Contrast-enhanced dynamic ultrasonography of the liver: optimization of hepatic arterial phase in normal volunteers

Obstruction at middle hepatic venous tributaries in modified right lobe grafts after living-donor liver Transplantation: diagnosis with contrast-enhanced US

PURPOSE

To investigate the ability of contrast material-enhanced ultrasonography (US) to help diagnose obstruction of middle hepatic venous (MHV) tributaries soon after living-donor liver transplantation with modified right lobe grafts.

MATERIALS AND METHODS

The institutional review board approved the study and waived requirement for informed consent. Sixty-five consecutive patients (48 men, 17 women; mean age, 52.8 years; range, 33-69 years) who underwent living-donor liver transplantation with modified right lobe grafts between February and May 2009 were included. All patients underwent contrast-enhanced US and Doppler US on postoperative day 1 and underwent computed tomography (CT) within 7 days after US. At contrast-enhanced US, parenchymal enhancement patterns in the territory of each MHV tributary during arterial and portal venous phases were evaluated. With use of most frequent enhancement patterns in patients with obstruction at MHV tributaries as a criterion, diagnostic performance of contrast-enhanced US was compared with that of Doppler US for diagnosis of obstruction at MHV tributaries; CT was the reference standard. Generalized estimating equations were used to adjust for data clustering.

RESULTS

Of 148 MHV tributaries in 65 patients, 36 (24.3%) in 31 patients were diagnosed as obstructed at CT. With arterial high echogenicity or portal low echogenicity used as a criterion for hepatic venous obstruction, contrast-enhanced US had sensitivity, specificity, and accuracy of 91% (33 of 36), 97% (109 of 112), and 95% (142 of 148), respectively, whereas Doppler US had values of 83% (30 of 36), 86% (97 of 112), and 85% (127 of 148), respectively. Contrast-enhanced US was significantly more specific and accurate than Doppler US for diagnosis of obstruction at MHV tributaries (P=.024 and .01, respectively). Arterial high echogenicity was noted only in the hepatic venous obstruction group.

CONCLUSION

Contrast-enhanced US can help accurately assess hepatic venous obstruction at MHV tributaries after living-donor liver transplantation with a modified right lobe graft. Contrast-enhanced US was significantly more specific than Doppler US, with arterial hyperenhancement in the affected area being specific to hepatic venous obstruction.

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.