Contrast-enhanced harmonic endoscopic ultrasound imaging: Basic principles, present situation and future perspectives

Abstract

Over the last decade, the development of stabilised microbubble contrast agents and improvements in available ultrasonic equipment, such as harmonic imaging, have enabled us to display microbubble enhancements on a greyscale with optimal contrast and spatial resolution. Recent technological advances made contrast harmonic technology available for endoscopic ultrasound (EUS) for the first time in 2008. Thus, the evaluation of microcirculation is now feasible with EUS, prompting the evolution of contrast-enhanced EUS from vascular imaging to images of the perfused tissue. Although the relevant experience is still preliminary, several reports have highlighted contrast-enhanced harmonic EUS (CH-EUS) as a promising noninvasive method to visualise and characterise lesions and to differentiate benign from malignant focal lesions. Even if histology remains the gold standard, the combination of CH-EUS and EUS fine needle aspiration (EUS-FNA) can not only render EUS more accurate but may also assist physicians in making decisions when EUS-FNA is inconclusive, increasing the yield of EUS-FNA by guiding the puncture with simultaneous imaging of the vascularity. The development of CH-EUS has also opened up exciting possibilities in other research areas, including monitoring responses to anticancer chemotherapy or to ethanol-induced pancreatic tissue ablation, anticancer therapies based on ultrasound-triggered drug and gene delivery, and therapeutic adjuvants by contrast ultrasound-induced apoptosis. Contrast harmonic imaging is gaining popularity because of its efficacy, simplicity and non-invasive nature, and many expectations are currently resting on this technique. If its potential is confirmed in the near future, contrast harmonic imaging will become a standard practice in EUS.

Theranostic Multilayer Capsules for Ultrasound Imaging and Guided Drug Delivery

“…54 While B-mode imaging is a popular method of general sonography, harmonic mode provides better resolution for objects that exhibit a nonlinear response to US, including almost all US contrast agents. 55,56 …”

Romanian National Guidelines on Contrast Enhanced Ultrasound in clinical practice

“…Contrast harmonic imaging EUS (CHI-EUS) uses a low mechanical index (MI) mode, in order to better characterise focal pancreatic masses, improve staging for pancreatico-biliary and GI tract cancers, and possibly guide therapeutic EUS interventions, including EUS-fine needle aspiration (EUS-FNA) [165,166].…”

Role of ultrasound in colorectal diseases

“…Color power (flow) Doppler US is useful for estimating the presence, the density or absence of vascular signals in the large blood vessels, but it is not sensitive enough to detect slow and low-volume flow of smaller vessels of the gastrointestinal organs[6,13]. The flow of big intraabdominal veins and arteries (aorta, coeliac trunk, superior and inferior mesenteric artery, portal vain, etc .…”