Automated Ultrashort Echo Time (UTE) MRI Low Signal Volume Analysis in Stable Pediatric Cystic Fibrosis and After Elexacaftor/Tezacaftor/Ivacaftor Therapy.

BACKGROUND

Ultrashort echo time (UTE) MRI overcomes the low signal intensity and short T2* of pulmonary tissues, improving image quality. Abnormally low UTE signal intensities are associated with hallmarks of cystic fibrosis (CF), including gas trapping and lung hyperexpansion.

PURPOSE: To explore short-term repeatability and sensitivity to treatment of low signal volume (LSV) from UTE MRI in pediatric CF.

STUDY-TYPE: Single-site, retrospective, longitudinal.

SUBJECTS: Thirteen participants with stable CF (6M/7F, median age = 15 years old) were scanned at baseline and 1-month to evaluate short-term repeatability. Subsequently, 14 CF participants (7M/7F median age = 16 years old) were scanned pre- and 1-month post-initiation of elexacaftor/tezacaftor/ivacaftor (ETI).

FIELD STRENGTH/SEQUENCE: Three-dimensional stack-of-spirals for UTE, 2-dimensional gradient-echo for hyperpolarized xenon (Xe-MRI), 3-dimensional gradient-echo for thoracic cavity estimation at 3 T.

ASSESSMENT: LSV was analyzed from UTE MRI. Same-day spirometry, multiple-breath washout, and Xe-MRI were also performed to compare to LSV.

STATISTICAL TESTS: Differences were assessed with the Wilcoxon matched-pairs signed-rank test. Bland-Altman analysis and the Intraclass Correlation Coefficient (ICC) were used to assess 1-month repeatability in stable CF. Relationships between measures were assessed with Spearman correlation. p < 0.05 was considered significant.

RESULTS

Baseline LSV was correlated with forced expiratory volume in 1 s (FEV1), FEV1 to forced vital capacity ratio (FEV1/FVC), lung clearance index (LCI), and ventilation defect percent (VDP) (all |ρ| ≥ 0.50). LSV was not significantly different after 1-month (20.1 [10.9-25.5]% vs. 21.7 [12.7-28.2]%, p = 0.4548) in stable pediatric CF with Bland-Altman bias < 1% and ICC = 0.93. LSV was significantly reduced from 18.8 [12.0-30.3]% to 16.4 [7.8-19.6]% after 1-month of ETI and correlated with absolute differences in FEV1, FEV1/FVC, LCI, and VDP (all |ρ| ≥ 0.59).

DATA

CONCLUSION

LSV analysis was feasible and repeatable in pediatric CF over a 1-month period. LSV was significantly reduced 1-month after ETI treatment, indicating sensitivity to reduced gas trapping, hyperexpansion, and obstruction.

EVIDENCE LEVEL: 4.

TECHNICAL EFFICACY: 1.