Spin Echo Amplitude in Biological Tissue with Implications for Vessel Size Imaging

Introduction: Transverse relaxation in living tissue can be used as a probe of tissue structure. Vessel size imaging [1-3] is a realization of this potential: The mean size of microvessels can be evaluated by comparison of the gradient echo and spin echo amplitudes. In practical implementation, it is often convenient to use multiple refocusing pulses (CPMG-type measurement) instead of a single spin echo (the corresponding imaging sequences are termed RARE, Turbo Spin Echo or Fast Spin Echo). The problem with these techniques is that the vessel size imaging relies strongly on theoretical interpretation of the signal, which is currently not available for echoes obtained with multiple refocusing pulses. The aim of this study is to provide for such a theory in the static dephasing regime, which is the most relevant for measurements with a contrast enhancement at high fields.