By Topic

Microwave Theory and Techniques, IEEE Transactions on

Issue 5 • Date May 1986

Filter Results

Displaying Results 1 - 25 of 34
  • [Front cover - May 1986 [T-MTT]]

    Page(s): f1 - f2
    Save to Project icon | Request Permissions | PDF file iconPDF (184 KB)  
    Freely Available from IEEE
  • Foreword (May 1986 [T-MTT])

    Page(s): 481 - 483
    Save to Project icon | Request Permissions | PDF file iconPDF (352 KB)  
    Freely Available from IEEE
  • Discussion of Capabilities of Microwave Phased Arrays for Hyperthermia Treatment of Neck Tumors

    Page(s): 495 - 501
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (884 KB)  

    The power deposition capabilities of phased arrays are investigated by means of numericaf modeling. Integral formulation and gradient conjugate techniques have been used to calculate the power deposited by complete or limited annular arrays in cylindrical neck cross sections. Comparisons with the power deposition patterns obtained by means of other heating modalities (RF capacitive electrodes, single microwave applicator or nonphased arrays) show that, even with a moderate number of elements, phased arrays are expected to provide better uniformity and larger penetration depths although improvements offered by phased arrays largely depend on the possibility to conveniently check the initial amplitude/phase adjustment of the array elements. Some existing and potential control procedures are addressed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Patent Abstracts (May 1986 [T-MTT])

    Page(s): 649 - 652
    Save to Project icon | Request Permissions | PDF file iconPDF (350 KB)  
    Freely Available from IEEE
  • Call for Papers (May 1986 [T-MTT])

    Page(s): 653
    Save to Project icon | Request Permissions | PDF file iconPDF (70 KB)  
    Freely Available from IEEE
  • Membership application

    Page(s): 654
    Save to Project icon | Request Permissions | PDF file iconPDF (94 KB)  
    Freely Available from IEEE
  • IEEE Press Books [advertisement]

    Page(s): 655
    Save to Project icon | Request Permissions | PDF file iconPDF (149 KB)  
    Freely Available from IEEE
  • IEEE Finding Your Way [advertisement]

    Page(s): 656
    Save to Project icon | Request Permissions | PDF file iconPDF (60 KB)  
    Freely Available from IEEE
  • [Back cover - May 1986 [T-MTT]]

    Page(s): b1 - b2
    Save to Project icon | Request Permissions | PDF file iconPDF (129 KB)  
    Freely Available from IEEE
  • Optimization of Simulated Two-Dimensional Temperature Distributions Induced by Multiple Electromagnetic Applicators

    Page(s): 589 - 596
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1352 KB)  

    A computer simulation to calculate transient temperature distributions in realistic cross sections of the human body is described. In the simulation, the therapeutic effect of hyperthermia administration is maximized by optimum use of the electromagnetic applicators. The time-dependent mathematical optimum for the levels of energy going to the applicators as well as for the waterbolus separating the applicators from the patients is computed. Among other applications, this modeling is useful for predicting limitations to certain types of hypertherrnia systems, and has the potential for realistic computer-aided therapy planning. As an example, the treatment planning for a tumor in the lower limb is given in the case of incoherent sources. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Control of the SAR Pattern Within an Interstitial Microwave Array through Variation of Antenna Driving Phase

    Page(s): 568 - 571
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    The interstitial microwave antenna-array hyperthermia (IMAAH) system produces a pattern of specific absorption rate (SAR) that is nonuniform within a 2-cm square array driven in phase at 915 MHz. Theory and experiment show that the point of phase coherence (maximum SAR) can be shifted to a point where the SAR is small by changing the antenna driving phases. Rapid shifting makes the time-average SAR more uniform in the direction perpendicular to the antennas. In 95 percent of the antenna junction plane, the time-average SAR is constant within 10 percent. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Localized Hyperthermia with Electromagnetic Arrays and the Leaky-Wave Troughguide Applicator

