Increasing bandwidth of spatially selective transmit SENSE pulses using constrained optimization

Introduction: Multiple-channel transmission has been shown to offer acceleration of multidimensional spatially-selective pulses. Main applications of such pulses would be performing a homogenous excitation in a varying B1 field or localized spectroscopic imaging. A major problem is the small bandwidth of such localized pulses. Small off-resonances (either induced by B0 inhomogeneities or spectroscopic frequency shift) deteriorate the resulting magnetization profile. On ultra high field systems (>4T) the off-resonance effects are especially problematic. It is therefore important to have explicit control of the bandwidth of multiple-channel transmission pulses for either imaging or spectroscopy. Method: The method we propose is based on the spectral-spatial pulse design introduced in Ref. [1] and expanded to use the benefits of parallel RF transmission. In this method, the frequency axis is mapped to a virtual additional spatial axis applying a constant gradient in the new direction. The desired spatial pattern as a function of the frequency mdes(f) is sampled in the frequency and spatial domain (see Figure 1 a). The virtual gradient applied in the frequency direction is calculated from the virtual field of view (FOV) and the desired