Influence of detector collimation and beam pitch for identification and image quality of ground-glass attenuation and nodules on 16- and 64-detector row CT systems: Experimental study using chest phantom

Objective: The purpose of the present study was to determine the influence of detector collimation and beam pitch for identification and image quality of ground-glass attenuation (GGA) and nodules on 16- and 64-detector row CTs, by using a commercially available chest phantom. Materials and methods: A chest CT phantom including simulated GGAs and nodules was scanned with different detector collimations, beam pitches and tube currents. The probability and image quality of each simulated abnormality was visually assessed with a five-point scoring system. ROC-analysis and ANOVA were then performed to compare the identification and image quality of either protocol with standard values. Results: Detection rates of low-dose CTs were significantly reduced when tube currents were set at 40 mA or less by using detector collimation 16 and 64 × 0.5 mm and 16 and 32 mm × 1.0 mm for low pitch, and at 100 mA or less by using detector collimation 16 and 64 × 0.5 mm and 16 and 32 mm × 1.0 mm for high pitch (p < 0.05). Image qualities of low-dose CTs deteriorated significantly when tube current was set at 100 mA or less by using detector collimation 16 and 64 × 0.5 mm and 16 and 32 × 1.0 mm for low pitch, and at 150 mA or less by using detector collimation 16 and 64 × 0.5 mm and 16 and 32 × 1.0 mm for high pitch (p < 0.05). Conclusion: Detector collimation and beam pitch were important factors for the image quality and identification of GGA and nodules by 16- and 64-detector row CT.