Alexey Samsonov^1
1Radiology, University of Wisconsin, Madison, WI, United States

IDEAL fat/water imaging often suffers from estimation errors such as fat/water swaps, which can't be removed even by sophisticated algorithms based on field map smoothness regularization. However, these errors may be minimized by supplying the algorithms with an adequate FM prior, which, however, is not generally available. We propose a new method to improve IDEAL robustness which exploits a phenomenon of absence of magnetization transfer (MT) effect in fat for estimation of sufficiently accurate IDEAL field map prior.

Stefan Ruschke¹, Dominik Weidlich¹, Maximilian Diefenbach¹, Holger Eggers², Hendrik Kooijman³, Houchun H. Hu⁴, Ernst J. Rummeny¹, Axel Haase⁵, Jan S. Kirschke⁶, Thomas Baum¹, and Dimitrios C. Karampinos^1
1Department of Diagnostic and Interventional Radiology, Technische Universität München, Munich, Germany, ²Philips Research, Hamburg, Germany, ³Philips Healthcare, Hamburg, Germany, ⁴Radiology, Phoenix Children’s Hospital, Phoenix, AZ, United States, ⁵Zentralinstitut fu¨r Medizintechnik, Technische Universität München, Garching, Germany, ⁶Neuroradiology, Technische Universität München, Munich, Germany

Simultaneous T2 and T2' mapping is highly desirable in applications investigating changes in blood oxygenation, iron content and bone mineral density.  Simultaneous T2 and T2' mapping is highly desirable in applications investigating blood oxygenation changes (in tumors), iron deposition (in patients with blood transfusions) and trabecular bone matrix weakening (in osteoporosis patients). Gradient echo imaging using adiabatic T2-preparation has enabled T2 mapping in the presence of inhomogeneous B1 fields. In addition, the presence of water and fat components has to be considered in the extraction of T2 and T2' parameters in many organs. The simultaneous quantification of the proton-density fat fraction (PDFF) can be also of particular interest (e.g. in the liver and in, fat fraction, bone marrow fat fraction). Multi-echo gradient echo imaging can separate water and fat components and quantify PDFF. Therefore, the purpose of the present work was to introduce a novel method for simultaneous T2, T2' and PDFF mapping, relying on an adiabatic T2-preparation combined with a time-interleaved multi-echo gradient echo acquisition scheme.

Gastao Cruz¹, René Botnar¹, and Claudia Prieto^1
1Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom

Fat suppression is required for visualization of coronary arteries with MRA. Studies have shown that cardiac fat may provide diagnostic information and thus water/fat coronary imaging is desirable. Respiratory motion is a major problem in whole-heart coronary imaging as respiratory gating leads to long and unpredictable scan times. Translational motion correction (TC) may be of limited value as it may introduce ghosting artefacts from static fat tissue. Here, we propose a 100% scan efficiency, two-step motion correction framework using translational and nonrigid correction for water/fat coronary MRA. The proposed approach outperforms TC, minimising ghosting artefacts from static tissues.

Thomas Benkert^1,2, Daniel K. Sodickson^1,2, Hersh Chandarana^1,2, and Kai Tobias Block^1,2
1Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, NY, United States, ²Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States

This work presents a model-based fat/water separation technique for radial sampling, which takes into account the off-resonant blurring of fat and integrates both compressed sensing and parallel imaging. By combining this reconstruction scheme with 3D radial stack-of-stars sampling, volumetric and motion-robust water and fat maps as well as in-phase/opposed-phase images can be generated under free-breathing. The approach is demonstrated at 1.5T and 3T, including volunteer and patient measurements.

Hahnsung Kim¹ and Jaeseok Park^2
1Center for Neuroscience Imaging Research, Institute for Basic Science, Suwon, Korea, Republic of, ²Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of

Most water-fat separation methods based on chemical shift effect require multiple image acquisitions at different echo times, which prolong the total scanning time. Recently, to resolve aforementioned problems, variable-flip-angle (VFA) fast/turbo SE is developed. In addition, partial Fourier and/or parallel imaging techniques are incorporated with VFA fast/turbo SE imaging to speed up acquisition time but directly trade off with signal-to-noise ratio. To avoid multiple measurements and to tackle spatially variant noise amplification, we develop a novel water-fat separation method employing: 1) single-slab 3D VFA GRASE using phase-encoding blips for imaging time efficiency, 2) phase-independent reconstruction exploiting spatially complementary information along the echo direction, and 3) phase-corrected water-fat separation method using robust field distribution. 

