Second-generation intravenous blood-pool ultrasound contrast agents are increasingly
used in endoscopic ultrasound (EUS) for characterization of microvascularization,
differential diagnosis of benign and malignant focal lesions, and improving staging
and guidance of therapeutic procedures. Although initially used as Doppler signal
enhancers, second-generation microbubble contrast agents are now used with specific
contrast harmonic imaging techniques, which benefit from the highly nonlinear behavior
of the microbubbles.
Contrast-specific modes based on multi-pulse technology are used to perform contrast-enhanced
harmonic EUS based on a very low mechanical index (0.08 – 0.12). Quantification techniques
based on dynamic contrast-enhanced ultrasound have been recommended for perfusion
imaging and monitoring of anti-angiogenic treatment, mainly based on time–intensity
curve analysis. Most of the clinical applications include the differential diagnosis
of focal pancreatic masses, with adenocarcinoma having a distinct hypovascular (hypo-enhanced)
appearance compared with neuroendocrine tumors, which are hypervascular (with strong
arterial hyper-enhancement). However, pseudotumoral chronic pancreatitis and autoimmune
pancreatitis also have an iso- or hypervascular appearance, making the differential
diagnosis difficult. Even more promising is the use of dynamic contrast-enhanced harmonic
EUS for the longitudinal monitoring of the effects of chemotherapy and/or anti-angiogenic
therapy in advanced digestive cancers, which are difficult to examine by conventional
cross-sectional imaging techniques.
