Magnetic particle imaging

Magnetic particle imaging (MPI) is an emerging non-invasive tomographic technique that directly detects superparamagnetic nanoparticle tracers. The technology has potential applications in diagnostic imaging and material science. Currently, it is used in medical research to measure the 3-D location and concentration of nanoparticles. Imaging does not use ionizing radiation and can produce a signal at any depth within the body. MPI was first conceived in 2001 by scientists working at the Royal Philips Research lab in Hamburg. The first system was established and reported in 2005. Since then, the technology has been advanced by academic researchers at several universities around the world. The first commercial MPI scanners have recently become available from Magnetic Insight and Bruker Biospin. Magnetic particle imaging (MPI) is an emerging non-invasive tomographic technique that directly detects superparamagnetic nanoparticle tracers. The technology has potential applications in diagnostic imaging and material science. Currently, it is used in medical research to measure the 3-D location and concentration of nanoparticles. Imaging does not use ionizing radiation and can produce a signal at any depth within the body. MPI was first conceived in 2001 by scientists working at the Royal Philips Research lab in Hamburg. The first system was established and reported in 2005. Since then, the technology has been advanced by academic researchers at several universities around the world. The first commercial MPI scanners have recently become available from Magnetic Insight and Bruker Biospin. The hardware used for MPI is very different from MRI. MPI systems use changing magnetic fields to generate a signal from superparamagnetic iron oxide (SPIO) nanoparticles. These fields are specifically designed to produce a single magnetic field free region. A signal is only generated in this region. An image is generated by moving this region across a sample. Since there is no natural SPIO in tissue, a signal is only detected from the administered tracer. This provides images without background. MPI is often used in combination with anatomical imaging techniques (such as CT or MRI) providing information on the location of the tracer. Magnetic particle imaging combines high tracer sensitivity with submillimeter resolution. Imaging is performed in a range of milliseconds to seconds. The iron oxide tracer used with MPI are cleared naturally by the body through the mononuclear phagocyte system. The iron oxide nanoparticles are broken down in the liver, where the iron is stored and used to produce hemoglobin. SPIOs have previously been used in humans for iron supplementation and liver imaging. The first in vivo MPI results provided images of a beating mouse heart in 2009. With further research, this could eventually be used for real-time cardiac imaging. MPI has numerous applications to the field of oncology research. Accumulation of a tracer within solid tumors can occur through the enhanced permeability and retention effect. This has been successfully used to detect tumor sites within rats. The high sensitivity of the technique means it may also be possible to image micro-metastasis through the development of nanoparticles targeted to cancer cells. MPI is being investigated as a clinical alternative screening technique to nuclear medicine in order to reduce radiation exposure in at-risk populations. By tagging therapeutic cells with iron oxide nanoparticles, MPI allows them to tracked throughout the body. This has applications in regenerative medicine and cancer immunotherapy. Imaging can be used to improve the success of stem cell therapy by following the movement of these cells in the body. The tracer is stable while tagged to a cell and remains detectable past 87 days. The SPIO tracer used in magnetic particle imaging is detectable within biological fluids, such as the blood. This fluid is very responsive to even weak magnetic fields, and all of the magnetic moments will line up in the direction of an induced magnetic field. These particles can be used because the human body does not contain anything which will create magnetic interference in imaging.