Variable flip angle 3D ultrashort echo time (UTE) T1 mapping of mouse lung: A repeatability assessment

Journal article, 2018

Background: Lung T1is a potential translational biomarker of lung disease. The precision and repeatability of variable flip angle (VFA) T1mapping using modern 3D ultrashort echo time (UTE) imaging of the whole lung needs to be established before it can be used to assess response to disease and therapy. Purpose: To evaluate the feasibility of regional lung T1quantification with VFA 3D-UTE and to investigate long- and short-term T1repeatability in the lungs of naive mice. Study type: Prospective preclinical animal study. Population: Eight naive mice and phantoms. Field strength/Sequence: 3D free-breathing radial UTE (8 μs) at 4.7T. Assessment: VFA 3D-UTE T1calculations were validated against T1values measured with inversion recovery (IR) in phantoms. Lung T1and proton density (S0) measurements of whole lung and muscle were repeated five times over 1 month in free-breathing naive mice. Two consecutive T1measurements were performed during one of the imaging sessions. Statistical Tests: Agreement in T1between VFA 3D-UTE and IR in phantoms was assessed using Bland–Altman and Pearson 's correlation analysis. The T1repeatability in mice was evaluated using coefficient of variation (CV), repeated-measures analysis of variance (ANOVA), and paired t-test. Results: Good T1agreement between the VFA 3D-UTE and IR methods was found in phantoms. T1in lung and muscle showed a 5% and 3% CV (1255 ± 63 msec and 1432 ± 42 msec, respectively, mean ± SD) with no changes in T1or S0over a month. Consecutive measurements resulted in an increase of 2% in both lung T1and S0. Data Conclusion: VFA 3D-UTE shows promise as a reliable T1mapping method that enables full lung coverage, high signal-to-noise ratio (∼25), and spatial resolution (300 μm) in freely breathing animals. The precision of the VFA 3D-UTE method will enable better design and powering of studies. Level of Evidence: 1. Technical Efficacy: Stage 2. J. Magn. Reson. Imaging 2018;48:846–852.