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.
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.
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.