The sustaining life blood of industry is the introduction of new products which are desireable to the customer and generate sufficient profit.

The methodology and results of an in-depth technical examination of new radiological equipment are discussed in this paper. High voltage kVp and MAS measurements and wave-forms have been obtained. The resolving capabilities of x-ray tubes and image intensifier systems have been measured using star and line pair resolution patterns, and focal spot images made using a pinhole camera. Tomographic performance in a variety of installations has been evaluated using a Littleton phantom and a pinhole plate. The complete radiographic, fluoroscopic, and mechanical operations and radiation safety compliance of x-ray rooms in all radiological specialties has been examined. The detailed procedures and methods of data recording involved in this study are discussed. Equipment problems encountered include the lack of accurate generator calibration, unacceptable fluoroscopic and spot film image quality, faulty tomographic motion and exposure termination.

One of the primary objectives of acceptance testing of a new radiological installation is the establishment of technique calibration of the x-ray generator. While we enthusiastically endorse the use of radiation penetrameters such as the Wisconsin Quality Control Cassette or a square root of 2 aluminum step wedge to assess the time dependent performance of an x-ray generator which is in clinical use, such tools are inappro priate for establishing calibration for a new facility. One must ascertain the behavior of the kilovoltage applied to the x-ray tube as a function of various conditions of loading and exposure control. That this is imperative should be made clear by the examples presented throughout this paper. The fourteen installations encompass five generator models produced by four manufacturers. Four of the generators are three phase twelve pulse. The fifth is further regulated to produce a nearly D.C. waveform. Three of these generators are furnished with mechanical type contacting while the other two are provided with silicon controlled rectifier exposure switching. The technique for observation of the performance of the kilovoltage waveform involves the introduction of a voltage divider or bleeder tank into the high tension secondary. It should be noted that all of the manufacturers who have installed equipment at Henry Ford Hospital utilize this technique. It has been our experience that kilovoltage calibration can be established to within 5%, and has often been obtained to better than 3% over the useful range of KV's and corresponding tube loads.

General considerations in organizing a quality assurance program are discussed. The development and general features of the program at UAB, which consist of a cooperative effort between the quality control technologist, the radiological service engineering staff and the radiation physicist, are briefly reviewed. The economic efficacy of such a program is justified by comparing data on film consumption before and after the program was established and by comparing estimates of x-ray vendor contracted service cost with that of inhouse service.

This presentation will describe methods used at the University of Minnesota Hospitals to determine the consistency and/or accuracy of the output of radiographic systems.

More than 300 diagnostic x-ray units are subjected to radiation protection surveys and calibrations annually in a medical physics practice involving more than 40 diagnostic facilities ranging from small private offices to several hospitals having 500-700 beds. In addition to traditional protection oriented analysis, performance characteristics are evaluated in order to improve quality assurance and reduce the needless patient exposure and cost associated with repeated examinations. A long term study, previously reported by the authors, includes development of ionization techniques for and results of analysis of linearity of exposure, mR/mas constancy, as functions of indicated time and current. Determination of accuracy of kVp was not done in the past because the cost-benefit ratio was considered excessive using conventional techniques such as voltage dividers in large scale measurements. The recent availability of the RMI Wisconsin X-ray Test Cassette based on the Ardran Crooks technique has made it possible to provide kVp accuracy tests as a part of the routine annual survey at minimal cost. During 1975-76, determinations of kVp accuracy have been made on more than 100 stationary radiographic x-ray units at 60,80, 100, and 120 kVp. These data have been analyzed in terms of the frequency distribution of actual/indicated kVp ratios. For 66% of all units the measured potentials were within + 5% of the indicated kVp. All focal spots measured were equal to or less than the specified size. We propose as practical acceptance test criteria that mR/mas variation on each unit for all currents and times (resulting in greater than 1 mas) be within ± 10%, that kVp be within ±5% of indicated kVp, and that focal spot size be within ±10% of that specified.

