Evaluation of liver parenchymal blood flow with contrast-enhanced US: preliminary results in healthy and cirrhotic patients

Functional imaging of the liver

Anatomical-based imaging is used widely for the evaluation of diffuse and focal liver, including detection, characterization, and therapy response assessment. However, a limitation of anatomical-based imaging is that structural changes may occur relatively late in a disease process. By applying conventional anatomical-imaging methods in a more functional manner, specific pathophysiologic alterations of the liver may be assessed and quantified. There has been an increasing interest in both the clinical and research settings, with the expectation that functional-imaging techniques may help solve common diagnostic dilemmas that conventional imaging alone cannot. This review considers the most common functional magnetic resonance imaging, computed tomography, and ultrasound imaging techniques that may be applied to the liver.

Application of a second-generation US contrast agent in infants and children--a European questionnaire-based survey

BACKGROUND

No US contrast agent (US-CA) is currently licensed for use in children.

OBJECTIVE

To survey the off-label use in children of a second-generation US-CA.

MATERIALS AND METHODS

Questionnaires were e-mailed to European paediatric radiologists, who were asked about their experience with the second-generation US-CA Sonovue® (Bracco, Milan, Italy). Number of examinations per indication and adverse effects were recorded. Examinations were categorised by intravenous or intracavitary use of US-CA.

RESULTS

Out of 146 respondents, 88 stated that they did not perform contrast-enhanced US in children, but 36 of these (44%) would appreciate paediatric approval. Forty-five centres reported 5,079 examinations in children (age mean: 2.9 years; range: birth-18 years, M/F: 1/ 2.8). The majority (4,131 [81%] in 29 centres) were intravesical applications. The minority (948 [19%] in 30 centres) were intravenous applications. No adverse effects had been recorded from intravesical use. Six minor adverse effects (skin reaction, unusual taste, hyperventilation) had been recorded after five intravenous studies (0.52%).

CONCLUSION

Responses suggest a favourable safety profile of this second-generation US-CA in children. It also demonstrates a demand for such US-CA from paediatric radiologists.

Evaluation of liver fibrosis by investigation of hepatic parenchymal perfusion using contrast-enhanced ultrasound: an animal study

PURPOSE

To investigate the value of assessing the hepatic parenchymal perfusion in contrast-enhanced ultrasound (CEUS) for evaluating liver fibrosis, using an animal model.

METHODS

Seventy Sprague-Dawley rats were divided into experimental (n = 35) and control (n = 35) groups. In the experimental group, liver fibrosis was induced by intraperitoneal injection of carbon tetrachloride. CEUS of the liver was performed at a 2-week interval for 14 weeks. Signal intensity of liver parenchyma was analyzed with time-intensity curves. Histologic examination of liver specimens of the animals was performed to assess the fibrosis stage.

RESULTS

The peak signal intensity of hepatic parenchymal perfusion in stage 2-3 fibrosis was significantly lower than that in stage 0-1. The time to peak intensity of hepatic parenchymal perfusion was significantly longer in the experimental group than the control group, and in the stage 3 fibrosis than in stages 0-2 fibrosis. Using time to peak intensity of hepatic parenchymal perfusion to distinguish stage 3 fibrosis and stages 0-2 fibrosis, the optimum cutoff was 75,000 milliseconds with the sensitivity and specificity of 67% and 78%, respectively.

CONCLUSIONS

This animal study showed that CEUS has the potential to be a complementary imaging tool in the evaluation of liver fibrosis.

Quantitative contrast-enhanced ultrasound imaging: a review of sources of variability

Ultrasound provides a valuable tool for medical diagnosis offering real-time imaging with excellent spatial resolution and low cost. The advent of microbubble contrast agents has provided the additional ability to obtain essential quantitative information relating to tissue vascularity, tissue perfusion and even endothelial wall function. This technique has shown great promise for diagnosis and monitoring in a wide range of clinical conditions such as cardiovascular diseases and cancer, with considerable potential benefits in terms of patient care. A key challenge of this technique, however, is the existence of significant variations in the imaging results, and the lack of understanding regarding their origin. The aim of this paper is to review the potential sources of variability in the quantification of tissue perfusion based on microbubble contrast-enhanced ultrasound images. These are divided into the following three categories: (i) factors relating to the scanner setting, which include transmission power, transmission focal depth, dynamic range, signal gain and transmission frequency, (ii) factors relating to the patient, which include body physical differences, physiological interaction of body with bubbles, propagation and attenuation through tissue, and tissue motion, and (iii) factors relating to the microbubbles, which include the type of bubbles and their stability, preparation and injection and dosage. It has been shown that the factors in all the three categories can significantly affect the imaging results and contribute to the variations observed. How these factors influence quantitative imaging is explained and possible methods for reducing such variations are discussed.

