Search PubMed⌕ Search

Biomedical subjects

M D Evans

Publications and source records attributed to M D Evans.

95 records · Page 6Linked to original sources
PubMedDate not supplied

Finite element method evaluation: articulations and diagonals in an 8-pin type 1B external skeletal fixator.

OBJECTIVE: To determine the mechanical properties of articulations and diagonals in an 8-pin type 1b external skeletal fixator (ESF). STUDY DESIGN: Finite element method-computer simulation. METHODS: The control type 1b ESF was supplemented with different articulations and diagonals. The parameters of frame angle, articulation diameter, and pin- or connector-based fastening were altered. The configurations were loaded for axial compression, torsion, and craniocaudal and mediolateral bending as single loads and as a combination. Three-dimensional linear and rotational gap strain and Von Mises stress maxima were determined. RESULTS: For 90 degrees , 60 degrees , and 30 degrees frame angles and 0.48-cm-diameter articulations and diagonals, the best configurations, based on lower gap strain combined with decreased or minimally increased stress maxima for the combined load, were single or double diagonals or four horizontal articulations. Combining double diagonals with double wide horizontal articulations further lowered gap strain. For a 90 degrees frame angle and 0.32-cm-diameter articulations and diagonals, the superior configurations, showing the lowest gap strain combined with decreased or minimally increased stress maxima for the combined load, were double diagonals, four horizontal, or wide double horizontal articulations. The 0.48-cm articulations and diagonals provided lower or similar gap strain than 0.32-cm articulations and diagonals. The connector-to-connector version of these superior configurations provided slightly lower or similar gap strain and stress maxima than the pin-to-pin version. Only pin-to-pin-fastened double diagonals provided better stress maxima than the corresponding connector-to-connector version. CONCLUSIONS: Supplementing a type 1b ESF with double diagonals and wide double articulations results in the greatest increase in stability at the fracture gap for complex fractures or in the initial phase of bone healing.

Animals↗
PubMedDate not supplied

The influence of phantom size on output, peak scatter factor, and percentage depth dose in large-field photon irradiation.

Machine outputs, peak scatter factors, and central axis percentage depth dose distributions were measured for various phantom sizes in large radiation fields produced at extended distances by cobalt, 6-MV, and 10-MV photon beams. The results can be applied to practical total body irradiation procedures which usually involve treatment volumes smaller than the actual field sizes in order to provide a uniform total body exposure to radiation. Our study addresses the question of the appropriate phantom dimension to be used in the calibration of photon beams employed in total body irradiations. The measurements show that the machine outputs are only slightly dependent on phantom size; the percentage depth dose distributions, however, are strongly dependent on the phantom size, suggesting that machine data for total body irradiations should be measured in phantoms whose dimensions approximate the patient during the total body irradiation. Peak scatter factors measured in large-field/small-phantom configurations link up well with the published small-field/large-phantom data. The finite patient thickness lowers the dose to points close to the beam exit surface by a few percent, when compared to dose measured at the same depths in infinitely thick phantoms. The surface doses in large radiation fields are essentially independent of phantom cross sections and range from 40% for the 10-MV beam, to 65% for the 6-MV beam and 80% for the cobalt beam.

Cobalt Radioisotopes↗
PubMedDate not supplied

Tumor localization using fundus view photography for episcleral plaque therapy.

The accurate localization of ophthalmic tumors on the scleral surface is important when calculating radiation dose to the tumor and adjacent structures from episcleral I-125 plaques. This is particularly true for tumors close to the fovea or optic nerve. A fundus view diagram of the eye is often used by ophthalmologists to describe the size and shape of the tumor perimeter as well as its geographical location on the retinal surface. There is, however, an inherent inaccuracy associated with the use of a hand drawn diagram to obtain physical measurements. A computer planning program has been developed which uses CT and a digitized photographic montage of the posterior hemisphere to estimate the size and location of posteriorly located tumors. A simple phantom was constructed to test the software and a direct comparison made between planned versus measured tumor size and location in an excised eye.

Brachytherapy↗
PubMedDate not supplied

Technique to improve lateral cervico-thoracic radiographs.

Lateral radiographs taken during radiotherapy simulation of the upper thoracic and lower cervical region are often of poor quality because of the difference in separation seen by the incident beam. A simple method of compensating for this is the application of a thin foil of lead on the simulator that obscures the light field in the superior portion of the field. This technique has the advantage of being simple, fast and easily reproducible.

Humans↗