Rapid B1+ mapping using a preconditioning RF pulse with TurboFLASH readout

Abstract

In MRI, the transmit radiofrequency field (B) inhomogeneity can lead to signal intensity variations and quantitative measurement errors. By independently mapping the local B variation, the radiofrequency‐related signal variations can be corrected for. In this study, we present a new fast B mapping method using a slice‐selective preconditioning radiofrequency pulse. Immediately after applying a slice‐selective preconditioning pulse, a turbo fast low‐angle‐shot imaging sequence with centric k‐space reordering is performed to capture the residual longitudinal magnetization left behind by the slice‐selective preconditioning pulse due to B variation. Compared to the reference double‐angle method, this method is considerably faster. Specifically, the total scan time for the double‐angle method is equal to the product of 2 (number of images), the number of phase‐encoding lines, and approximately 5T₁, whereas the slice‐selective preconditioning method takes approximately 5T₁. This method was validated in vitro and in vivo with a 3‐T whole‐body MRI system. The combined brain and pelvis B measurements showed excellent agreement and strong correlation with those by the double‐angle method (mean difference = 0.025; upper and lower 95% limits of agreement were −0.07 and 0.12; R = 0.93; P < 0.001). This fast B mapping method can be used for a variety of applications, including body imaging where fast imaging is desirable. Magn Reson Med, 2010.