A square focused ultrasound transducer with radius of curvature of with driving frequency of and side length of . The transducer is split into four equal square elements and driven with different modes to form different focal power patterns. (a) Three focal power patterns on the focal plane produced by the transducer. (b) A heating unit produced by switching the three focal modes with appropriate power weightings. The contour lines from inside to outside indicate TD equal to 300, 100, and , respectively.
Schematic diagram of the proposed heating strategy. (a) The breast was modeled as a hemisphere with a radius of , the chest wall as a -thick slab, and the ultrasound transducer was tilted 45°. (b) The breast was sonicated from four directions with the focal center of each sonication away from the geometrical center of the planned target volume (PTV), and the sonication sequence was also indicated.
(a) A prototype of the transducer in this study. (b) Focal pattern of mode 0 measured by hydrophone (normalized to peak value, unit: dB). (c) The set-up used for in vitro tissue model experiments in this study.
Simulation results for heating a PTV centered at . (a–c) show the TD distributions on the , , and planes respectively. The contour lines from inside to the outside indicate TD equal to 300, 100, and , respectively.
Simulation results for heating a PTV located at different locations. (a–c) show the TD distributions on the plane for the PTV centered at , , and , respectively.
Simulation results for heating a PTV centered at with different heating strategies. (a) a single ultrasound transducer sonicated from four directions sequentially (total heating ); (b) four ultrasound transducers sonicated from four directions simultaneously; (c) four ultrasound transducers sonicated from four directions simultaneously, followed by 45° rotation of the transducers for a second set of four sonications.
Thermal lesion on and planes, produced by single transducer with multidirectional heating.
Simulation results for heating a PTV centered at using an experimental heating method. (a–c) TD distributions on , , and plane, respectively.
The responses of peak temperatures in the PTV, surrounding tissue of PTV, and rib tissue for different sonication strategies. (a) Using a single transducer with sonications from four different directions sequentially, (b) using four transducers sonicated from four directions simultaneously, and (c) using four transducers sonicated from four directions simultaneously, followed by four sonications from transducers rotated 45°.
Phase combination and computed acoustic power weighting for each focal mode.
Properties of tissues used in the simulation (Refs. 14 and 18).
Detailed information of heating PTVs with various locations in simulations.
Parameters of each mode used to form a heating unit in experiments.
Comparison of heating PTV centered at with different strategies in simulations.
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