Tuned fiducial markers to identify body locations with minimal perturbation of tissue magnetization.

A fiducial marker is described in which a small cell containing a short T1 solution is surrounded by single- or quadrature-tuned windings. It is shown how these can be used to enhance small externally applied RF pulses, which do not significantly perturb the magnetization of the tissue, to excite the fiducial sample, and get substantial signals from it. The fiducials can be used to mark locations on the body unambiguously for, for example, frameless stereotaxy, and to identify coils, catheters, or other inserted devices.