MR perfusion imaging using encapsulated laser-polarized 3He

In this work, the use of a new carrier agent for intravascular laser-polarized He-3 imaging is reported. Lipid-based helium microbubbles were investigated. Their average diameter of 3 mum, which is smaller than that of the capillaries, makes it possible to conduct in vivo studies. The NMR relaxation parameters T-1, T-2, and T-2* of a microbubble suspension were measured as 90 s, 300 ms, and 4.5 ms, respectively, and in vivo images of encapsulated He-3 with signal-to-noise ratios (SNRs) larger than 30 were acquired. Dynamic cardiac images and vascular images of encapsulated He-3 were obtained in rats using intravenous injections of microbubble suspensions. Excellent preservation of He-3 polarization through the lung capillaries and heart cavities was observed. The first images of He-3 microbubble distributions in the lungs were obtained. Additionally, the potential of this technique for lung perfusion assessment was validated through an experimental embolism model with the visualization of perfusion defects. (C) 2001 Wiley-Liss, Inc.