The Dynalyzer II can be used as a troubleshooting aid, or as a calibration tool for diagnostic x-ray. generators. The High, Voltage Unit can measure anode current, filament current as well as NVP. The Digital Display has features to provide accurate numerical values to these parameters. The operation of the system. in typical applications is discussed.

The x-ray spectrum of a diagnostic x-ray unit has a fundamental influence on the performance of the unit, i.e., the required patient exposure and image quality. This article describes a method of obtaining approximate spectral distributions from computer analysis of ionization chamber measurements of attenuation of the beam by a standard material. The results are compared with measurements made under identical conditions with a lithium drifted silicon solid state spectrometer. The value of attenuation analysis data for radiologic physics calculations and possible modifications of the technique are discussed.

Performance evaluations of three phase diagnostic radiologic equipment indicate the need for a reassessment of the concept of exposure time. Measurements of exposure time as defined by the equipment manufacturer (kV pulse width at 75% of peak value) demonstrates a lack of proportionality between exposure time and radiation intensity. In this paper, a method of determining an effective exposure time is presented. This effective time is defined as teff = tind + ▵t, where tind is the time indicated at the control and At is the correction required to achieve proportionality. Measurements show a wide variation in the value of At among different manufacturers and for different operating conditions, ranging from 0 to 6 ms.

It was found that an abnormal voltage waveform, present in equipment supplied by a prominent manufacturer, was responsible for the generation of medically unproductive radiation. An investigation of equipment supplied by five other major manufacturers indicated that this radiation. is not only unproductive but also unnecessary. Under normal operating conditions, this unproductive radiation can be as high as 25 mR at the skin level. Possible adverse effects of this radiation are discussed and corrective measures are suggested.

A device utilizing a fluorescent screen was fabricated to assist in the evaluation of x-ray beam alignment of fluoroscopic systems. This device is employed for routine equipment checks and adjustments of the following physical factors: (1) alignment of the x-ray beam with respect to the image intensifier (and television chain), (2) field size congruence with the spot filming device and/or the image intensifier, and (3) source-to-tabletop distance (S.T.D.). The description and operational procedure of this device are demonstrated in detail.

This paper concerns service cost, qualifications of service and service engineers. The qualification of the x-ray service personnel for the in-house repair work demands our attention. No formal education is offered in this field. The only prerequisite today is electronics; mechanical and electro-mechanical qualifications are neglected. A person is considered a service engineer if he can troubleshoot and repair general x-ray equipment. The replacement of a piece of x-ray equipment in a large department can make the in-house serviceman obsolete due to a completely new technology used in the design, unless the department is willing to carry the burden of continued education for the in-house service engineer. It is not only equipment knowledge the service engineer needs, it is also basic knowledge and, in most instances, knowledge in physics, for a good common sense approach. The government agency places an ever-increasing burden upon the service engineer with impractical laws or laws amended ad infinitum. I request and demand that fewer laws be written regarding the regulation of radiology and radiological procedures. Instead, an educational approach should be taken throughout the country.

The purpose of the paper is to describe a method of focal spot size measurement. A two dimensional smeared filament image focus model is presented. The model contains four adjustable parameters but average values for the two smearing parameters are sufficient. The two remaining scaling parameters can be determined from MTF minima frequencies. "Equivalent" size descriptors such as RMS equivalent rectangle or the noise equivalent aperture can be calculated using the focus model parameters. The use of the star test pattern to obtain these parameters is described. Results for nine foci are compared with pin hole camera measurements. Star pattern size measurements for 76 focal spots are presented and compared to nominal size. A majority of the foci exceed tolerance in at least one direction.

A system-model for computer-aided densitometric evaluation of focal spot images of diagnostic x-ray tubes is described. The procedure is almost fully automated. It extracts a specified number of optical density profiles from the focal spat image and computes the area, the base-width and the full width at half maximum for each profile. The Fourier-transform of selected profiles, the isodensity contour diagram and a three-dimensional display of the focal spot image are also rendered. Such complex assessment is recommended primarily for microfocal spots. Since the proposed evaluation requires both costly equipment and sophisticated computer programs, which are beyond the reach of most hospital facilities, it is suggested that an organization should be set up at which the analysis could be done at modest costs.

