Showing papers in "Physics in Medicine and Biology in 1970"
TL;DR: It is suggested that the biological toxicity of iodine-125 is not only due to energy deposition of its radiation but also to molecular fragmentation caused by charge transfer in consequence of the Auger effect.
Abstract: Some essential physical properties of the transmutation of iodine-125 are discussed and the range of its electrons calculated. Its suitability for autoradiographs is compared with that of tritium. The dose distribution around a point source and the dose absorbed by a cell nucleus labelled with 125I and 3H are calculated. It is suggested that the biological toxicity of iodine-125 is not only due to energy deposition of its radiation but also to molecular fragmentation caused by charge transfer in consequence of the Auger effect.
103 citations
TL;DR: The relationship between resonant frequency, length, and speed of sound for a long bone is given by F0L=KC, where K is a proportionality constant depending on geometrical factors, boundary conditions, and the mode of vibration.
Abstract: The relationship between resonant frequency (F0), length (L) and speed of sound (C) for a long bone is given by F0L=KC, where K is a proportionality constant depending on geometrical factors, boundary conditions, and the mode of vibration. Since the speed of sound in a material is related to its modulus of elasticity, the relative Young's modulus of a long bone such as the ulna may be estimated by determining F0L. The resonant frequency of the ulna was obtained by recording the response of this bone at the distal end to sinusoidal vibration applied at the olecranon process as a function of driving frequency. The reproducibility of the frequency measurement was studied.
92 citations
TL;DR: Two designs of radiation balance are described which are suitable for the absolute measurement of acoustic power in diagnostic and therapeutic type beams respectively and it is considered that their use in combination provides a good practical approach to the problem of ultrasonic beam calibration.
Abstract: The important parameters of ultrasonic beams used in current medical applications are briefly surveyed. Two designs of radiation balance are described which are suitable for the absolute measurement of acoustic power in diagnostic and therapeutic type beams respectively. The sensitivities of the two instruments are of the order of 0.3 mW and 0.05 w. A description is also given of the construction and use of a small piezoelectric hydrophone probe which is suitable for measurements of beam shape and pulse shapes (spatial and temporal distribution of acoustic energy). The two types of measurement provide complementary information and it is considered that their use in combination provides a good practical approach to the problem of ultrasonic beam calibration.
86 citations
TL;DR: Significant fall in emissivity is indicated as the angle to the normal is increased beyond 90°, corresponding to a reduction of 4°C or more in apparent surface temperature and it would be possible for a 'hot spot' associated with significant pathology to remain undetected on a surface viewed obliquely.
Abstract: In clinical thermography the amount of heat energy received by the detector is interpreted in terms of a distribution of skin temperature but it also depends on the emissivity of the surface. It has been concluded previously that the emissivity in the range 2-5 μm for skin at normal incidence is about 0.98, and that variations are not likely to represent a difference in apparent temperature of more than ±0.5°C. However, theoretical considerations are presented for the variation of emissivity with the angle at which the surface is viewed. These indicate a significant fall in emissivity as the angle to the normal is increased beyond 90°, corresponding to a reduction of 4°C or more in apparent surface temperature. Thus it would be possible for a 'hot spot' associated with significant pathology to remain undetected on a surface viewed obliquely. Examples of this obliquity effect in clinical and experimental thermographs are demonstrated.
82 citations
TL;DR: An improved method for automatic chromosome analysis consists of a preprocessing procedure and a boundary algorithm that makes the threshold selection less critical and partially restores the degradation of the imaging process.
Abstract: An improved method for automatic chromosome analysis consists of a preprocessing procedure and a boundary algorithm. The starting point is a transparency, converted by a flying spot scanner into an array of about 6*105 points, with a six-bit grey scale. Preprocessing applies to each grey level a Laplacian operator extended to a suitable region, corresponding to a high pass filter. This makes the threshold selection less critical and partially restores the degradation of the imaging process. The boundary algorithm isolates connected regions of the array by following isodensity contours and codes the boundary using three successive chains. From these chains the arm tips and centromeres are localized. A symmetry index is defined to check the reliability of the localizations.
