Determination of regional V A /Q by hyperpolarized 3 He 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 A O 2 ) measured by hyperpolarized 3 He gas MRI (HP 3 He 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 3 He gas mixture was administered during breathhold and imaging performed. P A O 2 was measured based on the decay rate of 3 He signal. Subjects' blood gas concentrations were measured and these values and P A O 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 3 He MRI may be an accurate, quantitative, noninvasive, and nonradioactive method for acquiring V A /Q for small regions of the lung. Magn Reson Med 52:65–72, 2004. © 2004 Wiley‐Liss, Inc.