The purpose of any radiographic examination is to produce a film or films with the maximum information, clearly presented at the lowest possible dosage to the patient. The requisite parameters are sharpness, contrast, grain and exposure. This discussion will attempt to relate these to focal spot size, magnification, motion, film, screens and exposure techniques.

The principles of material certification and other quality assurance procedures have been developed by the photofinishing and reconnaissance communities. The Radiology Department of Duke University Medical Center has adapted these to radiographic materials. The program which was instituted over three years ago has been operational in its refined state for nine months and has uncovered unacceptable film before the film was used with patients. The material certification has benefitted both Duke University Medical Center and the well being of its patients.

The reasons for fog in radiographic films are reviewed. Fog can be caused by chemical reactions forming catalytic development centers in the emulsion layer, by unwanted exposure to radiation, or by the attack of the developer on silver halide crystals lacking catalytic development centers.

The effect of development temperature on image characteristics was investigated for several medical x-ray films. Speed, fog, and granularity increased as temperature was increased from 85 to 110°F. The effect of increasing temperature on fog was different for each film. Contrast increased with increasing temperature until fog reached levels that caused the contrast to decrease. Greater quantum mottle was observed at higher temperatures because of increased speed and contrast. The quantum mottle produced when a given radiographic screen is used can be expressed as a function of film speed and contrast, irrespective of whether the film type or the development temperature has been changed.

The effects of variations in processor operation on the diagnostic quality of radiographs are discussed. Many processing problems are related to the design of the processor, the external water regulation system, and maintenance of the machine. Means of improving processor operation and a method of establishing a quality control program are presented.

The criteria determining thermal loading of x-ray tubes is reviewed. Major parameters of maximum rated heat storage capacity and maximum continuous dissipation are defined as related to the thermal characteristics of the x-ray tube target and its radiographic loadability. The resulting anode thermal characteristic chart is proposed and provides for a 25% target storage capacity value on which to base radiographic ratings. For procedures in which the target heat storage exceeds 25% of the maximum rated storage capacity, a reduction to 0.8 of the maximum radiographic load rating is proposed. A target design capable of withstanding greater thermal loads and results of qualification tests are reviewed.

Attempts to improve the resolution capability of an x-ray imaging system have to include the presence of the patient, particularly the effect of subject motion. From this it follows that the loading capability of the x-ray machine should be an integral part of the analysis and optimization of systems resolution. We have tried to quan-tify both resolution and load capacity and to merge them in a "figure of merit", which seems helpful in judging focal spot performance. A true falling load characteristic for the focal spot distribution as well as for the exposure load characteristic appears to give optimum performance in terms of systems resolution. With computer help, we have calculated the pertinent parameters, such as intensity, modulation transfer, load, and temperature as functions of spatial and temporal coordinates.

The loadability of a rotating anode X-ray tube is discussed as a function of such parameters as rotational speed, focal spot size and anode material, and in particular the thermal constants. Resulting possibilities for further increasing the output and the additional technical effort involved are discussed. Limits of loadability are indicated. Finally the influence of the intensity distribution on the loadability is discussed and demonstrated in model distributions such as Gaussian or twin-peaked distribution.

Conventionally, ratings of rotating x-ray tubes are calculated using the law: p oc w3^/2, where P is peak power and w is the focal spot width. This formula is only true if the electron beam energy is deposited at the surface of the target ("surface mode of heating"), and is usually sufficient for focal spots larger than 0.5mm and tungsten as target material. For smaller focal spots, and/or target materials of lower atomic number, peak power capability is higher, especially at higher tube volt-age. The reason is the penetration of the electrons into the material ("Volume mode of heating"). A computer program was developed to calculate peak power versus maximum temperature and was applied to tungsten and various composites as target materials. For a 50μm focal spot, the power increase is 80% at 80kV (4" tungsten target, 10,000 rpm). This is verified by actual focal spot performance. Further, we compare power capability of rotating targets versus stationary targets, particularly with regard to micro focal spots. For a 100 μm focus, the difference is more than a factor of 20 in favor of the rotating anode.

