Transmit B1+ Field Inhomogeneity and T1 Estimation Errors in Breast DCE-MRI at 3 Tesla

Purpose: To quantify B-1(+) variation across the breasts and to evaluate the accuracy of precontrast T-1 estimation with and without B-1(+) variation in breast MRI patients at 3 Tesla (T). Materials and Methods: B-1(+) and variable flip angle (VFA) T-1 mapping were included in our dynamic contrastenhanced (DCE) breast imaging protocol to study a total of 25 patients on a 3.0T GE MR 750 system. We computed precontrast T-1 relaxation in fat, which we assumed to be consistent across a cohort of breast imaging subjects, with and without compensation for B-1(+) variation. The mean and standard deviation of B-1(+) and T-1 values were calculated for statistical data analysis. Results: Our measurements showed a consistent B-1(+) field difference between the left and right breasts. The left breast has an average 15.4% higher flip angle than the prescribed flip angle, and the right breast has an average 17.6% lower flip angle than the prescribed flip angle. This average 33% flip angle difference, which can be vendor and model specific, creates a 52% T-1 estimation bias in fat between breasts using the VFA T-1 mapping technique. The T-1 variation is reduced to 7% by including B-1(+) correction. Conclusion: We have shown that severe B-1(+) variation over the breasts can cause a substantial error in T-1 estimation between the breasts, in VFA T-1 maps at 3T, but that compensating for these variations can considerably improve accuracy of T-1 measurements, which can directly benefit quantitative breast DCE-MRI at 3T.