On the parameters affecting the sensitivity of MR measures of pressure with microbubbles.
Recently, it has been suggested that gas encapsulated distensible microbubbles may serve as pressure probes in the MR field through the relationship between bubble size and 1/T(2) or 1/T(*)(2). Currently, in vivo application of this technique is hindered by the ability of T(2) or T(*)(2) to detect pressure changes that are clinically relevant. This work identifies and characterizes, through numerical simulations, the set of parameters which optimize the ability of this technique to detect small pressure changes. Results show that when the bubbles do not interact magnetically, the T(2)- and T(*)(2)-based measurements of pressure are strongly influenced by the bubble size at atmospheric pressure, static magnetic field strength, magnitude of the susceptibility difference between the encapsulated gas and plasma, bubble volume fraction, and the refocusing interval. In particular, to detect clinically relevant pressure changes, microbubbles need to be approximately 2-3 microm in radius, distributed at a volume fraction of 0.15%, and have a volumetric magnetic susceptibility difference of at least 34 ppm.
Dharmakumar
Rohan
R
Department of Medical Biophysics, Sunnybrook and Women's College Health Sciences Center, University of Toronto, Toronto, Canada. rohan@sten.sunnybrook.utoronto.ca
Plewes
Donald B
DB
Wright
Graham A
GA
D001794:Blood Pressure / Q000502:physiology*; D003198:Computer Simulation; D003287:Contrast Media; D006801:Humans; D006976:Hypertension, Pulmonary / Q000503:physiopathology; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008962:Models, Theoretical; D009010:Monte Carlo Method; D011669:Pulmonary Wedge Pressure / Q000502:physiology; D012680:Sensitivity and Specificity; D016278:Ventricular Function, Right / Q000502:physiology*
D003287:Contrast Media