Lawrence M. Jordan

A variable resolution x-ray detector for computed tomography: II. Imaging theory and performance.

A computed tomography (CT) imaging technique called variable resolution x-ray (VRX) detection provides variable image resolution ranging from that of clinical body scanning (1 cy/mm) to that of microscopy (100 cy/mm). In this paper, an experimental VRX CT scanner based on a rotating subject table and an angulated storage phosphor screen detector is described and tested. The measured projection resolution of the scanner is > or = 20 lp/mm. Using this scanner, 4.8-s CT scans are made of specimens of human extremities and of in vivo hamsters. In addition, the systems projected spatial resolution is calculated to exceed 100 cy/mm for a future on-line CT scanner incorporating smaller focal spots (0.1 mm) than those currently used and a 1008-channel VRX detector with 0.6-mm cell spacing.

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.

Initial clinical performance of a large-field KCD digital radiography system

The initial clinical performance of a research prototype digital radiographic system based on a large-field (2016-channel) kinestatic charge detector and data acquisition system is discussed. The first clinical images from the large-field system are compared with images of the same patients taken with commercial systems. Future directions are discussed.

Entrance Window Design Parameters for High-Pressure Gas X-Ray Imaging Detectors

Gas ionization x-ray detectors operating at pressures up to 100 atm offer inherently high spatial and contrast resolution. However, incorporating the detector x-ray entrance window in a conventional pressure vessel designed for such pressures can result in high primary beam loss in the window and a much reduced overall detective quantum efficiency. The design of a gas chamber cover plate for a strip beam detector which mechanically isolates the x-ray entrance window from the lateral tensile stresses in the chamber body is described. A number of test windows of this design, varying in three geometric parameters—thickness, window curvature, and fillet radius—were fabricated from wrought aluminum [6061-T651] and subjected to pressures of up to 400 atm for the purpose of selecting an optimum window for a prototype digital x-ray imaging detector. The experimental data indicate that windows can be designed for a detector admitting a 1.0 cm wide x-ray beam that have rupture pressures exceeding 500 atm while maintaining x-ray transmittances of as much as 93.4% for a 120 kVp tungsten anode spectrum.

Advanced clinical KCD scanner for digital radiography

One of the goals of medical imaging scientists and bioengineers remains the development of digital electronic technologies that can replace film-based methods of acquiring x-ray images. With the achievement of this goal, all diagnostic imaging technologies would be based on digital techniques with all the attending benefits. Based on the performance of numerous research prototype small-field and one large-field Kinestatic Charge Detector (KCD) system for digital radiography, a large-field clinical KCD scanner is currently being designed and built for technical evaluation and for clinical evaluation of 200 volunteer patients (including clinical comparisons with film, storage phosphor, and other available clinical systems). The state of development of this clinical KCD system, including detector, data-acquisition system and scanning gantry design, is reviewed in this paper.

Improved image processing techniques for multiple-angle x-ray bone densitometry

A method utilizing digital dual-energy substraction x-ray radiography for measuring calcium densities localized to the cortical and cancellous regions of bone cross sections is described. The method is proposed as a technique for studying calcium loss in femurs of rats used in experiments modeling the temporal of osteoporosis. The densitometry data obtained for a rat leg consists of six x-ray projection images acquired at 30 degree(s) angular intervals about the bone axis by an intensifying screen/CCD camera imaging system. Images of bone cross sections are reconstructed by application of a maximum entropy algorithm constrained by the six projection images. The observed density data are further discriminated into cortical, cancellous and external regions on the basis of reference levels found on image density histograms.

Detection Of Demineralization In Rat Legs Using Multiple Angle X-Ray Bone Densitometry

A method utilizing digital dual-energy subtraction X-ray radiography for measuring calcium densities localized to the cortical and cancellous regions of bone cross sections is described. The method is being used to study calcium loss in femurs of two differently treated groups of rats. In each experimental cohort, one group of rats is restrained from weightbearing on hind limbs by suspension from a tail harness. The other (control) group is allowed normal weightbearing on all limbs. The densitometry data for each rat leg consists of six X-ray projection images acquired at roughly equal angles about the bone axis by an intensifying screen/CCD camera imaging system. Images of bone cross sections are reconstructed by application of a maximum entropy algorithm constrained by the six projection images. The observed density data are further discriminated into cortical, cancellous and external regions on the basis of reference levels found on image density histograms.