Ultrasonographic Assessment of Cirrhosis and Portal Hypertension

A sonographic Doppler study of the hepatic vein, portal vein and hepatic artery in liver cirrhosis: Correlation of hepatic hemodynamics with clinical Child Pugh score in Singapore

Objective

Liver cirrhosis has been a rising complication of chronic liver disease in Singapore. Ultrasound has been widely accepted as a non-invasive imaging modality for the evaluation of hepatic haemodynamics. This study aims to correlate the Doppler ultrasound values with the progression of liver cirrhosis to allow further understanding and possible prediction of clinical events for timely intervention.

Methods

Study sample of 56 eligible patients with liver cirrhosis was divided according to their Child-Pugh clinical score into Child's A (n = 29 patients), B (n = 19 patients) and C (n = 8 patients). The maximum portal vein velocity, maximum hepatic vein velocity, maximum hepatic artery velocity and hepatic artery resistive index were assessed by Doppler ultrasound.

Results

The incidence of ascites increases with the severity of cirrhosis. Flattening of the hepatic vein waveforms was dependant on degree of liver cirrhosis. Maximum hepatic vein velocity was higher in cirrhotic patients (where p = 0.05). Maximum portal vein velocity was found to be lower in cirrhosis (where p < 0.001) and mean maximum portal vein velocity decreases as severity of cirrhosis worsens. Hepatic artery resistive index was significantly higher in cirrhosis (where p < 0.001). Significant association was found between maximum hepatic vein velocity and maximum hepatic artery velocity and significant negative correlation was observed with the maximum portal vein velocity and hepatic artery resistive index.

Conclusion

The study demonstrated that these parameters can supplement the evaluation of liver cirrhosis and will be able to distinguish the different grades of liver cirrhosis using Doppler ultrasound.

Congenital Extrahepatic Abdominal Arteriovenous Fistula and Apparent Patent Ductus Venosus in a Dog

A 3 mo old male German shepherd dog presented with a 2 wk history of diarrhea with possible melena followed by inappetence and progressive abdominal distension. Clinical findings, serum biochemical analysis, and abdominal ultrasound were highly suggestive of an extrahepatic abdominal arteriovenous fistula and concurrent patent ductus venosus, which were confirmed during an abdominal exploratory surgery. Renal biopsies taken at the time of surgery confirmed a chronic glomerulopathy. The dog made a good initial recovery from the procedure but was euthanatized 6 wk postoperatively for medically unresponsive renal disease.

Changes in portal hemodynamics after TIPS in liver cirrhosis and portal hypertension

OBJECTIVE

The objective of this study is to analyze the changes in portal hemodynamics that occurs in portal hypertension before and after transjugular intrahepatic portosystemic shunt (TIPS), to investigate the relationship between these changes and portal pressure (PP) and to determine the significance of sonographic parameters in measuring PP.

METHODS

Ultrasonography of the portal and splenic veins and direct measurement of the PP were performed in 92 patients before and after TIPS. The differences observed in the portal and splenic vein diameters, the blood flow velocity in the portal and splenic veins and the PP were measured, and the correlations between PP and the other parameters were assessed using the SPSS 13 (SPSS Inc., Chicago, IL, USA). P < 0.05 was considered statistically significant.

RESULTS

We observed a significant decrease in the PP and the diameters of the portal and splenic veins compared to preoperative conditions (p < 0.001). The velocity of blood flow in the portal and splenic veins was significantly increased after TIPS (p < 0.001). The PP correlated with the diameter and velocity of blood flow in portal (r = 0.46, p = 0.020; r = 0.47, p = 0.017) and splenic vein (r = 0.57, p = 0.003; r = 0.33, p = 0.003) only in Child's A and was absent in Child's B cirrhosis patients.

CONCLUSION

The PP is influenced by the complex interaction between intrahepatic vascular resistance, collaterals and the amount of portal blood flow, which varies considerably between individuals. Once a certain pressure threshold is reached, collaterals form, and the correlation between the ultrasonographic parameters and PP becomes limited.

On the implementation of an automated acoustic output optimization algorithm for subharmonic aided pressure estimation

Incident acoustic output (IAO) dependent subharmonic signal amplitudes from ultrasound contrast agents can be categorized into occurrence, growth or saturation stages. Subharmonic aided pressure estimation (SHAPE) is a technique that utilizes growth stage subharmonic signal amplitudes for hydrostatic pressure estimation. In this study, we developed an automated IAO optimization algorithm to identify the IAO level eliciting growth stage subharmonic signals and also studied the effect of pulse length on SHAPE. This approach may help eliminate the problems of acquiring and analyzing the data offline at all IAO levels as was done in previous studies and thus, pave the way for real-time clinical pressure monitoring applications. The IAO optimization algorithm was implemented on a Logiq 9 (GE Healthcare, Milwaukee, WI) scanner interfaced with a computer. The optimization algorithm stepped the ultrasound scanner from 0% to 100% IAO. A logistic equation fitting function was applied with the criterion of minimum least squared error between the fitted subharmonic amplitudes and the measured subharmonic amplitudes as a function of the IAO levels and the optimum IAO level was chosen corresponding to the inflection point calculated from the fitted data. The efficacy of the optimum IAO level was investigated for in vivo SHAPE to monitor portal vein (PV) pressures in 5 canines and was compared with the performance of IAO levels, below and above the optimum IAO level, for 4, 8 and 16 transmit cycles. The canines received a continuous infusion of Sonazoid microbubbles (1.5 μl/kg/min; GE Healthcare, Oslo, Norway). PV pressures were obtained using a surgically introduced pressure catheter (Millar Instruments, Inc., Houston, TX) and were recorded before and after increasing PV pressures. The experiments showed that optimum IAO levels for SHAPE in the canines ranged from 6% to 40%. The best correlation between changes in PV pressures and in subharmonic amplitudes (r=-0.76; p=0.24), and between the absolute PV pressures and the subharmonic amplitudes (r=-0.89; p<0.01) were obtained for the optimized IAO and 4 transmit cycles. Only for the optimized IAO and 4 transmit cycles did the subharmonic amplitudes differ significantly (p<0.01) before and after increasing PV pressures. A new algorithm to identify optimum IAO levels for SHAPE has been developed and validated with the best results being obtained for 4 transmit cycles. The work presented in this study may pave the way for real-time clinical applications of estimating pressures using the subharmonic signals from ultrasound contrast agents.

