Table of contents

The 1986 Association Lecture of the Hospital Physicists Association is concerned with the application of physical science to the diagnosis, treatment and prevention of human disease. The author of this lecture attempts to show how patients have benefited in health care from the development and application of science generally and looks beyond its help in diagnosis and treatment of illness and bodily defects to its relation to and its possibilities in preventive medicine and to possible improvements in the quality of life.

The authors re-evaluate the distribution of the intracellular alkali metals in humans and offer an approach for selecting reference concentrations for the organs of a typical adult human. For non-skeletal tissues, reference values for K, Rb and Cs are determined as a trimmed weighted mean of reported values remaining after studies involving apparently questionable populations or measurement techniques have been eliminated. The skeleton is treated as a special case, with explicit consideration being given to the heterogeneous distribution of these elements among different regions and different types of skeletal tissue. The most significant suggested changes for the intracellular alkali metals are for Rb in the skeleton and total body. ICRP Reference Man has a total Rb content of 0.68 g, compared with the present estimate of only 0.25 g, and a skeletal Rb content of 0.21 g, compared with an estimate of only 0.013 g. This has important dosimetric implications for radiorubidium.

A method of measuring total body chlorine (TBCI) by prompt gamma in vivo neutron activation analysis is described which depends on the same NaI(Tl) spectra used for determinations of total body nitrogen. From these spectra counts ratios of chlorine to hydrogen are derived and TBCI is determined using a model of body composition which depends on measured body weight, total body water (by tritium dilution) and protein (6.25*nitrogen) as well as estimated body minerals and glycogen. The precision of the method based on scanning an anthropomorphic phantom is at present only approximately 9% (SD), for a patient dose equivalent of less than 0.30 mSv. It is suggested that an improvement in precision will be achieved by increasing the scanning time (thereby increasing the radiation dose equivalent) and by adding two more detectors.

A ⁵⁷Fe Mossbauer-effect study of autopsied lung tissue from Canadian asbestos mine workers is presented. The spectra typically show large quantities of iron storage protein. This exhibits a quadrupole-split doublet at room temperature and both a doublet and a Zeeman-split sextet at 4.2 K, due to a distribution of particle sizes. A comparison is made with Mossbauer spectra of lung tissue from an individual not occupationally exposed to respirable asbestos, and with spectra of respirable chrysotile asbestos taken from Canadian mines.

In 1979 ICRU recommended the value W=(33.85+or-0.05) eV for the average energy required for electrons to produce an ion pair in dry air. A re-evaluation is presented which is based on recently published stopping-power data. The new result is W/e=(33.97+or-0.05) JC^-1, where all stated uncertainties are estimated standard deviations.

A phantom electrically adaptable for simulation of various tissues, was developed using agar as the jelly. This phantom has the following features: (i) the dielectric property is specified in the range 5-40 MHz, (ii) the conductivity can be varied between 0.02 and 1.23 Sm^-1, (iii) the permittivity can be varied between 35 and 80, (iv) preparation and handling are readily facilitated; the original shape is retained for over one year, and (v) it is free from deterioration caused by mould for at least one year.

A potential source of hazard during gynaecological surgery with a CO₂ laser is the reflection of the laser beam from the surfaces of the metal speculum. An experimental method of measuring the levels of radiation reflected from a variety of surfaces is described. Results which compare the effectiveness of different surface treatments in reducing reflections and show how this varies over a range of angles of incidence are presented. The significance of the results in terms of hazard to patients and staff is discussed.

In order to improve the accuracy of dosimetric measurements in pion radiotherapy it is necessary to produce materials which are tissue-equivalent for pions. The feasibility of constructing muscle - and bone-equivalent mixtures for pions has been investigated.

The authors show how measurements on patients over a long period of time to monitor either their bone loss as a result of disease or a change in bone calcium as a result of treatment, can be used to obtain a measurement of the long term precision of total body neutron activation analysis in vivo.

Proton build-up curves were calculated for thin-walled detectors irradiated with high-energy neutrons. The results of this work show that the changes in the hydrogen content in the skin of the inner wall of moulded TE plastic would not produce significant changes in the detector response for neutron energies of the order of 14 MeV but would be significant at lower energies such as 4 MeV.

The geometrical independence of radionuclide techniques for the measurement of left ventricular ejection fraction is commonly quoted. The authors have shown this to be theoretically invalid in many clinically applicable situations, due to the effects of photon attenuation within the ventricle.

El Yousef et al. (1983, 1984), Stelling et al. (1985) and Wolfman et al. (1985) have considered the clinical potential of proton NMR imaging of the female breast. All of these groups used specialised close-fitting radiofrequency (RF) receiver coils to improve the signal to noise ratio (SNR) and hence image quality. A suitable breast receiving coil is described and images are presented from the Aberdeen 0.08 T 3.4 MHz resistive imager.

The choice of the beam shape allows additional control over the degree of equalisation and scatter rejection. The relation between beam shape and image quality is investigated for SER and an optimum is chosen for applications in chest imaging.