Showing papers in "Physics in Medicine and Biology in 1990"
TL;DR: The results indicate that scatter exceeds absorption by at least two orders of magnitude, and systematic differences between the optical properties of some tissue types are demonstrated.
Abstract: The optical absorption and scattering coefficients have been determined for specimens of normal and diseased human breast tissues over the range of wavelengths from 500 to 1100 nm. Total attenuation coefficients were measured for thin slices of tissue cut on a microtome. The diffuse reflectance and transmittance were measured for 1.0 mm thick samples of these tissues, using standard integrating sphere techniques. Monte Carlo simulations were performed to derive the scattering and absorption coefficients, as well as the mean cosine of the scattering angle. The results indicate that scatter exceeds absorption by at least two orders of magnitude. Absorption is most significant at wavelengths below 600 nm. The scattering coefficients lie in the range 30-90 mm-1 at 500 nm, and fall smoothly with increasing wavelength to between 10 and 50 mm-1 at 1100 nm. The scattering coefficient for adipose tissue differs, in that it is invariant with wavelength over this spectral range. For all tissues examined, the scattered light is highly forward peaked, with the mean cosine of the scattering angle in the range 0.945-0.985. Systematic differences between the optical properties of some tissue types are demonstrated.
442 citations
434 citations
TL;DR: 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.
Abstract: 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
431 citations
TL;DR: It is shown that the main image reconstruction methods, namely filtered backprojection and iterative reconstruction, can be directly applied to conformation therapy and first theoretical results are presented.
Abstract: The problem of optimizing the dose distribution for conformation radiotherapy with intensity modulated external beams is similar to the problem of reconstructing a 3D image from its 2D projections. In this paper we analyse the relationship between these problems. We show that the main image reconstruction methods, namely filtered backprojection and iterative reconstruction, can be directly applied to conformation therapy. We examine the features of each of these methods with regard to this new application and we present first theoretical results.
411 citations
TL;DR: The method developed may prove to be useful in establishing an index of risk for breast cancer and, ultimately, in determining intervals between examinations for individuals in a mammographic screening programme.
Abstract: A consistent, quantitative, observer-independent method of characterising mammographic parenchymal pattern is described. The method is based on the calculation of the 'fractal dimension' of digitised mammograms. The degree of correlation between the parenchymal pattern classifications by a fractal-based system and those of radiologists is assessed. For a set of 70 mammograms, average weighted proportion agreement among three radiologists in calling Wolfe grades was 85%, while agreement between the radiologists and the fractal classifier was 84%. The method developed may prove to be useful in establishing an index of risk for breast cancer and, ultimately, in determining intervals between examinations for individuals in a mammographic screening programme.
253 citations
TL;DR: This model can be used to characterise the performance of other shapes of stimulating coils and the dependence on fibre orientation, and suggest that nerve fibres running parallel to the skin surface are more likely to be stimulated than those running obliquely.
Abstract: Magnetic stimulation of the nervous system is being used as an alternative to electrical stimulation, principally because it is painless. The spatial distribution of induced currents from the stimulating coil is calculated from a computer model with graphical output. Two configurations of a plane circular coil are considered: parallel to the tissue surface and perpendicular to the surface. The surface is assumed planar and infinite in extent. The tissue is modelled as a uniform, isotropic volume conductor. A quasi-static approximation is made in calculating the electric field. Maps of current density, J, as a function of position, including depth, are shown. In both configurations, J is always parallel to the surface, and is maximum at the surface. There is no perpendicular (vertical) current. For a one-turn 10 cm diameter coil, spaced 1 cm from conducting tissue and parallel to it, with rate of change of current 10(8) A s(-1), Jmax = 6.8 A m(-2) (assuming conductivity 0.2 omega -1 m(-1)). In the perpendicular configuration Jmax = 4.1 A m(-2). These results suggest that nerve fibres running parallel to the skin surface are more likely to be stimulated than those running obliquely; and that it is extremely difficult to stimulate nerve fibres running perpendicularly. This model can be used to characterise the performance of other shapes of stimulating coils and the dependence on fibre orientation.
179 citations
TL;DR: The automatic detection of clusters of calcifications in digital mammograms has been investigated using image analysis techniques and shows that the computer system achieves a 25/25 true positive film classification with false positive clusters detected in 4/50 films.
