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.

Feasibility, Repeatability, and Correlation to Lung Function of Phase-Resolved Functional Lung (PREFUL) MRI-derived Pulmonary Artery Pulse Wave Velocity Measurements.

BACKGROUND: Pulse wave velocity (PWV) in the pulmonary arteries (PA) is a marker of vascular stiffening. Currently, only phase-contrast (PC) MRI-based options exist to measure PA-PWV. PURPOSE: To test feasibility, repeatability, and correlation to clinical data of Phase-Resolved Functional Lung (PREFUL) MRI-based calculation of PA-PWV. STUDY TYPE: Retrospective. SUBJECTS: 79 (26 female) healthy subjects (age range 19-78), 58 (24 female) patients with chronic obstructive pulmonary disease (COPD, age range 40-77), 60 (33 female) patients with suspected pulmonary hypertension (PH, age range 28-85). SEQUENCE: 2D spoiled gradient echo, 1.5T. ASSESSMENT: PA-PWV was measured from PREFUL-derived cardiac cycles based on the determination of temporal and spatial distance between lung vasculature voxels using a simplified (sPWV) method and a more comprehensive (cPWV) method including more elaborate distance calculation. For 135 individuals, PC MRI-based PWV (PWV-QA) was measured. STATISTICAL TESTS: Intraclass-correlation-coefficient (ICC) and coefficient of variation (CoV) were used to test repeatability. Nonparametric tests were used to compare cohorts. Correlation of sPWV/cPWV, PWV-QA, forced expiratory volume in 1 sec (FEV1) %predicted, residual volume (RV) %predicted, age, and right heart catheterization (RHC) data were tested. Significance level α = 0.05 was used. RESULTS: sPWV and cPWV showed no significant differences between repeated measurements (P-range 0.10-0.92). CoV was generally lower than 15%. COPD and PH patients had significantly higher sPWV and cPWV than healthy subjects. Significant correlation was found between sPWV or cPWV and FEV1%pred. (R = -0.36 and R = -0.44), but not with RHC (P-range -0.11 - 0.91) or age (P-range 0.23-0.89). Correlation to RV%pred. was significant for cPWV (R = 0.42) but not for sPWV (R = 0.34, P = 0.055). For all cohorts, sPWV and cPWV were significantly correlated with PWV-QA (R = -0.41 and R = 0.48). DATA CONCLUSION: PREFUL-derived PWV is feasible and repeatable. PWV is increased in COPD and PH patients and correlates to airway obstruction and hyperinflation. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY: Stage 2.

Comparison of Free-Breathing 3D Phase-Resolved Functional Lung (PREFUL) MRI With Dynamic 19 F Ventilation MRI in Patients With Obstructive Lung Disease and Healthy Volunteers.

BACKGROUND: Non-contrast-enhanced 1 H magnetic resonance imaging (MRI) with full lung coverage shows promise for assessment of regional lung ventilation but a comparison with direct ventilation measurement using 19 F MRI is lacking. PURPOSE: To compare ventilation parameters calculated using 3D phase-resolved functional lung (PREFUL) MRI with 19 F MRI. STUDY TYPE: Prospective. POPULATION: Fifteen patients with asthma, 14 patients with chronic obstructive lung disease, and 13 healthy volunteers. FIELD STRENGTH/SEQUENCE: A 3D gradient-echo pulse sequence with golden-angle increment and stack-of-stars encoding at 1.5 T. ASSESSMENT: All participants underwent 3D PREFUL MRI and 19 F MRI. For 3D PREFUL, static regional ventilation (RVent) and dynamic flow-volume cross-correlation metric (FVL-CM) were calculated. For both parameters, ventilation defect percentage (VDP) values and ventilation defect (VD) maps (including a combination of both parameters [VDPCombined ]) were determined. For 19 F MRI, images from eight consecutive breaths under volume-controlled inhalation of perfluoropropane were acquired. Time-to-fill (TTF) and wash-in (WI) parameters were extracted. For all 19 F parameters, a VD map was generated and the corresponding VDP values were calculated. STATISTICAL TESTS: For all parameters, the relationship between the two techniques was assessed using a Spearman correlation (r). Differences between VDP values were compared using Bland-Altman analysis. For regional comparison of VD maps, spatial overlap and Sørensen-Dice coefficients were computed. RESULTS: 3D PREFUL VDP values were significantly correlated to VDP measures by 19 F (r range: 0.59-0.70). For VDPRVent , no significant bias was observed with VDP of the third and fourth breath (bias range = -6.8:7.7%, P range = 0.25:0.30). For VDPFVL-CM , no significant bias was found with VDP values of fourth-eighth breaths (bias range = -2.0:12.5%, P range = 0.12:0.75). The overall spatial overlap of all VD maps increased with each breath, ranging from 61% to 81%, stabilizing at the fourth breath. DATA CONCLUSION: 3D PREFUL MRI parameters showed moderate to strong correlation with 19 F MRI. Depending on the 3D PREFUL VD map, the best regional agreement was found to 19 F VD maps of third-fifth breath. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY: Stage 2.

Influence of gadolinium, field-strength and sequence type on quantified perfusion values in phase-resolved functional lung MRI.

PURPOSE: The purpose of this study is to evaluate the influences of gadolinium-based contrast agents, field-strength and different sequences on perfusion quantification in Phase-Resolved Functional Lung (PREFUL) MRI. MATERIALS AND METHODS: Four cohorts of different subjects were imaged to analyze influences on the quantified perfusion maps: 1) at baseline and after 2 weeks to obtain the reproducibility (26 COPD patients), 2) before and after the administration of gadobutrol (11 COPD, 2 PAH and 1 asthma), 3) at 1.5T and 3T (12 healthy, 4 CF), and 4) with different acquisition sequences spoiled gradient echo (SPGR) and balanced steady-state free precession (bSSFP) (11 COPD, 7 healthy). Wilcoxon-signed rank test, Bland-Altman plots, voxelwise Pearson correlations, normalized histogram analyses with skewness and kurtosis and two-sample Kolmogorov-Smirnov tests were performed. P value ≤ 0.05 was considered statistically significant. RESULTS: In all cohorts, linear correlations of the perfusion values were significant with correlation coefficients of at least 0.7 considering the entire lung (P<0.01). The reproducibility cohort revealed stable results with a similar distribution. In the gadolinium cohort, the quantified perfusion increased significantly (P<0.01), and no significant change was detected in the histogram analysis. In the field-strength cohort, no significant change of the quantified perfusion was shown, but a significant increase of skewness and kurtosis at 3T (P = 0.01). In the sequence cohort, the quantified perfusion decreased significantly in the bSSFP sequence (P<0.01) together with a significant decrease of skewness and kurtosis (P = 0.02). The field-strength and sequence cohorts had differing probability distribution in the two-sample Kolmogorov-Smirnov tests. CONCLUSION: We observed a high susceptibility of perfusion quantification to gadolinium, field-strength or MRI sequence leading to distortion and deviation of the perfusion values. Future multicenter studies should strictly adhere to the identical study protocols to generate comparable results.