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Biomedical subjects

K H Thunthy

Publications and source records attributed to K H Thunthy.

At least 19 recordsLinked to original sources
PubMed1992

Sensitometric comparison of direct- and indirect-exposure films used in intraoral radiography.

In Japan, some dentists use indirect-exposure (screen) films for intraoral radiography, without the use of intensifying screens. The purpose of the present investigation was to determine whether film speed, inherent contrast, and latitude of Japanese indirect-exposure films used without intensifying screens were comparable to those of direct-exposure (non-screen) films used for intraoral radiography. The characteristic curves of Kodak Ektaspeed ("E" speed) and Ultra-speed ("D" speed) films were used as standards for comparison. Indirect-exposure films without intensifying screens were extremely slow compared with direct-exposure "E" and "D" speed films. Therefore, they should not be used for intraoral radiography because they needlessly expose the patient to excessive X-ray radiation. The direct-exposure films Hanshin Hi-Fi and Hanshin New Silver were equivalent in speed, higher in contrast, and narrower in latitude than Kodak Ektaspeed film. In general, the indirect-exposure films had lower speed, lower contrast and wider latitude than the direct-exposure films. Their speed and contrast would have been increased if intensifying screens had been used. Therefore, indirect-exposure films without intensifying screens should not be used for intraoral radiography.

Radiation Dosage↗
PubMed1991

Automatic processing: effects of temperature and time changes on the sensitometric properties of light-sensitive films.

The effects of changes in the processing temperature and time of automatic processors were studied with three light-sensitive Kodak films: (1) blue-sensitive X-Omat RP film, (2) green-sensitive T-Mat G film, and (3) ultraviolet-sensitive X-Omat duplicating film. Speed and inherent contrast were derived for each of the three films from sensitometric curves at six different temperatures and at five different processing times. The T-Mat G film (T-grain technology) was comparatively less sensitive than conventional films (X-Omat RP) to increases in processing temperature or time. Unlike dental intraoral films, which cannot be processed at low processing time or temperature, the light-sensitive films were of archival storage quality even at a low processing time of 2.5 minutes or at a low processing temperature of 21 degrees C. Therefore the processing time of an automatic processor may be decreased for light-sensitive films.

Chelating Agents↗
PubMed1991

Automatic processing: effects of temperature and time changes on sensitometric properties of ULTRA-SPEED and EKTASPEED films.

The effects of changes in the processing temperature and time of automatic processors were studied with Kodak ULTRA-SPEED and EKTASPEED dental x-ray films. Speeds and inherent contrasts were derived for the two films from sensitometric curves at seven different temperatures and at five different processing times. As opposed to manual processing, only a slight change in film fog was observed with increases in automatic processing temperature or time. Film speed and contrast could be increased by increasing the processing temperature or time. The EKTASPEED film was more sensitive to these changes than was the ULTRA-SPEED film. Temperature had a stronger influence than processing time. All films were of archival storage quality except those processed at the low processing times of 2.5 or 3.5 minutes, and at the low processing temperature of 21 degrees C.

Evaluation Studies as Topic↗
PubMed1990

Sensitometric comparison of unexpired and expired duplicating films used in dentistry.

This investigation compared the sensitometric properties of unexpired and expired duplicating films. The characteristic curve derived for a duplicating film is the negative slope of a solarization curve; that is, it is different in direction to that of a regular x-ray film. An expired duplicating film is slower than an unexpired duplicating film. Unlike a negative working film, which gains fog past its expiration date, a positive working film (for example, a duplicating film) gains contrast past its expiration date. An expired duplicating film has a narrower latitude than that of an unexpired duplicating film for a useful density range. Clinically, a duplicating film can be used years after its expiration date even though there is a change in its speed and contrast.

Copying Processes↗
PubMed1990

Electrolytic recovery of silver from dental radiographic films.

Silver (Ag) was removed from unexposed Kodak X-OmatRP; T-MatG; X-Omat duplicating; and ultraspeed periapical dental radiographic films by immersing them into a fixer solution until the films were completely translucent. The silver was recovered from the fixer solution by the electrolytic plating technique. The number of unexposed films needed to be fixed in order to recover one troy ounce of silver by electrolysis was as follows: 250 panoramic films or 200 cephalometric films or 2,000 posterior periapical films. The silver was assayed for its purity by energy dispersive x-ray analysis, coupled to a scanning electron microscope. Depending on the sample tested, the purity of the silver recovered by electrolysis varied from 78 to 89 percent.

Electrolysis↗
PubMed1988

Technique for using films accidentally exposed to light.

Light-exposed films cannot be used clinically because, after processing, they are completely black. Two methods are described in which light-exposed films could be used clinically with application of the principle of solarization: (1) as duplicating films with the use of sunlight and (2) as receptors for images of foliage with the use of sunlight. Light-exposed duplicating films could be used as receptors for images of foliage through use of sunlight exposures.

Light↗
PubMed1986

Sensitometric and image analysis of T-grain film.

The new Kodak T-grain film is the result of a new technology that makes fast films with high image resolution. The purpose of the investigation was to determine the sensitometric properties and image quality of a T-grain film (T-Mat G) and also to compare this film with a green-sensitive orthochromatic film (Ortho G) and a blue-sensitive film (XRP). The criteria for film evaluation were relative speed, average contrast, exposure latitude, and image resolution. The results showed that the T-Mat G film is twice as fast as the X-Omat RP film and, one and one-third times as fast as the Ortho G film. T-Mat G also produces high resolution and high contrast. This is contrary to the widely held notion that speed is inversely proportional to image quality.

Absorptiometry, Photon↗
PubMed1985

A special technique to retrieve images from a dark cephalogram.

A high-density, unreadable cephalogram was made readable by duplicating it at 7 to 10 times the usual ultraviolet light exposure. Soft tissue images were retrieved from a readable cephalogram of normal density by duplicating it at 12 to 20 times the usual ultraviolet light exposure. However, the hard tissue images disappeared in the duplicating process. A correctly made duplicate radiograph had a higher image resolution than the image resolution of the original corresponding high-density radiograph. The difference was not significant clinically.

Absorptiometry, Photon↗
PubMed1978

Effect of mAs and kVp on resolution and on image contrast.

Two clinical experiments were conducted to study the effect of kVp and mAs on resolution and on image contrast percentage. The resolution was measured with a "test pattern." By using a transmission densitometer, image contrast percentage was determined by a mathematical formula. In the first part of the experiment, the density of the film was kept constant by changing the kVp and mAs. In the second part of the experiment, different mAs's were chosen, and for each mAs, several kVp's were used. Five observers read the radiographs. The first experiment showed that, when the film density is kept constant, the higher the kVp, the lower the resolution and image contrast percentage; also, the higher the mAs, the higher the resolution and image contrast percentage. The second experiment showed that when the film density is not kept constant, the correlation between kVp and resolution and between kVp and image contrast percentage was the same as in the first experiment. However, there was negligible correlation between mAs and resolution and between mAs and image contrast percentage. A high positive correlation was found between resolution and image contrast percentage, but a high negative correlation was found between resolution and film density.

Absorptiometry, Photon↗
PubMed1978

Comparison of xeroradiographs with occlusal and screen films.

Since the advent of xeroradiography, many questions have been asked about its image quality and speed relative to that of periapical and screen films. The experiment reported here measures the "resolution" of occlusal film, screen film, and xeroradiographs at different k Vp and mAs settings. The occlusal film was used instead of the periapical film because it has the same speed as a periapical film and is sufficiently large for the placement of the measuring instrument (a test pattern).

Dental Equipment↗