Echo Time-Dependence of Observed Lung T 1 in Patients With Cystic Fibrosis and Correlation With Clinical Metrics.

Background: Noninvasive monitoring of early abnormalities and therapeutic intervention in cystic fibrosis (CF) lung disease using MRI is important. Lung T ₁ mapping has shown potential for local functional imaging without contrast material. Recently, it was discovered that observed lung T ₁ depends on the measurement echo time (TE).
Purpose: To examine TE-dependence of observed T ₁ in patients with CF and its correlation with clinical metrics.
Study Type: Prospective.
Population: In all, 75 pediatric patients with CF (8.6 ± 6.1 years, range 0.1-23 years), with 32 reexamined after 1 year.
Field Strength/sequence: Patients were examined at 1.5T using an established MRI protocol and a multiecho inversion recovery 2D ultrashort echo time (UTE) sequence for T ₁ (TE) mapping at five TEs including TE ₁ = 70 μs.
Assessment: Morphological and perfusion MRI were assessed by a radiologist (M.W.) with 11 years of experience using an established CF-MRI scoring system. T ₁ (TE) was quantified automatically. Clinical data including spirometry (FEV1pred%) and lung clearance index (LCI) were collected.
Statistical Tests: T ₁ (TE) was correlated with the CF-MRI score, clinical data, and LCI.
Results: T ₁ (TE) showed a different curvature in CF than in healthy adults: T ₁ at TE ₁ was shorter in CF (1157 ms ± 73 ms vs. 1047 ms ± 70 ms, P < 0.001), but longer at TE ₃ (1214 ms ± 72 ms vs. 1314 ms ± 68 ms, P < 0.001) and later TEs. The correlations of T ₁ (TE) with patient age (ρ _TE1-TE5 = -0.55, -0.44, -0.24, -0.30, -0.22), and LCI (ρ _TE1-TE5 = -0.43, -0.42, -0.33, 0.27, -0.22) were moderate at ultra-short to short TE (P < 0.001) but decreased for longer TE. Moderate but similar correlations at all TE were found with MRI perfusion score (ρ _TE1-TE5 = -0.43, -0.51, -0.47, -0.46, -0.44) and FEV1pred% (ρ _TE1-TE5 = +0.44, +0.44, +0.43, +0.40, +0.39) (P < 0.05).
Data Conclusion: TE should be considered when measuring lung T ₁ , since observed differences between CF and healthy subjects strongly depend on TE. The different variation of correlation coefficients with TE for structural vs. functional metrics implies that TE-dependence holds additional information which may help to discern effects of tissue structural abnormalities and abnormal perfusion.
Level of Evidence: 2 TECHNICAL EFFICACY STAGE: 1 J. MAGN. RESON. IMAGING 2020;52:1645-1654.
(© 2020 The Authors. Journal of Magnetic Resonance Imaging published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)