Image Intensifier Television Systems Research Articles

Assessment of distortion in a three-dimensional rotational angiography system.

The purpose of this project was to determine the degree of geometrical distortion in a three-dimensional (3D) image volume generated by a digital fluorography system with rotational image acquisition capabilities. 3D imaging is a valuable adjunct in neuroangiography for visualization and measurement of cerebral aneurysms and for determination of the optimum projection for intervention. To enable spatially accurate 3D reconstruction the system must correct for geometrical distortion in the image intensifier television system as well as for deviations in gantry motion. 3D volumes were reconstructed from 100 X-ray projections acquired over a 180 degrees arc over a period of 8 s. A phantom was constructed to assess geometrical distortion in the three dimensions. The phantom consisted of 1 mm diameter ball bearings embedded in Perspex in a cubic lattice configuration. The ball bearings were placed at 20 mm intervals over a 140 mm cubic volume. Distortion was assessed by taking measurements between points of known separation and using a differential distortion measurement. The maximum error in the 3D location of objects was found to be 1.4 mm, while the differential distortion was found to range from -1.0% to +2.3%. The 3D images were found to have negligible visual distortion, enabling subjective assessments to be made with confidence to aid intervention.

Book reviews

This book is intended as an introductory text book on medical imaging, however the emphasis is very much on reconstruction techniques and imaging devices employing them. Readers expecting to read about films/screens, image intensifier television systems and computed radiography, as implied by the general nature of the title, will be disappointed. The treatment of the subjects is rigorous though it is not a textbook for the mathematically compromised. The section on the photoelectric effect is shorter than that on the marked transform. The description of each modality included in the book is of a very high standard. It clearly indicates that the authors have a comprehensive knowledge and insight into the subject matter.

Analysis of variations in contrast-detail measurements performed on image intensifier-television systems

The magnitude of the observer variations intrinsic to contrast-detail measurements were found to be independent of the type of image used in their determination. The two sources of variation identified, within-observer and between-observer variation, were deduced to be 0.115 and 0.111, respectively (variations expressed as a relative standard deviation). When using the Leeds fluoroscopy test objects, an uncertainty on the measured threshold contrasts of 16% for one observer and 11% for two observers may be anticipated when each observer makes one independent reading. This then implies that a change of one perceived disc on the T010 test object (in which the contrast step between discs is approximately 40%) for one independent measurement made by one observer will be significant within two standard deviations. A further implication is that a more sensitive contrast-detail test object could be developed (with approximately 20% contrast steps between discs), provided that the test object is viewed by two or more observers.

Digital TV tomography: Description and physical assessment

A digital TV tomography system, capable of retrospective reconstruction of multiple digital tomographic images, has been developed and its basic physical characteristics have been evaluated. The multiple tomographic images were formed through retrospective reconstruction of digital data acquired on a linear tomographic x-ray unit and an image intensifier-television system. Digital data were obtained with a series of 30 pulsed exposures during linear motion of the system. A distortion correction algorithm for the convex surface of the image intensifier was developed in order to reduce image distortion. A phantom study showed that the square-wave response at the fulcrum plane was slightly inferior to that in conventional tomography. There was also a slight decrease in the square-wave response away from the fulcrum plane and upon application of a correction algorithm, as compared with the response of the original reconstructed image at the fulcrum plane. The exposure dose for a single image was approximately half that in conventional tomography. Because of many advantages, including low exposure, short examination time, digital image manipulation, and applicability to picture archiving and communication systems, this is likely to become an important method in radiology when further technical refinements have been made.

Digital grey-scale fluorography: a new approach to digital radiographic imaging.

In this paper we show that the presence of structure noise, shading and vignetting limits the low-contrast performance of radiological imaging systems which incorporate an X-ray image intensifier. As these imperfections are reproduced exactly at each exposure they are eliminated, along with the patient's background anatomy, during digital subtraction angiography. We have developed an imaging algorithm, based on the digital subtraction technique, which eliminates systematic imperfections from grey-scale (radiographic) images. Preliminary studies indicate that this algorithm, which we call “digital greyscale fluorography” (DGF), offers new opportunities to apply digital imaging techniques in classical radiography. A radiologist's ability to discriminate low-contrast lesions is limited by, among other factors, the power of the noise in the diagnostic image. If a single static image is recorded via a digital X-ray image intensifier television system, four sources of noise can be identified: X-ray quantum mott...

