Eeffects of tube voltage on image quality and radiation dose of paranasal sinus CT examination

Objective To explore the effects of tube voltage on the image quality and radiation dose of paranasal sinus CT on a 16 cm wide-detector CT. Methods The sinus area of head specimen was scanned with sequential scanning mode and tube voltages of 70, 80, 100, 120 and 140 kV, respectively. The parameters were set as follows: NI=9, automatic tube current modulation, Smart mA with the maximum range at the corresponding tube voltage, 120 mm detector width. The images were reconstructed with bone and soft tissue algorithms separately.The slice thickness was 0.625 mm for all reconstructed images. The axial, coronal and sagittal images were reformatted as 2 mm thickness with clinical baseline. The CT value and standard deviation (SD) were measured in the region of interest(ROI) of central axial image and the contrast-to-noise ratio (CNR) was calculated. The volume CT dose index(CTDIvol) and dose length product (DLP) were recorded, and the figure of merit (FOM) of images was computed. The images obtained in the study were subjectively evaluated by two experienced radiologists and one technician using a five-point scoring system. Results The subjective evaluation of images obtained in the study met the diagnostic requirements. With the reconstruction of bone algorithm, the CNR at the tube voltages of 100 and 80 kV were 66.98 and 64.75, respectively, which was significantly higher than those at the tube voltages of 70, 120 and 140 kV (51.61, 61.56 and 57.76, respectively). The maximum and minimum CTDIvol were 34.11 mGy at 140 kV and 17.45 mGy at 70 kV. The FOM value was 152.26 at 100 kV. With the reconstruction of soft tissue algorithm, the maximum CNR was 195.62 at 80 kV, which was markedly greater than those at 70, 100, 120 kV and 140 kV (139.46, 154.49, 148.06 and 155.58 respectively). The maximum FOM value was 1273.56 at 80 kV, which was significantly higher than those at the tube voltages of 70, 100, 120 kV and 140 kV (1114.56, 809.98, 735.63 and 709.62, respectively). Conclusions For the sinus CT of head specimen, the scan protocols with 100 kV combined with bone reconstruction algorithm and 80 kV combined with soft tissue reconstruction algorithm can provide relatively lower radiation dose and good image quality. Key words: CT; Paranasal sinus; Tube voltage; Radiation dose