Synchrotron-based angiography for investigation of the regulation of vasomotor function in the microcirculation in vivo.

1. Real-time imaging of the vascular networks of any organ system in vivo is possible with synchrotron radiation (SR) angiography. In this review, we discuss the advantages of SR angiography over clinical X-ray imaging and other non-ionizing imaging modalities. Current limitations are also described. 2. The usefulness of dual-energy and temporal subtraction approaches to K-edge iodine imaging are compared. 3. High-resolution images of the microcirculation in small animals are now being collected routinely by multiple research groups through public access research programmes at synchrotrons worldwide. Such images are permitting unrivalled insights into vasomotor regulation deep within intact organ systems, such as the brain, kidney, lung and heart. For example, recent observations indicate changes in vascular control mechanisms in pulmonary hypertension that are specific to certain branching segments of the pulmonary circulation. 4. New possibilities for non-iodinated contrast agents in SR angiography are briefly described. 5. High-resolution angiography in vivo using SR will now allow us to identify vessels with localized or non-uniform vasoconstriction in states such as diabetes or to characterize the extent of endothelial dysfunction in the circulation following hypertension or ischaemic-reperfusion injury. In the near future, this research is expected to reveal the contribution of resistance vessel dysfunction to diverse pathophysiological states, such as stroke, hypertension and ischaemic heart disease.