Surveys the different types of microwave sensors and reviews the latest developments reported by European institutes and companies. Attention is given to resonator, transmission, reflection, radar, and radiometer sensors, and to active imaging. >

Industrial microwave sensors

Near-field microwave radiometry and radiometric imaging are non-invasive techniques that are able to provide temperature information at a depth of up to several centimetres in subcutaneous tissues They are based on the measurement of microwave electromagnetic thermal noise This paper describes the basic principles, measurement methods and limitations of the techniques and the results of clinical studies, and it reviews recent progress

https://iopscience.iop.org/article/10.1088/0967-3334/19/2/001/pdf

Non-invasive microwave radiometry thermometry

Knowledge of the in vivo dielectric properties of human tissues is essential to the development of biomedical techniques which make use of radiofrequency and microwave radiation The sensors used for measurement of tissue properties can be conveniently calibrated using dielectric reference liquids, but this in turn requires that the dielectric properties of such liquids be accurately known Many complex permittivity measurements on suitable liquids, such as the primary alcohols and saline solutions, have been reported in the literature, but unfortunately there are in some cases significant discrepancies between reported values The authors describe a program of work undertaken to resolve some of these anomalies A number of techniques which make use of 14 mm coaxial cells and sensors coupled to an automatic network analyser are under investigation Comparison of the different techniques should facilitate evaluation of systematic uncertainties The liquid measurement geometries and the associated computational methods are described Details are given of the uncertainty analysis, and examples of mappings from the complex permittivity plane on to the scattering coefficient plane are shown Some preliminary results are presented, which highlight the value of the comparative approach that has been adopted

http://iopscience.iop.org/article/10.1088/0957-0233/1/8/005/pdf

Dielectric measurements on reference liquids using automatic network analysers and calculable geometries

Presents a synthesis of works undertaken by the Hyperthermia Group of Lille (France) concerning the utilization of microwave radiometry for temperature control in hyperthermia therapy. This technique of noninvasive temperature control within biological tissues has been integrated on many hyperthermia systems now commercialized. The authors describe the principle of a new radiometer as well as the calculation of the radiometric signals. This allows a noninvasive determination of thermal maps inside tissues during the hyperthermia treatments. Many comparisons between theory and experiment have validated the authors' models of thermal dosimetry and provide a quantitative guidance for the planning of hyperthermia treatments.

Temperature control and thermal dosimetry by microwave radiometry in hyperthermia

Microwave radiometry has been used during the last few years in some clinical centres (Lille, Freiburg, Strasbourg, Brussels) for the non-invasive control of temperature during microwave hyperthermia. The principal objective of this paper is to present an atraumatic thermal dosimetry system based on numerical simulations of hyperthermia and radiometric temperature measurements for TEM propagation. To gauge the feasibility and performance of the method, a one-dimensional model in a homogeneous medium is considered, neglecting the curvature of the tissue layer. The good correlation between the theoretical and experimental values obtained allowed the likely thermal profile on the probe axis to be computed using the dielectric and thermal properties of the medium and measurement of the radiometric and cutaneous temperatures.

A new method for thermal dosimetry in microwave hyperthermia using microwave radiometry for temperature control.

This paper refers mainly to the inversion of microwave radiometric data for the determination of temperature distributions in the human body. The analysis is restricted to a simple one-dimensional stratified model and special attention is devoted to a skin-fat-muscle structure (SFM) and to a muscle-bone-muscle structure (MBM). In both cases the technique of singular system analysis is applied to the corresponding integral equation in order to quantify the information content of the data. Numerical computations indicate that the information content is much greater in the MBM than in the SFM case, as one can guess from qualitative physical considerations. The results of some numerical inversions are also presented in order to assess the effectiveness and the practicability of the mathematical technique.

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Singular system analysis of the inversion of microwave radiometric data: applications to biological temperature retrieval

The potential of the singular function method for retrieving temperature profiles in biological structures from microwave radiometric data is examined. A numerical simulation has been carried out in which the temperature distribution during hyperthermic treatments is reconstructed from radiometric measurements both at six and four frequencies. The results are compared and discussed in view of the practically relevant case of noise-corrupted data.

Inversion of Microwave Thermographic Data by the Singular Function Method

This paper refers to the retrieval of two-dimensional thermal fields in biological bodies from multispectral microwave measurements by a scanning waveguide applicator A formulation of the inverse radiometric problem suitable for a two-step solution (transverse deconvolution and profile retrieval) is outlined The performance of the inversion procedure is tested by a numerical evaluation of the impulse response of the resulting algorithm

Biological Temperature Retrieval by Scanning Radiometry

The subcutaneous temperature distribution of a simulated hyperthermic treatment is retrieved from a set of noisy radiometric measurements at six equally spaced frequencies in the range 1.5?6.5 GHz. Temperature profiles reconstructed by the combined use of both the singular value decomposition of the radiometric integral equation and Kalman filtering are shown.

Retrieval of hyperthermia-induced temperature distribution from noisy microwave radiometric data

The feasibility of reconstructing the thermal field in biological tissues from brightness data measured by an array of microwave antennas is investigated through a numerical simulation. The array does not make use of phase information and is synthesized through the Kalman filter algorithm. The obtained results indicate that, by a multispectral technique, such a synthetic array might be able to achieve spatial resolution not only in a transverse direction, but also in depth.

M. Mongiardo

Papers

Singular system analysis of the inversion of microwave radiometric data: applications to biological temperature retrieval

Inversion of Microwave Thermographic Data by the Singular Function Method

Biological Temperature Retrieval by Scanning Radiometry

Retrieval of hyperthermia-induced temperature distribution from noisy microwave radiometric data

Synthetic Array for Radiometric Retrieval of Thermal Fields in Tissues