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

Abstract

Inhalation of hyperpolarized 3 He allows magnetic resonance imaging (MRI) of ventilated airspaces. 3 He 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 3 He 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 ([Formula: see text]). With the use of a specifically designed applicator, 3 He (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 cm 3 ), taken at two different radio-frequency excitations, permitted calculation of [O 2 ] in these regions of interest. The [O 2 ] fractions in the regions of interest correlated closely with[Formula: see text]( R = 0.879; P < 0.0001). O 2 -sensitive 3 He-MRI may allow noninvasive study of regional distribution of ventilation and alveolar[Formula: see text] in the lung.