Image Intensifier Television 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.

Physical and clinical evaluation of a 2,048 x 2,048-matrix image intensifier TV digital imaging system in bone radiography.

To evaluate the potential utility of a 2,048 x 2,048-matrix image intensifier television digital radiography (DR) system versus a conventional screen-film (S-F) system for bone radiography. Basic imaging properties were evaluated including resolution properties, Wiener spectra, and detectabilities of low-contrast signals. DR images were obtained with the same exposure (iso-dose) or one-third the exposure (low-dose) used with the S-F system. The visibility of pathologic details of metastatic disease on bone radiographs of 27 patients was evaluated subjectively by six radiologists. Resolution properties of the DR system were slightly superior to those of the S-F system at low-frequency range, but the S-F system showed considerably higher resolution properties at the high-frequency range. The noise levels for iso-dose DR were slightly greater than those for S-F imaging at low spatial frequency; however, low-dose digital radiographs showed higher noise levels. Visibility of details of diagnostic features on bone radiographs was similar with both systems, but the low-dose digital radiographs were slightly inferior. High-resolution image intensifier television DR systems may be clinically useful for bone radiography.

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.

Hospital-wide PACS with a digital image intensifier TV system

Tokyo Hitachi Hospital, Hitachi Ltd., has used a hospital-wide PACS for over 1 year. The system runs a 100 Mb/s optical fiber network over the whole hospital including wards and outpatient clinic rooms, with 11 image workstations. The network links digital imaging modalities such as X-CT, MRI, computed radiography (CR) and digital radiography (DR) with a 2048 x 2048 (2k x 2k) matrix image intensifier television (I.I.-TV) system. These modalities generate about 200 images/day. The system has managed over 300,000 images of about 8000 patients so far. Although being still under improvement, the system has really been used for routine work. The hospital-wide PACS of a small hospital has been proved to be very useful for both image diagnosis and image management.

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.

Dynamic Digital Subtraction Evaluation of Regional Pulmonary Ventilation with Nonradioactive Xenon

A method of evaluating pulmonary ventilation with a 57-cm image intensifier/television (II/TV) digital chest system is reported. With this method, the patient inhales a mixture of xenon and oxygen gases while dynamic imaging of the chest is done. Images of the airways and ventilated portions of the lungs are obtained by subtraction of images acquired before and after the xenon-oxygen mixture is administered. The feasibility of the method was evaluated by studies with xenon-filled tubes, an airway phantom, and a ventilation phantom. The results indicate that tubes larger than 3.2 mm in diameter are detectable at a xenon concentration of 41%, and that gas flow and flow distribution can be examined after image subtraction. If background subtraction is incomplete because of motion, the visibility of small airways is reduced greatly, although unventilated regions can still be delineated. The initial evaluation of this technique included imaging a healthy volunteer during xenon inhalation.

Optical image processing with liquid-crystal display for image intensifier/television systems.

We have studied the effect of real-time optical image processing (OIP) in an image intensifier/television (II-TV) radiographic imaging system by using a liquid-crystal display (LCD) placed between the II and the TV camera. The LCD compresses the dynamic range of the transmitted image by modulating the spatial distribution of the light intensity of the image from the output phosphor of the II. The degree of dynamic-range compression can be designed so that the dependence of the signal-to-noise ratio (SNR) of the LCD-TV system on x-ray intensity matches that of the quantum noise. We measured the physical properties of an LCD and evaluated its capability for OIP. Our experimental results demonstrate that it is feasible to use an LCD to compress the dynamic range and to improve the SNR of the image. The advantages of implementing OIP with an LCD in image acquisition systems in which a TV camera is used are discussed.

Noise Reduction in Real Time X-Ray Images

The signal-to-noise ratio of real-time digital X-ray imaging systems consisting of an X-ray image intensifier-television chain was investigated while concentrating on the effect of the X-ray quantum nature. Along with conventional signal accumulation, logarithmic conversion and subtraction, a new technique called the peak hold method is introduced. Theoretical and simulational studies were made with practical parameters. Theory and simulation showed good agreement. An accumulation of signal is most effective for improving the signal-to-noise ratio; the peak-hold method comes next. The peak hold method, however, offers a new image-display mode. Moreover, this method is superior to signal accumulation for specific conditions.

中枢性めまい症例に対するＤＳＡ（Ｄｉｇｉｔａｌ Ｓｕｂｔｒａｃｔｉｏｎ Ａｎｇｉｏｇｒａｐｈｙ）の応用

Digital subtraction angiography (DSA) is a recently developed non-invasive intravenous angiography which has become possible through real time digital subtraction of x-ray transmission data from an image intensifier and television system. The output signals of the image intensifier-television camera system are digitized by an analogdigital converter. The digital information, 512×512 pixels and 9 bits deep, is fed into the image processing assembly after logarithmic amplification, where 2-8 frames are added and subtracted from mask images for the final digital images. Intravenous digital subtraction angiography was performed in 21 patients with intractable dizzy spells of central origin resistant to treatment. These patients showed some signs of CNS disturbance, although there were no significant findings on CT scans.DSA resultsCases Percentagenormal 7 33.3abnormal 14 66.7unilateral vertebral obstruction 4 19.0stenosis 6 28.6reduced flow 2 9.5bilateral vertebral stenosis 2 9.5Surprisingly, findings were abnormal in 14 of 21 patients (66.7%).DSA is, therefore, considered to be an important aid in the diagnosis of vertigo of the central type.

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.

