Fabian J Kratzer¹, Sebastian Flassbeck^1,2,3, Sebastian Schmitter^1,4, Tobias Wilferth⁵, Peter Bachert¹, Mark E Ladd¹, and Armin M Nagel^1,5
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Center for Biomedical Imaging, New York University, New York, NY, United States, ³Center for Advanced Imaging Innovation and Research, New York University, New York, NY, United States, ⁴Physikalisch Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany, ⁵Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen Nürnberg (FAU), Erlangen, Germany

This work investigates the bias in the quantified relaxation times due to partial volume contributions of CSF for ²³Na magnetic resonance fingerprinting (MRF) and reference methods. In simulations, a CSF contribution of only 10% resulted in an overestimation of 17% (31%) in T_2l^* in brain tissue for MRF (the reference). Further, a simple approach for CSF bias correction for ²³Na MRF is proposed. This reduced the average absolute T₁ deviation in brain tissue from 15% to 4%. The deviation in T_2l^* (T_2s^*) was reduced from 17% (35%) to 9% (5%). Finally, the correction was applied to in vivo MRF data.

Gonzalo G Rodriguez¹, Zidan Yu^1,2, Lauren O'Donnell¹, Liz Calderon¹, Martijn A Cloos^3,4, and Guillaume Madelin^1,2
1Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, ²Vilcek Institute of Graduate Biomedical Sciences, NYU Langone Health, New York, NY, United States, ³Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia, ⁴ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, Brisbane, Australia

In this work, we assess the repeatability of proton density, T₁, T₂ and sodium density maps measured with simultaneous 3D ¹H MRF/²³Na MRI in the brain at 7T. We scanned seven healthy subjects three times each. The coefficients of variation (CV) were in the range 1-3% for mean values in GM, WM and CSF, and the intra-class correlation (ICC) was in range 0.44-0.99.

Anna K. Scheipers^1,2, Daniel Peach³, Armin M. Nagel^1,4, Mark E. Ladd^1,2,5, and Tanja Platt^1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Faculty of Physics and Astronomy, Ruprecht Karl University of Heidelberg, Heidelberg, Germany, ³Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ⁴University Hospital Erlangen, Institute of Radiology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany, ⁵Faculty of Medicine, Ruprecht Karl University of Heidelberg, Heidelberg, Germany

²³Na-MRI offers the possibility for non-invasive quantification of the sodium concentration in-vivo. The obtained functional information can provide interesting insights into the degeneration state of the human intervertebral discs¹ (IVDs). The presented work thus aimed to quantify the tissue sodium concentration (TSC) in the human intervertebral discs via ²³Na-MRI at 7T and to compare the obtained concentrations for two healthy volunteers after the course of one year. The estimate average concentration for all IVDs of both volunteers was found to be (96.5±8.8)mM and (113.6±9.5)mM, respectively.

Marco L. Wittrich^1,2, Armin M. Nagel^1,3, Sebastian Schmitter^1,4, Peter Bachert^1,2, Mark E. Ladd^1,2,5, and Fabian J Kratzer^1,2
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany, ³Institute of Radiology, University Hospital Erlangen, Friedrich‐Alexander‐Universität Erlangen‐Nürnberg (FAU), Erlangen-Nürnberg, Germany, ⁴Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany, ⁵Faculty of Medecine, University of Heidelberg, Heidelberg, Germany

In this work, a 2D radial ²³Na sequence with half-VERSE pulses was developed to reduce SAR and achieve ultra-short TEs. Simulations and measurements of the slice profiles showed good agreement between full- and half-VERSE pulses with a maximal deviation in the FWHM of 7%.

In measurements, the TE_min was reduced from 1.41ms to 0.1ms by the use of half- instead of full-VERSE pulses. This resulted in an SNR gain of up to 18% in phantom, 7% in brain and 26% in calf measurements.

Last, rapid single-slice ²³Na images (2.9x2.9x12mm³) were obtained in a clinically feasible acquisition time of 2:56min.

