Showing papers in "Physics in Medicine and Biology in 1975"
TL;DR: An attempt has been made to clarify the two most important issues relevant to personal eye dosimetry, which involves the identification of the cells which are most at risk from radiation and the specification of their position in the eye.
Abstract: An attempt has been made to clarify the two most important issues relevant to personal eye dosimetry. This involves the identification of the cells which are most at risk from radiation and the specification of their position in the eye. A survey of the radiobiological literature concerning animals and humans shows that the epithelial cells in the equatorial region of the lens are those which are involved in radiation cataract induction. The depth of these cells has been evaluated in the human eye by means of geometrical construction. The relevant dimensions have been determined from a survey of published anatomical data and supplemented by new data obtained by slit-image photography. In a normal adult population (20-65 years) the minimum depth of the incriminated cells is 2.3 plus or minus 0.4 mm; the upper and lower values are associated with young and old subjects respectively. Approximate calculations for isotropic 90Sr/90Y and 106Rh beta-radiation fields indicate that a planar dosemeter, which integrates the tissue dose between depths of 2.5-3.5 mm, should give a reasonable measure of the mean equatorial dose for the variety of eye and irradiation geometries likely to be met during a life-time exposure. The long established, but tentative, value of 3 mm for the effective depth of the lens is thus confirmed.
131 citations
108 citations
TL;DR: Neutron production from targets of Be, C, Mo, Cu, Ta and Au bombarded with deuterons of 16, 33 and 50 MeV has been studied at the isochronous cyclotron at Louvain-la-Neuve.
Abstract: Neutron production from targets of Be, C, Mo, Cu, Ta and Au has been studied at the isochronous cyclotron at Louvain-la-Neuve. Neutron spectra were measured by the time of flight method. The yields of neutrons and gamma rays were also measured, and the greatest ratio of neutrons to gamma rays in the forward direction was found to occur with 50 MeV deuterons on a Be target. The angular distribution of neutrons from Be was measured at 16, 33 and 50 MeV, and neutron spectra were measured as a function of angle with 50 MeV deuterons on Be.
106 citations
TL;DR: A modification of the filter often used in corrected tomography which produces very small ringing in such regions is described, and a transmission device such as the EMI Scanner was computer simulated.
Abstract: In many transverse tomographic reconstruction techniques using filtered projections, ringing or overshoot is found in regions where the attenuation suddenly changes. Such artifacts are obtained with iterative techniques as well. A modification of the filter often used in corrected tomography which produces very small ringing in such regions is described. A transmission device such as the EMI Scanner was computer simulated. Projections were calculated through a phantom and the phantom then reconstructed using different filters. The phantom consisted of a disc with diameter 32 arbitrary units centred at the origin of the plane.
77 citations
TL;DR: The proton induced X-ray method with a finely focused beam was used to measure the variation of trace elements across the diameter of human hairs in the hope that this will throw light on the origin of the trace elements in hair and assist the correlation of other analytical data as mentioned in this paper.
Abstract: The proton induced X-ray method with a finely focused beam to measure the variation of trace elements across the diameter of human hairs in the hope that this will throw light on the origin of the trace elements in hair and assist the correlation of other analytical data.
66 citations
TL;DR: The paper reports some backscattering measurements on formalin-fixed samples of human fat, liver and spleen in the frequency range 0-5- 5-0 MHz, and suggests that the approach may have diagnostic value in a clinical situation, in the characterization of structure in specific volumes of soft human tissue.
Abstract: The dearth of information on the physical processes involved in the propagation of ultrasound in tissue and the growing need for such information are discussed. The physical nature of the ultrasonic diagnostic process is considered in terms of a wave phenomenon and the limitations and advantages of frequency spectral analysis as a means of obtaining information are briefly analysed. A description is given of an experimental measuring system using a time-gate to select echoes scattered from a particular volume at a depth in soft tissues. The influence of attenuation by overlying tissue and the choice of the duration of the acceptance gate on the frequency spectra obtained are considered. Some backscattering measurements on formalin-fixed samples of human tissue in the frequency range 0.5-5.0 MHz are reported.
