Steady‐state double‐angle method for rapid B1 mapping

Purpose To introduce an accurate, rapid, and practical method for active B 1 field mapping based on the double‐angle method (DAM) in the steady‐state (SS) signal regime. Methods We introduced and evaluated the performance of the SS‐DAM approach to map the B 1 field and compared the results to those calculated from the conventional DAM approach. Similar to DAM, SS‐DAM uses the signal intensity ratio of 2 magnitude images acquired with different flip angles using the spoiled gradient recalled echo sequence. However, unlike DAM, in SS‐DAM, these 2 spoiled gradient recalled echo images are acquired with very short TR, which allows substantially reduced acquisition time. Numerical, phantom, and in vivo brain imaging analyses, representing a wide range of T 1 s and large B 1 variation, were conducted. Methods for further accelerating acquisition were also investigated. Results Our results demonstrate the potential of the SS‐DAM approach to be applied widely in the clinical setting. B 1 maps derived from SS‐DAM were demonstrated to be quantitatively comparable to those derived from DAM but were derived much more rapidly. Large‐volume B 1 maps were obtained at a field strength of 3 tesla within clinically acceptable acquisition times. Conclusion SS‐DAM permits accurate B 1 mapping in the clinical setting, with whole‐brain coverage in less than 1 min.