Aims:​ to develop a reliable and accurate method to co-register magnetic resonance imaging (MRI) and cone-beam computed tomography (CBCT) images for improved assessment of TMJ internal derangement in adolescents and adults, and to utilize this MRI-CBCT co-registration tool to quantify TMJ changes in several clinical settings. The TMJ articular disc derangement is a three-dimensional (3D) problem that is commonly described and diagnosed from two-dimensional (2D) images. This project also aimed to construct 3D models of the TMJ to enable quantitative analysis of tissue changes in all directions.

Methods:​ 1) Two techniques of the MRI-CBCT image co-registration were tested for image quality, and the technique with the highest image quality was tested for accuracy. 2) Reliability of evaluation of TMJ disc position and osseous pathology from MRI alone, CT alone, and fused MRI-CBCT images was tested among radiologists. 3) Accurat and reliability of assessment of TMJ disc position by novice examiners from MRI-CBCT images was tested. 4) Applicability of the MRI-CBCT images to evaluate the TMJ disc position in adolescents was tested. 5) Feasibility of using MRI-CBCT image co-registration as a tool to reconstruct 3D models of the TMJ to evaluate changes of the TMJ articular disc and condyle was tested in patients pre- and post-surgical treatment of oropharyngeal cancer.

Results:​ 1) The intrinsic MRI-CBCT image co-registration technique produced high image quality to visualize TMJ and was proved accurate. 2) The MRI-CBCT images improved the reliability among examiners of varying experience levels in classifying disc position compared to MRI alone. The diagnostic value of the MRI-CBCT images to detect osseous abnormality is comparable to CBCT alone except for small osseous changes such as erosions. 3) The MRICBCT images improved the reliability of novice examiners to evaluate the TMJ disc position compared to MRI alone. 4) The examiners’ reliability to evaluate the disc position in adolescents was not improved due to the low quality of the CBCT images obtained for adolescents. 5) Using the TMJ 3D reconstructed models were useful to quantify disc and condyle position and morphology changes after oral cancer surgical treatment.

Conclusions:​ The MRI-CBCT image co-registration is a reliable and accurate tool to assess the TMJ internal derangement that may be particularly helpful for readers inexperienced in MRI, and provides a 3D representation of TMJ tissues that allows quantification of changes in TMJ soft and hard tissues after treatment and over time. The MRI-CBCT image co-registered images are seem to be useful for TMJ diagnostic research and educational fields, and has a great potential a routine clinical application to evaluate the TMJ soft and hard tissues.