Abstract: The automatic detection of clusters of calcifications in digital mammograms has been investigated using image analysis techniques. The calcifications were segmented from the background of normal breast structure in the mammogram using a local area thresholding process. This procedure also identified other breast structures and the digital image properties of all segmented objects were analysed to extract clusters of calcifications. Seventy five clinical mammograms were digitised. These were divided into training and test sets of 25 and 50 films respectively. The results for the test set of 50 complete clinical mammograms show that the computer system achieves a 25/25 true positive film classification (i.e. those containing clusters of calcifications) with false positive clusters detected in 4/50 films. There were no false negative film classifications.
178 citations
161 citations
TL;DR: The radiation-response characteristics of agarose gels prepared with Fricke dosemeter solution have been studied and it has been observed that freshly prepared gels are slightly more sensitive than those more than 24 h old.
Abstract: The radiation-response characteristics of agarose gels prepared with Fricke dosemeter solution have been studied. The response mechanism is an increase in the NMR longitudinal relaxation rate of protons caused by ferric ions. It has been observed that: (i) oxygen saturation assures consistent and maximum sensitivity; (ii) agarose concentrations in the range 1.0-2.0% have no effect upon sensitivity; (iii) the initial G value is 150 Fe3+/100 eV for gels containing 0.5 mM Fe2+ ions; (iv) increasing NMR frequencies only causes a moderate increase in sensitivity; (v) the gel dosemeters are dose rate independent in the range 4.7-24.2 Gy min-1; (vi) sensitivity is pH dependent, being zero at pH 7; (vii) freshly prepared gels are slightly more sensitive than those more than 24 h old; and (ix) the diffusion coefficient for ferric ions in a 1.0% agarose gel containing 0.0125 M H2SO4 is 1.83 x 10(-2) cm2 h-1, and this will require consideration for the NMR imaging of dose distributions.
148 citations
TL;DR: The measurement of attenuation and velocity of ultrasound in cancellous bovine femora has been studied and the clinical consequences for the use of low frequency ultrasound as a diagnostic tool in bone disease are discussed.
Abstract: The measurement of attenuation and velocity of ultrasound in cancellous bovine femora has been studied. The dependence of both attenuation between 0.2 and 0.8 MHz and velocity on the bone density has been measured. The results show a correlation coefficient of around 0.5 for attenuation and density, and a value of roughly 0.85 for velocity and density. The clinical consequences for the use of low frequency ultrasound as a diagnostic tool in bone disease are discussed.
133 citations
TL;DR: Investigating the heat transfer between a single vessel and the surrounding vascularised tissue, comparing the conventional bioheat transfer theory and the recently developed keff model using analytical and numerical methods revealed a faster diffusion of heat at higher perfusion rates.
Abstract: The verification of thermal models for use in hyperthermia treatment planning is essential. The authors investigated the heat transfer between a single vessel and the surrounding vascularised tissue, comparing the conventional bioheat transfer theory and the recently developed keff model using analytical and numerical methods. A plastic tube inserted into the tissue of an isolated perfused organ served as an artificial vessel. This enabled the authors to vary the blood flow in the vessel and in the tissue independently. The organ used was a bovine kidney, turned into a perfused tissue phantom using an alcohol fixation technique. The temperature profile within the tissue was mapped with constantan-manganin thermocouple wire sensors with a total diameter of 50 mu m. The temperature profile relative to the temperature difference between the vessel and organ was measured; increased perfusion caused a reduction of the vessel wall temperature but did not affect the width of the profile.
TL;DR: The Monte Carlo method was used to calculate backscatter factors for a cylindrical water phantom irradiated by X-rays of various radiation qualities generated at voltages between 10 and 280 kV and three monoenergetic radiations with energies up to 661 keV.
Abstract: The Monte Carlo method was used to calculate backscatter factors for a cylindrical water phantom (diameter, 33 cm; thickness along the beam direction, 20 cm) irradiated by X-rays of various radiation qualities generated at voltages between 10 and 280 kV and three monoenergetic radiations with energies up to 661 keV. To study the influence of the irradiation geometry on the backscatter factor, the calculations were performed for conical photon beams of field diameters between 1 and 20 cm at the phantom front face and at source-to-phantom distances between 10 and 100 cm. The numerical results-the statistical uncertainties of which are less than 0.5%-are compared with other known data.