Shannon L Taylor^1,2, Kevin D Harkins^2,3, Daniel C Colvin^2,3, Joseph M Rutkowski⁴, Mark D Does^1,2,5, John C Gore^1,2,3,6,7, and Rachelle L Crescenzi^1,2,3
1Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, ²Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, United States, ³Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, United States, ⁴Medical Physiology, Texas A&M University College of Medicine, Bryan, TX, United States, ⁵Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN, United States, ⁶Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, United States, ⁷Physics and Astronomy, Vanderbilt University, Nashville, TN, United States

To investigate questions regarding the physiology of salt storage in skin and muscle and its relationship with lymphangiogenesis, we are developing sodium ²³Na-MRI protocols for a mouse model of controllable lymphangiogenesis in adipose tissue. We acquired images at 15.2T from a UTE center-out sequence and quantified sodium longitudinal and bi-exponential transverse relaxation times and tissue sodium content (TSC) in the skin and muscle. Baseline TSC was reduced in animals undergoing lymphangiogenesis compared to littermates, while ²³Na-relaxometry was similar. These results will be used for protocol development in this animal model to study sodium and lymphatic physiology.

Michael Pridmore^1,2, Jorge Gamboa³, Michelle Ormseth^3,4, Annette Oeser³, C. Michael Stein³, and Rachelle Crescenzi^1,2,5
1Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, United States, ²Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, United States, ³Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, United States, ⁴U.S. Department of Veterans Affairs, Tennessee Valley Healthcare System, Nashville, TN, United States, ⁵Biomedical Engineering, Vanderbilt University Medical Center, Nashville, TN, United States

Adipose tissue depositions between muscle compartments, known as intermuscular adipose tissue (IMAT), occurs in various conditions such as with obesity and aging. Tissue sodium content (TSC) measured by sodium magnetic resonance imaging increases with aging and may be associated with insulin resistance. In this study, we found a correlation between IMAT volume percentage and muscle TSC (r=0.52, p=0.01). Additionally, mean TSC in the IMAT region was higher than mean TSC in total muscle (p<0.001). The relationship between tissue sodium content and IMAT opens avenues for understanding the mechanisms of sodium storage and fat depositions in tissue compartments of the leg.

Ben Prestwich¹ and Susan Francis^1
1Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, United Kingdom

The repeatability of sodium (²³Na) MRI measures must be understood to allow for its application in clinical studies of patient groups or response to therapy. A series of ²³Na scans were performed on the calf of healthy subjects, this included a  3D GRE ²³Na scan and phase sensitive B₁ mapping to measure tissue sodium concentration (TSC). Subjects were scanned twice for assessment of repeatability of measures. A multi echo UTE scan was used to measure the T₂* decay. TSC was shown to have a coefficient of variation of 16±4 % between visits and the bi-exponential decay curve was characterized.

Samuel Rot^1,2, Aaron Oliver-Taylor³, Xavier Golay^3,4, Bhavana Solanky¹, and Claudia AM Gandini Wheeler-Kingshott^1,5,6
1NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Queen Square Institute of Neurology, Faculty of Brain Sciences, University College London, London, United Kingdom, ²Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom, ³Gold Standard Phantoms, London, United Kingdom, ⁴Department of Brain Repair and Rehabilitation, UCL Queen Square Institute of Neurology, Faculty of Brain Sciences, University College London, London, United Kingdom, ⁵Department of Brain & Behavioural Sciences, University of Pavia, Pavia, Italy, ⁶Brain Connectivity Centre Research Department, IRCCS Mondino Foundation, Pavia, Italy

Accuracy in quantitative ²³Na (sodium) MRI is impacted by the quality of the signal calibration phantom. Agarose phantoms, the current benchmark, exhibit various unfavourable qualities. To move towards standardisation in ²³Na-MRI, the objective was to develop a synthetic, polymer-based calibration phantom for traceable, reliable and accurate quantification in ²³Na-MRI. Crosslinked polyacrylamide gel (PAG) was selected as the most suitable choice, for its bi-exponential ²³Na T2 decay. Here, we present the T1, T2 properties and ²³Na-MRI data of prototype PAG phantoms at different ²³Na concentrations. PAG emerges as a reliable choice to replace the ubiquitous agarose gel phantom.

