What is Magnetic Particle Imaging (MPI) ?

Basics and educational pieces to learn about a fascinating new imaging technology

Magnetic Particle Imaging is a new quantitative functional imaging technology that uses the magnetic properties of iron-oxide nanoparticles injected into the bloodstream. This technology has the potential to generate real-time 3D images of arterial blood flow and volumetric heart motion.

Magnetic particle imaging (MPI) is a new imaging modality developed by B. Gleich and J. Weizenecker at Philips research, Hamburg. As was shown in the first publication in Nature [1], MPI is capable of imaging the distribution of superparamagnetic iron oxide particles (SPIOs) with high sensitivity, high spatial resolution and high imaging speed. In the following, an introduction into the basic principle of MPI is given.

Signal Encoding

The principle of MPI is based on the nonlinearity of the particles' magnetization curve. When exposed to an oscillating magnetic field (drive field), the spectrum of the responding magnetization contains not only the base frequency f but also higher harmonics that are exploited for imaging. This basic principle of signal encoding is illustrated in the figure below.

Basic principle of MPI.

Spatial Encoding

Spatial encoding is achieved by superposition of a static non-uniform selection field providing a single field-free point (FFP) and high field strength in its vicinity. The FFP is steered through the object of interest by means of the aforementioned drive field. In this way, data for reconstructing the particle distribution can be acquired with a recording coil. Here, it is exploited that only particles in the direct neighborhood of the FFP contribute to the signal, whereas afar particles stay in saturation.

Particle response to an oscillating magnetic field with high offset.


[1] B. Gleich, J. Weizenecker: Tomographic imaging using the nonlinear response of magnetic particles, Nature, 2005, 435, p. 1214-1217
[2] J. Weizenecker, B. Gleich, J. Rahmer, H. Dahnke, J. Borgert: Three-dimensional real-time in vivo magnetic particle imaging, Physics in Medicine and Biology, 2009, 54, p.L1-L10

Courtesy: University of Lübeck - Institute of Medical Engineering


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