Determination of regional V_A/Q by hyperpolarized ³He MRI

Alveolar ventilation/perfusion ratio (V_A/Q) is a, key parameter in functional imaging of the lung. Herein, regional V_A/Q was calculated from regional values of alveolar partial pressure of oxygen (P _AO₂) measured by hyperpolarized ³He gas MRI (HP ³He MRI). Yorkshire pigs (n = 7, mean weight = 25 kg) were paralyzed and maintained under isoflurane anesthesia. Animals were placed into a birdcage coil, then transferred to the bore of a 1.5 T MRI unit. Prior to imaging, animals were manually ventilated with room air for 5 min, then a ³He gas mixture was administered during breathhold and imaging performed. P _AO₂ was measured based on the decay rate of ³He signal. Subjects' blood gas concentrations were measured and these values and P_AO₂ values entered into a system of four equations with four unknowns. Calculated V_A/Q values were analyzed by preparing frequency distributions for the entire lung and compared to V_A/Q frequency distributions previously established in the literature as normal using other diagnostic techniques. Distributions were consistent with those in the literature, indicating that HP ³He MRI may be an accurate, quantitative, noninvasive, and nonradioactive method for acquiring V _A/Q for small regions of the lung.