Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL): application with fast spin-echo imaging. Magn Reson Med

Stanford University, Palo Alto, California, United States
Magnetic Resonance in Medicine (Impact Factor: 3.57). 09/2005; 54(3):636-44. DOI: 10.1002/mrm.20624
Source: PubMed


Chemical shift based methods are often used to achieve uniform water-fat separation that is insensitive to Bo inhomogeneities. Many spin-echo (SE) or fast SE (FSE) approaches acquire three echoes shifted symmetrically about the SE, creating time-dependent phase shifts caused by water-fat chemical shift. This work demonstrates that symmetrically acquired echoes cause artifacts that degrade image quality. According to theory, the noise performance of any water-fat separation method is dependent on the proportion of water and fat within a voxel, and the position of echoes relative to the SE. To address this problem, we propose a method termed "iterative decomposition of water and fat with echo asymmetric and least-squares estimation" (IDEAL). This technique combines asymmetrically acquired echoes with an iterative least-squares decomposition algorithm to maximize noise performance. Theoretical calculations predict that the optimal echo combination occurs when the relative phase of the echoes is separated by 2pi/3, with the middle echo centered at pi/2+pik (k=any integer), i.e., (-pi/6+pik, pi/2+pik, 7pi/6+pik). Only with these echo combinations can noise performance reach the maximum possible and be independent of the proportion of water and fat. Close agreement between theoretical and experimental results obtained from an oil-water phantom was observed, demonstrating that the iterative least-squares decomposition method is an efficient estimator.

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    • "The second issue besides sensitivity is the larger chemical shift dispersion of 31 P (~24 ppm for endogeneous phosphorous metabolites ) compared to that of 1 H (~10 ppm). Therefore, we employed an extension of the multi-peak iterative decomposition of water and fat signal with echo asymmetry and least-squares estimation (MP-IDEAL) labeled as multipoint-Dixon (MP-Dixon) in the following [21] [22]. "
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    ABSTRACT: The purpose of this study is to develop nuclear-Overhauser-enhanced (NOE) [(1)H]-(31)P magnetic resonance imaging (MRI) based on 3D fully-balanced steady-state free precession (fbSSFP). Therefore, two implementations of a 3D fbSSFP sequence are compared using frequency-selective excitation (FreqSel) and multipoint-Dixon (MP-Dixon). (31)P-containing model solutions and four healthy volunteers were examined at field strengths of B0 = 3 T and 7 T. Maps of the distribution of phosphocreatine (PCr), inorganic phosphate (Pi), and adenosine 5´-triphosphate (ATP) in the human calf were obtained with an isotropic resolution of 1.5 cm (1.0 cm) in an acquisition time of 5 min (10 min). NOE-pulses had the highest impact on the PCr acquisitions enhancing the signal up to (82 ± 13) % at 3 T and up to (37 ± 9) % at 7 T. An estimation of the level of PCr in muscle tissue from [(1)H]-(31)P MRI data yielded a mean value of (33 ± 8) mM. In conclusion, direct [(1)H]-(31)P imaging using FreqSel as well as MP-Dixon is possible in clinically feasible acquisition times. FreqSel should be preferred for measurements where only a single metabolite resonance is considered. MP-Dixon performs better in terms of SNR if a larger spectral width is of interest. Copyright © 2015. Published by Elsevier Inc.
    Magnetic Resonance Imaging 08/2015; 33(10). DOI:10.1016/j.mri.2015.07.017 · 2.09 Impact Factor
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    • "Fractional water contents were calculated in the same ROIs as above using IDEAL (iterative decomposition of water and fat with echo asymmetry and least-squares estimation), which enables fractional fat and water contents to be measured on the assumption that the total signal arises only from fat and water (Glover 1991; Reeder et al. 2005). Results are shown as fractional water (fractional fat is equal to 1 − fractional water). "

    01/2015; 2(1):101-112. DOI:10.1080/23335432.2015.1070686
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    • "(iv) Quantitation Fat-Water (IDEAL) imaging: In four subjects, including one participant from our younger cohort and three additional participants, a special sequence which yielded as the output separate fat and water images and enabled fat quantification, was made available. This sequence used the "iterative decomposition of water and fat with echo asymmetry and least-squares estimation" (IDEAL) method [20,24] combined with 3D gradient echo acquisition. This technique combines six asymmetrically acquired echoes with parallel imaging with an iterative least-squares decomposition algorithm to maximize noise performance. "
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    ABSTRACT: Background In human skeletal muscles, the aging process causes a decrease of contractile and a concomitant increase of intramuscular adipose (IMAT) and connective (IMCT) tissues. The accumulation of non-contractile tissues may contribute to the significant loss of intrinsic muscle strength typically observed at older age but their in vivo quantification is challenging. The purpose of this study was to establish MR imaging-based methods to quantify the relative amounts of IMCT, IMAT and contractile tissues in young and older human cohorts, and investigate their roles in determining age-associated changes in skeletal muscle strength. Methods Five young (31.6 ± 7.0 yrs) and five older (83.4 ± 3.2 yrs) Japanese women were subject to a detailed MR imaging protocol, including Fast Gradient Echo, Quantitative Fat/Water (IDEAL) and Ultra-short Echo Time (UTE) sequences, to determine contractile muscle tissue and IMAT within the entire Triceps Surae complex, and IMCT within both heads of the Gastrocnemius muscle. Specific force was calculated as the ratio of isometric plantarflexor force and the physiological cross-sectional area of the Triceps Surae complex. Results In the older cohort, total Triceps Surae volume was smaller by 17.5%, while the relative amounts of Triceps Surae IMAT and Gastrocnemius IMCT were larger by 55.1% and 48.9%, respectively. Differences of 38.6% and 42.1% in plantarflexor force and specific force were observed. After subtraction of IMAT and IMCT from total muscle volume, differences in intrinsic strength decreased to 29.6%. Conclusions Our data establishes that aging causes significant changes in skeletal muscle composition, with marked increases in non-contractile tissues. Such quantification of the remodeling process is likely to be of functional and clinical importance in elucidating the causes of the disproportionate age-associated decrease of force compared to that of muscle volume.
    BMC Musculoskeletal Disorders 06/2014; 15(1):209. DOI:10.1186/1471-2474-15-209 · 1.72 Impact Factor
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