Contrast-enhanced ultrasound (CEUS) has come a long way from the early pioneering days of ‘Doppler rescue’, interpreting the increased signal from vascular structures within potentially malignant tumours in the liver and the breast, and the improvement in the enhancement of large vessels. Early agents have fallen by the wayside, with newer agents allowing for lengthier imaging, using techniques that preserve the integrity of the microbubbles, and with improvement in separation of the acoustics of normal tissue and the microbubbles. The safety of microbubble contrast agents in the liver is undoubted, with adverse reactions seen less commonly than contrast agents used in other imaging modalities, further allowing for the safe progression into imaging other body structures. The true intra-vascular nature of the microbubble contrast is unique, potentially giving much better information in perfusion studies. The early indications for the use of CEUS, bound by the licensing constraints, were in the breast, liver, heart and peripheral vasculature. The legality of using the agents outside the licensing constraints is established and accepted, which has allowed clinicians to move into many other areas of the body, utilising the undoubted improvements microbubble contrast brings to the ultrasound (US) examination. CEUS is continuously being added to clinical practice in many areas by imaging pioneers, allowing the establishment of CEUS in many new areas. The addition of CEUS to the kidneys, pancreas, testis, aorta, spleen and salivary glands US examination improves the interpretation of findings, potentially reducing downstream imaging costs and alleviating patient anxiety. The singe area where non-licensed use of CEUS has been the most beneficial is in the assessment of the kidney. From the confirmation of normality, assessment of the simple and complex cyst to the establishment of intra-lesion vascularity in malignancy, CEUS has been unsurpassed for useful additional information to alter management. The kidney is likely to become the organ where CEUS is most frequently used, perhaps second to the liver in radiological practice. The use of percutaneous techniques to treat aneurysmal dilatation of the aorta, stent grafts in endovascular aortic repair (EVAR) results in life-long surveillance of complications, traditionally provided by computed tomography (CT). The use of CEUS has the potential to reduce the number of surveillance CT performed, with the additional benefit of alleviating the need for nephrotoxic contrast agents. Microbubble contrast agents are unique in two aspects: they are truly intravascular agents and any microbubbles in the aneurysmal sac indicate an endoleak, and they are not nephrotoxic, with no necessity to monitor renal function. The application in venous disease would also open opportunities for more accurate imaging. The usefulness of microbubble contrast agents in small parts is less clear; the interaction of the microbubbles with the transducer frequency is complex with the higher frequencies used in small parts imaging necessitating higher concentrations of microbubbles at the optimal size. Often, the use of CEUS in small parts is a component of the entire gamut of US: B-mode, colour and spectral Doppler, tissue elastography and CEUS, termed multiparametric US. This special issue contains articles that illustrate all the aspects of CEUS described above, allowing the establishment of the usefulness of this technique in clinical practice, increasing the knowledge pool that will eventually allow this technique to be fully accepted as an ideal and robust imaging tool. Most importantly, CEUS adds another layer of safety to the already safe US examination. This is surely also the tool for imaging in paediatrics – this may be just over the horizon.
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