The invention relates to a rod-shaped body comprised of one or more filaments and of a non-ferromagnetic matrix material. The matrix material surrounds the filament(s) and/or adheres them to one another. The rod-shaped body is also comprised of a dopant consisting of particles that generate magnetic resonance tomographic artifacts that is introduced into the matrix material. Rod-shaped bodies of this type can be used to construct guide wires, catheters and other instruments to be used in minimally invasive surgical interventions.