In general, electro-optical imaging devices act as photon converters and/or amplifiers. They may convert and/or amplify a spectral distribution of input photons to output photons having a different spectral distribution. Alternatively, the input photons may be con-verted to an electron output current. Figure 1 is a generalized scheme which shows the multitude of possible image transfer and con-version routes which may be taken after the absorption of the input photons.

PICTUREPHONE® service, the Bell System's two-way audio-visual telephone service, is currently available as switched network systems in the Chicago Loop and Oak Brook areas and in certain other parts of the country as switched intercom systems. A PICTUREPHONE system has many potential applications in health care such as remote interactive consulta-tion, remote viewing of patients, charts, instruments, some X-rays and microscope slides. It can also be used to retrieve patient data from computerized medical record files. This paper briefly describes PICTUREPHONE systems, the character-istics of the camera tube, signal conditioning and the display unit. Overall performance data are given for optical sensitivity, spectral response, MTF and luminance transfer function. The transmission of electrocardiograms, X-rays and microscope slides are used as examples to illustrate image clarity. By means of alternative lenses and filters the performance of a PICTUREPHONE system, which was pri-marily designed for face-to-face visual telephony, can be improved for transmitting medical data.

It has been estimated that in 1970, 129 million people in this country were exposed to 210 million medical and dental X-ray examinations. According to the U.S. Bureau of Radiological Health, about 30% of the X-ray exposure does not contribute any useful information to the radiologist. There is no doubt in the mind of anyone that the advantages gained from X-ray examinations far exceed any possible late biological effects resulting from this exposure. All radiologists employ equipment and techniques designed to decrease X-ray exposure as much as possible while providing adequate diagnostic information. Still, there is increasing concern on the part of radiation scientists that medical and dental X-ray examinations are a significant public health hazard because of their increased frequency of application.

This paper discusses the development and performance of a 9-inch X-ray Image Intensifier featuring a continuously variable magnification from a 9-inch useful input diameter to a 5-inch useful input diameter at a fixed 20mm diameter output image. The pentode electron optical structure in this device was designed through utilization of a digital computer electron optics evaluation program. A brief analysis of the design technique is presented, with particular emphasis directed towards techniques used for prediction and optimization of electron optical performance parameters from computer analysis data. The described techniques resulted in a design which not only demonstrates geometric distortion of less than 5 percent and a flat focal plane surface, but also enables a single voltage divider magnification control which continuously varies the magnification while maintaining focus. This particular result enables incorporation of an integral power supply within the intensifier housing that provides complete operating voltages and subsecond zooming between 9-inch and 6-inch modes. Performance parameters of the device are also investigated with particular atten-tion to an MTF evaluation technique which applies to all X-ray image intensifiers. In addition to superior MTF, this new device also exhibits a conversion gain in excess of 5,000 with 125 linepairs per inch limiting resolution in the 6-inch input mode. Nine-inch mode gain is at least 10,000 with a limiting resolution of 90 linepairs per inch. The high gain and resolution of this new intensifier, in conjunction with its capability of rapid zooming with entire control provided by an integral power supply render it an excellent device for use in x-ray diagnostic equipment.

This paper describes a new simple technique for the fast readout of autoradiographic images from tissue slices. The tissue slice is taken from an animal which has been given a radioactively labeled drug. The autoradiographic image enables one to determine where the drug accumulates in the animal, by detecting the electrons given off by the radioactive material as it decays. The technique uses a microchannel plate electron image amplifier to detect electrons emitted from a radioactively labeled tissue sample. The microchannel plate will be described first, then an experiment performed to detect tritium in a labeled tissue sample.

In the past few years, basic technical developments have become available in the field of x-ray image conversion and amplification. In this paper we shall speculate on the applications of the medical x-ray image amplifier in the year 1980. We shall be conservative in our speculations by confining them to the possible application of devices already on the market or in advanced development.

Over the past years image intensification has come into widespread use to increase detection and recognition capabilities for objects of, or in, radiation of low intensity. The type of radiation, for which image intensification can be used, ranges from x-rays into the near infrared region. The principle of operation is explained through Figure 1. (See also Reference 1.) Radiation from the scene is imaged onto the first stage, where a percentage of the radiation is converted into electrons, forming an electron image. For x-ray intensifiers this stage consists of a phosphor screen and a cathode, whereas for other types of radiation only a cathode is needed. By the intensifier stage, the electron image is transferred to the output, where the electrons--in most cases--are used to generate radiation in a suitable wavelength region and of sufficient intensity. Sufficient intensity is obtained through a gain mechanism.

