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Biomedical subjects

R L Webber

Publications and source records attributed to R L Webber.

At least 55 records · Page 3Linked to original sources
PubMed1991

Optical determination of dental pulp vitality.

In this preliminary study, we explored the feasibility of employing photoplethysmography and pulse oximetry to assess the status of the blood circulation in the dental pulp. A simple photometer that measures diffuse light transmission at 575 nm was built to record tooth plethysmograms, and the ability to distinguish vital from surgically devitalized teeth of a dog using plethysmography was demonstrated. As an extension of the photoplethysmographic technique, red-infrared pulse oximetry applied to the measurement of the oxygen saturation (SO2) of blood in the pulp was also examined using an in vitro test setup. Results suggest that the measurement of relative SO2 changes is feasible, but standard dual-wavelength pulse oximetry does not enable determination of SO2 independent of tooth geometry and sensor placement.

Adult↗
PubMed1990

Dental radiology. Present limitations and future prospects.

The diagnostic process is likely to be limited by one or more of the following factors: (a) ambiguous signal definition, (b) inappropriate data sampling strategy, (c) inadequate signal strength, and (d) misinterpretation of data. Controlled tests suggest that the first two factors largely control performance of common dental diagnostic tasks.

Humans↗
PubMed1990

Calibration errors in digital subtraction radiography.

Two methods for the measurements of osseous change detected by digital subtraction radiography have been evaluated. Estimates of errors introduced by soft and hard tissues that overlay the region of interest (ROI) or by soft tissue that replaced the bone are made. All estimates are made assuming that the radiation source is a 40 keV monoenergetic beam and the reference standard is equivalent to compact bone. These assumptions facilitate a theoretical analysis of calibration errors on a relative scale. The radiographic image method uses a calibration wedge on each of the two films. The mean gray value of the ROI on each film is converted into an equivalent thickness of bone by matching the ROI mean gray value to a gray value along the wedge. These thickness values are then subtracted to obtain a measurement of the amount of change. The subtraction image method makes use of a wedge on only one of the two films. The image of the subtraction of the two radiographs is used for detection of the area of change and the mean gray value of the ROI is matched to a gray value along the wedge. The thickness of the wedge at this point is the measured change. The errors introduced by inclusion of the cheek over the ROI and the replacement of bone by soft tissue are estimated for the radiographic image method. The influence of unequal beam attenuation between the reference ramp and the ROI is estimated for the subtraction image method. Other factors influencing the accuracy of estimates of osseous change which are nonlinear in their effects are also considered.(ABSTRACT TRUNCATED AT 250 WORDS)

Calibration↗
PubMed1989

The effects of beam hardening on digital subtraction radiography.

Quantitative assessment of osseous changes attributable to periodontal disease is made possible by digital subtraction radiography. Tissues through which x rays travel to produce dental radiographs essential to this process alter the energy spectrum of the beam such that calibration errors result when densitometry is attempted using a homogeneous calibration standard such as a step wedge. The following controlled in vitro investigation evaluates the extent of such errors caused by these spectral differences, called beam hardening. Simulated osseous lesions of known size were computed densitometrically using selectively filtered radiation to produce the x-ray images. The resulting data confirm the theory and demonstrate with statistically meaningful accuracy that beam hardening can contribute a significant component of variance to absolute estimates of lesion size. They also suggest that other errors (probably attributable to low contrast) may be even more important at high peak kilovoltages.

Densitometry↗
PubMed1989

In vitro study into the influence of X-ray beam angulation on the detection of artificial caries defects on bitewing radiographs.

Little is known about the influence of errors in angulation of the X-ray beam on the correct diagnosis of interproximal caries defects from bitewing radiographs. In this study radiographs were made of 10 artificial lesions resembling initial interproximal caries defects in mandibular teeth at different projection angles within a range of +/- 15 degrees in horizontal and in vertical direction and presented in a random order to 25 dentists. The result show that the best angle for lesion detection was site-specific with about a 7 degrees tolerance range. On the average, best detection performance was achieved with horizontal angulation perpendicular to the tooth surfaces, and vertical angulation with a positive or negative tilt of 12-15 degrees relative to the perpendicular. Deviations from the best horizontal angle resulted mainly in loss of sensitivity, while vertical misangulations caused mainly a drop of the specificity. The classification of lesions with an actual depth less than halfway into the enamel is influenced to a larger extent than that of deeper lesions.

Dental Caries↗
PubMed1989

Determination of projections for subtraction radiography based on image similarity measurements.

The reliability of subtraction radiography strongly depends on the ability to obtain two identical projections. Generally this is done by connecting mechanically the X-ray source, the patient and the film. However, this method has certain disadvantages, which restrict its use to small groups of patients in other than routine clinical situations. A computer-aided radiographic imaging technique (tomosynthesis) brings the reconstruction of arbitrary projections within reach. This technique can be used to reconstruct the projection required for a proper subtraction. However, in order to do so, the coordinates of the source position of one projection, relative to the source positions of the set of projections used for fomosynthesis, has to be determined. A method is described based on similarity measurements, in pairs of images (expressed in the form of standard deviations) to achieve this. The coordinates of the unknown source position could be determined with an average accuracy of 0.513 degrees (range 0.000-1.289 degrees), which is well within the range of deviations tolerable for the clinical application of subtraction radiography.

