A catheter for imaging a cavity. The catheter includes a sheath having a distal end that is introduced into a cavity to be imaged and a proximal end that resides outside of the cavity. The sheath includes a tubular member with a first fixed probe located proximate to the distal end and fixed in relation to the tubular member while the cavity is being imaged. The catheter also includes a transducer for delivering an energy pulse in a predetermined direction relative to the transducer and collecting echoes generated by the pulse. The transducer is located within the sheath proximate to the distal end of the sheath and includes a transducer probe affixed to the transducer. A drive cable in the catheter causes the transducer and the transducer probe to rotate relative to the sheath. The drive cable connects the transducer to a mechanical drive mechanism located at the proximate end of the sheath. A tracking circuit measures the electrical coupling between the transducer probe and the first fixed probe to determine the location of the transducer relative to the sheath.