Transmit B 1 + field inhomogeneity and T 1 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 MethodsB 1 + and variable flip angle (VFA) T 1 mapping were included in our dynamic contrast‐enhanced (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. J. Magn. Reson. Imaging 2013;38:454–459. © 2012 Wiley Periodicals, Inc.