Designed edge-lit NIR planar marker for orthopedic surgical locators

Orthopedic surgical robots utilize near-infrared (NIR) optical locators to enable precise navigation during operations. Markers are crucial in the locator system, capturing the positions and orientations of surgical instruments and patients during operation. While spherical markers can be easily detected, they are less robust owing to limited feature points. In contrast, planar markers offer more feature points and greater resistance to occlusion. However, the demanding nature of orthopedic surgeries necessitates specific requirements for NIR-based planar markers, such as size, illumination, weight, and heat dissipation. To address these challenges, we designed an edge-lit NIR calibration board (300 mm × 300 mm) to calibrate the constructed NIR camera, with its effectiveness validated through extensive experimental studies. Based on the fundamental design data obtained from the designed edge-lit NIR calibration board, and considering the luminous flux density and the available 12 V battery on the market, we proposed an edge-lit active NIR planar marker with dimensions of 70 mm × 60 mm and equipped with eight LEDs (1.5 V, 0.085 W each). The experiential data illustrates the max relative standard deviation are around 0.93% and 0.78% for the measurement precision subjected to 10 mm × 10 mm square (5 × 5 squares) with 16 and 36 feature points, respectively. Further, we validated the following from the experimental results: (1) A 12 V 1000 mAh alkaline battery has an autonomy of approximately 16 h for the eight NIR LEDs. (2) The total heat energy conversion of 0.408 W for the marker is within acceptable limits for use in an operation room. (3) The total weight of approximately 21.6 g, including the planar marker and the selected battery, is manageable. Therefore, the designed edge-lit active NIR planar marker presents a viable option for integration into the locator system of orthopedic surgical robots.