The invention relates to a rod-shaped body (1) comprised of one or more filaments (2) and of a non-ferromagnetic matrix material (3). The matrix material (3) surrounds the filament(s) (1) 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 (3). 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.