**2.1 Characteristics of ultrasound diagnosis**

Ultrasound diagnosis of liver tumors involves two stages: detection and characterization.

*Tumor detection* is based on the performance of the method as already presented and should include morphometric information (three axes dimensions, volume) and topographic information (number, location specifying liver segment and lobe/lobes). The specification of these data is important for staging liver tumors and prognosis.

Tumor characterization is a complex process based on a sum of criteria leading towards tumor nature definition. Often, other diagnostic procedures, especially interventional ones are no longer necessary. Ultrasound examination has the same morphological and hemodynamic criteria as those of CT and MRI imaging procedures. However, semiology will be adjusted to the specifics of this method. Tumor characterization using the ultrasound method will be based on the following elements: consistency (solid, liquid, mixed), echogenity, structure appearance (homogeneous or heterogeneous), delineation from adjacent liver parenchyma (capsular, imprecise), elasticity, posterior acoustic enhancement effect, the relation with neighboring organs or structures (displacement, invasion), vasculature (presence, Doppler and CEUS characteristics). The substrate on which the tumor condition develops (if the liver is normal or if there is evidence of diffuse liver disease) and the developing context (oncology, septic) are also added. Particular attention should be paid to the analysis of the circulatory bed. Microcirculation investigation allows for discrimination between benign and malignant tumors. Characteristic elements of malignant circulation are vascular density, presence of vessels with irregular paths and size, some of them intercommunicating, some others blocked in the end with "glove finger" appearance, the presence of arterio-arterial and arterio-venous shunts, lack or incompetence of arterial precapillary sphincter made up of smooth musculatures (Weidener et al, 1991).

Diagnosis and characterization of liver tumors require a distinct approach for each group of conditions, using the available procedures discussed above for each of them. The correlation with the medical history, the patient's clinical and functional (biochemical and hematological) status are important elements that should also be considered.
