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

Valerij G. Kiselev¹

Transverse relaxation in living tissue is contributed by the dephasing of spins due to diffusion in mesoscopic magnetic fields induced, for example, by paramagnetic tracer in the blood pool. The associated correlation time is commensurate with the echo time of typical measurement sequences. Varying the echo time changes the character of dephasing from reversible for short TE to irreversible for long TE. This dependence is quantified by calculating the transverse relaxation rate in the capillary network for multiple refocusing pulses in the static dephasing regime. This yields a modified formula for the mean vessel size in the vessel size imaging.