Gadolinium chelates are not the only contrast agents used in perfusion MRI.
USPIOs (Ultrasmall SuperParamagnetic Iron Oxide) can be used as an alternative in perfusion imaging thanks to their strong magnetic susceptibility effect and vascular remanence. They are chiefly used in research, in steady-state cerebral perfusion MRI, but also in the study of visceral perfusions (kidney, liver tumors…).
In steady-state perfusion MRI, it is possible to measure regional cerebral blood volume but not cerebral blood flow. This technique presents the advantage of a better signal-to-noise ratio and better spatial resolution, at the cost of longer acquisition time.