65 citations
TL;DR: Two correction functions are derived for one- and two-dimensional convolution methods for reconstructing a section image from multiple projections to yield a maximum 'signal-to-noise power ratio' for a given RMS resolution width.
Abstract: Two correction functions are derived for one- and two-dimensional convolution methods for reconstructing a section image from multiple projections. The functions are optimized to yield a maximum 'signal-to-noise power ratio' for a given RMS resolution width, where 'signal power' is the integrated squared line spread function (signal power regarding one-dimensional position information per count) and 'noise power' is the variance of the image density at the centre of a locally uniform source. The point spread function of the reconstructed image is Gaussian, and the standard deviation of noise associated with a locally uniform image is found to be proportional to D-32/, where D is the RMS resolution width. The autocovariance function for uniform noise is also given.
59 citations
TL;DR: This study provides a guide to an understanding of the high resolution of the currently existing X-ray transmission CTAT scanner (EMI scanner) and to the future development of high resolution scanners.
Abstract: The ultimate capabibity and a detailed study of contrast and modulation in the context of photon transmission tomography (or computerized transverse axial tomography (CTAT)) is presented. Quantitative evaluation of atomic number, density and electron density of compound materials were made by X-ray fluorescence and combustion analysis, and the attenuation coefficients of photoelectric and Compton effect were measured with high resolution Ge(Li) and Si(Li) detectors. This study provides a guide to an understanding of the high resolution of the currently existing X-ray transmission CTAT scanner (EMI scanner) and to the future development of high resolution scanners.
50 citations
TL;DR: Neutron capture gamma-ray analysis has been applied to the in vivo detection of Cd in man and a number of cadavers were studied to establish normal limits prior to commencement of clinical investigation.
Abstract: Neutron capture gamma -ray analysis has been applied to the in vivo detection of Cd in man. The technique was designed for the screening of industrial workers at risk. The limit of sensitivity in a liver-sized phantom is 0.5 ppm for a dose of 0.4 rad. Reproducibility and the effects of positional uncertainties have been investigated. A number of cadavers were studied to establish normal limits prior to commencement of a programme of clinical investigation. A patient with known Cd poisoning was estimated to contain 65-110 ppm of Cd in his liver. A liver dose of 0.05 rad was required.
45 citations
TL;DR: Electron spin resonance studies of this tissue in vitro reported by Commoner and Ternberg in 1961 have demonstrated that it exhibits the 'tissue radical' signal.
Abstract: In vivo ESR studies have been made using travelling wave helices implanted in the left lobe of the liver. Tissue regenerates completely around the Teflon-enclosed turns of the coil and histological studies have shown that it is composed of liver cells and connective tissue. Electron spin resonance studies of this tissue in vitro reported by Commoner and Ternberg (1961) have demonstrated that it exhibits the 'tissue radical' signal. The implanted coils have detected, in vivo, a three-line spectrum due to a strong concentration of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical ('tempol'), a nitroxide spin label, and 'spin-labelled chlorpromazine', a tranquilizing drug to which this nitroxide spin label has been attached.
42 citations
TL;DR: This ionization chamber has been designed at the National Physical Laboratory in collaboration with the Hospital Physicists' Association; it is especially suitable for use with electron beams below 10 MeV, allowing the chamber to be used with most existing dosemeter electrometers.
Abstract: This ionization chamber has been designed at the National Physical Laboratory in collaboration with the Hospital Physicists' Association; it is especially suitable for use with electron beams below 10 MeV. The sensitive volume is disc-shaped, 20 mm in diameter and 2 mm deep along the beam axis. Polarity effect is less than 0.1% at energies up to 6 MeV, allowing the chamber to be used with most existing dosemeter electrometers. The chamber is intended to be calibrated by the user against a secondary standard X-ray chamber using a Perspex phantom in 60Co gamma -radiation. Factors for converting 'exposure' readings to absorbed dose in water are tabulated for beam energies up to 7 MeV.
