Figure 3a. HCC near the heart on conventional and harmonic power Doppler US images. (a) Conventional power Doppler US images. The image obtained before injection of the contrast agent shows minimal dotlike power Doppler US signals within a hypoechoic tumor. Despite the use of low-power Doppler US gain to reduce motion-related artifacts from cardiac pulsation when obtaining these images, artifacts (arrow) are noted in the liver near the heart. Conventional power Doppler US images obtained at 30 seconds (sec), 60 seconds, 2 minutes (min), 3 minutes, and 5 minutes after injection show an increase in the number and intensity of intratumoral power Doppler US signals. (b) Harmonic power Doppler US images. The image obtained before contrast agent injection shows no intratumoral power Doppler US signals. Harmonic power Doppler US images obtained at 30 seconds (sec), 60 seconds, 2 minutes (min), 3 minutes, and 5 minutes after injection show marked intratumoral power Doppler US signals. The extent of power Doppler US signals in the tumor and hepatic vessels in b is larger than in a.