Professor Ton van der Steen is head of Biomedical Engineering at the Erasmus MC Thorax Centre. Together with Professor Paul Breedveld of TU Delft, he is developing innovative techniques to visualise atherosclerosis. “Twelve percent of atherosclerosic patients find themselves back in the catheterisation room within one year after intervention. We want to drastically reduce that percentage,” says Van der Steen.
Atherosclerosis is a condition in which cholesterol, calcium and connective tissue form plaques inside the arteries. As the deposit grows, the artery slowly clogs up and the blood flow becomes restricted. If this occurs in the blood vessels that supply the heart with oxygen-rich blood (the coronary arteries), the heart does not receive enough oxygen. These patients often suffer from chest pain. Sometimes plaques consist of fatty material covered by a thin film. If this film ruptures, the fat leaks into the blood, triggering the formation of a blood clot. “This clot may completely block an artery, which is the cause of most heart attacks and strokes,” explains Van der Steen.
Atherosclerosis is very common. “In the Netherlands, we treat around 57,000 people for atherosclerosis annually,” says Van der Steen. “This treatment usually consists of placing a stent, a kind of spring that widens and supports the artery. Unfortunately, approximately 12% of patients find themselves back on the treatment table within twelve months of having had this procedure. We want to drastically reduce that percentage. This is possible if the cardiologist can properly inspect the arteries during the procedure.”
The usual imaging technique to guide placing the stent is X-ray angiography. This allows the cardiologist to roughly locate the plaque, but it is not possible to identify the risky fatty plaques. “We started a collaboration with TU Delft to improve the procedure. My own research group is good at translating technologies into the clinic. But there are gaps in our knowledge. For instance, in the field of Fine Mechanics, Paul’s group is filling these gaps seamlessly; our collaboration is very pleasant,” says Van der Steen.
“My own research group is very good at translating technologies into the clinic. But there are gaps in our knowledge. TU Delft is filling these gaps seamlessly.”
Prof.dr.ir. Ton van der Steen
Ultrasound and laser light
The researchers are jointly developing dedicated imaging catheters. Van der Steen shows such a catheter. It is a long tube of one millimetre diameter, which can reach the coronary artery from a blood vessel in the wrist or groin. The last ten centimetres are composed of transparent plastic. He points to a tiny speck inside. "That’s the ultrasound element. It emits short sound pulses inside the blood vessel. We can distil an image from the sound waves that bounce back from the vessel wall. Just like echography in a pregnant woman, but made from inside the vessel.”
“We’re developing catheters with ultrasound, laser light, or both. With ultrasound, we can determine a plaque’s size and the extent to which it interferes with the blood flow. With the combination of laser light and ultrasound, we can determine the plaque’s composition and detect risky fatty plaques. The cardiologist can offer a tailored treatment based on this information. For instance, certain patients may benefit from drugs that convert the fats in the plaque into connective tissue.”
While the research team in Rotterdam is addressing the imaging functionalities of the catheters, their collaborators in Delft are focusing on catheter steerability. Breedveld explains: “It is important for the cardiologist to inspect the plaque from multiple angles, so the tip should be manoeuvrable. However, it’s quite difficult to steer the tip of a long flexible tube. The tube follows the anatomy of the patient’s blood vessels, so it may bend more than 180 degrees. In addition, the tube is ‘unwilling’, in the sense that it will easily flip in the wrong direction. I think we’ve come a long way in solving these problems with a smart cable system that allows the cardiologist to precisely steer the catheter tip. This technique can also be applied in other cardiologic interventions. For instance, our PhD candidate, Awaz Ali, is developing a catheter that can be steered towards specific locations inside a beating heart, which is useful for biopsies.”
The team in Rotterdam has also made good progress. Van der Steen: "Our engineer, Min Wu, has developed a catheter with both an ultrasound and a laser element. This combination catheter works in our laboratory setup, which consists of arteries of deceased people who donated their bodies to science. We will soon start testing the catheter in laboratory animals. Next, we hope that we can switch over to humans. I’m expecting that this technique will dramatically reduce the number of patients that need to return for a new treatment in the future.”
Interview by: Linda van den Berg