Morphologic images of the lung have been obtained in excellent quality in small animals and humans in vivo using hyperpolarized (HP) noble gas MRI. Whereas 3He seems to be superior regarding imaging of the lung gas spaces, 129Xe has some unique properties which makes it a potential probe for pulmonary perfusion: (a) xenon has a decent solubility in blood and tissues, (b) the large range of 129Xe chemical shifts in vivo (approx. 200 ppm between gas and tissue phases) can be used for the selective investigation of xenon in different environments, such as alveolar gas space, pulmonary blood and parenchyma. While the frequency separation between xenon in parenchymal tissue and pulmonary blood is small, the differences in the motional behavior of both compartments can be used for the exclusive selection of the blood pool: rapid application of large flip angles leads to a saturation of the parenchyma signal whereas uptake of HP 129Xe by the blood is repeated with each cardiac cycle. Purpose of the project is therefore the selective imaging of HP 129Xe dissolved in the pulmonary blood as a measure of local pulmonary perfusion. Initial spectroscopy studies will be used to develop projection-encoding strategies for non-slice-selective 2D imaging with chemical-shift-selective excitation and detection.
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