Robert J. Endorf

Engineering Aspects of a Kinestatic Charge Detector

The engineering aspects of a nine-channel digital radiographic system developed for bioimaging research, based on high gas pressure ionography and kinestatic principles, are presented. The research imaging system uses a pulsed x-ray beam which allows one to study simultaneously the ionic signal characteristics at 10 different ionization sites along the drift axis. This research imaging detector system allows one to investigate methods to improve the detection and image quality parameters as part of the development of a large scale prototype medical imaging system.

Study of detection efficiency of Cd/sub 1-x/Zn/sub x/Te detectors for digital radiography

In this paper, the signal-to-noise ratio (S/N) of resistive Cd/sub 1-x/Zn/sub x/Te semiconductor detectors, at different directions of irradiation, within the X-ray diagnostic energy range, has been experimentally studied. In addition, the dependence of the spatial resolution of a planar Cd/sub 1-x/Zn/sub x/Te substrate both on the applied bias voltage and thickness has been experimentally determined. The detection efficiency of semiconductor detectors depend upon the energy absorption efficiency as well as the collection efficiency. This study suggests that high signal-to-noise ratios can be obtained by optimally choosing which polarizing electrode is directly exposed to the incident X-ray beam, as well as on both the detector thickness and applied bias voltage. In addition, the experimental results on the temporal system MTF indicate a spatial resolution of >6 cy/mm. Besides the intrinsic charge transport characteristics of the semiconductor sample, by decreasing the collector size and optimizing the X-ray digital system geometry and temporal response, the temporal system MTF can be improved significantly. The research imaging detector system allows one to investigate methods to improve the detection and imaging performance parameters as part of the development of a digital radiographic system.

Preliminary performance characteristics of a dual-energy KCD

A kinestatic charge detector (KCD) with segmented signal-collection fingers was constructed to evaluate the dual-energy x-ray imaging performance of a KCD. The front segments of the KCD signal-collectors produce a digital low-energy image and the back segments produce a digital high-energy image. A gap between the front and back signal-collectors is used as a filter to increase the separation between the mean energies absorbed in the front and back segments. Preliminary measurements have been performed on the dual-energy KCD to determine its dual-energy imaging characteristics. The KCD output signal has been measured as a function of depth in the chamber. The ion drift velocity, modulation transfer function (MTF), detective quantum efficiency (DQE) and Wiener spectrum have been determined for both the front (low-energy) and back (high-energy) signal detection regions of the KCD.

Clinical applications of a dual-energy KCD

We have investigated possible clinical applications of a Kinestatic Charge Detector (KCD) for dual-energy x-ray imaging. The KCD is a good candidate as a detector for dual-energy radiography, because it is a digital detector with a high detective quantum efficiency, good spatial resolution and good scatter rejection. Computer simulations have been performed to design and optimize dual-energy KCDs for specific clinical applications. The clinical applications that have been investigated for dual-energy KCD imaging are chest radiography, mammography and osteoporosis. Experimental data have also been taken with a small research dual-energy KCD.

Evaluation of a CdZnTe dual-energy system

The purpose of the study is to optimize the input and the output parameters of a dual energy CdZnTe semiconductor detector for chest radiography. The optimal detector parameters were obtained by maximizing the figure of merit, defined as the ratio between the square of the signal-to- noise ratio and the absorbed dose, for chest radiography.

Enhanced X-Ray Detectors Using Polar Dopants for KCD Digital Radiography.

The goal of this study is to develop high resolution imaging detectors with applications in digital radiography and computed tomography. A physical treatment aimed at a better understanding of the line-spread function response of kinestatic charge detector (KCD) gas media, using dopants with permanent electric dipoles, is presented. Experimental results were obtained by operating a KCD krypton-filled detector at pressures up to 60 atm and constant electric field-to-gas density ratio doped with small amounts of polar or nonpolar polyatomic molecules with low or high ionization potential. The results clearly indicate that the addition of dopants having both low ionization potential and high dipole moment significantly enhance the imaging signal quality. An analysis of the experimental results aimed at providing a plausible interpretation of the reported observations is offered.

Contrast resolution study of CdZnTe detectors for medical imaging

The detected signal and noise contributions were measured and related to the radiation exposure and tube current tube setting. Furthermore, the detector contrast has been experimentally determined. The experimental results indicate that Cd1-xZnxTe detectors have high detector contrast resolution. Therefore, they appear to be very attractive for x-ray digital imaging applications.

Detected contrast and dynamic range measurements of CdZnTe semiconductors for flat-panel digital radiography

The detected contrast and dynamic ranges of Cd/sub 1-x/Zn/sub x/Te semiconductor detectors have been measured, within the X-ray diagnostic energy range, using a contrast sensitivity phantom. The aim of this study is to optimize the image quality parameters of these solid state ionization devices for flat panel digital radiographic applications. The experimental results of this study indicate that Cd/sub 1-x/Zn/sub x/Te detectors have excellent detected contrast response and large dynamic range.

Dual-energy imaging using a kinestatic charge detector

A small research non imaging kinestatic charge detector (KCD), with segmented signal- collection fingers, has been used to investigate the dual-energy capability of a KCD. The front segments of the signal-collectors produce a digital low-energy x-ray image and the back segments produce a digital high-energy x-ray image. A gap between the front and back signal- collectors may be used as a filter to increase the separation between the mean energies absorbed in the front and back segments. The dual-energy imaging capability of the large-field (2016-channel) KCD, without segmented signal-collection fingers, has also been evaluated using the two-exposure technique of taking two sequential x-ray exposures at different x-ray kilovoltages of a fixed phantom. Dual-energy calibrations, based on various decomposition algorithms, were performed for both the segmented non imaging KCD and the large-field imaging KCD. The calibration parameters were calculated from measurements taken with various thicknesses of aluminum and Plexiglas. The rms errors in aluminum and Plexiglas thicknesses for the various dual-energy decomposition algorithms are compared for each KCD.

An efficient, novel microstrip collector architecture for digital radiographic imaging CZT semiconductor sensors

The purpose of this paper is to study the impact of a novel microstrip collector design on the temporal response of CdZnTe (CZT) semiconductor detectors for digital radiographic imaging applications. The experimental results of this paper clearly indicate a significant improvement of the temporal response of the CZT imaging detectors due to the enhanced collection efficiency.