TL;DR: The theoretical formulation was used to design a fan beam collimator for SPECT imaging and was shown to agree well with the experimental results.
Abstract: Geometric response functions are derived for both cone and fan beam collimators for the scintillation camera. The formulation is based on an effective response function which is determined by the geometric response of a single hole. The technique provides an accurate description of the spatial resolution by characterising the complete geometric response function which includes the effects of the shape and orientation of the collimator holes. The theoretical formulation was used to design a fan beam collimator for SPECT imaging and was shown to agree well with the experimental results.
TL;DR: In this paper, an energy-dispersive X-ray diffraction tomography (EXDT) was proposed to measure the properties of small voxels of an extended object to be measured in vivo.
Abstract: A novel tomographic imaging technique is described based on the energy analysis, at fixed angle, of coherent X-ray scatter excited in an object by polychromatic radiation. The authors term their technique 'energy-dispersive X-ray diffraction tomography' (EXDT). It permits the X-ray diffraction properties of small voxels of an extended object to be measured in vivo. Tomographic information is obtained directly without the need to reconstruct from projections. EXDT images of a simple test object comprising water and various plastic materials are presented to illustrate the feasibility of the technique. Potential applications of EXDT in bone imaging are discussed.
TL;DR: This is a true 3D dose measurement technique which will have a number of applications in radiation therapy, since it is possible to mould the gel to arbitrary geometries, mix different radiation qualities and integrate the absorbed dose from different kinds of fields.
Abstract: The measurement of absorbed dose distributions using dosemeter gel and magnetic resonance imaging (MRI) in a standard geometry has been investigated. Absorbed depth-dose curves and profiles measured with this new technique show good agreement with corresponding measurements using diodes. This was proven in a 60Co beam as well as an electron beam. The dosemeter gel is made of agarose and ferrous sulphate solution. The dose response is linear (r = 0.9996) in the investigated dose interval, 0-40 Gy. The sensitivity is a factor of about six higher compared to ordinary ferrous sulphate solution, known as 'Fricke'. This is a true 3D dose measurement technique which will have a number of applications in radiation therapy, since it is possible to mould the gel to arbitrary geometries, mix different radiation qualities and integrate the absorbed dose from different kinds of fields.
TL;DR: A field placement analysis (FPA) method has been developed for detailed evaluation of patient setup by comparing positions of corresponding radiation field edges in digitised simulator and portal images, and meaningful results can be obtained.
Abstract: Correct placement of radiation fields relative to patient anatomy is essential in radiotherapy in order to minimise serious side effects to reduce the probability of recurrence of the tumour. One way to determine patient setup accuracy is to analyse portal images obtained in the therapy beam distal to the patient. A field placement analysis (FPA) method has been developed for detailed evaluation of patient setup by comparing positions of corresponding radiation field edges in digitised simulator and portal images. A simulator image is matched to a portal image using similar anatomical landmarks in both images and mapping these landmarks against each other applying a least squares minimisation approach. Discrepancies between the simulator field edge (reference) and a portal field edge are determined by comparing the distances between the central axis of the beam and corresponding edge segments and the angles of these segments with a reference line. Uncertainties in these distances and angles are to a large extent determined by the magnification, rotation and translation procedure. Uncertainties due to the FPA method itself are of about 1.0 mm and 0.5 degrees in portal images of head and neck fields. These FPA uncertainties are in general smaller than the variations due to patient setups. Matching of simulator and portal images of lateral pelvic fields revealed larger uncertainties: 1.7 mm and 1.1 degrees. Setup variations in this kind of pelvic radiation field are usually also larger, and therefore meaningful results can be obtained with the new FPA method.
TL;DR: Pinhole ECT showed the distribution of inhales particles to be considerably different in two rabbits, subjected to different modes of mechanical ventilation, and in planar images, on the other hand, it was difficult to appreciate the difference.
Abstract: A method for pinhole emission computed tomography (ECT) using the image-processing capabilities of a gamma camera system is described and evaluated. The tomographic imaging capability of the method was assessed by studies of phantoms and its practical use by the distribution of inhaled 99Tcm-labelled aerosol particles in rabbits. The phantom studies demonstrate the tomographic properties in central and non-central planes. A reconstructed resolution of 4.4 mm (FWHM) and an overall homogeneity of +or-10% was obtained for a radius of rotation of the pinhole of about 8 cm. Pinhole ECT showed the distribution of inhaled particles to be considerably different in two rabbits, subjected to different modes of mechanical ventilation. In planar images, on the other hand, it was difficult to appreciate the difference.
