ABSTRACT
The index of refraction n of the many mammalian tissues is an important but somewhat neglected optical constant. Archival and oral papers have quoted the use of values of n for tissue generally ranging from 1.35 to 1.55. However, these values are frequently without experimental basis. They have arbitrarily used values near that of water, which is a major component of mammalian tissue, or have calculated a theoretical n from the weighted elemental composition of tissue. Since these values have not been precise and little information is available on specific indices for each tissue, a study was undertaken to develop a simple, rapid, and reliable method for the experimental determination of n. This was done using the ubiquitous quartz optical fiber. By substituting the usual cladding found on commercial quartz optics by the tissue in question and utilizing the principle of internal reflection, the value of n for the specific tissue can be calculated. This is done by utilizing the known indices for air and quartz and measuring the angle of the emergent cone of light from the output of the optical fiber. A number of indices for mammalian tissue (bovine, porcine, canine, and human) have been determined at 632.8 nm. With few exceptions, for tissues at this wavelength, n was in the 1.38-1.41 range. The species type did not appear to be a factor. Bovine muscle showed normal dispersion characteristics through the visible wavelengths. The denaturation of tissue was shown to alter significantly the refractive index.
Subject(s)
Lymphedema/diagnosis , Cadmium , Elementary Particles , Extremities , Humans , Lymphedema/therapy , RadioisotopesSubject(s)
Adipose Tissue , Cadmium , Radioisotopes , Adult , Arm , Female , Humans , Male , Middle AgedABSTRACT
The application of a dual photon beam to the measurement of tissue and tissue-like substances has generally required the use of a filter to attain the required monochromaticity of the lower-energy x-ray photons. In many cases this has the undesirable effect of also severely attenuating the desired low-energy beam. A method for circumventing the use of the filter is described. The technique relies on a knowledge of the initial intensities of the components of the x-ray portion of the dual beam and involves an iterative mathematical procedure. Experimental verification of the method using both tissue and nontissue substances has been carried out. R values obtained with the iterative system show good correlation with filtered values.
