Measurement of pulmonary partial pressure of oxygen and oxygen depletion rate with hyperpolarized helium-3 MRI: A preliminary reproducibility study on pig model

Rational and Objectives. Pulmonary partial pressure of oxygen (pO(2)) and oxygen depletion rate (R) are two important parameters of lung function. The dependence of hyperpolarized He-3 (Hp He-3) T, on local oxygen concentration provides the basis for high-resolution mapping of the regional distributions of pO(2) and R in the lung. Although the oxygen-sensitive Hp 3He magnetic resonance imaging technique has been applied in human subjects and several animal species, reproducibility studies are rarely reported in the literature. This work presents a preliminary reproducibility study on a pig model. In this study, important scan parameters, such as measurement timing and flip angle, are optimized to minimize the noise-induced measurement uncertainty. Materials and Methods. In the in vivo study, five normal pigs and one diseased pig with simulated pulmonary emboli were scanned with a small flip angle gradient echo sequence. The pulmonary oxygen measurement was repeated two to four times in each pig. In each measurement, a series of six images were acquired with optimal timing and flip angle. The parametric maps were generated using a bin-based data processing procedure that applied the multiple regression fitting method to extract the pO(2) and R. Variations of global mean, percentiles, and regions of interest were calculated from the maps to analyze reproducibility. Results. The global statistical analyses show that average variation of global mean is 10.7% for pO(2) and 23.8% for R, and that the average variation of percentiles (10th, 25th, 50th, 75th, and 90th) and interquartile range is 14.8% for pO(2) and 30.4% for R. The region-of-interest analysis on the manually selected regions shows that the average variation of mean is 12.6% for pO(2) and 21.9% for R. Conclusion: In this work, a preliminary study on the reproducibility of measuring pO(2) and R with HP He-3 magnetic resonance imaging on a pig model is presented.