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Biomedical subjects

R L Webber

Publications and source records attributed to R L Webber.

At least 73 records · Page 4Linked to original sources
PubMed1983

Effective exposure level and diagnostic performance in endodontic radiography.

Image quality is limited by the information capacity of the image-forming system and can be computed from three parameters: contrast, resolution, and noise. These parameters can be combined to yield a single measure which determines the maximum amount of information obtainable from any x-ray system and is called the noise-equivalent number of quanta (NEQ) per unit area. The effects of image quality, expressed as noise-equivalent number of quanta (NEQ) per unit area, on the radiographic performance by dentists reading the position of an endodontic file in a root canal were studied. Three different speed films were used in conjunction with a fixed screen. NEQ values ranged between 0.64 x 10(4) and 14.3 x 10(4) per square millimeter. Components of variance associated with the position of the tooth apex and the tip of an endodontic file in a root canal were compared for the effect of different NEQs and observers. Results show that the standard deviation in locating a file tip and tooth apex may be a linear function of log NEQ. The estimated standard deviation associated with changes in NEQ was found to be relatively small compared to that observed among dentists. These findings indicate that a significant reduction in exposure would have a relatively small effect on the precision of endodontic distance measurements.

Dental Pulp Cavity↗
PubMed1983

Computerized tomosynthesis of dental tissues.

A digital method that produces an arbitrary number of tomographic slices from a finite number of dental radiographs is described. The relation between the slice thickness of the tomograms, the number of radiographs required, and the tomographic angle is determined on the basis of existing theory. In order to test the method, a series of radiographs of a radiographic phantom were taken and subsequently digitized to facilitate computer processing. From eight radiographs with an angular disparity of 4.5 degrees, tomograms with a slice thickness of about 3 mm, were produced. These not only indicate the relative position of the dental tissues in space but also show clinical relationships that are not visible in the original radiographs.

Humans↗
PubMed1983

A digital subtraction technique for dental radiography.

The relative accessibility and stability of the teeth facilitate generation of geometrically identical radiographs over a period of time. When such radiographs are digitized with the aid of a TV camera coupled to an analog to digital converter and a computer, it is possible to conveniently produce subtraction images of high diagnostic value. A digital subtraction technique for longitudinal dental radiography is described; this technique should be applicable to diagnostic situations characterized by a need to detect small changes occurring over a period of time in areas where substantial amounts of structured noise limit their detectability.

Computers↗
PubMed1983

Digital subtraction radiography for diagnosis of periodontal bone lesions with simulated high-speed systems.

Standardized radiographs were obtained of the molar and premolar areas of dry human mandibles before and after small lesions were induced in the alveolar bone crest. The radiographs were digitized, and various amounts of random noise were added to simulate images produced by more efficient, low-radiation-dose systems. Subtraction images were produced from these noise-degraded radiographs. The diagnostic performance of human observers from these images was then compared with that obtained from both subtraction images made from nondegraded radiographs and from the original, conventional images. The diagnostic accuracy obtained with subtraction images, even if they were made from severely noise-degraded images, was equal or superior to that obtained with the conventional radiographs. This indicates that structured noise, which is reduced by the subtraction procedure, is a predominant, limiting factor in the diagnosis of small periodontal bone lesions. It also suggests that the application of a subtraction technique for the detection of such changes occurring over a period of time can make possible the use of significantly faster imaging systems than those currently employed.

Alveolar Process↗
PubMed1983

Microbiological and clinical effects of topical subgingival antimicrobial treatment on human periodontal disease.

