Instrumentation in micro Magnetic Resonance Imaging for Tissue Biopsies

The demand on hospital MRI is towards high resolution with possible lower magnetic field. The method for micro imaging on tiny sample in sub-millimeter level has been researched in the RF scope for this publication. A middle-high gradient set of planar coils was design to image dandelion slice in size of 1.5 mm. A group of Radio Frequency electronics modules was utilized and characterized. Considering the isolation is not good according to current transceiver probe & amplification scheme, further an active RF switch would be add. And the current gradient coils integrated on the insertion of probe have the ability to carry 0.01 mm resolution experiment without cooling.

General MRI can have a resolution of 0.1 mm without too much difficulty. But in some cases, a more fine precision was required, say 0.01 mm with localized volume 200microm*200microm*200microm, for a single germ or nerve cell[1,2]. One of the most challenges is the ultra high magnetic field gradient necessarily. Compared to routine MRI, the amplitude increases roughly order of 100.
On the other hand, to obtain a sufficiently high signal-to-noise-ratio (SNR) within a reasonable measurement time becomes a critical issue[3]. The low SNR is mainly due to the signal amplitude decreasing with the third power of the resolution, assuming an isotropic voxel size. This can partly be compensated for by means of optimised RF coils[4-11] and high magnetic field strength[7]. And, considering the molecules walking randomly in space with normal the mean diffusion lengths, which comparable to microMRI's voxel, there must be some high speed nonconventional consequences involved.
In this paper, the following is a principle of planar pairs of 3D gradient coils for microMRI described first. Based on a commercial set of C-shape permanent magnet, scanning spectrometer and gradient amplifier (United Imaging Healthcare, Beijing, China), a Radio Frequency front-end was constructed. Electrical Performances were characterized totally in according to signal processes towards MRI. Based on preliminary results, potential improvements for phantom micro-imaging were guided. The hardware setup of 0.3 T microMRI was concluded finally with simulation prospects.

In this publication, a hardware set of Radio Frequency for micro Magnetic Resonance Imaging was studied. Some factors which influence or were required special to high resolution research have been outlined. For 10 microm level of microscope, the gradient has to be several hundreds of kilo-herz/mm, for a Field of volume with 2 mm in dimension. Based on current spectrometer, gradient amplifier and C-shape permanent magnet (all supplied by United-Imaging, Beijing China), a dandelion stem slice is engaged to be imaging by micro Nuclear Magnetic Resonance.