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Application of Microwaves in Medicine, IEE Colloquium on

Date 28 Feb 1995

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Displaying Results 1 - 12 of 12
  • Investigations of the behaviour of microwave thermography antennas when coupled to layered tissue regions

    Page(s): 7/1 - 7/5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    Test structures providing realistic simulations of the layering of body tissues have been used to investigate the radiometric response to be expected from common skin-fat-muscle regions. The electric field distributions in these models have been measured by the nonresonant perturbation method at 3.25 GHz, the mid-frequency of the range used for the radiometric measurements. Investigations have been made of the response patterns of dielectric loaded rectangular TE10-mode and cylindrical TEll-mode radiometry antennas coupled to uniform media and models of layered tissue regions. Sucrose solutions of 30% to 50% concentration have been used for skin and muscle simulation. At 3 GHz sucrose solutions conveniently provide dielectric properties close to those of medium to high water content tissues. Sheets of thermo-compressed fabric-phenolic resin insulating material have been used for low permittivity fat layer simulation. These provide a relative permittivity of 3.7 and a loss factor of 0.24. Measurements have also been made using porcine skin-fat layers, with the electric field distribution being measured in sucrose solution below the fat. The field perturbers used are hollow glass spheres of about 2 mm diameter, and low permittivity dielectric sheets 1 to 2 mm thick. A linear heterodyne reflectometer is used to measure the amplitude and phase of the reflection coefficient produced by the presence of the perturber in the fields of the test structure View full abstract»

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  • Applications of microwave active imaging in medicine: past and future

    Page(s): 3/1 - 3/5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    Presents a review of past research efforts devoted to the development of microwave imaging techniques for biomedical applications. After explaining basic principles and different approaches of this new imaging modality, some examples are used to illustrate some promising features and to explain relative disappointment resulting from ten years of investigations devoted to phantom experiments and in vivo assessments. Then, microwave active imaging is considered under a more prospective point of view. Expected developments and future trends are discussed View full abstract»

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  • The current status of microwave induced hyperthermia and radiotherapy for the treatment of recurrent breast cancer

    Page(s): 1/1 - 1/6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    Hyperthermia involves the use of heat as a technique for the treatment of cancer patients. It has been most often employed with radiotherapy, and more recently, with chemotherapy. The purposes of this paper are to highlight some electromagnetic techniques that have proved useful in clinical practice and to present a summary of the results of a clinical trial involving microwave induced hyperthermia and radiotherapy in the treatment of breast cancer carried out at the Hammersmith Hospital, London. The results of this trial are placed in context with other recent results. Finally, a summary of the areas where further technical development is likely to lead to improvements in clinical practice is presented View full abstract»

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  • FDTD modelling for microwave dosimetry and thermography

    Page(s): 11/1 - 11/6
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    The work on the canonical problems to date has demonstrated how the FDTD code can be developed to investigate both the interaction of radiofrequency waves with biological-like structures and the characteristics of the sources themselves. Although the canonical problems are but the first step in the evaluation of dosimetry in the head resulting from mobile telecommunications, the SAR distributions produced by various modelling techniques show promising similarities and it is planned to validate them experimentally in the future using an inhomogeneous head shaped phantom. The ability to evaluate characteristics of EM sources will be of considerable value in the authors' other work involving the simulation of RF fields produced by the coils used in magnetic resonance Imaging. It has also been shown that the FDTD method can be used to develop an understanding of the relationship between the power received at a radiometer and the microwave (thermal) radiation sources within the body under investigation. The advantages of using the FDTD approach to study radiometry include the ability to model accurately the characteristics of the radiometer, particularly in the near field region, and to incorporate complex biological bodies into the model View full abstract»

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  • Microwave forceps-the use of microwave energy to weld tissue

    Page(s): 13/1 - 13/6
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    The novel concept of microwave forceps is introduced, and some of the authors' preliminary findings presented. The authors feel that it is far too early to claim that this approach to sealing blood vessels will be ultimately successful, but they think that the outlook is promising. Certainly, the authors are sufficiently encouraged to propose continuation of the work View full abstract»

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  • Influence of the permittivity of breast tissues on the robustness of microwave radiometric imaging

    Page(s): 6/1 - 6/5
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    Microwave radiometric imaging (MWI) is a passive method of thermal investigation which allows the observation of subcutaneous thermal gradient. Recently, the authors have defined a method of inversion by deconvolution and Wiener filtering, which leads to a consequent improvement of the spatial resolution in the case of compact thermal structures. One of the applications the authors are considering is the detection of possible thermal gradients associated to nonpalpable breast tumors. For this reason, they have tested this method for different cases of known permittivities of breast tissues. The conclusion of this simulation shows the robustness of the inversion process even if the permittivity of the tissues is not exactly known. Positive results have been registered in the field using MWI, which are summarised here. Encouraging conclusions have been obtained during a clinical evaluation related to the characterisation (malignancy or benignity) of nonpalpable breast tumors. A new radiometric imaging system is now being built, which allows the acquisition of the radiometric image in a reasonable time interval (an image obtained in four minutes). The spatial resolution of the images is improved by application of deconvolution and Wiener filtering View full abstract»

