Christoph Juchem PhD, (Dr. rer. nat. Dipl. Phys.)
Assistant Professor of Diagnostic Radiology and of Neurology
Functional MR imaging and spectroscopy methods are commonly applied to study cognitive function in the human and animal brain. Strong and localized magnetic field homogeneities in brain areas such as the human prefrontal cortex, however, limit the achievable data quality and the validity of the results. These magnetic field distortions are caused by air-tissue interfaces and scale with the scanner B0 field strength. The continuous trend towards ultra-high field MR for improved sensitivity and spectral dispersion therefore further enhances the problem. Conventional, low order spherical harmonic correction fields are able to compensate ('shim') for the large-scale, shallow field variations, but they are not able to deal with such strong and localized field foci.
My current research focuses on the development of advanced magnetic field modeling techniques for shimming the human/animal brain as a whole or slices thereof. Optimal magnetic field homogeneity is essential for meaningful functional MR imaging and spectroscopy and will open up a large range of fundamental neuroscience applications.
Together with my co-workers, I was able to show that generic, individual coils can be used to establish a powerful field modeling system. The combination of simple, unspecific (i.e. not spherical harmonic shaped) basis fields allows the flexible synthesis of complex and high amplitude shim fields in the human and animal brain that are much better suited for the task at hand than the shallow low-order spherical harmonics used so far. In fact, the multi-coil approach permits the simultaneous generation of linear MRI encoding fields and complex shim fields by the same setup and allows the integration of conventional imaging and shim coils into a single multi-coil system.