The purpose of this study is to investigate the feasibility of using a 1 MHz cylindrical ultrasound phased array with multifocus pattern scanning to produce uniform heating for breast tumor thermal therapy. The breast was submerged in water and surrounded by the cylindrical ultrasound phased array. A multifocus pattern was generated and electrically scanned by the phased array to enlarge the treatment lesion in single heating. To prevent overheating normal tissues, a large planning target volume (PTV) would be divided into several planes with several subunits on each plane and sequentially treated with a cooling phase between two successive heatings of the subunit. Heating results for different target temperatures (T(tgt)), blood perfusion rates and sizes of the PTV have been studied. Furthermore, a superficial breast tumor with different water temperatures was also studied. Results indicated that a higher target temperature would produce a slightly larger thermal lesion, and a higher blood perfusion rate would not affect the heating lesion size but increase the heating time significantly. The acoustic power deposition and temperature elevations in ribs can be minimized by orienting the acoustic beam from the ultrasound phased array approximately parallel to the ribs. In addition, a large acoustic window on the convex-shaped breast surface for the proposed ultrasound phased array and the cooling effect of water would prevent the skin overheating for the production of a lesion at any desired location. This study demonstrated that the proposed cylindrical ultrasound phased array can provide effective heating for breast tumor thermal therapy without overheating the skin and ribs within a reasonable treatment time.

This study investigated the feasibility of using a split-focused ultrasound transducer to perform thermal surgery on breast tumors, based on a multidirectional heating scheme. The transducer is a square section of a sphere with a radius of 10 cm. The transducer was tilted such that its acoustic beam was 45 degrees relative to the rib surface, and its focal zone was arranged by a shift of 6 mm away from the center of the planning target volume. The multifocus switching technique was employed to enhance the heating efficiency. When a single transducer was used, the transducer sonicated from a certain position for a given duration, and then rotated sequentially to continue the heating. Computer simulations and in vitro phantom experiments have been studied for this heating system. Both simulation and experimental results demonstrated that the system based on a multidirectional heating scheme is capable of generating a proper thermal lesion within 8 min. Meanwhile, from the simulation results, the rib heating was effectively alleviated by tilting the transducer to induce the total reflection at the muscle/bone interface. While using multiple ultrasound transducers, an appropriate arrangement was designed to have the same configuration of acoustic beams as is used for a single-transducer strategy. The simulation results from the four-transducer strategy indicated that the heating results could be further improved. This study revealed that it is very promising to have an appropriate arrangement of a single split-focused ultrasound transducer with mechanical rotation, or to have multiple split-focused transducers that use multidirectional heating for breast tumor thermal therapy.

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The goal of this study was to develop a rapid three-dimensional High Intensity Focused Ultrasound (HIFU) beam plotting system for visualizing the acoustic energy distribution, achieved using a three-dimensional positioning system and data acquisition hardware. Beam plots of a 1.1MHz HIFU transducer were performed to evaluate the capability of the proposed system. A three-dimensional beam plotting was completed in only about 30 minutes and covered a predetermined volume of 5mm x 20mm x 5mm with a spatial resolution of 0.2mm x 0.001mm x 0.2mm. The FWHM (Full Width at Half Maximum) dimensions of the ultrasound field on axial and lateral directions were measured at 12.51mm and 1.4mm respectively. The proposed system can not only perform 2-dimensional beam plots but also can aid in the visualization of a three-dimensional ultrasound beam pattern volume within a relatively short scanning time.

The purpose of this study is to investigate the feasibility of a cylindrical ultrasound phased-array with multiple-focus scanning strategy to produce a uniform heating for breast thermal therapy. In this study, a breast is surround by a 1-MHz cylindrical ultrasound phased-array consists of 200 elements with a radius of 10 cm and a height of 2 cm. To prevent overheating in the normal tissue, a scanning region of 1 cmt x 1 cm was selected as a single heating unit. Planning target volume (PTV) larger than this size would be divided into several sub-heating units, and then be treated sequentially with cooling phase to prevent overheating in the surrounding normal tissue. Parameters such as the target temperature, blood perfusion rate and the size of PTV are evaluated. Simulation results show that the target temperature affects the thermal lesion size and the blood perfusion rate increases the heating time significantly. This method provides efficient heating for breast tumor thermal therapy while preventing overheating the ribs.