In the exemplary case of protons, which will be used hereafter for illustration, it may be desired to portray as separate images the water and fat components of the subject. Often it is desired to “decompose” the NMR image into its several chemical shift components. The difference between the Larmor frequencies of such different species of the same nucleus, viz., protons, is termed chemical shift, reflecting the differing chemical environments of the two species. The Larmor frequency of protons in fat is shifted approximately 225 Hz from those of protons in water in a 1.5 Tesla polarizing magnetic field B0. Materials other than water, principally fat, are found in biological tissue and have different gyromagnetic ratios. An NMR signal is emitted by the excited spins, and after the excitation signal B1 is terminated, this signal may be received and processed to form an image. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. More particularly, the invention relates to the separation of fat and water signals in MR images produced using the Dixon method. ‘Multiecho water-fat separation and simultaneous R2* estimation with multifrequency fat spectrum modeling’.The field of the invention is nuclear magnetic resonance imaging methods and systems. ‘Multiecho reconstruction for simultaneous water-fat decomposition and T2* estimation’. ‘Multicoil Dixon chemical species separation with an iterative least-squares estimation method’.ĭetection, Estimation and Modulation Theory. ‘Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL): application with fast spin-echo imaging’. ‘Water-fat separation with IDEAL gradient-echo imaging’. ‘Cramer–Rao bounds for three-point decomposition of water and fat’.

Piscataway, NJ:Wiley-IEEE Press Google Scholar Principles of Magnetic Resonance Imaging: A Signal Processing Perspective. ‘T1 independent, T2* corrected MRI with accurate spectral modeling for quantification of fat: validation in a fat-water-SPIO phantom’. ‘In vivo characterization of the liver fat (1)H MR spectrum’. ‘Multipoint Dixon technique for water and fat proton and susceptibility imaging’. ‘Noise analysis for 3-point chemical shift-based water-fat separation with spectral modeling of fat’. ‘Independent estimation of T*2 for water and fat for improved accuracy of fat quantification’. ‘Lung parenchyma: magnetic susceptibility in MR imaging’. Hoboken, NJ:Wiley-Interscience Google Scholar In this work, we analyse the performance of multi-peak IDEAL algorithm with self-calibrated fat spectrum by theoretical calculation, simulation, and experiments, and find optimal echo time increments which provide reliable water-fat separation. However, the fat spectra vary in different tissues, thus a self-calibration method which estimates the fat spectrum directly from the data provides more accurate results. Recent studies have discussed the performance of this algorithm assuming that the frequencies and relative amplitudes of fat peaks are constant among all subjects. IDEAL (Iterative decomposition of water and fat with echo asymmetry and least-squares estimation) algorithm with multi-peak fat spectral modelling has been developed. It provides an effective way to measure fat fraction, or to suppress fat signal which might obscure underlying pathology. Chemical shift-based water-fat separation method utilises water–fat resonance frequency difference to decompose signals into water and fat partitions in magnetic resonance imaging (MRI) on a pixel-wise basis.

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