Correction factors are computed for pinhole images of x-ray tube focal spots to be applied along the anode-cathode dimension and the dimension perpendicular to the anode-cathode axis. These correction factors are based upon comparison of MTF's of focal spots with uniform intensity distribution to the MTF's of focal spots with single and double peaked intensity distributions.

In an x-ray imaging system, there are three primary sources of blqr. These are the finite size of the x-ray tube focal spot, movement of the object during the exposure, and the inherent blur of the receptor. An analysis of the composite blur and the optimization of system performance can be greatly simplified by the use of a special nomograph. The quantity of blur, with respect to the dimensions of the object, is a function of the object's position between the focal spot and receptor surface. The position of the object is specified in terms of a parameter, s, which forms one scale of the nomograph. Blur values are linear functions of this parameter. Blur from each primary source is graphed as a function of object position by drawing straight lines between points located on the blur and focal-spot scales. A second nomograph is used to combine the blur from the different sources at a specific object location.

An evaluation of the DuPont Cronex Sensitometer, the Picker Pro-Cal Sensitometer and the Wejex Sensitometer was undertaken in order to determine which. Processor Control. Sensitometer was going to be used at Duke University Medical Center. The evaluations performed on the three sensitometers led to the acceptance of the Picker Pro-Cal. No nation wide recommendations are made as the sample size (number of sensitometers) is much too small to support such a recommendation.

This paper discusses long-term results obtained using sensitometry techniques for monitoring radiograph processing in a cardiac catheterization laboratory. The elema and cine radiographic films are processed automatically in a Profexray and Combilabor processor, respectively. Techniques are described for quality control and reproducibility of both cine and elema radiographs. Comparisons are made of radiographs developed prior to implementation of the sensitometric system and after implementation. Automated continuous temperature monitoring is discussed as an additional tool for recording developer - bath temperature fluctuations. Trouble shooting hints are presented to aid in distinguishing between processor and x-ray equipment as the source of radiographic problems. Suggestions are also provided for implementing a sensitometric system in departments using radiographic films.

Several methods have been formulated for reconstructing the density (image) from a set of its projections. For a review of methods, see Gordon and Herman and Budinger and Gullberg. Some of the algebraic methods are known to optimize certain properties of the reconstructions. For instance, the least-squares solution gives an estimate of the image density such that the discrepancy between the given projection data and the projection data corresponding to the reconstructed picture is a minimum.

While the reconstruction algorithm utilized in computerized tomography (CT) is important, the overall performance of the system is limited by the quality of the measured transmission data which is used as the basis for the reconstruction process. If the projection values derived from the measured data do not adequately represent the line integrals of the linear attenuation coefficients within the slice being scanned, even a perfect reconstruction algorithm will give rise to a distorted image. Phenomena which tend to deteriorate the quality of the measured data, and hence the final image, include the effective finite dimensions of the scanning aperture, distortions introduced by the detector system such as afterglow, and nonlinearities related to the spectral distribution of x-ray photons used in scanning. Computer methods of preprocessing the x-ray transmission data to minimize these distortions are discussed and illustrated.

This paper investigates the effect of additive white noise in the projection data on the reconstructions obtained by the use of a wide class of algorithms of the convolution type.

We previously described techniques for extracting complete energy dependent information from simple measurements. In this paper we discuss the noise properties of this technique.

Image artifacts in computed tomography originate either in the hardware or software components of the system. Software artifacts may be classified as qualitative or quantitative depending, respectively, upon whether the rms artifact converges within the image field or whether it diverges. As an example of quantitative artifact, we demonstrate that truncated algorithms, often recommended for reducing reconstruction time, inherently generate aperature-error or size-effect artifact. As an example of qualitative artifact, we demonstrate that algorithms giving sharpest edge-definition do not yield generally superior point resolution. These "sharp" algorithms, however, do generate large qualitative artifact, and require relatively long computer time. Prereconstruction and postreconstruction averaging, often introduced to alleviate noise and artifact problems, can be eliminated completely. One achieves the same final result by initially choosing a different, and often simpler, reconstruction convolution.

