Abstract
Freehand three-dimensional ultrasound system allows intra-operative imaging of pathologic tissue for image-guided surgical procedures. Accurate registration of ultrasound image for surgical navigation requires calibration that is time-consuming and tedious. We present a novel automatic and robust calibration method without a phantom. In the proposed method, a needle equipped with an electromagnetic tracking sensor is moved in the vicinity of an ultrasound imaging plane taken by a fixed ultrasound probe also equipped with an EM tracking sensor. The ultrasound images, tracker’s and needle tip’s physical coordinates are recorded simultaneously. For each ultrasound image, the needle tip is recognized and the image coordinates are identified automatically. A point registration between the needle tip image and physical coordinates is performed to estimate the calibration matrix. RANSAC is applied to minimize the registration error. Experiments are performed to verify the accuracy of the new calibration method. Results show that the needle tip can be accurately recognized in ultrasound images and the average fiducial registration error is 1.2 mm and hence applicable to the calibration for freehand ultrasound.
