Paul Richard Granfors

Performance characteristics of an amorphous silicon flat-panel x-ray imaging detector

An x-ray imaging detector designed for both radiographic and fluoroscopic medical applications has been developed. The requirement that the detector provide superior imaging in both fluoroscopic and radiographic operation put severe constraints on its design. User requirements and a translation of those requirements to detector performance parameters guided detector design. This paper reports on the performance of a 20.5 X 20.5 cm prototype detector which was a product of this design effort. The detector was tested using both physical measurements and clinical imaging trials. The frequency dependent DQE is used as a measure of contrast to noise performance. Measurements of DQE were made at both fluoroscopic and radiographic signal levels. In fluoroscopic operation, measurements of lag were also made. The detector performance is compared to that of existing and emerging technologies. Results of clinical studies in both radiographic mode (chest imaging) and fluoroscopic mode (cardiac imaging) are reported.

A computer‐controlled x‐ray imaging scanner using a kinestatic charge detector

A prototype scanning imaging system which employs a kinestatic charge detector (KCD) and is under the control of a VAXstation II/GPX computer is described. The operating principles and advantages of the KCD method are reviewed. The detector is a 256‐channel ionization drift chamber which creates a two‐dimensional x‐ray projection image by scanning the detector past the object of interest. The details of the drift chamber design, the signal collection electrodes (channels), and the Frisch grid geometry are given. Also described are the scanning gantry design, computer‐controlled drive motor circuit, and safety features. The data acquisition system for the capture of a 1 M byte digital image is presented. This includes amplification, filtration, analog‐to‐digital conversion, data buffering, and transfer to the VAXstation II computer. The image processing and display techniques specific to the KCD are outlined and the first two‐dimensional image taken with this system is presented.

Progress On Strip Beam Digital Radiography Using The Kinestatic Charge Detector

Strip (or slot) beam digital radiography has been proposed as an ideal compromise between the excellent scatter rejection of pencil-beam or single-line scanned projection radiography systems and the excellent x-ray utilization of wide area beam systems. Moreover, the Kinestatic Charge Detector (KCD) has been proposed as a strip beam detector candidate with a potential for achieving a spatial resolution of over 5 cy/mm, a quantum detection efficiency (QDE) near unity ( > 90% and a local exposure time at a given contrast resolution which is less than other detection techniques (i.e., reduced motion blurring). Several laboratory KCDs containing various numbers of channels have now been constructed and tested which allow a better understanding of the practical performance which can be expected from a strip beam digital radiography system using a KCD.

Noise Properties Of A Kinestatic Charge Detector

Recent breakthroughs in electronic detector technology have allowed digital radiographic images to become competitive with, or superior to, those produced with classical film-screen techniques. A summary of these technologies is given in ref. 1. Our group is involved in the research and development of a recently proposed imaging technology (2,3) based on the kinestatic charge detector (KCD). The modulation transfer function (MTF) of the KCD technique has been discussed in refs. 1 and 4. The low frequency detective quantum efficiency (DO(0)) of several KCD designs has been modeled and a value of approximately 0.75 is expected for future detectors (1,5). In this paper, the noise power spectrum (NPS) and the frequency-dependent DOE (MEM) are discussed. Noise contributions from x-ray quanta (random and structured) and data acquisition electronics are considered and preliminary experimental results are given for a recently installed imaging detector. A brief comparison is made of our theoretical and experimental results with published results for film-screen radiography.

Performance Parameters Of A Kinestatic Charge Detector

The goal of developing an on-line electronic digital radiographic (EDR) system to replace conventional film-screen radiography (FSR) is important for at least two reasons. First, theoretical arguments show that EDR can have improved diagnostic quality, reduced patient dose and faster image accessibility than FSR. Secondly, the availability of EDR systems will remove the final impediment to the realization of the PACS concept inasmuch as FSR is the only major nonelectronic imaging modality left in the modern radiology department. The Kinestatic Charge Detector (KCD) has properties which make it a candidate for an on-line EDR systems-10. The KCD is a strip detector with high spatial resolution in two dimensions. However, mechanically and electronically, it operates like a one-dimensional detector. Thus, it can effectively scan on the order of 64 to 128 parallel x-ray lines simultaneously but with a 64 to 128-fold reduction in the number of actual detector cells and electronic channels. Moreover, this can be done at quantum detection efficiencies approaching unity. In this paper, theoretical calculations and experimental measurements of the performance parameters of a KCD are presented. Some of the particular parameters discussed include spatial, contrast, and temporal resolution.