Pegah Takook

Fast analysis of gap waveguides using the characteristic basis function method and the parallel-plate Green's function

The Characteristic Basis Function Method is employed in conjunction with the parallel-plate dyadic Greens function method to obtain the impedance characteristics of electrically large gap-waveguide structures. Numerical results are shown for the groove gap waveguide demonstrating reduced execution times relative to the HFSS software, while the solution accuracy is barely compromised.

Compact self-grounded Bow-Tie antenna design for an UWB phased-array hyperthermia applicator

Abstract Using UWB hyperthermia systems has the potential to improve the heat delivery to deep seated tumours. In this paper, we present a novel self-grounded Bow–Tie antenna design which is to serve as the basis element in a phased-array applicator. The UWB operation in the frequency range of 0.43–1 GHz is achieved by immersing the antenna in a water bolus. The radiation characteristics are improved by appropriate shaping the water bolus and by inclusion of dielectric layers on the top of the radiating arms of the antenna. In order to find the most appropriate design, we use a combination of performance indicators representing the most important attributes of the antenna. These are the UWB impedance matching, the transmission capability and the effective field size. The antenna was constructed and experimentally validated on muscle-like phantom. The measured reflection and transmission coefficients as well as radiation characteristics are in excellent agreement with the simulated results. MR image acquisitions with antenna located inside MR bore indicate a negligible distortion of the images by the antenna itself, which indicates MR compatibility.

A computational study using time reversal focusing for hyperthermia treatment planning

In hyperthermia treatment planning (HTP) the goal is to find the amplitudes and phases of antennas in the applicator to efficiently heat the tumor. To do this prior information regarding tumor characteristics such as the size, position and geometry, in addition to an exact model of the hyperthermia applicator is needed. Based on this information, the optimal frequency of operation can be determined. In this paper the optimum frequency for hyperthermia treatment based on the tumor and applicator characteristics, using time reversal as the focusing technique, is studied. As prior information, we consider tumor size and position, the number of the antennas in the applicator and the frequency characteristics. The obtained optimal frequency range is found using hyperthermia quality indicator values calculated from simulations. We also determine the optimum position of the virtual source in the initial step of the time reversal method to increase the quality of the treatment.

Evaluation of 3D Time-Reversal Focusing Method in Microwave Hyperthermia Treatment: Head and Neck Tumors

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Microwave based diagnostics and treatment in practice

Globally, around 15 million people each year suffer a stroke. Only a small fraction of stroke patients who could benefit from thrombolytic treatment reach diagnosis and treatment in time. To increase this low figure we have developed microwave technology aiming to differentiate hemorrhagic from ischemic stroke patients. The standard method for breast cancer diagnosis today is X-ray mammography. Despite its recognized ability to detect tumors it suffers from some limitations. Neither the false positive nor the false negative detection rates are negligible. An interesting alternative being researched extensively today is microwave tomography. In our current strive to develop a clinical prototype we have found that the most suitable design consists of an antenna array placed in a full 3D pattern. During the last decade clinical studies have demonstrated the ability of microwave hyperthermia to dramatically enhance cancer patient survival. The fundamental challenge is to adequately heat deep-seated tumors while preventing surrounding healthy tissue from undesired heating and damage. We are specifically addressing the challenge to deliver power levels with spatial control, patient treatment planning, and noninvasive temperature measurements.

Performance evaluation of 2 hyperthermia applicators for deep-seated brain tumors

The performance of two hyperthermia applicators in heating deep seated brain tumors is investigated in terms of hyperthermia quality indicators. The antenna elements in both applicators are arranged in a helmet-shape format on a spherical phantom of head. Self grounded bow-tie antennas immersed in conical water containers, are employed as the antenna elements. The first applicator consists of 26 antenna elements placed on a thin water layer over the phantom. We increased the number of antennas to 58 in the second applicator by employing reduced-sized antenna elements. The computed quality indicators at two tumor locations, deeply seated in the head show that the applicator with 58 antennas presents less absorbed power in healthy tissues at higher frequencies. This decrease is more pronounced for the tumor located in the center of the phantom.

Microwave technology in medical diagnostics and treatment

There is a great need for novel diagnostics and treatment tools in todays healthcare. In this paper we describe our development and progress in novel microwave based diagnostics and treatment applications. The target applications are stroke diagnostics, breast cancer detection and microwave hyperthermia.