Minireviews
Copyright ©2014 Baishideng Publishing Group Inc. All rights reserved.
World J Radiol. Aug 28, 2014; 6(8): 607-612
Published online Aug 28, 2014. doi: 10.4329/wjr.v6.i8.607
Bone mineral density in cone beam computed tomography: Only a few shades of gray
Marcio José da Silva Campos, Thainara Salgueiro de Souza, Sergio Luiz Mota Júnior, Marcelo Reis Fraga, Robert Willer Farinazzo Vitral
Marcio José da Silva Campos, Thainara Salgueiro de Souza, Sergio Luiz Mota Júnior, Marcelo Reis Fraga, Robert Willer Farinazzo Vitral, Department of Orthodontics, Juiz de Fora Federal University, 36036-900, Minas Gerais, Brasil
Author contributions: Campos MJS and de Souza TS contributed equally to this work, drafted and wrote the manuscript; Mota Júnior SL and Fraga MR revised the manuscript; Campos MJS and Vitral RWF were responsible for final approval of the version to be published.
Correspondence to: Robert Willer Farinazzo Vitral, DDS, MD, PhD, Professor and Chair of Orthodontics, Department of Orthodontics, Juiz de Fora Federal University, Juiz de Fora, 36036-900, Minas Gerais, Brasil. robertvitral@gmail.com
Telephone: +55-32-21023879 Fax: +55-32-21023879
Received: December 27, 2013
Revised: March 11, 2014
Accepted: April 25, 2014
Published online: August 28, 2014
Abstract

Cone beam computed tomography (CBCT) has often been used to determine the quality of craniofacial bone structures through the determination of mineral density, which is based on gray scales of the images obtained. However, there is no consensus regarding the accuracy of the determination of the gray scales in these exams. This study aims to provide a literature review concerning the reliability of CBCT to determine bone mineral density. The gray values obtained with CBCT show a linear relationship with the attenuation coefficients of the materials, Hounsfield Units values obtained with medical computed tomography, and density values from dual energy X-ray absorciometry. However, errors are expected when CBCT images are used to define the quality of the scanned structures because these images show inconsistencies and arbitrariness in the gray values, particularly when related to abrupt change in the density of the object, X-ray beam hardening effect, scattered radiation, projection data discontinuity-related effect, differences between CBCT devices, changes in the volume of the field of view (FOV), and changes in the relationships of size and position between the FOV and the object evaluated. A few methods of mathematical correction of the gray scales in CBCT have been proposed; however, they do not generate consistent values that are independent of the devices and their configurations or of the scanned objects. Thus, CBCT should not be considered the examination of choice for the determination of bone and soft tissue mineral density at the current stage, particularly when values obtained are to be compared to predetermined standard values. Comparisons between symmetrically positioned structures inside the FOV and in relation to the exomass of the object, as it occurs with the right and left sides of the skull, seem to be viable because the effects on the gray scale in the regions of interest are the same.

Keywords: Tomography, Cone-Beam computed tomography, Bone mineral density, Reproducibility of results

Core tip: The development of cone beam computed tomography (CBCT) has allowed for more frequent use of these images in dentistry for the evaluation of dentomaxillofacial structures. Yet, there is no consensus regarding the accuracy of CBCT to determine mineral density of craniofacial bone structures, although this technique has been used for this purpose in several types of analyses. According to the studies available to date, it may be concluded that CBCT should not be considered the examination of choice for the determination of mineral density of osseous and soft tissues, especially when values obtained are compared with predetermined standard values.