79 citations
TL;DR: The distribution of FaL for randomly selected clinically normal women more than 45 years old is bimodal; this suggests that rapid bone loss is not a universal phenomenon and the so-called senile or postmenopausal osteoporosis appears to be an abnormality and not a normal concomitant of the ageing process.
Abstract: For pt.I. see ibid. vol.15, 427 (1970) The product of ulnar resonant frequency and length (FaL) was measured for 172 normal men, 265 normal women, and for 28 osteoporotic and 15 diabetic women and was shown to be a function of age; for women after age 55, it decreases rapidly (about 1%/year). The distribution of FaL for randomly selected clinically normal women more than 45 years old is bimodal; this suggests that rapid bone loss is not a universal phenomenon; the so-called senile or postmenopausal osteoporosis appears to be an abnormality and not a normal concomitant of the ageing process. Women with symptomatic osteoporosis exhibit FaL values averaging about 44% less than those of age-matched controls, while diabetic women have values between these two extremes.
64 citations
TL;DR: Experimental data on the dose dependence of RBE are consistent with the assumption that the dose-effect relation is linear for neutrons of high LET (energies of the order of 1 MeV) and quadratic for X- and gamma -rays.
Abstract: Energy deposition in cells exposed to ionizing radiation occurs through the agency of individual charged particles. At low doses the number of these particles is of the order of 1. One may then expect comparatively simple inactivation dynamics, and, in particular, the relative biological effectiveness (RBE) should become a simple function of the absorbed dose either of the radiations under comparison. Experimental data on the dose dependence of RBE are consistent with the assumption that the dose-effect relation is linear for neutrons of high LET (energies of the order of 1 MeV) and quadratic for X- and gamma -rays.
58 citations
TL;DR: A very low sensitivity to thermal neutrons, a fairly high sensitivity to gamma -rays, and a good energy response enable beryllium oxide to be used successfully in mixed fields of Thermal neutrons and gamma -ray, such as exist in nuclear reactor facilities.
Abstract: The results of a preliminary study on the dosimetric characteristic of three different grades of commercial sintered beryllium oxide are reported. Among useful features of this promising thermoluminescent material a very low sensitivity to thermal neutrons (0.2 gamma -rads equivalent per 1010 neutrons cm-2), a fairly high sensitivity to gamma -rays, and a good energy response, are emphasized. These properties enable beryllium oxide to be used successfully in mixed fields of thermal neutrons and gamma -rays, such as exist in nuclear reactor facilities.
55 citations
TL;DR: The decrease in sensitivity of 7 LiF to high energy electrons and X-rays when compared with 7LiF exposed to 60Co gamma -rays was investigated and the energy dependence measurements were also done for CaF2 Li2B4O7.
Abstract: The decrease in sensitivity of 7LiF to high energy electrons and X-rays when compared with 7LiF exposed to 60Co gamma -rays was investigated and the energy dependence measurements were also done for CaF2 Li2B4O7. Measurements were made at electron energies of 6 to 18 MeV, X-ray energies of 18.5 and 22 Mv, for gamma -rays from 137Cs and 60Co. The difference in response between 7LiF and the other phosphors can be considered as real, since the exposures at each energy were made using the same calibrations. To explain the results, the general cavity theory has been used.
40 citations
TL;DR: Differences between curves obtained in this way are shown to indicate a change of flexibility of the erythrocytes; for instance, after treatment with formaldehyde the rate is much slower than with normal cells.
Abstract: A technique is described for automatically measuring the rate at which erythrocytes pack together during centrifugation, by photographically recording the transmission of light through a micro-capillary centrifuge tube. Differences between curves obtained in this way are shown to indicate a change of flexibility of the erythrocytes; for instance, after treatment with formaldehyde the rate is much slower than with normal cells. A comparison with a procedure involving stopping and starting the centrifuge indicates that no re-expansion or change occurs on slowing the speed of rotation.
36 citations
TL;DR: Convenient and relatively cheap determinations of X-ray spectra using LiF dosemeters are discussed, and the spectrum from a 500 kev single-shot flash X-rays machine is determined as a demonstration of the method.
