Effect of acoustic power on in vivo molecular imaging with targeted microbubbles: implications for low-mechanical index real-time imaging.
BACKGROUND
The aim of this study was to evaluate the influence of acoustic power on ultrasound molecular imaging data with targeted microbubbles.


METHODS
Imaging was performed with a contrast-specific multipulse method at mechanical indexes (MIs) of 0.18 and 0.97. In vitro imaging was used to measure concentration-intensity relationships and to assess whether damping from microbubble attachment to cultured endothelial cells affected signal enhancement. Power-related differences in signal enhancement were evaluated in vivo by P-selectin-targeted and control microbubble imaging in a murine model of hind-limb ischemia-reperfusion injury.


RESULTS
During in vitro experiments, there was minimal acoustic damping from microbubble-cell attachment at either MI. Signal enhancement in the in vitro and in vivo experiments was 2-fold to 3-fold higher for high-MI imaging compared with low-MI imaging, which was due to greater pixel intensity, the detection of a greater number of retained microbubbles, and increased point-spread function. Yet there was a linear relationship between high-MI and low-MI data indicating that the relative degree of enhancement was similar.


CONCLUSIONS
During molecular imaging, high-MI protocols produce more robust targeted signal enhancement than low-MI protocols, although differences in relative enhancement caused by condition or agent are similar.
Kaufmann
Beat A
BA
Cardiovascular Division, Oregon Health & Science University, Portland, Oregon 97239, USA.
Carr
Chad L
CL
Belcik
Todd
T
Xie
Aris
A
Kron
Benjamin
B
Yue
Qi
Q
Lindner
Jonathan R
JR
D000818:Animals; D002478:Cells, Cultured; D003199:Computer Systems; D003287:Contrast Media; D016503:Drug Delivery Systems / Q000379:methods; D042783:Endothelial Cells / Q000000981:diagnostic imaging*; D004735:Energy Transfer; D051379:Mice; D045423:Microbubbles; D011829:Radiation Dosage; D015427:Reperfusion Injury / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014463:Ultrasonography / Q000379:methods*
D003287:Contrast Media