Biomedical subjects

D K Benn

Publications and source records attributed to D K Benn.

15 recordsLinked to original sources

PubMed1992

Frequent, low-dose, improved-contrast radiographic images with the use of narrow x-ray beams.

Conventional dental radiography uses 60 mm-wide x-ray beams that irradiate the cheeks. To reduce the dose of radiation, months or years can separate serial films and prevent short-term assessment of disease activity. A technique that uses a 13 mm narrow x-ray beam that avoids the cheeks was compared with a wide x-ray beam by using a contrast phantom, a cheek substitute, and a serially sectioned dry mandible. Phantom contrast was measured densitometrically at 50 kVp, 65 kVp, and 90 kVp with wide x-ray beam and narrow x-ray beam and with and without cheek scatter. The narrow x-ray beam without cheek scatter technique resulted in better contrast (0.06 to 0.04 OD) than the wide x-ray beam with cheek scatter (0.05 to 0.02 OD). A posterior interdental crest was irradiated and a trabecular rod was removed. The bone detail was best in the images produced with the narrow x-ray beam without cheek scatter. The area of the narrow x-ray beam was 4.35% of the area of the wide x-ray beam with approximately 5% of the dose. Short-interval (weekly), very-low-dose radiography should be possible with improved contrast to assess alveolar bone changes.

Cheek↗

PubMed1992

A computer-assisted method for making linear radiographic measurements using stored regions of interest.

Accurate detection of changes in alveolar bone height requires radiographic measuring methods with a reliability of standard deviation (SD) of 0.15 mm or better. No periodontal digital imaging system has reached this reliability, although 3 analogue methods have achieved this goal. However, existing linear methods are time-consuming, difficult to use, unsuitable for measuring all possible (unsharp) anatomical sites and do not provide a confidence estimate for sites of change observed in serial standardized films. A rapid computer-assisted method using stored image regions of interest (ROI) has been developed which allows retest measurements for all possible sites and automatically calculates a 90%, 95%, 98%, or 99% confidence threshold value, derived from duplicate measurement variation, for sites of apparent crest height change. 28 examiners, with minimal training in operating the system, measured 14 different cement-enamel junction to crest height distances from a standard bitewing image, with and without the ROI method. The measurements were repeated 4 weeks later. 13/14 sites achieved an intra-examiner SD threshold of less than or equal to 0.15 mm with the ROI method but 0/14 without. A higher inter-examiner SD threshold of less than or equal to 0.22 mm was achieved for 13/14 sites using ROI and 0/14 without (p less than 0.001). The measurement of crest height changes in a region of previous severe vertical bone loss is demonstrated using serial films. The potential for using trabecular bone patterns as reference sites in regions where traditional measurement points are absent is demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Alveolar Bone Loss↗

PubMed1992

Estimating the validity of radiographic measurements of marginal bone height changes around osseointegrated implants.

The accuracy of determining marginal bone height changes around osseointegrated implants depends on the validity of comparing serial films and the reliability of the measurements. X-ray beam orientation changes can alter the validity of serial films. A human dry mandible containing a Brånemark implant was irradiated +/- 12 degrees in the vertical plane at 1-degree intervals to the perpendicular to the long axis of the fixture. The thread width was recorded on both sides of each fixture image using a computer. Twenty-five randomized unclassified images were remeasured and the vertical angle of the x-ray beam was estimated from the previous measurements to test for validity of comparing images. The reliability of measurements with altered image magnification and penumbra were calculated. The reliability of 24 repeated thread width measurements was a SD of 0.01 mm. Of the 25 unknown beam angulations, 32 percent matched correctly, 20 percent +/- 1 degree, 16 percent +/- 2 degrees, or 68 percent < or = +/- 2 degrees. Alteration from a short to a long cone technique was estimated to produce magnification errors similar to the reliability SD of 0.01 mm. Similarly the penumbra varied from 0.057 mm to 0.032 mm with short to long cones using a 1.0-mm focal spot. With a 0.6-mm focal spot, the smallest penumbra of 0.19 mm was twice the measurement reliability. This method demonstrated x-ray beam angulation and validity for comparing serial films can be estimated for the extreme variations but not accurately for +9 to -6 degrees from a tangent to the fixture.(ABSTRACT TRUNCATED AT 250 WORDS)

Alveolar Bone Loss↗

PubMed1991

Automatic analysis of radiographic images: I. Theoretical considerations.

Making accurate measurements from radiographic images is time consuming and expensive. Simple and inexpensive diagnostic/monitoring systems will require a high degree of automation if they are to be used by radiographers or nurses in routine clinical practice without special training. Completely automatic image analysis systems are rare in radiology, although a number of experimental automated (initial human interaction) systems do exist. No fully automatic system exists for analysing dental bitewing radiographs. The role of multiple layer image models and multiple sources of information are discussed in relation to dental images. The potential role of interdental spaces is suggested as necessary key image regions to be identified for the model building process. A theoretical image model data structure is proposed which is experimentally tested in the following paper.

