R. Guntupalli

Sensitometric response of Cd/sub 1-x/Zn/sub x/Te detectors for chest radiography

The sensitometric response of Cd/sub 1-x/Zn/sub x/Te semiconductor detectors using a geometrical chest phantom, within the X-ray diagnostic energy range, has been studied with the aim of optimizing the image quality parameters of these solid state-ionization devices. In addition, the dependence of the spatial resolution of a planar Cd/sub 1-x/Zn/sub x/Te substrate on the phantom thickness has been experimentally determined. The results of this study indicate that Cd/sub 1-x/Zn/sub x/Te detectors exhibit a high signal-to-noise ratio (S/N).

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.

Sensitometric response of CdZnTe detectors for digital radiography

The sensitometric response of the CdZnTe semiconductor detectors, within the X-ray diagnostic energy range, have been studied with the aim of optimizing the image quality parameters of these solid state-ionization devices. The detected signal and noise contributions were measured and related to the tube setting current parameters. Furthermore, the detector contrast has been experimentally determined. The experimental results indicate that CdZnTe detectors have high resistivity, high signal-to-noise ratio, and high detector contrast resolution. Therefore, they appear to be potential candidates for imaging applications with applications in X-ray digital radiography, dual-energy radiography, and computed tomography (CT).

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.

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.

Timing characteristics of a Cd/sub 1-x/Zn/sub x/Te detector-based X-ray imaging system

The timing characteristics of a planar Cd/sub 1-x/Zn/sub x/Te sample at each frequency of a scanning square-wave test pattern, has been measured. This study is aimed at evaluating the speed characteristics of a Cd/sub 1-x/Zn/sub x/Te detector for X-ray imaging and computed tomographic (CT) applications. The experimental results of this study indicate that the temporal response of a Cd/sub 1-x/Zn/sub x/Te detector based X-ray system, improves significantly by optimizing the X-ray tube and detector parameters.

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.

An efficient collector architecture for digital radiographic imaging czt semiconductor sensors

The objective of this study is to design, evaluate and optimize a novel sensor, proposed by Giakos [ I 1-[3] for direct x-ray conversion semiconductor medical imaging applications. Specifically the detector’s amplitude response, temporal response, signal response (linear spread function), and modulation transfer function have been studied experimentally over the range commonly used in diagnostic x-ray. Different detector technologies and beam geometries have been proposed for a variety of x-ray digital imaging applications [ 11-[22]. Some of the disadvantages presently faced relate to the relatively high initial cost of digital radiographic systems as well as to the limited detector resolution, although rapid advances are being made. The technology of choice depends on several image quality criteria such as high quantum and energy absorption efficiency, high detector quantum efficiency (DQE), high spatial resolution, negligible scatter acceptance, high contrast resolution, sensor geometry, fast readout, high dynamic range, image correction and display capabilities, and acceptable cost. Of the many solid-state detectors available for imaging applications, CdTe (CT) and CdZnTe (CZT) are preferred for quantitative studies [19]-[45]. However CdTe has high leakage current, low collection efficiency and a non-ideal ohmic contact, which limits its use in medical imaging applications. Poor collection efficiency is due to impurities present in the materials. The impurities act as traps, which reduce the mobility-lifetime product of the carriers and induce charges on the signal collector due to the slow motion of the charge carriers. Recombination of electrons and ions caused by this impurity further reduces the signal quality. Overall, the charge transport characteristics of CZT material are dependent on the charge carriers (electrons or holes), and are described by Hecht’s equation. On the other hand, growth of the high quality CZT semiconductor crystal using High Pressure Bridgman Technique has improved the purity of the detector [25]-[27], [35], [39]. CZT has high bulk resistivity and high stopping power due to their high mass density (5.8 pmicm3) and high atomic number (49.6). However, collection efficiency in the compound semiconductor materials is limited by the slow ion transport characteristics [35], [39]. Therefore, an optimal CZT based detector design relies on the collection of electrons, which exhibit a mobility-life time product ( ~ T J of 100 times better than the mobility-life time product of holes ( p j , ~ h ) and by applying a sufficiently high electric field (100 V/mm collection efficiency can be achieved [35]-[36], [39].

Detective quantum efficiency [DQE(0)] of CZT semiconductor detectors for digital radiography

In this paper, the detective quantum efficiency (DQE) of cadmium zinc telluride (CZT) detector samples for digital radiography has been measured. Specifically, this study is aimed at investigating the zero-frequency DQE(0) under different X-ray tube and detector parameters. The experimental results of this study indicate that the DQE(0) of the CZT samples is strongly dependent upon the irradiation geometry. This is attributed to the incomplete charge collection process, which can be further improved by controlling the purity of the samples and the contact type.