Calibration of bi-planar radiography with minimal phantoms

Abstract

In this paper we propose a method for the geometrical calibration of bi-planar radiography that aims at minimising the impact of calibration phantoms on the content of radiographs. These phantoms are required for determining scale or to estimate the geometrical parameters of the system. Unfortunately, they often overlap anatomical structures. For accomplishing this goal, we propose a small extension to conventional imaging systems: a distance measuring device that enables to estimate some of the geometrical parameters. This leads to a reduction of the search space of solutions, which makes possible reducing requirements of calibration phantoms.The proposed method was tested on 17 pairs of radiographs of a phantom object of known dimensions. For calculating scale, only a reference distance of 40mm was used. Results show a RMS error of 0.36mm with 99% of the errors inferior to 0.85mm. Additionally, the requirements of the calibration phantom are very low when compared with other methods, but experiments with anatomical structures should be conducted to confirm these results.