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Biomedical subjects

P W Henson

Publications and source records attributed to P W Henson.

18 recordsLinked to original sources
PubMed1996

Potential ocular hazard from a surgical light source.

A surgical light source has been examined to determine the potential for retinal damage to staff in the operating theatre. It has been shown that under certain circumstances the light source examined can give an irradiance at the cornea which is well in excess of accepted safety standards. Calculation using data on the retinal irradiance required to produce retinal damage indicates that for an accidental exposure at a distance of 500 mm there is a significant possibility of retinal damage. At closer distances the probability of retinal damage is even higher. It is possible that other surgical light sources produce a similar degree of hazard and hospitals should establish suitable safety measures where necessary.

Biophysical Phenomena↗
PubMed1989

Determination of electron density, mass density and calcium fraction by mass of soft and osseous tissues by dual energy CT.

Techniques of CT analysis of trabecular regions are concerned with bone mineral assessment, with considerable attention being paid to the effect of unknown fat content. Information concerning mass density and electron density might provide a more complete picture but is not normally obtained. A method for the calculation of mass and electron density, as well as the fraction of calcium by mass, is described and requires only a measurement of effective beam energy on the skin in addition to the CT numbers from a dual energy scan. The method uses the six major elements, H, C, N, O, P and Ca as compartments for the analysis and can also be applied to soft tissue by using only the first four. The calculated mass fraction of Ca is found to be sensitive to fat content and difference between surface and internal energies which can lead to serious underestimates below a fraction of about 0.04. Mass and electron density results are independent of fat content and only marginally affected by energy differences. Results were obtained with simple materials confirming mass density can be calculated to the order of 3% and electron density to considerably better than 1%.

Body Composition↗
PubMed1984

The electron density of bone for inhomogeneity correction in radiotherapy planning using CT numbers.

A CT scanner has been used to measure the electron density of a range of bone types in vivo. It is shown that there is a linear relationship between the CT number of bone and its electron density, which is expected theoretically if different bone types are treated as a variable mixture of osseous material and marrow. A method of calibrating any CT scanner using a simply prepared solution is proposed, which should enable electron densities of bone to be estimated from CT numbers with an accuracy of 5%.

Adult↗
PubMed1978

Protection of the eye during carotid angiography.

An eye shield was developed for use in neurological examinations in projections in which it does not interfere with the information sought. Use of this shield in A.P., oblique, 30 deg Towne's and 12 deg carotid Towne's projections reduced the corneal dose to approximately 5% of the unshielded value. For lateral projections, doses were reduced to approximately 5-15%. Use of the shield resulted in corneal doses of the order of 0.5 mrad/mAs and 1.0 mrad/mAs for standard and magnified projections respectively, with the exception of the lateral projections for which the corresponding values were approximately 0.3 mrad/mAs and 0.7 mrad/mAs. Corneal dose for a typical carotid angiogram was estimated to be reduced from 6.2 rad to 0.33 rad by the use of the shield.

Carotid Arteries↗
PubMedDate not supplied

A general method for optimizing tissue discrimination in magnetic resonance imaging.

The basic partial differential formulation for small differences has been applied to the equations for the inversion recovery and saturation recovery sequences with spin-echo rephase pulses and the spin-echo sequence itself. The result is a generalized expression which is proportional to tissue discrimination expressed as the signal-difference-to-noise ratio for a pair of tissues. The expression is a function of the fractional differences in the tissue relaxation times and proton densities, T1, T2, and n, respectively, and the sequence parameters TR and TI, or TE. From it can be derived the conditions which lead to optimum tissue discrimination for a given pulse sequence. It is also possible to predict the optimum pulse sequence to use for any pair of tissues of interest. The method requires a knowledge of the fractional differences in T1, T2, and n for both tissues.

Biophysical Phenomena↗