determined by the two-point calibration using tungsten K photons and iodine K fluorescence. Using the YAP(Ce)-MPPC detector, first-generation dual-energy computed tomography was accomplished using iodine and gadolinium contrast media.
In the near-infrared-ray computed tomography (NIR-CT) scanner, NIR rays are produced from a light-emitting diode
(LED) and detected using an NIR phototransistor (PT). The wavelengths of the LED peak intensity and the PT high
sensitivity in the data table are both 940 nm. The photocurrents flowing through the PTR are converted into voltages
using an emitter-follower circuit, and the output voltages are sent to a personal computer through an analog-digital
converter. The NIR projection curves for tomography are obtained by repeated linear scans and rotations of the object,
and the scanning is conducted in both directions of its movement.
To obtain four tomograms with four different photon energy ranges simultaneously, we have developed a quad-energy Xray
photon counter with a cadmium telluride (CdTe) detector and four sets of comparators and frequency-voltage
converters (FVCs). X-ray photons are detected using the CdTe detector, and the event pulses from a shaping amplifier are
sent to four comparators simultaneously to regulate four threshold energies of 20, 35, 50 and 65 keV. Using this counter,
the energy ranges are 20-100, 35-100, 50-100 and 65-100 keV; the maximum energy corresponds to the tube voltage. Xray
photons in the four ranges are counted using the comparators, and the logical pulses from the comparators are input
to the FVCs. The outputs from the four FVCs are input to a personal computer through an analog-digital converter (ADC)
to carry out quad-energy imaging. To observe contrast variations with changes in the threshold energy, we performed
spectral computed tomography utilizing the quad-energy photon counter at a tube voltage of 100 kV and a current of 8.0
μA. In the spectral CT, four tomograms were obtained simultaneously with four energy ranges. The image contrast varied
with changes in the threshold energy, and the exposure time for tomography was 9.8 min.
Quasi-monochromatic photon counting was performed using a cadmium telluride detector and an energy-selecting device, consisting of two comparators and a microcomputer (MC). The two threshold energies are determined using low and high-energy comparators, respectively. The MC produces a single logical pulse when only a logical pulse from a low-energy comparator is input to the MC. Next, the MC never produces the pulse when two pulses from low and high-energy comparators are input to the MC, simultaneously. The logical pulses from the MC 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 70 kV and a current of 12 μA. Iodine (I) K-edge CT was performed using contrast media and X-ray photons with a count rate of 2.2 kilocounts per second and energies ranging from 34 to 50 keV, since these photons with energies beyond I-K-edge energy 33.2 keV are absorbed effectively by I atoms.
To obtain two tomograms with two different photon energy ranges simultaneously, we have performed dual-energy Xray photon counting using a cadmium telluride (CdTe) detector, two comparators, two frequency-voltage converters (FVCs), and an analog digital converter (ADC). X-ray photons are detected using the CdTe detector with an energy resolution of 1% at 122 keV, and the event pulses from a shaping amplifier are sent to two comparators simultaneously to regulate two thresholds of photon energy. The logical pulses from a comparator are sent to an FVC consisting of two integrators, a microcomputer, and a voltage-voltage amplifier. The smoothed outputs from the two FVCs are input to the ADC to carry out dual-energy imaging. To observe contrast variations with changes in threshold energy, we performed energy-dispersive computed tomography utilizing the dual-energy photon counting at a tube voltage of 100 kV and a current of 8.7 μA. Two tomograms were obtained simultaneously at two energy ranges of 34.0-50.2 keV and 50.2-100 keV. The photon-count subtraction was carried out using a computer program. The maximum count rate was 5.4 kilocounts per second with energies of 10.0-100 keV, and the exposure time for tomography was 10 min.
Dual-energy photon counting was performed using an energy-selecting device (ESD) and a detector, consisting of a Lu2(SiO4)O [LSO)] crystal and a multipixel photon counter (MPPC). The ESD is used to determine a low-energychannel range for CT and consists of two comparators and a microcomputer (MC). The two threshold channels in proportion to energies are determined using low and high-energy comparators, respectively. The MC in the ESD produces a single logical pulse when only a logical pulse from the low-energy comparator is input to the MC. To determine the high-energy-channel range for CT, logical pulses from the high-energy comparator are input to the MC outside the ESD. Logical pulses from the two MCs are input to frequency-voltage converters (FVCs) to convert count rates into voltages. The output voltages from the two FVCs are sent to a personal computer through an analog-digital converter to reconstruct tomograms. Dual-energy computed tomography was accomplished at a tube voltage of 70 kV and a maximum count rate of 14.3 kilocounts per second, and two-different-energy tomograms were obtained simultaneously.
To develop a dual-energy X-ray CT (DE-CT) system, we have performed investigation of high-speed dual-energy photon counting using two comparators and a low-dark-counting LSO-MPPC (multipixel photon counter) detector. To measure X-ray spectra, electric charges produced in the MPPC are converted into voltages and amplified by a highspeed current-voltage amplifier, and the event pulses are sent to a multichannel analyzer. The MPPC was driven under pre-Geiger mode at an MPPC bias voltage of 70.7 V. The event pulses are sent to two high-speed comparators for selecting two threshold energies to perform DE-CT. The ED-CT is accomplished by repeated linear scans and rotations of the object, and two sets of projection curves of the object are obtained simultaneously by the linear scan. In the DECT, two different-energy tomograms are obtained simultaneously, and photon-count energy subtraction imaging was carried out.
To develop a dual-energy X-ray CT (DE-CT) system, we have performed investigation of high-speed dual-energy photon counting using two comparators and a low-dark-counting LSO-MPPC (multipixel photon counter) detector. To measure X-ray spectra, electric charges produced in the MPPC are converted into voltages and amplified by a highspeed current-voltage amplifier, and the event pulses are sent to a multichannel analyzer. The MPPC was driven under pre-Geiger mode at an MPPC bias voltage of 70.7 V. The event pulses are sent to two high-speed comparators for selecting two threshold energies to perform DE-CT. The ED-CT is accomplished by repeated linear scans and rotations of the object, and two sets of projection curves of the object are obtained simultaneously by the linear scan. In the DECT, two different-energy tomograms are obtained simultaneously, and photon-count energy subtraction imaging was carried out.
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