As blood flows through a vessel in an MR field, what phenomenon occurs?

Flow potential is the correct choice because it refers to the phenomenon that arises when blood moves through a magnetic resonance (MR) field. As blood, which is a conductive fluid, flows in the presence of a magnetic field, it experiences a change in magnetic flux due to its motion. This movement generates an electric potential, referred to as "flow potential." This potential can lead to artifacts in the MR imaging process if not properly accounted for, affecting the quality and accuracy of the images obtained.

Translational forces, although they might sound relevant in the context of objects in a magnetic field, generally refer to the forces acting on objects due to gradient fields rather than the specific effects seen with flowing blood. Magnetophosphenes involve visual disturbances some individuals may see when exposed to strong magnetic fields, which is unrelated to the flow of blood itself. The fringe field relates to the external magnetic field surrounding the MR scanner but does not directly describe the effect on blood flow within a vessel in the magnetic field. Thus, flow potential accurately describes the phenomenon of interest when considering how blood behaves in an MR environment.