For the single vessel simulations, the artery was simulated with a diameter of 4 mm and a length of 9 mm, and it was positioned directly below the drill. The expected diameter of an internal carotid artery is 3.7 to 8 mm,13,14 and the simulated artery is within this range. Though the drill placement directly above the artery may seem counterintuitive, it demonstrates that the system will work in the worst-case scenario, if the surgeon is in danger of damaging the internal carotid artery. The bone thickness was varied from 0 to 8 mm, the distance between vessel and bone was varied from 0 to 5 mm, and the distance between the source fiber and the drill shaft was varied from 0 to 5 mm. Only one parameter was varied at a time, otherwise, the bone thickness, fiber distance, and vessel distance (bt, , and , respectively, in Fig. 3) were held constant at 2.5, 1.25, and 1 mm, respectively.