Hyperthermia therapy of superficial skin disease has proven clinically useful, but current heating equipment is somewhat clumsy and technically inadequate for many patients. The present effort describes a dual-purpose, conformal microwave applicator that is fabricated from thin, flexible, multilayer printed circuit board (PCB) material to facilitate heating of surface areas overlaying contoured anatomy. Preliminary studies document the Feasibility of combining Archimedean spiral microstrip antennas, located concentrically within the central region of square dual concentric conductor (DCC) annular slot antennas. The motivation is to achieve homogeneous tissue heating simultaneously with noninvasive thermometry by radiometric sensing of blackbody radiation from the target tissue under the applicator. Results demonstrate that the two antennas have complimentary regions of influence. The DCC ring antenna structure produces a peripherally enhanced power deposition pattern with peaks in the outer corners of the aperture and a broad minimum around 50% of maximum centrally. In contrast, the Archimedean spiral radiates (or receives) energy predominantly along the boresight axis of the spiral, thus confining the region of influence to tissue located within the central broad minimum of the DCC pattern. Analysis of the temperature-dependent radiometer signal (brightness temperature) showed linear correlation of radiometer output with test Load temperature using either the spiral or DCC structure as the receive antenna. The radiometric performance of the broadband Archimedean antenna was superior compared to the DCC, providing improved temperature resolution (0.1/spl deg/C-0.2/spl deg/C) and signal sensitivity (0.3/spl deg/C-0.8/spl deg/C//spl deg/C) at all four 500 MHz integration bandwidths tested within the frequency range from 1.2 to 3.0 GHz.

Dual-mode antenna design for microwave heating and noninvasive thermometry of superficial tissue disease

Recent results have demonstrated the feasibility of quasi-real-time, active as well as harmless microwave imaging for biomedical purposes. Such a process allows tomographic reconstructions based on differences in the complex permittivity of tissues, the temperature dependence of which can be used for remote thermal sensing. A basic experiment conducted in water at 3-GHz yielded information on spatial resolution and temperature sensitivity. Discussion is devoted to potential capabilities and limitations of this remote-sensing approach in more complicated situations.

/pdf/on-the-possible-use-of-microwave-active-imaging-for-remote-4idb3s2fhs.pdf

On the Possible Use of Microwave-Active Imaging for Remote Thermal Sensing

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

A breast tumor is visible by a passive microwave radiometer if it changes the radiometric output of a healthy breast to an extent that overcomes the radiometric resolution for the given sensing antenna and integration time. We modeled breast temperature by the standard Pennes equation using thermal parameters found in the literature for normal and cancerous breast tissue. An apparent thermal volume and its dependence on blood perfusion have been estimated. The radiometric weighting function has been evaluated as a function of the size of a contacting antenna modeled as an aperture antenna. For comparison with the radiometric resolution, the difference signal between the outputs in the presence of a lesion and in its absence has been evaluated for different tumor sizes and depths. The results of the numerical analysis show that this difference signal depends on the average over-temperature in the lesion times the heating efficiency, given by the fraction of power delivered to the tumor when the antenna radiates onto the breast in active modality. A tumor of 6 mm (10 mm) diameter is visible by a 0.1 K radiometer and a 3 cm aperture antenna when it is not deeper than 1.2 cm (2.8 cm) under the assumption of ideal radiometer and antenna.

Modeling the Visibility of Breast Malignancy by a Microwave Radiometer

In the treatment of cancer, microwave hyperthermia has been established as an efficient adjunctive procedure to radiation therapy and chemotherapy. Wider acceptance of this method awaits schemes to measure volumetric temperatures noninvasively in human tissue for control of the heating process. This effort describes the design and performance of a new microstrip applicator intended for homogeneous heating of superficial tissue while at the same time monitoring temperature of the underlying tissue by noninvasive radiometric sensing of black-body radiation from the heated volume. Radiometric capabilities are assessed in terms of accuracy of up to six measured brightness temperatures applied in an inversion algorithm from which one-dimensional depth temperature profiles are generated. Based on radiometric signals recorded over the 1-4-GHz range, the temperature accuracy determined from statistical analysis of 200 realizations of the process is better than /spl plusmn/0.2/spl deg/C to a depth of 5 cm in phantom. Aperture heating uniformity is assessed with electric field scans in a homogeneous muscle phantom. As long as sufficiently thin (< 5 mm) water boli are used, SAR distributions at 1-cm depth in phantom extends effectively just outside the aperture perimeter, making this microstrip antenna an excellent building block element of larger multi-antenna array applicators.

Multifrequency radiometric determination of temperature profiles in a lossy homogeneous phantom using a dual-mode antenna with integral water bolus

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.

Microwave systems combining microwave heating generators (434, 915 or 2450 MHz) with microwave radiometers (1-2 GHz or 2-4 GHz) have been used for two years in hyperthermia therapy Technical aspects (generator, radiometer, applicator), experiments and first clinical results are detailed

Microwave Hyperthermia Controlled by Microwave Radiometry: Technical Aspects and First Clinical Results

We present here experiments and clinical results obtained with microwave systems combining microwave local heating (at IGHz and 2.45GHz) and microwave thermography in the 2-4GHz frequency range. A radiofrequency hyperthermia apparatus (13.56MHz) has also been associated with the same 2-4GHz microwave radiometer to be used as complementary process for temperature control in clinical hyperthermia tumor treatment; obtained clinical results are discussed.

Microwave (1GHz and 2.45GHz) and Radiofrequency (13.56MHz) Hyperthermia Monitored by Microwave Thermograpmy

Previous feasibility experiments have indicated the possibility of achieving microwave local heating and microwave thermography with the same system.1,2 This combined process is now available for measurement and control of the local increase of temperature in hyperthermia therapy. Several systems have been built according to this principle3,4,5 which are intended for biomedical applications.

Progress in Microwave and Radiofrequency Hyperthermia Controlled by Microwave Thermography

The microwave and thermal performance of a microwave interstitial hyperthermia system with temperature controlled by microwave radiometry is discussed. Miniature coaxial antennas have been designed for heating at 915 MHz or 434 MHz and for radiometric temperature measurements around 3 GHz and 9 GHz. The feasibility of this system has been demonstrated by experiments on an acrylamide phantom, and the first clinical results are promising. >

http://ieeexplore.ieee.org/iel2/846/3080/00096132.pdf

M. Plancot

Papers

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

Microwave Hyperthermia Controlled by Microwave Radiometry: Technical Aspects and First Clinical Results

Microwave (1GHz and 2.45GHz) and Radiofrequency (13.56MHz) Hyperthermia Monitored by Microwave Thermograpmy

Progress in Microwave and Radiofrequency Hyperthermia Controlled by Microwave Thermography

Microwave interstitial hyperthermia controlled by microwave radiometry: technical aspects, animal experiments and first clinical results