Idose level 2

All of the CT images were obtained from a DLCT scanner (Spectral IQON, Philips
Healthcare, Best, Netherlands). The CT scanning parameters were listed as the
following: tube voltage 120 kVp with automated attenuation-based dose
modulation, rotation time 0.5 s, pitch 0.359, collimation 64 × 0.625, slice
thickness 3 mm, filed of view (FOV) 220 × 220 mm. The subjects only received the
CT scan with a closed mouth, and the open mouth position CT scan was not
performed in the current study.
Conventional images and spectral base images (SBI) were reconstructed from the
same dataset with an axial slice thickness of 0.67 mm and an increment of
0.67 mm. Conventional images were reconstructed using iDose level 2 (Philips
Healthcare), and SBI data were reconstructed based on Spectral level 2 (Philips
Healthcare).

Conventional polyenergetic images (CIs) were reconstructed using an IR algorithm (iDose Level 2, Philips Healthcare, Cleveland, OH, USA) at 120 kVp, which is used in clinical practice. MAR images were reconstructed from CI with an orthopedic MAR algorithm (O-MAR, Philips Healthcare). VMI were generated from spectral raw data using a dedicated workstation (Intellispace Portal, Philips, Best, the Netherland) at settings ranging from 50 keV to 200 keV in increments of 10 keV. Then, the VMI were transferred to the PACS system workstations (INFINITT; Infinitt Healthcare, Seoul, Korea) for the imaging analysis of the monoenergetic CT images. All images were reconstructed at a 2 mm slice thickness with 1 mm of overlap and a YD filter.