Patent ID: 7787931

Claim:
In a system for detecting in human or animal tissue a surgical implement used during an operating procedure carried out in an operating room wherein a marker attached to said surgical implement changes its impedance at a preselected interrogating frequency in the presence of an electromagnetic interrogating field which provides said marker with signal-identifying characteristics, the improvement wherein: said marker comprises at least one marker element adapted to undergo resonance at a preselected resonant frequency and radiate a marker dipole field in response to said interrogating field; said signal-identifying characteristic is a ring-down of said dipole field; the surgical implement is deployed within the wound during the operating procedure; and said signal-identifying characteristics are detected by a freely movable, portable detection unit comprising: an interrogating means that comprises a frequency-generating means for generating said preselected interrogating frequency, a field-generating means for receiving said preselected interrogating frequency and generating within said interrogation zone said electromagnetic interrogating field having said preselected interrogating frequency modulated as a series of pulses, and a field-changing means for varying at least one of the amplitude and direction of said electromagnetic interrogating field to alter the electromagnetic dipole coupling between said marker element and said interrogating field, said field-generating means comprising a plurality of antenna elements and said field-changing means comprising a switching system that connects a preselected one or more of said antenna elements to said frequency-generating means with a preselected polarity for each element; a detecting means for detecting said ring-down between said pulses, said detecting means comprising a detecting antenna, an antenna-changing means, and a detector circuit connected to said detecting antenna, said detecting antenna receiving said marker dipole field and comprising at least one selectively activatable receiver element and said antenna-changing means comprising means for moving said at least one receiver element to change at least one of the position and orientation of said receiver element relative to said marker, thereby to alter the electromagnetic dipole coupling between said receiver element and said marker, the means for moving said at least one receiver element comprising at least one of a mechanical, electrical, or pneumatic element or a combination thereof; and an indication means activated by said detecting means in response to the detection of the presence of said ringdown of said marker.