This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Although the effectiveness of the magnetic field gradients employed in ESR microimaging is closely related to the imaging sequence employed, it is nonetheless important to achieve as intense and geometrically intense gradients as possible. For microimaging work at 16GHz, we have already demonstrated phase gradients with peak values of ~26T/m, which corresponds to ~3 ?m resolution. At 35GHz the imaging probe and its constituent components will be even smaller and the gradient coils will obtain peak values of more than 40T/m, required for 1 ?m resolution. Although the gradient efficiency increases as the probe and coil size decreases, the problem of maintaining geometric accuracy will be proportionally magnified. It is also evident that, in the topic of gradient coils development at both 16GHz and 35GHz, further optimization of the gradient efficiency may enable even higher resolution. Our approach to gradient coil design will be a combination of simulation and empirical testing. For these reasons, we have initiated a program to enable high resolution mapping of individual coils and assembled gradient coil sets which have been designed for the microimaging probes. Our current investigation is the viability of subminiature Hall devices for micron-resolution field mapping. We have obtained suitable ~1mm Hall sensors of adequate sensitivity and are in the process of designing a translation platform suitable for field mapping of the test coils. This mapping assembly is expected to be assembled in an initial form and usable during fall 2008.
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