Digital Fluoroscopic Angiography in the Diagnosis of Central Nervous System Diseases

Digital fluoroscopic angiography (DFA) is a recently developed non-invasive intravenous angiography which has become possible through real-time digital subtraction of X-ray transmission data from an image intensifier and television fluoroscopic system. Prototype units were developed and installed. The output signal of the image intensifier-television camera system was digitized by an analog-digital converter. The digital information, 512×512 pixels and 9 bits deep, was fed into the image processing assembly after logarithmic amplification, where 2-8 frames were added and subtracted from the mask images for the final digital images. Up to 32 serial digital images could be stored in real time in the frame memories, while additional images were transfered to other recording units as necessary. Fifty-five examinations were performed on 49 patients with various clinical symptoms referable to the central nervous system. Diagnostic information was obtained in 26 of the 55 examinations (47.3%), which included brain tumors, aneurysms, and atherosclerotic diseases in the neck. Examinations of “fair” quality were obtained 19 times (34.5%), most being intracranial arterial occlusive diseases. No information was obtained in 10 examinations (18.2%), mostly due to technical failures or misregistration artifacts. Although spatial resolution of DFA is inferior to conventional angiography, this technique will replace it in certain conditions such as: 1) screening and postoperative follow-up of cervical diseases; 2) visualization of carotid arteries in contemplated transsphenoidal hypophysectomy; 3) diagnosis of large tumors or vascular tumors; 4) visualization of faint tumor stains; 5) diagnosis of sinus occlusions; 6) screening of vascular lesions such as subarachnoid hemorrhage and megadolichobasilar artery; and 7) patency of STA-MCA anastomosis. Future development of DFA should be directed towards improvement of spatial resolution and removal of misregistration artifacts.

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.

Intravenous Angiography Using Computerized Fluoroscopy

During the past several years, we have developed dedicated digital algorithms for real time processing of X-ray transmission imaging data obtained from an image intensifier television fluoroscopy system. Three imaging modes called Mask Mode Fluoroscopy, Mask Mode Radiography, and Time Interval Difference (T. I. D.) Imaging have been tested in over 100 patients since installation of this. apparatus at the University of Wisconsin Clinical Science Center. Feasibility studies have been conducted to determine the capability of these techniques for imaging the entire cardiovascular system, including peripheral arteries, using intravenous injections of iodinated contrast material.

Morphology of the magnetospheric barium release

The magnetospheric barium release experiment of September 21, 1971, was observed by a high-performance image intensifier television camera system from Kitt Peak National Observatory, Tucson, Arizona. The system produced high-resolution video recordings of the dynamic morphology of the barium ion cloud. The system was calibrated for absolute sensitivity, thus enabling the reconstruction of the barium density profiles in the cloud. The ionized plasma expands along the field line with the velocity somewhat greater than the neutral expansion velocity. Perpendicular to the magnetic field line, the expansion of the cloud is limited by the forces exerted by the earth's magnetic field. Thus, the cloud takes up a field-aligned filamentary structure. As early as 30 sec after release, two major filaments could be distinguished. Two minutes after release, the cloud already consisted of at least 8 or 10 filamentary striationlike structures. These are formed in the low-density expanded part of the cloud. These striations and the diffuse parts of the cloud move in a direction perpendicular to the magnetic field with a velocity different from that of the main dense core of the cloud. This differential velocity moves the lower-density parts away from the main core. These lower-density parts appear to be highly structured in the form of fieldaligned striations. During the first 8 min after release, the high-density main core part erodes to a very narrow strip, which is about 12 km wide. This width of the central core is less than the diameter of the gyro-orbit of the initial velocity barium ions in the ambient magnetic field. The rapid fragmentation of the cloud to such narrow forms has interesting implications for the stability of dense magnetospheric plasma clouds.

Television and Practice

To the Editor.— The informative article in Medical News (217:575, 1971) neglected one application of television to medical practice which I feel is of equal significance to those discussed. While the transmission of images by television is a well-accepted technique, the extraction of physiologic data from medical fluoroscopy using image intensifier-television chains may turn out to be the most significant application of television to modern medicine. It is certainly possible at this time to assess accurately pulmonary ventilation and perfusion using this technique, and the analysis of human vascular disease seems equally promising. In no way do I wish to dilute the impact of image transfer through closed circuit television on the practice of medicine. However, this other application does exist and is the focus of a significant amount of current research in both the United States and Europe at this time.

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.

Auroral pulsations—Television image and X-ray correlations

The association between auroral X-rays and luminosity has been studied for pulsating auroras by coordinated observations with a balloon borne X-ray detector and a ground based image intensifier-television system viewing the N 2 + ING emissions. The degree of correlation between X-ray and luminosity variations was found to depend upon the number of pulsating forms common to both detector fields of view. Correlation was good in those cases when one form occupied the optical field of view but poor when several, asynchronously pulsating, forms were present.

Image Intensifier TV Camera System, Its Performance and Applications

A number of electrooptical and optical devices developed in recent years, such as electronic image intensifiers, high sensitivity image orthicon tubes with a thin film target, and high resolution fiber optics, enable one to design a practical image intensifier television camera system. Such a system will operate at light levels below the threshold sensitivity of the human eye and produce useful images on real time basis. One practical application of such a system is the observation of Gaussian and diffraction images produced by an electron microscope. Extended periods of observations of various specimens are being made at a much reduced electron beam current density level where irradiation from the electron beam bombardment will not harm or alter the original characteristics of the specimen. Under the reduced beam density level, the light output from the microscope viewing screen is of such low light level that direct observation is impossible.