Evaluation of the impact of reduced scan field-of-view (SFOV) on CT radiation dose and image quality in a chest CT – a phantom study

Sammanfattning: Background: Technical development of image detectors and dose-reduction techniques in computed tomography (CT) have contributed to reduce radiation dose for patient and staff. The scan field of view (SFOV) generally affects the radiation dose the patient will beexposed. The aim of this phantom study is to assess how radiation dose and image quality are affected by changing the SFOV from 50cm to 32cm on a CT chest examination Material and methods: A chest phantom and CatPhan 504 phantom were scanned with different SFOV (50cm and 32cm SFOV) to assess variation in CTDIvol and image quality between the two SFOV. A RaySafe CT-sensor was scanned with both SFOV at different position in the gantry to assess the variation in absorbed dose between the two SFOV. Image quality between the two SFOV was compared for the chest phantom and the CatPhan 504. Results: The difference in CTDIvol for the two SFOVwas not statistically significant p>0,05 (p=0,89 for the chest-phantom and p=0,96 for the CatPhan 504). No difference in image quality was found between the two SFOV and for both phantoms. The absorbed dose measured with RaySafe CT sensor shows that the absorded dose decreases from the center to the periphery for both SFOV. There was a difference in standard error of the mean between the two scan methods Discussion: Different bowtie filters were chosen automatically by the CT for different SFOV. This might affect the tube-current modulation and the reduction of the radiation dose in the periphery due to the use of different bowtie-filters. Further studies are needed where restricted SFOV is used in combination with other methods for reducing dose, such as dynamic bowtie filters and automatic exposure can be recommended.  Keywords: Computed tomography, CT, Scan field-of-view, SFOV, Radiation dose