This study was undertaken to evaluate the microbiological and clinical effects of a subgingivally applied mixture of H2O2-NaCl and NaHCO3 followed by subgingival irrigation with 1% Betadine in the treatment of periodontal disease. 20 adults with moderate to severe periodontal disease were included in a split mouth design study. All patients were given oral hygiene instruction and were subjected to supragingival scaling in all 4 quadrants, and subgingival scaling and root planing of half the dentition. 10 patients were instructed to use the chemical antimicrobial mixture twice a day instead of dentifrice, and also received professional application of the mixture once every 14 days for 3 months in connection with reinstruction in oral hygiene procedures. The remaining 10 patients received oral hygiene instructions combined with professional tooth cleaning without use of chemicals once every 14 days during a 3-month period. The effect of treatment was evaluated by monitoring the subgingival microflora, clinical periodontal parameters, and by computer assisted subtraction analysis of serial standardized radiographs to determine changes in mass of the supporting alveolar bone. The present study revealed that subgingival debridement combined with mechanical plaque control resulted in decreased numbers of subgingival microorganisms including spirochetes and motile rods, and arrested the progressive breakdown of the periodontal tissues. Topical antimicrobial agents used in combination with subgingival scaling further reduced the subgingival microflora and substantially improved early periodontal healing including gain of probing attachment level and gain in radiographic alveolar bone mass during the 12 months of observation. No clinical improvement but a tendency to further periodontal breakdown was found in the unscaled quadrants, even in those which were subjected to a personal application of the topical antimicrobial mixture. This study indicates that professional and personal subgingival application of a mixture of H2O2-NaCl and NaHCo3 will significantly enhance the microbiological and clinical effects of periodontal scaling and root planing. These agents, and the topical mode of antimicrobial therapy seem promising in the management of human periodontal diseases.

Administration, Topical↗
PubMed1982

Effect of quantum noise on the detection of incipient proximal caries.

The effect of quantum noise on the radiographyic detectability of proximal carious lesions was studied. Bitewing radiographs obtained from patients considered to be free of caries were digitized and stored in a computer using a sampling interval comparable to screen-film systems. Lesions limited in depth to one half the thickness of the enamel were induced by means of computer simulation. Various amounts of randomly generated quantum noise were added to each radiographic image. The results from observer-performance studies show that the lesions can be detected reliably in the presence of substantial amounts of quantum noise, suggesting that comparable diagnostic performance could be obtained with significantly faster imagining systems than those currently used in dentistry.

Analog-Digital Conversion↗
PubMed1982

Statistical contrast enhancement of subtraction images for radiographic caries diagnosis.

The effects of the nonlinear contrast-enhancement technique are examined in terms of diagnostic performance obtainable from subtracted dental radiographs for a variety of simulated exposures. Conventional bitewing radiographs of patients known to be free of caries were digitized by means of a computer interfaced with a conventional television camera. The resulting images were duplicated and stored in the computer. Radiolucencies similar in appearance to interproximal caries were simulated analytically in one set of the images. Reference images were superimposed spatially and subtracted from their counterparts containing the induced interproximal lesions after simulating the effects of quantum limited exposure on both sets. This was done for each separate image element independently by replacing original gray levels in each image with levels determined by a Poisson random deviate. The resulting difference images were contrast enhanced by a method which first smooths out local variations in gray level and then reassigns gray-level values in a way determined by the observed second-order spatial statistics. To aid in localization, these images were then again subtracted from the original noise-degraded pictures without lesions, rendering images similar to conventional radiographs but contrast enhanced. Observer performance by means of these enhanced images was compared with that produced from unenhanced-lesion-containing controls. The results suggest that enhancement increases the certainty with which diagnosis can be made and, further, that diagnostic accuracy can be improved in severely degraded images which simulate the effects of reduced levels of exposure.

Computers↗
PubMed1982

Toward a better understanding of radiographic contrast.

Contrast is a familiar term that relates directly to the ability of human observers to detect differences in optical density. It also has been used to describe changes in x-ray fluence determined by attenuation differences in tissues of diagnostic interest. Ambiguous conclusions in the literature can be often traced to a lack of specificity in what is being measured and the validity of the implicit assumptions involved. Particularly troublesome are nonspecific bases for normalization and the assumption that a finite change in fluence can be accurately represented as a differential. These practices also tend to obscure consideration of system nonlinearities which can result in contrast enhancement produced by exposure to fogging radiation. Precisely defined components of contrast are symmetrically determined by the concept of modulation. This concept provides a powerful basis for mathematical description of linear systems. Bases for linearization of radiographic systems are also confusing unless thay are explicitly stated. This is particularly true for transfer functions as defined in many radiographic applications. Special functions which account for nonlinearity commonly associated with contrast gain in the detector simplify description and provide a quantitatively meaningful basis for specifying system performance in terms of information theory.

