T1 mapping for diagnosis of early cardiac cellular allograft rejection.

Background: Non-invasive surveillance of acute cellular rejection (ACR) has become a primary focus in heart transplantation (HTx), aiming to reduce the frequency of invasive endomyocardial biopsies (EMB). While cardiac magnetic resonance (CMR) with T1 mapping has shown promise as a diagnostic tool, its application during the early post-transplant phase remains a significant knowledge gap, as perioperative tissue injury can confound imaging interpretation. Objective: To evaluate the accuracy of cardiac T1 mapping for ACR in heart transplant recipients within the first 60 days post-transplantation, using EMB as the reference standard. Methods: This prospective single-center study included adult HTx recipients within 60 days post-transplant. All patients underwent CMR with native T1 mapping and extracellular volume (ECV) quantification. EMB served as the gold standard, classifying patients into non-significant (<2R) and significant (≥2R) rejection groups. Results: Forty-five recipients were included; 14 (31.1%) presented with cellular rejection ≥2R. Baseline characteristics such as recipient mean age (50.1 vs 49.6 years, Conclusion: The diagnostic accuracy of standalone T1 mapping for identifying ACR was modest in this early post-HTx period. However, native T1 and ECV were significantly higher in the rejection group, and their integration into a multiparametric approach, including LGE, demonstrated a high NPV in this cohort. These findings highlight CMR's potential for monitoring myocardial changes even in the early post-transplant stage.