Multiple studies in MR provide irrefutable evidence that the use of high order shims for controlling magnetic field inhomogeneity brings significant improvement to image quality, particularly at high fields and in challenging shimming regions, such as in the inferior frontal and temporal lobes of the human head. MRI manufacturers however, have been very resistant to the idea of improving the performance of shims in high field scanners even though it has been demonstrated that the performance of the conventional 2nd order shims available in all 3T and 7T systems is unsatisfactory. The cost and complexity of the upgrade to higher order shim capability, the necessary improvement in shimming software and the applications development create serious barriers for rectifying this situation and in bringing about an improvement. The only commercial 7T scanner with 3rd order shims is manufactured by Philips but in many applications it lacks some software capabilities for rendering the shims useful. The goal of this proposal is to develop a high order (3rd, 4th and 5th) shim insert for head MR that overcomes the cost and complexity of integrating those shims into the magnet bore, and renders a highly practical arrangement for efficient shimming of the human head. An unequivocal demonstration of significant improvements in performance using 3rd order shims has been documented in the preliminary results leading to this proposal. We are now leading the development of the practical implementation of the 4th order shims. The novel aspect of our development will be the construction of a high order resistive shim coil set which has strength and performance sufficient to null the 4th order spherical harmonic field components present in challenging regions of the brain and which can also be retrofitted inside an existing gradient coil. In particular, neurological applications require extended shimming performance. For such a purpose, by using a highly optimized head RF coil, enough space can be saved in a whole body scanner to mount an insert capable of delivering the 3rd and 4th order shims at high strength, while not compromising the accessibility for other applications. Demonstrating the safety and efficacy of the proposed in-bore shim coil set will make possible the commercial use of this technology in the form of an upgrade that can be applied to a large number of commercial scanners that presently lack this capability.
Magnetic resonance imaging (MRI) and spectroscopy (MRS) are the leading techniques for obtaining high-quality images and metabolic profiles of intact healthy and diseased human tissues. Unfortunately, tissue susceptibility induced spatial variations of magnetic field can severely degrade the quality of MRI and MRS data, to the extent that distinction between normal and diseased areas may be compromised. The current project focuses on developing and implementing novel technology that can be used in new scanners or retrofitted to existing scanners thereby leading to greatly increased quality of MR data with consequent benefit to public health.
| Pan, J W; Duckrow, R B; Spencer, D D et al. (2013) Selective homonuclear polarization transfer for spectroscopic imaging of GABA at 7T. Magn Reson Med 69:310-6 |
| Pan, Jullie W; Lo, Kai-Ming; Hetherington, Hoby P (2012) Role of very high order and degree B0 shimming for spectroscopic imaging of the human brain at 7 tesla. Magn Reson Med 68:1007-17 |
