Method of T1-weighted resonance imaging of RES organs

The invention provides a method of contrast enhanced MR angiography of the human or non-human animal body, said method comprising administering into the vasculature thereof a contrast effective amount of a contrast agent composition comprising magnetic particles having a r2/r1 ratio of no more than 5, and, at a time when sufficient of said magnetic particles remain in the vasculature to provide positive contrast enhancement thereof in a T1-weighted image while sufficient magnetic particles have been taken up into an organ of the reticuloendothelial system to provide negative contrast enhancement thereof in said T1-weighted image, generating a T1-weighted image magnetic resonance image of at least said organ.