Multiple-focus Patterns Research Articles

Multiple-Focus Patterns of Sparse Random Array Using Particle Swarm Optimization for Ultrasound Surgery.

This study aims to investigate the feasibility and potential of sparse random arrays driven by the particle swarm optimization (PSO) algorithm to generate multiple-focus patterns and a large scanning range without grating lobes, which extends the scanning range of focused ultrasound in the treatment of brain tumors, opening the blood-brain barrier, and neuromodulation. Operating at 1.1 MHz, a random spherical array with 200 square elements (sparseness 58%) and a sparse random array with 660 square elements (sparseness 41%) driven by PSO are employed to simulate different focus patterns. With the same radius of curvature and diameter of transducer and element size, the scanning range of the off-axis single focus of a random 200-element array is two times that of an ordinary array using symmetric arrangement. The focal volume of multiple-focus patterns of the random array is 18 times that of the single focus. The single focus of the sparse random array with 660 elements could steer up to ±23 mm in the radial direction, without grating lobes. The maximum distance between two foci in a multiple-focus "S"-shaped deflection is approximately 25 mm. Simulation results illustrate the capability of a focused beam steered in 3-D space. Multiple-focus patterns could significantly increase the focal volume and shorten the treatment time for large target volumes. Simulation results show the feasibility and potential of the method combining PSO with a sparse random array to generate flexible focus patterns that can adapt to different needs in different tissue treatments.

Broadband transskull multi-focus wavefront synthesis

Multiple-focus pattern synthesis using ultrasound arrays has been previously demonstrated. Furthermore, an optimal synthesis method was shown to provide well-behaved solutions. This method creates predefined focus patterns at a single frequency for an ultrasonic array operating in continuous wave. In this paper, we extend the approach to the broadband case using orthogonal frequency-division multiplexing (OFDM). A broadband multiple-focus pattern is formed by summing the results of the synthesis algorithm at a set of discrete frequencies within the transducer bandwidth. The OFDM approach allows for achieving a predictable focusing gain at the target point(s) due to the waveform orthogonality. Outside the target region, the different frequency components can be expected to provide a larger degree of destructive interference. Hydrophone scans of multiple-focus patterns in plain water as well as transskull were performed using a phased array with a multichannel arbitrary waveform generator. The array has a 3.5 MHz center frequency with a 6-dB bandwidth in the range 2.2 MHz–4.8 MHz. The skull samples were obtained from 300 to 350 g rats that were used in other in vivo experiments. The results show greater focus resolution than for any single frequency pattern while reducing the interference patterns outside the target region.Multiple-focus pattern synthesis using ultrasound arrays has been previously demonstrated. Furthermore, an optimal synthesis method was shown to provide well-behaved solutions. This method creates predefined focus patterns at a single frequency for an ultrasonic array operating in continuous wave. In this paper, we extend the approach to the broadband case using orthogonal frequency-division multiplexing (OFDM). A broadband multiple-focus pattern is formed by summing the results of the synthesis algorithm at a set of discrete frequencies within the transducer bandwidth. The OFDM approach allows for achieving a predictable focusing gain at the target point(s) due to the waveform orthogonality. Outside the target region, the different frequency components can be expected to provide a larger degree of destructive interference. Hydrophone scans of multiple-focus patterns in plain water as well as transskull were performed using a phased array with a multichannel arbitrary waveform generator. The array has a 3...

