A visible and/or MRI visualizable permanent image is formed in a gel in a container which maintains the gel a dimensionally stable shape, which gel contains uniformly dispersed therein in storage stable form at least one radiant energy, e.g., ionizing radiation, or mechanical, e.g., ultrasonic or sonic shock wave, polymerizable monomer in a concentration effective to form a polymer in the gel which alters the NMR relaxation time of the solvent in any area thereof in which the polymer is formed, e.g., a mixture of (a) a linearly homopolymerizable monomer and (b) a comonomer which is cross-linkably copolymerizable with the monomer, the polymerization of the monomer initiated by the radiant or mechanical energy being restricted to any area of the gel which receives that energy, which image is representative of the dose distribution of the energy to which the gel is exposed, by exposing the gel to a non-uniform dose of the energy until a polymer which produces a permanent image representative of the dose of the energy received by the gel is formed therein. The image can be used for dosimetric purposes; to provide reference standards for quality control of magnetic resonance imaging techniques and equipment; and as a three- or two-dimensional array detector in industrial radiography (nondestructive testing techniques).