title: Development of a novel magnetic resonance imaging contrast agent for pressure measurements using lipid-coated microbubbles.
abstract: The aim of this study was to prepare gas-filled lipid-coated microbubbles as potential MRI contrast agents for imaging of fluid pressure. Air-filled microbubbles were produced with phospholipid 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) in the presence or absence of cholesterol and/or polyethylene-glycol distearate (PEG-distearate). Microbubbles were also prepared containing a fluorinated phospholipid, perfluoroalkylated glycerol-phosphatidylcholine, F-GPC shells encompassing perfluorohexane-saturated nitrogen gas. These microbubbles were evaluated in terms of physico-chemical characteristics such as size and stability. In parallel to these studies, DSPC microbubbles were also formulated containing nitrogen (N2) gas and compared to air-filled microbubbles. By preventing advection, signal drifts were used to assess their stability. DSPC microbubbles were found to have a drift of 20% signal change per bar of applied pressure in contrast to the F-GPC microbubbles which are considerably more stable with a lower drift of 5% signal change per bar of applied pressure. By increasing the pressure of the system and monitoring the MR signal intensity, the point at which the majority of the microbubbles have been damaged was determined. For the DSPC microbubbles this occurs at 1.3 bar whilst the F-GPC microbubbles withstand pressures up to 2.6 bar. For the comparison between air-filled and N2-filled microbubbles, the MRI sensitivity is assessed by cycling the pressure of the system and monitoring the MR signal intensity. It was found that the sensitivity exhibited by the N2-filled microbubbles remained constant, whilst the air-filled microbubbles demonstrated a continuous drop in sensitivity due to continuous bubble damage.
authors.affiliation: Medicines Research Unit, Aston Pharmacy School, Aston University, Birmingham, 894 60Y, UK.
authors.forename: Randip
authors.initials: R
authors.lastname: Kaur
authors.forename: Robert
authors.initials: R
authors.lastname: Morris
authors.forename: Martin
authors.initials: M
authors.lastname: Bencsik
authors.forename: Anil
authors.initials: A
authors.lastname: Vangala
authors.forename: Thomas
authors.initials: T
authors.lastname: Rades
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Perrie
mesh_terms: D020099:Coated Materials, Biocompatible / Q000138:chemical synthesis*; D003287:Contrast Media / Q000138:chemical synthesis*; D007089:Image Enhancement / Q000379:methods*; D008055:Lipids / Q000737:chemistry*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008365:Manometry / Q000379:methods*; D045423:Microbubbles; D011312:Pressure
chemical_list: D020099:Coated Materials, Biocompatible; D003287:Contrast Media; D008055:Lipids