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: 3.4). 09/2005; 54(3):636-44. DOI: 10.1002/mrm.20624
Source: PubMed

ABSTRACT 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.

  • Source
    • "Since excitation is broad band, and in the presence of the readout gradient, other novel excitation based fat suppression strategies cannot be used [3]. In addition, since there is no phase evolution during an echo time (SWIFT yields FID type signal after processing), Dixon type techniques cannot be used [4][5]. We have previously developed an interleaved CHESS pulse strategy utilizing a 4 ms Gaussian pulse every 8-16 SWIFT views [6] at 4 Tesla. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Target Audience Researchers, Technicians, and Clinician/Scientists interested in emerging breast imaging methodology, and related applications. Purpose: Breast MRI is increasingly indicated as a diagnostic tool for breast cancer and as a screening tool in high risk populations including younger women with dense breasts or women with breast implants [1]. We are interested in improving Breast MRI in order to provide more and higher quality imaging information in less total scanning time. This could provide greater effectiveness and access, and reduce cost for breast MRI. Currently, fat suppressed T1 weighted images are the preferred method for evaluating contrast enhanced dynamic and morphological breast images. We report here an optimized T1 weighted SWIFT (SWeep Imaging with Fourier Transform) sequence [2] with interleaved adiabatic fat suppression for dual breast imaging using an in-house designed dual breast transmit receive coil on our 4 Tesla, Agilent console, 90 cm bore human imaging system.
    Proc. Intl. Soc. Mag. Reson. Med.; 04/2013
  • Source
    • "Current methods collect multiple echo time data to improve the estimation of the fat and water images and these have been applied successfully in the liver and musculoskeletal system using an iterative least squares solution (e.g. IDEAL) (Reeder et al., 2004, 2005). The method our research group at Northwestern University currently uses in the Table 2 A sample of studies supporting the presence of central nervous system hyperexcitability in whiplash-associated disorders (WAD) e adapted from Sterling and Kenardy (2008). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Whiplash associated disorder (WAD) represents an enormous economic, social and personal burden. Five out of 10 people with WAD never fully recover and up to 25% continue to have moderate to severe pain-related disability. Unfortunately, clear and definitive reasons as to why half of individuals with WAD recover uneventfully and the other half do not, remain elusive. Identifying the factors that can reliably predict outcome holds considerable importance for not only WAD, but arguably for other acute musculoskeletal traumas. The precise pathology present in WAD has been controversial and often biased by outdated models. Fortunately, a combination of new measurement technology that illuminates pain processing, physical and social functioning and post-traumatic stress responses (and possibly markers of altered muscle size/shape/physiology) is providing a clearer picture of the multisystem pathophysiology in individuals with persistent WAD. The aim of this professional issues paper is to illuminate the clinical and research communities with regards to the growing body of knowledge for determining the trajectory of a patient with whiplash.
    Manual therapy 03/2013; 18(6). DOI:10.1016/j.math.2013.02.002 · 1.76 Impact Factor
  • Source
    • "While we report non-contractile tissue content and changes to muscle volumes as a result, our method for determining fat content from MRI has not been validated. A recent technique involving iterative decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL) has been reported to be a more reliable method for estimating fat content in MR imaging (Reeder et al., 2005). A comparison between our method for fat-suppression and IDEAL may be necessary for proper validation. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Muscle atrophy is one of many factors contributing to post-stroke hemiparetic weakness. Since muscle force is a function of muscle size, the amount of muscle atrophy an individual muscle undergoes has implications for its overall force-generating capability post-stroke. In this study, post-stroke atrophy was determined bilaterally in fifteen leg muscles with volumes quantified using magnetic resonance imaging (MRI). All muscle volumes were adjusted to exclude non-contractile tissue content, and muscle atrophy was quantified by comparing the volumes between paretic and non-paretic sides. Non-contractile tissue or intramuscular fat was calculated by determining the amount of tissue excluded from the muscle volume measurement. With the exception of the gracilis, all individual paretic muscles examined had smaller volumes in the non-paretic side. The average decrease in volume for these paretic muscles was 23%. The gracilis volume, on the other hand, was approximately 11% larger on the paretic side. The amount of non-contractile tissue was higher in all paretic muscles except the gracilis, where no difference was observed between sides. To compensate for paretic plantar flexor weakness, one idea might be that use of the paretic gracilis actually causes the muscle to increase in size and not develop intramuscular fat. By eliminating non-contractile tissue from our volume calculations, we have presented volume data that more appropriately represents force-generating muscle tissue. Non-uniform muscle atrophy was observed across muscles and may provide important clues when assessing the effect of muscle atrophy on post-stroke gait.
    Journal of Biomechanics 09/2011; 44(16):2741-6. DOI:10.1016/j.jbiomech.2011.09.001 · 2.50 Impact Factor
Show more