Changes in Kupffer-phase Echogenicity and the Kupffer cell Fraction. (A) In the representative case, the bile duct dilatation became increasingly clear from the four-week to eight-week follow-up in the experimental group. The liver parenchymal echogenicity on Kupffer phase by contrast-enhanced ultrasound imaging (CEUS) decreased compared to that of the control group. (B) The vertical axis is the signal intensity (dB) and the horizontal axis is the period of N-nitrosodimethylamine or normal saline administration. The parenchymal echogenicity in the experimental group at six- and eight-week on the Kupffer phase of CEUS decreased compared to those of the control group (all P < 0.001). (C) There was significant increase in CD68 count in the experimental group at six- and eight-week specimen (P < 0.001) (original magnification; lower power: ×40 and high power: ×200, scale bars = 100 µm). (D) The KC fraction of the experimental group tended to increase slightly from six weeks to eight weeks (24.1 ± 4.7 vs. 12.0 ± 2.2% and 27.4 ± 7.8 vs. 12.6 ± 3.6%). *P < 0.05.