Jingfei Ma¹, Jong Bum Son¹, Ken-Pin Hwang¹, and Basak Dogan^1
1The University of Texas MD Anderson Cancer Center, Houston, TX, United States

Silicone-specific imaging can be performed using various combinations of selective inversion, selective saturation, and Dixon methods. In this work, we propose and demonstrate a new silicone-specific imaging method with a unipolar flexible fast spin echo triple echo Dixon pulse sequence.  The method treats the water and fat signals as a single component by acquiring images only when water and fat are in-phase, and to use Dixon processing with flexible echo times to separate the remaining silicone signal. Among its many advantages, the method maintains high SNR and scan efficiency, is insensitive to field inhomogeneity, and is not subject to chemical shift misregistration.

Xinzeng Wang¹, Joshua S. Greer^1,2, Ivan Pedrosa^1,3, Neil M. Rofsky^1,3, and Ananth J. Madhuranthakam^1,3
1Radiology, UT Southwestern Medical Center, Dallas, TX, United States, ²Bioengineering, University of Texas at Dallas, Richardson, TX, United States, ³Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States

Breath-held single shot TSE sequence is a widely used in abdominal imaging due to its speed combined with robustness to field inhomogeneities and motion. Fat suppression techniques, such as SPAIR and Dixon method are often used in SShTSE to increase the conspicuity of the anatomical details. However, SPAIR is sensitive to B0 inhomogeneity resulting in incomplete fat suppression and Dixon method requires prolonged acquisition times. In this work, we implement a dual-echo SShTSE acquisition acquiring the in-phase (IP) and out-of-phase (OP) echoes in the same repetition, providing a true single shot acquisition with robust fat/water separation.

Vanessa Stahl¹, Armin M. Nagel^1,2, Martin T. Freitag³, Ralf O. Floca⁴, Moritz C. Berger ¹, Reiner Umathum¹, Mauricio Berriel Diaz⁵, Stephan Herzig⁵, Marc-André Weber⁶, Antonia Dimitrakopoulou-Strauss⁷, Peter Bachert¹, Mark E. Ladd¹, and Florian Maier^1
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany, ²Department of Diagnostic and Interventional Radiology, University Medical Center Ulm, Ulm, Germany, ³Department of Radiology, German Cancer Research Center, Heidelberg, Germany, ⁴Medical and Biological Informatics, German Cancer Research Center, Heidelberg, Germany, ⁵Institute for Diabetes and Cancer, Helmholtz Zentrum München German Research Center for Environmental Health, München, Germany, ⁶Diagnostic and Interventional Radiology, University Hospital of Heidelberg, Heidelberg, Germany, ⁷Clinical Cooperation Unit Nuclear Medicine, German Cancer Research Center, Heidelberg, Germany

Brown adipose tissue (BAT) is subject of ongoing metabolic and obesity research having the ability to dissipate energy through non-shivering thermogenesis. This study was performed to evaluate reproducibility of recently shown time-resolved fat-fraction (FF) MR measurements during cold exposure for BAT assessment. BAT mass and activity were compared to the previous results assessed in the interscapular BAT depots. Potential BAT depots were observed at reproducible anatomic positions, showing a reproducible FF evolution with a mean FF decrease of (-2.31±1.05)%/h during cold-activation.

Dongyeob Han¹, Min-Oh Kim¹, Honpyo Lee¹, Taehwa Hong¹, and Dong-Hyun Kim^1
1Yonsei University, Seoul, Korea, Republic of

 A simultaneous, free-breathing water/fat separation and T1, T2 quantification method was proposed. Dual TR (in-phase and out-phase TR) and varying sinusoidal flip angle was used with FISP acquisition. For motion robustness, random rotating golden angle trajectories were applied. T1, T2 and Δφ_fat of fat were pre-determined using the fat dominant region mask, then water/fat signal combined dictionary was generated. The results show that the water/fraction maps from the proposed method were in good agreement with conventional breath-hold results. Furthermore, measured T1, T2 values were in good agreement with the values from the previous research.  

Maximilian N. Diefenbach¹, Stefan Ruschke¹, Hendrik Kooijman², Anh T. Van³, Ernst J. Rummeny¹, Axel Haase³, and Dimitrios C. Karampinos^1
1Department of Diagnostic and Interventional Radiology, Technische Universität München, Munich, Germany, ²Philips Healthcare, Hamburg, Germany, ³Zentralinstitut fu¨r Medizintechnik, Technische Universita¨t Mu¨nchen, Munich, Germany

To avoid swaps in water-fat imaging a pre-processing step to standard fieldmap estimation methods is proposed. Based on spherical harmonic expansion the shimfield and the inhomogeneities of the main magnetic field are calculated. Thereby obtained details of the field inside the empty scanner are used to calculate an object-based fieldmap based on the tissue geometry and the susceptibility of tissue and air. The superposition of these three contributions to the fieldmap serves as an initial estimate for the water-fat separation algorithm and can reduce swaps in cases of large FOVs and when shimming is used.