TL;DR: A formula was derived from the age diffusion equation which is able to generate a spatial electron dose distribution with good approximation to experimental values given only the incident electron energy and field size.
Abstract: It is difficult to obtain electron dose distributions in a phantom by calculation. A formula was derived from the age diffusion equation, which includes terms for the electron dose, the distance from the central axis of the field, the depth in the phantom, the width of the field on the surface, the diffusion coefficient of the medium, the extrapolated electron range and an 'age' parameter which increases as the electron energy is degraded in the medium. This formula is able to generate a spatial electron dose distribution with good approximation to experimental values given only the incident electron energy and field size.
TL;DR: A device employing a slit collimator which limits the angle of acceptance of the gamma -rays in only one direction is introduced, and it is felt that the sensitivity of such a device in inherently greater than conventional gamma cameras.
Abstract: A device employing a slit collimator which limits the angle of acceptance of the gamma -rays in only one direction is introduced. Each point in the activity distribution is thus emitting into an appreciable solid angle and it is felt that the sensitivity of such a device in inherently greater than conventional gamma cameras.
TL;DR: A tabulation of the existing data on the response of LiF to electrons measured by various authors and it is concluded that the predictions made by the two approaches differ significantly.
Abstract: A tabulation of the existing data on the response of LiF to electrons measured by various authors is presented. Theoretical calculations are carried out using the Burlin et al. theory (1969) and its modified version by Almond and McCray (1970). Experimentally measured response by the authors is also reported. It is concluded that the predictions made by the two approaches differ significantly.
TL;DR: A summary of the present state of knowledge of characteristic X-ray production by electron and other charged particle bombardment, with particular reference to the work of the past 10 or 12 years, is presented in this paper.
Abstract: A summary is presented of the present state of knowledge of characteristic X-ray production by electron and other charged particle bombardment, with particular reference to the work of the past 10 or 12 years. Applications of characteristic X-rays are reviewed, in particular the techniques of X-ray emission microanalysis, with special reference to medical and biological applications.
TL;DR: As a preliminary step to evaluating recent theories concerning the biological effect of ionizing radiation, the charged particle fluence distributions and the dose distribution in linear energy transfer have been computed analytically for targets of biological and dosimetric interest irradiated by neutrons.
Abstract: As a preliminary step to evaluating recent theories concerning the biological effect of ionizing radiation, the charged particle fluence distributions and the dose distribution in linear energy transfer have been computed analytically for targets of biological and dosimetric interest irradiated by neutrons Specifically, 147 MeV neutrons, the 252Cf neutron spectrum and a cyclotron generated neutron spectrum are considered to irradiate water, tissue-equivalent plastic and standard man tissue and results are given for all these cases From a knowledge of the target composition, and the cross-sections and kinetics of all the possible neutron induced reactions in the elements hydrogen, carbon, nitrogen and oxygen, the secondary particle spectrum is calculated By combining with stopping power data for the ions in the target, the charged particle fluence spectra and dose distribution in linear energy transfer are derived Secondary quantities computed are kerma, energy expended as nuclear elastic scattering, specific ionization and mean quality factor Stopping powers have been derived from published atomic stopping powers by summing according to the Bragg rule A comparison between tissue-equivalent plastic and standard man tissue had been made for each of the neutron spectra
TL;DR: Central axis depth absorbed dose distributions of the electron beam from a medical microtron accelerator have been measured and a larger absorbed dose build-up and a sharper dose fall-off are obtained in close agreement with theoretical calcuations for monoenergetic electron beams.
