Assessment of microcirculation by contrast-enhanced ultrasound: a new approach in vascular medicine

Contrast-enhanced ultrasound (CEUS) has emerged as a valuable imaging modality that complements and enhances standard vascular ultrasound imaging. Ultrasound contrast agents are gas-filled microbubbles that are injected intravenously and serve as intravascular tracers. Based on the properties to enhance and to quantify the macro- and microcirculation down to the capillary perfusion level in different vascular territories and organs, CEUS imaging has the potential to improve the diagnostic performance in the detection and characterisation of various vascular disorders reviewed in this article. In carotid atherosclerotic disease, CEUS imaging provides additional information on plaque vulnerability by illustrating the presence and extent of intraplaque neovascularisation. This new imaging modality may be helpful for further risk stratification of arteriosclerotic lesions and for detecting patients at risk for vascular events, eventually leading to more specific individually tailored therapeutic recommendations. CEUS imaging is also a helpful tool for the diagnosis and for monitoring of inflammatory vascular diseases. It increases the diagnostic performance of ultrasound in detecting inflammatory changes of the vessel wall such as hypervascularisation and hyperaemia. Changes in vessel wall enhancement may also reflect the response to anti-inflammatory therapy. Moreover, CEUS imaging is also a valuable tool for the assessment of the microcirculation and the tissue perfusion in solid organs including native and transplanted kidneys. The technique provides more accurate information on perfusion deficits of the parenchyma in patients with kidney infarction, necrosis or graft dysfunction. CEUS also has great potential in the assessment of the microcirculation of the skeletal muscle, particularly in patients with peripheral artery disease or diabetic microangiopathy. In the future, the use of targeted on site microbubbles could further enhance and expand the diagnostic capabilities of current vascular ultrasound by assessing specific molecular processes that play a role in the pathophysiology of vascular diseases. Furthermore, ultrasound-directed, site-specific drug and gene delivery using microbubble contrast agents could gain great clinical value in the future. The combination of CEUS for diagnosis and therapy will provide unique opportunities for vascular clinicians to image the microcirculation and directly treat vascular diseases.