In-addition to their clinical standard-dose chest CT ( SD , 120 kV mean CTDIvol , 6 1 mGy ) , ULD-CT was subsequently performed at three-dose-levels ( 0.9 mGy [ 120 kV ] ; 0.5 mGy [ 100 kV ] and 0.2 mGy [ 80 kV ] ) .