MRI susceptometry: image-based measurement of absolute susceptibility of MR contrast agents and human blood.

We present a novel NMR imaging technique that allows absolute determination of the magnetic susceptibility constant, chi, of a solution. By comparing the phase difference of MR images produced with an instant (echo planar) "offset" spin-echo sequence, we obtain a direct measure of the magnetic field perturbations caused by the solution. We demonstrate this method with Gd(DTPA), Dy(DTPA), human red blood cells, and superparamagnetic iron oxide particles.