Evaluation of a device for indirect assessment of automatic exposure control systems.

A test device which can indirectly measure the performance of an automatic exposure control system and which offers the potential to reduce the time and film requirements for such tests has been evaluated. Evaluation results demonstrate that the device can successfully predict image optical density to within +/- 0.10 optical density units over a wide range of imaging technical factors and image optical densities.

A survey of fluoroscopic exposure rates: AAPM Task Group No. 11 Report.

Fluoroscopic procedures, in general, result in much higher exposures to patients than do most types of radiographic procedures [National Council on Radiation Protection, Report 100, p. 31 (1989)]. In spite of this, fluoroscopic exposure rates can vary widely between systems, and often for no apparent reason. The charge of AAPM Task Group No. 11 was to evaluate fluoroscopic exposure rates at the entrant surface of the x-ray image intensifier, and to disseminate this information so that medical physicists could compare their own exposure rate measurements with typical values. The measurement protocol was defined for various system configurations. Sheets of copper were used to attenuate the x-ray beam, and the input exposure rate at the image intensifier (at the input mode closest to 23-cm diameter) in the absence of a scattering medium was determined. With 2 mm of copper as x-ray beam filtration, the median fluoroscopic exposure rate at the image intensifier was found to be 16.5 nC/kg/s (64.0 microR/s), with an average kV of 77 and mA of 2.0 (n = 62).

Chest roentgenographic techniques for demonstrating human lung tumour xenografts in nude rats.

Roentgenographic techniques were investigated for imaging orthotopic lung tumours in anaesthetized nude rats endobronchially implanted with human lung cancer cells. A conventional radiographic unit with a dual-screen, double-emulsion film mammographic receptor produced images preferable to those from a mammographic unit because of superior resolution. Typical exposure factors were 300 mA, 29 kVp, and 17 ms at a focus-film distance of 76 cm with a 2.11 by 2.41 mm effective focal spot and inherent filtration of 1.2 mm aluminium. Sensitivity for tumour detection was 0.93 for 59 animals with pathologically proved tumours and 0.96 for 54 animals with tumours larger than 4 mm or 50 mg. For 24 pathologically tumour-free animals, specificity was 1.00. For 55 animals radiographically judged to have tumours, positive predictive value was 1.00. For all 83 animals, accuracy was 0.95. This technique effectively demonstrates orthotopic human lung tumours in nude rats and should be useful for noninvasive monitoring of tumour presence, location, size, and changes in size.

Broad beam transmission properties of some common shielding materials for use in diagnostic radiology.

Broad beam geometry was used to measure the x-ray transmission properties of gypsum wallboard, steel, plate glass, and concrete for x-ray tube potentials of 50-125 kVp using an x-ray generator having a three-phase, twelve-pulse waveform and total initial beam filtration sufficient to provide half-value layers representative of those found in common practice and required by regulatory agencies. Measurement results are presented graphically and as numerical fits to a mathematical model of broad beam transmission to permit their use in the design of protective barriers for medical diagnostic x-ray facilities.

Bullet identification with radiography.

The authors provide a simple radiographic method for estimating bullet weight and caliber of both deformed and undeformed bullets that enables accurate determination of caliber for the gamut of bullet shapes, with known degrees of confidence. The weight-determination procedure is based on the correlation between bullet cross-sectional area, as derived from three orthogonal radiographs, and bullet weight, as determined from a data base of the properties of 48 bullets removed from humans. Different equations were developed for bullets weighing 5.8 g or less, or more than 5.8 g. For relatively undeformed bullets an additional method calculated caliber directly from the diameter of the bullet body on radiographs. Both methods enabled correct prediction of the weight and caliber of the bullets; if one method could not be used, results of the other were reliable. Testimony based on these results has been accepted in a local police case and may meet requirements for testimony in U.S. court cases involving gunshots.

Equipment maintenance: a cost comparison of vendor and inhouse service.

The total cost associated with the services provided by Radiological Engineering for the maintenance and repair of imaging equipment for fiscal year 1987-1988 (inclusive of salaries and benefits of $66,725) was $146,643. To obtain similar services from outside vendors an expenditure of approximately $345,788 would have been required. The experience of the Department of Radiology, University Hospital, Denver, Colorado, is similar to that of others and has demonstrated the cost-effectiveness of an inhouse program for the maintenance and repair of imaging equipment. In other institutions, particularly smaller ones, the effectiveness of such programs would depend on individual circumstances. In most instances, an inhouse service engineer can be justified for a hospital with imaging equipment valued at approximately $2,000,000 (1989 prices), and for remotely located hospitals with less equipment that require greater vendor travel. In a smaller hospital, the individual employed need not have the highest level of skill and experience to function effectively. Since many routine service problems can be handled by a person with limited experience, this will still achieve a considerable overall savings. Such an individual may also be assigned certain aspects of equipment quality control to realize additional benefits--while vendor service can be reserved for more complex problems. Inhouse service can be cost effective in most large and many smaller hospitals and is an effective way for a hospital to simultaneously improve patient care and reduce operational costs. In addition to direct cost savings, an inhouse radiological engineering program can provide less tangible, but nonetheless important benefits, to the efficiency of departmental operation and patient care.(ABSTRACT TRUNCATED AT 250 WORDS)

Methods of technique selection in radiographic imaging.