In order to calculate the heat loading parameters of a rotating anode X-ray tube, it is necessary to make some assumptions. Because of this, it is extremely important that accurate measurement techniques be employed to check the thermal data. We shall review some of these measurement techniques, as well as see how this laboratory approach can be used to develop an application program.

Rotating anode X-ray tube radiographic ratings have historically been established as a single set of exposure curves intended to provide adequate tube life over a wide range of applications. The problems encountered with this approach in modern radiographic techniques are described, with emphasis on the permissible latitude in the parameters which influence tube ratings and on the dynamic nature of actual tube ratings due to changes in the base temper-ature of the target over the specified range of heat stored in the anode. The use of two radiographic ratings is proposed, the choice of which will be dependent on the level of anode heat storage expected in the primary usage of the tube, an approach which will provide an improved basis for establishing more accurate ratings for the specific application of the rotating anode X-ray tube.

An investigation was made to evaluate currently used subtraction radiography techniques. The first order subtraction technique was found to be adequate for conventional clinical use. However when using fine grain high contrast films for the originals, the second order technique gave a more accurate subtraction image. The limiting factor in the sensitivity of the radiographic subtraction technique for detecting small contrast changes over an area of about 2 cm in diameter was found to be film noise and not quantum statistics. Extra fine grain films were compared with conventionally used films. While these extra fine grain films gave slightly better results, they also required x-ray exposures which would be too high for routine clinical use.

The difference image produced by digitally subtracting one member of a pair of sequential PA chest radiographs from the other has been investigated as a possible tool for detecting primary lung cancer and for measuring response to treatment of cancer that is metastatic to the lungs. The resultant images show a variation from a uniform neutral gray level wherever significant changes exist between conjugate regions on the two x-rays; such changes occur, for example, when a lesion has grown during the interval between the two radiographic examinations. Such difference images might improve the ability of the radiologist to locate clinically significant features in the original radiographs, which might otherwise be overlooked because of the faintness of the detail. Certain demands of the process place restrictions on the repeatability of patient positioning during X-ray exposure. A method is suggested for facilitating more exact repositioning and also for producing usable difference images directly.

A novel image processing technique simulating mechanisms of the human visual system is described. An experiment is detailed, applying the principles of this technique to the digital manipulation of a defocused 35 mm image, and shows the spatial frequency improvement in the resolution of a processed image over the original. The design of a quasi-real time electronic system to rapidly process degraded images in quick succession is discussed.

Our concept of quality control -- arrived at over a period of more than 5 years -- can be defined: Quality control is an objective system designed to determine that the performance of components in a radiology system is or is not as labeled by the manufacturer.

The factors that I consider to be absolute essentials in our quality control program at Mayo Clinic are x-ray generator calibration, sensitometric regulation of film processing, x-ray exposure technique system, and on-line quality control. Other aspects of a complete system such as measurement of x-ray tube focal spot size, radiation output checks, checks on the performance of our image systems, and evaluation of new products are desirable to improve our work; these have been incorporated as they have become available. An effective quality control program can minimize patient exposure, can improve and maintain the overall diagnostic quality of the radiographs accepted for interpretation, and can save money in the institution.

In 1969 Congress passed the Federal Coal Mine and Safety Act, Public Law 91-173. This law is sometimes referred to as the Pneumoconiosis law or the "Black Lung" law. It called for periodic radiographic examination of the chests of all coal miners working in underground mines. This law was unique in that it called for multiple readings of the radoigraphs, the second reading to be made by a radiologist not associated with the facility where the radiograph was made. The great variation in the radiographs received led to a need for greater uniformity in the radiographs. A Quality Control Group was set up in an attempt to accomplish this objective. So far as we know this was the first general use of the term "Quality Control" in radiological terminology. The term or idea caught on and in the last couple of years it or its equivalent, Quality Assurance, has become an In subject. No meeting involving radiographic procedures has been without one or more presentations using one of these terms as the subject of the presentation.

Quality control has long been practiced, diligently, in the photographic manufacturing, motion picture, and aerial reconnaissance/mapping industries. Manufacturers spend large sums of money on quality control tests and analysis in each step of the manufacturing process including the selection and processing of the gelatin, the testing of each constituent chemical, the testing and certification of the final product, and the testing of the containers used for packaging. Between the first step in the manufacturing process and the final packaging many quality control checks are carried out. This assures that the product, as it leaves the manufacturer's warehouse, meets the specified criteria in terms of speed, contrast, shelf life, fog levels, uniformity, etc.