A special cassette was designed to enhance radiographic image contrast using two intensifying screens which preferentially absorb in different regions of the x-ray energy spectrum, and which expose corresponding emulsions. The emulsions are developed in subtractive colors to display the structure of interest as variations in both intensity and hue. Theoretical expressions for contrast enhancement available with various screen combinations were made. Preliminary phantom color radiographs show the potential of this technique for contrast enchancement.

Ionography, which is currently receiving much attention, is an x-ray image recording system in which the detector is a thin ionization chamber usually containing a heavy, high pressure (10 atmospheres), gas. Ions formed by x-rays in the gas are swept across the chamber by an electric field onto a thin insulating film to form a charge image. In current systems the chamber is then depressurized, the film removed, and its charge image made visible using powder or liquid toner. An alternative method is herein described for making the charge images visible which overcomes the mechanical problems of film and gas handling of present techniques. An added advantage is that it produces instantaneous bright, stored, projected images which offers the potential of fluoroscopic ionography. In the new technique charges are collected onto a thin clear deformable layer of oil or soft elastomer coating a front surface mirror in the chamber. Electrostatic forces between the surface charges and the conducting mirror cause imagewise deformations which are immediately made visible on a external screen by a Schlieren Optical Projection System using light which enters and leaves the chamber through a high pressure glass window. Images, with resolution better and sensitivity close to film/screen methods, have been obtained.

Solid state thermocurrent and radioconductivity (electrical conductivity during irradiation) experiments have indicated the feasibility of using ionic solids for radiographic imaging. In gaseous systems, the process is called ionography; the image is formed by collection and trapping of charge. A charge yield of about 10-10 coulomb/cm2-mR at a field of 105 V/cm was measured for Al203; the charge yield varies linearly with the electric field. This material also shows good charge sensitivity for the room temperature region. Gadolinium Gallium Garnet, although not as sensitive as Al203, has also shown potential for radiographic imaging. Ionographic images were made at atmospheric pressure using 80 kVp x-rays collecting the charge on an aluminum backed mylar film. The aluminum backing electrode is then removed to produce a transparency, which can then be viewed as a conventional radiographic image. An image of a JEDEC-JT-4.2 pattern demonstrated that the imaging system can easily resolve 4 line pairs/mm and seems limited at our exposure levels only by quantum statistics.

While radiographic mottle is predominantly statistical noise and fundamentally dependent on the number of screen absorbed x-ray photons per exposure, the noise recorded on film and perceived by the radiologist is also dependent on sharpness. To measure this effect quantitatively, we have compared Wiener spectra for systems with equal statistics, but with sequential reductions in the modulation transfer function. The data suggest that many examinations, such as tomograms, gall bladders and angiograms could benefit from a deliber-ate reduction in screen/film sharpness so as to decrease noise in an already unsharp radiologic image.

A method for evaluating the imaging properties of film-screen combinations is described. This method incorporates Schade's noise equivalent bandpass, Ne, and Selwyn's concept of granularity into a figure of merit which can be derived from measurements of the sensitometric and frequency response characteristics of the system. Details of the techniques involved in obtaining the H F, D curve and MTF of the system are presented along with the formalisms involved in calculating Ne and the figure of merit.

Intensified Minification Cameras have been used to reduce the x-ray skin exposure for specific routine radiographic procedures. Such cameras are basically photofluorographic devices which contain conventional image intensifier tubes used in night vision applications. Overall system speed and modulation transfer characteristics are discussed together with preliminary clinical evaluation data.

The use of narrow x-ray spectra to produce the radiographic image allows a reduction in patient exposure without any appreciable degradation in image quality. When this method is combined with the use of rare-earth intensifying screens, the performance of the screens is improved primarily in terms of patient exposure. A number of screens have been tested in a case of bone imaging with aluminum filtered beams and with ytterbium filtered beams. A summary of the results in terms of radiation doses and image quality is presented.

