The influence of the field of view and voxel size on the contrast-to-noise ratio in cone-beam computed tomography imaging.

Purpose: This study investigated the impact of the field of view (FOV), voxel size, and exposure parameters on the contrast-to-noise ratio (CNR) in cone-beam computed tomography (CBCT).

Materials and methods: A SedentexCT phantom was scanned using 3D Accuitomo 170 across 3 FOVs (40×40 mm, 60×60 mm, 80×80 mm). Each FOV had 4 settings for kVp and 3 for mA. Volumes were reconstructed with voxel sizes from 80 to 250 µm. The CNR was calculated using ImageJ (ver. 1.41, National Institutes of Health, Bethesda). Statistical analyses included Pearson correlation coefficients and regression (R²).

Results: Positive correlations were observed in the 40×40 FOV between voxel size, kVp, mA, rotation degree, and CNR. The 60×60 FOV showed positive correlations between mA, kVp, and CNR, while the 80×80 FOV exhibited correlations for voxel size, kVp, and mA. In the 40×40 (R²=0.551) and 80×80 (R²=0.550) FOVs, mA, kVp, and voxel size influenced CNR. For the 60×60 FOV, mA and kVp were significant contributors (R²=0.389). Using a constant 80-µm voxel size, both mA and kVp significantly influenced CNR (R²=0.467); neither FOV nor rotation degree had substantial impacts.

Conclusion: CNR increased with higher mA, kVp, and larger voxel sizes for 40×40 and 80×80 FOVs. mA was the most influential factor across all FOVs. Regression models showed significant effects of mA and kVp on CNR with 80-µm voxels, while FOV had no effect.