We live in an era of consumerism, in which people are demanding that the products and services they receive be of uniform high quality. This attitude increasingly prevails in the area of health care services, where the patient-consumer expects to receive the highest quality medical care which a facility can provide. In diagnostic radiology, the issue of quality involves three separate assumptions: first, that a necessary and appropriate examination was ordered for the patient; secondly, that the image on the radiograph or fluoroscopic viewing system is of such quality that an accurate diagnosis can be made; and thirdly, that the image is interpreted correctly by a qualified individual.

(General Comment) You have stated that the performance specifications of modern densitometers exceed the needs of radiology for routine densitometric checks. If the acceptable range of density variation in the finished radiograph is of the order of 0.2 as has been stated by some speakers, and if you accept the usual rule that the precision of a measuring instrument should be ten times as good as that of the process being measured, then the instrument should have a precision of 0.02, which is axactly what is specified by densitometer manufacturers.

The wide range of variables in the x-ray imaging process makes it important to be discriminating when establishing a routine quality control program. In Ontario in particular, the value of such a program will be subject to close scrutiny. This paper considers those measurements which have been found to have some benefit, either economically or in improved picture quality, and questions the value of many routine checks which have been recommended. In particular it suggests that measurement of x-ray waveforms may be very significant both in quality control and in detecting equipment malfunction. The justification of a control program in terms of radiation safety and economics is considered briefly.

An aggressive program of quality assurance in the Radiology Department can do much to insure the diagnostic content of radiographs while reducing patient and operator doses. To establish the program it was first necessary to identify the parameters to be evaluated and to place realistic limits on the allowable tolerances for each. The methods of measuring each parameter are described.

The use of a random object distribution for the characterization of x-ray focal spots for quality control purposes is described. This technique, utilizing a coherent optical processor, allows for the direct generation of the two dimensional modulation transfer function (MTF). The distance between the first zeroes of the MTF, in the orientation of interest, are then measured to provide an estimation of the x-ray focal spot size. This technique is compared to the conventional pinhole image measurement technique and the failure of resolution (star measurement) technique and is found to produce similar variability and sensitivity to changes in the focal spot size.

A method is described that can be applied in a clinical environment to measure the linepairs/mm resolution, to test the electro-optical focusing, and to measure a quantity Q proportional to the conversion factor of x-ray image intensifiers. The resolution can be determined and electronically optimized by using a monocular of 7.3-12x power to view the image of a metal test pattern placed at the entrance plane of the intensifier. To determine Q, a photometer is used to measure the brightness of the output screen as a function of input exposure rate. The measured data can be fitted with a straight line, the slope of which is proportional to the conversion factor of the image intensifier. According to the results the precision in the measurements of Q was better than 5%.

A block diagram representation of the circuitry is shown in Figures 1 and 2. Figure 1 shows the basic elements of an automatic exposure control with an ionization chamber as a detector. (Phototubes may also be used in place of ion chambers.) Figure 2 shows a typical automatic exposure control system with several ionization chamber detectors, and a photospot detector. It also shows an optional tomographic exposure control with current feedback and kVp servo compensation.

Production of a diagnostic quality radiograph requires the delivery of a predetermined amount of x-radiation to the film-screen combination. Variations in patient thickness and absorption make it difficult to predict the x-ray exposure values necessary to produce an incident beam which will yield the predetermined transmitted amount of radiation at the film-screen. Automatic exposure control devices largely solve this problem when properly designed. Design problems facing the automatic exposure control designer are discussed along with a summary of the characteristics of a diagnostic quality radiographic image.

