Development of an opto-electronic positioning device for serial direct digital images of oral structures

The aim of this study was to develop and test in vitro an opto-electronic p ositioning device for serial direct digital images of oral structures, i.e. to associate direct digital imaging with the principles of computer-aided surgery. This system registered positions of infrared light emitting diodes (LED) on carriers, establishing local coordinate systems. With LED markers attached on the sensor holder, the X-ray tube and a fix reference, the opt o-electronic camera (Optotrak(R)) registered the geometric source/detector relation. A specially designed tracking and guidance software was developed which enabled the operator to reposition the X-ray source. A graphical use r interface guided the operator in aligning 2 circles to the reference axis , one indicating the origin of the beam, the other its tip. In addition, de pth control was provided. An in vitro calibration was performed. A sensor h older/bite block carried the Sens-A-Ray(R) sensor with a hair-cross. In fro nt of the object a second hair-cross was fixed. A steel ball fixed to the c enter of the X-ray cone allowed to verify the alignment. The mean angulatio n error in the vertical plane was 0.06 degrees and 0.04 degrees in the hori zontal one. Translation mean errors were small and ranged between -0.02 mm and 0.37 mm. The translation in the Z axis is negligible. This resulted in pairs of images suitable for digital subtraction. Although still in an expe rimental state, the results showed that opto-electronic navigation was usef ul to standardize projection geometry without any mechanical link and to ac hieve digital subtraction images based on direct digital imaging.