High-accuracy MR tracking of interventional devices: the Overhauser marker enhancement (OMEN) technique

A new technique for visualization of interventional devices in magnetic resonance imaging is presented. Determination of the position of an invasive device is made possible by incorporating into the device a small marker that emits the NMR signal. This signal is enhanced by the use of the Overhauser phenomenon. This technique differs from the earlier reported techniques for marking interventional instruments in the sense that the contrast between the marker and tissue is not based on different relaxation rates, but on NMR signal enhancement. A prototype marker was constructed and inserted into an inductively fed loop-gap resonator that couples saturation energy with the marker. Circuit analogies are presented that model the Overhauser phenomenon and the coupling circuit. In vitro experiments demonstrated that the marker is visible in MR images up to a slice thickness of 50 mm when inserted in excised animal liver and fat tissues.