Measurement of Bone Mineral Content by Rotational Panoramic Radiography: Using Dual Energy Subtraction of Computed Radiographic Images in a Single Exposure

Abstract

The purpose of this study was to measure bone mineral content by rotational panoramic radiography. The dual energy subtraction method was applied to panoramic radiographs to allow accurate measurement of bone mineral content without hindrance by soft tissue. A one-shot dual energy subtraction method was carried out using Fuji Computed Radiography (FCR 7000) and a CR-workstation. Panoramic radiographs were obtained using a Morita Super-Veraview with a tube voltage of 80kV, total filtration of 2.0mm of aluminum and tube current of 10mA. A Cu-filter was placed between the first and second imaging plates (IP). Ce, Sm and Gd filters were used as additional filters for single exposure dual energy subtraction using preliminary computer simulation. To separate bone mineral content from soft tissue on panoramic radiographs, weighting factors which eliminated the effects of bone or soft tissue were obtained using an experimental phantom which consisted of water and aluminum cylinders. Aluminum cylinders (3∼12mm) were arranged in a tooth-shaped rows in water and used as the reference for the mandible. This phantom was placed on the panoramic equipment in place of the mandible, and the panoramic phantom image was taken. This phantom image or subtraction image was processed with weighting factors and the aluminum cylinders were evaluated by converting into CaHPO₄ of standard Phantom (Compact Bone). The Sm filter was concluded to be the most effective. Adequate correlation between compact bone density and aluminum cylinder thickness was demonstrated.