Signal-to-noise ratio ( SNR ) and contrast-to-noise ratio ( CNR ) in the proximal right coronary artery ( RCA ) and left main coronary artery ( LMA ) were all lower in 80-kV than 120-kV images ( SNR in the proximal RCA : 16.5 1.8 vs. 19.4 2.8 ; SNR in the LMA : 16.3 2.0 vs. 19.6 2.7 ; CNR in the proximal RCA : 19.4 2.3 vs. 22.9 3.0 ; CNR in the LMA : 18.8 2.4 vs. 22.7 2.9 ; all p < 0.0001 ) .