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  • Modelling of different types of applicators used for microwave hyperthermia based on FDTD method

    Page(s): 5/1 - 5/5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    The authors have developed a two dimensional model based on the finite difference time domain (FDTD) method for the study of interstitial and intracavitary applicators. This model takes into account the different lossy media surrounding the antenna (water, plastic catheter, metallic reflector...) in order to optimise the applicator at heating and radiometric frequencies: computation of the return losses (reflection coefficient) and of the power deposition gives the performances of the applicator and are very useful for thermal dosimetry based on the resolution of the bioheat equation. The theoretical results obtained with the FDTD method have been compared to experimental measurements View full abstract»

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  • Dielectric tissue measurements using a co-axial probe with a quarter-wave choke

    Page(s): 10/1 - 10/6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    As part of a programme to develop combined microwave and thermal computational modelling of body tissue regions, it is necessary to compare thermal conductivity and dieiectric permittivity measurements made on the same tissue samples. This paper is primarily concerned with the design and calibration of a suitable co-axial probe, and the dielectric measurements made with this probe. These permittivity measurements are made at 3 GHz, the frequency corresponding to the minimum loss tangent in water, which is the substance whose properties have the greatest influence on the overall thermal and dielectric properties of body tissue. Permittivities of a variety of animal tissues were measured. Porcine tissues form the greatest category as pork most closely resembles human tissue in constitution. A table listing selected average results where the standard deviation is simply that of the scattering is given. This data is comparable with that reported in Brady et al. (1981) and Burdette et al. (1980). Although the reported data was taken at 37 °C rather than 21-25 °C, tests have shown that the difference incurred is less than the calibration error reported View full abstract»

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  • Medical microwave radiometry and its clinical applications

    Page(s): 2/1 - 2/5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    In clinical medicine, microwave radiometry is used to obtain information about internal body temperature patterns by the measurement of part of the centimetric wavelength component of of the natural thermal radiation from the tissues of the body. In appropriate circumstances, knowledge of such thermal patterns can assist clinical disease detection and diagnosis, and may have a role in the monitoring of therapeutic processes. The technique has important practical advantages for clinical medical applications through being noninvasive and inherently completely safe. The author discusses the development, principal applications and future development of the technique View full abstract»

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  • Capabilities and limitations of electromagnetic hyperthermia applicators

    Page(s): 12/1 - 12/5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    The heating profiles of different electrically small applicators are shown to be similar and field penetration to be a function of aperture size, frequency and tissue conductivity. Below 100 MHz field penetration of a given applicator is almost independent of low values of conductivity. Single or multiple surface applicators cannot effectively treat deep tumours. It is considered that the practical usefulness of hyperthermia using superficial electromagnetic applicators is limited View full abstract»

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  • Iterative 2D reconstruction algorithms for microwave active imaging systems

    Page(s): 9/1 - 9/4
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    The definition study of a new microwave scanner using the most recent quantitative reconstruction algorithms has been performed experimentally on a true scale model in the presence of phantoms simulating a whole human body configuration. Reconstruction of such a biological cross-section inside a 60 cm cavity filled with water is possible using an operating frequency of 434 MHz. These encouraging results justify to consider the next step consisting of studying and starting the development of a prototype using a multiplexed antenna array instead of the mechanical rotating system. This step is very important for two major reasons. First, the acquisition time will be reduced to only a few seconds, making possible real trials inside the hyperthermic applicator. Second, the elimination of any mechanical movement will allow to avoid any positioning error; such errors have been shown to introduce nonnegligible perturbations on the reconstructions. Simulation studies have shown that the reconstruction of a whole body with a cell size of 1 cm will be possible by using an array of 64 transmitters/receivers elements View full abstract»

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  • Recent investigations of combined thermal and microwave modelling of body regions for interpretation of microwave thermographic images

    Page(s): 8/1 - 8/6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    It is considered that the physiological heat supply or equivalent perfusion estimated for a tissue region using environmental, oral, microwave and infra-red surface temperature and combined thermal and microwave modelling may provide a clinically useful objective measure of disease activity for the larger joints of the human body. Good agreement has been found between modelled and measured values for the knee and quadriceps regions and it can be concluded that the tissue heat supply is primarily due to arterial blood perfusion. Microwave thermography may be useful in the evaluation of patients suffering from rheumatoid arthritis in their wrist and finger joints View full abstract»

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