Computed Tomography (CT)

Abstract

Computed tomography (CT) is based on attenuation of X-ray beam passing through an examined object. Linear X-ray attenuation coefficient is calculated separately for each voxel, i.e. cuboid volumetric element which constitutes each scanned layer, and the coefficients are transformed into the Hounsfield units (HU), which make it possible to estimate densities, and are arranged in the form of a Hounsfield scale. In many cases CT examination is performed in two phases-before and after contrast medium injection resulting in the so-called contrast enhancement of blood vessels and highly vascularized tissues or lesions. Advantages of CT include short scanning time, cross-sectional imaging, high quality of multiplanar reconstructions, high contrast resolution, objective density measurements using HU and assessment of contrast enhancement. Disadvantages of CT include average to high radiation exposure dose, image artefacts and side effects of administered iodine contrast media. There are no absolute contraindications for a CT scan, and relative contraindications are pregnancy as well as side effects of contrast media administration. The use of CT in diagnostics of TMJ lesions comprises congenital malformations, arthropathies, osteoarthritis, condylar fractures, bone and fibrous ankylosis, benign and malignant tumours and evaluation of condyle morphology in relation to sagittal split osteotomy and virtual surgical planning.