For frequent visualization of the fine blood vessels within the brain substance, geo-metric magnification is required at angiography. However, full skull geometric magnification on large size film changers may also prove insufficient for visualization of these vessels. Further magnification of most cerebral arteries in lateral projection can be obtained without compromising full skull coverage and without additional radiation exposure! This is accomplishable when a true 0.2mm focal spot of uniform intensity distribution is substituted for the nominal 0.3mm and the usual position of the tube and film changer is reversed relative to the skull. This tube-changer reversal contradicts the standard technique for non-magnification radiography. The additional capacity for gaining moderately high magnifications with the 0.2mm focal spot is also advantageous. It is recommended that the 0.2mm focal spot become the standard tube manufactured for magnification neuroangiography. If a second focal spot accompanies it, either a 0.1mm size can be used for higher magnifications or a high kilowatt loading larger spot can be matched with it for general radiographic or conventional angiographic use.

A technique for viewing film, in which the film is sandwiched between two partially transmitting reflectors, can greatly increase the apparent optical contrast and the information available in low-density regions of the film. The contrast in the toe region of the photographic characteristic curve may be increased by a factor of 7 or more while the contrast in intermediate and high density regions remains unchanged. This "stretching out" of the characteristic curve is useful in salvaging underexposed transparencies. Characteristics the film and reflectors must have to produce the contrast enhancement are discussed.

A quantitative comparison of the capabilities to produce computerized tomograms was made between the EMI head scanner and reconstructions from images provided by a large screen low light level -TV camera fluoroscopic system. A phantom made from lucite containing rods of various materials and sizes was used. The computer printout of each was analyzed and a high degree of correlation (r = 0.98) was noted between the results of both systems. The differential attenuation detectability of the fluoroscopic system was found to be comparable to or better than the EMI unit. As expected from a consideration of the quantum statistics for each system, the noise in the obtained reconstructions was also comparable. It is concluded that such a fluoroscopic system performs favorably when compared to the presently available commercial systems.

Two in vivo methods for the determination of bone mineral content are compared. It is concluded that computed tomography represents the only accurate in vivo method capable of determining bone mineral content per volume of bone. In addition, it has the distinct advantage of being able to determine the bone mineral content of virtually any bone of the skeleton.

The computed-tomography scanner is a new tool for the medical profession in which a narrow, moving x-ray beam, controlled and measured by a computer, is used to image transverse planes in patients. Because scanners have several unique features, commissioning tests performed during installation can only be partially accomplished by using equipment and procedures designed for conventional x-ray devices. Additional equipment and procedures are required to commission scanners. This paper identifies 21 parameters that should be considered for testing in a scanner commissioning program. Generalized descriptions as to how such tests may be accomplished are outlined and difficulties in testing are cited.

The development and use of a phantom for evaluation, comparison, and quality assurance of CT scanners will be discussed. Examples of measurements on seven CT scanners using early prototypes of the phantom will be presented along with measurements on several scanners using the final phantom configuration. The phantom contains four modular sections which are removable to allow for future fabrication and replacement of individual sections for specialized applications. Section I is used to measure contrast sensitivity and scan slice geometry of the system. Section II is used to measure the sensitometric response of the system. Section III is used to determine the spatial resolution of the system at various contrast levels. Section IV is used to determine the noise, spatial uniformity, alignment, and MTF of the system. In addition, it contains a part with fittings where items may be placed such as in vitro samples, dosimeters, or a motion phantom.

The success of radiation therapy depends upon the correct diagnosis of disease and the accurate delivery of radiation dose to that disease. An important part of radiotherapy is treatment planning in which various possibilities for the type, energy, size, and orientation of therapy beams are considered to insure that the intended volume is adequately irradiated. Treatment planning requires that the shape, size and depth of tumors as well as radiation-sensitive tissues be accurately identified. Furthermore, any distortions to radiation dose distributions caused by the presence of tissue inhomogeneities should be corrected. This paper discusses how computed-tomography scanners may be utilized to advantage in radiotherapy. Major benefits of scanners are described and difficulties associated with using scanner images in radiotherapy treatment planning are indicated.

