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B1 mapping with selective pulses



Knowledge of Binline image distribution is crucial for many applications, such as quantitative MRI. A novel method has been developed to improve the accuracy of the conventionally applied double-angle method for Binline image mapping. It solves the remaining issues raised by the use of selective pulses for slice selection to accelerate the acquisition process. A general approach for reconstructing Binline image maps is presented first. It takes Binline image-induced slice profile distortions over off-resonance frequencies into account. It is then shown how the ratio between the prescribed flip angles can be adjusted to reach a compromise between the level of noise propagated onto Binline image maps and the width of the range in which the field can be mapped. Lastly, several solutions are proposed for reducing the Binline image-dependent pollution of regions distal to the image slice which participates significantly in the inaccuracy of Binline image mapping. These methods were experimentally tested by comparison with gold standard Binline image maps obtained on a phantom using a non-selective and thus much slower technique. As they are independent and lead to significant improvements, these solutions can be combined to achieve high precision and fast Binline image mapping using spin-echo DAM. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.