Chengchuan Wu¹, Leigh A. Johnston¹, and Yasmin Blunck^1
1Department of Biomedical Engineering, The University of Melbourne, Parkville, Australia

This work implements 2D ultra-short TE (UTE) imaging for ²³Na using half-pulse excitation. The sequence was examined in numerical simulations and phantom experiments at 7T. 2D UTE ²³Na imaging is shown to be less prone to partial volume effects than conventional radial 3D sodium imaging and able to produce high in-plane resolution ²³Na images.

Cameron Nowikow^1,2, Paul Polak^1,2,3, and Michael D Noseworthy^1,2,4
1School of Biomedical Engineering, McMaster University, Hamilton, ON, Canada, ²Imaging Research Centre, St. Joseph's Healthcare, Hamilton, ON, Canada, ³Radiology, University of Colorado Anschutz Medical Campus, Aurora, CO, United States, ⁴Electrical and Computer Engineering, McMaster University, Hamilton, ON, Canada

Throughout the literature, the methods of quantifying total sodium concentration (TSC) brain maps vary. Some studies use a two calibration phantom approach, some use a one calibration phantom approach, and some use anatomical references to quantify the TSC maps. This abstract investigates the variability of using one method versus another to see if a chosen method will inherently bias the resultant maps. It was found that no bias is provided by one method versus another as they provide no significant variance to the data.

Benedikt Kamp¹, Miriam Frenken¹, Jan M. Henke^1,2, Daniel B. Abrar¹, Armin M. Nagel^3,4, Lena V. Gast³, Georg Oeltzschner^5,6, Lena M. Wilms¹, Sven Nebelung¹, Gerald Antoch¹, Hans-Jörg Wittsack¹, and Anja Müller-Lutz^1
1University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf, Germany, ²University Dusseldorf, Medical Faculty, Clinic of Nuclear Medicine, Dusseldorf, Germany, ³Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg 14 (FAU), Erlangen, Germany, ⁴Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ⁵Russell H. Morgan Department for Radiology and Radiological Science, The Johns Hopkins University 18 School of Medicine, Baltimore, MD, United States, ⁶F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States

²³Na relaxation times and concentrations were measured in patellar cartilage with a clinical 3T MRI scanner. Because of the low resolution in ²³Na imaging, a focus was set on reducing the influence of synovial fluid. To estimate T₁ a biexponential two-compartment fitting model was applied. In T₂* measurements, an inversion pulse was used to suppress the signal from synovial fluid. ²³Na parameters were successfully determined and are in good accordance to literature results measured at higher field strengths.

Christian Licht¹, Lothar R. Schad¹, and Stanislas Rapacchi^2
1Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany, ²CRMBM, Aix Marseille University, CNRS, Marseille, France

Sodium (²³Na) MRI offers great potentials to be a clinical marker for disease states. Besides the single quantum signal, the triple quantum signal of ²³Na could provide novel and complementary information. 3D volumetric ²³Na multi-quantum coherences imaging, however, suffers from poor signal-to-noise ratios, which limit spatial resolution. Finer structures such as tissue boundaries are therefore barely observable. In addition, partial volume effects become more severe and diminish image quality as well as diagnostic applicability. The purpose of this work is to develop a reconstruction framework that addresses these shortcomings of ²³Na multi-quantum coherences imaging by utilizing ¹H prior constraints.

Frank Riemer¹, Marco Reisert², Bhavana S Solanky³, Claudia AM Wheeler-Kingshott^3,4,5, Golay Xavier³, Renate Grüner^1,6, and Ivan I Maximov^7
1MMIV, Haukeland University Hospital, Bergen, Norway, ²University Medical Center, Freiburg, Germany, ³UCL Queen Square Institute of Neurology, London, United Kingdom, ⁴Brain Connectivity Centre, IRCCS Mondino Foundation, Pavia, Italy, ⁵Department of Brain and Behavioural Sciences, University of Pavia, Pavia, Italy, ⁶Department of Physics and Technology, University of Bergen, Bergen, Norway, ⁷Western Norway University of Applied Sciences, Bergen, Norway

Due to quadrupolar interactions, 23Na exhibits a bi-exponential T2. Previous approaches to estimate T2* have relied on simple least squares approaches or treating it as an inverse problem. Here we present a fast method based on Bayesian estimation and illustrate it on an in vivo dataset.