Although many exciting correlations have been obtained between various NMR spectroscopic components and tumor diagnosis and treatment, this has yet to become a robust clinical tool. In this application we introduce an array of novel, verified techniques which provide high-resolution images of the important spectroscopic components. These images will provide an excellent clinical tool because of their specificity to tumor activity and their ability to be correlated with conventional anatomic images of the same region. They can therefore be readily interpreted as compared to classical NMR spectra of a volume of tissue. The problems of spectroscopic imaging are legion. Sensitivity dominates the scene, since the desired components are many orders of magnitude below that of the water signal. In addition, inhomogeneity, caused by imperfect magnets and magnetic susceptibility variations in the body, can shift and broaden the components of interest. Thusfar the limited use of spectroscopic images have produced images with very coarse voxels, with questionable value, and very long imaging times. We propose a combination of novel proven techniques which will provide the desired spectroscopic images in a robust fashion. These techniques include: water-referencing to correct both the inter-voxel and intra-voxel frequency errors; estimation theory which, in combination with water-referencing, using a priori information to provide the optimum estimate of weak metabolites buried in noise; time-varying gradients which enable a versatile tradeoff between resolution and imaging time; and correlative filtering which provide high- resolution spectroscopic images by providing the correct amount of high spatial frequencies from the high SNR water image. In addition to these generalized techniques, we plan to apply a variety of novel specialized techniques including a multiple quanta excitation sequence which can separate the important lactate component from the large lipid signals, and a system of imaging components with short T2 relaxation times, such as those found in the phosphorous spectrum.
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