• Reza Basiri, Paolo Federico, and Robert Marc Lebel.
• Biomedical Engineering, University of Calgary, 2500 University Dr NW, Calgary, AB, T2N 1N4, Canada. rbasiri@ucalgary.ca.
• MAGMA. 2019 Dec 1; 32 (6): 669-677.

ObjectivePurely exponential decay is rarely observed in conventional mono-exponential T2 mapping due to transmit field inhomogeneity and calibration errors, which collectively introduce stimulated and indirect echo pathways. Stimulated echo correction (SEC) requires an additional fit parameter for the transmit field, resulting in greater uncertainty in T2 relative to mono-exponential fitting. The aim of this study was to develop an accurate and precise method for T2 mapping using SEC.MethodsThe proposed method, called two-step SEC (tSEC), leverages spatial correlations in the transmit field to reduce the number of fully independent fitting parameters from three to two. The method involves a two-pass fit: the first pass involves a fast but standard SEC fit. The initially estimated transmit field is smoothed and provided as a fixed input to the second pass.ResultsSimulations and in vivo experiments demonstrated up to 38% and 27% decreases in relative T2 variance with tSEC relative to SEC. Average T2 values were unchanged between tSEC and SEC fits. The proposed method uses the same input data as SEC and exponential fits, so it is applicable to existing data.DiscussionThe proposed method generates reliable and reproducible quantitative T2 maps and should be considered for future relaxometry studies.

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