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Biomedical subjects

D R Dance

Publications and source records attributed to D R Dance.

10 recordsLinked to original sources
PubMed1992

Calculation of dose and contrast for two mammographic grids.

To aid in selecting optimal conditions for screening mammography practice in Sweden, the performance of two mammographic grids (one moving and one stationary) has been investigated. Monte Carlo techniques were used to simulate photon transport in the breast. Transport through the breast support, grid covers, grid and image receptor (33.9 mg cm-2 Gd2O2S) was treated analytically. The contrast of a 100 microns calcification has been evaluated for three tissue compositions (adipose, glandular, 50:50 fractions by weight of adipose and glandular tissue) as a function of breast thickness (2-8 cm) and potential difference (25-30 kV, Mo anode). Contrast for a 5 cm 'average' breast at 28 kV was improved by 40% using the moving grid and by 30% using the stationary one; the corresponding increases in breast absorbed dose, keeping the energy imparted to the image receptor constant, were 90% and 150%, respectively. The superior properties of the moving grid were due to (i) equal scatter rejection ability and higher transmission of primary photons yielding lower scatter-to-primary ratios behind the grid, and (ii) less attenuation and filtering of the primary photons in the interspace material yielding lower degradation of primary contrast.

Breast Neoplasms↗
PubMed1991

Measurement of small-angle photon scattering for some breast tissues and tissue substitute materials.

For photon energies encountered in diagnostic radiology the shape of the scattering distributions for low-atomic-number media exhibits peaks in intensity close to the forward direction that are not predicted by conventional theoretical models. The positions and shapes of the peaks depend upon the interatomic and intermolecular configurations of the scatterers. The phenomenon is of particular interest because of its relevance to the understanding and modelling of x-ray imaging processes and the possibility that the peaking may be characteristic of tissue type. In the present study, peaks in the forward scattering distributions have been demonstrated for 19 samples of breast tissue and three tissue substitute materials using a position-sensitive photon detector and a 60 kVp x-ray source. Prominent features were observed for all samples investigated. Large differences were found in the shapes of the distributions between adipose and fibroglandular tissues and only small differences were found between carcinomas and fibroglandular tissues.

Adenofibroma↗
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↗