Today, the liver is regarded with high importance by our clinical colleagues. The obesity epidemic, with its considerable impact in North America, is associated with severe metabolic disturbances including nonalcoholic fatty liver disease (NAFLD). Further, liver cancer is the only solid organ cancer with an increasing incidence in North America. Where do we as ultrasonographers fit into the imaging scheme to most appropriately deal with these new challenges?
The liver is the largest organ in the body, and certainly the most easily accessed on an abdominal ultrasound (US). It has been the focus of countless publications since the introduction of abdominal ultrasound many decades ago. Exquisite resolution allows for excellent detailed liver evaluation allowing US to play an active role in the study of both focal and diffuse liver disease. Focal liver masses are often incidentally detected on US examinations performed for other reasons and on scans performed on symptomatic patients. Abdominal pain, elevated liver function tests and nonspecific systemic symptoms may all be associated with liver disease. The introduction of color Doppler to abdominal US scanners many years ago elevated the role of US by allowing for improved capability of US to participate in assessment of the hemodynamic function of the liver as well.
The well-recognized value of abdominal US, including detailed morphologic liver assessment, has made this examination the most frequent study performed in diagnostic imaging departments worldwide. However, in recent years, US has been relegated to an inferior status relative to CT and MR scan, as their use of intravenous contrast agents has made them the corner stone modalities for virtually all imaging related to the presence of focal liver masses. As we now live in an era of noninvasive diagnosis of focal liver disease, greyscale US has fallen out of favor, as it is nonspecific for liver mass diagnosis. While US is the recommended modality for surveillance scans in those at risk for development of hepatocellular carcinoma, today, all identified nodules are then investigated further with contrast-enhanced CT and/or MR scan.
In the more recent past, US has been augmented by 2 incredible noninvasive biomarkers: elastography, which measures tissue stiffness, and contrast-enhanced ultrasound, which shows perfusion to the microvascular level for the first time possible with US. These noninvasive additions are invaluable and their adoption in routine US practices may allow the reemergence of US as a major player in the field of liver imaging.
Most conventional US machines today are equipped with the capability to perform elastography, especially with point shear wave techniques (pSWE). In pSWE, an ARFI pulse is used to generate shear waves in the liver in a small (approximately 1 cm3) ROI. B mode imaging is used to monitor the displacement of liver tissue due to the shear waves. From the displacements monitored over time at different locations from the ARFI pulse, the shear wave speed is calculated in meters per second, with higher velocities associating with increased tissue stiffness. The accuracy for the determination of liver fibrosis and cirrhosis with pSWE as compared with gold standard liver biopsy, is now undisputable. Because of the great significance of liver fibrosis secondary to fatty liver and the obesity epidemic, the development of this technique as a routinely available study is essential. Because of the frequent selection of US as the first test chosen for any patient suspect to have undiagnosed diffuse liver disease, the opportunity for elastography to be included with the diagnostic morphologic US test should be developed as a routine.
Contrast-enhanced US (CEUS), similarly, is available on most currently available mid- and high-range US systems, allowing for nondestructive low MI techniques to image tumor and liver vascularity following the injection of microbubble contrast agents for US. This allows for a similar algorithmic approach to contrast-enhanced CT and MR scan for noninvasive diagnosis of focal liver masses. CEUS additionally offers unique imaging benefits that include no requirement for ionizing radiation and also imaging without risk of nephrotixity, invaluable in the many patients who present for imaging with high creatinine, preventing injection of both CT and MR contrast agents.
Incorporation of pSWE and CEUS into standard liver US in patients with suspect diffuse or focal liver disease is a cost-effective and highly appropriate consideration as this is readily available, performed without ionizing radiation, and at a considerable cost saving over all other choices.
Can you diagnose a hepatocellular carcinoma or other liver tumor with CEUS? And, can you determine if a liver is cirrhotic or not? With the addition of pSWE and CEUS to your liver US capability, yes, you can.
What is your experience with treating liver disease? What aspect is most difficult for you? What other area do you think would benefit from the addition of CEUS? Comment below or let us know on Twitter: @AIUM_Ultrasound.
Stephanie R Wilson is a Clinical Professor at the University of Calgary.