Impact of B1 field inhomogeneity on DESPOT-based T1 and T2 mapping at 1.5T

Rapid quantitative imaging is very important for planning and guidance of MRI-guided oncological therapy. The normal liver tissue and metastases have different T1 and T2 relaxation times and their ratio T1/T2 , which makes these parameters relevant quantitative imaging biomarkers. Conventional T1 and T2 mapping techniques are relatively time-consuming, which has led to the development of promising rapid techniques, such as DESPOT1 and DESPOT2. However, in practice, even at 1.5T, electromagnetic fields are imperfect, which may influence the accuracy and precision of quantitative imaging techniques. In this study we have investigated the impact of B1 field inhomogeneity on the performance of 3D DESPOT1 and DESPOT2 methods and demonstrated that DESPOT1 method is sensitive to B1 field inhomogeneity, even at 1.5T. A 5% error in nominal flip angle significantly influences the calculated T1 value and leads to a 10% error in the observed T1 value. However, the T2 estimates are minimally affected, when T2 is calculated using non-B1 corrected T1 values. Thus, the influence of B1 deviations on T2 mapping is negligible, so, B1 field correction for T2 mapping based on DESPOT2 method, is not required.

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