A superconducting magnetic imaging apparatus includes a vacuum vessel (16) having a central helium reservoir (20) in which superconducting magnetic coil windings (12) are maintained at a superconducting temperature. The vacuum vessel defines an internal bore (22) within which a self-shielded gradient coil assembly (26) and an RF coil (30) are received. The self-shielded coil assembly includes a single former (50) which defines an imaging region (14) within which an imaged portion of a subject is received. Primary x, y, and z-gradient coils (72-76) are positioned over an RF ground screen (70) that is bonded to the former (50). A number of comb-like spacers (84) extend from the former to supporting shield x, y, and z-gradient coils (110-114). The comb-like spacers define passages between the primary and secondary gradient coils which receive inner and outer cooling tubes (90, 92) and shim tray molds (108). The fully assembled gradient coil assembly is potted to form a unitary structure in a single potting step. The shim tray molds are subsequently removed to define channels or pockets suitable for receiving shim trays (118).