Determination of regional VA/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 (PAO2) measured by hyperpolarized He-3 gas MRI (HP He-3 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 He-3 gas mixture was administered during breathhold and imaging performed. PAO2 was measured based on the decay rate of He-3 signal. Subjects blood gas concentrations were measured and these values and PAO(2) 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 He-3 MRI may be an accurate, quantitative, noninvasive, and nonradioactive method for acquiring V-A/Q for small regions of the lung. (C) 2004 Wiley-Liss, Inc.