New imaging procedure without radiation exposure
11/2/2023 Production of the future News

New imaging procedure without radiation exposure

A team of physicists and doctors from the University of Würzburg has developed a mobile scanner for endovascular interventions that does not require ionising radiation or nephrotoxic contrast media. The scanner is based on radiation-free imaging diagnostics called "Magnetic Particle Imaging" (MPI), which uses magnetic fields in combination with magnetic nanoparticle tracers for visualisation.

Doctors with X-ray
Common imaging methods such as fluroscopy and digital subtraction angiography provide information about movements in vessels. For patients and hospital staff, though, this involves increased exposure to radiation. In addition, contrast media containing iodine, which are administered for better visibility, can harm patients with limited kidney function. 

The new portable interventional MPI scanner (iMPI) uses magnetic fields to determine the spatial distribution of tracers made of magnetic nanoparticles. These are injected in advance as markers. After that, external magnetic fields manipulate the magnetisation of the nanoparticles, which makes it possible to detect their position in the human body.

MPI as a diagnostic imaging technique is not new

Previous MPI scanners were too large, expensive and had a small viewshed of a few centimetres. The first human-sized MPI scanner had limitations in terms of acquisition time, portability and gradient strength. The latter is essential for high spatial resolution, but also causes high power consumption and a rise in temperature.

Within the framework of a research project funded by the German Research Foundation, these barriers could be overcome. The developed iMPI scanner has a gradient strength of about 0.36 tesla per metre with a power consumption of 14 kilowatts, which allows a spatial resolution of about 5 millimetres. To get an idea of the temperature rise of the iMPI scanner, the physicists estimate a temperature rise per image of 0.18 Kelvin.
X-ray setup

Minimalistic design for fast 2D projection images

The iMPI scanner consists of two overlapping pairs of saddle coils in a "Helmholtz" arrangement. They generate a field-free line with a frequency of 60 Hertz and a phase shift of 90 degrees and move it along the symmetry axis of the scanner. An additional pair of magnets with a frequency of 2480 Hertz directs the field-free line along a sinusoidal trajectory through the desired field of view, which generates 2D projections in real time.

X-ray window enables hybrid application

The iMPI scanner works in an unshielded environment and has a special X-ray window, which enables parallel imaging with the gold standard X-ray technology. This could simplify its implementation in clinical applications for vascular interventions. However, the iMPI holds particular potential for endovascular interventions without ionising radiation, reducing radiation exposure for patients and hospital staff and reducing the use of potentially nephrotoxic contrast agents.
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