Optimization of image quality and radiation dose using different cone-beam CT exposure parameters.

Purpose: To investigate and optimize the impact of different exposure parameters on image quality and radiation dose for a latest generation orthopedic cone-beam CT system.

Materials And Methods: 110 consecutive scans of the same cadaver forearm were performed before and after the insertion of a distal radius plate on the palmar radius to achieve highest intra-individual comparability. All scans were conducted on a latest generation cone-beam CT scanner (Carestream OnSight 3D Extremity System, Carestream Health, Rochester, NY, USA). Extremity imaging was performed using different combinations of tube voltage (kV) and tube current - exposure time product (mAs). Radiation dose (DLP and CTDI) was recorded to widely varying combinations. Subjective and objective image quality analysis included a blinded evaluation by five different readers independently using 5-point-Likert scales.

Results: Highest radiation dose was achieved using the manufacturers' suggested standard protocol (90-kV and 5.0 mAs with DLP of 111.91 mGy*cm and CTDI of 4.49 mGy), while 70-kV and 2.0 mAs provided the most dose reduction with DLP of 20.34 mGy*cm and CTDI of 0.79 mGy. Regarding subjective image quality, higher tube voltage improved depiction of cortical bone (p ≤ 0.038) and cancellous bone (p ≤ 0.001) as well as overall image quality (p ≤ 0.027). Changes of the tube current - exposure time product did not show significant alterations of image quality (p ≥ 0.063). After plate insertion, only the subjective overall image quality showed reduced subjective perception (p < 0.001). Between the different scan protocols, no relevant changes were observed in the objective image quality analysis (SNR: p ≥ 0.125; CNR: p ≥ 0.086). However, presence of osteosynthesis significantly lowered the mean SNR and CNR (p < 0.001).

Conclusion: Even with lowest exposure settings, orthopedic extremity CBCT revealed good overall image quality. The best result regarding subjective image quality was achieved with 85-kV / 4.7 mAs with a dose reduction of 18,9% compared to the manufacturer's recommended protocol (90-kV and 5.0 mAs).