In computed tomography (CT), any reconstruction algorithm relies upon input data that accurately reflect true line integrals of some physical quantity. In x-ray transmission tomography, x-ray beam hardening alters the polychromatic x-ray source spectrum resulting in inconsistent data if simple exponential attenuation is assumed. Four models relating intensity of the emerging polychromatic beam to thickness of the absorber are examined in this paper. A cubic polynomial relation suggested by Macovski et allis compared with more physically motivated models of Greening2, Joseph3 and the present authors. Results given indicate that for moderate x-ray prefiltering (.75mm Cu), all models provide better than .05% accuracy for computing thickness of a single material; while for small material thicknesses and lighter x-ray filtration (<6.mm Al), Greening's formula is most accurate.

The resources of radiology have been tremendously augmented by CT scanning. Developing from brain scanners, through slow body scanners, the present, third generation of fast whole-body CT scanners provide images of unprecedented detail and quantitative informa-tion content. The technological level required is high: precise mechanical alignment, efficient and linear multi-channel X-ray detectors, electronics of enormous dynamic range, a fast computer with large memory and special reconstruction hardware, flexible controls, and powerful data display and storage system. Performance must be evaluated carefully. The specification and measurement of X-ray density resolution and spatial resolution are straightforward, but optimization is tricky since they interact. Both, but more especially density resolution, tend to be limited by X-ray photon statistics. Because CT scanning is still a rapidly developing field, flexibility is perhaps the most important feature of a CT scanner. Some images from the first year of operation of the Varian 6-second CT scanner are shown.

The two experiments described, one in vivo and the other in vitro, correlate CT (Computerized Tomograph-ic) numbers with mass densities in a cross-sectional scan and CT numbers with the calcium concentration in bones. The in vivo experiment is based on patient scan results and theories used in computerized tomography, specifically the concept of average effective energy (AEE) and the convolution Method in picture reconstruction. The in vitro experiment is based on scans of fresh excised lumbar vertebrae and on the physical analysis (by conventional methods) of the cancellous bone from the vertebrae.

To expand the medical utility of X-ray Computerized Tomography System to the entire body, the system must be capable of high-speed scan to minimize the effect of voluntary and involuntary body motion. High speed (5 sec.) and fan beam geometry in which the x-ray measurements are made by a continuous rotating scanner with simultaneous data acquisition per projection appears to be an optimum technical approach in terms of performance, reliability and producibility. The technical issues of x-ray physics, dosage, scanner and computing system will be discussed in this paper.

Little technical information has been made available on CT image format or viewers. For large matrix displays (320 x 320 or 512 x 512), a high quality TV monitor with a bandwidth of 10 MHz or greater is required. If only a single field of a two to one positive interlaced TV monitor is displayed, an 875 line rate TV would be required in order to display the entire matrix. For image recording, a transparency system such as a multi-format unit or a 105 mm roll film camera will generally provide the best results. Finally, in order to improve the final CT image, various picture processing routines may be used. These include pre- and post-reconstruction smoothing, edge enhancement and image subtraction.

The technology of computerized-tomographic scanners is rapidly evolving. Current body scanners employ fan beams of x-radiation in combination with large arrays of Xenon-ionization or scintillation-phototube detectors. Two-motion or pure rotary scanning configurations are used. Curent specifications include: scan times of 5 seconds, image matrices up to 512 x 512 , processing times of tens of seconds and spatial resolution in the range of 1.5 mm FWHM. A typical current scanner, the EMI-5000 has been characterized with respect to noise, detectability, resolving power, motion artefact, dosimetry, and precision.

