13N-ammonia positron emission tomography/magnetic resonance imaging in patients with ischemia with non-obstructive coronary arteries: focus on feature tracking and T1 mapping.

BACKGROUND: Ischemia with non-obstructive coronary arteries (INOCA) is associated with elevated cardiovascular risk, yet early subclinical myocardial changes often go undetected by conventional imaging. This study aimed to determine whether patients with INOCA exhibit subclinical tissue alterations identified by T1 mapping and left ventricular wall motion abnormalities assessed by cardiac magnetic resonance feature tracking (CMR-FT), in comparison with matched healthy controls (HC). METHODS: A total of 44 patients with INOCA and 22 matched HC were prospectively enrolled from August 2024 to February 2026, and all underwent hybrid cardiac positron emission tomography/magnetic resonance imaging (PET/MRI) examination. CMR-derived parameters were obtained and compared across the study groups. RESULTS: Native T1 values increased progressively across three groups: HC, INOCA with myocardial flow reserve (MFR) >2, and INOCA with MFR <2 (1,196±19 vs. 1,213±8 vs. 1,244±20 ms; P<0.001). In contrast, the absolute values of global longitudinal strain (GLS) showed a gradual reduction (-19.21%±1.84% vs. -17.83%±0.92% vs. -16.25%±1.59%; P<0.001), whereas no significant intergroup differences were observed in left ventricular ejection fraction (LVEF) or extracellular volume (ECV) (both P>0.05). Both native T1 and GLS were negatively correlated with MFR (r=-0.739, P<0.001; r=-0.638, P<0.001, respectively). Similarly, native T1 and ECV were positively correlated with GLS (P<0.001 and P=0.004). CONCLUSIONS: Native T1 and GLS correlate with impaired MFR in patients with INOCA, consistent with subclinical left ventricular (LV) systolic dysfunction related to myocardial ischemia. Incorporating CMR into clinical practice may aid in the monitoring and treatment of patients with INOCA, and further studies exploring the underlying mechanisms are warranted.