Quantitative and semiquantitative measures of regional pulmonary microvascular perfusion by magnetic resonance imaging and their relationships to global lung perfusion and lung diffusing capacity: the multiethnic study of atherosclerosis chronic obstructive pulmonary disease study

Abstract

Objectives: The aim of this study was to evaluate the quantitative and semiquantitative measures of regional pulmonary parenchymal perfusion in patients with chronic obstructive pulmonary disease (COPD) in relationship to global lung perfusion (GLP) and lung diffusing capacity (DLCO).

Materials and methods: A total of 143 participants in the Multiethnic Study of Atherosclerosis COPD Study were examined by dynamic contrast-enhanced pulmonary perfusion magnetic resonance imaging (MRI) at 1.5 T. Pulmonary microvascular blood flow (PBF) was calculated on a pixel-by-pixel basis by using a dual-bolus technique and the Fermi function model. Semiquantitative parameters for regional pulmonary microvascular perfusion were calculated from signal intensity-time curves in the lung parenchyma. Intraoberserver and interobserver coefficients of variation (CVs) and correlations between quantitative and semiquantitative MRI parameters and with GLP and DLCO were determined.

Results: Quantitative and semiquantitative parameters of pulmonary microvascular perfusion were reproducible, with CVs for all parameters of less than 10%. Furthermore, these MRI parameters were correlated with GLP and DLCO, and there was good agreement between PBF and GLP. Quantitative and semiquantitative MRI parameters were closely correlated (eg, r = 0.86 for maximum signal increase with PBF). In participants without COPD, the physiological distribution of pulmonary perfusion could be determined by regional MRI measurements.

Conclusion: Regional pulmonary microvascular perfusion can reliably be quantified from dynamic contrast-enhanced MRI. Magnetic resonance imaging-derived quantitative and semiquantitative perfusion measures correlate with GLP and DLCO.

Figures

Figure 1. Quantitative maps of pulmonary parenchymal perfusion at MRI and placement of ROIs in a control subject

Corresponding central slices of subtracted signal intensity TRICKS image of pulmonary perfusion (a), pulmonary blood flow (PBF) map (b) and mean transit time (MTT) map (c). ROIs were placed on subtracted signal intensity images to cover the lung periphery while excluding greater vessels and were copied to parameter maps. PBF and MTT maps show homogeneous distribution of perfusion in this participant without COPD. Mean PBF in this slice was 49 mlblood per min and 100mllung and mean MTT was 4.4 s.

Figure 2. Semi-quantitative MRI parameters of pulmonary parenchymal perfusion

A γ-variate function was fitted to the signal intensity-time curve of the lung parenchyma and semi-quantitative parameters were determined as follows: maximum signal increase (SI) is the difference between maximum and 20% signal intensities of the γ-variate function, upslope is the maximum signal increase per time interval (b), time to peak (TTP) is the time difference between 20% and maximum signal intensities of the curve and full width half maximum (FWHM) is the time difference between 50% signal intensities (c). Note that the curves in b and c represent signal intensity-time curves and not the respective γ-variate function.

Figure 3. Numbers of participants for the different analysis

Depicted are the numbers of included participants (controls and COPD patients) for the different analysis. The number of participants for comparison with global lung perfusion (GLP) was lower, because bodyplethysmography and MRI flow measurements, which are necessary for calculation of GLP, were not available for all participants. Regional lung perfusion was only assessed in controls.

Figure 4. Regression analysis between pulmonary blood flow with the semi-quantitative measures maximum signal increase and upslope

Depicted are the significant positive correlations of pulmonary blood flow (PBF) with maximum signal increase (SI, r=0.86, p

Figure 5. Bland-Altman plots of pulmonary blood flow and global lung perfusion

Bland-Altman plots show the difference between pulmonary blood flow (PBF) and global lung perfusion (GLP) against the mean of both values. Data of controls with available measures (n=26; A) and COPD participants are plotted (n=48; B). The center line displays the mean difference between PBF and GLP. The dashed lines represent the 95% confidence interval. As differences in PBF measured by MRI GLP were not independent of the observed perfusion values, a modified rather than standard Bland-Altman plot was generated as recommended by Bland and Altman for such situation [32]. The plot demonstrates that PBF by MRI under-estimates GLP for very low perfusion values and over-estimates for very high perfusion values. For perfusion values within the normal range PBF measured by MRI and GLP are in excellent agreement.

Figure 6. Regional distribution of pulmonary blood flow in a participant without COPD

In this participant without COPD, PBF maps are shown of the posterior (a), middle (b) and anterior (c) coronal slice. PBF in the posterior lung is higher (PBF = 112 mlblood per min and 100mllung; a) than in the anterior lung parenchyma (PBF = 74 mlblood per min and 100mllung; c) as an effect of gravity in the posterior, dependent portion of the lungs in the supine position.