This proposal seeks to upgrade our existing animal MR imaging and spectroscopy system. Our current system consists of a l.9 Tesla 33 cm bore magnet and a 4.7 Tesla 40 cm bore magnet both interfaced to a single General Electric Sigma 4.x computer and console. The gradient strength and switching speed of our current configuration is more than adequate for all our present and anticipated needs. The major deficiencies of the present system are the inability to scan large animals (such as dogs and minipigs), and the outdated software of the 4.x system. Therefore, we are requesting a GE Sigma 4.x to 5.x upgrade, as well as a larger RF amplifier. The 5.x upgrade will enable the NIH funded users of the animal MR scanner (whose number is approximately twelve at the time of this application) to utilize the latest state of the art pulse sequences, some of which have been developed on the whole-body clinical research 5.x systems in our department. Examples include pulse sequences for measuring blood perfusion in the brain, for quantitative measurement of diffusion coefficients without motion artifacts, and pulse sequences for performing in vivo microscopic imaging with optimized signal-to-noise ratio. The addition of the more powerful RF amplifier will enable us to build a large animal body coil for MR imaging and spectroscopy. The need for hardware and software improvements to bring this instrument to the leading edge of MR technology was the impetus for the submission of this proposal.