Analysis of intrapulmonary O2concentration by MR imaging of inhaled hyperpolarized helium-3

Abstract

Inhalation of hyperpolarized 3He allows magnetic resonance imaging (MRI) of ventilated airspaces.3He hyperpolarization decays more rapidly when interacting with paramagnetic O2. We describe a method for in vivo determination of intrapulmonary O2 concentrations ([O2]) based on MRI analysis of the fate of measured amounts of inhaled hyperpolarized3He in imaged regions of the lung. Anesthetized pigs underwent controlled normoventilation in a 1.5-T MRI unit. The inspired O2 fraction was varied to achieve different end-tidal [O2] fractions ([Formula: see text]). With the use of a specifically designed applicator,3He (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[Formula: see text]. Signal intensity measurements in regions of interest of the animals' lungs (volume range, 54–294 cm3), taken at two different radio-frequency excitations, permitted calculation of [O2] in these regions of interest. The [O2] fractions in the regions of interest correlated closely with[Formula: see text]( R = 0.879; P < 0.0001). O2-sensitive3He-MRI may allow noninvasive study of regional distribution of ventilation and alveolar[Formula: see text] in the lung.