The purpose of this paper is to communicate some observations on a some-what subtle aspect of the performance of x-ray phototimers: viz, the way in which their response depends on the x-ray energy spectrum and on the presence of scattered radiation. We specifically avoid the more basic question of sta-bility, reliability, and speed of response. Much of the phenomena which we have studied would, in the jargon of the radiological engineer, fall under the heading of "KVP dependence." However, from the point of view of the physicist, it is the effective energy, n, of the beam which emerges from the patient, ra-ther than the KVP, which is the relevant variable. The point is that E depends on both KVP and the amount and nature of the absorbing substance in the beam. For example, we would expect the beam emerging from a skull study at 80 KVP to have higher R than that of a chest film at the same KVP. If this difference were significant to the phototimer, then it would be meaningless to speak of a "KVP correction."

A protocol for acceptance testing and performance monitoring of radiographic phototimers is described, together with results obtained during application of the protocol to evaluation of the response characteristics of phototimers on two new x-ray generators.

Automatic exposure controls for Diagnostic X-Ray procedures are in use today in four basic configurations. Entrance type ion chamber sensor Entrance type photo multiplier sensor Exit type ion chamber sensor Exit type photo multiplier, sensor

Three different types of phototimer systems are compared, utilizing a simple method for performance evaluation. A phototimer system using an ionization chamber as a radiation sensor located between the grid and the film cassette is found to be the most reliable phototimer system and is therefore recommended for phototiming techniques. The minimum reaction time of the phototimer system and the backup timer are also discussed briefly.

Early in 1972 the Bureau of Radiological Health undertook a program in its Division of Electronic Products to assess the exposure and imaging characteristics of rare-earth intensifying screens. Several internal reports together with publications in the open literature summarize the principal finding of this program to date, namely, that a new technology has emerged which allows medical radiography to be carried out with exposure reductions between roughly 1.6 and 2.5 when the rare-earth systems are compared to calcium tungstate systems with comparable image quality. This exposure reduction is due to the increased quantum efficiency, or stopping power of these screens. We believe that the mixed reviews which the rare-earth systems have received are due to a misapplication of the additional brightness of the rare-earth phosphors which is inappropriate to the particular radiographic task.

It is shown that the level of magnification which is optimal is similar for both high speed rare-earth intensifying screens and medium-speed calcium-tungstate screens. The amount of perceivable information obtained with calcium-tungstate screens is, however, higher than that obtained with rare-earth screens. This difference is attributed to the increased radiographic mottle in the rare-earth screens.

The properties of intensifying screens depend mainly on the type and amount of phosphor, the binder, and its ratio to the phosphor. Screens with different speed and definition properties can be made by changing these ratio. Further improvements can be achieved by phosphors with a higher quantum efficiency. The recently introduced rare-earth phosphors give interesting results which are compared with those of conventional screens. The technical and clinical problems are discussed.

X-ray beam spectra varying from conditions approximating those found in mammographic studies to conditions for general purpose diagnostic radiography were obtained for the primary beam as well as for radiation scattered by a radiographic subject. The transmission spectra of various intensifying screens also were measured for these conditions. From the latter it was possible to determine phosphor absorption as a function of x-ray beam quality. The lanthanide phosphors were shown to be less sensitive to scattered radiation than CaW0₄, BaSrSO₄ or Y₂0₂S.

The use of rare earth screens in diagnostic radiology results in new complexity. However, there is increased radiographic flexibility and diagnostic yield. Magnification techniques are enhanced and patient motion is minimized. The system considerations include higher ratio stationary grids, very fast exposure timing, smaller focal spot tubes and flat table tops. However, the nonlinearity of automatic exposure controls is a problem with the new phosphors and demands close attention.

A number of rare-earth imaging systems have been studied to determine their applicability to medical radiography. The characteristics evaluated for each system include the relative speed, average gradient, base plus fog density, resolution, reciprocity failure and noise. A summary of the results of this evaluation is reported.

Radiographic screens with improved phosphors were evaluated in terms of their impact on image quality and system design. Using tungstate screens as a reference it was shown that system performance can be improved by reducing one or more of the following parameters: MAS, KVP, Focal Spot Size, and Exposure Time. In the case of cardiovascular angiography for instance, maximum benefit was obtained by reductions in exposure time and focal spot size.

