Two‐point water‐fat imaging with partially‐opposed‐phase (POP) acquisition: An asymmetric Dixon method

Xiang, Qing

doi:10.1002/mrm.20984

Cited by 96 publications

(157 citation statements)

References 27 publications

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“…When ␣ 120°, NSA is generally less than 3. Similarly, a maximum NSA of 2 is achieved for the two-point Dixon data sampled at (0, ␣) only when ␣ ϭ 180° (29,33).…”

Section: The Data Acquisition Strategy and Other Considerationsmentioning

confidence: 94%

“…As another variation to the original two-point Dixon technique, Xiang recently reported a two-point Dixon technique that accommodates acquisition of an inphase image and a partially opposed-phase image (where water and fat signals are not exactly at 180°) (33). On the basis of the in-phase and partially opposed-phase images, two phasor candidates can be computed for every pixel.…”

Section: The Extended Two-point Dixon Techniquesmentioning

confidence: 99%

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Dixon techniques for water and fat imaging

2008

Magnetic Resonance Imaging

514

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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“…When ␣ 120°, NSA is generally less than 3. Similarly, a maximum NSA of 2 is achieved for the two-point Dixon data sampled at (0, ␣) only when ␣ ϭ 180° (29,33).…”

Section: The Data Acquisition Strategy and Other Considerationsmentioning

confidence: 94%

Section: The Extended Two-point Dixon Techniquesmentioning

confidence: 99%

Dixon techniques for water and fat imaging

2008

Magnetic Resonance Imaging

514

442

View full text Add to dashboard Cite

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“…water ambiguity problem (2)(3)(4). Ambiguity is intimately related to B0 field homogeneity, which in turn is related to the problem of multidimensional phase unwrapping (5).…”

Section: Introductionmentioning

confidence: 99%

Relaxation effects in the quantification of fat using gradient echo imaging

Bydder

Yokoo

Hamilton

et al. 2008

Magnetic Resonance Imaging

370

579

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Quantification of fat has been investigated using images acquired from multiple gradient echos. The evolution of the signal with echo time and flip angle was measured in phantoms of known fat and water composition and in 21 research subjects with fatty liver. Data were compared to different models of the signal equation, in which each model makes different assumptions about the T1 and/ or T2* relaxation effects. A range of T1, T2*, fat fraction and number of echos was investigated to cover situations of relevance to clinical imaging. Results indicate that quantification is most accurate at low flip angles (to minimize T1 effects) with a small number of echos (to minimize spectral broadening effects). At short echo times the spectral broadening effects manifest as a short apparent T2 for the fat component.

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“…Results and Conclusions: The average treatment time was around 1h23 (0h30-2h30). Volume reductions were on average 18.5% [1,,4%] at M1 (n=15), 35% [6,,7%] at M2 (n=13), 50.6% [28,,4%] at M3 (n=10) (Figure 1, 2), 55.5% [40,.6%] at M6 (n=4) and 68,5% (63,9-73%) at M12. A patient who became pregnant one month after the HIFU treatment, showed a reduction of volume of 73% at M12 (Figure 3, 4) In Vivo Evaluation of a Breast-Specific MRgFUS System in a Goat Udder Model Background/Introduction: Magnetic resonance-guided focused ultrasound (MRgFUS) has the potential to provide completely non-invasive treatments for women with breast cancer, adding to the treatment options available.…”

Section: -Btmentioning

confidence: 99%

“…Animals with volumes ablated approximately 2 cm 3 or greater had significant edematous tissue present. This edematous tissue seems to correspond to a larger nonenhancing tissue volume when compared to the accumulated thermal dose volume (animals [4][5][6]. Histological analysis shows features indicative of ischemic necrosis including vessel wall thickening, atrophic lobules and hyalinization of tissues.…”

Section: -Btmentioning

confidence: 99%

Letter to the Editor: Trigeminal neuralgia

Zheng

Lin

et al. 2015

JNS

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Dear Colleagues:Everyone working in the field of focused ultrasound has been intrigued and inspired by the therapeutic potential and promise of this exciting technology. While still at an early stage, our push to develop focused ultrasound applications is increasing in scope and intensity. To me, the best gauge of our progress is the 3rd International Symposium on Focused Ultrasound.What makes this year's symposium different from its predecessors is the inclusion of more presentations, more indications and more advances in R&D and commercialization. All signal that the pace of progress in our field is escalating.I hope that clinicians attending this year's symposium gain meaningful insight into the full range of applications that focused ultrasound can provide to them and, therefore, to their patients. After all, having patients live longer, healthier lives is the driving force in all of our work. From the Foundation ChairmanDear Colleagues:Welcome to the 3rd International Symposium on Focused Ultrasound. You are participating in the most extensive program we have hosted to date featuring more than 170 oral and poster presentations spotlighting the latest developments in our field. This represents more than a 50% increase compared to the 2010 symposium and reflects the accelerating progress being achieved by the focused ultrasound community.In keeping with the Foundation's intense patient-centric orientation, the program emphasizes the translational and clinical research that is moving focused ultrasound into the realm of patient care.The potential focused ultrasound to improve the quality of life and longevity for millions of people around the world with serious medical disorders has never been more apparent. Effective therapies to decrease death, disability and suffering are now on the horizon, no longer beyond it. But we still need to shorten the distance. We will do that through capitalfinancial and, more importantly, human capital.The number of focused ultrasound investigators is continuing to grow as evidenced by the applications received for the Young Investigator Travel Awards. In 2010, there were 11 applications; this year, there were 44. But in order to move focused ultrasound forward more rapidly, we need more human capital. The most expeditious way to achieve this is to leverage the people who are currently engaged.The symposium is an important vehicle for disseminating knowledge and sharing ideas, the most important role is to serve as an incubator to foster collaboration -collaboration being the ultimate force multiplier for human capital. Please take advantage of the opportunities to establish new partnerships and collaborations, particularly during the Tuesday evening poster session.Several special events are planned during the symposium, including keynote talks by Dean Kamen, one of the international leaders in medical device innovation and inventor of the Segway, at Sunday's opening reception and by John Grisham, best-selling author and Foundation board member, on Tuesday morning.The Focused U...

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Two‐point water‐fat imaging with partially‐opposed‐phase (POP) acquisition: An asymmetric Dixon method

Cited by 96 publications

References 27 publications

Dixon techniques for water and fat imaging

Dixon techniques for water and fat imaging

Relaxation effects in the quantification of fat using gradient echo imaging

Letter to the Editor: Trigeminal neuralgia

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