title: Dynamic microPET imaging of ultrasound contrast agents and lipid delivery.
abstract: Interest in ultrasound contrast agents (lipid-shelled microbubbles) as delivery vehicles is increasing; however, the biodistribution of these agents remains uncharacterized, both with and without ultrasound. In this study, an (18)F-labeled lipid ([(18)F]fluorodipalmitin), incorporated in microbubble shells, was used as a dynamic microPET probe for quantitative 90-minute biodistribution measurements in male Fischer 344 rats (n=2). The spleen retained the highest concentration of radioactive lipid at approximately 2.6%-injected dose per cubic centimeter (% ID/cc) and the liver demonstrated the largest total accumulation (approximately 17% ID). The microbubble pharmacokinetic profile differed from free lipid, which is rapidly cleared from blood, and liposomes, which remain in circulation. Additionally, region of interest (ROI) analysis over 60 minutes (post-ultrasound treatment) quantified the delivery of lipid by therapeutic ultrasound from microbubbles to kidney tissue (n=8). The ultrasound sequence consisted of a 200 kPa, 5.3 MHz radiation force pulse followed by a 1.6 MPa, 1.4 MHz fragmentation pulse and was applied to one kidney, while the contralateral kidney served as a control. ROI-estimated activity in treated kidneys was slightly but significantly greater at 0 and 60 min than in untreated kidneys (p=0.0012 and 0.0035, respectively). This effect increased with the number of microbubbles injected (p=0.006). In summary, [(18)F]fluorodipalmitin was used to characterize the biodistribution of contrast microbubble shells and the deposition of lipid was shown to be locally increased after insonation.
authors: University of California, Davis, Davis, CA 95616, United States. mstartis@nmt.edu
authors: Michaelann S
authors: MS
authors: Tartis
authors: Dustin E
authors: DE
authors: Kruse
authors: Hairong
authors: H
authors: Zheng
authors: Hua
authors: H
authors: Zhang
authors: Azadeh
authors: A
authors: Kheirolomoom
authors: Jan
authors: J
authors: Marik
authors: Katherine W
authors: KW
authors: Ferrara
mesh_terms: D000818:Animals; D003287:Contrast Media / Q000008:administration & dosage*; D003952:Diagnostic Imaging / Q000379:methods*; D004075:Diglycerides / Q000097:blood / Q000493:pharmacokinetics; D004337:Drug Carriers / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry*; D008297:Male; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D019275:Radiopharmaceuticals / Q000097:blood / Q000493:pharmacokinetics; D051381:Rats; D011916:Rats, Inbred F344; D014465:Ultrasonics
chemical_list: C534455:3-fluoro-1,2-dipalmitoylglycerol; D003287:Contrast Media; D004075:Diglycerides; D004337:Drug Carriers; D008055:Lipids; D019275:Radiopharmaceuticals