Epipolar Geometry-Based Visual Servoing of Soft Endoscopic Manipulator for Transoral Laser Ablation

Soft manipulators integrated with optical laser fibers offer new opportunities for endoscopic noncontact laser surgery. To achieve precise laser projection in a confined workspace and avoid damage, a controller with high accuracy and stability is required. An effective way is to close the control loop. Therefore, a visual servo controller that allows automatic laser spot steering using soft manipulators is proposed. An epipolar geometry model is established to acquire the inverse transition mapping from image to actuation. With this mapping, a feedback controller is derived without prior information of tissue surface geometry. Experimental validation demonstrates accurate path following using a magnetic resonance-safe manipulator, with root-mean-square (RMS) tracking errors <4 pixels (140 mu m) in the camera view. This is maintained even throughout 70 repeated cycles, with a maximum tracking error <11.32 pixels (approximate to 396.2 mu m). The controller enables laser spot following of the mouse cursor with an RMS tracking error of 3.97 pixels (approximate to 180.5 mu m). Ex vivo tissue ablation tests are conducted to validate the laser ablation pattern, with an RMS tracking error of about 5.75 pixels (approximate to 201.3 mu m). A laser ablation test is conducted under magnetic resonance imaging (MRI) to validate the feasibility of MRI-guided laser surgery.