Routinely CEUS is an examination mostly done to asses liver focal lesions  as stated in the current EFSUMB guidelines , but there is a multitude array of non-hepatic uses that can benefit from this examination method.

• Introduction-Ultrasound contrast agents consist of small gas microbubbles the size of erythrocytes stabilized in a biocompatible membrane. Being purely intravascular, makes them perfect for imaging blood distribution and flow. Specific ultrasound modern software can differentiate static ultrasound echo signals from dynamic contrast agent signals in realtime, allowing selective imaging of the contrast agent. The signal intensity obtained lies in a linear relationship with the concentration of contrast agent in the region of interest (ROI), which allows a reliable assessment of relative blood pool . Ultrasound imaging using ultrasound specific contrast agents depicts a wash-in and wash-out after bolus injection, or more precisely using the flash-replenishment technique, allows assessment of regional blood flow velocity. Commercially available modern software packages can calculate time-related intensity curves and values from the contrast wash-in and wash-out phase for each image pixel from stored video clips after software postprocessing, according to the respective kinetic model used. Specific parameters can be derived, such as peak intensity, area under the curve, or mean transit time. Also, color-coded parametric maps on top of the anatomical (B-mode) image can be obtained, to rapidly identify hypovascular or hypervascular regions inside the ROI.
• Technique- In current clinical practice the selected ROI is examined after contrast medium injection through a peripheral vein (cubital). A ROI is selected and dynamically and continuously without moving the transducer from the interested area is examined through all the angioperfusional phases (arterial, venous and delayed phase). All the obtained images from the examination are stored on a storage medium in DICOM format.
• Kinetics- There are two major types of contrast medium kinetics used in practice: Bolus kinetics and flash-replenishment kinetics.

Bolus Kinetics

In the bolus kinetic method, the contrast agents are injected and a S-shaped wash-in of contrast medium is observed, followed by an exponential wash-out. The intensity of the microbubble signal at the peak of the curve or, rather, in the case of complex feeding vessel architecture, the area under the curve (AUC) is a parameter of relative blood volume in the examined parenchymal tissue. The mean transit time corresponds to the mean blood flow velocity in the region of interest and can be estimated by the time difference between the respective 50% peak intensity values in the wash-in part and wash-out part of the TIC , or by the time point dividing the AUC into two equal parts. The quotient of relative blood volume (AUC) and blood flow velocity (MTT) results in the perfusion index, which is a parameter of parenchymal perfusion (blood flow).

Fig 1: Calculated parameters after bolus kinetics . PI- Peak intensity, AUC-Area under...

Flash-replenishment kinectics

Flash-replenishment kinetics is a more accurate quantification of perfusion . After contrast injection and complete wash-in, the whole vascular bed in the ROI is filled with microbubbles due to continuous and steady injection of contrast agent with specialized automated syringes.  During the peak enhancement the initial low mechanic index is changed to a high value (“Flash”) resulting in the destruction of microbubbles in the image plane, after that the mechanic index is set back to normal resulting with new microbubbles feeding the ROI. By using the flash mode, microbubbles that previously accumulated within the ROI can be annihilated. This sudden loss of the microbubbles can be of advantageous, e.g. to evaluate the portal venous phase refilling dynamics of a liver lesion, which had previously already filled in completely during the early arterial phase.

Fig 2: Example of TIC after “flash” replenishment kinetics. Β-Wash in Slope ,...