Active echo: a new paradigm for ultrasound calibration

In ultrasound-guided medical procedures, accurate tracking of interventional tools with respect to the US probe is crucial to patient safety and clinical outcome. US probe tracking requires an unavoidable calibration procedure to recover the rigid body transformation between the US image and the tracking coordinate system. In literature, almost all calibration methods have been performed on passive phantoms. There are several challenges to these calibration methods including dependency on ultrasound image quality and parameters such as frequency, depth, and beam-thickness. In this work, for the first time we introduce an active echo (AE) phantom for US calibration. The phantom actively detects and responds to the US beams from the imaging probe. This active approach allows reliable and accurate identification of the ultrasound image mid-plane independent of the image quality. It also enables automatic point segmentations. Both the target localization and segmentation can be done automatically, so the user dependency is minimized. The AE phantom is compared with a gold standard crosswire (CW) phantom in a robotic US experimental setup. The result indicates that AE calibration phantom provides a localization precision of 223 μm, and an overall reconstruction error of 850 μm. Autosegmentation is also tested and proved to have the similar performance as the manual segmentation.