Echo time-dependent observed T1 and quantitative perfusion in chronic obstructive pulmonary disease using magnetic resonance imaging.

INTRODUCTION

Due to hypoxic vasoconstriction, perfusion is interesting in the lungs. Magnetic Resonance Imaging (MRI) perfusion imaging based on Dynamic Contrast Enhancement (DCE) has been demonstrated in patients with Chronic Obstructive Pulmonary Diseases (COPD) using visual scores, and quantification methods were recently developed further. Inter-patient correlations of echo time-dependent observed T [T(TE)] have been shown with perfusion scores, pulmonary function testing, and quantitative computed tomography. Here, we examined T(TE) quantification and quantitative perfusion MRI together and investigated both inter-patient and local correlations between T(TE) and quantitative perfusion.

METHODS

22 patients (age 68.0 ± 6.2) with COPD were examined using morphological MRI, inversion recovery multi-echo 2D ultra-short TE (UTE) in 1-2 slices for T(TE) mapping, and 4D Time-resolved angiography With Stochastic Trajectories (TWIST) for DCE. T(TE) maps were calculated from 2D UTE at five TEs from 70 to 2,300 μs. Pulmonary Blood Flow (PBF) and perfusion defect (QDP) maps were produced from DCE measurements. Lungs were automatically segmented on UTE images and morphological MRI and these segmentations registered to DCE images. DCE images were separately registered to UTE in corresponding slices and divided into corresponding subdivisions. Spearman's correlation coefficients were calculated for inter-patient correlations using the entire segmented slices and for local correlations separately using registered images and subdivisions for each TE. Median T(TE) in normal and defect areas according to QDP maps were compared.

RESULTS

Inter-patient correlations were strongest on average at TE = 500 μs, reaching up to |ρ| = 0.64 for T with PBF and |ρ| = 0.76 with QDP. Generally, local correlations of T with PBF were weaker at TE than at TE or TE and with maximum values of |ρ| = 0.66 (from registration) and |ρ| = 0.69 (from subdivision). In 18 patients, T was shorter in defect areas than in normal areas, with the relative difference smallest at TE.

DISCUSSION

The inter-patient correlations of T with PBF and QDP found show similar strength and TE-dependence as those previously reported for visual perfusion scores and quantitative computed tomography. The local correlations and median T suggest that not only base T but also the TE-dependence of observed T in normal areas is closer to that found previously in healthy volunteers than in defect areas.