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Effect of object location on the density measurement and Hounsfield conversion in a NewTom 3G cone beam computed tomography unit

¹Orthodontic Graduate Program, Faculty of Medicine and Dentistry, University of Alberta, Canada; ²Mechanical Engineering, Faculty of Engineering, University of Alberta, Canada; ³Division of Oral Radiology, College of Dentistry, University of Saskatchewan, Canada

*Correspondence to: Dr Manual O Lagravère, Faculty of Medicine and Dentistry, Room 4048, Dentistry/Pharmacy Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2N8. E-mail: mlagravere{at}ualberta.ca

Received 1 May 2007; revised 20 September 2007; accepted 5 October 2007

Objectives: The purpose of this study was to determine the effect of an object's location in a cone beam CT imaging chamber (CBCT-NewTom 3G) on its apparent density and to develop a linear conversion coefficient for Hounsfield units (HU) to material density (g cm^–3) for the NewTom 3G Scanner.

Methods: Three cylindrical models of materials with different densities were constructed and scanned at five different locations in a NewTom 3G Volume Scanner. The average HU value for each model at each location was obtained using two different types of software. Next, five cylinders of different known densities were scanned at the exact centre of a NewTom 3G Scanner. The collected data were analysed using the same two types of software to determine a standard linear relationship between density and HU for each type of software.

Results: There is no statistical significance of location of an object within the CBCT scanner on determination of its density. A linear relationship between the density of an object and the HU of a scan was = 0.001(HU)+1.19 with an R2 value of 0.893 (where density, , is measured in g cm^–3). This equation is to be used on a range between 1.42 g cm^–3 and 0.4456 g cm^–3.

Conclusions: A linear relationship can be used to determine the density of materials (in the density range of bone) from the HU values of a CBCT scan. This relationship is not affected by the object's location within the scanner itself.

Keywords: Hounsfield value; computed tomography; bone density