An Efficient Platform for Freehand US Calibration

Freehand three-dimensional ultrasound system allows intra-operative imaging of pathologic tissue for image-guided injection. Accurate registration of ultrasound image for injection navigation requires calibration that is timeconsuming and tedious. We present an efficient calibration system based on a clinical injector. The injector equipped with an optical tracking sensor is moved in the vicinity of an ultrasound imaging plane taken by a fixed ultrasound probe also equipped with an optical tracking sensor. The ultrasound images, ultrasound probe’s and injector tip’s physical coordinates are recorded simultaneously. For each ultrasound image, the injector tip is recognized and the image coordinates are identified automatically. A point registration between the injector tip image and physical coordinates is performed to estimate the calibration matrix. Experiments are performed to verify the accuracy of the calibration system. Results suggest that the calibration system is applicable to the calibration of freehand ultrasound for image-guided injection.