Joseph S. Laughter

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.

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.

Use of a kinestatic charge detector for megavoltage portal imaging

The potential of a research prototype Kinestatic Charge Detector and data acquisition system for megavoltage portal imaging is discussed. Monte Carlo modeling of, and experimental results for, the line-spread function, modulation transfer function, energy efficiency and quantum detection efficiency are given and compared with those of portal film detectors. The first phantom images from the small-field system are compared with images of the same phantoms taken with commercial portal film systems. Future directions are discussed.

New calibration technique for KCD-based megavoltage imaging

In megavoltage imaging, current commercial electronic portal imaging devices (EPIDs), despite having the advantage of immediate digital imaging over film, suffer from poor image contrast and spatial resolution. The feasibility of using a kinestatic charge detector (KCD) as an EPID to provide superior image contrast and spatial resolution for portal imaging has already been demonstrated in a previous paper. The KCD system had the additional advantage of requiring an extremely low dose per acquired image, allowing for superior imaging to be reconstructed form a single linac pulse per image pixel. The KCD based images utilized a dose of two orders of magnitude less that for EPIDs and film. Compared with the current commercial EPIDs and film, the prototype KCD system exhibited promising image qualities, despite being handicapped by the use of a relatively simple image calibration technique, and the performance limits of medical linacs on the maximum linac pulse frequency and energy flux per pulse delivered. This image calibration technique fixed relative image pixel values based on a linear interpolation of extrema provided by an air-water calibration, and accounted only for channel-to-channel variations. The counterpart of this for area detectors is the standard flat fielding method. A comprehensive calibration protocol has been developed. The new technique additionally corrects for geometric distortions due to variations in the scan velocity, and timing artifacts caused by mis-synchronization between the linear accelerator and the data acquisition system (DAS). The role of variations in energy flux (2 - 3%) on imaging is demonstrated to be not significant for the images considered. The methodology is presented, and the results are discussed for simulated images. It also allows for significant improvements in the signal-to- noise ratio (SNR) by increasing the dose using multiple images without having to increase the linac pulse frequency or energy flux per pulse. The application of this protocol to a KCD system under construction is expected shortly.

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.

Imaging performance of a large-field kinestatic charge detector for digital radiography

The initial performance of a digital radiographic system incorporating a large-field (2016- channel) kinestatic charge detector and data acquisition electronics is discussed. The measured modulation transfer function of the system is 20% at 4 cy/mm. The measured detective quantum efficiency is 40 - 60%. These results are comparable with or better than those of current clinical (rare-earth film-screen and storage phosphor) systems. First images from the large-field system are shown and compared with those from commercial systems. Future system improvements in process or in planning are discussed.

Development of a clinical KCD digital radiography system

The Kinestatic Charge Detector (KCD) digital radiography system has proven itself experimentally to be comparable with or superior to other x-ray imaging systems in the production of quality images at the same dose. The prototype large-field detector design has obtained images that have relatively high spatial and contrast resolution with low scatter and low quantum noise compared with current commercially available clinical x-ray systems. The NIH has approved a grant to develop and construct an advanced clinical KCD digital radiography system. The goals of this project are to design the gantry and clinically evaluate the new system. This system will allow for improved diagnosis, reduced patient dose, and provide other features unique to a digital radiography system.

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.

Pulse width variation along the x-ray direction in the segmented KCD system

The kinestatic charge detector (KCD) built and researched at the University of Tennessee, Memphis, is now being studied as a possible dual-energy x-ray imager. The present study aims at quantifying the change in the arrival time spectrum (ATS) as a function of the detectors depth, i.e., in the x-ray direction. We measured the change in the full width at half maximum (FWHM) along the x-ray direction in the chamber using a segmented signal- collector board. The FWHM of the ionic signal exhibit a dependence on the x-ray beam intensity, and electric field strength. Furthermore, the average arrival time is almost constant along the detector depth.

Chest imaging protocol for a kinestatic charge detector: the effect of patient density distributions on kinestatic settings

Kinestatic charge detector (KCD) systems have potential uses in all fields of digital radiography including chest, abdominal, vascular, peripheral, dual energy subtraction and mammography. The purpose of this study was to investigate the development of a chest imaging protocol for a full field of view KCD system with regard to the effect of significant variations in patient chest thickness and its possible influence on kinestatic electric field settings. This was investigated by optimizing the kinestatic setting for a 5 lp/mm bar pattern imaged with 0, 5, 10, 15, and 20 cm of added Lucite to simulate varying patient chest thickness. Preliminary results demonstrate that variation in kinestatic settings due to variations in patient thickness affects the kinestatic electric field setting. Since only one field setting is available per image scan it becomes necessary to either optimize kinestatic settings for an estimated average patient thickness or for the density function of the expected region of interest (ROI).