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Keywords:

  • cartilage;
  • Gd-DTPA;
  • relaxivity;
  • diffusion;
  • glycosaminoglycan

Abstract

Prior work indicates that the distribution of Gd(DTPA)2- (as measured by T1) is a good surrogate measure of the distribution of gycosaminoglycan (GAG) in cartilage. In addition to the measured T1 in the presence of Gd(DTPA)2-, the precision of the measurement of Gd(DTPA)2- concentration depends on the T1 without Gd(DTPA)2- (Tmath image), and the relaxivity (r) of Gd(DTPA)2- in cartilage, parameters that are influenced by cartilage composition. These parameters were measured in native and GAG-depleted cartilage in order to estimate the bounds on the values one might expect for cartilage in arbitrary states of degeneration. The range of Tmath image was 0.3 sec; the range of r was 0.6 (mM*s)-1 at 8.5 T and 1.4 (mM*s)-1 at 2 T. These data suggest that Gd(DTPA)2- will be underestimated (and GAG overestimated) if the values for Tmath image and r are assumed to be those of native cartilage. (For example, in a severe case a 90% loss of GAG would be underestimated as a 70% loss.) Gd(HPDO3A) was investigated as a nonionic “control agent” and found to have relaxivity and diffusion properties that were comparable to Gd(DTPA)2- (rGd(HPDO3A)/rGd(DTPA) ≈ 1; DGd(HPDO3A)/DGd(DTPA) ≈ 0.85). Since Gd(HPDO3A) distributes uniformly through cartilage (independent of GAG), the distribution of T1 with Gd(HPDO3A) can be used as a surrogate measure of variations in Tmath image and r, if present. From the perspective of transport, if Gd(HPDO3A) has fully penetrated the cartilage, Gd(DTPA)2- would have in the same time frame. Therefore, the data confirm the efficacy of using Gd(HPDO3A) as a “control agent” for dGEMRIC. Magn Reson Med 48:1068–1071, 2002. © 2002 Wiley-Liss, Inc.