The nature of interpolation required during image reconstruction using Filtered Back-Projection has been studied. It has been found that the usual method, called linear interpolation, may easily be refined to a better method, which we call trapezoidal approximation. The error associated with this method has been analyzed in the frequency domain for circularly symmetric objects. There is moderate distortion and diminshed response at high frequencies, with the amplitude envelope falling to about 60% of ideal at the Nyquist fre-quency for 100 sampling points. The error is reduced with more sampling points.

Ultrasonic pulse-echo systems have proven a clinically effective means of obtaining detailed cross-sectional images of soft-tissue structures. These B-scan images are now employed in a diverse range of medical specialties including obstetrics, gynecology, cardiology, and ophthalmology. Initially, the diagnostic utility of ultrasonic imaging was restricted because of severe constraints imposed on image dynamic range by equipment components, including the CRT display itself. Because of these limitations, diagnosis was made on the basis of rather coarse morphological features such as the geometry of tissue interfaces. While echo amplitudes were known to be diagnostically significant they could only be assessed indirectly. The most common approach consisted of generating a series of images at a variety of sensitivity levels. "Strong" echoes persisted at low sensitivity settings while "weak" echoes were displayed only at high sensitivity settings.

In the synthetic-aperture method of acoustical imaging, reflections are processed to achieve resolution improvements expected from transducers larger than commonly used in diagnostic ultrasonography. Since in practice transducers cannot exceed about 3 cm in diameter, electronic aperturing simulates a larger transducer with increased azimuthal resolution. All depths in the field of view are equally in focus, eliminating beam divergence. This inexpensive system functions in real time, providing immediately displayed high-resolution B-scans. A single-channel transducer is rapidly driven by novel mechanical means achieving high frame rates and high transducer position densities without costs and complexities of transducer arrays. Data acquisition, processing, and display occur on line, eliminating much memory storage and programmable time-delay functions typical of synthetic aperture systems. Novel optical-electronic computational methods are utilized. Range and azimuthal resolutions of stationary and moving phantoms are compared for identical insonifying frequencies against conventional diagnostic B-scanners.

A grey scale display system for ultrasound contact B scanning has been developed that produces six shades of grey on a high resolution storage oscilloscope. Clinical advantages of our system are: (1) the ability to display rapid serial images in full resolution, a technique not readily possible with alternate grey scale display system involving either scan converters or nonstorage oscilloscopes, and (2) the images produced have grey-level rendition and spacial resolution comparable to those of scan converter display systems at a significantly lower equipment cost.

In Part I of this paper, Terrance Matzuk described the engineering aspects of an ultrasound system which directly displays the image in final form on a high resolution bistable storage oscilloscope. This part will describe the clinical applications of the system and its advantages as compared to other grey scale display systems.

The value of the use of computers in ultrasound for improving image quality and provid-ing more scan data has been speculated on for some time. This paper describes a micro-processor based B-Scan system in which the microcomputer plays a key role in improving sys-tem resolution, dynamic range, and ease of operation. The way the computer interacts with the system is discussed in detail, comparisons with conventional systems are made, and clinical results are shown.

The simplicity of the mechanical real-time ultrasonic sector scanner makes it an attractive device for medical diagnosis. A new scanner has been developed that incorporates electronic position control of the transducer; thus permitting electronic programming of scan linearity and sector width. The system employs a reversible low-inertia servo motor that moves the transducer by means of a three-to-one gear reduction. The use of the gear reduction enables the transducer rotational inertia to be counterbalanced by that of the motor, thus reducing the mechanical vibration of the system. Sine and cosine voltages necessary for display purposes are generated photoelectrically from a rotating disc mounted on the rear of the motor shaft. Curved slits in the disc are machined to permit light intensity proportional to the sine and cosine of the sector position to reach the detector. The gear reduction to the transducer was accounted for in the calculations of the slit geometry. A coil spring attached to the motor shaft was selected for a system mechanical resonance of approximately 10 Hz in order to reduce the electrical power consumed by the system. The sine voltage from the scanner is employed as a position signal for the feedback control. With this system, the sector size may be adjusted from 0 to ± 25 degrees.

