Estimation and compensation of in-situ ultrasound intensity using a 2-D array therapy system and high frame rate imaging

A noninvasive measurement of in situ acoustic intensity is useful in a variety of therapeutic applications such as ultrasound induced drug and gene delivery. Some previously proposed methods assumed other acoustic parameters such as scattering coefficient to be constant. This paper proposed a method free of such restrictions, by estimating all the relevant parameters using the highly nonlinear behaviors of injectable microbubble contrast agents. Briefly, the amplitude of the transmitted ultrasound is varied over a range so that the microbubbles are destroyed. The relationship between bubble destruction can be used to calibrate both the unknown phantom attenuation and the unknown in vivo bubble concentration (which depends primarily on blood flow) due to the high nonlinearity of the bubble destruction process. Using the Verasonic high frame rate imaging system and a custom built 2D array therapeutic platform, attenuation by various tissue simulating layers were estimated and compensation to an accuracy of 0.6 dB was demonstrated.