Portable Low-Cost MRI System Based on Permanent Magnets/Magnet Arrays

Portable low-cost magnetic resonance imaging (MRI) systems have the potential to enable “point-of-care” and timely MRI diagnosis, and to make this imaging modality available to routine scans and to people in underdeveloped countries and areas. With simplicity, no maintenance, no power consumption, and low cost, permanent magnets/magnet arrays/magnet assemblies are attractive to be used as a source of static magnetic field to realize the portability and to lower the cost for an MRI scanner. However, when taking the canonical Fourier imaging approach and using linear gradient fields, homogeneous fields are required in a scanner, resulting in the facts that either a bulky magnet/magnet array is needed, or the imaging volume is too small to image an organ if the magnet/magnet array is scaled down to a portable size. Recently, with the progress on image reconstruction based on non-linear gradient field, static field patterns without spatial linearity can be used as spatial encoding magnetic fields (SEMs) to encode MRI signals for imaging. As a result, the requirements for the homogeneity of the static field can be relaxed, which allows permanent magnets/magnet arrays with reduced sizes, reduced weight to image a bigger volume covering organs such as a head. It offers opportunities of constructing a truly portable low-cost MRI scanner. For this exciting potential application, permanent magnets/magnet arrays have attracted increased attention recently. A magnet/magnet array is strongly associated with the imaging volume of an MRI scanner, image reconstruction methods, and RF excitation and RF coils, etc. through field patterns and field homogeneity. This paper offers a review of permanent magnets and magnet arrays of different kinds, especially those that can be used for spatial encoding towards the development of a portable and low-cost MRI system. It is aimed to familiarize the readers with relevant knowledge, literature, and the latest updates of the development on permanent magnets and magnet arrays for MRI. Perspectives on and challenges of using a permanent magnet/magnet array to supply a patterned static magnetic field, which does not have spatial linearity nor high field homogeneity, for image reconstruction in a portable setup are discussed.

The Expression of Ephrin A2 during the Reinnervation and the Regeneration of the Hair Cells in the Chick Cochlea following Kanamycin Ototoxicity / 听力学及言语疾病杂志

Objective To investigate the role of Ephrin A2 in the regeneration and reinnervation of hair cells in the chick cochlea following kanamycin ototoxicity.Methods 66 newly hatched Roman chickens (3 days old) were randomly divided into experimental group and control groups. Experimental chickens (n=48) received intramuscular kanamycin (200 mg/kg:Sigma,St Louis,MO) for 10 consecutive days and were subsequently sacrificed 2 days before the last injection,and 1,3,7,10,15,21,30,and 60 days after the last injection (n=6 per subgroup). Control chickens (n=18) were untreated and sacrificed 3,13 and 43 days after hatching (n=6 per subgroup). Ephrin A2 protein expression in acoustic ganglia was determined by western blot analysis in all chickens after sacrifice. Results Ephrin A2 protein expression was found and the protein level was almost same in acoustical ganglia of all normal chickens. After kanamycin exposure,the Ephrin A2 protein expression level in the cochlea of the experiment chickens from 2 to 7 days after last kanamycin injection was lower than that in control chickens,respectively. Ephrin A2 expression increased obviously at 15 days after kanamycin last injection. By 30 days after the cessation of kanamycin treatment,the level of Ephrin A2 protein approximated to that in normal control group.Conclusion The expression of Ephrin A2 protein in the acoustical ganglia basically synchronizes with the regeneration and the reinnervation of the hair cells in the chicken cochlea following kanamycin damage,indicating that Ephrin A2 may play an important role in this process.