Field map estimation with a region growing scheme for iterative 3‐point water‐fat decomposition

Yu, Hong; Reeder, Scott B.; Shimakawa, Ann; Brittain, Jean H.; Pelc, Norbert J.

doi:10.1002/mrm.20654

Cited by 203 publications

(332 citation statements)

References 16 publications

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“…DPE makes a selection from the two solutions by comparing the relative phase angle between X and Y. According to the definition in Equations [19]- [20], the physically correct solution should have Y with a leading phase relative to X because of the fact that fat has a lower resonant frequency than water. Thus, DPE can correctly determine water and fat on a pixel basis without the actual determination of the phase angle or 0 .…”

Section: Pixel-based Analytical Methodsmentioning

confidence: 99%

“…From the complex signals sampled at (␣ 0 , ␣ 0 ϩ ␣, ␣ 0 ϩ 2␣), two possible algebraic solutions for X and Y can be directly obtained. Because X and Y are defined (see Equations [19] and [20]) as the magnetization vectors of the water and fat, respectively, the correct solution should have Y with a leading phase relative to X. The phase relationship can be checked when X and Y are not exactly anti-symmetric (e.g., ␣ 180°).…”

Section: Pixel-based Analytical Methodsmentioning

confidence: 99%

“…Another requirement is that both X and Y should have measurable amplitudes (i.e., appreciable amounts of both water and fat should exist in a pixel). (Reprinted from Xiang and An (16) biguity with two sets of possible solutions (19). Even for pixels with a mixture of both water and fat, the cost function used for the linear least-square fitting usually contains multiple local minima.…”

Section: Pixel-based Analytical Methodsmentioning

confidence: 99%

“…Therefore, the iterative process by itself may converge to the incorrect solution for W and F if the initial guess for is not close to its true value. As an improvement, a region growing algorithm has been proposed to generate a more accurate initial guess for before the iterative process is applied (19). The region growing used in Yu et al (19) starts from an initial seed pixel that has a "median" value of among all the pixels based on an initial round of iterative processing with ϭ 0.…”

Section: Pixel-based Analytical Methodsmentioning

confidence: 99%

“…As an improvement, a region growing algorithm has been proposed to generate a more accurate initial guess for before the iterative process is applied (19). The region growing used in Yu et al (19) starts from an initial seed pixel that has a "median" value of among all the pixels based on an initial round of iterative processing with ϭ 0. The region growing then propagates to the rest of the image in a predetermined square-spiral trajectory.…”

Section: Pixel-based Analytical Methodsmentioning

confidence: 99%

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Dixon techniques for water and fat imaging

2008

Magnetic Resonance Imaging

513

442

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In 1984, Dixon published a first paper on a simple spectroscopic imaging technique for water and fat separation. The technique acquires two separate images with a modified spin echo pulse sequence. One is a conventional spin echo image with water and fat signals in-phase and the other is acquired with the readout gradient slightly shifted so that the water and fat signals are 180°out-of-phase. Dixon showed that from these two images, a water-only image and a fat-only image can be generated. The wateronly image by the Dixon's technique can serve the purpose of fat suppression, an important and widely used imaging option for clinical MRI. Additionally, the availability of both the water-only and fat-only images allows direct imagebased water and fat quantitation. These applications, as well as the potential that the technique can be made highly insensitive to magnetic field inhomogeneity, have generated substantial research interests and efforts from many investigators. As a result, significant improvement to the original technique has been made in the last 2 decades. The following article reviews the underlying physical principles and describes some major technical aspects in the development of these Dixon techniques. MR IMAGES ACQUIRED IN VIVO usually contain signals from both water and fat. In many pulse sequences, fat appears hyperintense. However, the contribution from water is often of the primary interest for many practical applications. Without suppression, the bright fat signal may result in aggravated motion-related artifacts and, more importantly, reduce the underlying lesion conspicuity. Because of its chemical shift, fat is also responsible for the well-known spatial misregistration artifacts, which can appear both along the frequency encode direction and along the slice select direction. For a few other applications such as diagnosis of bone marrow diseases or hepatic steatosis, detection rather than suppression of the fat signal can also be valuable.Several approaches have been proposed and developed for achieving fat suppression. Perhaps the most popular is the chemical shift selective saturation (1) or its variants. In this approach, a frequency selective radiofrequency (RF) pulse and a spoiler gradient pulse are used in conjunction to first excite and then saturate the fat magnetization before water is excited for imaging. Alternatively, a frequency selective RF pulse can be used to directly excite only the water magnetization and leave the fat magnetization alone along the longitudinal axis. These techniques, particularly the selective saturation technique, are easy to implement and have been widely used with great success. However, both selective saturation pulses and selective excitation pulses increase the scan time. Another limitation for fat suppression by the selective saturation pulses is that it typically requires an accurate 90°flip angle, and as a result, its performance can be dependent on B1 homogeneity. Perhaps most importantly, fat suppression using the frequency selective approach...

