Magnetic Particle Imaging: A New Imaging Modality
“MPI is the most promising emerging imaging technology in the last 20 years and is expected to change the landscape of modern medical imaging and in vivo translational research.”
– IWMPI 2014
Magnetic Particle Imaging (MPI) is a new imaging modality that directly detects iron oxide nanoparticle tracers using time-varying magnetic fields. Because the tracer is not normally found in the body, MPI images have exceptional contrast and high sensitivity.
Magnetic Particle Imaging uses a unique geometry of magnetics to create a field free region (FFR). This is something you may have experienced when pointing two magnets at each other. That sensitive point controls the direction of a nanoparticle.
Two strong magnets pointing at each other produce a magnetic field gradient with an FFR at the center. The FFR is then rapidly moved across the sample to produce an image.
Rapidly Moving the FFR causes a “flip” in the magnetic direction of an SPIO nanoparticle which induces a signal in a receive coil. Since we know where the sensitive point is at all times, we can assign the signal to the known position to produce a quantitative MPI image.
Learn more about MPI, the first imaging modality to combine high sensitivity, high resolution and positive contrast, by downloading our white paper.
The MPI technique is straightforward and can be described classically with three key concepts:
1. Magnetic Nanoparticles Align with an Applied Magnetic Field
Figure 1: Magnetic nanoparticles saturate with an applied magnetic field. (A, C) With a strong field, magnetic nanoparticles magnetically saturate and align. (B) With no applied field, magnetic nanoparticles randomly orient and produce no magnetization.
2. A Strong Magnetic Field Gradient Produces a Field Free Region (FFR)
Figure 2: Two strong magnets pointing at each other (shown here as loops of wire) produce a magnetic field gradient with an FFR at the center. The FFR is then rapidly moved across the sample to produce an image.