Implicit in any discussion on the digital analysis of medical imagery is the assumption that the photographic data can be converted into computer compatible form.

Two of the most fundamental parameters which influence the fidelity of clinical radionuclide images are the information den-sity and the composite resolution of the instruments which are utilized in the scintigraphic imaging process. We can basically describe such images as being inherently "noisy" and "out-of-focus" for these respective reasons. The interrelated conditions which contribute to this situation are briefly described as follows: 1) there are limitations on the amounts of radioactive substances which can safely be injected into patients as as the time available for performing the imaging procedure. 2) The design considerations for lead collimators place such factors as resolution, overall efficiency, and depth of focus at odds with one another. 3) The "state-of-the-art" in terms of the intrinsic resolution available from existing gamma ray detection and imaging devices leaves much to be desired.

The first commercial image analysis system to use television scanning was introduced in the United States in 1966. Since then, this quanitative tool has gained widespread acceptance in the material science field. Applications utilizing particle and chord size distributions, area and phase fraction determina-tions, and mean linear intercept are well documented in the metallurgical and powder chemistry fields. To date there are nearly 500 systems in use worldwide.

It is the purpose of this paper to present a brief overview of the problems and partial solutions in the study of radiographic image quality.

The following briefly summarizes the background on how the Bureau of Radiological Health became involved in the image analysis area. In October 1968 the Radiation Control for Health and Safety Act, Public Law 90-602, gave the Secretary of the Department of Health, Education, and Welfare and by delega-tion to the Food and Drug Administration new functions involving the radiation safety responsibility to control ionizing and nonionizing radiation emitted from electronic products. A majority of the responsibilities under the law have been redelegated to the Bureau of Radiological Health.

Radiographic imaging systems appear, at the outset, to be a relatively simple class of image forming devices. The radiologist relies on the equipment to provide him with images upon which he must base, in some cases, life and death decisions. One would then assume that the quality of the images, or radiographs, which the radiologist utilizes should provide him with the highest quality diagnos tic information that our technology can produce. The cost of most radiological equipment would imply that he is surely utilizing the best equipment available from the industry today. However, much of the effort in design and technology of radiological equipment disregards one of the simplest yet most important limiting factors in the radiographic imaging system, the x-ray focal spot.

For the evaluation and diagnosis of many craniofacial abnormalities, a standardized profile x-ray film of the head (sometimes called a cephalogram) is often a convenient radiological aid available to the clinician. From these radiographs one may observe, in a qualitative sense, such syndromes as Pierre-Robin, Downes' syndrome, Aperts, Thallassemia, as well as less severe abnormalities such as disharmonious development of the jaws resulting in malocclusion.

The significant steps in computer anal-ysis of radiographic images are 1) digitization of the x-ray image; 2) preprocessing of digital images; 3) extraction of significant features; and 4) automatic classification for normal, abnormal, and differential diagnosis. A typical digital image processing facility is described, including the needed interactive type digital displays. Techniques used for preprocessing radio-graphic images are detailed; typically, these are used to ensure a higher degree of success in the later stages of digital processing. Contour tracing and region enumeration algorithms are detailed for use in the com-puter analysis of radiographs. The important descriptive approach to the problem of feature extraction is provided along with illustrative examples. A case study of rheumatic and congenital heart disease is presented for the cardiac shape analysis of PA chest films.

Many specific diagnoses of diseases of the heart can be obtained in cardiac catheteriza tion laboratories. Dynamic changes in volume and distributions of coronary blood flow are studied by means of injecting roentgen-opaque (i.e., x-ray dense) material into the left ventricle or the right ventricle through a catheter. At the time of the injection of contrast media, the chest of the patient is irradiated with x-ray and dynamic movements of the opacified heart are projected onto a fluoroscopic screen and then recorded on videotape by a television system or on film by a photographic system. Although cine roentgenography that using film) can have higher spatial and temporal resolution (Ref. 1) than video roentgenography (that using television), the cine systems require a longer time to complete the diagnosis since the film must be developed.