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Section: Pixel-based Analytical Methodsmentioning

confidence: 99%

Section: Pixel-based Analytical Methodsmentioning

confidence: 99%

Section: Pixel-based Analytical Methodsmentioning

confidence: 99%

Section: Pixel-based Analytical Methodsmentioning

confidence: 99%

Section: Pixel-based Analytical Methodsmentioning

confidence: 99%

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Dixon techniques for water and fat imaging

2008

Magnetic Resonance Imaging

513

442

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Continuum heterogeneous biofilm model—A simple and accurate method for effectiveness factor determination

Gonzo

Wuertz

Rajal

2012

Biotech & Bioengineering

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We present a novel analytical approach to describe biofilm processes considering continuum variation of both biofilm density and substrate effective diffusivity. A simple perturbation and matching technique was used to quantify biofilm activity using the steady-state diffusion-reaction equation with continuum variable substrate effective diffusivity and biofilm density, along the coordinate normal to the biofilm surface. The procedure allows prediction of an effectiveness factor, η, defined as the ratio between the observed rate of substrate utilization (reaction rate with diffusion resistance) and the rate of substrate utilization without diffusion limitation. Main assumptions are that (i) the biofilm is a continuum, (ii) substrate is transferred by diffusion only and is consumed only by microorganisms at a rate according to Monod kinetics, (iii) biofilm density and substrate effective diffusivity change in the x direction, (iv) the substrate concentration above the biofilm surface is known, and (v) the substratum is impermeable. With this approach one can evaluate, in a fast and efficient way, the effect of different parameters that characterize a heterogeneous biofilm and the kinetics of the rate of substrate consumption on the behavior of the biological system. Based on a comparison of η profiles the activity of a homogeneous biofilm could be as much as 47.8% higher than that of a heterogeneous biofilm, under the given conditions. A comparison of η values estimated for first order kinetics and η values obtained by numerical techniques showed a maximum deviation of 1.75% in a narrow range of modified Thiele modulus values. When external mass transfer resistance, is also considered, a global effectiveness factor, η(0) , can be calculated. The main advantage of the approach lies in the analytical expression for the calculation of the intrinsic effectiveness factor η and its implementation in a computer program. For the test cases studied convergence was achieved quickly after four or five iterations. Therefore, the simulation and scale-up of heterogeneous biofilm reactors can be easily carried out.

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Prognostic factors and outcome of recurrence in childhood acute myeloid leukemia

Rubnitz

Razzouk

Lensing

et al. 2006

Cancer

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Dixon imaging techniques derive chemical shift‐separated water and fat images, enabling the quantification of fat content and forming an alternative to fat suppression. Whole‐body Dixon imaging is of interest in studies of obesity and the metabolic syndrome, and possibly in oncology. A three‐point Dixon method is proposed where two solutions are found analytically in each voxel. The true solution is identified by a multiseed three‐dimensional region‐growing scheme with a dynamic path, allowing confident regions to be solved before unconfident regions, such as background noise. 2π‐Phase unwrapping is not required. Whole‐body datasets (256 × 184 × 252 voxels) were collected from 39 subjects (body mass index 19.8‐45.4 kg/m2), in a mean scan time of 5 min 15 sec. Water and fat images were reconstructed offline, using the proposed method and two reference methods. The resulting images were subjectively graded on a four‐grade scale by two radiologists, blinded to the method used. The proposed method was found superior to the reference methods. It exclusively received the two highest grades, implying that only mild reconstruction failures were found. The computation time for a whole‐body dataset was 1 min 51.5 sec ± 3.0 sec. It was concluded that whole‐body water and fat imaging is feasible even for obese subjects, using the proposed method. Magn Reson Med 63:1659–1668, 2010. © 2010 Wiley‐Liss, Inc.

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Field map estimation with a region growing scheme for iterative 3‐point water‐fat decomposition

Cited by 203 publications

References 16 publications

Dixon techniques for water and fat imaging

Dixon techniques for water and fat imaging

Continuum heterogeneous biofilm model—A simple and accurate method for effectiveness factor determination

Prognostic factors and outcome of recurrence in childhood acute myeloid leukemia

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