/spl mu/m precision achieved for measuring the position of surgical tools using two-frequency method

Using the new two-frequency approach, the ultrasonic tracking of the microsurgical tools becomes possible with accuracy better than 80 mum and enables the development of a large spectrum of acoustic systems applied, from laparoscopy to neurosurgery. The novelty of our approach is related to the time of flight (TOF) measurements. These are performed using an ultrasound burst which consists of the summation of two different frequency signals corresponding to the transducers resonance peaks, applied simultaneous to the ultrasound transmitter. The 20 cycles of 40 kHz and 25 cycles of 50 kHz applied to the transmitter generate an ultrasound burst characterized by a series of zero-crossing points with a periodicity of 100 mus. Using the zero crossing series as the time reference for the burst, the TOF is estimated