The following settings are applied in all cases of contrast agent investigations: Contrast program preset with low mechanical index (MI) of < 0.13 (acoustic output 4 %), depth 4 - 5 cm, one focus zone adapted to the depth of the investigated vein area, dynamic range 72, pulse repetition interval 1.25, B (brightness-)-mode amplification 30. The ultrasound pulses will not be triggered. An optimized manual technique is applied to minimize movement artefacts. After 10 seconds of B-mode assessment, a bolus of 5 ml SonoVueTM solution will be injected into a peripheral foot or calf vein using a butterfly needle (20 gauge). The SonoVueTM - injection is followed immediately by 10 ml saline bolus to flush the injection line. The investigations will be documented by digital saving of the cineloops in avi- and dicom format. Image analysis is performed offline, using the time intensity curve (TIC) analysis program provided by GE Healthcare Technologies, implemented into the LOGIQ 9 ultrasound system. Using the ultrasound raw data, the image displays the acoustic intensity measured in decibel (dB) during acquisition time in the manually defined region of interest (ROI) i.e. the vessel wall and the intraluminal thrombus in cross section. The signal intensities are measured at baseline and peak (in decibel) in the centre and in the peripheral part of the vein. The differences are calculated. Measurements are done 3 times, mean values are used for further calculation.