David Vrba

Focused ultrasound for treatment of bone tumours

Abstract Purpose: Focused ultrasound (FUS) is a modality with rapidly expanding applications across the field of medicine. Treatment of bone lesions with FUS including both benign and malignant tumours has been an active area of investigation. Recently, as a result of a successful phase III trial, magnetic resonance-guided FUS is now a standardised option for treatment of painful bone metastases. This report reviews the clinical applications amenable to treatment with FUS and provides background on FUS and image guidance techniques, results of clinical studies, and future directions. Methods: A comprehensive literature search and review of abstracts presented at the recently completed fourth International Focused Ultrasound Symposium was performed. Case reports and older publications revisited in more recent studies were excluded. For clinical studies that extend beyond bone tumours, only the data regarding bone tumours are presented. Results: Fifteen studies assessing the use of focused ultrasound in treatment of primary benign bone tumours, primary malignant tumours, and metastastic tumours meeting the search criteria were identified. For these clinical studies the responders group varied within 91–100%, 85–87% and 64–94%, respectively. Major complications were reported in the ranges 0%, 0–28% and 0–4% for primary benign, malignant and metastatic tumours, respectively. Conclusions: Image-guided FUS is both safe and effective in the treatment of primary and secondary tumours. Additional phase III trials are warranted to more fully define the role of FUS in treatment of both benign and malignant bone tumours.

Novel Applicators for Local Microwave Hyperthermia Based on Zeroth-Order Mode Resonator Metamaterial

It is demonstrated that a theory of zero-order mode resonator (ZOR) metamaterial (MTM) structure can be used for the development of a novel class of applicators for microwave thermotherapy, for example, for hyperthermia in cancer treatment or for physiotherapy. The main idea of creating such an applicator is to generate and radiate a plane electromagnetic (EM) wave into the treated biological tissue, at least in a certain extent. The main aim of this paper is to investigate whether an EM wave generated by ZOR MTM structure and emitted into the biological tissue can produce a homogeneous SAR distribution in the planes parallel to the applicator aperture and achieve a penetration depth approaching the theoretical limit represented by SAR distribution and penetration depth of an ideal EM plane wave. EM field distribution inside a virtual phantom of the treated region generated by the applicator that is based on the proposed ZOR MTM principle is investigated using a well-proven full-wave commercial simulation tool. The proposed applicator type shows both a low unwanted leaked electromagnetic field and a fairly homogeneous electric field in its aperture as well as in the virtual phantom of the treated region.

Metamaterial Antenna Arrays for Improved Uniformity of Microwave Hyperthermia Treatments

2 Abstract |Current microwave hyperthermia applicators are not well suited for uniform heating of large tissue regions. The objective of this research is to identify an optimal microwave antenna array for clinical use in hyperthermia treatment of cancer. For this aim we present a novel 434 MHz applicator design based on a metamaterial zeroth order mode resonator, which is used to build larger array congurations. These applicators are designed to effectively heat large areas extending deep below the body surface and in this work they are characterized with numerical simulations in a homogenous muscle tissue model. Their performance is evaluated using three metrics: radiation pattern-based Effective Field Size (EFS), temperature distribution-bas Therapeutic Thermal Area (TTA), and Therapeutic Thermal Volume (TTV) reaching 41{45 ◦ C. For 2 � 2 and 2 � 3 array congurations, the EFS reaching > 25% of maximum SAR in the 3.5 cm deep plane is 100% and 91% of the array aperture area, respectively. The corresponding TTA for these arrays is 95% and 86%, respectively; and the TTV attaining > 41 ◦ C is over 85% of the aperture area to a depth of over 3 cm in muscle, using

Improvement of the Radiation Efficiency of the Metamaterial Zero-Order Resonator Antenna

In this paper a technique for improvement of radiation efficiency of metamaterial zero order antenna based on increasing of vertical antenna height is presented. Comparison of the two microstrip line implementation of the zero order resonator (ZOR) antennas with different height over ground plane is demonstrated. Improved ZOR antenna exhibit 75% efficiency compared to 10% of the reference antenna.

