Patent ID: 7784468

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, said system comprising a surgical implement detector and a marker attached to said surgical implement that changes its impedance at a preselected interrogating frequency in the presence of an electromagnetic interrogating field, whereby said marker is provided with a signal-identifying characteristic, the improvement wherein: said surgical implement detector is placed outside of the operating room and comprises an interrogating means, a detecting means, and an indication means; said interrogating means is configured to generate said electromagnetic interrogating field, said field having said preselected interrogating frequency modulated as a series of pulses; said marker resonates at a preselected resonant frequency and radiates a marker dipole field in response to said interrogating field; said signal-identifying characteristic is a ring-down of said dipole field; said detecting means is configured to detect said ring-down between said pulses; and said indication means is configured to be activated by said detecting means in response to the detection of said marker; said interrogating means comprises a frequency-generating means, a field-generating means, and a field-changing means, said frequency-generating means generating said preselected interrogating frequency, said field-generating means receiving said preselected interrogating frequency and generating within an interrogation zone said electromagnetic interrogating field, and said field-changing means 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, and said interrogation zone is located outside said operating room; wherein said surgical implement detector is configured to detect when said signal-identifying characteristic is found within said wound and said interrogation zone.