In Vitro Specimen Study for Parameter Optimization of Multislice Spiral CT Orbital Scanning

Purpose Isolated skull specimens underwent a conventional-dose and different low-dose orbital scans using a 16-slice spiral CT,to explore the feasibility of low-dose orbital scanning.Materials and Methods 15 in vitro fixed skull specimens with preservative treatment underwent orbital scanning of 120 kV,110 kV,80 kV with a fixed tube current of 180 mA;scanning of 180 mA,90 mA,45 mA with fixed tube voltage of 120 kV;and scanning of 180 mA,90 mA,50 mA,25 mA with fixed tube voltage of 80 kV,CT dose index,dose-length product,effective dose,average CT value,image signal to noise ratio(SNR),contrast to noise ratio(CNR) and image quality score of scanning with different doses were compared.Results Image SNR,CNR and radiation dose could be significantly reduced with lower tube voltage(110 kV,80 kV) and exponentially lower tube current(90 mA,50 mA,25 mA)(P0.05),while the image quality scores all remained three points or more;there was no obvious change of average CT value of the tissue when the tube voltage was reduced;but significant differences(P0.05) were shown when comparing the orbital and its inner anatomy,lesions' structure and the number of lesions detected of different low-dose groups with the conventional dose(120 kV,180 mA) group.The radiation dose reduced by approximately 92% when scanned with 80 kV,50 mA,with soft tissue and orbital bones well displayed.The radiation dose reduced by approximately 96% when scanned with 80 kV,25 mA,periorbital fractures could be well shown,while the soft tissue was poorly displayed.Conclusion There is great potential for radiation dose reduction of orbital CT scanning,compared with conventional scanning,radiation dose can be reduced by approximately 92% when soft tissue and orbital bone lesions are scanned with 80 kV,50 mA,while the diagnosis won't be affected,radiation dose even can be further reduced when only the periorbital fractures are to be observed.