CBCT-based bone quality assessment: are Hounsfield units applicable?

Cone-beam CT (CBCT) is a widely applied imaging modality in dentistry. It enables the visualization of the high-contrast structures of the oral region (bone, teeth, air cavities) at a high resolution. CBCT is now commonly used for the assessment of bone quality, primarily for pre-operative implant planning. Traditionally, bone quality parameters and classifications were primarily based on bone density, which could be estimated through the use of Hounsfield units derived from Multi Detector Computed Tomography (MDCT) data sets. However, there are crucial differences between MDCT and CBCT which complicates the use of quantitative gray values for the latter. From experimental as well as clinical research, it can be seen that great variability of gray values can exist on CBCT images due to various reasons which are inherently associated with this technique (i.e. the limited field size, relatively high amount of scattered radiation, and limitations of currently applied reconstruction algorithms). Although attempts have been made to correct for gray value variability, it can be postulated that the quantitative use of gray values in CBCT should be generally avoided at this time. In addition, recent research and clinical findings have shifted the paradigm of bone quality from a density-based analysis to a structural evaluation of bone. The ever-improving image quality of CBCT allows it to display trabecular bone patterns, indicating that it may be possible to apply structural analysis methods which are commonly applied in micro computed tomography (μCT) and histology.status: publishe