We have developed a laser projection system, which can project laser on corresponding position to surgical planning drawn at a fluoroscopic image without an optical tracking system. In this paper, we introduce a spatial calibration method between a laser module and a fluoroscope for the laser projection and evaluate its accuracy with a mimic experimental system. The experimental system consists of a laser module, a distance measurement unit and a CCD camera. The laser modules can project arbitrary line on surface by reflecting a point source laser with two galvanometers. We designed a calibration phantom by combining a collimator for accurate laser pattern positioning and stainless steel ball arrays for calculation of an extrinsic parameter of a C-arm fluoroscopy. We set a projection plane having ruler in 400mm distance from the CCD camera, and set 54 points on the screen. The laser module projects points with respect to the set points, and a distance error between set points and projected points and angular error are calculated. The distance errors is 1.5±1.9 mm (average ± standard deviation). Maximum error was 7.5 mm. Angular error was smaller than 2 degrees. The laser projection system and its calibration method shows clinically acceptable accuracy and the clinical application is the next step.
Optimization of a Calibration Phantom for Quantitative Radiography
