Evaluation of cone beam computed tomography with respect to effective radiation dose and diagnostic properties

Abstract

Cone beam computed tomography (CBCT) is an x-ray modality providing three-dimensional x-ray images. CBCT devices have high resolution compared to traditional medical CT, making them suitable for examination of fine details. However, CBCT devices are worse at showing contrast differences, making them less suitable for examinations of soft tissue such as the brain and many other internal organs. An x-ray modality suitable for imaging of small details and hard tissue fits dental and maxillofacial radiology well. After the introduction of dentomaxillofacial CBCT in 1998, CBCT examinations have spread to become a common and important diagnostic tool in odontology. Today, CBCT examinations complement or replace examinations previously performed by other methods.

When choosing an x-ray imaging modality and examination parameters, concern must be taken for the diagnostic value and the radiation dose. The examination should be chosen to provide as low radiation dose as possible while not sacrificing the diagnostic value. In order to provide guidelines on the use of CBCT, scientific knowledge on CBCT and alternative examinations are needed. What is the radiation dose for different examinations and how does the examination affect diagnosis and treatment? This thesis aims to provide additional information in this field, to provide reference data when considering the choice of examination and the establishment of guidelines.

In the first paper, examinations of the temporomandibular joint, using CBCT and traditional medical multi-detector CT (MDCT), were compared to determine if CBCT examinations would result in lower radiation dose. The examinations were optimized to find the lowest suitable dose levels, and at these optimized dose levels no significant difference was found between CBCT and MDCT. The second paper investigated the radiation dose from multiple different x-ray examinations of possible resorption impacted maxillary canines in children. CBCT examinations were compared to two-dimensional examinations using intraoral radiographs, and in some cases panoramic radiographs. CBCT examinations ranged from 15 to 140 times higher radiation dose, depending on x-ray device. The third paper investigated the possibility of reducing the image size, and therefore the x-ray dose, in panoramic radiographs. A full-size panoramic radiograph was required in 20% of adult patient cases. The introduction of two different image sizes for adult patients would reduce the collective radiation dose from panoramic examinations by about 40% in our university clinic. The fourth paper investigated radiation doses from different examinations and settings using the Newtom 5G CBCT device. This CBCT model use automatic exposure control and does not allow manual adjustment of exposure parameters. The resulting effective doses should be applicable to examinations of adult patients using this CBCT model.