The performance of a Z-pinch as a source of x-ray or neutron radiation crucially depends on the symmetry and stability of the implosion. The symmetry of the implosion can be degraded or destroyed by the development of magnetic Rayleigh-Taylor instability (MRTI), that reduces the density and temperature at stagnation. One of the suggested methods of mitigating the MRTI is the use of a seeded axial magnetic field. Here, the effects of an axial magnetic field on a z-pinch implosion are studied using 2-D images and interferometry. The measurements clearly show mitigation of MRTI, slower implosion velocities, and larger stagnation radii with increased magnitude of the preembedded axial magnetic field. Introducing the axial magnetic field also gives rise to new helical structures, implying regions in the plasma with comparable azimuthal and axial magnetic field magnitudes. The present results are used for testing various MHD codes.