Comparison of Quantitative Multiple Breath Specific Ventilation Imaging Using Co-localized 2D Oxygen Enhanced MRI and Hyperpolarized 3 He MRI.

Two magnetic resonance specific ventilation imaging (SVI) techniques namely, oxygen enhanced proton (OE-1H) and hyperpolarized 3 He (HP-3He) were compared in eight healthy supine subjects (age 32(6) yr). An in-house radio-frequency coil array for 1 H configured with the 3 He transmit-receive coil in-situ enabled acquisition of SVI data from two nuclei from the same slice without repositioning the subjects. Following 3×3 voxel-down-sampling to account for spatial registration errors between the two SV images, the voxel-by-voxel correlation coefficient of two SV maps ranged from 0.11 to 0.63 (0.46 mean (0.17 SD), (p < 0.05). Several indices were analysed and compared from the tidal volume matched SV maps; the mean of SV log-normal distribution (SVmean), standard deviation of the distribution as a measure of SV heterogeneity (SVwidth) and the gravitational gradient (SVslope). There were no significant differences in SVmean: OE-1H: 0.28(0.08) and HP-3He: 0.32(0.14), SVwidths: OE-1H: 0.28(0.08) and HP-3He: 0.27(0.10) and SVslopes: OE-1H: -0.016(0.006) cm-1 and HP-3He: -0.013(0.007) cm-1 . Despite the statistical similarities of the population averages, Bland-Altman analysis demonstrated large individual inter-technique variability. Standard deviations of differences in these indices were SVmean: 42%, SVwidths: 46%, and SVslopes: 62% of their corresponding overall mean values. The present study showed that two independent, spatially co-registered, SVI techniques presented a moderate positive voxel-by-voxel correlation. Population averages of SVmean, SVwidth and SVslope were in close agreement. However, the lack of agreement when the data sets were analysed individually might indicate some fundamental mechanistic differences between the techniques.