**4.1 Techniques for evaluating the efficiency of therapy**

The efficiency of 2D ultrasound is low in assessing the effects of HCC or metastasis therapy, as it is unable to differentiate viable tumor tissue from post-therapy tumor necrosis. However, it is able to detect the appearance of new lesions and to assess the occurrence of any complications of disease progression (ascites or portal vein thrombosis). Color Doppler ultrasound can be useful sometimes being able to show the presence of intratumoral vasculature as a sign of incomplete therapy or intratumoral recurrence. The absence of Doppler signal does not exclude the presence of viable tumor tissue. CEUS exploration, by its ability to enhance intra-lesion microcirculation, has proved its utility in monitoring therapeutic efficacy. Its indications are defined for HCC ablative treatments (pre, intra and post-therapy), while monitoring of systemic therapies of HCC and metastases are not validated indications at this time, but with proved efficacy in extensive clinical trials (Claudon et al, 2008). CEUS examination cannot completely replace the other imaging diagnostic methods currently in use because of the known limitations of the ultrasound method (operator/ equipment dependent, ultrasound examination limitations). In addition to bloating, in cancer patients post-therapy steatosis occurs, which prevent deep visibility. Spiral CT scan remains the method of choice in monitoring cancer therapies because it provides an overview of tumor extension and it is not limited by bloating or steatosis (Bartolozzi et al, 1999).

Gadolinium MRI examination is a procedure used more and more often, and its advantages are the absence of irradiation and its high sensitivity in tumor vasculature detection, especially in smaller tumors (Dromain et al, 2002). However it remains an expensive and not a very accessible procedure, although it has a high specificity. Currently, CEUS and MRI are considered complementary methods to CT scan.
