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Figure 1b. HCC. (a) Conventional power Doppler US images. The image obtained before injection of the contrast agent shows a minimal dotlike power Doppler US signal (solid straight arrow) in the peripheral portion of a hypoechoic tumor. The conventional power Doppler US images obtained at 30 seconds (sec), 60 seconds, 2 minutes (min), 3 minutes, and 5 minutes after injection show a marked increase in the intratumoral power Doppler US signals. The contrast-enhanced area is maximal on the image obtained at 60 seconds and decreases subsequently. Diffuse partial filling of the tumor with power Doppler US signals is noted on 1- and 2-minute images (open straight arrows). Power Doppler artifacts (curved solid arrow) are seen along the diaphragm. (b) Harmonic power Doppler US images. The image obtained before contrast agent injection shows no intratumoral power Doppler US signals. The harmonic power Doppler US images obtained at 30 seconds (sec), 60 seconds, 2 minutes (min), 3 minutes, and 5 minutes after injection show dotlike and linear power Doppler US signals within the tumor. The intratumoral signals are lower in intensity in b than in a. The diffuse intratumoral filling with power Doppler US signals and the artifactual signals along the diaphragm are not seen in b.