Exercise‐Induced Alterations in Lung Water Density in Heart Failure Using Single–Breath–Hold <scp>3D</scp> Ultrashort Echo Time <scp>MRI</scp>

BACKGROUND: Evaluating pulmonary congestion after exercise in heart failure (HF) may reveal perturbations not apparent at rest and provide insight into dyspnea and exercise intolerance. PURPOSE: To investigate the reproducibility and exercise-induced alterations in lung water density (LWD) using 3D ultrashort echo time (UTE) MRI. STUDY TYPE: Prospective. FIELD STRENGTH/SEQUENCE: 3-T MRI with a prototype 3D stack-of-spirals UTE Volumetric Interpolated Breath-hold Examination (VIBE) sequence. POPULATION: Sixty-nine HF patients (59 ± 12 years; 39 males) across a range of left ventricular ejection fraction (23 HFpEF, 16 HFmrEF, 18 HFimpEF, and 12 HFrEF); 34 healthy subjects. ASSESSMENT: UTE MRI was performed at rest and after exercise. Images were normalized to yield relative LWD (%). LWD was quantified as the mean normalized pixel intensity within the segmented parenchyma, and lung volume was also measured. Reproducibility was evaluated in a separate scan/rescan study. STATISTICAL TESTS: test or Fisher's exact test; Bland-Altman analysis. p < 0.05 was considered significant. RESULTS: In healthy controls, LWD decreased significantly after exercise with an absolute change of -1.25% (interquartile range [IQR]: -2.92% to 0.38%) and relative change of -4.35% (IQR: -9.55% to 1.30%). Compared with controls, HFpEF showed a significantly greater absolute change (0.47%, IQR: -0.91% to 2.10%) and relative change in LWD (1.46%, IQR: -2.65% to 6.45%), not apparent in other HF subgroups (p = 0.053-0.821). Changes in lung volume did not differ between each HF subgroup and healthy controls (p = 0.056-0.498). Bland-Altman analysis demonstrated good agreement for LWD and lung volume. DATA CONCLUSION: Single-breath-hold 3D UTE MRI provides reproducible LWD measurements at rest and enables detection of exercise-induced LWD alterations. This approach captures pulmonary fluid changes following exercise and identifies greater LWD response in HFpEF. TECHNICAL EFFICACY: Stage 1.