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S H R Hosseini
Physics of Life Reviews 07/2012; 9(3):346-7. · 7.21 Impact Factor
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ABSTRACT: The paper describes experimental and numerical studies of the effects of gas pockets on a high-intensity focused ultrasound (HIFU) field. Air bubbles ranging from 0.8 to 2.4 mm in radius were produced in transparent polyacrylamide tissue-mimicking gels. A single-element 3.5-MHz HIFU transducer was used to sonicate the gel phantoms. The changes in the HIFU beam pattern for air bubbles at different positions were visualized by the Schlieren method. Quantitative measurements of pressure at the HIFU focus by a calibrated needle hydrophone showed considerable reduction in the focal pressure with the presence of an air pocket. The presence of a single 1.2-mm-radius air bubble, at a 5 mm axial pre-focal position, reduced the focal intensity by 50% and increased the lateral focal dimension by 50%. For air bubbles at pre-focal position close to the focus, lesion formation was observed not at the theoretical focus, but in front of the air bubble and the air bubble became a barrier for the post-focal ultrasound propagation. The effects of reflection were simulated numerically and were compared with the experiments. The results can be used as guidelines for evaluation of potential safety concerns produced by trapped gas-pockets in various HIFU therapies.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 07/2011; · 1.69 Impact Factor
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ABSTRACT: The high reliability, high repetition rate, high performance, and compactness of pulsed-power generators are required for industrial applications. Also, the control of a pulsed-power generator becomes more complicated with increasing functions. An all-solid-state pulsed-power generator can be controlled by using a field-programmable gate array (FPGA). The pulsed-power generator consists of a charger, a magnetic pulse compression circuit, and a controller using the FPGA. The performance characteristics of the pulsed-power generator, such as the variable firing interval from shot to shot and the diagnosis of incorrect operation, are easily achieved by rewriting the programming of the Verilog hardware description language on the FPGA.
IEEE Transactions on Plasma Science 11/2010; · 1.17 Impact Factor
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ABSTRACT: This paper describes the effects of an output peaking capacitor on the propagation of an underwater streamer. A pulsed-power modulator using a magnetic-pulse-compression circuit was employed to generate 20-30-kV pulses with 2-mus pulsewidth. A point-to-plane electrode setup with 2-cm gap in tap water was used. A copper line with 0.43-mm tip diameter was used as the discharge electrode, and an aluminum plate was set in water and connected to ground. Underwater-streamer propagation was visualized by an intensified-charge-coupled-device camera with a high-speed gate. An optional output peaking capacitor was connected in parallel to the electrodes to get pulses with different rise time and higher peak voltage and current. Thin and well-distributed channels were observed when the peaking capacitor was used. In contrast, the number of streamer channels was small, and each of them was thick and bright when the peaking capacitor was removed from the circuit. It is concluded that the peaking capacitor has a favorable effect on the generation and propagation of the underwater streamer.
IEEE Transactions on Plasma Science 11/2009; · 1.17 Impact Factor
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ABSTRACT: The paper describes the effects of 50 to 300 nanosecond pulsed electric field on the embryonic development of the medaka fish egg (Oryzias latipes). In the recent years it has been reported that applying short (less than 100 ns) pulses increased the possibility of electric field interactions with subcellular structures, which leaded to secondary cellular events, such as temporally increase in cell membrane permeability and induction of apoptosis. The goal of the current study was to find the effects of short pulsed electric field in-vivo during embryo development. A pulsed power modulator using a magnetic compression circuit was employed to generat 0.5 to 20 kV pulses with 50 to 300 nanosecond pulse durations. Input voltage and current were measured by using an oscilloscope and a current monitor. Fertilized eggs of d-rR medaka were used. The age of the experimental eggs were 6 hours, 1 day and 2 days post fertilization. In each experiment, a single medaka egg (about 1.2 mm diameter) was set at the middle of a 2 mm or 4 mm cuvette and a single electric pulse was applied. After the experiments the eggs were observed under a microscope until they hatched or died. A fluorescent plasma membrane integrity indicator, propidium iodide (PI), was used to study electroporative uptake kinetics of the embryo cells after the electric pulse exposure. By applying 300 ns electric pulses, extensive damage of eggs were observed immediately after pulse application. For shorter 50 ns width pulses and low electric field, delayed hatching consistent with electric field intracellular interaction was observed, whereas stronger electric field affected the eggs immediately after the pulse and those eggs could not survive and died a few days later.
Pulsed Power Conference, 2009. PPC '09. IEEE; 08/2009
