Correlation of relaxation time with water content in muscle and brain tissues

Proton T₁ of water in muscle and brain tissues was studied as a function of water content at 25°C and 5, 30, and 100 MHz. Muscle samples were bathed in modified Krebs solutions that have the same ionic strength but different osmolarity in order to change the water content. At all three frequencies their 1/T₁ extrapolated to the same value of 0.6 s^?1 for zero dry weight, indicating that T₁ for the majority of water molecules in normal muscle and brain is frequency-independent. Dehydrated muscle, homogenized brain tissue suspended in modified Krebs solution and dehydrated brain tissue provide samples with wide ranges of water content. Their T₁ values at all three frequencies can be well accounted for by a simple equation derived from the two-state model.