The objective of this project is to improve the analytical and technological foundations of 4-dimensional NMR spectroscopic imaging using continuous oscillating gradients and demonstrate the feasibility of these methods for in vivo applications. The main challenge is to accomplish the necessary spatial encoding in a practical period of time. In addition, spectroscopic imaging of the heart requires strategies to freeze or compensate motion. This project will develop techniques for spectroscopic imaging using oscillating magnetic field gradients to provide rapid spatial encoding. Continuous oscillating gradients minimize induction of non-stationary eddy currents and can be produced efficiently using resonant circuits. Deterministic and stochastic RF excitations for use in oscillating gradient experiments will be developed. Strategies for motion compensated spectroscopic imaging will be based on characterizing the motion using spin tagging and incorporation of voxel trajectories into the reconstruction of the spectroscopic data. Improved hardware for production of oscillating gradients will be designed and constructed to allow experimental evaluation of these techniques for 1H, 23Na, 31P and 39K spectroscopy in phantoms and animal models. The experimental program is designed to determine the image resolution, signal-to-noise ratio and speed of spatial encoding attainable with oscillating gradients, and the feasibility of saturation transfer, water suppression, motion compensation and imaging of spins with very short T2 relaxation time with oscillating gradient techniques.
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