Classical B-mode ultrasound can only demonstrate anatomical information.

(Color-)Doppler ultrasound can demonstrate blood flow, but is dependent from a minimum flow velocity (above tissue movements) and a defined flow direction. Therefore, Doppler ultrasound can not demonstrate blood flow in the microcirculation and no different enhancement phases (depending from the arrival time of a tracer) can be discriminated. Initially it was thought that Color-Doppler imaging can allow characterisation of focal liver lesions, but once contrast-enhanced CT and MRI imaging came up ultrasound was not any longer competitive.

With the introduction of ultrasound contrast agents (Microbubbles) the assessment of microvascular blood flow as well as enhancement phases in focal lesions became possible, allowing characterisation of focal lesions with ultrasound with comparable accuracy as CT and MRI imaging.