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Biomedical subjects

R L Webber

Publications and source records attributed to R L Webber.

At least 19 recordsLinked to original sources
PubMed1992

Fractal dimension from radiographs of peridental alveolar bone. A possible diagnostic indicator of osteoporosis.

The purpose of this study was to investigate whether a radiographic estimate of osseous fractal dimension is useful in the characterization of structural changes in alveolar bone. Ten dry mandibular bone segments were radiographed from three controlled projection angles (-5, 0, +5 degrees), before and after acid-induced partial decalcification. Fractal dimension was estimated by regression analysis of power spectra computed by Fourier transform of selected regions of interest in digitized images of the radiographs. Repeated-measures ANOVA showed that fractal dimension so determined varied over anatomic locations (p less than .01), but increased after acid-induced demineralization (p less than .0005), irrespective of the radiographic projection angles (p greater than .99). In vivo fractal dimension was computed from randomly selected intraoral radiographs of six premenopausal (ages, 32.8 +/- 3.9) and six postmenopausal (ages, 62.5 +/- 4.1) women. A significantly (p less than .01) higher fractal dimension was observed in the older group.

Adult↗
PubMed1992

Digital subtraction radiography for the assessment of bone changes in rheumatoid arthritis.

A digital subtraction radiography (DSR) method was developed to assess changes of bony erosions in the hands of patients with rheumatoid arthritis (RA). The method initially was validated in vitro using simulated lesions in cadaver hands. The sensitivity, specificity and accuracy in detecting simulated lesions were 84.6, 100, and 92.3%, respectively. This technique was then pilot tested clinically using 17 patients with RA and 5 controls with no arthritis. All subjects received the nonsteroidal antiinflammatory drug, flurbiprofen, during the 6-month study period. No progressive changes in bone were observed in the control group; however, 18% of the target joints studied in the group with RA showed significant erosive changes (positive or negative) which correlated with the clinical assessment. The results indicate that DSR may be useful in detecting small changes in erosions on hand/wrist radiographs of patients with RA.

Adult↗
PubMed1991

Magnetic resonance imaging of canine salivary glands after ductal ligation and stimulation by pilocarpine.

We performed magnetic resonance imaging in six dogs after submandibular ductal ligation on one side, followed by secretory stimulation with intraperitoneal injection of pilocarpine (5 mg/kg). On the images obtained after ductal ligation but before stimulation, there was no significant change in signal intensity on either side. After injection of pilocarpine the signal intensity of the ligated gland increased significantly (p less than 0.01) in T2-weighted images and nonsignificantly in inversion recovery images, and remained constant in T1-weighted images. Significant (p less than 0.01) volume increases of the glands after ligation and stimulation were measured for the T1, T2, and inversion recovery protocols. These findings likely reflect the retention of saliva caused by pilocarpine stimulation and the absence of drainage through the obstructed duct. The results indicate that the T2-weighted images obtained after pilocarpine stimulation may be useful for studying patients with disturbance of major salivary gland function and may provide an objective basis for the noninvasive diagnosis of unilateral stenosis.

Animals↗
PubMed1991

Studies on focal alveolar bone healing with technetium (Tc)-99m labeled methylene diphosphonate and gold-collimated cadmium telluride probe.

The benefit of using a collimator for a miniaturized cadmium telluride probe was evaluated by monitoring the bone-healing processes for 13 weeks after the induction of small iatrogenic alveolar bone lesions in one side of the mandible in beagles. Technetium (Tc)-99m labeled methylene diphosphonate (200 to 300 MBq, 5.1 to 8.1 mCi, in a solution of 0.5 to 1 ml, intravenously) was used as a bone-seeking radiopharmaceutical. The radioactivity over the bone lesion (L) and the contralateral normal site (C) in the mandible were measured between 1.5 and 2 hours after injection of the tracer, and the activity ratio L/C served as an index of relative bone uptake. A study of six dogs revealed that the healing response to a hemispheric bone defect of 2 mm diameter in the cortical bone could not be detected by an uncollimated probe, and in a repeated study in two dogs the use of a gold collimator (5 mm in diameter, 5 mm in length) did not increase the L/C ratio significantly. A second study in six dogs with 5 mm lesions showed that although systematic trends in the time courses of the L/C ratio obtained both with and without the collimator could be demonstrated, the L/C ratio of collimated versus uncollimated measurements was significantly (p less than 0.005) increased. In three of the latter six dogs, abscesses developed after 9 weeks, leading to a second increase (p less than 0.05) of the L/C ratio with collimation compared with the noninflammation group; without collimation no significant (p greater than 0.15) difference between the two groups could be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Alveolar Process↗
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↗