TL;DR: Three-dimensional x-ray microtomography provides for the investigation of small-scale structures in biological specimens and some illustrative images of dead insects are shown.
Abstract: Three-dimensional (3D) X-ray microtomography is a technique for obtaining the 3D distribution of X-ray attenuation coefficients within small objects. To obtain microtomographic images apparatus has been developed which consists of a microfocal X-ray source, a computer-controlled stage for rotating the object, a 2D multi-wire gas proportional X-ray counter and a microcomputer to control image acquisition. Projection data were generated by rotating the object to discrete orientations around a single axis until of the order of 100 2D projection images of the object were collected. The projection images were transferred to a VAX 11/750 computer for subsequent 3D reconstruction using a convolution and back-projection algorithm in cone-beam geometry. The reconstructed data, comprising cubic voxels, may be displayed as sets of sequential transaxial, sagittal and coronal planes through the object. Alternatively, perspective displays of individual orthogonal sections may be formed with either intersecting planes or with these planes projected onto the surfaces of a box-like structure.
TL;DR: The enhancement of dose to soft tissue (or water) close to high electron-density materials and to measure the detailed lateral and depth-dose profiles in soft-tissue-simulating polymer adjacent to planar interfaces of several higher atomic-number materials are investigated.
Abstract: Soft-tissue damage adjacent to dental restorations is a deleterious side effect of radiation therapy which is associated with low-energy electron scatter from dental materials of high electron density. This study was designed to investigate the enhancement of dose to soft tissue (or water) close to high electron-density materials and to measure the detailed lateral and depth-dose profiles in soft-tissue-simulating polymer adjacent to planar interfaces of several higher atomic-number materials: 18-carat gold dental casting alloy; Ag-Hg dental amalgam alloy; Ni-Cr dental casting alloy; and natural human tooth structure. Interleaved stacks of calibrated thin radiochromic dosimeter films and tissue-simulating polymer were used for these measurements. Assemblies of these polymer-dosimeter stacks on both sides of the dental materials were irradiated in one fixed direction by collimated 60Co gamma-ray or 10 MV x-ray beams directed perpendicularly to the material interfaces. In another test, designed to simulate more closely therapeutic treatment conditions, a phantom constructed on both sides of a row of restored and unrestored whole teeth (restoration materials: gold alloy crown; Ni-Cr alloy crown; Ag-Hg mesial-occlusal-distal (MOD) amalgam filling; unrestored tooth) was irradiated in one fixed direction by the collimated photon beams. Results indicate that the dose-enhancement in 'tissue' is as great as a factor of 2 on the backscatter side adjacent to gold and a factor of 1.2 adjacent to tooth tissue, but is insignificant on the forward-scatter side because of the predominant effect of attenuation by the high-density, high atomic-number absorbing material.
TL;DR: An improvement to Schwan's model of the dielectric response of biological tissues is proposed which is based on a fractal interpretation of the power law behaviour (epsilon' alpha epsilon" alpha f"-1) often observed.
Abstract: An improvement to Schwan's model (see Adv. Biol. Med. Phys., vol.5, p.147-209, 1957) of the dielectric response of biological tissues is proposed which is based on a fractal interpretation of the power law behaviour often observed. This interpretation allows the response to be more specifically related to the sub-cellular and cellular organization of the tissue through its self-similar hierarchical nature. A number of examples are discussed ranging in tissue type from the mostly cellular liver tissue to nerve tissue (grey matter). Applications of the technique to diseased and damaged tissue are briefly touched upon so as to illustrate its potential for precisely defining their effect upon the cells' electrical behaviour at a specific organizational level.
TL;DR: Reported models on laser tissue ablation need to be extended to include explosive vaporisation ('popcorn') at the onset and cyclic carbonisation during steady-state crater formation.
