Clinicians want to be able to 3D map an internal organ with a hand-held ultrasound probe.
3D mapping of an organ with a hand-held probe, generating 2D sections, requires continuous registration into a single "world" coordinate system. This is normally done with a 6 degrees-of-freedom (DoF) electromagnetic navigation device.
If the patient suddenly moves in the middle of the procedure, it is extremely difficult to ensure consistent mapping of the organ. This is because both parts of the organ – the one mapped before the movement, and the one mapped after the movement – may not coincide.
Since attaching the transmitter directly to the body of the patient is often not practical, a solution to the above challenge would need to bridge between those two systems – the transmitter's coordinate system and the patient's coordinate system.
The problem boils down to working with the right coordinate system. While an electromagnetic navigation device measures location and orientation in the coordinate system of its transmitter, the eventual organ map needs to be associated with the coordinate system of the patient.
Bridging between the systems can be done by finding the transformation between them. This can be achieved by measuring the 6 DoF of the body using a sensor that would serve as a reference to the coordinate system of the transmitter.
If we denote the body-to-transmitter transformation by Tbody and the probe-to-transmitter transformation by Tprobe, then preventing the patient's sudden movement from affecting the scan will be achieved by converting the scanned images to the coordinate system of the body, applying this operation on the collected coordinates Pprobe:
While the patient is not moving, Tbody remains constant. As soon as the patient moves, Tbody will change and thus immediately demonstrate that the new Tbody, present in equation 1, will ensure that the coordinates Pbody before the movement will coincide with those taken after the movement.
A 3D organ scan that would have previously been corrupted if the patient moved during the procedure can now be salvaged and used as intended.