A. Vera

Improved Thermal Ablation Efficacy Using Magnetic Nanoparticles: a Study in Tumor Phantoms

Magnetic heating used for inducing hyperthermia and thermal ablation is particularly promising in the treatment of cancer provided that the therapeutic temperature is kept constant during the treatment time throughout the targeted tissue and the healthy surrounding tissues are maintained at a safe temperature. The present study shows the temperature increment produced by different concentrations of magnetic nanoparticles (ferrofluid and magnetoliposomes) inside a phantom, after irradiating tissuemimicking materials (phantoms)with a minimally invasive coaxial antenna working at a frequency of 2.45GHz. This frequency was chosen because maximum dielectric loss of water molecules begins at 2.4GHz and because this is an ISM (industrial, scientific and medical) frequency. Temperature sensors were placed inside and outside the tumor phantom to assess the focusing effect of heat produced by nanoparticles. Results have shown that the temperature increments depend on the nanoparticles concentration. In this way, a temperature increment of more than 56◦C was obtained with a ferrofluid concentration of 13.2 mg/mL, whereas the increment in the reference phantom was only of ≈ 21◦C. Concerning the magnetoliposomes, the temperature achieved was similar to that obtained with the ferrofluid but at a lesser concentration of nanoparticles. These results Received 1 February 2012, Accepted 27 March 2012, Scheduled 30 May 2012 * Corresponding author: Joan Estelrich (joanestelrich@ub.edu). 230 Garcia-Jimeno et al. demonstrate that it is possible to achieve higher temperatures and to focus energy where the nanoparticles are located.

Noninvasive Temperature Estimation in Oncology Hyperthermia Using Phase Changes in Pulse–Echo Ultrasonic Signals

An accurate and noninvasive temperature measurement inside phantoms and tissues is important to improve hyperthermia treatment. The use of ultrasonic echo-pulses for this purpose is a promising line of research. In this paper, we propose an alternative method for processing echo-signals received from inner regions in phantoms. Ultrasonic estimation of temperature is carried out using a phase demodulation technique, which gauges the indirect effects in the phase domain of the previously reported time-shifts in the echo position. The potential performance and high sensitivity of this procedure is explained and verified with several simulated examples. Finally, the proposed procedure is applied to the experimental assessment of phase changes with temperature in ultrasonic echoes successively acquired from different milieus. In all cases, the results show good performance and high sensitivity. This is an interesting alternative to measurements in waveforms of the very small delays (nanoseconds) associated with this ultrasonic temperature estimation.

Acoustic field modeling for physiotherapy ultrasound applicators by using approximated functions of measured non-uniform radiation distributions

The strongest therapeutic effects in ultrasonic physiotherapy are mainly produced at the first centimeters, i.e. close to the applicator surface and, in general, only in the near-field zone. The acoustic field produced in practice by this type of transducers differs from the classical models because the vibration distribution on the real transducer surfaces is non-uniform. However, neither models using uniform distribution, nor those using typical non-uniform distribution patterns for the source accurately represent the radiation of this kind of transducers. Although this therapy is widely used and many efforts have been made in experimentally studying the patterns of ultrasound radiation produced during physiotherapy applications (IEC-61689, 1998), additional modeling researches still would be needed in order to achieve improved models giving field patterns closer to the measured ultrasonic results. In this paper, acoustic patterns produced from two source radiation functions are proposed and evaluated for field modeling of physiotherapy applicators. Both the functions are approximations to the pressure distribution measured close to the emitting surface and they are based on the modulation of the classical simply-supported function using either sinusoidal or Bessel-type distributions. The simply-supported function is accounted for the radiator-fixing condition and the modulation function simulates the complex vibration distribution of this kind of transducer. The modulator Bessel function is based on reports about Bessel-type vibration distributions found in piezoelectric disk resonators. The use of a selected sinusoidal segment represents another analytical option for obtaining an approximated behavior of the measured data in a real applicator. Both the field models are implemented using the finite element method (FEM) to obtain the numerical solution of wave equation at each point in the radiated space. The solution is reached by considering axisymmetric radiation in attenuation-free media. The results indicate the viability of applying an adequate model for acoustic field calculation by simulating the radiating distribution on the emitting surface as either sinusoidal or Bessel-modulated functions. Models using both the functions describe reasonably real behaviors, but those based on Bessel functions are better correlated with the measurements. The results for three commercial applicators indicate the possibility of representing, with adequate verisimilitude, the acoustic field radiated by physiotherapy ultrasound transducers using linear combinations of Bessel profiles describing the radiation source.

Measurement of breast - tumor phantom dielectric properties for microwave breast cancer treatment evaluation

Most phantom models do not include distinct definitions of tumor and normal tissue. This article proposes a novel solid breast - tumor phantom for microwave hyperthermia in breast cancer treatment. According to tissue dielectric properties reported, we performed phantom. A Network Analyzer and Dielectric Probe Kit measured dielectric constant and electrical conductivity for both breast normal tissue and tumor phantom. Measurements were through at frequency range from 2 to 3 GHz due microwave operation frequency is usually 2.45 GHz. At 2.45 GHz breast phantom had an electrical conductivity of 0.1304±0.0680 S/m and a dielectric constant of 4.4401 ± 1.2514. At the same frequency, tumor phantom had an electrical conductivity of 2.7015 ± 0.0783 S/m and a dielectric constant of 55.2566 ± 1.1899. The presented results highly correlate with the expected values. Therefore this phantom can be used for microwave hyperthermia in breast cancer treatment and antenna performance analysis and optimization.