Abstract: The phenomena at the onset of and during tissue ablation using continuous wave lasers were studied. Aortic and myocardial bovine tissues were exposed in air and in water to Nd-YAG (10 to 60 W) and argon (3.5 W) laser light. The transmitted light was measured, the surface of the tissue was filmed and the tissue was processed for histology. Three distinct phases were observed. Phase A was tissue denaturation. Phase B started with explosive vaporisation ('popcorn') in conjunction with a drop of about 50% in light transmission due to enhanced reflection and scattering. The 'popcorn' is possibly associated with a layered structure of the tissue. Phase C started with carbonisation of the tissue beginning in the centre and expanding in a cyclic fashion while the tissue was vaporised leaving a crater. Forward light transmission did not decrease. Thin layers of carbon (20 microns) and vacuoles (30 microns) suggested a large temperature gradient along the tissue ablation front. The ablation velocity was constant (r greater than 0.92) and tissue dependent. Reported models on laser tissue ablation need to be extended to include explosive vaporisation ('popcorn') at the onset and cyclic carbonisation during steady-state crater formation.
TL;DR: This paper examines some of the difficulties associated with the generalisation of the filtered backprojection algorithm to 3D, paying particular attention to the approximations and variable transformations required for application to data from a multi-ring PET scanner.
Abstract: In view of the number of PET studies involving low count rate acquisitions, there has been increasing interest recently in the development of positron cameras capable of fully three-dimensional acquisition and reconstruction. This interest has given impetus to the study of algorithms for 3D reconstruction, including those algorithms suitable for application to multi-ring PET scanners. While ZD reconstruction methods can often be generalised to 3D, a numbw of implementation problems arise which are unique to the 31) approach. This paper examines some of the difficulties associated with the generalisation of the filtered backprojection algorithm to 3D, paying particular attention to the approxima- tions and variable transformations required for application to data from a multi-ring scanner.
TL;DR: Exact solutions are obtained to the classical time-dependent linear bioheat equation in one-dimensional multiregion cartesian and spherical geometries with temperature-invariant physiological parameters that enable the study of transient temperature behaviour in an arbitrary number of coupled physiologically distinct regions.
Abstract: Exact solutions are obtained to the classical time-dependent linear bioheat equation in one-dimensional multiregion cartesian and spherical geometries with temperature-invariant physiological parameters. These solutions enable the study of transient temperature behaviour in an arbitrary number of coupled physiologically distinct regions.
TL;DR: In this article, a statistical criterion for determining an optimal stopping point developed in an earlier paper is compared with two statistics derived and applied in this paper to obtain better image reconstructions.
Abstract: Emission tomography involves the reconstruction of images representing the radionudide concentration throughout a patient's body. Maximum likelihood estimation yields excessively noisy images due to the non-uniqueness of the solution and the noise in the emission data. Many investigators have noted that better image reconstructions are obtained by stopping an iterative maximum likelihood algorithm early, well before convergence. This paper explains why better results can be obtained by suchan approach. A statistical criterion for determining an optimal stopping point developed in an earlier paper is compared with two statistics derived and applied here.
TL;DR: In this article, an analytic theory for calculating the point source nonuniformity correction factor for thick-walled ionisation chambers is developed, which is compared with Monte Carlo calculations for chambers with pancake, cylindrical and spherical geometries similar in size to the instruments employed by Standards laboratories.
Abstract: In exposure and air kerma measurements, axial and radial nonuniformity perturbation correction factors are used to account for the nonuniformity of the incident photon field in the vicinity of the ionisation chamber cavity. An analytic theory for calculating the point source nonuniformity correction factor for thick-walled ionisation chambers is developed. The theory developed herein is compared with Monte Carlo calculations for chambers with pancake, cylindrical and spherical geometries similar in size to the instruments employed by Standards laboratories. The perturbations, which differ from those calculated or measured by some Standards laboratories, suggest that corrections of the order of 0.3% should be applied to typical pancake geometries, smaller corrections of the order of 0.05% or less for typical Farmer-type chambers, and no correction for spherical chambers.
TL;DR: In this paper, a theory for calculating the correction due to source nonuniformity is developed which applies to thick-walled ionisation chambers irradiated by point-source photon field with arbitrary incident energy distributions.
