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P G Howell

Publications and source records attributed to P G Howell.

42 records · Page 3Linked to original sources
PubMedDate not supplied

Correlative light and backscattered electron microscopy of bone--part II: automated image analysis.

Detailed studies of biological phenomena often involve multiple microscopy and imaging modes and media. For bone biology, various forms of light and electron microscopy are used to study the microscopic structure of bone. Integrating information from the different sources is necessary to understand how different aspects of the bone structure interact. To accomplish this, methods were developed to prepare and image thin sections for correlative light microscopy (LM) and backscattered electron imaging in the scanning electron microscope (BSE-SEM). Images of the same fields of view may then be analyzed for degrees of relationships between specimen features not observed by LM or SEM alone. These methods are applied here to study possible associations between the degree of bone mineralization and pattern of collagen fiber orientation in the mid-shaft of the human femur. The "relational images" obtained allow us to examine the relationship between these two variables, both objectively and quantitatively.

Femur↗
PubMedDate not supplied

Light collection efficiency and light transport in backscattered electron scintillator detectors in scanning electron microscopy.

Experimentally, scintillator detectors used in scanning electron microscopy (SEM) to record backscattered electrons (BSE) show a noticeable difference in detection efficiency in different parts of their active zones due to light losses transport in the optical part of the detector. A model is proposed that calculates the local efficiency of the active parts of scintillator detectors of arbitrary shapes. The results of these calculations for various designs are presented.

Journal Article↗
PubMedDate not supplied

Monte Carlo simulations of electron scattering in bone.

Relative changes in the mineralization level within bone can be studied using backscattered electron (BSE) imaging in a scanning electron microscope (SEM). We calculated the size and shape of the volume element studied, choosing conditions which are typical for practical experimental work with polymethylmethacrylate (PMMA)-embedded bone. Absolutely flat surfaces of embedded bone blocks cannot be generated, and a further aim was to examine the effect of the surface topography on the detected BSE signal level. For normal beam incidence, 20 kV, and modeling an annular detector by collecting BSE with take-off angles of between 45 degrees and 75 degrees to the flat sample surface, it was found that the collectable BSE signal intensity peaks for electrons which leave the specimen surface at a radial distance of approximately 1 micron from the beam impact point. The layered structure of the bone generates topographic relief on polishing. Modeling this by a sinusoidal profile of wavelength 5.0 and amplitude 0.5 micron and again for 20 kV, it was found that the signal derived from the troughs is reduced by 14.4% and that from the crests is increased by 17.2%. The two effects may add constructively to generate the frequently observed strong contrast correlating with the distribution of bone lamellae. No net change in mineral packing density would be expected from a change in collagen orientation, and the lamellar contrast observed in practice can be explained solely by the topographic contrast.

Bone Density↗
PubMedDate not supplied

Evaluation of eccentric occlusal contacts in complete dentures.

Three edentulous patients were evaluated using the kinesiograph and a specially designed computer program to identify the length of eccentric contacts between their dentures when masticating test foods. Three different interchangeable occlusal arrangements were constructed and tested. Results of the evaluation of more than 1,400 chewing cycles showed that while 25% of masticatory contacts were eccentric, the great majority of contacts were within a distance of 1 mm from centric occlusion. More eccentric contacts occurred in the opening phase than might be expected. Posterior tooth form did not appear to affect the range of eccentric contacts.

Aged↗