A SURE way of imaging the microvasculature Ultrasound is an enormously valuable medical imaging tool, yet it is not currently able to image the smallest blood vessels in the body. We spoke to Dr Charlotte Mehlin Sørensen, Professor Jørgen Arendt Jensen, Professor Erik Vilain Thomsen and Professor Michael Bachmann Nielsen about their work in developing a new imaging approach designed to give clinicians insights into the microvasculature. An ultrasound scanner is an enormously valuable tool in modern medicine, enabling doctors to image soft tissue and rapidly diagnose patients, and the technique is widely used across the world. However, currently ultrasound is relatively limited in terms of the resolution of the imaging system. “The resolution is on the order of half a millimetre, or maybe a little less. However, the smallest blood vessels in the body are actually on the micron level, down to around 10-20 microns, so we can’t currently see the microvasculature,” explains Jørgen Arendt Jensen, Professor of Biomedical Signal Processing at the Technical University of Denmark (DTU). This is an issue Professor Jensen is working to address as part of his work in an ERCbacked initiative. “We’re trying to develop a new imaging system called SURE that can show the microvasculature,” he explains. This has previously been done by injecting small, gas-filled bubbles as contrast agents into the blood, then following them through the body. This allows medical professionals to see the smallest vessels in the body, yet it takes a long time, which is not practical
for patients. “When you are measuring very small things people have to stay extremely still, which is very difficult for sustained periods,” points out Professor Jensen. The SURE system takes just a couple of seconds however, while still providing highly detailed images of the microvasculature. “Our approach allows us to see vessels down to a size of maybe 25 micrometres,” outlines Professor Jensen. “Then we can
cells – erythrocytes – are used as a target. “There are a huge amount of erythrocytes in the blood stream, around 5 million cells within just a cubic millimetre, so there are lots of targets,” says Professor Jensen. Erythrocytes can’t be seen directly from a normal ultrasound image however, as Professor Jensen says the signal is very weak. “The signal from the blood is often 100 times weaker than from the tissue. So it’s vital for
“Our approach allows us to see vessels down to a size of maybe 25 micrometres. Then we can start observing these small vessels. How much blood do they carry, how fast does it flow?” start observing these small vessels. How much blood do they carry, how fast does it flow? We can put on a normal ultrasound transducer, acquire data, and within seconds we can see these kinds of images.”
SURE imaging The project team are working to both develop and improve the SURE approach, and also test it with a view to its future application. In the SURE approach red blood
us to make a really good ultrasound image, with no movement,” he explains. “We do what is called motion compensation, so that it’s a completely fixed image. Then we take all the tissue signals and remove them, we essentially subtract out the tissue, which leaves the blood signal.” This approach involves isolating the blood signal, locating the blood vessel, then locating it over time. This procedure takes just a couple of seconds to provide
SURE image of the blood vessels in a healthy rat kidney. In the left lower corner an artery/vein pair is seen as a small and a large vessel running alongside each other from the center of the kidney towards the left side. Stretching towards the kidney surface are cortical radial arteries with a size of ~100 µm. The image is recorded over 1.9 sec without the use of contrast agents using erythrocytes as the tracking target.
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