Optimization of Bloch-Siegert B1 Mapping Sequence for Maximum Signal to Noise

Abstract: Adiabatic Bloch-Siegert B1+ mapping method addresses the long TE and high RF power deposition problems of conventional Bloch-Siegert B1+ mapping by introducing short frequency-swept ABS pulses with maximum sensitivity. Here, it is shown how maximum signal to noise ratio can be achieved in adiabatic Bloch-Siegert B1+ mapping. Signal to noise ratio of B1+ maps is maximized by optimizing the adiabatic pulse parameters such as width, amplitude and shape of the Bloch-Siegert pulse within a specified scan time and under approved SAR guidelines. Equations for optimized Bloch-Siegert pulse parameters are derived, which are dependent on the base pulse sequence used for B1+ mapping as well as tissue properties and transmit coil configuration. It is shown that by this optimization it is more efficient to increase TR rather than using the averaging method to increase signal to noise ratio.