Myocardial iron quantification using modified Look-Locker inversion recovery (MOLLI) T1 mapping at 3 Tesla

Abstract

Background Quantification of myocardial iron overload is critical for the management of patients with hemochromatosis. The effects of excess iron on T1 and T2* relaxation times correlate directly with tissue iron concentration. T2* became the clinical standard at 1.5T as it can be easily obtained in a fast one breath-hold ECG gated multi-echo GRE sequence. At 3T, however, T2* quantification can be limited by pronounced susceptibility artifacts and signal sampling restraints due to shorter T2* times at higher iron concentrations . Since myocardial T1 time is up to thirty times longer than T2*, it can be quantified with short echo-time inversionrecovery sequences even at high iron concentrations, and is less sensitive to susceptibility artifacts. We aimed to validate a recently developed modified LookLocker inversion recovery (MOLLI) sequence to quantify myocardial T1 in healthy controls and patients with iron overload at 3T, comparing to standard GRE based multi-echo T2* times at 1.5T. Methods A total of 15 normal volunteers and 7 chronic anemia patients (with a myocardial T2* measure <20 ms at 1.5T in the last 2 years, five of these on iron chelating therapy) were prospectively enrolled. Myocardial T2* and T1 times were quantified in the same day, the former using a breath-hold multi-echo GRE sequence at 1.5T (Symphony, Siemens, Erlangen, Germany) and the latter using the T1 mapping -MOLLI sequence at 3T (Verio, Siemens, Erlangen, Germany). All ROIs were placed at mid-interventricular septum, carefully avoiding the blood pool (Fig 1). All analyses were blinded. Results All patients had regular heart rhythm and all MRI exams showed diagnostic image quality. Volunteers and patients had significantly different mean myocardial T2* (27.2 ms +/- 3.9 vs. 15.4 ms +/- 6.3 p<0.05 respectively) and T1 times 1175.7 ms +/- 22.8 vs. 952.1 ms +/- 173.2 p<0.05 respectively). 3T T1 times strongly correlated with 1.5T T2* times (r=0.95 and Fig 2). Using the 3T T1 cut-off of 1130 ms, sensitivity and specificity for 3T