In vivo measurement of bound and free water density in normal human brain by MRI

Objective To measure bound and free water density of human brain in vivo Methods New formulas were developed to obtain bound and free water density Some parameters in those formulas that can be measured are proton density, magnetization transfer ratio (MTR), T 1 relaxation times both with and without off resonance irradiation Seven normal volunteers were studied using various pulse sequences The bound and free water density in white matter, gray matter, and cerebrospinal fluid (CSF) were calculated Results The bound and free water densities were 565 7±115 9 and 811 5±111 0 in gray matter, higher than those (512 3±102 3 and 632 5±65 5 )in white mater ( P 0 01) While MTR was 0 263±0 029 in gray matter lower than that (0 344±0 028)in white matter ( P 0 01) Conclusion Bound water is another parameter for tissue characterization which is different from MTR Our bound water formula indicated their relationship in mathematics