Abstract: A computer program has been written and tested which will rapidly produce reliable X-ray spectral distributions in intensity or photon flux density from measurements of attenuation data through metal filters under narrow beam conditions. Spectra of two 2 Mev sources have been produced which may be compared with a spectrum derived by the Laplace Transform method of analysing attenuation data, and with a spectrum produced by crystal scintillation spectrometry. Convenient and relatively cheap determinations of X-ray spectra using LiF dosemeters are discussed, and the spectrum from a 500 kev single-shot flash X-ray machine is determined as a demonstration of the method.
TL;DR: A hybrid positron scanner, which combines the simplicity of a mechanical scanner with the increased sensitivity of a large area array, has been designed utilizing nine crystal pairs and 25 coincidence circuits.
Abstract: A hybrid positron scanner, which combines the simplicity of a mechanical scanner with the increased sensitivity of a large area array, has been designed utilizing nine crystal pairs and 25 coincidence circuits. This technique has the advantage over single-pair positron systems in that greatly increased source activity may be viewed. The instrument functions reliably in clinical studies and has proven useful in supplying data for computer studies of radioisotope scan data processing. Valuable experience with multi-detector systems and fast timing techniques has been gained.
TL;DR: The LiF dosemeter presents two main glow peaks, one at 210 degrees C and the other at a temperature between 250 and 300 degrees C, and it is shown that the two-peak ratio depends on the type of incident radiation.
Abstract: The LiF dosemeter presents two main glow peaks, one at 210 degrees C and the other at a temperature between 250 and 300 degrees C. It is shown that the two-peak ratio depends on the type of incident radiation. This characteristic makes it possible to use LiF to measure doses in mixed fields (slow neutrons and electromagnetic radiations). The method is reliable for personal dosimetry.
TL;DR: Calculations of response to mono-energetic photons show that lithium borates containing 0, 0.1%, 0.25%, and 0.34% of Mn are equivalent to soft tissue, water, ICRU muscle, and air respectively.
Abstract: Calculations of response to mono-energetic photons show that lithium borates containing 0, 0.1%, 0.25%, and 0.34% of Mn are equivalent to soft tissue (C5H40O18N), water, ICRU muscle, and air respectively. Results obtained with monochromatic and broad-spectrum x-rays of effective energies between 12 and 115 kev are in agreement with this finding. The monochromatic and broad-spectrum x-ray beams were also used to explore the discrepancies in response of LiF TLD-100 to low energy photons. Only small discrepancies were found which were attributed either to breadth of x-ray spectra or to additional absorbed dose due to scattered x-rays amounting to 5% at 40 keveff.
TL;DR: An optimal data processor for detecting a small lesion in a large organ (background) is derived theoretically by maximizing the signal-to-noise (S/N) ratio by a 'matched filter' which has the same response as that of the source-collimator-imaging detector system.
Abstract: An optimal data processor for detecting a small lesion (target) in a large organ (background) is derived theoretically by maximizing the signal-to-noise (S/N) ratio The highest S/N ratio is obtained with a 'matched filter' which has the same response as that of the source-collimator-imaging detector system The method is suitable when the S/N ratio is of prime importance but the resolving power is unimportant A good compromise between S/N ratio and resolution can be attained with an 'optimum filter' which yields the highest signal amplitude for a given 'smoothing area' without over-enhancement for any frequency component of the source distribution pattern The relation between the resolving power and the random noise is obtained quantitatively assuming a Gaussian collimator response The condition for optimal choice of the collimator is also discussed
TL;DR: Spectral distributions are calculated for bremsstrahlung generated at 10, 15, 20, 25, 30, 40 and 50kv in a tungsten target tube having a 1 mm beryllium window and the total emission derived by calculation agrees well that determined experimentally.
Abstract: Spectral distributions are calculated for bremsstrahlung generated at 10, 15, 20, 25, 30, 40 and 50kv in a tungsten target tube having a 1 mm beryllium window, and allowance is made by two methods for attenuation within the target. Differential filtration by the target is shown to give rise to sharp peaks in the distributions which simulate characteristic radiation. The emission of true L-characteristic radiation is also calculated and is found to be about one-third of the total emission for generating potentials between 15 and 30 kv. The total emission derived by calculation agrees well that determined experimentally.
