Selective parity RARE imaging

This work describes a novel method for rapid acquisition with relaxation enhancement (RARE)/fast spin-echo (FSE) imaging that removes the constraint of compliance with the Carr-Pur-cell-Meiboom-Gill (CPMG) condition. In a multiecho sequence, echoes with either odd or even parities are acquired. The refocusing angles are chosen using a recursive algorithm, so that the signal amplitude satisfies a predetermined modulation function. In the examples given in this article an exponential decay to a plateau is used. At each echo the echo parity that gives the desired signal amplitude for the minimum refocusing angle is selected. It is further shown that in the presence of an initial magnetization having an arbitrary phase distribution, the complex conjugate of the signal of one echo parity has to be taken and its k-space coordinates reversed. T(2)*-weighted images are presented and initial applications to diffusion-weighted imaging (DWI) and functional imaging shown.