Nonrigid registration improves MRI T₂quantification in heart transplant patient follow-up

BACKGROUND: To evaluate the use of a nonrigid registration technique for detecting acute heart transplant rejection by MRI T2 quantification. METHODS: Myocardial T2 quantification was achieved in 279 consecutive examinations from 78 different patients. The protocol consisted of 10 successive black-blood fast spin echo sequences with varying echo times, and a postprocessing based on image registration and exponential fitting. An automatic nonrigid registration method was applied to correct for myocardium misalignment. Finally T2 values were compared with those obtained with a conventional rigid registration followed by manual correction. RESULTS: Nonrigid registration was feasible in 98% of the datasets and was judged of higher quality compared with conventional processing (P < 0.001). No significant difference was found in the clinical outcome (average septal T2 ) between nonrigid and conventional registration (P = 0.66). Interobserver variability was improved with 95% limits of agreement of 2.7 ms (against 3.7 ms with conventional registration). The quality of T2 fitting, as assessed by the coefficient of determination R(2) , was significantly improved (P < 0.001). CONCLUSION: Nonrigid registration improves T2 quantification in heart-transplant patient follow-up.