Input Resistance of Electrically Short Not-Too-Closely Spaced Multielement Monopoles With Uniform Current Distribution

In this letter, we derive an analytical expression for the mutual resistance of two electrically short not-too-closely spaced dipoles with uniform current distribution based on an induced electromotive forces method. We go on to apply the relations for folded dipoles for an investigation of the input resistance of a short multielement dipole arrangement. It is shown that the factor ranging from <i>N</i>^1.77 to <i>N</i>^1.97 takes into account the increase in input resistance arising from the mutual coupling of <i>N</i>={2,3,4} dipoles when they are spaced within the range from λ₀/20 to λ₀/5. Thus, even a larger distance between the dipoles than λ₀/20 , which is usually considered if the term <i>N</i>² is used, still leads to a significant improvement in radiation resistance. To verify the proposed concept, we compared the results provided by the electromagnetic (EM) simulation and by measurements on the prototype of an electrically small, winding-connected three-element monopole antenna, which occupies a cylindrical geometry with the diameter of the base equal to λ₀/10 and the monopole height equal to λ₀/20. The measured bandwidth for VSWR=2 corresponds to the quality factor, which is only 2.2 higher than the principal Gustafsson bound for cylindrical geometry with vertical polarization.

Efficiency Treatment of Composite Right/Left-Handed TL Zeroth-Order Resonator Antenna

Antenna efficiency of zeroth-order resonator (ZOR) antenna implemented in composite right/left-handed transmission line (CRLH TL) microstrip structure is treated by method of moment simulator IE3D. Radiation is investigated from individual portions of the antenna structure according to calculated amplitude of surface current density. Dominantly radiating regions are identified, geometrically emphasized, and efficiency improved version of CRLH ZOR antenna is designed, realized, measured and compared with initial design. Improvement of simulation antenna efficiency from 10 to 75% and 4x increased measured gain at design ZOR frequency has been found.

Phantoms for Development of Microwave Sensors for Noninvasive Blood Glucose Monitoring

A suitability of two different liquid phantoms of blood-glucose solutions as phantoms for development of microwave sensors for noninvasive blood glucose monitoring is compared. The two phantoms are physiological saline-glucose and pig blood-glucose solutions. For this purpose a simple microwave sensor is developed for in vitro monitoring of blood glucose levels. The sensor consists of a microstrip antenna and of a small rectangular container on the top of the antenna. The container is filled with one of the liquid phantoms. Both phantoms with different glucose concentrations ranging from 0 to 500 mg/dL are considered. Dependence of sensor’s resonant frequency on glucose concentration of LUTs is both estimated by aid of numerical simulations and measured. The results are discussed and compared with some results reported in the literature.

Numerical investigation of novel microwave applicators based on zero-order mode resonance for hyperthermia treatment of cancer

In this paper, three novel microwave applicator prototypes based on zero-order mode resonators are proposed for use in hyperthermia treatment of cancer. The ability of all three applicators to homogenously irradiate muscle tissue-equivalent phantoms is demonstrated with results of numerical simulations, and relative performance of the applicators is compared.

Microwave Medical Imaging and Diagnostics

Future trends in medical applications of microwave technique and technology can be seen in development of new diagnostic and imaging methods based on high frequency EM field. A significant importance for the future can be identified for the following methods: Microwave tomography, Microwave radiometry, Measurement of complex permittivity, Imaging in the Terahertz waves band and Microwave diagnostic radars.

Metamaterial Sensor for Microwave Non-invasive Blood Glucose Monitoring

In our previous paper, a metamaterial and microstrip transmission line sensors for non-invasive blood glucose level monitoring were designed. In this paper two different models of dielectric properties of blood glucose solutions are used to evaluate sensors’ sensitivity by means of numerical simulations. Model A is adopted from professional literature and the model B was created by our group using information about dielectric properties of blood plasma-glucose solutions, recently published dielectric properties of red blood cell cytoplasm-glucose solutions and an electromagnetic mixing formula. Both sensors shows smaller sensitivity for the model B than for the model A. Due to non-linear dependency of dielectric properties on glucose concentration predicted by model B a lower sensitivity for high glucose concentrations was observed. The metamaterial sensor shows approximately 10-times higher sensitivity than the microstrip sensor of the same length.