The Relationship Between Pulsed High Intensity Focused Ultrasound Parameter Setting And Focal Region Acoustic Pressure

High intensity focused ultrasound is a burgeoning and booming noninvasive therapeutic technology,it is used in many kinds of cancer and nontumorous illness treatment nowadays,and rewards commendable curative effect.The mechanism of action of HIFU includes thermal effect,cavitational effect and mechanical effect,on clinic,the HIFU is used mainly on its thermal effect and cavitational effect to achieve the ablation purpose.During HIFU therapeutic process,the cavitaion phenomenon can produce many cavitational bubbles and so accelerates the temperature rising, therefore to a certain degree contribute to the ablation of focal region tissue,however,during the continuous HIFU insonation,vast cavitaional bubbles can absorb and scatter acoustic energy in the front of the focal region and cause acoustic energy deposits there,meanwhile lesion shift toward the transduser direction and the lesion acreage become more bigger,the evenly distributed "cigar" lesion shape so became to like the tadpole shape, therefore reduce the precision of treatment. With the development of HIFU research and the clinical application goes deepened,the pulsed high intensity focused ultrasound get into sight with its low duty cycle and short duration which can precisely smash the target region tissue on its mechanical effect and cavitation effect without sharp focal region temperature rising therefore have potential advantages in guaranteeing accuracy and operation controllability during ultrasound treatment,it is an urgent problem to study the relationship between different pulse parameter setting and focal region acoustic pressure, especially after cavitation bubbles appeared.Based on this, this paper have analysed present sound fields measuring methods, and find an approximation of acousto-optic method when using in the measurement of HIFU sound field. In view of the present HIFU transduser can not generate pulse signal, we present a pulse adjustable signal generator whose pulse parameter can be setted conveniently. Finally,Using acousto-optic refraction method,this paper proposes the measurements results of focal region acoustic pressure of different pulse widths and intervals setting under increasing input voltages,and meanwhile compare the results with CW insonation, to find out the changing regularity of focal region acoustic pressure and the maximum value of acoustic pressure under different pulse parameters,and therefore to offer a theory basis for the subsequent clinical research and instrumentaion development. It is shown that when pulse width longer than lms, the regularity of focal region acoustic pressure changing with input voltage of different pulse parameter settings in accord with each other.After cavitation bubbles appeared,the focal region acoustic pressure continue rising with the increasing input voltage and reaches a maximum value, when vast cavitation bubbles appeared,the focal region acoustic pressure decreases. The maximum acoustic pressure in focal region reaches lOMPa.