The specification of performance characteristics for a diagnostic radiologic imaging system involves an interplay between purchaser and supplier which often results in inadequate understanding of the imaging requirements by the supplier, and unfulfilled expectations of the imaging system by the purchaser. To diminish the impact of these results, the communicative linkage between supplier and purchaser should be as strong as possible during the development of performance specifications and acceptance testing protocols for the imaging system. As an aid in establishing this linkage, we have developed a statement of performance specifications which accompanies requests for bid proposals distributed to suppliers of diagnostic radiologic equipment. This statement is presented here in its general form; certain modifications may be necessary in its adaptation to any specific radiologic imaging systems.

There are few jobs in the lives of radiologists which equal the frustrations encountered in the purchase of new equipment. The objectives of the purchase from the radiologist's point of view are quite simple; that is to produce radiographs of excellent image quality with great efficiency and reliability built into the machine at the lowest possible cost. Unfortunately, most of these objectives are diametrically opposed to one another. While most salesmen would have us believe that image quality is directly proportional to cost, I am not convinced that this is true, since radiographic image quality seems to have changed very little over the decades, while the cost has continuously and steeply increased. I realize of course that the fluoroscopic image has improved considerably with image amplification. Efficiency and convenience of operation certainly are inversely proportional to the reliability of any piece of equipment. I cannot ever remember anything going wrong with the bracket on the wall which held up the 14 x 17 cassette for a chest x ray, while the transport mechanisms in the automated chest units periodically strike, because the humidity in the room makes the films too sticky, or, if the film is alright, the microswitches stick. On the other hand, the number of patients which can be accommodated per unit time with an automated chest unit is truly astronomical. This example of course is an absurd one, and I use it only to emphasize the incompatibility of objectives, which we attempt to meet in purchasing equipment.

The concept of the radiological consumer writing specifications for x-ray equipment prior to purchase is both very new and well established. It is new in that many medical centers, who are now employing full time professional physicists and engineers to evaluate their existing equipment, are quite logically beginning to generate pre purchase specifications. However, at least one federal agency, the Veterans Administration, has for years required that all x-ray equipment purchased for their hospitals meet a long list of fairly demanding qyccifications. These requirements, published as Federal Specifications GG-X-635' , are an example of the kind of thing which a customer can demand and the industry can provide. If anything, the VA specifications err in the direction of being too specific and detailed, and most hospitals would be foolishi to adopt them in a wholesale manner. For example, they require that the MA meter shall have double or triple scales, that the unit fit in a room of between 9 and 10-1/2 feet, that an electrical steroscopic shift be available, etc. Obviously, also, any set of specifications must be upgraded to allow for new technologies as they come along. However, the VA has demonstrated that the x-ray industry can meet these standards of quality. By contrast, it has been our experience that, in the absence of any hospital based program of quality evaluation, even brand new x-ray installations can be seriously deficient in some way or other. For example, we have not only suffered from installation errors in such areas as TV systems, KV calibration, or tube protection circuits, but also from faults of design wherein the equipment could not possibly meet performance standards as good as those in GG-X-635. For example, we have a generator used in tomographic examinations at low KVP, where the KVP changes by 10 when switching MA stations. Other examples include timers with incorrect resistors values used in the design, KVP values which change by as much as 10 KVP during a given exposure (see figure 1) and between successive angiographic exposures, and phototimers that simply do not work. I emphasize that these faults were apparently not due to faulty installation or failure of components, but represent designed limitations in the original equipment.

The x-ray industry designs, manufactures, sells, and services the tools needed by the radiologists to diagnose their patients.

The radiologic consultant may function as interpreter from the user to the supplier to effect bid requests, and from the supplier to the user in the evaluation of response. A technique is described as well as conventions contributing to the requirement for the service.

Purchase Guidelines are a part of a three-pronged effort to improve the practices and procedures for procuring technology in the health care institution being conducted by the Alliance for Engineering in Medicine and Biology under grants from the National Science Foundation and the Rippel Foundation. The other two prongs to the effort are; one, a handbook and course intended for purchasing department people, and; two, an executive summary booklet and briefing course to be given at professional society meetings and intended for the executive hierarchy.

