Contrast-enhanced ultrasonography of the hepatic vein in normal dogs

Abstract

Contrast-enhanced ultrasonography (CEUS) of the hepatic vein can assess intrahepatic hemodynamic changes and has been studied as a noninvasive method to assess the severity of portal hypertension and hepatic fibrosis in humans. However, few reports have described its usefulness in veterinary medicine. The purpose of this study was to characterize CEUS findings of the hepatic vein in normal dogs and assess the repeatability of this method both in a conscious group (n=6) and a sedated group (n=6). Sonazoid^® (0.01 ml/kg) was used as a contrast agent, and scanning of the hepatic vein was performed for 2 min. Time-intensity curves were generated from regions of interest in the hepatic vein. Four perfusion parameters were measured for quantitative analysis: hepatic vein arrival time (HVAT), time to peak (TTP), time to peak phase (TTPP) and wash-out ratio (WR). CEUS examinations were performed three times in each dog. The median (range) values of HVAT, TTP, TTPP and WR in the conscious group were 13.5 sec (9-22 sec), 12.5 sec (6-24 sec), 8 sec (6-13 sec) and 78.0% (60.7-91.7%), respectively. Median (range) values of HVAT, TTP, TTPP and WR in the sedated group were 12 sec (8-17 sec), 12.5 sec (9-17 sec), 9 sec (7-13 sec) and 84.1% (63.0-94.4%), respectively. The coefficients of variation of these parameters in the conscious and sedated groups were 7.6-29.7% and 11.8-14.8%, respectively.

Fig. 1.

Color Doppler and CEUS images of the right HV obtained using a right intercostal approach. (A) Right HV displayed in blue with color Doppler flowed into the caudal vena cava (CVC). The operator visualized this transverse image before the CEUS study. (B) At 8 sec, the HV, outlined by a dashed line, was not enhanced, although surrounding liver parenchyma was slightly enhanced. Region of interest (ROI) was manually placed in the HV (circle) to measure the tissue intensity. (C) HV reached its PI, which was similar in intensity to the liver parenchyma (shown here 23 sec after bolus injection of contrast agent). (D) At the end of the examination (120 sec), the contrast agent in the HV appeared washed-out and hypoechoic compared to the liver parenchyma.

Fig. 2.

Schematic illustration of the TIC and measured parameters. The TIC remained unchanged until the contrast agent flowed into the HV. Hepatic vein arrival time (HVAT) was the time when the TIC first reached 20% of peak intensity (PI). Time to peak (TTP) and time to peak phase (TTPP) were defined as the time when TIC reached to PI and to 90% PI, respectively. Wash-out ratio (WR) indicated the attenuation rate from PI to the end of the study.

Fig. 3.

TIC showing the median pixel intensity in the HV. (A) Conscious group (●, n=6). (B) Sedated group (□, n=6). The vertical bars represent the range of the values. The line graphs in the two groups are nearly identical, but the peak intensity was higher in the conscious group.