In Vivo 17O Measurements of Water Rotational Correlation Time and Hydrodynamic Radius in Rat Brain

Xiao-Hong Zhu¹, Wei Chen¹

This study aims to exploit new MR approaches for noninvasively measuring the rotational correlation time (τ _c) and hydrodynamic radius (R_h) of the brain tissue water. in vivo ¹⁷O MRS was used to measure T₁ of the quadrupolar ¹⁷O spin of water in the rat brain at 9.4T, and to calculate τ _c according to a simple, field-independent relation. ¹H MRI was applied to image the brain translational diffusion coefficient (D_t); and the value of R_h was derived from the D_t/T₁ ratio. It was found that i) the brain water τ _c was in a range of several picoseconds and sensitive to brain temperature change, ii) R_h was about 1 that is in line with the water molecular size. This work indicates excellent utilities of in vivo ¹⁷O MRS for potentially imaging the microscopic matrix of brain tissue water properties in vivo.