Study of proton spin-lattice relaxation variation induced by paramagnetic antibodies

A murine anti-human melanoma monoclonal antibody fragment was labeled with gadolinium and its proton relaxation efficiency compared to controls at frequencies ranging from 2 to 300 MHz. Relaxation time variations were about 30-40% in 10-15 microM solutions. The labeled fragment showed proton relaxation enhancement relative to free gadolinium, while preserving its immunoreactivity. A tentative labeling of a melanoma pellet by means of the fragment, just at the borderline of a minimum expected T1 variation, gave no detectable difference.