    Page(s): 636 - 643
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    Noninvasive microwave hyperthermia is an attractive cancer treatment modality. Understanding the advantages and limitations of focusing are vital for the practical implementations of electromagnetic heating of deep tumors. These, as well as the important issues of tissue coupling and proper choices of polarization and frequency are herein examined. An optimal theoretical source distribution and an applicator design that approximates this distribution are discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optimal Temperature Control with Phased Array Hyperthermia System

    Page(s): 597 - 603
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    A strategy for controlling the temperature distribution in tissue, irradiated by a phased array of RF applicators, described. Using the amptitudes and relative phases from the individual applicators as control inputs, feedback control is established from a corresponding number of measured tissue temperatures. Optimal control theory based on a state-space model of the thermal process is used for designing the multi-variable self-toning controller. Simulations of the two-dimensional temperature distribution in cylindrical homogeneous muscle tissue indicate that it is possible to place a temperature maximum near a given point and to maintain therapeutic temperatures in a specified tumor area while the temperatures in the surrounding tissue are lower. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • 915-MHz Phased-Array System for Treating Tumors in Cylindrical Structures

    Page(s): 502 - 507
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (800 KB)  

    A phased-array 915-MHz microwave system consisting of four 13x13 cm square applicators was constructed and tested for its design in heating both deep and superficial tumors in cylindrical structures such as the upper and lower extremities or neck. Since each applicator produced SAR patterns in cylindrical phantoms in a plane through the array similar to those produced by a plane wave, a theoretical analysis of the SAR patterns due to the superposition of four plane waves incident on a cyIindrical tissue was done. By altering the orientation of the E-field (either parallel or perpendicular to the axis of the cylinder), as well as the phase and amplitude of the incident waves, various distinct SAR patterns were predicted. Thermograms used to experimentally verify the SAR patterns produced by the four applicators showed similar results with those predicted by the plane-wave analysis. A patient with recurrent melanomas on a lower leg was subjected to a clinical trial of hyperthermia in which high tissue temperatures were produced by utilizing two sets of the phased-array system in series. A therapeutic temperature of 43°C in tumor tissues was confirmed by invasive thermometry with high-resistance thermistors. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Phased-Array Design Considerations for Deep Hyperthermia through Layered Tissue

    Page(s): 526 - 531
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (808 KB)  

    Results are presented which demonstrate localized heating at depth, by a phased array in a homogeneous thorax phantom and the problems caused by a more realistic case of a layered tissue equivalent phantom. A phased array of contacting radiators is proposed for overcoming the difficulty of selective heating within the body cavity caused primarily by the muscle layer. The field from one aperture radiator in contact with layered tissue is predicted by a planar spectral diffraction algorithm incorporating transmission and reflection operations on the plane wave spectrum. This prediction process is validated by experimental results. The algorithm enables the prediction of a minimum number of phased contacting radiators required for selective heating within lung tissue through fat and muscle layers at 2.45 GHz, and provides a guide for the design requirements of a multiapplicator system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Theoretical Analysis and Clinical Demonstration of the Effect of Power Pattern Control Using the Annular Phased-Array Hyperthermia System

    Page(s): 514 - 519
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    The phase and amplitude control of power deposition patterns for the BSD Annnlar Phased Array (APA) has been theoretically analyzed at a frequency of 60 MHz. Absorbed power patterns in simple circular cross-sectional cylindrical dielectric structures were studied first to compare with published experimental results. Models based on computerized tomography (CT) scans from the pelvic region have been used for predicting the specific absorption rate (SAR) patterns in patients. Significant changes were observed with phase changes of 30° and relative amplitude changes of 20 percent. The theoretical predictions qualitatively agree with the experimental results reported for simple phantoms. It is also shown that these techniques result in a better control of the SAR patterns and thus more effective heating of tumors situated eccentrically within the pelvis, which we have confirmed in clinical treatments. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Absorbed Power Distributions from Coherent Microwave Arrays for Localized Hyperthermia

