Recent advances in contrast material-enhanced ultrasonography (US) mainly include (a) development of low-acoustic-pressure (low-mechanical-index) harmonic software, capable of obtaining real-time images without disrupting contrast material microbubbles, and (b) commercialization of new contrast media ("second-generation" contrast media), capable of producing intense echo signals in this low-mechanical-index setting. With use of low-mechanical-index continuous-mode contrast-enhanced US, the circulatory kinetic models of various focal liver lesions can be displayed dynamically. Hepatic lesions usually have typical perfusion characteristics and enhancement patterns through the various phases of parenchymal enhancement, which helps characterize lesions and, in most cases, allows definitive diagnosis, even among lesions that exhibit very similar baseline appearances. Because of the use of harmonic technologies at low emission frequencies, there is some loss of spatial resolution and overall image quality, typically resulting in a grainy appearance. In addition, lesion depth affects the detectability of vascularity to some degree in that poor signal arises from deep-seated lesions. Moreover, liver attenuation (eg, in patients with steatosis or chronic liver disease) further reduces the sensitivity of contrast-enhanced US. Nevertheless, with its unique capacity to provide images in real time, low-mechanical-index contrast-enhanced US is the dynamic imaging modality of choice in the differential diagnosis of focal liver lesions.

OBJECTIVE. Low mechanical index contrast-specific sonography is a new technique that uses the harmonic capabilities of second-generation contrast agents to produce real-time contrast-enhanced gray-scale images. We describe the contrast-specific sonographic findings of pyogenic hepatic abscesses.CONCLUSION. Contrast-specific sonography was used to assess eight cases of aspiration-confirmed pyogenic liver abscesses. All cases were correlated with multiphasic helical CT findings. Continuous sonographic exploration allowed recognition of morphologic details not detectable on CT images. Contrast-specific sonograms showed features including rim enhancement, arteries along abscess margins and internal septa, dense and persistent septal enhancement, absent microcirculation in fluid and necrotic components, transient arterial phase hypervascularity around abscesses, and portal phase hypovascularity around abscesses. This constellation of findings is suggestive of liver abscess.