MODULATED GRADIENT COIL DRIVER FOR CW ESR IMAGING

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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. Construction of the complete Modulated Gradient Coil Driver (MGCD) for c.w.-ESR microimaging continues, as described in our most recent (2003) progress report. Fabrication, test and implementation of a prototype MGCD output section electronic assembly has been completed, and this subsystem has been integrated into our 3-D c.w. ESR imaging microscope/spectrometer which has achieved resolution to date of 10¿m x 10¿m x 30¿m (described in a recently-accepted Rev. Sci. Inst. article). The primary incentive for continuing development of the MGCD has been the readily evident need for real-time waveform generation hardware which is capable of providing rapidly-updated, complex modulation of imaging resonator gradient magnetic fields. Our MGCD hardware-based waveform generator, in its final version, will take the place of the existing software-generated waveform subsystem. By incorporating pre-defined coil excitation functions and a capability of preloading and rapidly updating individual coil drive levels, the deadtime between discrete voxel acquisitions will be reduced by an order of magnitude or more relative to our present interpretive computer-driven excitation system. Computer overhead will also be reduced by an order of magnitude or better, since the CPU will no longer be required to calculate and update the gradient coil currents in real-time. An important secondary feature of the MGCD system module is that it includes common-mode offsetting of B0 as necessary to augment spectrometer AFC action. Anticipating possible future investigation of stochastic CW imaging techniques, we have also designed into the MGCD sufficient processing and driver bandwidth to permit gradient field modulation by fast pseudo-random sequences. Presently, in Phase II, we have completed construction of the main signal processing circuit board, which will be debugged and soon installed in the c.w.-ESR microscope with a companion wire-wrapped version of the function generator/controller electronics subsystems as we proceed with the 3-D c.w. microimaging project.