On the Diffusion Sensitivity of 2D- and 3D-Turbo Spin Echo Sequences

INTRODUCTION AND MOTIVATION: A common assumption in literature is that fast / turbo spin echo sequences (FSE/TSE) do not demonstrate any distinct diffusion weighting, since the permanent refocusing of magnetization does not lead to noticeable diffusion effects. This statement, however, does actually refer to standard TSE imaging with 180° refocusing pulses. The use of low refocusing flip angles, as used for specific absorption ratio (SAR) mitigation, introduces considerable fractions of dephased transversal and longitudinal magnetization components. These experience higher diffusion sensitivity due to b~k, with k being a measure for dephasing (e.g. ‘k-space’). Furthermore, modern types of 3D-TSE sequences such as SPACE or CUBE [1] use very long RF pulse trains with variable flip angles. This work investigates therefore the effective diffusion sensitivity of such contemporary TSE sequences by using a recently published extended phase graph (EPG) approach [2-4].