N. Shah

Noninvasive imaging for the new century

Noninvasive imaging technologies are expected to play a significant role in the area of medical diagnosis and industrial imaging. The engineers of the 21st century will need the appropriate skill to master the power of new technologies. To face the challenges of the new century, a strong impulse toward a multidisciplinary and diversified engineering knowledge will be essential. Some examples of noninvasive imaging (spiral CT, microwave imaging, hybrid modalities) and image enhancement techniques are presented.

Signal evaluation of a novel dual-energy multimedia imaging sensor

In this study, experimental results on the signal quality of a multimedia imaging detector, operating on gaseous solid state ionization principles, with specific emphasis on single X-ray exposure dual-energy radiography, are presented. The results of this study indicate that the multimedia detector technology exhibits excellent signal characteristics suitable for a large number of 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.

Signal-to-noise measurements utilizing a novel dual-energy multimedia detector

Dual-energy measurements are presented utilizing a novel slot-scan digital radiographic imaging detector, operating on gaseous solid state ionization principles. The novel multimedia detector has two basic functional components: a noble gas-filled detector volume operating on gas microstrip principles, and a solid state detector volume. The purpose of this study is to investigate the potential use of this multimedia detector for enhanced dual-energy imaging. The experimental results indicate that the multimedia detector exhibits a large subtracted signal-to-noise ratio. Although the intrinsic merit of this device is being explored for medical imaging, potential applications of the multimedia detector technology In other industrial areas, such as aerospace imaging, aviation security, and surveillance, are also very promising.

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.

Signal dispersion measurements on the gas detector volume of a dual-energy multimedia digital imaging sensor

In this study, experimental results on the signal dispersion of a gas detector volume of a multimedia imaging detector, operating on both gaseous and solid-state ionization principles, with specific emphasis on single X-ray exposure dual-energy radiography, are presented. The results of this study indicate that the gas detector volume of the multimedia detector technology exhibits excellent signal characteristics suitable for a large number of imaging applications. By focusing on the gas detector element, drift distance causes significant effects on both the amplitude and full-width at half maximum due to mobility dispersion and space-charge. An improved signal results with increasing gas pressure.

Optimization of the signal dispersion parameters of a dual-energy multimedia imaging sensor

In this study, experimental results on the signal dispersion of a multimedia imaging detector, operating on gaseous solid state ionization principles, with specific emphasis on single x-ray exposure dual-energy radiography, are presented. The results of this study indicate that the multimedia detector technology exhibits excellent signal characteristics suitable for a large number of imaging applications. On the other hand, drift distance causes significant effect on both the amplitude and full-width at half maximum (FWHM) due to mobility dispersion and space-charge. An improved signal results with increasing gas pressure.