1,721,005 research outputs found
Exploring 434 MHz phased array for hyperthermia heating of semi-deep targets
No full textThe problem of effective power delivery to a semi-deep tumor by a near-field phased array is addressed with reference to hyperthermia treatments. Phased array are evaluated on the basis of their ability to deliver the largest fraction of the available power from the generators to a target. With this aim, some efficiencies and an array factor are estimated for each cell of the body segment, when that cell is considered as target. The results are presented as color maps of heating efficiency and array factor. A model of tumor is the union of some of these cells. The maps may help in appreciating its heatability by the phased array. Different arrays can thus be numerically experimented to select the one which delivers most power to the tumor. Field polarization is taken into account and loss of efficiency related to polarization mismatch is considered, too. As an example, an array of 8 antennas, operating at 434 MHz, is positioned around a numerical modelling of a human head. The following figures show, for this example,: a) the Array Factor (each pixel of this image shows the Array Factor when the same pixel is the target of the optimization process); b) the polarization status for the Electric field inside the head, when one of the antennas is energized
Phased Arrays Pre-treatment Evaluation in Antitumoral Hyperthermia
No full textThere is general consensus that quality of hyperthermia treatment is a key factor
for clinical effectiveness. The optimal treatment is defined by efficient tumor heating without
patient discomfort by hot spots. Two optimization methods with the constraint on amplifier
nominal power are presented. A voxel-based numerical analysis is performed for 8 dipoles on two
rings, positioned around a head/neck volume within a distilled-water bolus. The optimization
methods are compared on the basis of the maximal absolute power delivered to the target and
other previously defined parameter
Figures of merit and their bounds in radiofrequency heating by phased arrays
No full textPurpose: The problem of effective power delivery to a semi-deep target by a phased array has
been addressed for application to hyperthermia treatment of some tumours in the thorax.
Methods: Three efficiencies have been introduced, which estimate system ability in power
transfer from generators to body, from body to tumour, and from generators to tumour. They
are formulated in terms of a dissipation matrix and an interference matrix. Bounds to achievable
efficiencies are obtained. Further figures of merit have also been introduced. The necessary
mathematics has been developed.
Results: A numerical analysis has been carried out for a partially interdigitated planar array of
resonant dipoles. Results show how the new parameters can be exploited for optimal selection
of the array’s degrees of freedom.
Conclusion: The figures of merit and their bounds allow comparisons between RF heating
devices and provide guidelines to phased array design
A Voxel-Based Approach in Phased-Array Optimization for Microwave Hyperthermia
No full textThe problem of effective power delivery to a deep
target by a near-field phased array has been addressed for
application to oncological hyperthermia. Phased arrays are
evaluated on the basis of their ability to deliver the largest
fraction of the available power from generators to a tumor. Each
voxel of the heated volume was considered as a target, a tumor
being the union of some such voxels. Maps of efficiencies and an
array factor have been produced for a head-neck volume. These
maps may help in appreciating tumor heatability by the phased
array
A Projective Approach to Electromagnetic Propagation in Complex Environments
No full textHigh frequency methods resort to numerical ray tracing
for application to complex environments. A new method based on
the geometrical projection performed by a ray-congruence has been
developed as a preconditioning of the ray tracing procedure. It builds
a visibility tree, i.e., a database, storing information on all possible
ray paths inside a scenario. The method gives a solution to a class of
open problems of ray tracing techniques: ray missing, double (multiple)
counting, termination criterion, calculation upgrade. Other features of
the method are the multipath map and the multipath classification
that allow the user to know the relevance of multipath at any point of
the scenario in advance, before ray-tracing calculation.
The method can be systematically applied to scenarios pertaining
to different applications provided that the objects belong to the class
of polyhedrons. Reflected and diffracted contributions in a scene are
modelled as secondary sources which are handled with an off-line
electromagnetic field calculation.
Numerical analysis is provided showing the efficiency of the
method
A method for multiple diffracted ray sampling in forward ray tracing
No full textAn analytical method for determining the diffraction points in ray tracing is proposed. The general case of diffraction by oblique straight wedges in 3D is considered. The sampling problem is solved for a first order diffracted ray congruence in such a way to provide a suitable sampling of the rays diffracted by a second wedge. The method can be extended to the sampling of higher-order diffracted rays. An example is provided for a couple of orthogonal edges lighted by a point source
Performance evaluation of astigmatic beam tracing in the application to picocell scenarios
No full textA NEW MULTIFREQUENCY MICROWAVE RADIOMETER FOR MEDICAL OPERATION
No full textMulti-frequency microwave radiometry has been considered for the measurement of sub-surface temperature distributions of human tissues, envisaged applications being mainly related to the non-invasive temperature monitoring in hyperthermia treatment of cancer. The sensor consists of a broadband microwave receiver, which generates a signal proportional to input radiation power, then a calibration processor averages the receiver output and computes an estimate of the input power in each frequency band. We have developed a new radiometer system of the radiation balance type to counteract the reflectivity errors which may affect the multi-frequency radiometric data to an intolerable amount. In this paper we discuss the reflectivity error of our system on the basis of a model of both incoming radiation and receiver. A formula, which propagates this error to temperature retrieval uncertainty, is also given
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