The influence of tissue layering on microwave thermographic measurements

Abstract

Non-invasive thermal imaging and temperature measurement by microwave radiometry has been investigated for medical diagnostic applications and monitoring hyperthermia treatment of cancer, in the context of heterogeneous body structure. The temperature measured by a radiometer is a function of the emission and propagation of microwaves in tissue and the receiving characteristics of the radiometric probe. Propagation of microwaves in lossy media was analysed by a spectral diffraction approach. Extension of this technique via a cascade transmission line model provides an efficient algorithm for predicting the field patterns of aperture antennas contacting multi-layered tissue. A coherent radiative transfer analysis was used to relate the field pattern of a radiating antenna to its receiving characteristics when used as a radiometer probe, leading to a method for simulating radiometric data. Measurements and simulations were used to assess the effect of overlying fat layers upon radiometer response to temperature hot spots in muscle-type media. Results suggest that dielectric layering in tissue greatly influences measured temperatures and should be accounted for in the interpretation of radiometric data.

Multi-layer RF tissue phantoms for mimicking a human core

“…Such phantoms are usually developed using simple solid, semi-solid (gels), or liquid solutions [2], [3]. Previous studies have proven that "dielectric layering greatly influences" the radiometric measurement, therefore single layer phantoms cannot accurately mimic the emissive properties of layered volumes human tissue [1] & [4]. This loss in accuracy, could create considerable measurement errors, since microwave radiometers detect very low brightness temperature (TB) emissions which are dependent on the electrical properties of the tissue.…”

Radiative Transfer: Application to Indoor Propagation

“…Chandrasekhar first studied the RTE within the context of astrophysics [10]. Later, the same formulation was employed successfully for many other applications, such as propagation modeling in the atmosphere or in forested environments, heat transfer through insulating materials, neutron scattering, and power absorption within biological tissues [11][12][13][14].…”

Microwave radiometry in biomedicine: A reappraisal

“…Guy's analysis was recently extended to microwave radiometry by Cheever and colleagues [Cheever et al, 1987;Cheever andFoster, 1988, 1992;Cheever, 19891. Several other groups have also studied the problem [Barrett and Myers, 1975;Audet et al, 1980;Leroy et al, 1987;Hawley et al, 1988;Mamouni et al, 19911. The following discussion is based on the Ph.D. dissertation of Cheever [ 19891, which presents the experimental and numerical procedures in detail.…”

“…The radiometer signal is the integral of power as received by the antenna, which depends on the distribution of temperature and dielectric properties of the medium and the electrical characteristics of the antenna. This problem has been analyzed for several simplified systems, including bilayered media (e.g., Leroy et al, 1987;Mamouni et al, 19911 and media containing cylindrical targets [Hawley et al, 1988;Cheever, 19891.…”