Question by Mr. A. Van Art, Litton Medical Systems: Can the customer modify his certified equipment as he wishes without taking on the burden of himself becoming a "manufacturer" as defined by the standard? Answer by Robert G. Britain, Director, Div. of Compliance, BRH: Unless the question is further qualified as to what type of modification would be made, such action would not be recommended on the basis of the policy expressed in the preamble to the Federal standard for diagnostic x-ray equipment when it was published in the FEDERAL REGISTER as a final rule on August 15, 1972 (37 FR 16462): "The purchaser who redesigns or modifies certified components in, or removes certified components from, an x-ray system would also be considered an assembler, hence a manufacturer, and thus must be authorized by a variance for changes which cause certified components in the systems not to meet the stan-dard. If he orders special, nonconforming equipment from a component manufacturer, the component manufacturer must also petition for a variance. There would be no need to obtain a variance to modify systems which are not to be used for diagnosis or visualization of humans, nor to perform routine repair or maintenance."

Ultrasound imaging of soft tissues places severe demands on the design of imaging systems because of the large range of echo amplitudes which may be encountered at any point in the body. Simple TGC curves are often inadequate in producing optimum gray scale images since the ultrasound traverses a variety of structures with substantially different attenuation coefficients. Phased array systems are shown to suffer from increased image ambiguity as compared to simple transducers, a result of discrete sampling of the aper-ture, which reduces the effective dynamic range which can be presented accurately. For a 16 element 1.7MHz array with 1.76 wavelengths interelement spacing the maximum side-lobes are only 6db below the main lobe. The use of different transmit and receive array geometries can improve the overall system spatial response. Experimental results from a 16 element 1.7 MHz transmit array with .88 wavelength interelement spacing and a receive array of the same frequency with 1.76 wavelength spacing indicated a reduction in the sidelobes to 13db below that of the main beam.

This paper was presented at the meeting, but is not being published in these' Proceedings. Herewith are the questions and answers which followed the oral presentation: Question from K. F. Etrold, RCA Laboratories: What are the problems due to imperfect registration of the scanning equipment when using peak detection mode (writing-in of adjacent areas on target)? Answer by Waxman: You get no benefit from peak detection in eliminating scanning equipment errors.

The emergence of grey scale echography over the previous storage tube methods of ultrasonic scanning leads to a reappraisal of equipment requirements, scanning techniques and criteria for classifying tissue. The use of grey scale to accurately display the magnitude of echoes requires the use of photographic film, scan convertor or computor storage to record the echogram. It's diagnostic ability is improved by fast automatic scanning, high resolution or annular array transducers, compression amplifiers and the use of simple as well as compound scanning. We have developed criteria for differentiating solid and cystic lesions, classifying normal tissue and pathological processes both localised and diffuse.

Modern diagnostic ultrasound scanners use grayscale representation of echo amplitude to show anatomy clearly. The quality of the scans is a function of both the equipment design and equipment operation. This paper deals with the practical aspects of gray-scale ultrasound which the operator can control to get optimum diagnostic information. Transducer selection, control settings, image photography and equipment calibration are discussed.

X-ray C.A.T. has proved to be invaluable to display intracranial and orbital lesions and should be valuable in the thorax. However, instantaneous imaging provided by ultrasound allows the heart to be displayed while the lack of ionising radiation hazard permits its use in obstetrics and in screening healthy populations. In the non-gravid abdomen, ultrasound has many advantages including excellent resolution, no radiation exposure and economy. The relative merits of x-ray C.A.T. in the abdomen have yet to be evaluated.

The medical diagnostician can advise instrument engineers on the optimal display of a given pathologic entity. The introduction of artifacts may sometimes be diagnostically useful and paradoxically, the loss of data may improve accuracy by accentuating small differences between normal and malignant tissues. Clinical ultrasound requires application of techniques for image enhancement which are becoming available.

Effects of kVp, voltage wave form, added filter, and tube current on three-dimensional reconstruction from x-rays have been investigated in relationship to sampling time,spectral heterogeneity, contrast, quantum noise, and patient dose. Comparison of statistical limitations with and without a water-bath indicates that scanners which employ a water-bath are comparatively inflexible in this regard. A degree of flexibility in the choice of kilovoltage and filter seems both desirable and feasible in scanners which do not use a water-bath. Minimization of patient dose is also limited by statistical factors. Reconstructions from measured data have been carried out to demonstrate the relationship between these factors.