Depth from Projector^|^apos;s Defocus Based on Multiple Focus Pattern Projection

Depth from Projector^|^apos;s Defocus Based on Multiple Focus Pattern Projection

Depth from Projector's Defocus Based on Multiple Focus Pattern Projection

Depth from Projector's Defocus Based on Multiple Focus Pattern Projection

Study on an underwater focused acoustic phased array and the sound fields characteristics

Regarding to the fact that the hydrodynamic characteristics of supercavitating torpedoes strongly depend on the supercavity envelops, this paper describes a high intensity underwater focused acoustic phased array used to remotely disrupt this envelope surface. First, the demand of designing an underwater focused acoustic phased array was discussed, and then an efficient sound field calculation formula for the convex spherical-section phased array was obtained. Furthermore, the effects of element size and array aperture on the valid focusing region of above array were analyzed based on pseudo-inverse method. It is demonstrated, via simulation, that the arrays composed of minimum element size with large beam angle perform well on the intensity of focus pressure, and the valid focusing region under the similar size of emission area. However, the change of valid focusing region is small when merely enlarge the aperture of array. And the possible application of multiple-focus pattern was investigated.

Axial multiple foci of radially polarized hollow Gaussian beam

Axial multiple foci patterns of radially polarized hollow Gaussian beam (HGB) with radial wavefront distribution is investigated theoretically. The wavefront phase distribution is cosine function of radial coordinate. Simulation results show that the multiple foci patterns can be adjusted considerably by the beam order of HGB and cosine parameter that indicates the phase change degree. The foci number fluctuates on increasing cosine parameter for certain beam order. And when the beam order is small, there occur five foci in focal region, and the cases are more frequently than that under the condition of higher beam order. Gradient force distributions are also given to show that the multiple foci of radially polarized HCB may be applied to construct tunable optical traps. OCIS codes: 140.3300, 260.5430, 140.7010.

Focused beam control for ultrasound surgery with spherical-section phased array: sound field calculation and genetic optimization algorithm

This study aims at a sound field calculation for the spherical-section phased array and an optimization algorithm for the focus patterns of phased array ultrasound surgery. An efficient field calculation formula represented as an explicit expression is derived by the strategies of projection and binomial expansion. An optimization algorithm based on genetic algorithm is constructed by the suitable fitness function and the selection strategies. The simulation results of 256-element spherical-section phased array show the capability of controlling focus accurately and effectively with the combined method made up of the explicit expression method and the genetic optimization algorithm. The simulation results of single focus, multiple foci, on-axial focus, and off-axial focus further convince the feasibility of three-dimensional (3-D) focus steering with excellent acoustic performances. A single focus with the focus dimension of 1.25 mm x 1.25 mm x 7 mm and with the intensity of 6080 W/cm2 is formed. The multiple-focus pattern can enlarge the treatment volume 22 times larger than that of single focus with a sonication. In addition, a comparison between the explicit expression approach and the point source approach testifies to the applicability of the explicit expression approach. The experiment and simulation results of 16-element array actually confirm the feasibility of the combined method.

Temperature Distribution in the Human Brain During Ultrasound Hyperthermia

One of the important applications of ultrasound hyperthermia is the temperature elevation at specified locations in the human brain. The ultrasound applicator used is the circular phased array surrounding the human head. The human head model is assumed to be two concentric spheres of skin and bone contains a semi-sphere of brain. The single and multiple foci patterns of the ultrasound intensity generated by the circular phased array is investigated. The heating patterns, temperature distributions, corresponding to the absorption of ultrasound in the brain region is determined by solving the bioheat equation.

Theoretical design of a spherically sectioned phased array for ultrasound surgery of the liver

Goal: The theoretical explantion of the limits of an array transducer to coagulate large tissues volumes. Methods: A theoretical model is used to illustrate the focal limitations of a spherically sectioned array designed for the treatment of deep seated tissue, e.g. liver. The design optimizes the acoustic dose as a function of the focal depth and available acoustic aperture with the goal of coagulating large volumes in a single sonication period. A quantitative measure of the possible region of focal necrosis is modeled as a function of array parameters with the limiting criteria being near field heating and patient pain. Results: Acoustic simulations show that the maximum distance to produce continuous necrosis between foci in a multiple focus pattern and in a temporally multiplexed pattern is approximately 50% larger than the distance needed between sequential foci. Conclusion: Multiple focus patterns or rapidly scanned single foci are significantly advantageous to sequential sonications of a single focus transducer.

