Relationship between physical factors and subjective image quality of cone-beam computed tomography images according to diagnostic task.

Objective: This study was designed to investigate the relationship between physical factors and the subjective quality of cone beam computed tomography (CBCT) images used for different diagnostic tasks.

Study Design: CBCT images of a real skull phantom and a SedentexCT IQ phantom were acquired under different exposure conditions (one Dinnova3 CBCT scanner, 60-110 kV and 4-10 mA). Radiologists evaluated subjective image quality of real skull phantom images for each diagnostic task. On the basis of the evaluation results, the images were classified into two groups: acceptable and unacceptable. The modulation transfer function (MTF), contrast-to-noise ratio (CNR), and image uniformity were measured using the SedentexCT IQ phantom images. The differences in physical factors were evaluated.

Results: MTF and CNR values showed statistical differences in image quality in two groups with regard to all diagnostic tasks. In the maxilla, MTF and CNR values showed no significant differences between periapical diagnosis and implant planning in the acceptable groups. Higher MTF and CNR values were required in the periapical diagnosis compared with the implant planning of the mandible.

Conclusions: This study proved that MTF and CNR values have a significant association with subjective image quality. The diagnostic task should be considered in evaluation of CBCT image quality.