In-plane motion correction for MR spectroscopic imaging.

A motion-detection method is described that is specifically suited for MR spectroscopic imaging (MRSI) studies. Information on in-plane rotation and translation of the subject was obtained using external spatial reference markers that are uniquely identified via their chemical shift. The marker locations were obtained directly from the acquired data at each encoding step, and no additional data acquisition was required. This method was applied to brain 1H MRSI studies that include subcutaneous lipid signals, which otherwise result in enhanced sensitivity to subject motion.

Multiple-echo proton spectroscopic imaging using time domain parametric spectral analysis.

A multiple-echo MR spectroscopic imaging (MRSI) method is presented that enables improved metabolite imaging in the presence of local field inhomogeneities and measurement of transverse relaxation parameters. Short echo spacing is used to maximize signal energy from inhomogeneously line-broadened resonances, and time domain parametric spectral analysis of the entire echo train is used to obtain sufficient spectral resolution from the shortened sampling periods. Optimal sequence parameters for 1H MRSI are determined by computer simulation, and performance is compared with conventional single-echo acquisition using phantom studies at a field strength of 4.7 T. A preliminary example for use at 1.5 T is also presented using phantom and human brain MRSI studies. This technique is shown to offer improved performance relative to single-echo MRSI for imaging of metabolites with shortened T2* values due to the presence of local field inhomogeneities. Additional advantages are the intrinsic measurement of metabolite T2 values and determination of metabolite integrals without T2 weighting, thereby facilitating quantitative metabolite imaging.