Relevant parameters in fitting the NMRD profiles of contrast agents

Relevant Parameters in Fitting the NMRD Profiles of Contrast Agents 

The number of inner sphere water molecules has an obvious effect on the relaxivity. Doubling the value of q will imply a doubling of and then a substantial increase in the relaxation efficacy of the Gd(III) complex, as shown in Pig. 7. Knowing q is then crucial for a proper analysis of the NMRD profile, but this parameter cannot be extracted from a best fit procedure as, at best, only the term q/r can be obtained. Prom a qualitative point of view, for relatively small Gd(III) complexes and in the absence of 

Since Gd(III) is in between Eu(III) and Tb(III) in the periodic table this procedure represents the most accurate, though indirect method for the evaluation of q. One has only to be aware of the possible change in the coordination number across the Ln series and therefore a determination of both qeu and q b is preferable. 

Finally, it is worth mentioning that the presence of hydration equilibria could result in effective fractional q values. This can be checked by UV- ds measurements on the Elu(III) complex as a function of temperature 12). 

Because of the dependence of the inner sphere relaxivity on l/r, the Gd-water proton distance is extremely important in determining the efficacy of a CA. In Fig. 8 the experimental profile of [GdDTPA(H20)] is shown and also the best-fit curve obtained with a th value of 3.1 A, compared with two calculated profiles corresponding to th values of 2.95 (upper curve) and 3.25 A. A variation of this parameter of only 0.15 A changes the relaxivity about 16% at low fields. Estimates from X-ray data of the Gd-0 distance are affected by some errors as the tilt angle of the water molecule in solution is not defined with precision. 

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III. Relevant parameters in fitting the NMRD profiles of contrast agents... 

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