**4. The examination technique**

Prior to the examination, a peripheral vein (preferably the antecubital vein) is catheterized with a 20–22 Gauge needle. The examination methodology goes through the following steps: gray scale (for ROI detection), Doppler technique (for circulatory specificity assessment), and contrast media assessment (for ROI characterization).

The patient's position is adapted for examination of the organ of interest. For retroperitoneal organs, it is recommended that the patient adopts a shallow breath to facilitate the maintenance of the area of interest in the ultrasound examination plan.

After activating the contrast mode, the following settings of the ultrasound equipment must be done: the "Focus" position below the region of interest, the mechanical index at 0.09–0.11, and reduce "Gain" function.

The injection of the contrast agent (at an average dose of 2.4 ml) is followed by 10 ml of saline solution is bolus. At the time of injection, the ultrasound timer and record videos are started. The region of interest is dynamically tracked for up to 5 min postinjection. Theoretically, a second injection can be made immediately, although this is rarely necessary in clinical practice [7].

The quality of the CEUS image is limited, as in the case of the B mode ultrasound, by the localization of the region of interest, the presence of the intestinal gas or bone margins, and the patient weight [7].

For kidney CEUS examination, the literature proposed various contrast phase terminologies. One is similar to the terminology used by multiphase contrast-enhanced computer tomography (CE-CT) and magnetic resonance imaging (MRI) [8]. This terminology uses three phases: corticomedullary (enhancing cortex with medullary pyramids not yet perfused, approximately 15–30 s after contrast agent injection), nephrographic (homogenously enhancing renal parenchyma, approximately 30–70 s postinjection), and delayed (>70 s postinjection) [8]. Other groups used the following terminology: arterial phase <30 s postinjection and delayed phase 30–90 s postinjection [9]. Other authors proposed other terminologies: cortical (8–35 s after injection), corticomedullary (36–120 s), and delayed (>120 s) [10].