Book reviewsMeasurement of the Performance Characteristics of Diagnostic X-ray Systems used in Medicine. (HPA Topic Group Report 32). II. X-ray Image Intensifier Television Systems. 44 pp. 1981 (Obtainable from Hospital Physicists' Association, 47 Belgrave Square, London SW1X 8QX), £6.00 ISBN 0–904181–22–7

This is the second in a series which is designed to provide a comprehensive guide to the monitoring of performance of all aspects of X-ray diagnostic systems. Image intensifiers and television chains are vital components of X-ray screening apparatus, and their poor performance can easily nullify any benefits that may be derived from modern X-ray tubes and generators.

A physical assessment of the imaging performance of panel-type X-ray image intensifier.

The performance of a commercial panel-type X-ray image intensifier has been investigated by physical methods, both objective and subjective. The objective measurements show that the manufacturer's claims are justified, except perhaps in regard to contrast loss. The subjective measurements reveal that the conversion factor ("gain") of the device is such that dark-adaptation is not necessary, though best results are obtained in a nearly dark room. Hence the device confers a significant advantage, both in information and in dose to the patient, over traditional fluoroscopy. However, the conversion factor is nearly three orders of magnitude smaller than that of a conventional X-ray image-intensifier television system. Therefore, at modern fluoroscopic exposure rates, the eye is operating at light levels at which its own deficiencies set a limit to the perceptible information. To equal the performance of modern fluoroscopy the exposure rate to the intensifier must be increased to about 20 times the value customary in modern fluoroscopy. This can be done only by increasing the X-ray factors (kV and mA), resulting in a corresponding increase in dose to the patient of about one order of magnitude. Such an increase is in many circumstance unacceptable.

Television fluorodensitometry. A simple and rapid method for the evaluation of image intensifier-television systems.

Television fluorodensitometry provides a simple and accurate objective measurement of the ability of an image intensifier-television system to transmit information. The need for the calculation of modulation transfer function curves is discussed with respect to this technique.

Comparison of the light output of image intensifier tubes.

Image intensifiers are now beyond the realm of experimentation and have become an integral part of the routine equipment in diagnostic radiology. Since the day of W. E. Chamberlain's Carman Lecture, “Fluoroscopes and Fluoroscopy” (1), the need for raising image brightness to cone vision level has been generally recognized. The Westinghouse Corporation in 1949 produced the first practical model of the Coltman image-intensifier tube; Chamberlain, in our institution, Temple University, used this in clinical work. Since that time our interest in image intensification has continued and we have had many tubes available for clinical and experimental purposes. In the desire to standardize photographic procedures utilizing the image-intensifier tubes, we intercompared tubes and evaluated their responses. The data and conclusions that follow are based on both the physical and the practical operating aspects of the tubes tested. The image intensifier is a large vacuum tube containing at the x-ray input end a fluorescent screen which converts the roentgen image into a light image. A photoelectric layer then converts the light image into an electron image. An electrostatic field accelerates the electrons and refocuses them to a sharp image at the small output phosphor layer at the other end of the tube. The output phosphor reconverts the electron image to a visible light image. In this process the original image is reduced in size about twenty-five-fold. Because of this concentration of electrons and the energy they have received from the electrical field, the viewing image is 500 to 3,000 times as bright as the image on a Patterson type B fluoroscopic screen. The light image may be directly viewed through an optical system of lenses and/or mirrors, it may be photographed with a still or motion-picture camera, or it may be displayed via television. The properties of the image-intensifier tubes evaluated were mainly their responses to different qualities and quantities of incident x-ray. Image qualities, i.e., contrast and detail perception, were not considered. We are now evaluating a number of the different image-intensifier television systems at present available for their “efficiency” in transmitting radiologic information; the results will be recorded in a subsequent communication. The variables studied are: (a) the incident x-ray intensity in roentgens per minute at the input end of the intensifier, (b) the intensity of light in millilamberts at the output phosphor screen, and (c) the electron emission in microamperes by the input photoelectric screen (sometimes referred to as the “brightness level”). The tubes are operated according to the specifications of the manufacturer. To simulate operating conditions most closely, the majority of the comparisons were done with a 10-cm. Presdwood phantom in the beam adjacent to the image intensifier. The field size was adjusted to include the entire input screen of the intensifier.