    Page(s): 484 - 489
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    Absurbed power distributions in a homogeneous muscle-like tissue due to a planar coherent array consisting of 16 small direct contact applicators at 434 and 915 MHz are calculated, assuming various relative phases and amplitudes are compared with that of a single aperture source at the same frequency with the same overall dimensions. The array applicator may offer improvement in field size or, when focused, a small improvement in penetration, but in practice the performance is very dependent upon bolus thickness. An additional advantage of the array applicator is the ability to modify absorbed power distributions during use by changing the amplitudes of individual applicators. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Large Waveguide Applicator for Deep Regional Hyperthermia

    Page(s): 644 - 648
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    A large waveguide applicator is proposed for deep regional hyperthermia, where a part of a patient's body is exposed to the TE10 -mode waves in the rectangular waveguide through the holes made to fit the body cross section in the broad walls. The electric field and the specific absorption rate distribution produced by the applicator in a realistic model of a human body cross section calculated by a two-dimensional (2-D) numerical method are given. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Concentric-Ring and Sector-Vortex Phased-Array Applicators for Ultrasound Hyperthermia

    Page(s): 542 - 551
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1432 KB)  

    Concentric-ring phased arrays subdivided into sectors (radial slices) can, with appropriate phasing, produce power absorption patterns useful for hyperthermia cancer therapy. The ability of a concentric-ring array to move a focal region along the central axis of the transducer is well known. Less well known is the ability of such an array to produce variable diameter annular (or ring) focal regions. Such focal rings can be effective in heating some tumors if directed around the tumor periphery. These focal rings have been produced in the past by fixed annular focus lenses, or effectively by mechanical scanning of "point" focus ultrasonic transducers. Production of these focal rings by a concentric-ring phased array has the advantage of allowing the focal ring diameter and focal length to be easily changed and scanned by phasing providing much greater heating flexibility. However, under some conditions such arrays produce very large secondary focus effects along the central axis of the amay. Concentric-ring arrays can also provide only patterns of circular symmetry. These problems can be partially solved by dividing the disk of the array into sectors. By appropriate phasing of the sectors, the intensity along the central axis can be greatly reduced. Moreover, appropriate phasing of the rings and sectors can produce patterns that are circularly asymmetric. By controlling these asymmetries, nonspherical tumors can be heated more optimally. Power absorption patterns in Iossy media for this class of applicators are analyzed numerically allowing a quantitative evaluation of both advantages and limitations of this approach. A thermal model based on the bioheat equation is also used to predict temperature distributions in volumes where important thermal parameters, particularly blood flow, are varied. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Low-Frequency RF Twin-Dipole Applicator for Intermediate Depth Hyperthermia

    Page(s): 612 - 619
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1016 KB)  

    In studies on heating deep-seated tumors, various attempts have been made to develop radiofrequency applicators and to confine the controlled volumes into limited sizes at variable useful depths. Results of the present investigation show that the conduction-current mechanism dominates the heating with magnetic dipoles working at frequencies as low as 27 MHz, and that two single-magnetic dipoles forming a loosely coupled pair (twin-dipole applicator) fed by low-frequency, in-phase currents, give a better performance than a single dipole of the same size, due to the phase coherence of the superimposing fields. A number of single-dipole and twin-dipole applicator working at 27 MHz have been developed and given the fundamental tests on phantoms simulating muscle and fat tissues. The results obtained show the feasibility of the proposed applicator to produce a penetration depth up to 7 cm and a power deposition pattern showing a well-defined maximum, which may undergo a controlled shift of a few centimeters in depth. Moreover, the surface overheating may be easily controlled. A circuit design is described that improves the matching and the uniformity of the power deposition pattern. A preliminary calculation in the quasi-static-fields approximation of the electric field induced by the twin-dipole applicator in air is also described. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Predictive-Adaptive, Multipoint Feedback Controller for Local Heat Therapy of Solid Tumors

    Page(s): 604 - 611
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (784 KB)  

