A better image

In-Depth

Philips is claiming a breakthrough in medical technology with a high resolution scan using magnetic particle imaging.

Magnetic Particle Imaging (MPI) is potentially a useful complementary technology to magnetic resonance imaging (MRI), but has been held back by the inferior quality of scans produced.

But now, a team at Philips Research said a successful test scan of a small object has suggested these problems can now be overcome. MPI could also have further applications in areas such as materials analysis and crack detection, Philips believes.

To test their idea, the team scanned a 9.4mm x 9.4mm plastic container filled with a contrast agent, demonstrating that a higher-resolution image can be produced by scanning the magnetic particles than is possible using an MRI scan.

For several decades scientists have been able to scan patients by injecting them with magnetic particles. But the technology has so far failed to take off because it provides an uneven image of the subject being scanned.

In the new Philips system, the magnetic particles are first subjected to a time-varying sinusoidal magnetic field. Due to this fact, they emit high-frequency harmonic signals that can be easily extracted by filtering. If the magnetic particles are simultaneously exposed to a time-constant magnetic field of sufficiently large magnitude, the particles become completely magnetized, or saturated, and the generation of harmonics is suppressed. 

A signal containing harmonics can then only be detected from magnetic particles located in the vicinity of what the researchers call the 'field-free point' - at all other points the magnetic particles are fully saturated by the time-constant field and produce no signal. And by scanning the field-free point through the volume of interest, it is possible to develop a 3D image of the magnetic-particle distribution.

When Gleich and his team tested the scan on a phantom, they used a robot to move the field-free point over the area being scanned. This took 45 minutes. But if MPI is to be used to scan patients, a different method of moving the field-free point will have to be developed, said Gleich.

In use, MPI could be used for clinical situations where MRI currently delivers poor-quality results. MRI, for example, is less effective when scanning images of moving body parts. It is thought that the system could even scan a single heartbeat.