Influence of echo time on pulmonary ventilation and perfusion derived by phase‐resolved functional lung (PREFUL) MRI using multi‐echo ultrashort echo time acquisition

Non‐contrast enhanced 1H magnetic resonance imaging (MRI) is promising for ventilation/perfusion (V/Q) assessment of the lung but the influence of the echo time (TE) on V/Q parameters is lacking. Therefore, the purpose of this study was to investigate the influence of different TEs on pulmonary V/Q parameters derived by phase‐resolved functional lung (PREFUL) MRI using a multi‐echo ultrashort TE (UTE) acquisition. A 2D multi‐echo UTE sequence with radial center out readout and tiny golden angle increment was developed. Forty‐eight participants were enrolled in this study: 25 healthy subjects, six patients with asthma, and 17 patients with pulmonary fibrosis. Participants underwent two acquisitions of 2D multi‐echo UTE MRI with three TEs per acquisition (TE1–6: 0.07, 0.82, 1.72, 2.47, 3.37, and 4.12 ms). Regional ventilation (RVent), flow‐volume loop cross‐correlation metric (FVL‐CM), and normalized perfusion‐weighted signal (QN) maps were calculated. V/Q defect percentages (VDP/QDP) were determined. To assess repeatability, the measurement was repeated in healthy subjects. Median and interquartile range of RVent, FVL‐CM, QN, VDP, and QDP were calculated. To assess significant differences between parameters obtained at different TEs, Friedman's test and Dunnett's test were performed. Pearson correlation coefficients between RVent derived at TE1 and the difference in RVent between TE2,3 and TE1 were calculated. For repeatability assessment, coefficient of variation (CoV) and intraclass correlation coefficient (ICC) were determined. Significant differences were found comparing V/Q parameters obtained at TE3–6 compared to TE1. CoV increased with TE. For ICC, values between 0.35 (QDP at TE1) and 0.83 (VDPRVent at TE2) were obtained for T1,2. Statistically significant differences for ventilation and perfusion parameters derived by PREFUL were found for TE3–6 compared to TE1. All V/Q parameters were well repeatable for TE1–2. With increasing TE and respiratory volume, RVent shows a T2*‐dependency leading to biased ventilation assessment compared to TE1. Comparison of perfusion (Q) and ventilation (V) parameters derived by phase‐resolved functional lung (PRREFUL) MRI using a 2D multi‐echo UTE sequence acquisition (TE1–6: 0.07, 0.82, 1.72, 2.47, 3.37, and 4.12 ms) showed significant differences for TE3–6 compared to TE1. For TE2 compared to TE1, only small differences were found and all V/Q parameters were well repeatable for TE1–2. With increasing TE and respirato