Simultaneous intrinsic and extrinsic calibration of a laser deflecting tilting mirror in the projective voltage space

PURPOSE  : During the past five decades, laser technology emerged and is nowadays part of a great number of scientific and industrial applications. In the medical field, the integration of laser technology is on the rise and has already been widely adopted in contemporary medical applications. However, it is new to use a laser to cut bone and perform general osteotomy surgical tasks with it. In this paper, we describe a method to calibrate a laser deflecting tilting mirror and integrate it into a sophisticated laser osteotome, involving next generation robots and optical tracking. METHODS  : A mathematical model was derived, which describes a controllable deflection mirror by the general projective transformation. This makes the application of well-known camera calibration methods possible. In particular, the direct linear transformation algorithm is applied to calibrate and integrate a laser deflecting tilting mirror into the affine transformation chain of a surgical system. RESULTS  : Experiments were performed on synthetic generated calibration input, and the calibration was tested with real data. The determined target registration errors in a working distance of 150 mm for both simulated input and real data agree at the declared noise level of the applied optical 3D tracking system: The evaluation of the synthetic input showed an error of 0.4 mm, and the error with the real data was 0.3 mm

The applicability of robot-guided laser osteotomy in a clinical environment and the interaction of laser light and bone tissue

Laser is an integral part of diagnostics and therapy in modern medicine. However, removing hard tissue with laser became successful only recently. The advantages of laser osteotomy are high precision and complete freedom in designing the cutting geometry. Nevertheless, these can be fully realized only when the laser system is guided by a robot. The most important challenges here are the miniaturization and the ergonomic design of the entire system. In this dissertation, I presented our first experience with a computer-assisted, integrated and miniaturized laser system, which is driven by a surgical robot. An Er:YAG laser source was integrated into a housing with an optical system and attached to the surgical robot arm. Pre-operatively generated planning data was imported and used to execute the osteotomies. Intraoperatively, a navigation system performed the positioning. In the actual operation room environment, the laser osteotome was used to produce different defect geometries in the mandibular bones of six minipigs. On the contralateral side of the mandible, surgeons used a PZE osteotome to create the same defects for comparison. The performance of the laser osteotome was analyzed in terms of the workflow, ergonomics, bone healing, user-friendliness, and safety. We were able to demonstrate that the laser osteotome could be ergonomically integrated into the operation room environment. It showed a high precision and the complex cutting geometries were transferred as planned. We expect that the computer-assisted and robot-guided laser osteotome will routinely used in the future, whenever special incision and high precision are required in osteotomies