A contrast agent for magnetic resonance imaging comprising a complex of a paramagnetic cation, preferably Gd.sup.+3, Dy.sup.+3, and Fe.sup.+3 with three equivalents of a charge neutralizing chelator that provides a lipid soluble complex of the paramagnetic cation is described. The complex is retained intracellularly when introduced into a mammalian cell. A method of providing an image of an internal pathology of a patient by magnetic resonance imaging (MRI) by administering the MRI contrast agent or tagged cells to the patient and scanning the patient using magnetic resonance imaging to obtain visible images of the internal pathology of the patient is also set forth.

A compound useful for in vivo imaging of organs and tumors is provided of formula: ##STR1## wherein ##STR2## is a cobalamin, ##STR3## is derived from a corrin carboxylic acid group of said cobalamin, Y is a linking group and X is a chelating group, optionally comprising a detectable radionuclide or a paramagnetic metal ion, and n is 1-3.

The invention provides cobalamin compounds linked to a neutron capture therapy target (e.g. Boron-10 or Gadolinium-157), and optionally linked to a detectable moiety, as well as pharmaceutical compositions comprising the compounds, and methods for using the compounds in medical diagnosis and therapy.

The invention provides detectably labeled cobalamin derivatives which are useful for medical treatment and diagnosis.

A compound useful for in vivo imaging of organs and tumors is provided of formula: ##STR00001## wherein ##STR00002## is a cobalamin, ##STR00003## is derived from a corrin carboxylic acid group of said cobalamin, Y is a linking group and X is a chelating group, optionally comprising a detectable radionuclide or a paramagnetic metal ion, and n is 1 3.