TL;DR: Errors in the measurement of ferric ion concentrations are now one of the major contributions to the overall uncertainty in ferrous sulphate dosimetry.
Abstract: Ferrous sulphate (Fricke) dosemeter solutions from five laboratories have been intercompared. Differences in their ferric ion yields do not exceed 0.5% and are not statistically significant. For all the solutions precautions were taken to remove impurity effects arising from the sulphuric acid. Spectrophotometers used in these five laboratories for measurement of ferric ion concentrations were also intercompared. Significant differences of over 1% were found between independent determinations of the ferric ion extinction coefficient made on them. Errors in the measurement of are now one of the major contributions to the overall uncertainty in ferrous sulphate dosimetry.
TL;DR: The optimum size of the test area relative to the resolution diameter (FWHH) of a scanning device is derived, and is found to correspond to an isocontour of 25% to 30%, normalized to 100% at the central peak of the point source distribution.
Abstract: Statistical tests used by various authors have yielded dissimilar values of statistical index n for the threshold detection of small abnormalities in radioisotope concentrations (n = 2.5 to 3 by Dewey and Sinclair, Matthews and others, as compared with n = 5 to 6.5 by Rose and Vernon). This paper explains the relationship between these two types of statistical test. The optimum size of the test area relative to the resolution diameter (FWHH) of a scanning device is derived, and is found to correspond to an isocontour of 25% to 30%, normalized to 100% at the central peak of the point source distribution. Experiments were carried out in which ohservers recorded the threshold detection of spherical sources in radioactive tanks. Two categories of discrimination were necessary: "only definite" and " all possible". The statiatical indices required to give correct detection in 95% of 20 pictures scored by 16 observers were n = 5 and 4 respectively for the two categories.
TL;DR: By means of phantom studies, it is shown that three-dimensional scintigraphy is possible with gamma - gamma -cascade isotopes, such as 75Se.
Abstract: By means of phantom studies, it is shown that three-dimensional scintigraphy is possible with gamma - gamma -cascade isotopes, such as 75Se. Large plastic scintillators and slit collimators are proposed for additional coincidence detectors which observe one plane only. The necessary conditions for the technical performance of the apparatus are derived. Some suitable isotopes are discussed.
TL;DR: A method of analysis is described which uses gamma camera data previously stored on analogue magnetic tape to obtain quantitative information on renal function and the effective renal plasma flow and the input and output rate of hippuran for each kidney are calculated.
Abstract: A method of analysis is described which uses gamma camera data previously stored on analogue magnetic tape to obtain quantitative information on renal function. The effective renal plasma flow and the input and output rate of hippuran for each kidney are calculated. Information on the intra renal transport of hippuran permits an estimate of tubular transit time. Examples of the practical application of the analysis are presented.
TL;DR: Distributions of energy fluence with respect to energy were measured by three methods for x-rays produced in a tungsten target tube with a 1 mm beryllium window in reasonable agreement with one another and with theory.
Abstract: Distributions of energy fluence with respect to energy were measured by three methods for x-rays produced in a tungsten target tube with a 1 mm beryllium window. The tube was energized by a constant potential generator operated at 15, 20, 25 and 30 kv. The methods used were gas proportional counting, scintillation counting and attenuation analysis. The percentage of the total energy fluence due to tungsten L-characteristic radiation was measured by each of the above techniques and also by using balanced (Ross) filters. It reached a maximum of about 33%. The methods gave results which were in reasonable agreement with one another and with theory.
TL;DR: Using Monte Carlo methods gamma -ray scattering in the detector has been studied in relation to its effect on the spatial resolution attainable in gamma cameras and the application of pulse height discrimination to various types of gamma camera is discussed.
Abstract: Using Monte Carlo methods gamma -ray scattering in the detector has been studied in relation to its effect on the spatial resolution attainable in gamma cameras. Gamma-ray energies ranging from 0.10 to 0.67 Mev were considered, with crystal thicknesses between 6.3 and 50.8 mm of NaI(Tl) and 5 to 20 mm of germanium. For a monoenergetic gamma -ray, incident along the axis of a cylindrical detector, the distribution of energy depositions occurring in individual interactions in the detector is given as a function of the perpendicular distance from the incident ray to the location of the interaction. The application of pulse height discrimination to various types of gamma camera is discussed.