All methods of technique selection are capable of producing high quality radiographs on a consistent basis. Each has its own specific advantages and disadvantages. These advantages and disadvantages need to be carefully considered to determine the appropriateness of a given method for a given imaging situation.

Reduction of radiation exposure in radiography of the chest.

Reduction of patient exposure in chest radiography by means of copper filtration was investigated for a range of filter thicknesses at kilovoltages commonly employed for the postero-anterior and lateral projections. The influence of copper filtration on tube output, beam quality, entrance and midplane exposures, tube load, and image contrast was determined from physical measurements and evaluation of phantom images. The results indicate that entrance exposure may be reduced by 30-40% and midplane exposure by approximately 24% through the use of a 0.32-mm copper filter, with an acceptable increase in tube load and only minor changes in the appearance of the images.

X-ray equipment performance: a 3.5 year case history.

The continuing performance of radiographic imaging systems has become increasingly important as the complexity and cost of these systems continue to escalate, as replacement funding becomes more difficult to obtain, and as advisory and regulatory agencies place increasing emphasis on equipment-oriented quality control procedures. As a guide to the continuing performance of these imaging systems, selected performance indicators for two general-purpose radiographic-fluoroscopic units have been monitored for a 3.5 year period. The observations suggest that with inspection and adjustment at 6 month intervals for generator, x-ray tube, and beam restriction systems, and at 2 month intervals for the intensified fluoroscopic imaging system, the overall performance of the imaging systems can be maintained at a high level of consistency equivalent to the performance achieved when the equipment was initially installed.

Low-dose radiography of children.

During the past five years, over 50,000 routine examinations in pediatric radiology have been performed utilizing a high-speed, rare-earth system. A detailed study of the physical characteristics as well as subjective qualities of all of the commercially available rare-earth systems was performed. Our extensive clinical experience with a gadolinium oxysulfide system is described in detail. Practical points on how to avoid certain pitfalls when instituting a system of low-dose radiography are discussed. The present system allows a significant reduction in radiation dosage with maintenance of fine to excellent radiographic resolution.

A variable aperture fluoroscopic unit for reduced patient exposure.

A real time fluoroscopic imaging system which provides capability for reduced patient exposure by as much as a factor of five has been developed. Modifications to the system include the incorporation of a variable aperture iris between the image intensifier output phosphor and television camera and the use of the video signal as the feedback element in the fluoroscopic automatic exposure rate control system. Quantitative and qualitative performance of the system is described.

The application of fast screen-film systems to excretory urography.

Rare earth and barium fluorochloride screen-film combinations of different relative speeds were compared to conventional calcium tungstate systems in patients undergoing excretory urography under controlled conditions. Radiographs were ranked by subjective impressions of detail, contrast, mottle, motion unsharpness, overall quality, and acceptablility. Compared to a medium speed calcium tungstate screen/film combination (assigned a speed of 1), screen-film systems in the 2-5 speed range offered improvement in overall quality due to diminished respiratory motion unsharpness at the cost of some loss of detail and increase in mottle. Other advantages and disadvantages of fast screen-film systems are discussed.

Radiation exposure in radiographic examinations of the newborn.

Radiation exposure of the newborn during routine chest and abdominal radiographic examinations has been determined. The exposure has been measured at sites representing the entrance and exit chest, entrance, midline, and exit abdomen, the gonads, and the thyroid. Results of these measurements are reported as a function of kVp and in terms of mR received at the anatomical site per mR output of the generator at 24 in. (61 cm). This reporting procedure facilitates application of the results to exposure estimates under similar conditions at other institutions.

An evaluation of rare earth screen/film combinations.

The physical and imaging characteristics of a number of commercially available rare earth screen/film combinations were evaluated and compared to those of conventional calcium tungstate/X-Omat RP-14 systems. All systems were evaluated for base-plus-fog density, relative speed, resolution, noise, and overall performance. The results indicate that despite certain limitations, rare earth screen/film combinations offer significant advantages for imaging.