The application of pulse compression to medical ultrasound is discussed. This approach can decrease peak power and increase sensitivity in ultrasonic diagnosis. A prototype system with 8:1 compression ratio and 0.6 is resolution is described. Compressed echo wave-forms were obtained from an aluminum bar and from a human heart in vivo.

The quality and convenience of the display of ultrasound B-scan images is critical to their diagnostic usefulness. The perceived dynamic range of present displays is too limited, and display artifacts are sometimes encountered. Many displays do not permit the user to optimize the image presentation by varying image parameters, to store and retrieve images, to display multiple images simultaneously, to label images easily, and to carry out other actions which increase the usefulness of a display system. And those that do have these capabilities are too expensive to be used routinely. This paper discusses the needs of a display system in detail and reports the design of a display system of reasonable cost which meets these needs. This system includes both a basic display module which is useful for many medical imaging applications and an inter-face between it and an ultrasonograph.

Ultrasonography has become a valuable tool for the assessment and management of a number of obstetrical problems. This communication describes the diagnostic capabilities of the currently available units and the use of ultrasonography as an essential component of amniocentesis, intrauterine transfusion, and fetoscopy.

Two thermal methods capable of determining time averaged, total radiated ultrasonic power at diagnostic levels are described. The first, a portable instrument, utilizes a parabolic reflector to focus the ultrasonic beam onto a thin film thermistor sensing element mounted on sound absorbing rubber. The sensor's temperature rise alters its resistance, which is monitored with a simple bridge circuit. Maximum sensitivity of the device is 0.1 mW and beams up to 19 mm diameter can be accomodated. Calibration was performed using 1 MHz, 2.25 MHz, 3.5 MHz, 5 MHz and 10 MHz resonant transducers. The second device, a twin, series flow, ultrasonic comparator, is a primary measurement laboratory system. Ultrasound is absorbed by a series of rubber wafers within a vessel and is compared with measured dc electrical power dissipated in a second, identical vessel. The heat produced within the vessels is carried to twin, resistance thermometer temperature sensors by an inert perfluorinated liquid, within a closed circuit. In automatic mode the bridge is coupled to a feedback circuit which applies electrical power to regain bridge balance. Unwanted heat produced within the transducer being tested is carried away by a flow of water between the transducer and absorbing vessel. This instrument can measure power from 0.2 MW to 10 W and can accomodate transducers resonant at 1 to 15 MHz and up to 26 mm in diameter.

Since August of 1974, the Food and Drug Administration has been testing the performance of diagnostic x-ray equipment certified to be in compliance with the Federal Performance Standard. The testing is performed in user locations as well as in Federal laboratories. Testing to date has revealed the general level of performance of diagnostic x-ray equipment and specific problem areas that are common to several manufacturers. Results of routine field testing, more rigorous follow-up testing, and laboratory tests will be discussed.

Sources of error associated with the measurement of four performance parameters are discussed in this paper. These are the measurement of half-value layer (HVL), light field edge location, x-ray and light field congruence, and x-ray field size. HVL measurement parameters discussed are field size, the detector energy-dependent response, and x-ray beam filtration. Light field edge location by both visual and photometric methods are compared and differences quantified for one x-ray beam collimator. The impact of the different methods of light field edge location on x-ray and light field congruence are described. X-ray field size measurements for x-ray systems having large focal spots are discussed. The effect of the large focal spot as it impacts on small x-ray field size measurements is described.

As radiologic imaging systems continue to increase in sophistication and cost, and as the complexity and diversity of procedures performed with the systems continue to expand, both the purchaser and supplier of radiologic equipment find themselves in a quandry. How can these individuals he sure a given piece of enuipment will fulfill the demands made of it in the clinical environment? All too frenuently, a lack of understanding of technical equipment specifications by the purchaser, and an unfamiliarity with specific imaging requirements hy the supplier, combine to produce overexpenditures for radiologic equipment and unfulfilled expectations of eguipment performance. To reduce the frequency of these undesirable results, an extensive interchange of information is required between the purchaser and the supplier of radiologic equipment.