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Biomedical subjects

U Welander

Publications and source records attributed to U Welander.

At least 73 records · Page 4Linked to original sources
PubMed1989

A method to maintain a constant magnification factor throughout the exposure of rotational panoramic radiographs.

The magnification factor can be held constant throughout the exposure of a panoramic radiograph by maintaining the physical centre of rotation equidistant from the central plane of the image layer. This may be accomplished with computer-controlled movement patterns while the effective centre of rotation follows a path selected to provide an optimal projection of the jaws. Theoretical considerations for creation of a constant magnification factor are presented and the practical implementation of the technique in a commercially available device (OrthOralix SD, Philips, Monza, Italy) is described. This technique minimizes distortion in panoramic radiographs and makes horizontal measurements possible in certain selected cases.

Computers↗
PubMed1989

The effect of system parameters on resolution in rotational panoramic radiography. A mathematical analysis.

The unsharpness in rotational panoramic radiography is the combined effect of motion unsharpness, screen-film unsharpness and geometrical unsharpness. A computer program was written to calculate the noise equivalent passband (Ne) from the modulation transfer function (MTF) of each of the three sources of unsharpness in both the horizontal and vertical dimensions for a typical panoramic machine. Effects on system resolution resulting from changing the size of the focal spot, the screen-film combination, the width of the beam, and the effective projection radius were computed and the interaction of the various parameters was evaluated. Data of this type is essential for evaluation of system performance and for optimizing the operation of panoramic systems.

Computers↗
PubMed1988

Dental and mandibular arch widths in three ethnic groups in Texas: a radiographic study.

The dimensions of the dental and mandibular arches were determined in 210 subjects belonging to Mexican American, black American, and white American ethnic groups. The measurements were taken from axial radiographs in which it was possible to trace the intrabony structures of the dentition and the position of the condyles. The study revealed that ethnic and sexual differences in the dental and mandibular arch widths were statistically significant. Males were 0.6 to 1.1 mm wider in their dentitions than females. Mexican Americans had the widest dental arch, although theirs was only 0.2 mm wider than black Americans. White Americans were significantly different; their dental arch was measured as 0.8 to 1.2 mm narrower than that of the other ethnic groups.

Adult↗
PubMed1986

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.

Computers↗
PubMed1986

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.

Evaluation Studies as Topic↗
PubMed1985

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.

Humans↗