Medical procedure related objects (e.g., instruments, supplies) tagged with transponders (e.g., RFID transponders, dumb transponders) are accounted for via an accounting system using a number of antennas and interrogators/readers. The antennas and interrogators/readers are included on a cannula of the trocar so the tagged medical procedure related objects passing through the cannula are detected. A first set of antennas and RFID interrogator(s) interrogate a first portion of the cannula, such as proximate a proximal end at which the medical procedure related objects are introduced to the cannula. A second set of antennas and RFID interrogator(s) interrogate a second portion of the cannula, such as proximate a distal end at which objects exit the cannula for use in a medical procedure. A data store may maintain information including a current status or count of each supply, for instance, as entering or exiting the cannula.