Humans↗

PubMed1991

Automatic analysis of radiographic images: II. Software implementation and testing on bitewing radiographs.

A prototype, completely automatic image-analysis system for dental bitewing radiographs was implemented in 'C' on a Unix workstation. A multiple layer hierarchical image model was created in software for each radiograph using production rule-based knowledge. The highest model layer formed an English-like description of anatomical structures including tooth type, interdental alveolar bone crest margins and spaces. A representation of spatial relationships between anatomical structures was formed, providing a method for comparing similar regions of a patient in serial, but not absolutely standardized, images. In 31 clinical radiographs, the system automatically identified 93% (193) of all available interdental spaces which are the key image regions for model creation. Each image required 2 minutes of processing time. The reproducibility of finding 34 interdental spaces in five films revealed one error. Further work is required to improve the recognition rate of the interdental regions towards 100% and to develop automatic comparisons between areas of change (disease?) in serial films.

Humans↗

PubMed1990

A review of the reliability of radiographic measurements in estimating alveolar bone changes.

Despite their widespread use, dental radiographs have numerous shortcomings for measuring alveolar bone changes. In order to develop guidelines for improving the reliability of radiographic measurements, factors affecting the formation of an image were reviewed. These were considered regarding the design of a clinical monitoring system, capable of detecting the loss of small amounts of alveolar bone crest from serial films. Dentists need a monitoring system to assess whether bone loss is progressing or to judge whether a treatment is successful. 2 models were constructed to predict how long it would take to detect marginal bone loss occurring at a linear rate of 0.1 mm/year. The 1st model assumed a CEJ-crest measurement error of +/- 0.3 mm and the second +/- 0.9 mm, both using a 0.1 mm measuring interval. These error values were derived from the literature. The 1st model predicted it would take between 7 and 13 years for the system to measure a 1.0 mm loss in crest height caused by an actual loss of between 0.7 and 1.3 mm. The 2nd model predicted that a 1.0 mm measurement would occur between 1 and 19 years, caused by an actual crestal bone loss of between 0.1 and 1.9 mm. From these models, it appears that routine screening of patients by general dental practitioners for small amounts of bone loss is unlikely to be successful without the use of (i) repositionable stentless film holders to standardise the irradiation geometry, (ii) a very accurate reproducible measuring technique which (iii) will probably require an automatic computer-based measuring system.(ABSTRACT TRUNCATED AT 250 WORDS)

Alveolar Process↗

PubMed1990

Further investigation of the predictors of outcome following first schizophrenic episodes.

The outcome at two years of patients who were eligible for a study of first schizophrenic episodes was assessed in terms of occupation (n = 237) and in terms of number of days spent as an in-patient from the time of first admission (n = 252), and was related to social, behavioural, mental state and neurological measures during the initial admission. Poor outcome was in general associated with more social withdrawal, inactivity and abnormal social presentation and with more 'neurological soft signs'. Good occupational outcome in patients with a relatively short pre-treatment duration of illness was associated with the prescription of placebo medication during the follow-up period.

Activities of Daily Living↗

PubMed1990

Limitations of the digital image subtraction technique in assessing alveolar bone crest changes due to misalignment errors during image capture.

The digital image subtraction method depends critically on the very precise registration of sequential radiographs. A method of using a single radiograph to form two identical digital images was created, eliminating any potential effects from irradiation or processing variation, to investigate the effects of misregistration between images. These images were displaced by 0.1-0.42 mm in the X, Y and XY directions before subtraction. A total of 35 alveolar crest margins from five bitewing radiographs were investigated for the extent of false bone loss or gain produced in the subtracted images. The mean grey level gradient across the interdental space/crestal margin interface was 3.1 (SD 1.4) grey levels per 0.05 mm pixel. Small displacements between subtracted images of 0.1-0.14 mm in the Y or XY directions caused 20-25% of crestal pixels to vary by greater than or equal to +/- 2.5% of the grey range. Larger displacements of 0.3-0.42 mm caused 65% of crestal pixels to vary by greater than or equal to +/- 2.5% of the grey range. A higher threshold of greater than or equal to +/- 4.1% of the grey range still showed up to 48% of crestal pixels were in this higher deviation band. A high noise threshold of +/- 8% of the grey range should be used to discriminate against false grey values. A visual method for estimating the direction of displacement error between images is discussed together with a method for setting noise thresholds for individual alveolar crest grey level gradients. In any radiograph, a range of alveolar crest gradients will be found and those with the higher gradients will produce the largest subtraction errors for any given displacement between images.

Alveolar Bone Loss↗

PubMed1989