Considerable effort has been directed toward the calculation of left ventricular volume from angiographic images. The research techniques are now sufficiently advanced to permit an examination of the factors that will influence their clinical acceptance on a wide scale. Our clinical/biomedical engineering team considers the following factors to be important: 1. The clinical protocol must cause minimal physiological interference in the cardio-vascular system, especially during the data collection period. 2. About 3 or 4 cardiac cycles must be available for analysis to determine beat-by-beat variations, and yield a representitive time-course curve for 1 cardiac cycle. 3. A single plane technique is advantageous compared to biplane methods for the obvious economic and data handling reasons. However, any single plane technique should be insensitive to variations in the plane of viewing of the ventricular chamber. 4. Technique should be insensitive to non-homogeneities in the image plane. 5. A minimum of human involvement should be necessary in the data collection and processing, and there should not be a need for human pattern recognition on a frame-by-frame basis. 6. The analysis must be reasonably insensitive to changes in the gain and bias controls in imaging system (X-ray controls, image intensifier, TV, video tape recorder and interface A/D controls). 7. The data conversion and analysis techniques should be such that they can be handled by a medium size process control computer (CDC 1700, IBM 1800, PDP 9, HP 2100, etc.). 8. It is desireable, but not necessary, that the technique be capable of on-line conversion.

The development of high resolution image intensifier tubes, television cameras and electronic storage devices has opened up the possibility of significant advances in the techniques of diagnostic radiology. Systems incorporating these components can increase diagnostic information, reduce procedure time, decrease patient trauma, reduce radiation dose and permit new types of procedures to be undertaken that were previously not possible. These new electronic recording techniques have now been used in gastro-intestinal examinations, selective catheterization, pelvimetry, repair of intra cranial aneurysms and arterio-venous malformations as well as in the high-resolution transmission of radiographic film images from the emergency room to the diagnostic reading room.

A major problem in clinical neuro-radiology is evaluating the extra-cranial vessels; specifically, the origin of the great vessels from the aorta and the carotid artery bifurcations. These sites are frequently involved by arterio-sclerotic stenosis or occlusion.

Closed circuit television systems are now in use in most fluoroscopy rooms for a variety of reasons: 1) Obviation of dark adaptation 2) Simultaneous viewing of the images by many observers 3) Convenient positioning of the images 4) Image processing by electronic means 5) Recording by tape, disc, storage tube

The problem of radioisotope imag ing in nuclear medicine is to develop an image containing a maximum of in-formation formed by fly-rays which in turn have been "focussed" by only ap-erture limitation. Gamma-emitting radio-labeled medicinals are designed to be concentrated by certain tissues. Abnormal regions may be indicated by either enhanced or reduced concentra tion of the labeled compound. The distribution of the radionuclides, as revealed by their T-rays (e.g., 140 KeV in the case of 99mTc), may then be the basis for diagnosis not possible with X-rays or other nonsurgical techniques. Because the radiation exposure of the patient must be minimized, the images formed are limited by quantum statistics, and indeed the practical detectors are those which respond to single γ-ray quanta. The image quality available with current techniques is modest by the usual standards of X-ray or light imaging; a 25 cm diameter image field seldom contains more than 1000 resolved image elements. Indeed the total information content is often carried by a total of only 100,000 photons. Examples of isotope images useful for diagnosis are given in Figure 1: (a) a brain containing a tumor, (b) a frame of a cerebral blood flow study, and (c) a pair of adrenal glands. In view of the unique nature of the information gained, even this very modest image quality is invaluable in diagnosis. An illustration of this value is the fact that about 2,000,000 radionuclide diagnoses are now undertaken each year in the U.S.

Liquid surface acoustical holography offers a new and exciting method of medical imaging. In comparison to the conventional ultrasonic B scan, (pulse-echo tomography*) acoustical holography offers the advantage of a true focused image, a continuous gray scale image, and a through transmission mode which displays the object relative to both absorption contrast and phase contrast. In addition, it is a real time imaging system allowing for a wide range of dynamic studies. The purpose of this report is to compare the imaging properties of a prototype system with imaging properties which we forsee to be necessary for broad medical application.

The full value of tomography as a diagnostic procedure cannot be achieved with currently available techniques because they do not permit utilization of the total information obtained in a single tomographic exposure. Time-resolved acquisition and storage of this information, however, permits reconstruction of any desired layer from a single patient exposure, thereby increasing substantially the diagnostic value of tomography. Although this time-resolved system achieves sectional radiography using geometrical techniques similar to those commonly practiced in modern radiology departments, it'has two unique aspects: recognition of the fact that all of the sample, not just one layer, is projected clearly on the image sensing plane at any instant during the exposure, and development of a method for storing this information so that any desired layer may be displayed without need for further patient exposure.

Recent work has stimulated considerable interest in using radar pulse compression concepts to improve the quality of medical X-ray and gamma ray photographs. (Refs. 1 and 2) These techniques involve using a coded point spread function to obtain increased resolution and reduced ex posure time. The coded point spread function allows use of a larger aperture in the X-ray camera, but requires a post-detection processing step in order to decode the data and obtain the desired image. The point spread function must be coded in such a anner that its two-dimensional autocorrelation function is very sharply peaked. In the post-detection pro cessing; the coded data are cross-correlated with the chosen point spread function to obtain the desired image.