Abstract: Central axis depth absorbed dose distributions of the electron beam from a medical microtron accelerator have been measured. The measured distributions differ from those of existing betatrons and linear accelerators. A larger absorbed dose build-up and a sharper dose fall-off are obtained in close agreement with theoretical calculations for monoenergetic electron beams. The differences from other accelerators are explained by the narrow energy spectrum, the clean geometry and the small amount of scattering material in the electron beam of the microtron.
TL;DR: The energy dependence of lithium fluoride dosemeters is a complicated function of energy as well as of cavity size, and a semi-empirical theory was developed to account for the cavity effect, using Burlin cavity theory as a starting point.
Abstract: The energy dependence of lithium fluoride dosemeters is a complicated function of energy as well as of cavity size. In the application of TLD to charged particle dosimetry, a cavity perturbation effect may exist even though the ratios of the mass stopping powers are constant over the energies encountered. This effect was investigated for lithium fluoride rods in electron fields ranging in energy from 2-5 to 20 MeV. A 13% change of TL response per unit of absorbed dose was measured over that energy range. A semi-empirical theory was developed to account for the cavity effect, using Burlin cavity theory as a starting point. The agreement between theory and measurement is satisfactory.
TL;DR: The possibility of using the nuclear scattering of 500-1000 MeV protons was investigated, in order to obtain direct, three-dimensional reconstruction of an object with only one exposure, and preliminary measurements give a resolution of about 1 mm3.
Abstract: The possibility of using the nuclear scattering of 500-1000 MeV protons was investigated, in order to obtain direct, three-dimensional reconstruction of an object with only one exposure. The resolution should be about 1 mm3. Preliminary measurements with an incomplete set-up give a resolution of 10 mm3. Additional independent information on the relative concentration of hydrogen compared with other elements should also be obtainable by nuclear scattering radiography. The radiation doses involved are comparable with those of other techniques. The first experimental results are given.
TL;DR: The radiation distribution in water around caesium-137 K-type sources has been measured and the experimental results used to provide data for an expression for dose calculations which may be conveniently applied in computer programs.
Abstract: The radiation distribution in water around caesium-137 K-type sources has been measured and the experimental results used to provide data for an expression for dose calculations which may be conveniently applied in computer programs. The calculated absorbed dose rate obtained in this manner is estimated to be within 3% of the actual dose rate for any point in water up to 8 cm from the source. It is also suggested that the strength of a brachytherapy source be expressed in terms of an experimental exposure rate at some well-defined distance since this quantity may be determined more precisely and with less ambiguity than source activity.
TL;DR: A method of NMR diffraction of physiological studies is discussed and its use to provide one-dimensional, two-dimensional and three-dimensional images, and possible applications are described.
Abstract: A method of NMR diffraction of physiological studies is discussed. The apparatus, its use to provide one-dimensional, two-dimensional and three-dimensional images, and possible applications are described.
TL;DR: The sensitivity and performance of the counter are analysed, with specific references to total body in vivo neutron activation analysis, and shown to be at least comparable with those of many conventional shielded-room counters.
Abstract: The sensitivity and performance of the counter are analysed, with specific references to total body in vivo neutron activation analysis, and shown to be at least comparable with those of many conventional shielded-room counters.
TL;DR: The advantages of storing electron beam data in the form of narrow beam distributions are described with particular reference to the problem of irradiating heterogeneous tissue volumes.
Abstract: In a high energy electron beam the spatial distribution of absorbed energy is dominated by multiple scattering of the electrons. The dose distribution in a broad parallel electron beam entering a uniform phantom can be resolved into a series of narrow beams overlapping one another, in each of which the scattering conditions are identical. It is therefore possible to build up a broad beam dose distribution from a knowledge of the axial and radial dose distribution in a narrow beam. Measurements have been made of such narrow beam distributions using finely collimated electron beams in the energy range 4-10 MeV, and the resulting data added by computer to give broad beam distributions which are compared with measured isodose curves.
TL;DR: An analytical solution of the thermal conductivity equation describing the surface temperature distribution over a buried heat source is given in tabular form and can be used for the analysis of the skin temperature over biological heat sources such as breat tumours.
