Analysis of intrapulmonary O2 concentration by NIR imaging of inhaled hyperpolarized helium-3

Inhalation of hyperpolarized He-3 allows magnetic resonance imaging (MRI) of ventilated airspaces. He-3 hyperpolarization decays more rapidly when interacting with paramagnetic O-2. We describe a method for in vivo determination of intrapulmonary O-2 concentrations ([O-2]) based on MRI analysis of the fate of measured amounts of inhaled hyperpolarized He-3 in imaged regions of the lung. Anesthetized pigs underwent controlled normoventilation in a 1.5-T MRI unit. The inspired O-2 fraction was varied to achieve different end-tidal [O-2] fractions (FETO2) With the use of a specifically designed applicator, He-3 (100 ml, 35-45% polarized) was administered at a predefined time within single tidal volumes. During subsequent inspiratory apnea, serial two-dimensional images of airways and lungs were acquired. At least once in each animal studied, the radio-frequency excitation used for imaging was doubled at constant FETO2. Signal intensity measurements in regions of interest of the animals' lungs (volume range, 54-294 cm(3)), taken at two different radiofrequency excitations, permitted calculation of [O-2] in these regions of interest. The [O-2] fractions in the regions of interest correlated closely with FETO2 (R = 0.879; P < 0.0001). O-2-sensitive He-3-MRI may allow noninvasive study of regional distribution of ventilation and alveolar P-O2 in the lung.