Francis William Rennick Lukin.
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Australia↗
Biomedical subjects
M S Patterson
Publications and source records attributed to M S Patterson.
Breast imaging with a conical transducer/annular array hybrid scanner.
A hybrid conical scanner consisting of a 37.5 degrees, 4 MHz conical receiver and a five element 5 cm dia. 4 MHz annular array transmitter has been developed for breast imaging. The ultrasound fields and imaging characteristics of three interesting geometries are compared. These are: (1) the annular array used in conventional pulse-echo mode, (2) the conical transducer used in combination with the full annular array and (3) the conical transducer used in combination with the center element of the annular array (simple conical scanner). Both conical systems provide extremely narrow (0.3 mm) beamwidths at -6dB but the cone/annular array combination has significantly improved sidelobe characteristics compared with the simple conical scanner. The combination of high resolution and reasonable sidelobe levels for the cone/annular array hybrid results in images with very fine speckle patterns and good definition of small structures. Breast images from young normal volunteers show that this approach has considerable potential for clinical application.
Adult↗
Artifactual echoes in B-mode images due to multiple scattering.
In B-mode images, echoes, which appear to arise from inherently anechoic regions due to scattering from neighbouring echogenic regions, can be considered artifactual. We have observed multiple scatter contributions to such artifactual echoes in images of plane boundaries between random scattering phantoms and anechoic regions. For the strongest scattering phantom studied, multiple scatter echoes were 3-9% of the average phantom signal using two sharply focused transducers, an annular array in pulse echo mode, and an annular array/cone hybrid. Multiple scatter was less than 5% for a conventional transducer. Echo amplitudes were also measured in normal excised human liver and breast tissue. It was estimated that artifactual echoes due to multiple scatter would be negligible in B-mode images of liver. However, for breast imaging, the level of artifactual echoes was estimated to be similar to that found for our strongest scattering phantom.
Breast↗
How parents describe caring behaviors of nurses in pediatric intensive care.
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Adult↗
Characteristics of an 18 MV photon beam from a Therac 20 Medical Linear Accelerator.
The 18 MV photon beam characteristics of a Therac 20 Medical Linear Accelerator manufactured by Atomic Energy of Canada Ltd, are presented. Tissue phantom ratios (TRP's) and percent depth dose data are given; for a 10 x 10 cm field, the percent depth dose at a depth of 10 cm is 78.5 (SSD 100 cm). The relative dose factors (RDF'S) are given and are analyzed to elucidate the relative contributions from phantom scatter, collimator scatter, and backscatter from the top of the collimators into the monitor chambers. The effect of field size and depth on the penumbra is described. Crossplots of the beam at a depth of 5 cm indicate that the flattening filter could be improved; there are hot spots of 108% near the corners of 40 x 40 fields.
Humans↗
Improved method for the design of tissue compensators.
A program, WBEAM, is described which calculates dose distributions in planes perpendicular to the beam axis, taking into account both field shape and patient contour. WBEAM can be used to design compensators which when placed in the beam will produce uniform dose distributions in the plane of calculation. The program was tested in three different situations: a 30 x 30 cm field with a flat contour, a "mantle" field with a flat contour, a "mantle" field with a human-like contour. The program performs as designed: the dose distributions are accurate, and the compensators flatten the radiation beams to the specified limits.
Computers↗
Total attenuation coefficients and scattering phase functions of tissues and phantom materials at 633 nm.
Measurements have been made of the total attenuation coefficient sigma t and the scattering phase function, S(theta), of 632.8 nm of light for a number of animal model tissues, blood, and inert scattering and absorbing media. Polystyrene microspheres of known size and refractive index, for which sigma t and S(theta) can be calculated by Mie theory, were used to test the experimental methods. The purpose of the study was to define typical ranges for these optical properties of tissues, as a contribution to the development of experimental and theoretical methods of light dosimetry in tissue, particularly related to photodynamic therapy of solid tumors. The results demonstrate that, for the representative tissues studied, the total attenuation coefficients are of the order of 10-100 mm-1, and that the scattering is highly forward peaked, with average cosine of scatter in the range 0.6-0.97.
Adipose Tissue↗
A diffusion theory model of spatially resolved, steady-state diffuse reflectance for the noninvasive determination of tissue optical properties in vivo.
A model based upon steady-state diffusion theory which describes the radial dependence of diffuse reflectance of light from tissues is developed. This model incorporates a photon dipole source in order to satisfy the tissue boundary conditions and is suitable for either refractive index matched or mismatched surfaces. The predictions of the model were compared with Monte Carlo simulations as well as experimental measurements made with tissue simulating phantoms. The model describes the reflectance data accurately to radial distances as small as 0.5 mm when compared to Monte Carlo simulations and agrees with experimental measurements to distances as small as 1 mm. A nonlinear least-squares fitting procedure has been used to determine the tissue optical properties from the radial reflectance data in both phantoms and tissues in vivo. The optical properties derived for the phantoms are within 5%-10% of those determined by other established techniques. The in vivo values are also consistent with those reported by other investigators.
Diffusion↗