TL;DR: The results show that an oxygen parameter, with dimen- sions of oxygen concentration, may be measured with relatively large electrodes, and is related directly to variations in alveolar pO2.
Abstract: Gold oxygen cathodes, calibrated against a Hersch cell, have been used to monitor oxygen concentrations in the mouse testis. The technique of calibration of the electrodes is described, together with measurements made in mice breathing gas mixtures with different oxygen contents, from 5 to 100%. Mice were found to survive for at least four minutes breathing these mixtures, and the level of tissue hypoxia produced when breathing 10 or 5% oxygen is lower than can be achieved by breathing pure nitrogen. The results show that an oxygen parameter, with dimen- sions of oxygen concentration, may be measured with relatively large electrodes, and is related directly to variations in alveolar pO2.
TL;DR: The suitability of the method for measurements of iron assimilation is demonstrated and the day-to-day reproducibility of counting and validity of measuring radio-iron absorption and losses are established.
Abstract: A method for measuring whole-body 59Fe has been evaluated which employs longitudinal scan geometry, a unique arrangement of multiple NaI(Tl) detectors, and photon measurements in the Compton region. Radio-iron has been quantitated from a point source embedded in plastic pellets, from tracer localized in the gastrointestinal tract, and during movement of in vivo activity into and out of the erythroid marrow. In all instances, counting levels varied by no more than 2%. Measurements have also been made for two weeks following oral and intravenous radio-iron administration, to define the day-to-day reproducibility of counting and to establish the validity of measuring radio-iron absorption and losses by this technique. The suitability of the method for measurements of iron assimilation is demonstrated.
TL;DR: A method is discussed for locating the stopping position of pi - mesons in tissue by detecting their position with a plastic scintillator and a magnetostrictive wire spark chamber.
Abstract: A method is discussed for locating the stopping position of pi - mesons in tissue. The gamma -rays emitted following the capture process are collimated and converted to electrons. They are detected with a plastic scintillator and their position is determined with a magnetostrictive wire spark chamber. The sensitivity and resolution of the system are measured.
TL;DR: A method has been developed for separation of the components of multicompartment exponentials which seems free of many of the difficulties of other methods and provides a reasonable test for the number of components.
Abstract: A method has been developed for separation of the components of multicompartment exponentials which operates on a small computer. It seems free of many of the difficulties of other methods and provides a reasonable test for the number of components.
TL;DR: The initial tests and calibrations of a spherical tissue-equivalent proportional counter system designed by Rossi are described, with very good agreement obtained in the two cases compared with theoretical spectra calculated by Bewley.
Abstract: The initial tests and calibrations of a spherical tissue-equivalent proportional counter system designed by Rossi are described. The instrument has been used to obtain LET spectra for (d,n), (p,n) and ( alpha , n) neutron beams from a cyclotron, 14.6 Mev neutrons from a (d,t) generator, and the scattered radiation at a 7 Gev proton synchrotron, with sphere diameters in the range equivalent to 0.4 to 1.0 mu m of tissue. A LET spectrum for cyclotron (d,n) neutrons at 10 cm depth in a paraffin phantom was also measured, the only significant change being an increase in the gamma -ray component. Very good agreement was obtained in the two cases compared with theoretical spectra calculated by Bewley.
TL;DR: At least two procedures for determination of dose within an irradiated medium from ionization chamber measurements are in common use, one involves a determination of exposure in air and the application of conversion factors, and the other involves the introduction of the ion chamber directly into the medium.
Abstract: At least two procedures for determination of dose within an irradiated medium from ionization chamber measurements are in common use One involves a determination of exposure in air and the application of conversion factors The second involves the introduction of the ion chamber directly into the medium and a determination of exposure at that point followed by the application of conversion factors For each of these methods a small attenuation correction must be applied to the exposure determination The correction is commonly applied to ionization measurements made directly in the medium but is almost universally ignored when the reference exposure determination is made in air