title: Detection of retained microbubbles in carotid arteries with real-time low mechanical index imaging in the setting of endothelial dysfunction.
abstract: OBJECTIVE
  We sought to determine if intravenously injected microbubbles would be retained by the carotid arteries (CAs) in the setting of endothelial dysfunction (ED) using a linear transducer equipped with a low mechanical index pulse sequence scheme (PSS).
  
  
  BACKGROUND
  Microbubbles normally pass freely through large and small vessels but are retained in regions with ED. New high-frequency low mechanical index PSS can potentially be utilized to image these retained microbubbles.
  
  
  METHODS
  Intravenous albumin- and lipid-encapsulated microbubbles were administered in seven pigs while imaging the CAs before and after a 20% intralipid infusion to induce hypertriglyceridemia. The degree of microbubble retention was quantified by measuring endothelial acoustic intensity (AI) after clearance of free-flowing microbubbles. Microbubble adherence was also evaluated after selective balloon injury of the CAs. The CA diameter responses to acetylcholine were quantified.
  
  
  RESULTS
  After induction of hypertriglyceridemia, adherence of albumin-encapsulated microbubbles was visually evident in all CAs, and endothelial AI increased significantly (p < 0.001 compared with baseline). The CA responses to acetylcholine went from vasodilation at baseline to vasoconstriction during hypertriglyceridemia. Endothelial AI also increased in the balloon-stretched vessels (p < 0.01 compared with uninjured vessels) after albumin-encapsulated microbubble injection, with a ring of microbubbles selectively adhering to the injured segment. This retention was not observed with lipid-encapsulated microbubbles. Scanning electron microscopy confirmed that albumin-coated microbubbles adhered to endothelial cells.
  
  
  CONCLUSIONS
  Retention of intravenously injected albumin microbubbles occurs in the setting of both global and regional ED in large vessels and can be noninvasively imaged with high-frequency low mechanical index PSS.
authors.affiliation: Section of Cardiology, University of Nebraska Medical Center, Omaha, Nebraska 68198-1165, USA.
authors.forename: Jeane M
authors.initials: JM
authors.lastname: Tsutsui
authors.forename: Feng
authors.initials: F
authors.lastname: Xie
authors.forename: Martin
authors.initials: M
authors.lastname: Cano
authors.forename: James
authors.initials: J
authors.lastname: Chomas
authors.forename: Patrick
authors.initials: P
authors.lastname: Phillips
authors.forename: Stanley J
authors.initials: SJ
authors.lastname: Radio
authors.forename: John
authors.initials: J
authors.lastname: Lof
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Porter
mesh_terms: D000162:Acoustics; D000818:Animals; D002339:Carotid Arteries / Q000000981:diagnostic imaging*; D004730:Endothelium, Vascular / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005466:Fluorocarbons / Q000008:administration & dosage; D005947:Glucose / Q000008:administration & dosage*; D007089:Image Enhancement; D045423:Microbubbles; D008863:Microspheres; D012709:Serum Albumin / Q000008:administration & dosage*; D000075462:Serum Albumin, Human; D013010:Sonication; D013552:Swine; D014159:Transducers; D014463:Ultrasonography
chemical_list: D005466:Fluorocarbons; D012709:Serum Albumin; C094311:dextrose albumin solution; D005947:Glucose; D000075462:Serum Albumin, Human; C042852:perflutren