title: Effect of acoustic power on in vivo molecular imaging with targeted microbubbles: implications for low-mechanical index real-time imaging.
abstract: 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.
authors.affiliation: Cardiovascular Division, Oregon Health & Science University, Portland, Oregon 97239, USA.
authors.forename: Beat A
authors.initials: BA
authors.lastname: Kaufmann
authors.forename: Chad L
authors.initials: CL
authors.lastname: Carr
authors.forename: Todd
authors.initials: T
authors.lastname: Belcik
authors.forename: Aris
authors.initials: A
authors.lastname: Xie
authors.forename: Benjamin
authors.initials: B
authors.lastname: Kron
authors.forename: Qi
authors.initials: Q
authors.lastname: Yue
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Lindner
mesh_terms: 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*
chemical_list: D003287:Contrast Media