Abstract: A method of tracking progress of labor includes placing a magnetic field sensor array (14), which includes an array of magnetic sensors (16), close to a woman who is carrying a fetus, placing tracking devices (20, 22, 23, 24) at positions relative to the fetus, generating a magnetic field from each of the tracking devices (20, 22, 23, 24), each of the magnetic fields being unique to a particular one of the tracking devices (20, 22, 23, 24), sensing the magnetic fields of the tracking devices (20, 22, 23, 24) with the magnetic field sensor array (14), analyzing sensed magnetic fields of the tracking devices (20, 22, 23, 24) to identify positions of the tracking devices (20, 22, 23, 24) with respect to the fetus, and using the positions of the tracking devices (20, 22, 23, 24) with respect to the fetus to determine progress of labor of the woman.

Abstract: A method of calibration including placing an instrument on an arbitrary point and at an arbitrary rotational orientation on an ultrasonic probe, obtaining spatial coordinates of the instrument, obtaining spatial coordinates of three points on an external surface of the ultrasonic probe, and using the three points to define an ultrasonic image plane, obtaining spatial coordinates of a set of landmarks which have a known spatial relationship to the ultrasonic image plane, these landmarks defining a direction in which the ultrasonic probe is directed within the ultrasonic image plane, and obtaining spatial coordinates of a front point on a front facing surface of the ultrasonic probe, the front facing surface having a known relation with a reference axis of a scanning plane of the ultrasonic probe that defines where an ultrasonic image starts within the ultrasonic image plane.

Abstract: A method of calibration including placing an instrument on an arbitrary point and at an arbitrary rotational orientation on an ultrasonic probe, obtaining spatial coordinates of the instrument, obtaining spatial coordinates of three points on an external surface of the ultrasonic probe, and using the three points to define an ultrasonic image plane, obtaining spatial coordinates of a set of landmarks which have a known spatial relationship to the ultrasonic image plane, these landmarks defining a direction in which the ultrasonic probe is directed within the ultrasonic image plane, and obtaining spatial coordinates of a front point on a front facing surface of the ultrasonic probe, the front facing surface having a known relation with a reference axis of a scanning plane of the ultrasonic probe that defines where an ultrasonic image starts within the ultrasonic image plane.