Mathematics↗
PubMed1981

The effects of spectral distribution on x-ray image quality.

Broad and monoenergetic x-ray spectra were analyzed with a computer to determine the photon signal-to-noise ratio, exposure modulation, and integral dose in a simulated caries detection task. Assuming an ideal exposure geometry, it was possible to compute relative values which permit meaningful comparison of spectra in terms of these parameters. The broad spectra were measured with a high-resolution spectrometer system. The data were corrected for spurious effects and analyzed with an idealized attenuation model. The results suggest that spectral changes brought about by even relatively small amounts of selective filtration in region between 25 and 45 keV. measurably influence the potential for diagnostic quality.

Computers↗
PubMed1979

Angular invariants in developing human mandibles.

Recent studies of lateral cephalograms based on symmetric-axis analyses of the mandibular border yield angles that appear to be uninfluenced by gross changes in mandibular shape over age and between individuals.

Adolescent↗
PubMed1978

Clinical evaluation of a prototype intraoral source x-ray system.

A prototype dental roentgenographic system which incorporates a tightly collimated intraoral x-ray source and an extraoral Polaroid film screen cassette was evaluated both in vitro and in vivo. Findings indicate that the detectability of artificially induced incipient enamel lesions was significantly less than that demonstrable for conventional roentgenograms produced with an extraoral source, long-cone geometry, and Kodak Ultra Speed D film. Larger lesions were found to be reliably detected by either technique. The new intraoral approach reduces the dose to the patient by possibly as much as 98 per cent and yields positive dry prints in 15 seconds. This system was clinically tested and found to be useful in endodontics and presurgical evaluation. Modifications are discussed which could reduce some of the technical problems and many of the shortcomings encountered.

Acid Etching, Dental↗
PubMed1977

A nonlinear model for predicting radiographic contrast.

A computerized model has been developed which permits ideal maximum radiographic contrast, associated with clinically meaningful changes in x-ray attenuation for any combination of tissues, to be predicted from the spectral energy of the primary beam and the characteristics of the film. Results suggest that these factors influence available contrast in ways which depend on the specific diagnostic task to be accomplished. Hence, it appears that no single technique is optimal for all tissue configurations. Although contrast computed in this way does not take into account other factors of diagnostic interest, such as image resolution and context-dependent cues to lesion identity, it is an independent factor which can profoundly influence the detectability of specific changes in tissue attenuation and, as such, it may be considered a reasonable basis for predicting diagnostic performance.

Computers↗
PubMed1976

Radiographic detectability of occipital and temporal-parietal fractures induced in cadaver heads.

Diagnostic performance based on a double-blind evaluation of test and control radiographs produced from nine different fractured cadaver skulls was compiled for six radiologists. The data resulting from two different diagnostic tasks were analyzed statistically for accuracy and confirmed interpretability including an assessment of task-related performance differences. Performance was found to be relatively independent of differences among radiologists and lesion location. Little overall correlation was found to exist between demonstrated ability to detect lesions radiographically, and visual confirmation of known lesions from the same films. These results suggest that overall performance was probably limited by a number of undefined clinical factors which influence the amount of meaningful information available from the resulting radiographs. The distribution of these degrading influences was not uniform within the population sampled so that certain radiographs proved to be particularly misleading when considered in terms of their apparent diagnostic value. As a result, even relatively large depressed fractures were in some instances considered radiographically uninterpretable.

Autopsy↗
PubMed1975

An alternative approach to dose reduction in dental radiography.

A responsible approach to dose reduction in dental radiography requires that relative exposure be related to the specific diagnostic task performed. All but the most demanding tasks can be performed when suitable film is used in conjunction with high-speed screens. Placing the source of radiation inside the mouth permits radiographic information to be recorded on an improved Polaroid cassette that has a relatively high quantum efficiency. As a result, the radiation dose can be significantly reduced in a versatile system which provides for instantaneous processing and interpretation from prints rather than negatives.

Radiation Dosage↗