3D visualization of the cerebral vasculature by two-photon microscopy

Blood is a complex liquid medium responsible for transporting oxygen and nutrients to the body's various cells, as well as for eliminating the waste products generated by cell metabolism. In vertebrates, blood is made up of red blood cells, white blood cells and thrombocytes or platelets suspended in plasma. Plasma also contains proteins such as albumin, glucose and hormones.

The vascular system can malfunction, leading to transient or permanent ischemia; myocardial infarction and stroke, for example, often result in the necrosis of cells that have lost their oxygen supply. The vascular system can also undergo profound reorganization around and within cancerous tumors, with the creation of a dense, branched vascular network, a process known as "neoangiogenesis".

The brain is an organ with an extremely dense and complex vascular network. Techniques for visualizing the vascular system, and the cerebral vasculature in particular, are therefore essential tools in the biomedical sciences, used for both human diagnosis and fundamental animal research.

The techniques currently used to visualize blood vessels in humans are computed tomography angiography (angioCT) and magnetic resonance imaging (MRI). While these techniques are non-invasive, they do not offer microscopic resolution.

For applications requiring such high resolutions, two-photon fluorescence optical microscopy is a key tool. In this article, we will review the advantages and limitations of this technique, define its field of application, and present in detail the device used for image acquisition and the type of contrast agents used.