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 mGycm and CTDI of 4.49 mGy), while 70-kV and 2.0 mAs provided the most dose reduction with DLP of 20.34 mGycm 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).