Charles R. Morris

The effect of viewing conditions on the perceptibility of radiographic details

The effect of viewing conditions on the visual detection of radiographic detail has been studied by the method of perceptibility curves. Extraneous light and improper masking of radiographs reduce the amount of information available to the viewer.

The Intrex—a constant-potential x-ray unit for periapical dental radiography

Abstract A comparison of beam quality has been made between the constant-potential Intrex and the Marksman I, a conventional self-rectified, pulsating-potential machine made by the same manufacturer. The combined effects of a constant accelerating potential and an increased thickness of aluminum filtration in the Intrex make possible the production of a radiographs at reduced levels of radiation with no significant loss of radiographic information.

Abnormalities noted on panoramic radiographs.

Abstract An analysis was made of 5,556 panoramic radiographs of United States Air Force recruits. The results of the survey indicate that the panoramic radiographic screening examination provides a simple and rapid method of recording the general dental health of a large population and furnishes information concerning dental treatment requirements. The panoramic radiograph, used in conjunction with the Polaroid photograph of the dentition, is an excellent means of dental identification. Specific areas evaluated in this study include missing teeth, required extractions, deciduous and supernumerary teeth, retained roots, impactions, radiolucencies, radiopacities, and radiopacities/radiolucencies.

Dimensional reproduction in rotational panoramic radiography

The customary mathematical expressions for magnification in rotational panoramic radiography are examined. It is shown that although these expressions yield correct results for small objects placed perpendicularly to the central ray of the beam, they must be corrected in other situations.

Definitions of unsharpness and layer thickness in rotational panoramic radiography

The use of the modulation-transfer function in defining the layer thickness in rotational panoramic radiography is discussed. This method is compared with other methods and is shown to be a more accurate means for describing the layer.

Resolution of several screen-film combinations in rotational panoramic radiography.

Data for screen-film combinations suitable for panoramic radiography were obtained from the Eastman Kodak Company, Rochester, New York. Image resolution was calculated at various object depths with the use of system data for the Panorex 2 unit (S. S. White Company, Holmdel, New Jersey). An experimental test was performed in which clinicians ranked the various combinations with respect to diagnostic quality. The rankings by the observers generally reflected the resolution of the screen-film combinations.

A new method for image layer analysis in rotational panoramic radiography

The position and form of the image layer in rotational panoramic radiography vary from one manufacture to another. A method utilizing a digital computer to calculate the position, form, and relative thickness of the image layer from data obtained from two test radiographs is described. The image layer analysis permits the performance of different rotational panoramic radiographic units to be compared independent of various parameters such as beam width and magnification. The image layers for several commercially available units are illustrated.

Kodak T-Mat G film in rotational panoramic radiography

Panoramic radiographs were taken of a tissue-equivalent phantom to evaluate T-Mat G and Ortho G films in combination with rare earth screens. The radiographs were compared to radiographs made with high-speed calcium tungstate screens and Kodak XRP film. The reduction in the amount of radiation necessary for the use of rare earth screens (50% to 70%) was accomplished by lowering the mA and adding filtration. All evaluated films were diagnostically acceptable. There was a marked preference of the T-Mat radiographs over the Ortho G radiographs and a slight preference over radiographs made with the standard calcium-tungstate screen-film system.

The central plane of the image layer determined experimentally in various rotational panoramic x-ray machines

The location of the image layer with respect to how a patient is positioned in a rotational panoramic machine is very critical. At present, no simple method exists for routine testing of panoramic machines to verify that the image layer is where the manufacturer intended it to be. The purpose of this experiment was to locate the central plane of the image layer with respect to a reference point on various machines currently on the market. The data obtained from this study can be used for further evaluations of the consistency in the location of the image layer, first with the existing device and later with a test device that would be adaptable to these machines and serve as a quality-control device in assuring that the machines are functioning properly.

Blurring effects in rotational panoramic radiography.

Abstract A computer model was developed to investigate how accurately conventional expressions for unsharpness and layer thickness in rotational panoramic radiography approximate the situation encountered in real systems in which the rotational center slides and the effective projection radius varies continuously. Comparison of the results of the model with those of the approximate expressions show that the latter predict the unsharpness with a high degree of accuracy except at the center of the layer.