Calculation of GAG Content From A Measurement of Cartilage T1 in the Presence of Gd-DTPA 2-

The concentration of Gd-DTPA 2- in the tissue can be derived from measured T1 data according to Equation 1, where T1 Tissue+Agent is the measured T1 of tissue equilibrated in contrast agent, T1 Tissue is the measured T1 of tissue without contrast agent, and R is the relaxivity of the contrast agent in tissue. The relaxivity of Magnevist in tissue at 8.45 Tesla is R=4.5 mMs -1.

Eq. 1

Tissue Fixed Charge Density (FCD) is calculated from the measured Gd -2 concentration in the tissue and the known Gd -2 concentration in the bath using Equation 2. (See FCD Derivation.) The empirical factor of 2 appearing on the right side of Equation 2 is necessary to fit the Donnan-based prediction to biochemically measured FCD.

Eq. 2

 Calculation of tissue GAG content assumes -2 moles of charge per mole of GAG in the tissue and a molecular weight of 502.5 g/mole GAG, Equation 3.

Eq. 3