Figure 4. Strategies for the differentiation of bound and circulating microbubbles.

In each case, microbubbles are injected and circulate for ~7 minutes. When bound agents are present the image amplitude decays more slowly. (a) Red bar indicates the timing of a high-pressure ultrasound burst to destroy the bound and circulating agents. The pre-burst and post-burst images (yellow bars) are subtracted to yield the targeted agent image. (b) Alternatively, a ten second window of images can be obtained at the time of injection and a later time point (yellow bars), averaging over the ten second interval to suppress the contribution from circulating agents. The late-average image normalized by the early-average image quantifies accumulation.