Micrometer scale resolution of materials by stray-field Magnetic Resonance Imaging.

As Magnetic Resonance Imaging devices are becoming more and more powerful, resolutions as small as 10 μm can now be obtained. But, this is only possible when systems with slow transverse relaxation rates, like living tissues, are investigated. In this case, the time available for gradients space-encoding is long, and high k values can be reached in the Fourier domain. However, numerous materials have fast relaxation rates, thus limiting the spatial resolution to a few hundreds of microns. The Stray Field Imaging technique has solved this problem by using a very high (typically 5000 G/cm) static gradient. Consequently, the trajectory in k space is accelerated and it is possible, in principle, to reach a micrometer resolution in a few hundreds of microseconds. Most of the time, however, only resolutions in the millimeter range can be achieved due to mispositioning of the sample within the static magnetic field. Here, we show that by finely mapping the magnetic field and precisely positioning the sample, it is possible with a standard spectrometer to reach a micrometer resolution even on very fast relaxing materials.