The Impact of the Relaxivity Definition on the Quantitative Measurement of Glycosaminoglycans in Cartilage by the MRI dGEMRIC Method

The relaxivities (R-values) of the gadolinium diethylene triamine pentaacetic acid (Gd(DTPA)(2-)) ions in a series of skim-milk solutions at 0-40% milk concentrations were measured using NMR spectroscopy. The R-value was found to be approximately linearly proportional to the concentration of the solid component in the milk solution. Using the R-value at 20% solid component (approximately the solid concentration in bovine nasal cartilage), the glycosaminoglycan concentration in bovine nasal cartilage can be quantified using the MRI delayed gadolinium-enhanced MRI of cartilage method without the customary scaling factor of 2. This finding is also supported by the measurements using Na-23 NMR spectroscopy, Na-23 inductively coupled plasma analysis, and biochemical assay. The choice of the R-value definition in the MRI delayed gadolinium-enhanced MRI of cartilage method is discussed, and the definition of Gd(DTPA)(2-) ions as millimole per volume of tissue (or milk solution for substitution) should be used. Magn Reson Med 63:25-32, 2010. (C) 2009 Wiley-Liss, Inc.