X-ray tubes and gamma ray cameras have traditionally involved trade-offs between spatial resolution and radiation flux. Recently we have shown that the use of a Fresnel zone plate as a spatially-coded source or aperture can avoid this trade-off. In radiology, this technique can eliminate the need for a rotating anode and give higher resolution, while in nuclear medicine it can be used either to decrease patient dose or exposure time, or to increase resolution and greatly simplify the apparatus. With a coded source or aperture, the image is also coded, like a hologram and can be reconstructed optically. The system is tomographic with information about all planes contained in a single film.

The potential of negative pi mesons for radiation therapy has been informally suggested by many people, including Chaim Richman, now of the Los Alamos Scientific Laboratory. Fowler and Perkins (Ref. 1) were the first to make detailed calculations, and this work generated heightened interest in the use of negative pions for therapy. Their calculations showed that the strong nuclear inter-action experienced by pions when they come to rest could greatly increase the dose to the treatment volume. Figure 1 shows the depth-dose distribution expected from a 46 -MeV beam. The pions are captured by nuclei, primarily oxygen, nitrogen and carbon in tissue, which promptly break up into energetic but short-range charged fragments and neutrons. The total energy produced by breakup of the capturing nucleus is approximately 140 MeV; about 40 MeV goes into overcoming the binding energy of the capturing nucleus, about 70 MeV is carried off as kinetic energy of neutrons, a small amount as energetic nuclear gamma rays, and the rest (about 30 MeV) as kinetic energy of protons, alpha particles (helium nuclei) and heavier nuclear fragments (lithium and carbon nuclei). It is these high LET radiations (protons, alpha particles and heavier nuclei) that enhance the dose in the terminal region of the negative pion beam. Mesic X rays, nuclear gamma rays and neutrons are produced also but escape from the body without doing much damage either to the tumor or the surrounding normal tissue. Therefore, the depth-dose distribution from a pion beam does not drop off exponentially with depth (as with gamma rays, X rays and neutrons) but, rather, increases gradually until the stopping region is reached, where the high LET dose enhancement occurs. The finite range of pions in tissue also affords restriction of dose to normal tissue distal to the treatment volume to the muon and electron beam contamination.

Osteoporosis, a loss of bone mineral content accompanying certain diseases, endocrine disorders, and inactivity, is a relatively common medical problem which is difficult to detect in its early stages. Over the past few years, considerable interest has developed in procedures which promise to provide quantitative data concerning changes in bone mineral content during the development of a particular disorder or during the course of therapy for the disorder. These procedures have involved primarily densitometric measurements of radiographs of the extremities (Ref. 1, 2, 3) and use of a Nal(T1) detector to detect monoenergetic photons transmitted through the extremities. (Ref. 5, 6, 7, 8, 9) In general, the latter method, usually described as photon absorptiometric analysis, has provided measurements of highest accuracy and greatest reproducibility over extended periods of time. Also, photon absorptiometric measurements usually require orders of magnitude less exposure of the patient to radiation.

In 1895, Wilhelm Conrad Roetgen discovered the X-rays, which subsequently were also called "roetgen rays".

Dr. Krohmer (moderator): The purpose of this panel discussion is to acquaint members of the Society of Photo-optical Instrumentation Engineers, including some persons who are not familiar with all aspects of diagnostic radiology, with the views of radiologists, medical physicists, and manufacturers who are in the business of using, evaluating, and producing radiological equipment.

Mr. Siedband: While Dr. Tristan was talking, he reminded me of one of John Cameron's lines: "If I hadn't believed it, I would never have seen it." I have always respected the radiologist who can pick out images in a roentgenogram that are absolutely incomprehensible and not discernible to me.

Its historic development and areas for improvement. Fig. 1 shows a typical X-ray imaging system consisting of: the x-ray tube the collimator the filter the patient the grid the image intensifier the distributor the TV camera the TV monitor the film camera the processor the film viewer the observer

The topic that I would like to address today is a review of system performance requirements for imaging systems in diagnostic radiology. I intend to translate subjective performance factors related to clinical aspects into analytical engineering terms; a technique that manufacturers must attempt to better understand how to adequately design image equipment. For example, consider the vascular room pictured in Figure 1. I have picked a vascular system because it offers the greatest number of interacting design factors that effect or degrade diagnostic detail or resolution. These factors include cardiac motion, patient geometry, focal spot size, ma, KVp, exposure time and image system response.