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 @-kV than @-kV images ( SNR in the proximal RCA : @ @ vs. @ @ ; SNR in the LMA : @ @ vs. @ @ ; CNR in the proximal RCA : @ @ vs. @ @ ; CNR in the LMA : @ @ vs. @ @ ; all p < @ ) .