This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In the search for more signal, MR is using stronger and stronger magnets working at ever increasing frequencies. At these high frequencies conventional radiofrequency coils are no longer efficient and the engineering changes from conventional wire arrays to cavities. Since these coils are not commercially available, there is a need to develop and evaluate new coil designs. In accordance with Specific Aim #4 of Core 1, the design, construction and bench evaluation of volume coil designs has continued. We are continuing to investigate the severe B1 inhomogeneities reported in last year s Core 1 review. After additional modeling, a paper on the inhomogeneities has finally been accepted these models showing similar inhomogeneities have been made the Highlight of Core 1 (see below). Expanding on these studies, we have imaged phantoms of varying size and electrical characteristics to observe size dependency of the inhomogeneities, investigated current distributions in large coils and phantoms through simulation, and are investigating a solution to the B1 inhomogeneity problem in large samples through the use of multiple coils driven in a time dependent manner. Using simulations and experiment, we have shown that the inhomogeneous B1field generated is due to wave behavior in the phantom and not a severe disturbance of the current distribution in the coil. We have begun exploring ways to mitigate these image inhomogeneities. In one method, loading materials placed around the sample significantly reduce the interfering waves. Although helpful this method has limited practical application. Alternatively, we have investigated making space and time dependent images to generate a homogeneous B1 field. As a proof of concept, a CRC (counter rotating current) coil was rotated radially around a large cylindrical phantom to acquire independent images. Simulations confirm this effect. While it is understood that there are significant developments that need to occur to make this approach practical, we feel we have shown that the concept is sound.
Showing the most recent 10 out of 76 publications
