Abstract #0577

Fast 3D B1+ Mapping using An Optimized, Asymmetric Bloch-Siegert Method

Manojkumar Saranathan¹, Mohammad Mehdi Khalighi², Adam B. Kerr³, Brian Rutt¹

¹Radiology, Stanford University, Stanford, CA, USA; ²Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA; ³Electrical Engineering, Stanford University, Stanford, CA, USA

B1+ mapping is important in a number of high-field imaging applications including multi-transmit rf pulse design and MR relaxometry. The recently proposed Bloch-Siegert (BS) B1+ mapping method circumvents spoiling and saturation issues faced by magnitude-based methods such as Actual Flip-angle Imaging (AFI) and the Double Angle Method. While the BS method is relatively fast due to its T1 insensitivity, its accuracy depends on the power of the BS pulse, which is SAR limiting, especially at 7T. This SAR limit can prolong acquisition times, especially for multiple transmit channel B1+ mapping applications. We propose a novel, fast whole brain 3D Bloch-Siegert B1+ mapping method that is optimized for very short scan times and low SAR and demonstrate isotropically resolved whole human brain B1+ mapping in scan times on the order of 30 seconds at 3T and a minute at 7T.