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Biomedical subjects

D R Dance

Publications and source records attributed to D R Dance.

52 records · Page 3Linked to original sources
PubMed1990

Monte Carlo calculation of conversion factors for the estimation of mean glandular breast dose.

The IPSM report on the commissioning and routine testing of mammographic x-ray systems recommends that breast dose be specified as the mean dose to the glandular tissues within the breast and gives the size and compositions of a standard breast phantom for the comparison of doses. The dose to this standard breast phantom can be determined by measuring the incident air kerma to a Perspex phantom and applying appropriate multiplicative conversion factors. These conversion factors have been evaluated by Monte Carlo calculations for a wide range of mammographic x-ray spectra. Some factors are provided for a range of breast thicknesses to supplement existing tabulations. Results are also given for equivalent thicknesses of Perspex and breast tissue.

Female↗
PubMed1988

A quantitative analysis of the spatial relationships of grouped microcalcifications demonstrated on xeromammography in benign and malignant breast disease.

The mammograms of 444 patients who had a breast biopsy leading to a definitive histological diagnosis were reviewed. In 21 cases (4.7%) grouped microcalcifications were identified as the only mammographic abnormality. These groups of microcalcifications were analysed to determine whether there was any quantitative difference between benign and malignant lesions with respect to a shape parameter of the group, the spatial frequency of the particles and neighbour-to-neighbour relationships of the particles. This analysis did not reveal any significant difference between the spatial relationships of the grouped microcalcifications found in benign and malignant breast disease.

Biopsy↗
PubMed1984

The computation of scatter in mammography by Monte Carlo methods.

A Monte Carlo computer program has been used to calculate the ratio of the scatter-to-primary radiation recorded by a range of image receptors used in mammography. The dependence of this ratio on breast size and photon energy has been investigated and the contributions of different sources of scattered radiation examined. The use of magnification and grid techniques have been included in the program and the performance of the Philips mammographic grid examined in detail. The results of the calculations are in good agreement with the limited experimental data available.

Female↗
PubMed1980

The Monte Carlo calculation of integral radiation dose in xeromammography.

A Monte Carlo computer program has been developed for the computation of integral radiation dose to the breast in xeromammography. The results are given in terms of the integral dose per unit area of the breast per unit incident exposure. The calculations have been made for monoenergetic incident photons and the results integrated over a variety of X-ray spectra from both tungsten and molybdenum targets. This range incorporates qualities used in conventional and xeromammography. The program includes the selenium plate used in xeroradiography; the energy absorbed in this detector has also been investigated. The latter calculations have been used to predict relative values of exposure and of integral dose to the breast for xeromammograms taken at various radiation qualities. The results have been applied to recent work on the reduction of patient exposure in xeromammography by the addition of aluminium filters to the X-ray beam.

Computers↗
PubMed1979

Evaluation of a moiré imaging system.

Moiré fringe techniques can be used to measure surface topography. The factors that affect the formation of the fringes have been assessed theoretically by developing models of gratings and light sources of finite dimensions. In this way the effect of parameters such as the intensity distribution of the light source, the viewing aperture function, the lateral displacement of the source relative to the viewing axis, the viewing distance, the grating spacing and grating ratio have been evaluated. Other factors, related to the physical properties and geometry of the reflecting surface, are also investigated. Suggestions are made for the design of an optimum moiré imaging system.

Interferometry↗
PubMed1976

The uptake of gallium 67 in colonic macrophages.

A case is presented in which a patient with a well-differentiated adenocarcinoma showed high gallium concentration in the segment with melanosis coli proximal to the obstruction. Although in this case the Gallium was associated with an increased number of faecal pigment containing macrophages it is unlikely that macrophages are the main factor in tumour uptake of Gallium compounds.

Adenocarcinoma↗
PubMed1975

Digital reconstruction of point sources imaged by a zone plate camera.

Zone plate cameras are used for high sensitivity imaging of X- and gamma-ray sources. The image thus obtained requires decoding and numerical techniques are devised for this purpose. The response function and the signal-to-noise ratio for a single point source have been evaluated for zone plates with varying numbers of zones. Autocorrelation is the best of the methods examined, and the results are in good aggreement with those obtained using Monte Carlo techniques. The autocorrelation method can give a gain of 50% in signal-to-noise for a single point source over the maximum obtainable with optical decoding. Criteria for the choice of number of zones are discussed.

Computers↗
PubMed1975

Digital processing of images from a zone plate camera.

A method for the digital decoding of data obtained with a gamma camera fitted with a zone plate aperture is described. Taking a line source as the object, computer simulations have been used to examine the effects of noise, solid angle variations, shape of detector and detector resolution and methods of dealing with these effects are considered. Using an Anger gamma camera and a zone plate aperture both a line source and a thyroid phantom containing 99Tcm have been well reconstructed. The behaviour of the system with regard to resolution, signal-to-noise ratio and tomographic capability is discussed.

Computers↗
PubMed1972

Uptake of gallium-67 in colonic and rectal tumours.

The uptake of (67)Ga in biopsy specimens of normal and abnormal tissue was measured in 20 cases of colonic and rectal disease and the ratio between the (67)Ga uptake in these diseases and in the normal colon or rectum was determined. Uptake of the isotope was high in most of the 14 primary malignant tumours, being highest in poorly differentiated tumours. This uptake was found to be concentrated at the active tumour edge. Uptake of the isotope was generally low in non-malignant lesions.

Biopsy↗
PubMedDate not supplied

Quantitative measurement of small-angle gamma ray scattering from water, nylon, and Lucite.

The small-angle (2 degrees-10 degrees) total-differential-scattering cross sections of water, methyl methacrylate, and nylon 6 have been measured at a photon energy of 59.54 keV. An annular target geometry has been used with an acceptance of +/- 0.5 degrees and an experimental uncertainty of approximately 4% achieved. The experimental methods and data corrections necessary to obtain this accuracy are discussed in detail. The results demonstrate clearly the contribution of intermolecular effects to the scattering process and allow critical comparison with calculations using molecular form factors for water obtained from interpolated x-ray diffractometer data; agreement is obtained within the experimental uncertainties. They also support earlier Monte Carlo predictions of scattering in water at angles of the order of 2 degrees which are in disagreement with certain published experimental data.

Caprolactam↗