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• Open/close Dielectric properties of body tissues

  R Pethig 1987 Clin. Phys. Physiol. Meas. 8 5 Tag this article

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  A review is given of the dielectric properties of various mammalian tissues and biological fluids for the frequency range from 1 Hz to 10 GHz. The properties considered are the frequency variations of the relative permittivity and electrical conductivity. An attempt has been made to present data which can be considered to be the most typical for each material. The dielectric properties of aqueous solutions of amino acids, polypeptides, proteins, and then cells are first outlined in order to lay the groundwork for the understanding of the properties of tissues. The electrical characteristics of various tissues and blood are presented in tabular and graphical form, and the differences between normal and cancerous tissue are also discussed. The effects of necrosis and temperature changes are described and the important contribution that water makes to the overall properties is emphasised. An insight into some of the dominant physiological and biophysical processes responsible for the dielectric properties of biological materials is also attempted, since this should aid further developments of both the diagnostic and therapeutic applications of radiofrequency and microwave radiation. Such information is also relevant to an understanding of the possible biological hazards of such radiation. The ways in which dielectric studies can aid an understanding at the molecular level of the basic physiological differences between normal and cancerous tissue, as well as of the physico-chemical state of biological water, are also described.

• Open/close Non-invasive in vivo near-infrared optical measurement of the penetration depth in the neonatal head

  F Faris et al 1991 Clin. Phys. Physiol. Meas. 12 353 Tag this article

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  The non-invasive optical technique of near-infrared spectroscopy (NIRS) was used to measure the depths of light penetration at four wavelengths in the NIR region. Near-infrared absorbance measurements were carried out on ten preterm infants. The apparent absorbance data (in optical density units) collected at 775, 805, 845, and 904 nm were measured at different positions on the head. Linear relationships that satisfy the Lambert law were obtained when the apparent absorbance at a given wavelength was plotted against the inter-optrode distance. From the slopes of the resulting straight lines, the depth of penetration of the NIR light was calculated and found to be independent of the position of the probes on the head. Calculated average values of the depth of penetration of near-infrared light in the whole neonatal head ranged between 6.3 and 8.5 mm.