Figure 3.

Normalized UFM signal from fluorescent microbubbles filled in a microtube through a 2-mm-thick intralipid slab phantom as a function of the lateral location of the 1-MHz ultrasound transducer. The dotted square line shows ultrasonic echo data that were recorded based on the conventional pulse-echo method. The solid diamond line shows the UMF signal. The arrow in the inset indicates that the transducer was scanned across the tube repeatedly for three times. (A) A single type of dye was attached to the surface of the microbubble and a significant self-quenching effect occurred when no ultrasound was applied (Liu et al., 2014) (B) Microbubbles were simultaneously labeled with donor and acceptor fluorophores on the surface to minimize self-quenching and maximize FRET (Liu et al., 2015). Reproduced with permission. Copyright 2014 & 2015^©SPIE.