Spatially Selective Nmr with Broad-band Radiofrequency Pulses

The problem of non-invasive spatial localization in NMR is approached by constructing a spatially selective composite pulse sequence and incorporating it into a recently developed difference scheme. The composite sequence described, which requires nine phase-shifted n pulses, functions only over a narrow range of radio-frequency (rf) field strengths while remaining effective over a broad range of resonance frequencies. Relying upon the field gradient of a surface coil to label regions in space by local rf amplitudes, the pulse inverts all nuclear spins at a selected distance from the coil across a broad range of chemical shifts. This approach will allow the observation of chemically shifted NMR signals from specific regions of a material or organism. Computer simulations are presented, and the method is demonstrated experimentally on a phantom sample using a surface coil.