Comparison of arterial spin labeling and first-pass dynamic contrast-enhanced MR imaging in the assessment of pulmonary perfusion in humans: The inflow spin-tracer saturation effect

The flow-sensitive alternating inversion recovery (FAIR) and the first-pass dynamic contrast-enhanced MR imaging (CE-MRI) techniques have both been shown to be effective in the assessment of human pulmonary perfusion. However, no comprehensive comparison of the measurements by these two methods has been reported. In this study, healthy adults were recruited, with FAIR and CE-MRI performed for an estimation of the relative pulmonary blood flow (rPBF). Regions of interest were encircled from the right and left lungs, with right-to-left rPBF ratios calculated. Results indicated that, on posterior coronal slices, the rPBF ratios obtained with the FAIR technique agreed well with CE-MRI measurements (mean difference = -0.02, intraclass correlation coefficient R1 = 0.78, 95% confidence interval = [0.67, 0.86]). On middle coronal slices, however, FAIR showed a substantially lower rPBF by up to 43% in the right lung compared with CE-MRI (mean difference = -0.38, R1 = 0.34, 95% confidence interval = [-0.09, 0.68]). The location-dependent discrepancy between measurements by FAIR and CE-MRI methods is attributed to tracer saturation effects of arterial inflow when the middle coronal slice contains the in-plane-oriented right pulmonary artery, whereas the left lung rPBF is less affected due to oblique orientation of the left pulmonary artery, Intrasequence comparison on additional subjects using FAIR at different slice orientations supported the above hypothesis. It is concluded that FAIR imaging for pulmonary perfusion in the coronal plane provides equivalent rPBF information with CE-MRI only in the absence of tracer saturation effects; hence, FAIR should be carefully exercised to avoid misleading interpretations.