Image quality and radiation exposure in 320-row temporal bone computed tomography

Objectives: The aim was to define image quality and radiation exposure in the recently introduced 320-row CT of the temporal bone (tb) in comparison to a 16-row tb CT. Methods: A cadaveric head phantom was used for repeated tb volume CT studies (80120 kV, 25-150 mAs), performed in a 320-row scanner (single rotation, 0.5 mm slice thickness, kernel FC 51) in comparison to 16-row helical CT using standard acquisition parameters (SAP) of 120 kV and 75 mAs (kernel FC 53). Qualitative image evaluation was performed by two radiologists using a 5-point visual analogue scale. Image noise (D(SD)) was determined by region of interest (ROI) based measurements in cadaveric as well as water phantom studies. Dosimetric measurements of the effective dose (ED) and organ dose (OD) of the lens were performed. Results: Image quality of 320-row tb CT was equivalent to 16-row CT for SAP scans, resulting in image noise levels (D(SD) 16-/320-row) of 109/237 and 206/446 for air and bone respectively. D(SD) differences were predominantly (>90%) attributable to the different kernels available for tb studies in 16- and 320-row CT. Radiation exposure for 16-/320-row SAP scans amounted to 0.36/0.30 mSv (ED) and 10.0/8.4 mGy (lens dose). Conclusion: 320-row volume acquisition in tb CT delivers equivalent image quality to 16-row CT while decreasing radiation exposure figures by one sixth. Image noise increase in 320-row CT is negligible with respect to image quality. Dentomaxillofacial Radiology (2010) 39, 199-206. doi: 10.1259/dmfr/14139527