A deformable phantom, according to the present invention, has a housing made of a MRI invisible material enclosing a sealed reservoir filled with a MRI signal producing material, a piston slidably mounted within a sleeve and extending into the sealed reservoir, wherein the sleeve is slidably mounted to the housing and extends into the sealed reservoir, and a deformable structure within the sealed reservoir. The piston and sleeve move opposite to one another to conserve a constant fluid volume within the sealed reservoir as the piston moves in and out of the sealed reservoir to cause motion and/or deformation of the deformable structure.