Finding 3D Teeth Positions by Using 2D Uncalibrated Dental X-ray Images

Abstract: In Dental Radiology very often several radiographs (uncalibrated in position) are taken from the same person. The radiographs do not provide the depth details, and there is often requirement of three dimensional (3D) data to achieve better diagnosis by radiologist. The purpose of this project is a step forward to solve needs of dentists for evaluating the degree of severity of teeth cavities by 3D reconstruction implementing the uncalibrated radiographs. The 3D information retrieval from two radiographs can be achieved when the 3D position of radiographs are known and when we can find correspondent intensity matching points in the pair of radiographs of the same scene. However the intensity of a point in X-ray images is changed due to variation of proportional distance between X-ray source and detector. In the thesis we propose a novel approach to retrieve 3D information by retendering two radiographs from the same scene. For the retendering, the 3D plane of radiographs is moved to new positions where the intensity distortion due to the distance is minimized. By having the 3D retendered position of radiographs we are able to find accurately relative 3D positions of original radiographs to each other. The proposed methodology approach is tested on different data sets for visually and quantitatively verification and validation. A data set of simulated radiographs with known 3D information was required to validate our work. Due to lack of such data set a novel methodology is used to simulate the dental X-ray radiographs to validate the 3D positions of teeth obtained from the 2D dental X-ray images by the proposed methodology approach. The simulation of these images is generated by a virtual source of X-rays and optical images of the jaw model which bone and tissue were segmented and used separately. The simulation result is an image, namely the virtual X-ray image. The bone and tissue segmented part of an optical image undergo a process defined by an appropriate response function depending to optical density conversion of absorbed dose to a certain material (bone or tissue). The variables of changing thickness of the material, tube voltage and material of the detector are optional in the simulator. This method of simulating X-ray images is also useful in diagnosis phases for comparison between original and synthesized one.