Blood flow made visible: A newly developed portable scanner shows the blood flow in veins or arteries – and can thus make blockages, thrombosis or aneurysms visible. The device is strapped around the arm or leg like a thick splint and uses magnetic fields to detect magnetized nanoparticles in the blood. As a result, the mobile scan requires neither X-rays nor radioactive contrast media and could contribute to the early detection, prevention and treatment of vascular occlusions or damage.
Whether through X-rays , magnetic resonance imaging or ultrasound: looking inside our body is indispensable for medicine. Because many illnesses or internal injuries can only be recognized and treated by such imaging procedures. This also applies to blood flow disorders, for example due to thrombosis, narrowing of the veins or aneurysms. Angiography helps to detect such changes in the blood vessels and to prevent fatal consequences such as heart attacks, strokes or internal bleeding.
So far, computer tomography (CT) or magnetic resonance imaging (MRI) have mostly been used for angiography, the images of which show the veins using a contrast agent. However, these devices are bulky, can only be used while lying down, and CT also exposes the body to ionizing X-rays.
Magnetic nanoparticles as contrast media
That is why researchers from the University and the University Hospital of Würzburg led by Patrick Vogel have now developed the first portable vascular scanner. “Our iMPI scanner is so small and light that you can take it almost anywhere,” explains Vogel. iMPI stands for Interventional Magnetic Particle Imaging and refers to an imaging process in which magnetic fields make the movement and density of magnetized nanoparticles visible. These particles are injected like a contrast medium before the measurement.
The imaging is based on the response signal of the magnetic nanoparticles to magnetic fields that change over time. “The magnetization of nanoparticles is specifically manipulated with the help of external magnetic fields, which means that not only their presence but also their spatial position in the human body can be detected,” explains Vogel. The procedure is similar to MRI, but only causes a reaction of the nanoparticles. As a result, it only depicts the blood vessels in a targeted manner, all other body tissues remain dark.
Light vessels on a dark background
“As with positron emission tomography, which relies on the administration of radioactive substances as markers, the iMPI method has the great advantage of being sensitive and fast, without ‘seeing’ interfering background signals from tissue or bone. “, explains co-author Volker Behr. This enables it to show the blood flow in vessels and any constrictions or bulges without other structures obscuring or disturbing the view.
In principle, MPI imaging is not new, but until now it has been too slow and clumsy to also show dynamic changes in the human body. In addition, the devices were similar in size and bulky to typical MRI scanners. The Würzburg team has now further developed the technology so that their MPI scanner can be strapped on like a thicker splint. It consists of three flat magnetic coils that generate alternating magnetic fields and sensors that can record the reaction of the nanoparticles at eight frames per second and in a relatively large field of view.
First test with vessel dummy successful
In a first test, the researchers tried out their iMPI scanner on a special doll with simulated blood vessels and artificial blood. With these, constrictions, aneurysms or thromboses can be created for exercise purposes. Catheter interventions can also be practiced and tested on this model. For the test, Vogel and his team strapped the scanner to the model’s thigh and injected the nanoparticles. They then observed how well the blood flow could be seen.
The result: The portable MPI scanner was able to visualize constrictions and aneurysms in the artificial veins based on the changes in blood flow. The device is also suitable for imaging monitoring of catheter interventions thanks to its high temporal resolution, as the scientists report. However, the spatial resolution of their prototype was not yet very high because they had initially optimized it for speed.
“This is an important first step towards a radiation-free intervention. MPI has the potential to change this area in the long term,” said senior author Stefan Herz. The team is now working on improving the image quality of their scanner even further. (Scientific Reports, 2023; d oi: 10.1038/s41598-023-37351-2 )