Imaging with 80-kV/370-mAs instead of 100-kV/300-mAs was associated with 40 % lower radiation dose ( mean dose-length product , 35966 vs 628112 mGy [ Symbol : see text ] cm ; P < 0.001 ) with no significant difference in CNR ( 34.513.4 vs 33.510.4 ; P = 0.81 ) or MBF in non-ischaemic myocardium ( 0.950.20 vs 0.990.25 ml/min/g ; P = 0.66 ) .