Recent developments in MRI hardware have led to smaller magnets and higher magnetic fields. There are also growing demands for more accessible (open MRI) and more patient friendly scanners that can be used in interventional MRI procedures. Despite these advances, significant fringe magnetic fields exist in smaller systems strongly requiring every component of the MRI system to be shielded from each other. The investigators propose a new """"""""supershielding"""""""" design to actively shield the magnetic field for gradient coils and main magnet coils. Our method is based on a set of """"""""supershielding conditions"""""""" of static magnetic fields leading to significant shielding improvements in coil systems. From the beginning of the design procedure, it is assumed that both coils (the primary coil, that mainly produces the desired field, and the shielding coil) have finite dimensions. It is shown that the magnetic field can be significantly suppressed everywhere outside the secondary coil, even though the shielding coil only partially surrounds the primary coil. The supershielding approach provides the required currents for the coils and the magnetic field behavior inside the imaging volume. It also minimizes the eddy currents induced in the surrounding environment as well as the energy of the system. We have demonstrated, with an example of a short axial gradient coil, that our design gives as much as sixteen times better shielding compared to that of the conventional design. Based on the supershielding method, the investigators propose developing the required software to design short shielded gradient coils and main magnets. Several relevant systems for imaging different body parts will be examined and the two solutions will be integrated to ensure practical utility of the method. This approach will allow for further reductions in system size and cost. It may also lead to new applications in local imaging of the body.
| Cheng, Y-C N; Eagan, T P; Chmielewski, T et al. (2003) A degeneracy study in the circulant and bordered-circulant approach to birdcage and planar coils. MAGMA 16:103-11 |
| Cheng, Yu-Chung N; Eagan, Timothy P; Brown, Robert W et al. (2003) Design of actively shielded main magnets: an improved functional method. MAGMA 16:57-67 |
| Cheng, Y-C N; Eagan, T P; Chmielewski, T et al. (2003) A degeneracy study in the circulant and bordered-circulant approach to birdcage and planar coils. MAGMA 16:103-11 |
| Brown, R W; Cheng, Y-C N; Eagan, T P et al. (2002) Toward shielding improvements in MRI gradients and other systems. MAGMA 13:186-92 |
