Quantification of gray values corresponding to bone density using dental cone-beam computed tomography

抄録

Cone-beam computed tomography （CBCT） is frequently used for preoperative examination of implants; however, it cannot be used to determine the bone mineral density （BMD） owing to its incapability at providing the CT values obtained through a CT scan. An efficient and accurate technique for measuring BMD using CT is quantitative CT （QCT）. Herein, we examined whether jaw bone mineral content can be easily estimated from the CBCT gray value by applying the QCT method. Two CBCT systems, a 3DX multi-image microCT （3DX） and a KaVo 3D eXam （KaVo）, were used. Three dry human skull bones with calibration phantoms on the skin side and a target phantom on the intraoral side were used. For 3DX, X-ray tube voltage was altered to investigate the effect of exposure conditions on the grey value. The bone density （calcium carbonate density） and calibration phantom gray value were used to generate a conversion curve to estimate the bone density of the target phantom, and subsequently, the error from the true value was calculated. Errors were in the range of approximately 5％-15％ and 3％-4％ for 3DX and KaVo, respectively. KaVo, which has a wider irradiation field, yielded better results than 3DX. 3DX demonstrated smaller errors at higher tube voltages when the tube voltage was varied. Although the error differed depending on the device, CBCT could be used for the estimation of the approximate bone density of the implant site despite the error.