Jean Brochot

MR perfusion imaging using encapsulated laser‐polarized 3He

In this work, the use of a new carrier agent for intravascular laser‐polarized 3He imaging is reported. Lipid‐based helium microbubbles were investigated. Their average diameter of 3 μm, which is smaller than that of the capillaries, makes it possible to conduct in vivo studies. The NMR relaxation parameters T1, T2, 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 3He with signal‐to‐noise ratios (SNRs) larger than 30 were acquired. Dynamic cardiac images and vascular images of encapsulated 3He were obtained in rats using intravenous injections of microbubble suspensions. Excellent preservation of 3He polarization through the lung capillaries and heart cavities was observed. The first images of 3He 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. Magn Reson Med 46:535–540, 2001.

Vascular and perfusion imaging using encapsulated laser-polarized helium

In this work, the use of hyperpolarized (HP)3He for in vivo intravascular imaging on animal is reported. To overcome the problem of the low solubility of helium in blood, we propose an approach based on helium encapsulation in lipid-based carrier agents. The mean diameter of the3He microbubbles. measured equal to 3.0 ±0.2 µm, makes it possible to conduct in vivo studies. In vitro spectroscopy yielded a longitudinal relaxation time T1 equal to 90 s and an apparent transverse relaxation timeT2* of 4.5 ms. Angiographie imaging (venous and cardiac cavity visualization), as well as lung perfusion imaging, were demonstrated in rats using intravenous injections of microbubble suspensions. Suitable signal and spatial resolution were achieved. The potential of this technique for lung perfusion assessment was assessed using an experimental animal embolism model. Lung perfusion defects and recovery towards a normal perfusion state were visualized. This study was completed with the demonstration of a new ventilation-perfusion lung exploration method based entirely on HP3He.

Hyperpolarized Helium3 Encapsulated in Microbubbles: A New Class of Blood Pool MRI Contrast Agent

A novel blood pool agent, based on hyperpolarized helium3 (HP 3He), was investigated for tissue perfusion using MRI. The results are reported in this paper. Thanks to the considerable polarization value obtained by optical pumping process, HP 3He has already demonstrated a great potential for anatomical and functional lung ventilation studies (1,2). In order to benefit from this large polarization and NMR signal advantages, we have studied the feasibility of this new contrast agent for perfusion imaging. To overcome the problem of the low helium solubility in blood, methods based on helium transportation using carrier agents have been investigated (3). In our study, a phospholipid-based substrate has been developed for helium encapsulation. Injections of 3m-diameter microbubble solutions have been used for in vivo intravascular imaging. In this work, the lung parenchyma perfusion imaging (4) as well as imaging of the coronary arteries (5) and myocardium perfusion are investigated.