Effect of Acoustic Power on In Vivo Molecular Imaging with Targeted Microbubbles: Implications for Low-Mechanical Index Real-Time Imaging
published online 12 November 2009.
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.
Conclusion
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.
Cardiovascular Division, Oregon Health & Science University, Portland, Oregon
Reprint requests: Jonathan R. Lindner, MD, Oregon Health & Science University, Cardiovascular Division, UHN-62, 3181 SW Sam Jackson Park Road, Portland, OR 97239.
This study was supported by grants R01-DK063508, R01-HL078610, and R01-HL074443 to Dr Lindner from the National Institutes of Health (Bethesda, MD). Dr Kaufmann is supported by a research grant from the Lichtenstein Foundation (New York, NY), and Dr Carr is supported by a postdoctoral fellowship grant from the American Heart Association (Dallas, TX).
ABSTRACT