Scientists from Philips Research in Hamburg, Germany, are developing a new method for peering inside patients. Magnetic particle imaging, as the method is called, resembles magnetic resonance imaging in its use of magnetic fields to manipulate spins. But whereas MRI flips hydrogen nuclei, MPI flips the electronic spins of ferromagnetic particles.
The naturally occurring ferromagnetic particles in the human body, such as the iron atoms in hemoglobin, are too small to produce a detectable magnetization. Using an MPI-based medical scanner, if one were ever built, would entail introducing nanoscale tracers into the body through a syringe, catheter, or other device.
But the absence of a natural background means the injected tracers would provide the sole signal. Potentially, MPI offers exquisite sensitivity.
Whether MPI will lead to a practical scanner is unclear. So far, the method’s developers, Bernhard Gleich and Jürgen Weizenecker, have looked at modestly sized test objects. Even so,...
