Relationship between measurement errors in myocardial t₁ mapping and heart rate

Purpose: Modified Look-Locker inversion recovery (MOLLI) using a 5s(3s)3s scheme is robust to tachycardia, but some errors are occasionally observed in myocardial T₁ mapping. We sought to evaluate the relationship between measurement errors in T₁ mapping and heart rate (HR) using a confidence map. Methods: We enrolled 69 male patients with normal native T₁ values of the septal myocardium measured by a 5s(3s)3s MOLLI. The degree of measurement errors in the septal myocardium was assessed by two independent observers on a confidence map using a 4-point scale: 0, no errors; 1, errors located on the myocar-dial contour; 2, errors extended into the myocardial contour; and 3, errors extended into the midwall. We compared the scores of measurement errors and the average, maximum, minimum or variability of the HR indicated during the MOLLI scan (iHR), image phases of MOLLI or left ventricular ejection fraction (LVEF). Results: Patients with score >1 for the septal myocardium had significantly lower minimum iHR than those with a score ≤1 (P < 0.01; 49.8 ± 10.1 vs. 59.6 ± 9.7 beat per min). Conclusion: The confidence map shows more measurement errors in patients with lower minimum iHR. The myocardial T₁ values should be measured carefully in patients with bradycardia during MOLLI scanning.