Research On Registration Technologies In Image Guided Surgery System

Registration between patient and image is one of key point in image guided surgical robot system for prostate seed implantation.In this paper,we come up with a hybrid registration method,which is completed in two steps.In the first step,coordinates of markers on the patient's skin surface are obtained both in patient space and in image space,and then the first transformation matrix is calculated.In the second step,using the first transformation matrix to display the needle in image space,positon of needle tip is regarded as coordinate of anatomical landmarks.Transformation matrix that is produced by probe calibration experiment,is employed to convert 2D ultrasonic image point to electromagnetic locator receiver space then to electromagnetic locator generator space.The hybrid registration method employed both markers on the patient's abdominal surface and anatomical landmarks.Laser tracking system is used to calibrate the precision of electromagnetic locator,and introducing of calibration coefficient makes a higher accuracy of electromagnetic locator.Incorporating with principal components analysis algorithm,quaternion based algorithm and theory of iteration closest point,an algorithm is proposed,which uses principal components analysis algorithm to calculate initial registration matrix,and employs quaternion based algorithm in the iteration process to get optimization matrix.Organ group model of pelvic,which is attached with fiducial makers on surface and target markers on prostate,is designed to complete registration experiment.And a CT image sequence is obtained.Coordinates in real space are acquired by a puncture needle which is fixed with an electromagnetic receiver.Coordinates of makers in the image space are obtained by fitting standard sphere to actual sphere,which is reconstructed by sketching a series of 2D image sequences which contains the globule.Probe calibration matrix is used to get coordinate of anatomical landmark in the real spade.Coordinate of anatomical landmark in the image spade is acquired by the needle model tip which is tracked by the electromagnetic locator.Principle and process of probe calibration is elaborated,and a N-wire phantom is designed to implement the probe calibration experiment.Transformation matrix from 2D ultrasonic image to 3D electromagnetic locator is achieved by probe calibration experiment,and the calibration accuracy meets the registration system requirement.Contrast experiment between hybrid registration and regular registration indicates the theory has a reasonable accuracy and feasibility.