Finite element modeling of acoustic field of physiotherapy ultrasonic transducers and the comparison with measurements

This paper presents the modeling of the acoustic field of a physiotherapy ultrasonic transducer by using the finite element method. An ideal emission is presented obtained by using the approach developed by Rayleigh, called “piston in a baffle”. Simulations with FEM also are presented to compare them with the analytical results. The results of the model are also compared to those of the measurements in a physiotherapy transducer. The results show the efficacy of modeling the real transducers with ideal models in relation to the overlapping in the Fresnel zone and the characteristic parameters. A necessity is evident after this analysis: more appropriated models using more real boundary conditions. Results indicate that Fresnel zone is not correctly modeled using the ideal considerations.

Coaxial Double Slot Antenna Design for Interstitial Hyperthermia in Muscle Using a Finite Element Computer Modeling

An axisymmetric finite element method model was employed to demonstrate important techniques in the design of antennas for interstitial hyperthermia. To effectively treat deep-seated tumors, these antennas should produce a highly localized specific absorption rate pattern and be efficient radiators at different generator frequencies. A double slot antenna for interstitial hyperthermia in muscle was designed using COMSOL Multiphysicstrade 3.3. In this paper we propose the optimum power level according with the simulation results.

Design and Preliminary Evaluation of a superficial applicator for hyperthermia with a new coaxially fed antenna: Theoretical models

This paper describes 3 different stages: Modeling, Construction and Preliminary Evaluation of a superficial applicator, with a new coaxially fed antenna, for its use in oncology hyperthermia treatments. Modeling stage was developed by the Finite Element Method, using Maxwell and Bioheat equations; here, antenna dimensions were optimized. In the second stage, the optimized applicator was constructed in aluminum and copper, taking in count results achieved in the modeling stage. Finally, it was characterized for its clinical use. SWR, incident and reflected waves and calorimetric measurements are presented in this paper.

Ultrasonic attenuation in pure water: Comparison between through-transmission and pulse-echo techniques

The ultrasonic attenuation has been estimated by a variety of methods. However, even if the techniques are accurate, the measurement of this parameter is very difficult because it depends on the conditions of the experiment (frequency, temperature, internal structure of the specimen, artifacts, etc.). Attenuation measurements in tri-distilled and degasified water were made by pulse-echo and through-transmission techniques at 1 MHz, 25°C and 19.7°C. Besides the techniques, a micrometer and a scanner system were used to make the displacements. The attenuation coefficient α is been approximated by the exponential behavior of the ultrasonic signal record along 20 cm. Performance of ultrasound in water was analyzed in two zones, near and far lengths. At near zone, α is highly variant, while at far zone, an average α = −0.04417 np/cm is obtained. The purpose of this work is to compare the through-transmission and pulse-echo techniques to obtain the attenuation coefficient in pure water by the approximation of its exponential behavior.

Finite element HIFU transducer acoustic field modeling evaluation with measurements

This paper presents the finite element modeling of the acoustic pressure spatial distribution of a spherically-curved transducer with operation frequency of 1.965 MHz and its comparison with the transducer characterization using a PZTZ44-0400 hydrophone. Concave transducers are only one of the different techniques used to deliver high-intensity focused ultrasound (HIFU) into a target during oncologic treatments in order to provoke tumor ablation. However, the acoustic field characterization for HIFU transducers is made at low power level in order to avoid hydrophone damage, while in therapy high acoustic power is applied. HIFU focus size is usually in the order of mm, making difficult its location during experimentation. Finite element modeling is helpful method to simulate focused ultrasound propagation and interaction in a simulated medium with ultrasonic properties similar to soft tissues. In this work, comparison is made in water as propagation wave medium.

A comparison of direct and pattern recognition control for a two degree-of-freedom above elbow virtual prosthesis

Individuals with a transhumeral amputation have a large functional deficit and require basic functions out of their prosthesis. Myoelectric prostheses have used amplitude control techniques for decades to restore one or two degrees of freedom to these patients. Pattern recognition control has also been investigated for transhumeral amputees, but in recent years, has been more focused on transradial amputees or high-level patients who have received targeted muscle reinnervation. This study seeks to use the most recent advances in pattern recognition control and investigate techniques that could be applied to the majority of the transhumeral amputee population that has not had the reinnervation surgery to determine if pattern recognition systems may provide them with improved control. In this study, able-bodied control subjects demonstrated that highly accurate two degree-of-freedom pattern recognition systems may be trained using four EMG channels. Such systems may be used to better control a prosthesis in real-time when compared to conventional amplitude control with mode switching.