Alexander Pines and a team of scientists at Berkeley Lab have invented a single-sided magnet assembly for NMR and MRI that can be easily rotated with a gear mechanism to safely adjust the size and location of its sensitive volume, i.e., the volume subject to imaging. The device, an assembly of inexpensive, cylindrical, permanent magnets mounted on a frame, is extremely portable, weighing approximately 4 kg and measuring 23 cm x 16 cm x 6 cm. A simple computer program determines how the magnets should be rotated to adjust the sensitive volume as desired and to compensate for the imperfections that are typically present in all permanent magnets. The sensitive volume is homogeneous, i.e., it has a small gradient (little change in field strength). Therefore, the device can be used to analyze materials with significant diffusion, such as liquids.
In lab tests, the field strength and homogeneity, which limit signal-to-noise ratios in existing adjustable magnets, were sufficient within the sensitive volume to provide accurate images of lettershaped containers of water and to distinguish between fat and muscle in a sample of animal tissue. Furthermore, the homogeneous region's low gradients allowed imaging of these mostly liquid samples where diffusion attenuation would have limited the performance of other portable single-sided MR sensors. (Field test results: 500-700 Gauss and less than 8 Gauss/cm gradient.)
Portable, one-sided magnets are used in MRI and NMR to analyze objects that cannot be moved or contained in a multi-sided magnet. Currently, however, the one-sided magnets allow for only minor adjustments to the location of a low-gradient sensitive volume. Moving this volume to image or analyze regions at different depths within a subject or object had required building a new magnet assembly, which can be time-consuming, expensive, and hazardous.
More info: http://www.lbl.gov/Tech-Transfer/techs/lbnl2470.html
