New Technology Images Flowing Blood in Real Time

Understanding the dynamics of blood flow, or hemodynamics, provides critical information about various vascular diseases. Insights into factors like blood flow velocity and oxygenation are key indicators in the early detection and monitoring of conditions such as atherosclerosis, aneurysms, thrombosis, and more. While some existing clinical imaging methods can detect these hemodynamic properties, they often require the use of contrast agents or exposure to ionizing radiation, posing potential health risks. Despite their importance, routine clinical measurement of these hemodynamic properties has been limited due to technological constraints. Now, a breakthrough may be on the horizon following a new development.

A team of researchers at the California Institute of Technology (Caltech, Pasadena, CA, USA) and the University of Southern California (Los Angeles, CA, USA) has developed a low-cost, non-invasive 3D imaging method called Photoacoustic Computed Tomography through an Ergodic Relay (PACTER). This method has been shown to effectively image flowing blood in real-time in both animal and human studies. The team’s focus was on exploring alternatives based on the photoacoustic effect, a phenomenon that describes the transmission of sound waves following the absorption of light. This effect is utilized in photoacoustic imaging to visualize internal body tissues: biomolecules absorb laser pulse light and re-emit energy as ultrasonic waves, which are then used to create images.

Image: The PACTER photoacoustic imaging produces 3D images of flowing blood (Photo courtesy of Yide Zhang)

In this study, photoacoustic imaging was used to detect signals from hemoglobin in red blood cells, enabling real-time visualization of blood flow. While photoacoustic technology typically requires multiple expensive ultrasound sensors, the team’s previous system used just one sensor to create 2D images. To advance to 3D imaging while maintaining a cost-effective, single-sensor design, the researchers pre-calibrated their PACTER system with narrow laser beams aimed at 6,400 distinct points in a bovine blood sample. This intensive calibration allowed the system to later differentiate 6,400 signals from a single, wider laser beam during imaging, enabling rapid imaging while capturing extensive data.

The effectiveness of PACTER was demonstrated in experiments with mice, where the system mapped abdominal vasculature in 3D and detected breathing rates through periodic vessel size changes. The system was also applied to human subjects, visualizing vessels in hands and feet, common assessment areas for peripheral vascular disease and diabetes. The team could calculate blood flow speeds and observe expected changes in blood velocity and vessel shape when altering hemodynamics with blood pressure cuffs. Going forward, the researchers aim to enhance PACTER’s sensitivity and develop a more portable version. Some other potential applications of PACTER include measuring blood oxygenation in neck arteries and veins and monitoring brain metabolism.

“This technology takes several innovative concepts and packages them into one compact unit. I could see this type of tool potentially finding broad applications, including continuous monitoring in hospitals and at home,” said Randy King, Ph.D. from the National Institute of Biomedical Imaging and Bioengineering.

Related Links:
Caltech
University of Southern California