This paper discusses physical measurements of the EMI imaging system including resolution (MTF) and noise. Questions are raised regarding system linearity and isoplanacity and therefore general applicability of the above measurements. The scan slice geometry is also investigated and potential missing regions in the scan and dual imaging situations are explored.

Basic quality characteristics of computerized axial tomography images are defined and discussed with respect to the present state of the art systems. Characteristics described include accuracy, precision, noise level, contrast, and artifacts.

A phantom consisting of a 2.5 cm diameter aluminum rod, a balloon filled with castor oil and a balloon filled with a phenylated silicone fluid were imaged in water with ultrasound transaxial tomography of attenuation by reconstruction (UTTAR). This phantom was chosen to investigate the feasibility of detecting small changes in the ultrasound attenuation coefficient of soft tissues in planes containing bones. Opposed transmitting and receiving transducers were scanned on either side of the phantom just as an x-ray tube and detector are scanned in the EMI x-ray computerized axial tomography system for brain imaging.

The computational form of radiographic signal analysis using linear systems theory is such that optimization calculations would involve a large computational effort. An analytic approximation for angiography is described. Series expansions are used to include effects of film response, secondary and off-focus radiation, x-ray attenuation and blood vessel diameter. The degradated image profile is determined using a gaussian approximation with a Tchebycheff expansion correction term. It is found that this approach is accurate to within about 10% for blood vessels smaller than 1 mm in diameter.

We have developed and applied clinically a low cost electronic radiographic system for rapid intervention in neurosurgical procedures. The apparatus is operated by means of a single push-button control which pulses the x-ray tube, and simultaneously stores an individual television field on a magnetic disc, producing a frozen image which is instantly displayed on a small television monitor. During surgery this system has benefitted the neurosurgeon by enabling him to record and instantly display electronic radio-graphs for more rapid intervention with reduced risk of mortality and morbidity.

A practical technique for accurate and reproducible determination of coronary arterial stenotic lesions has been developed. This technique eliminates the shortcomings of the conventional subjective way of analysis. Its use in appropriate cases with obstructive lesions in the coronary circulation will result into objective angiographic data as a baseline for their possible hemodynamic significance. Comparative studies between the results of angiographic measurements of this type and clinical and hemodynamic data retrieved by other clinical applicable diagnostic methods should increase our understanding of the pathophysiology of the coronary circulation in patients with coronary artery disease.

The Roentgen densitometer comprises a conventional x-ray head and a compact cluster of six solid-state x-ray detectors in the place of conventional x-ray film. Each detector is connected via suitable amplifiers to one channel of a six-channel pen recorder. An infant or child is placed over the detectors such that the cardiac silhouette shadows the cluster, and a bolus of radio-opaque dye is injected into the external jugular vein. The dye coursing through the cardiopulmonary system modulates the intensity of X-radiation impinging upon the detectors thereby producing six simultaneous high-resolution densitometer curves from within the cardiac chambers. The curves are analyzed through a least mean square fit digitized program for abnormal hemodynamics resulting from intracardiac shunting and T, the exponential time constant, and the time to peak is computed for each curve. Analysis of these two parameters allows classification of the patients into four clinically distinguishable categories; right-to-left intracardiac shunt, left-to-right intracardiac shunt, bidirectional shunting,.and normal cardiac circulation. By this simple, inexpensive and relatively non-invasive means, congenital heart defects can be detected without resorting to cardiac catheterization procedures.

An optical system was devised which generates a parallelopiped grid interference pattern in 3-D space. When the pattern is projected on a given surface, the surface creates a well-defined modification of the grid pattern which is recorded (by photography, electronic video imaging, etc.) for subsequent topographic analysis. The inexpensive system, designed for safety, ease of use, and versatility in a clinical environment, has been used to record intra-oral surface topography of oral structures in-vivo , as well as other concave and convex structures of health sciences interest. Two low-powered lasers are used, each generating parallel fringe patterns by reflection from thin optical wedges. The two fringe patterns generated are optically adjusted and aligned so that they are of equal spatial frequency, mutually perpendicular, coaxial, and collimated. The spatial frequency of the optically generated parallelopiped grid may be adjusted to optimize topographic measurement of a variety of subjects.

