Microbubbles as novel pressure-sensitive MR contrast agents.
Magnetic resonance imaging contrast agents that are sensitive to pressure would be useful for evaluating cardiovascular function. One such potential contrast agent consists of gas-filled liposome microbubbles. The magnetic susceptibility of the microbubbles locally perturb the static magnetic field, which influences the transverse-relaxation properties of the surrounding medium. Changes in the pressure alter the bubble dimensions, which affects the magnetic field perturbations and, hence, the transverse-relaxation. The effect of these microbubbles on the T2 relaxation times of a water-based medium was measured for liposomes filled with different gases-nitrogen, argon, air, oxygen, xenon, neon, perfluoropentane, perfluorobutane, and sulfur hexafluoride. The air-filled, perfluoropentane-filled and the oxygen-filled liposomes demonstrated the largest effect on transverse-relaxation. The influence of pressure on both gradient-echo and spin-echo signal intensities for air-filled microbubbles was also evaluated. Pressure-induced changes in signal intensity were consistently observed for both the spin-echo and gradient-echo pulses sequences.
Alexander
A L
AL
Department of Radiology, University of Arizona, Tucson 85724, USA.
McCreery
T T
TT
Barrette
T R
TR
Gmitro
A F
AF
Unger
E C
EC
D003287:Contrast Media; D005740:Gases; D008081:Liposomes; D008279:Magnetic Resonance Imaging; D011312:Pressure
D003287:Contrast Media; D005740:Gases; D008081:Liposomes