Micro-probe visualises brain arteries from the inside

Researchers in China have developed an extremely small optical probe that can produce detailed images of blood vessels in the brain from the inside. The technology utilises optical coherence tomography (OCT) and can produce full 360-degree images. In time, the probe could provide doctors with greater insight into vascular diseases and the position of implants such as stents.

The probe has a diameter of just 0.55 millimetres and is four millimetres long. Researchers from Nanjing University and Nanjing University of Aeronautics and Astronautics describe the technology in *Biomedical Optics Express*. The application is still at the research stage and requires further development and testing before clinical use is possible.

OCT in small cerebral arteries

OCT is an imaging technique that uses light to produce detailed cross-sections of tissue. This makes it possible, amongst other things, to visualise the structure of vessel walls and changes such as plaque formation. However, existing intravascular OCT systems have primarily been developed for coronary arteries. These are generally larger and less tortuous than blood vessels in the brain.

In conventional systems, the optical probe is rotated by a motor outside the body. In the narrow and sharply curved cerebral vessels, friction and twisting of the long catheter can prevent the probe from rotating evenly. This can lead to distortions in the images.

The researchers therefore opted for a different approach. Instead of rotating the entire catheter, only a small lens at the tip rotates. An optical fibre transmits near-infrared light to this lens. The rotation is driven by a piezoelectric material that changes shape when an electrical voltage is applied. As it rotates, the lens directs the OCT light along the entire inner wall of the blood vessel. This produces a 360-degree cross-section. By then moving the probe through the blood vessel, multiple cross-sections can be combined to form a three-dimensional image.

Stents and vascular tissue in focus

During tests, the probe was found to be able to navigate through a life-size anatomical model of the human cerebral blood vessels and reach the middle cerebral artery. This is one of the brain’s most important arteries. The researchers first tested how uniformly the probe rotates. To do this, four metal tubes were imaged at known angles. The average angular deviation was approximately one degree, even after the catheter had been guided through the tortuous vascular model. Furthermore, the lens was able to reach a speed of up to 58 revolutions per second.

The technology was then used to produce two- and three-dimensional OCT images of increasingly complex structures. For example, the researchers imaged the fine network of nerves in a magnolia leaf, as well as a vascular stent in a model of the middle cerebral artery and a pig’s blood vessel examined outside the body.

Human vascular tissue containing atherosclerotic plaque was also examined. The OCT images revealed features associated with fatty areas and fibrous tissue. These observations corresponded with the findings from conventional histological examination.

Support for cerebral interventions

According to the researchers, intravascular OCT could eventually complement current imaging techniques used in neurovascular procedures. Doctors currently have limited options for viewing microscopic details directly from small, tortuous cerebral arteries.

One potential application is checking the position of a stent relative to the vessel wall. More detailed information on this could assist doctors in making treatment decisions and potentially contribute to more personalised interventions. However, further steps are required before the technology can be used on patients. The researchers aim to make the probe even smaller whilst simultaneously improving the optical resolution and depth of field. The stability and speed of the rotating lens also need to be further optimised.

In addition, further studies are needed to assess the image quality, reliability and safety under conditions that mimic actual neurointerventional procedures as closely as possible. Only then will it become clear what role the miniature probe can ultimately play in clinical practice.

Innovative imaging

Earlier this year, Chinese researchers developed a high-speed 3D imaging technology capable of mapping biological structures throughout the entire body of small animals at subcellular resolution. The technique could significantly improve research into the peripheral nervous system (PNS), which connects the brain with organs and regulates functions including breathing, heart rate, pain and temperature sensing.

Building on their earlier VISoR technology for rapid 3D brain imaging, the researchers developed a new strategy combining in situ cutting with 3D blockface imaging. This overcomes challenges caused by the size, irregular structure and different tissue types found throughout the body.

Using the new blockface VISoR system, the team imaged an entire adult mouse in approximately 40 hours at subcellular resolution. Each fluorescence channel generated around 70 terabytes of data. The technology could support research into PNS connectivity, neural regulation, developmental biology, comparative anatomy and other areas of biomedical research.