The natural frequency of nonlinear oscillation of ultrasound contrast agents in microvessels

Abstract

Prediction of natural frequency of oscillation of ultrasound contrast agents (UCAs) in microvessels plays an important role in UCA imaging and drug delivery. Here, the natural frequency of a microbubble in microvessels was studied in detail. Three models for blood vessel compliance have been considered, i.e., a rigid vessel, normal compliant vessel, and a stiff vessel which may correspond to the tumor-developing vasculature. Numerical results demonstrate that the natural frequency of a bubble in a rigid vessel is substantially decreased as compared to that in an unbounded field. However, within a compliant vessel, the natural frequency of bubble oscillation increases with decreasing vessel size. When a bubble with a radius of 4 m is confined in a compliant vessel (inner radius 5 m and length 100 m), the natural frequency of bubble oscillation increases by a factor of 1.7 as compared with that in an unbounded field. The natural frequency of bubble oscillation in a compliant vessel decreases with increasing values of vessel rigidity. This model suggests that contrast agent size, blood vessel size distribution, and the type of vasculature should be comprehensively considered for choosing the transmitted frequency in UCA imaging and drug delivery. [Work supported by NIH CA 103828.]