Table of contents

Bioelectrical impedance analysis (BIA) using a frequency of 30 kHz is an established method of predicting total body water (TBW). However, very little research has been performed to determine whether 50 kHz is the optimum frequency for the prediction of TBW from impedance measurements. The paper analyses a mathematical expression describing the equivalent electrical circuit for biological tissue, and derives a graphical representation of the resistive and reactive components. The nature of the resulting impedance locus was used in the analysis of measured whole-body impedance of 42 rats over a range of frequencies to determine the impedance at the characteristic frequency, Z_c, and also the impedance at zero frequency, R₀. Predictions of extracellular water (ECW) using the impedance at zero frequency, R₀, yielded a standard error of 3.2% compared with standard errors of 4.8% and 4.2% using single frequency BIA measurements at 5 kHz and 1 kHz, respectively.

There are a number of claims in the literature that specific combinations of low level DC and AC magnetic fields can cause biologically significant effects. The combinations of fields required to elicit these responses fulfil the theoretical conditions for classical cyclotron resonance of the selected ion. Because of the biological importance of calcium ions any effects on them are of particular interest, for instance the claimed increase in calcium uptake by electromagnetically exposed lymphocytes. The authors have measured the intracellular calcium concentration, by means of a sensitive fluorescent probe, during a 60 min exposure of mouse lymphocytes to 'cyclotron resonance' conditions for calcium ions. 'Resonance' conditions at two frequencies (16 Hz and 50 Hz) were tested, with a range of DC field amplitudes used to shift the frequency up to 25% either side of the calculated optimum. No change in intracellular calcium concentration could be detected when lymphocytes were exposed to 'cyclotron resonance' conditions or to the other magnetic field combinations used.

This paper presents finite-different time-domain (FDTD) calculations of the specific absorption rate (SAR) averaged over the mass of the eye, and over 1 g and 100 g of tissue in a realistic model of the head from a closely coupled half-wavelength dipole source. The SAR is predicted as a function of the separation between the vertical dipole and the surface of the eye. The feed point of the dipole is on the axis defined by the centre of the eye. Phantoms representing an adult and a one-year-old child have been considered for irradiation at 900 MHz and 1.9 GHz.

This paper reports a theoretical study on the distribution of blood flow in the human cardiovascular system when one or more blood vessels are affected by stenosis. The analysis employs a mathematical model of the entire system based on the finite element method. The arterial-venous network is represented by a large number of inter-connected segments in the model. Values for the model parameters are based upon the published data on the physiological and rheological properties of blood. Computational results show how blood flow through various parts of the cardiovascular system are affected by stenosis in different blood vessels. No significant changes in the flow parameters of the cardiovascular system were found to occur when the reduction in the lumen diameter of the stenosed vessels was less than 65%.

The paper looks at the development of a dual-energy probe that permits real time analysis. The technique is based on the local analysis procedure introduced by Speller and co-workers and uses spectral filtering for energy separation. The split-detector probe is optimized using computer models, and the effects of beam hardening and scattered radiation are considered. It is shown that a 0.25 mm Cs1/25 mm NaI combination of detector elements with a 0.3 mm Cu filter offers the best performance. Preliminary results using the probe for in vivo analysis of gall stone composition compare well with the more accepted methods of X-ray diffraction and atomic absorption spectroscopy.

A novel irradiation-detection geometry capable of enhancing sensitivity for the measurement of tibial lead content by K-shell X-ray fluorescence (XRF) is described. The high-count-rate system comprised a small-area high-specific-activity (0.147 GBq mm^-2) ¹⁰⁹Cd source and a large-area (nominally 20 cm^-2) uncollimated detector, forming an axially symmetric back-scattering arrangement. Precisions in the range+or-4.9 to+or-14.2 mu g Pb (g bone mineral)^-1 have been obtained in a study of cohort of 63 controls and 73 workers industrially exposed to lead. These precisions are comparable with those obtained in results using earlier systems, but at reduced source activities (less than 50% of the activity of other systems) and with significant reduction in measurement time (some 30% less than the measurement times of other systems).

The slowing down of the fast neutrons, resulting in a thermal neutron distribution of a phantom, has been computed using a Monte Carlo model. This model, which includes a deep-seated tumour, was experimentally verified by measurements of the thermal neutron fluence rate in a phantom using neutron activation of gold foil. When non-boronated water phantoms were irradiated with a total dose of 1 Gy at a depth of 6 cm, the thermal fluencies at this depth were found to be 2*10¹⁰ cm^-2. The absorbed dose in a tumour with 100 ppm ¹⁰B, at the same depth was enhanced by 15%.

The choice of gamma-ray detectors for in vivo nitrogen determination is examined. NaI(Tl), BiGeO and hyperpure Ge detectors are investigated. It is shown that several small (5.1 cm diameter*10.2 cm long) NaI(Tl) detectors offer advantages over a single large detector (15.2 cm diameter*15.2 cm long). BiGeO has the disadvantage of an interference peak at 10.2 MeV, whilst hyperpure Ge detectors are expensive, and therefore not cost effective, unless used for simultaneous multi-elemental analysis.

The paper presents Fricke-to-water dose conversion and wall correction factors for Fricke ferrous sulphate dosimetry in high-energy electron beams. The dose conversion factor has been calculated as the ratio of the mean dose in water to the mean dose in the Fricke solution with a water-walled vessel and the wall correction factor accounts for the change in the Fricke dose due to the presence of the non-water wall material. The EGS4 (electron gamma shower version 4) Monte Carlo code system has been employed in the work together with the application of a correlated sampling variance reduction technique. The results show that for a Fricke dosimeter of 1.534 cm diameter and 5.5 cm length the dose conversion factor is nearly constant at 1.004 (within 0.1%) for electron energies of 11-25 MeV if the dosimeter is placed at the depth of maximum dose but can vary by a few per cent if the dosimeter is placed on the descending portion of the depth-dose curve.

An ionometric method has been used for the determination of absorbed dose to water for ⁶⁰Co gamma rays. Reliable estimation of the perturbation correction, which accounts for the presence of the chamber inside the water phantom, allows an accurate determination of this quantity. Details of the experimental work are given together with the theoretical background necessary for evaluation of the perturbation correction. The results are discussed by comparing them with those obtained by other methods.

The technical difficulties in designing a SPAMM sequence to image pulsatile cerebrospinal fluid (CSF) flow at different phases of the cardiac cycle are described. The criteria used to select the most appropriate order of binomial SPAMM sequence are outlined. Data collection times required to view both cephalad and caudad flow for all R-R intervals were considered. The flip angles of the RF pulses required to produce images with equal CSF intensity throughout the cardiac cycle were also investigated.