    Uniform heating of tumor tissue to therapeutic temperatures without damaging surrounding normal tissue is required for optimal local heat therapy of cancer. This paper describes an algorithm for on-line computer control that will allow the therapist to minimize the standard deviation of measured intratumoral temperatures. The method is applicable to systems incorporating multiple surface and/or interstitial applicators delivering microwave, radiofrequency, or ultrasonic power and operating under control of a small computer. The essential element is a novel predictive-adaptive control algorithm that infers relevant thermal parameters from the responses of multiple temperature sensors as each of the power applicators is briefly turned off. Applied power and effective perfusion are estimated from transient slope changes of the temperature-time curves for each sensor. By substituting these values into a system of linear equations derived from the bio-heat transfer equation, the small computer can calculate the optimal allocation of power among the various applicators ("knob settings") to generate most uniform intratumoral temperature distribution with the desired mean, or minimum, tumor temperature. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Mini-Annular Phased Array for Limb Hyperthermia

    Page(s): 508 - 513
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB)  

    The design concepts of a thin-shell cylindrical or annular phased-array of conformal strip radiators is shown to be suitable for deep heating of phantoms simulating the limbs of the human body. The Mini-Annular Phased Array (MAPA) is presently under clinical investigation for treatment of cancer of the limbs at a limited number of institutions. The effect of frequency and tissue conductivity is shown under simulated conditions for a few sample power-density patterns illustrating the deep focusing of the radiated EM fields. These are compared to a numerical model pattern which can be used to estimate the patterns in varying diameter limbs. The effect of offsetting the limb within the array to steer pattern of heat deposition has also been shown to produce desirable asymmetrical patterns. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An Optimal Excitation Method in Multi-Applicator Systems for Forming a Hot Zone Inside the Human Body

    Page(s): 532 - 538
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (816 KB)  

    A method is proposed for determining the excitation amplitude and phase of each applicator in electromagnetic multi-applicator systems for forming a narrow high temperature zone inside the human body. The principal advantage of this method for determining the optimal amplitudes and phases is its simplicity and reasonableness. The general principle is explained by using the example of an elliptical body region, heated by several line current sources placed outside the body. Numerical examples are presented for the case where a human abdominal region composed of muscular and spinal layers surrounded by a cooling water layer is excited by several line sources at 40.68 MHz. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Phase-Controlled Circular Array Heating Equipment for Deep-Seated Tumors: Preliminary Experiments

    Page(s): 520 - 525
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    This paper presents some preliminary results on the development of a circular phased-array equipment for heating deep-seated tumors. It is shown that radiators having sharp directivity are needed to realize excellent focusing of SAR. Moreover, moment method calculations indicate that linearly polarized helical radiators inversely wound with double wires possess the desired directivity and the near field pattern. Field patterns were measured in phantom (plastic cylinders containing saline water) with a circular array formed by four pairs of azimuthally positioned radiators. Excellent focusing of SAR was observed. The ratio of valley to peak value was 0.74. Steering of SAR maximum by phase control was observed and the distance of movement coincided with that estimated from phase variation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Experimental Investigation of a Retro-Focusing Microwave Hyperthermia Applicator: Conjugate-Field Matching Scheme

    Page(s): 490 - 494
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    A seven-element array of dielectric-loaded open-ended waveguides totally immersed in a water tank is tested as a possible hyperthermia applicator. Experimental results show a substantial increase in focusing ability of the array if a conjugate matching scheme is used to adjust the phase of each element excitation. This scheme could offer a practical procedure for operating a focused hyperthermia applicator in a living patient. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

The IEEE Transactions on Microwave Theory and Techniques focuses on that part of engineering and theory associated with microwave/millimeter-wave components, devices, circuits, and systems involving the generation, modulation, demodulation, control, transmission, and detection of microwave signals. This includes scientific, technical, and industrial, activities. Microwave theory and techniques relates to electromagnetic waves usually in the frequency region between a few MHz and a THz; other spectral regions and wave types are included within the scope of the Society whenever basic microwave theory and techniques can yield useful results. Generally, this occurs in the theory of wave propagation in structures with dimensions comparable to a wavelength, and in the related techniques for analysis and design..

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Dominique Schreurs
Dominique.Schreurs@ieee.org

Editor-in-Chief
Jenshan Lin
jenshan@ieee.org