[Current state of the use of sonographic contrast agents with low acoustic pressure techniques in the study of focal...

Ultrasonography is the most commonly used screening modality for focal liver lesions in Europe. Over the past few years, to overcome the inherent limitations of B-mode imaging and colour-Doppler ultrasound in identifying and characterising focal liver lesions, intravenous agents capable of enhancing the ultrasound signal emitted by vascular and parenchymal structures have been developed. From December 1999 to December 2001, about 400 patients with a known tumour, HCV-related chronic cirrhotic liver disease, or with an indeterminate focal liver lesion discovered incidentally were evaluated by ultrasound of the liver parenchyma both in baseline conditions and after administration of contrast material. The ultrasound contrast agents used were: SonoVue (Bracco, Milan-Italy) and Optison (Mallinckrodt, London - UK). Our experience is based on low mechanical-index contrast-enhanced imaging, which acts conservatively, performed with different commercially available algorithms, in grey-scale mode alone (B-mode). We report the morphological patterns displayed by the main benign and malignant liver lesions after the administration of second-generation ultrasound contrast material, and review the main imaging patterns able to provide effective and practical guidance in formulating a diagnosis of benignity or malignancy. Our clinical experience confirmed the literature findings that the introduction of low mechanical index methods in grey-scale imaging has allowed qualitatively better results for detecting and characterising focal liver lesions than those obtained with baseline and colour-Doppler imaging. The ease of use, substantial repeatability and predictability of the enhancement effects obtainable with low mechanical index methods are the main reasons for the success of this approach. Broadening the scope of studies to obtain controlled data and comparisons with the other imaging modalities is crucial for the definitive validation of the method.