A k-Space Analysis of MR Tagging

We present a k-space approximation that directly relates a pulse sequence to its residual pattern of z-directed magnetization Mz, in a manner akin to the k-space approximation for small tip-angle excitation. Our approximation is particularly useful for the analysis and design of tagging sequences, in which Mz is the important quantity - as opposed to the transverse magnetization components Mx and My considered in selective excitation. We demonstrate that our approximation provides new insights into tagging, can be used to design novel tag patterns, and, more generally, may be applied to selective presaturation sequences for purposes other than tagging.