Chronic liver disease: noninvasive subharmonic aided pressure estimation of hepatic venous pressure gradient

PURPOSE

To compare subharmonic aided pressure estimation (SHAPE) with pressure catheter-based measurements in human patients with chronic liver disease undergoing transjugular liver biopsy.

MATERIALS AND METHODS

This HIPAA-compliant study had U.S. Food and Drug Administration and institutional review board approval, and written informed consent was obtained from all participants. Forty-five patients completed this study between December 2010 and December 2011. A clinical ultrasonography (US) scanner was modified to obtain SHAPE data. After transjugular liver biopsy with pressure measurements as part of the standard of care, 45 patients received an infusion of a microbubble US contrast agent and saline. During infusion, SHAPE data were collected from a portal and hepatic vein and were compared with invasive measurements. Correlations between data sets were determined by using the Pearson correlation coefficient, and statistical significance between groups was determined by using the Student t test.

RESULTS

The 45 study patients included 27 men and 18 women (age range, 19-71 years; average age, 55.8 years). The SHAPE gradient between the portal and hepatic veins was in good overall agreement with the hepatic venous pressure gradient (HVPG) (R = 0.82). Patients at increased risk for variceal hemorrhage (HVPG ≥ 12 mm Hg) had a significantly higher mean subharmonic gradient than patients with lower HVPGs (1.93 dB ± 0.61 [standard deviation] vs -1.47 dB ± 0.29, P < .001), with a sensitivity of 100% and a specificity of 81%, indicating that SHAPE may be a useful tool for the diagnosis of clinically important portal hypertension.

CONCLUSION

Preliminary results show SHAPE to be an accurate noninvasive technique for estimating portal hypertension.

Assessment of hepatic hemodynamics using high-frequency ultrasound in normal rats

AIM: To detect hepatic hemodynamic parameters in normal rats to provide a basis for further monitoring and evaluation of liver diseases in rats.

METHODS: One hundred Sprague-Dawley (SD) rats were used. A 5-12 MHz high-frequency linear transducer was applied to obtain liver ultrasonograms and measure the diameter and maximum velocity of the portal vein, the peak systolic velocity, end diastolic velocity and resistance index of the proper hepatic artery.

RESULTS: The portal vein of rats was well demonstrated by high-frequency ultrasound. The test showed that the diameter of the portal vein of normal SD rats was around 0.18 cm ± 0.03 cm, the maximum velocity of the portal vein was around 16.21 cm/s ± 3.86 cm/s, and the peak systolic velocity, end diastolic velocity and resistance index of the proper hepatic artery were around 57.60 cm/s ± 15.41 cm/s, 26.46 cm/s ± 10.96 cm/s and 0.54 ± 0.13, respectively.

CONCLUSION: High-frequency Doppler ultrasonography allows obtaining clear portal vein ultrasonograms and the hemodynamic parameters of the portal vein and hepatic artery in rats, representing an effective method for monitoring hepatic hemodynamic changes in experimental rats.

Investigating the efficacy of subharmonic aided pressure estimation for portal vein pressures and portal hypertension monitoring

The efficacy of using subharmonic emissions from Sonazoid microbubbles (GE Healthcare, Oslo, Norway) to track portal vein pressures and pressure changes was investigated in 14 canines using either slow- or high-flow models of portal hypertension (PH). A modified Logiq 9 scanner (GE Healthcare, Milwaukee, WI, USA) operating in subharmonic mode (f(transmit): 2.5 MHz, f(receive): 1.25 MHz) was used to collect radiofrequency data at 10-40% incident acoustic power levels with 2-4 transmit cycles (in triplicate) before and after inducing PH. A pressure catheter (Millar Instruments, Inc., Houston, TX, USA) provided reference portal vein pressures. At optimum insonification, subharmonic signal amplitude changes correlated with portal vein pressure changes; r ranged from -0.82 to -0.94 and from -0.70 to -0.73 for PH models considered separately or together, respectively. The subharmonic signal amplitudes correlated with absolute portal vein pressures (r: -0.71 to -0.79). Statistically significant differences between subharmonic amplitudes, before and after inducing PH, were noted (p ≤ 0.01). Portal vein pressures estimated using subharmonic aided pressure estimation did not reveal significant differences (p > 0.05) with respect to the pressures obtained using the Millar pressure catheter. Subharmonic-aided pressure estimation may be useful clinically for portal vein pressure monitoring.