US Patent 7784468 Surgical implement detection system

Surgical implements used during an operating procedure are detected in human tissue. Markers attached to the surgical implements change their impedance at a preselected frequency in the presence of an electromagnetic field. Each of the markers is thereby provided with signal-identifying characteristics. The signal-identifying characteristics are detected outside the operating room in an accurate, reliable manner. Potential interference with operating room electronic instrumentation is avoided, the possibility of operator error is reduced and system cost and space requirements are substantially lowered.