Probe Calibration for Image-Guided Surgery
Acknowledgement
This project was done in association with the Medical Image Guidance (MIG) team at the Indian Institute of Technology - Madras under the supervision of my principal investigator Dr. Ramya Balachandran, her PhD student Ms. Ruchitha Manne, and her Junior Research Fellow Mr. Swaminathan. I acknowledge the funding support of this work which was provided by the Department of Biotechnology, Govt. of India under the Ramalingaswami Fellowship Grant, and the Science and Engineering Research Board, Govt. of India under the Early Career Research Award (PI: Dr. Ramya Balachandran).
Description
Registration is the determination of a geometrical transformation, or “mapping”, that aligns points in one view of an object with corresponding points in another view of that object or another object. This project focuses on the registration of markers present on a surgical drill (probe) in the physical space, and using these coordinates of the markers to find the location of the tip of the drill – the tool tip. To do so, the probe, that is placed in front of a stereo camera, is moved around keeping the tool tip stationary: an experiment called probe calibration. The significance of keeping the tool tip stationary is that it allows us to exploit the mathematical equation governing this system where one variable (the location of tool tip) is common throughout the experiment; this exploitation is, however, not possible if the probe along with the tool tip is moved during the probe calibration experiment. After successfully locating the tool tip, the task is to track this tool tip by using the rotations and translations obtained during the registration of the markers on the probe from probe calibration. A coordinate reference frame (CRF) is used to represent points in space with respect to it; in our case, these points are the markers and the tool tip. In image-guided surgeries, the patient’s skull usually has screws mounted on it that act as CRFs. The last task is to convert the locations of the markers and the tool tip represented in one CRF to another – this being, predominantly, the initial CRF that is present before the surgery procedure commences.
Code
The code is simple to understand once the concept of Rotations and Translations has been understood. This is explained by Ch8 - Image Registration by J. Michael Fitzpatrick et al. Only some code files have been uploaded to this repository with the permission of my PI. Two code files (registration.m and probecalibration.m) that are the backbone of the processing, have not been uploaded.