Low-profile lenses for ultrasound surgery

Several flat lens designs have been simulated that focus a planar transducer at various depths and angular deflections. The use of flat lenses with planar phased arrays to create multiple focus patterns has also been explored. The simulations have shown that the discrete element size is practical to machine. Simulations predict that a flat polystyrene lens with an f number of 1.0 can produce a focal peak intensity that is 80% that of a geometrically focused transducer with the same focal depth, including the attenuation through the lens, by utilizing four discrete phase steps. These predictions were verified with a simplified experimental lens utilizing only two phase steps. Simulations predicted an attenuation within the lens of 18% and a focal peak intensity of 38%. Measurements resulted in an attenuation of 30% and a focal peak intensity of 30%. Experimental lens studies have indicated that sufficient power can be transmitted through the lenses for these designs to be feasible for use in ultrasound surgery.

Ultrasound surgery: comparison of strategies using phased array systems

In this paper the possibility of using phased array generated multiple-focus patterns to reduce the overall treatment time in ultrasound surgery while restraining prefocal heating was investigated. This was done by comparing through computer simulation the performance of different possible schemes, i.e., single-focus scans, multiple-focus scans, and simultaneous multiple focusing without scanning, when used to "ablate" a 10/spl times/10/spl times/10 mm/sup 3/ tissue volume 100 mm deep. In all cases, 41 foci were used to cover the treatment volume. Multiple-focus scans were arranged into nine groups which were scanned in a raster fashion, as with single-focus scans. Keeping the treatment time constant, the maximum intensities, maximum thermal doses, dose distributions, and prefocal necrosis zones for the different schemes were compared. It was found that the nonscanned simultaneous multiple-focus case required the smallest maximum intensity and dose, and resulted in the most even dose distribution. Single-focus raster scanning of individual lesions, as currently used with fixed-focus transducers, gave the worst results. These results show that multiple-focus patterns help considerably in reducing the maximum intensity and dose, and in generating a more even dose distribution assuming the same treatment time and prefocal heating. Alternatively, multiple-focus patterns can be used to significantly reduce treatment time while keeping the maximum intensity and prefocal heating below predetermined limits.

Experimental evaluation of a prototype cylindrical section ultrasound hyperthermia phased-array applicator

A prototype 64-element, 75 degrees cylindrical-section ultrasonic phased-array hyperthermia applicator has been designed and constructed. The ability of this applicator to focus ultrasonic energy at its geometric focus is verified in a water medium. The array is then driven by excitation vectors obtained using the pseudoinverse pattern synthesis method to generate shifted-focus and multiple-focus field patterns. Experimental results of single and multiple-focus patterns at 500 kHz are given and are in good agreement with theory. The results indicate that the main beam in single-focus patterns is generally insensitive to errors in the phases and amplitudes of the particle velocities of the array elements. The effect of such errors is largely exhibited in the sidelobes which, for all practical purposes, remain at levels acceptable for hyperthermia. This is true for both the geometric focus and shifted foci.

Optimization of the intensity gain of multiple-focus phased-array heating patterns

A new technique for enhancing the intensity gain at the focal points in multiple-focus patterns is introduced. The new technique is shown to be effective in reducing the interference typically associated with multiple-focus patterns. This reduction in interference patterns allows multiple-focus scanning to generate highly localized heating. Simulation results indicate that multiple-focus scanning not only provides an alternative to single-focus scanning, but also achieves better localization in the heating pattern. The maximization of intensity gain of multiple-focus heating patterns significantly reduces the pre-focal-depth high-temperature regions that can be caused by single-focus scanning. This is shown by computer simulation of a two-dimensional cylindrical-section array (CSA2D) as a heating applicator. Two series of simulations are presented in which different scan trajectories were used to therapeutically heat a small deep-seated target volume. In every case the heating pattern was generated using single-focus scanning and multiple-focus scanning (with and without intensity gain maximization). Multiple-focus scanning with gain maximization offers the best localization of heating to the target volume of the three methods.