A physical model of xeroradiography is described which predicts a visible and measureable effect of the x-ray radiation noise. Agreement between the theoretical and experimental magnitudes of the developed radiation noise and its dependence on the exposure energy is excellent. The results imply xeroradiography is capable in principle of the ultimate in sensitivity providing the photoreceptor absorbs all the incident x-rays.

The low macro response of xeroradiography leads to difficulties when comparing image parameters (D-logE curve, ASA speed, etc.) with conventional X-ray recording systems. Here micro response measurements of resolution and noise are presented, allowing an absolute comparison in terms of detective quantum efficiency.

A quantitative model has been developed to characterize the formation of an electro-static x-ray image on an amorphous selenium photoreceptor. The model is based on measurements of selenium x-ray photogeneration efficiency in the mammographic and radiographic energy ranges for internal fields E ranging from 1 to 12 volts per micron. The x-ray energy absorbed by the selenium for each neutralized surface charge is found to be 510 eV divided by E in volts per micron. X-ray source spectral distribution, kVp and mAs as well as photoreceptor thickness and initial surface potential are included in the comput-erized model. The effects of Compton back scatter and foreward scatter are included through judicious use of object absorption and attenuation coefficients. Discharge curves calculated from the model illustrating two extremes of object scattering are shown to be in close agreement with experimentally measured discharge curves.

By using grey scale echography and ultrasonic equipment with a resolution of the order of 1mm, echo patterns of the breast are obtained which contain characteristic features and these then form the basis of a classification criteria. The use of this criteria currently enables the detection and diagnosis of cysts and liquid filled ducts as small as 2mm in diameter with an accuracy approaching 100%. Solid lesions as small as 5mm have been recognised and in a series of patients with breast disease a correct interpretation was made in 85% of the cases with malignancies. Because there is no radiation hazard, this imaging technique can be used repeatedly without risk.

Theoretical considerations and experiments show that thermography at centimeter wavelengths offers an attractive penetration depth of more than one centimeter; however it is not well suited for remote imaging of the temperature of the human body because of its marginal spatial resolution and the required large distance between the receiver and the object. Millimeter wave thermography tests around 45 GHz show that a spatial resolution of a few millimeters and a temperature resolution of 0.1°K can be achieved. A penetration depth of several millimeters makes millimeter wave thermography more attractive for remote temperature sensing of deeper lying body tissues than infrared thermography.

Thermography may be a helpful modality in the detection of breast cancer. Utilizing agreed upon criteria for the evaluation of breast thermograms, approximately 15-20% of women will have a positive or abnormal thermogram. Some results suggest that this group may contain as many as 80% of breast cancer patients. (2) If these subjective impressions prove to be true over the next few years, thermography may be extremely useful in the future as a screening method.

A low light level electronic imaging system is being developed to be used in a mass screening program for breast cancer detection in asymptomatic women. In this technique a mammographic image formed from an x-ray beam collimated by a scanning slit is converted to an intensified visible image which is viewed by a high resolution isocon television camera. The signal which is displayed on a small flat-faced cathode ray tube is photographed onto 70 mm roll film. Some advantages of the system for mass screening are its low cost of operation, ability to eliminate detection of scattered x-rays, short examination time, small format film images, low radiation exposure to the breast and the capability of electronic image processing. The limiting resolution of the system has been measured using lead test patterns and a phantom containing small diameter wires. In these experiments the electronic technique clearly demonstrated a 50u wire and barely detected a 25u wire. Extensive studies of the imaging properties of the system indicate that the image quality is limited chiefly by the television noise. In a clinical study, the ratio of the radiation exposure for the electronic method compared to that for the Lo-Dose film screen technique was measured at 0.17 + 0.06. At this level of exposure, the quality of the images was adequate to demonstrate cancers, calciTications, tumors, skin thickening, and trabecular structure. Calcification can be demonstrated, but at this Stage of development, very fine calcifications are not adequately visualized.

With the four technical factors of controlled motion, long target-film distance, exquisite collimation and good processing meticulously cared for, conventional generators and type M film mammography can be done with skin dose less than or comparable to other contemporary mammographic techniques with far superior image quality.