Abstract: An analytical solution of the thermal conductivity equation describing the surface temperature distribution over a buried heat source is given in tabular form. The solution is applicable to experimental models for studies of the surface temperature over an implanted artificial heat source. The results can also be used for the analysis of the skin temperature over biological heat sources such as breast tumours.
TL;DR: 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.
Abstract: 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 agreement 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.
TL;DR: The elastic properties of rat skin previously irradiated with single doses form 1000 to 3000 rad have been studied, showing the stiffness of the collagen itself tends to decrease with increasing dose, exhibiting a shoulder in the dose response curve.
Abstract: The elastic properties of rat skin previously irradiated with single doses from 1000 to 3000 rad have been studied. The measurement were made 50 and 120 d after irradiation on skin specimens immersed in saline at 37 degrees C. The tests were carried out on a tensile testing machine. The load extension curve which was plotted to the point of rupture, exhibits two portions which are identified with the alignment of the collagen fibres and then their subsequent stretching. The elastic properties associated with fibre alignment are little affected by these doses of radiation but the stiffness of the collagen itself tends to decrease with increasing dose, exhibiting a shoulder in the dose response curve.
TL;DR: The experimental results show that a detectable surface temperature increase over the heat sources presupposes high power output or superficial implantation, and an implicit conclusion from experimental and theoretical work is that a localized 'hot spot' can only exceptionally be attributed to metabolic heat production conducted to the skin surface from a buried pathological process.
Abstract: The medical application of infrared thermography makes use of the skin temperature as an indication of an underlying pathological process. In order to study the relation between the heat production from a source in living tissue and the overlying skin temperature, artificial heat sources were implanted subcutaneously in human volunteers. The experimental results show that a detectable surface temperature increase over the heat sources presupposes high power output or superficial implantation. The effect of forced convective heat loss from the skin surface and lowered ambient temperature was studied. Forced convection markedly decreased the temperature contrast. An implicit conclusion from experimental and theoretical work is that a localized 'hot spot' can only exceptionally be attributed to metabolic heat production conducted to the skin surface from a buried pathological process.
TL;DR: The investigations were based on rat liver tissue, which has a high concentration of heavy metals and is very homogeneous, and the preparation of samples is discussed.
Abstract: The preparation of samples is discussed. The investigations were based on rat liver tissue, which has a high concentration of heavy metals and is very homogeneous.
TL;DR: Factors involved in the extension of the technique to medium-energy X-rays are discussed including the possibility of determination of beam quality by employing TLD-700 and CaSO4: Dy 'in tandem'.
Abstract: A technique is described for making thermoluminescence measurements on phosphor powder with a relatively high degree of precision. Factors such as the rate of fading of TL response and extent of supralinearity for TLD-700 in the therapy-dose range have been measured in relation to its use for precise absorbed dose inter-comparison studies in cobalt-60 beams. The results of such a trial intercomparison of six British radiotherapy centres are given, the performance of the TLD technique being matched against that of Fricke dosemeters. Factors involved in the extension of the technique to medium-energy X-rays are discussed including the possibility of determination of beam quality by employing TLD-700 and CaSO4:Dy 'in tandem'.
TL;DR: From cellular radiosensitivity parameters and theoretical particle-energy spectra in tissue, of the secondary particles from neutron and negative pion irradiations, RBE-Dose relations have been calculated and the theoretical results are compared with clinical and radiobiological data.
Abstract: From cellular radiosensitivity parameters and theoretical particle-energy spectra in tissue, of the secondary particles from neutron and negative pion irradiations, RBE-Dose relations have been calculated. The theoretical results are compared with clinical and radiobiological data for normal tissue, tumours and cells in culture. Formulae for calculation, cellular parameters and the needed properties of equivalent 'track-segment bombardments' are given, for several mammalian cells irradiated with pions and with neutrons of several energies.