Non-invasive dielectric measurements in bovine bones: a System Identification approach

RAMIRO M. IRASTORZA; M. MAYOSKY; J. RAÚL GRIGERA; FERNANDO VERICAT

Montevideo, Uruguay

Congreso; INTERNATIONAL CONFERENCE OF BIOLOGICAL PHYSICS; 2007

Sociedad Argentina de Biofísica y Sociedad Uruguaya de Física

Changes in physiological properties (i.e: tissue water content, thickness) ofhuman skin, subcutaneous fat, or deeper tissues can provide significantinformation from a clinical point of view. In some cases, these variationsproduce changes in the dielectric properties of the media under measurement.Open ended coaxial lines operating at microwave frequencies have beensuccessfully used for measuring dielectric properties of layered materials. Theirwide frequency response allows the study of different dielectric relaxationprocesses, providing relevant information not achievable with other kind ofprobes. As a non-invasive technique, it is well suited for application in biologicalmeasurements in vivo, without damaging the media under test. In search ofsuitable models, several authors have developed mathematical, empirical andnumerical approaches. In particular, in this work a simple exponentialapproximation is applied and compared with a theoretical one. The resultingapproach is useful to represent measurements in vivo of body areas that can bedielectrically modeled by layers. A fast procedure for estimating changes in therelaxation processes of layered biological tissues in a wide frequency spectrum isdeveloped, using time domain measurements and Fourier analysis. Time DomainReflectometry (TDR) and System Identification tools are used to obtain thefrequency response. For both techniques the media under measurement ismodeled as a causal linear time invariant (CLTI) system. The techniquedeveloped here is applied to measurements of bovine cortical and cancellousbones between 10 and 1300MHz. The results obtained are validated withfrequency measurements and literature data. Application of the proposedmethodology depends on a previous knowledge of the kind of tissues understudy and hence, on the expected values their dielectric properties can take.