Laser-polarized He-3 as a probe for dynamic regional measurements of lung perfusion and ventilation using magnetic resonance imaging

Magnetic resonance imaging (MRI) using laser-polarized noble gases, such as Xe-129 and He-3, allows unparalleled noninvasive information on gas distri bution in lung airways and distal spaces. In addition to pulmonary ventilat ion, lung perfusion assessment is crucial for proper diagnosis of pathologi cal conditions, such as pulmonary embolism. Magnetic resonance perfusion im aging usually can be performed using techniques based on the detection of w ater protons in tissues. However, lung proton imaging is extremely difficul t due to the low proton density and the magnetically inhomogeneous structur e of the lung parenchyma. Here we show that laser-polarized He-3 can be use d as a noninvasive probe to image, in a single MRI experiment, not only the ventilation but also the perfusion state of the lungs. Blood volume maps o f the lungs were generated based on the He-3 signal depletion during the fi rst pass of a superparamagnetic contrast agent bolus, The combined and simu ltaneous lung ventilation and perfusion assessments are demonstrated in nor mal rat lungs and are applied to an experimental animal model of pulmonary embolism. (C) 2000 Wiley-Liss, Inc.