A Phantom Study of a Dual Energy Dental Cone Beam Computed Tomography Prototype

The inaccuracy in Hounsfield unit (HU) of dental cone beam computed tomography (CBCT) systems has been reported in several previous studies. CT images produced by dental CBCTs cannot represent an object's density owing to the HU inaccuracy; therefore, dental surgeons do not trust or utilize the HU values from CBCT in dental surgical operations, especially in implant placement. To provide more accurate bone density, we considered the possibility of a dual energy (DE) imaging technique. A new dental CBCT system capable of switching kVps was developed. The projection images at different kVp were reconstructed independently; subsequently, a new set of CT images of more accurate HUs would be produced. Moreover, a new calibration procedure was proposed in addition to the conventional HU calibration. Cylindrical hydroxyapatite (HA) phantoms of different densities were developed for this calibration. The voxel values of CT images at different energies were correlated point-by-point, and the parameters for mapping more accurate HUs values were extracted in this calibration. The proposed calibration and 30 examinations were performed using an acrylic base with cylindrical HA phantoms of different densities. The differences between the HUs of resultant DE images and the CT values provided by the phantom manufacturer were approximately 1%, and the coefficients of variation (CV) from 30 repeated examinations were near 1%. The HUs from our new DE CBCT agreed well with the CT values in this phantom study.