Abstract: In absolute exposure and air kerma measurements, such as those performed at Standards' laboratories, axial and radial nonuniformity correction factors are used to account for the nonuniformity of the incident photon field in the vicinity of the ionisation-chamber cavity. A theory for calculating the correction due to source nonuniformity is developed which applies to thick-walled ionisation chambers irradiated by point-source photon field with arbitrary incident energy distributions. The equations are derived within the framework of a fundamental theory of ionisation-chamber response and are suitable for Monte Carlo calculation. Monte Carlo calculations for estimating the correction in pancake, cylindrical and spherical geometries are described and comparisons with the experimental results of Kondo and Randolph indicate agreement to better than 0.5% demonstrating the viability of the theory under even the most extreme measurement conditions.
TL;DR: Using the EGS4 system the authors show that Monte Carlo calculated Awall factors predict relative variations in detector response with wall thickness which agree with all available experimental data within a statistical uncertainty of less than 0.1%.
Abstract: In precision ion chamber dosimetry in air, the wall attenuation and scatter are corrected for by Awall. Using the EGS4 system the authors show that Monte Carlo calculated Awall factors predict relative variations in detector response with wall thickness which agree with all available experimental data within a statistical uncertainty of less than 0.1%. However, the calculated correction factors for use in exposure and air kerma standards are different by up to 1% from those obtained by extrapolating these same measurements. Using calculated correction factors would imply increase of 0.7-1.0% in the exposure and air kerma standards based on spherical and large diameter, large length cylindrical chambers and decreases of 0.2-0.5% for standards based on large diameter pancake chambers. Calculations are also shown to agree within 0.05% with the measurements of Rocha and co-workers for clinical chambers. These experimental data are not in exact agreement with the gamma values used in the AAPM protocol to obtain Awall. However, the AAPM final values of Awall agree within 0.2% with the more accurate values calculated.
TL;DR: It was found that stray light, the amounts of haemoglobin and melanin, and the level of blood oxygenation all contributed to the measured reflectance and had to be taken into account when calculating quantitative indices of skin pigments.
Abstract: Factors affecting the accuracy of the in vivo measurement of cutaneous pigments and blood oxygenation by reflectance spectrophotometry have been examined. It was found that stray light, the amounts of haemoglobin and melanin, and the level of blood oxygenation all contributed to the measured reflectance and had to be taken into account when calculating quantitative indices of skin pigments. Measurements on isolated sheets of epidermis demonstrated that over 50% of normally incident radiation is transmitted in a forward direction within 17' of the incident direction and approximately 20% is backscattered between 90' and 180' out of the sample, approximately 6.0% of it by specular reflection at the surface. The effective optical pathlength in suspensions of whole red cells was found to be 7% greater than in simple solutions containing the same concentration of haemoglobin.
TL;DR: It appears to be impossible to unambiguously discuss dielectric spectra of complex biological tissues in which different polarization mechanisms overlap, because two types of affected water might be considered 'bound': dielectrically saturated water in strong electric fields and water in regions with a high concentration of other molecules.
Abstract: Results of dielectric relaxation studies on binary aqueous solutions are summarized to look for indications of the presence of bound water. The solutes include simple inorganic and organic electrolytes, polyelectrolytes, small organic molecules and polymers. It is shown that even simple solutions exhibit a great variety of dielectric effects. It therefore appears to be impossible to unambiguously discuss dielectric spectra of complex biological tissues in which different polarization mechanisms overlap. The results for solutions taken as models for biological systems indicate two types of affected water which might be considered 'bound': dielectrically saturated water in strong electric fields and water in regions with a high concentration of other molecules. Characteristics of both states of water in mixtures are presented.
TL;DR: The magnetic resonance effect (MME) has been used for radiotherapy dosimetry as mentioned in this paper, and it has a number of interesting features, though it may be unfamiliar to many regular practitioners of clinical dosimometry.
Abstract: Almost every known effect of ionizing radiation on matter, whether it be physical, chemical or biological, has been suggested as a basis for dosimetry, especially if the matter is (or can be made) dosimetrically tissue-equivalent. The latest candidate for attention is the magnetic resonance effect, the dosimetric application of which has been pioneered by British, American and Swedish workers (Gore et al. 1984, Appleby et al. 1987, Olsson et al. 1989). The method has a number of interesting features, though it may be unfamiliar to many regular practitioners of clinical dosimetry. The author gives an introductory review intended to place the new method in the broad context of radiotherapy dosimetry.