Influence of Small, Midi, Medium and Large Fields of View on Accuracy of Linear Measurements in CBCT Imaging:...

This study aimed to assess the effect of changing the field of view on the dimensional accuracy of CBCT imaging.

The implant-bone models were randomly numbered from 1 to 13 by the principal researcher, and then on each model at the incisors region three positions were selected and marked on the model with a permanent blue marker. Then at each marked position three radio-opaque 'RO' markers "gutta-percha pieces" were glued on the model surfaces as following; two pieces on the facial surface one occlusally (at the alveolar crest) and one apically (at the inferior border of the model) both were on the same vertical line and perpendicular to the horizontal plane, while the third one was placed on the lingual surface opposing the occlusally placed buccal piece. CBCT examinations of each bone model were performed using Cranex3Dx CBCT (Helsinki, Finland) machine. Each model was scanned four times with standardised tube current and voltage of 12.5 mA and 90 kVp respectively at four different FOVs. The FOVs used were as following: Small FOV: 50 x 50 mm with voxel size 200 µm, Midi FOV: 61 x 78 mm with voxel size 300 µm, Medium FOV: 78 x 78 mm with voxel size 300 µm, Large FOV: 78 x 150 mm with voxel size 350 µm. The reference standard in this study was the real linear measurements that were obtained directly on the implant-bone models using high precision sliding electronic digital calliper with 0-150 mm internal and external measuring range and 0.01 mm resolution accuracy. The index test in the current study was the CBCT linear measurements obtained from CBCT images of implant-bone models using small, midi, medium and large FOVs.

The results of this study showed that both medium and large FOVs showed a statistically significant difference, which could be translated into clinical relevance only in thickness measurements.

The interpretation of these results leads to the assumption that increasing the FOV size together with voxel size could adversely affect the accuracy of CBCT linear measurements, especially when small distances are to be assessed.