Assessment of tissue perfusion by contrast-enhanced ultrasound

Contrast-enhanced ultrasound (CEUS) with microbubble contrast agents is a new imaging technique for quantifying tissue perfusion. CEUS presents several advantages over other imaging techniques in assessing tissue perfusion, including the use of microbubbles as blood-pool agents, portability, availability and absence of exposure to radiation or nuclear tracers. Dedicated software packages are necessary to quantify the echo-signal intensity and allow the calculation of the degree of tissue contrast enhancement based on the accurate distinction between microbubble backscatter signals and native tissue background. The measurement of organ transit time after microbubble injection and the analysis of tissue reperfusion kinetics represent the two fundamental methods for the assessment of tissue perfusion by CEUS. Transit time measurement has been shown to be feasible and has started to become accepted as a clinical tool, especially in the liver. The loudness of audio signals from spectral Doppler analysis is used to generate time-intensity curves to follow the wash-in and wash-out of the microbubble bolus. Tissue perfusion may be quantified also by analysing the replenishment kinetics of the volume of microbubbles after their destruction in the imaged slice. This allows to obtain semiquantitative parameters related to local tissue perfusion, especially in the heart, brain, and kidneys.

Diagnosis of liver cirrhosis with contrast-enhanced ultrasound

The assessment of the extent of liver fibrosis is very important for the prognosis and clinical management of chronic liver diseases. Although liver biopsy is the gold standard for the assessment of liver fibrosis, new non-invasive diagnostic methods are urgently needed in clinical work due to certain limitations and complications of biopsy. Noninvasive imaging studies play an important role in the diagnosis of focal liver disease and diffuse liver diseases. Among them, ultrasonography is the first choice for study of the liver in clinical work. With the development of ultrasound contrast agents and contrast specific imaging techniques, contrast-enhanced ultrasound (CEUS) shows good performance and great potential in the evaluation of liver fibrosis. Researchers have tried different kinds of contrast agent and imaging method, such as arrival time of contrast agent in the hepatic vein, and quantitative analysis of the enhancement level of liver parenchyma, to evaluate the degree of liver fibrosis during the past 10 years. This review mainly summarizes the clinical studies concerning the assessment of liver fibrosis using CEUS.

Microbubble ultrasound contrast agents: an update

Microbubble contrast agents for ultrasound (US) have gained increasing interest in recent years, and contrast-enhanced US (CEUS) is a rapidly evolving field with applications now extending far beyond the initial improvements achieved in Doppler US. This has been achieved as a result of the safe profile and the increased stability of microbubbles persisting in the bloodstream for several minutes, and also by the availability of specialized contrast-specific US techniques, which allow a definite improvement in the contrast resolution and suppression of signal from stationary tissues. CEUS with low transmit power allows real-time scanning with the possibility of prolonged organ insonation. Several reports have described the effectiveness of microbubble contrast agents in many clinical applications and particularly in the liver, spleen, and kidneys. CEUS allows the assessment of the macrovasculature and microvasculature in different parenchymas, the identification and characterization of hepatic and splenic lesions, the depiction of septal enhancement in cystic renal masses, and the quantification of organ perfusion by the quantitative analysis of the echo-signal intensity. Other fields of application include the assessment of abdominal organs after traumas and the assessment of vesico-ureteral reflux in children. Finally, tumor-targeted microbubbles make possible the depiction of specific biologic processes.

Blood flow changes in hepatocellular carcinoma after the administration of thalidomide assessed by reperfusion kinetics during microbubble infusion: preliminary results

OBJECTIVES

We sought to investigate whether thalidomide is able to produce tumor vascular changes in patients with untreatable hepatocellular carcinoma (HCC) that can be detected using microbubble contrast agents.

MATERIALS AND METHODS

Eleven consecutive patients with untreatable HCC underwent contrast-enhanced ultrasound before and during thalidomide administration. Real-time destruction reperfusion kinetics was obtained from a representative HCC nodule and from the surrounding liver parenchyma during SonoVue infusion (Bracco, Milan, Italy) at a constant rate of 0.10 mL/s by using a syringe pump and modelized according to the mathematical function SI = A(1 - exp(-betat)) where the plateau signal intensity A reflects the percent blood volume, the time constant beta reflects the average speed of blood, and their product A*beta reflects the nutrient blood flow.

RESULTS

Size of the representative nodule reduced significantly 3 to 6 months after the start of thalidomide treatment. Before thalidomide administration A, beta, and A*beta of the index lesion were 44 +/- 60 LIU, 0.31 +/- 0.40 seconds and 8.1 +/- 11.8 LIU/s, respectively). A and A*beta reduced significantly after 15 days (26 +/- 50 LIU and 2.9 +/- 4.8 LIU/s, P < 0.01), 3 months (12 +/- 18 LIU, and 4.3 +/- 7.7 LIU/s, P < 0.01), and 6 months (13 +/- 23 LIU and 2.4 +/- 3.7 LIU/s, P < 0.05) of treatment. No statistically significant changes of the exponential time constant beta were observed, nor changes of A, beta and A*beta in the liver parenchyma.

CONCLUSIONS

Contrast-enhanced ultrasound can be used effectively to evaluate changes in perfusion parameters of HCC nodules during thalidomide administration.