Extrapolated-B1-corrected Variable Flip Angle T1 Mapping in Cortical Bone with a Phase-Sensitive Method

Motivation: Unintended heating of the skull and nearby soft tissue during transcranial MR-guided Focused Ultrasound surgery needs to be monitored. However, T1-based thermometry in cortical bone may be biased with variable flip angles. Goal(s): Our goal was to correct flip angles to improve the T1 mapping accuracy in cortical bone. Approach: In phantom and human studies, B1 maps of soft tissue were measured with a phase-sensitive method, extrapolating from which B1 maps of bone were generated and were used to correct flip angles for T1 mapping. Results: Improved accuracy and homogeneity of T1 maps were demonstrated as validation. Impact: Extrapolated-B1 correction with a phase-sensitive method should improve accuracy and homogeneity of T1 maps in cortical bone and is promising in monitoring unintended heating in the skull and nearby brain tissue during transcranial MR-guided Focused Ultrasound surgery.