Moving the goal posts: enhancing the sensitivity of PARASHIFT proton magnetic resonance imaging and spectroscopy

Abstract

Paramagnetic probes for chemical shift imaging are described, in which a reporting tert-butyl resonance is integrated and placed about 6 to 6.5 Å from a lanthanide ion. At this distance, the resonance is shifted to a region of the ¹H NMR spectral window far away from the usual 0–12 ppm range, permitting selective observation. Furthermore, judicious selection of the lanthanide ion, according to the applied magnetic field strength, leads to relaxation rate enhancements of the order of 100–200, permitting more rapid data acquisition per unit time in both spectroscopy and imaging experiments. The enhanced sensitivity allows the detection of these complexes in mice within a few minutes using shift imaging, following tail vein injection of doses of the order of 0.1 mmol kg⁻¹.