Abstract: PURPOSE: To assess the capability of monochromatic energy images of gemstone spectral imaging(GSI) by using spectral CT in reducing metal artifacts of oral and maxillofacial region. METHODS: Spectral CT imaging was applied to 46 patients with metallic implants with GSI sequence to measure CT numbers (expressed in Hounsfield units, HU) and SD (standard deviation) numbers of the soft tissues. 11 monochromatic-image groups were obtained, ranging from 40 keV(kiloelectronvolts) to 140 keV (every 10 keV as one group). The data were analyzed with SPSS19.0 software package. RESULTS: Images in 20 subjects with orthodontic appliance, the minimal average AI ranged between (23.86±10.90) to (24.42±11.54) HU. Similarly, in 12 subjects with titanium implants, the minimal average AI ranged between (26.49±9.40) to (26.95±8.97) HU. In 10 images from 14 subjects with dental fillings or fixed dentures, the minimal average AI ranged between (29.84±13.04) to (30.97±13.15) HU. The average AI values were (63.36±70.52), (70.82±105.14) and (107.35±147.57) HU from 40 keV to 140 keV in 3 groups, respectively, which was similar to the average AI values of 70keV monochromatic images (61.46±32.06, 70.18±62.86, 110.28±78.70) HU in each corresponding group. There was a significant difference about AI value among 3 energy spectrum groups (P<0.05). CONCLUSIONS: Spectral CT imaging could obviously reduce metal artifacts, and improve the display capabilities of the structures around the metallic implants. 70 keV is the dividing point of metal artifact subtraction. The optimal energy range is at 110-140 keV in reducing metal artifacts of oral and maxillofacial region.

Key words: Computed tomography, Metal artifact, Spectral CT, Oral and maxillofacial region