Focal liver lesion: nonlinear contrast-enhanced ultrasound imaging


Conventional US, being readily available, economical and safe, remains the imaging modality most widespread throughout the world in detecting hepatic focal lesions. In detection with CEUS, the number of confirmed metastases increase from 3.06 to 5.42 in base-line comparison. After contrast medium administration the sensitivity for detecting individual liver metastases improves dramatically from 63% to 91%. Furthermore, the capability to detect very small metastases (> 10 mm) passes with CEUS from 54% to 92% (Albrecht et al., 2001). Comparing conventional US and CEUS in a multicenter series of 123, sensitivity in the detection of single metastasis improved from 71% to 87 %, while the specificity increased from 60% to 88% following contrast injection (Albrecht et al., 2003).
Moreover, contrast-enhanced intra-operative US (CEIOUS) also seems to improve these results in a recent report. In a series of twenty-four patients CEIOUS found lesions missed at preoperative imaging and at intra-operative US in four patients and confirmed all of the new findings of intra-operative US in four patients. In addition CEIOUS helped to define the tumor margins of the main lesion in 29% of patients with rectal colon liver metastases ( Torzilli et al., 2005). This intra-operative approach is suitable for the synchronous metastases of rectal-colon or other abdominal tumors. Contrast sectional imaging (US, CT and RM) conserve a central role for pre-treatment diagnosis of other kinds of secondary tumor. Surgeons’ and physicians’ interest in CEUS is rapidly increasing.
Earlier, we have described the guidelines for primary tumor management produced by the European Association for the Study of Liver Disease (EASLD) (Bruix et al., 2001). The American Association for the Study of Liver Disease (AASLD) has recently published “Practice Guidelines for the management of HCCs”. The use of only one contrast enhanced imaging modality including CEUS to demonstrate hyper-vascularization and diagnose a HCC was suggested for a lesion larger than 20 mm (Bruix and Sherman, 2005).
The characterization of the focal liver lesion  n by evaluation of hemodynamic contrast enhancement behavior is confirmed by an important number of studies, using both first or second-generation contrast media (Leen et al., 2002; Migaleddu et al., 2004; Wen et al., 2004; Quaia et al., 2004; Catalano et al., 2005).
Whereas some authors have emphasized the importance of observing enhancement at a late time, in our experience it is also important to observe arterial and early portal enhancement. Other experiences seem to confirm this (Nicolau et al., 2006). In particular, detection through good details resolution of peri- and intra-lesional macro- and micro-vessels contributes to the diagnosis of focal liver lesions, above all in the cirrhotic liver and therefore in differential diagnosis between Regenerative macro-nodules, Dysplastic nodules in the transformation phase and well-differentiated HCC; as well, early rim enhancement can suggest diagnosis of high flow hemangioma. The study of the only late phase is more useful in the diagnosis of metastases.
In order to obtain excellent details resolution, especially in the arterial phase, it is useful to read together fundamental echoes from tissue as well as nonlinear fundamental echoes from the contrast agent; the CPS (the most recent technological approach) permits this also with second-generation contrast media in real-time. The possibility of aiming at the lesion, and in particular seeing both extra- and intra-lesional vascular contribution in the arterial phase, considerably assists early phase characterization of HCC. Using second-generation of contrast media, nonlinear fundamental (CPS) and “conventional” harmonic imaging findings proves to be equivalent in the study of the late phase useful for metastases diagnosis. This is true except for the lesions positioned in the distal field because there is poor intensity of the contrast harmonic echoes in comparison  with  contrast  nonlinear fundamental ones (Migaleddu et al., 2005 ). Excellent details resolution especially in the arterial phase is also  valuable in outcome assessment of ablative therapy.