Radiography, Dental↗
PubMed1988

Effect of periodontal therapy on alveolar bone as measured by subtraction radiography.

Changes in the periodontal alveolar bone are often evaluated by comparing a series of radiographs taken over time. This investigation used a technique that allowed the image registration to be geometrically standardized each time a radiograph was taken. Radiographs of 24 patients from an ongoing double-blind, clinical study using metronidazole were obtained: (1) before any treatment, (2) at the completion of scaling and root planing and surgery (when performed) and (3) during the maintenance phase. One hundred six (106) paired comparisons were analyzed by subtraction radiography using a computerized system. Of these, 95 (89%) exhibited a minimal degree of geometric distortion and could be successfully substracted. Most areas (67%) showed no change in bone structure following periodontal treatment. Bone gain was noted in 12% of the sites examined, while bone loss was seen in 21% of the sites. This bone loss was statistically associated with sites that had received some form of surgical treatment.

Alveolar Process↗
PubMed1987

Dental radiography: efficacy in the assessment of intraosseous lesions of the face and jaws in asymptomatic patients.

In this investigation the efficacy of dental radiography for the detection of occult intraosseous lesions of the face and jaws was evaluated. An analysis of 30 million health insurance records indicated that the period prevalence of malignant lesions was less than 5 cases/million/year, and for benign lesions approximately 100 cases/million/year. Data from a controlled observer-performance study showed that radiographic sensitivities ranged between 50% and 80%. The cost per true-positive finding was estimated to be +8.6 million per malignant case and +430,000 per benign case. An assessment of the dosimetric literature indicated that the benefits of radiographic screening as a means for early detection of a malignancy appear to be counterbalanced by the risk of causing a radiation-induced malignancy. Taken together, these data demonstrate that dental radiography is not efficacious for the purpose of detecting occult lesions.

Costs and Cost Analysis↗
PubMed1986

Enhancement of tomosynthetic images in dental radiology.

In conventional projection radiography, anatomical structures superimposed on details of interest increase the difficulty of visual interpretation. Part of this problem can be resolved by tomographic reconstruction of specific "tissue" slices. Computer-aided tomosynthesis is one method which can reduce the superposition problem, but the reconstruction can benefit from further enhancement. In this investigation, we studied two such enhancement schemes: high-pass spatial-frequency filtration and iterative deconvolution. The performance of each technique was judged qualitatively in terms of the depiction of specific details of diagnostic interest, and quantitatively in terms of the degree of success afforded by each in rendering adjacent tissue slices independent. Both techniques demonstrated improved performance over the status quo.

Humans↗
PubMed1985

Computers in dental radiography: a scenario for the future.

The recent emergence of cost-effective computing power makes it possible to integrate sophisticated data-sampling and image-interpretation techniques into dental radiography for the first time. A prototype system is being developed to permit clinical information expressed in three dimensions--plus time--to be made visible almost instantly. The associated X-ray dose for a complete three-dimensional survey of a selected dental region is predicted to be less than that required for a single conventional periapical radiograph exposed on D-speed film.

Computers↗
PubMed1984

Influence of variations in projection geometry on the detectability of periodontal bone lesions. A comparison between subtraction radiography and conventional radiographic technique.

The influence of differences in imaging geometry on the detection of small periodontal bone lesions was studied when using a digital subtraction technique. The results were compared with those from conventional radiographs. Reference radiographs were obtained on human mandibular jaws before small lesions were made in the marginal alveolar bone. Subsequent radiographs were taken with the same imaging projection as well as with changes of the angulation in either vertical, or horizontal direction, or both. 10 dentists served as observers, who compared the conventional radiographs taken before and after the lesions were made, and registered the presence or absence of lesions using a diagnostic rating scale. The conventional radiographs were digitized, and subtraction images made. These images were interpreted by the same observers. For each observer, image modality and projection, the resulting rates of true positive and false positive diagnoses were plotted on a graph. The area under the curve, obtained by connecting the paired values of true positive and false positive results associated with the different diagnostic ratings, was used as a measure of diagnostic accuracy. Statistically significant differences could be demonstrated between the results obtained from the subtraction images, whether produced from identical or non-identical pairs of conventional radiographs, and the results from the conventional radiographs obtained under ideal conditions.

Alveolar Process↗
PubMed1984

Computer correction of projective distortions in dental radiographs.

Distortions in radiographic images caused by changes in shape and position of the film relative to the x-ray beam can result in registration artifacts which interfere with interpretation of subtracted images. A warping transformation is described which maps known points of reference in one image into homologous points in another. The corrected image pair can then be superimposed and subtracted with significantly-reduced differences in registration to facilitate the detection of localized changes of diagnostic interest.

Computers↗