A NEW YTTERBIUM CHELATE AS CONTRAST AGENT IN CHEMICAL-SHIFT IMAGING AND TEMPERATURE-SENSITIVE PROBE FOR MR SPECTROSCOPY

A paramagnetic Yb(III) complex that is the prototype of a novel class of probes for MRI and MRS has been developed, The complex displays hig hly shifted H-1 resonances that are characterized by short relaxation times and, as such, may prove to be a valuable alternative in applicat ions that currently require fluorine-containing probes. Selective exci tation of the paramagnetically shifted resonances allows the spatial d istribution of the complex to be mapped, This communication reports th e images that were obtained by selectively exciting the most intense m ethyl group (-14.2 ppm at 27 degrees C) for complex concentrations ran ging from 0.003-0.1 M. Spectroscopically, the complex may be used as a temperature probe since the proton chemical shifts exhibit a strong t emperature dependence, In human serum the chemical shift difference of a selected pair of proton resonances was observed to follow a gradien t of -0.42 +/- 0.01 ppm/degrees C. Furthermore, since the chemical shi ft of the methyl resonance displays a temperature coefficient of -0.04 +/- 0.01 ppm/degrees C, it should be possible to use the image phase for thermal mapping.