Jürgen Machann¹, Malte Niklas Bongers², Andreas Fritsche³, Hans-Ulrich Häring³, Mike Notohamiprodjo⁴, Andreas Greiser⁵, Konstantin Nikolaou⁴, and Fritz Schick^2
1Section on Experimental Radiology, Department of Diagnostic and Interventional Radiology, Institute for Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich, German Center for Diabetes Research (DZD), Tübingen, Germany, ²Section on Experimental Radiology, Department of Diagnostic and Interventional Radiology, University Hospital Tübingen, Tübingen, Germany, ³Department of Endocrinology and Diabetology, Angiology, Nephrology and Clinical Chemistry, Institute for Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich, German Center for Diabetes Research (DZD), Tübingen, Germany, ⁴Department of Diagnostic and Interventional Radiology, University Hospital Tübingen, Tübingen, Germany, ⁵Siemens Healthcare, Erlangen, Germany

¹H-MRS is increasingly applied in many organs for non-invasive tissue characterization, e.g. for quantification of ectopic lipids. Spectroscopic examinations of the myocardium often suffer from limited spectral dispersion, thus limiting the metabolic information content. Applying a new 60-channel body-array receive coil, high quality spectra with superior dispersion as compared to previous setups are shown in this work. A single voxel PRESS technique was applied in 10 subjects. After higher-order shimming, linewidths of <20 Hz were obtained with high SNR in a clinically acceptable measuring time. High reproducibility and performance of the method may promote 1H-MRS applications in metabolic research and sports medicine.

Ladislav Valkovic^1,2, William T Clarke¹, Benoit Schaller¹, Lucian A B Purvis¹, Stefan Neubauer¹, Ivan Frollo², Matthew D Robson¹, and Christopher T Rodgers^1
1Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, Oxford, United Kingdom, ²Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Bratislava, Slovakia

³¹P-MRS is of particular interest in cardiovascular medicine, as the PCr/ATP ratio can serve as a predictor of mortality. However, due to inherently low signal-to-noise ratio (SNR), cardiac ³¹P-MRS is not yet practical in the clinic. To increase SNR, the use of 7T and dedicated receive arrays has been proposed. However, the peak B₁⁺ was inadequate for the use of B₁ insensitive pulses, thus far. In this study, we demonstrate the feasibility of homogeneous adiabatic excitation for cardiac ³¹P-MRS using a novel quadrature ³¹P transceiver at 7T. This constitutes an important step towards absolute quantification of cardiac metabolites at 7T.

Ariane Fillmer^1,2, Andreas Hock^2,3, and Anke Henning^2,4
1Physikalisch Technische Bundesanstalt (PTB), Berlin, Germany, ²Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, ³Department of Psychiatry, Psychotherapy and Psychosomatics, Hospital of Psychiatry, University of Zurich, Zurich, Switzerland, ⁴Max Planck Institute for Biological Cybernetics, Tuebingen, Germany

¹H cardiac MRS is a promising tool for investigation of human heart disease. In this context the independent quantification of intramyocellular (IMCL) and extramyocellular lipids (EMCL) is desired. Quantification itself, however, remains challenging. This work investigates, whether quantification of metabolite signals within ¹H cardiac MR spectra could be improved by the use of prior knowledge about the behavior of metabolite signals in the quantification process.

William Thomas Clarke¹, Matthew D Robson¹, and Christopher T Rodgers^1
1Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, Oxford, United Kingdom

The creatine kinase (CK) forward rate constant k_f is a sensitive biomarker for heart failure. However, the low SNR of ³¹P-MRS at 1.5T and 3T has only allowed it to be measured at low spatial resolution by 1D-CSI. Here, we show how cardiac 7T ³¹P-MRS permits 3D resolved measurements for the first time. A 3D variant of the FAST k_f^CK method was combined with ³¹P Bloch-Siegert B₁⁺ mapping to enable 3D-resolved measurements at 7T. The first measurements of the creatine kinase rate in myocardium in the interventricular septum are obtained from four subjects. Our mean k_f = 0.36±0.04 s^-1 was consistent with literature values.

Maximilian Fuetterer¹, Christian Torben Stoeck^1,2, and Sebastian Kozerke^1,2
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, ²Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom

Second-order motion compensation for PRESS (PRESS^mc) is proposed to allow for robust single-voxel cardiac spectroscopy throughout the entire cardiac cycle. Motion-compensated spoiler gradients were designed and implemented into a cardiac-triggered PRESS sequence. A numerical 3D model of cardiac motion was used to optimize and validate the gradient waveforms. In-vivo measurements in healthy volunteers were obtained to assess SNR and triglyceride-to-water ratio (TG/W). SNR gains and variability of TG/W of PRESS^mc were evaluated against a conventional PRESS sequence with optimized gradients. PRESS^mc effectively reduces cardiac-motion induced signal degradation during FID spoiling providing higher SNR and less variability for TG/W quantification. 

Andreas Korzowski¹ and Peter Bachert^1
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany

The tissue–pH value is an important parameter to assess physiological function. The purpose of this work was to explore the potential of three-dimensional ³¹P–{¹H} echo–planar spectroscopic imaging at B₀ = 7 T for mapping of intracellular pH in the human calf muscle with high spatial resolution. The acquired data demonstrate that the proposed method allows the robust quantification of intracellular pH value of voxels with less than 1 ml volume and therefore may give insight into the pH heterogeneity of different muscle groups.

Sang-Young Kim^1,2, Wei Chen³, Dost Ongur², and Fei Du^1,2
1McLean Imaging Center, McLean Hospital, Harvard Medical School, Belmont, MA, United States, ²Psychotic Disorders Division, McLean Hospital, Harvard Medical School, Belmont, MA, United States, ³Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

 We demonstrates a novel strategy to simultaneously measure metabolites pool sizes and kinetic constants of CK/ATPase reactions using 31P-MST spectroscopy. Our method enables the corrections for T₁relaxation time and chemical exchanges effects due to short TR. The most important advantage of our proposed method is the reduction of TR for complete measurements of both metabolites ratios and reaction kinetics with high sensitivity. This can facilitate future applications requiring high temporal and/or spatial resolution. 

Bertrand Pouymayou¹, Tania Buehler¹, Roland Kreis¹, and Chris Boesch^1
1Depts. Radiology and Clinical Research, University of Bern, Bern, Switzerland

³¹P-MR spectroscopy inversion transfer (IT) is increasingly investigated as a complementary method to study ATP-synthesis and creatine kinase in vivo. Three aspects of the IT experiment are studied here, in a test-retest design (12 volunteers, resting vastus muscle): the ability to produce an efficient half band inversion in vivo with a short asymmetric adiabatic pulse, the repeatability of the kinetic parameters estimation at 3T and the impact of two different fitting strategies (individual spectrum vs. two-dimensional fitting). As a result, k[Pi>γ-ATP] can be reliably estimated within cohorts while k[PCr>γ-ATP] is accurate enough to be distinguished between individuals.

Brice Tiret^1,2, Vincent Lebon^1,2, Emmanuel Brouillet^1,2, and Julien Valette^1,2
1CEA/DSV/I2BM/MIRCen, Fontenay-aux-Roses, France, ²CNRS Université Paris-Saclay UMR 9199, Fontenay-aux-Roses, France

Localized ³¹P MRS with progressive saturation transfer was performed in the rat brain to estimate the exchange rate between inorganic phosphate (Pi) and adenosine-tri-phosphate (ATP). It was found that two Pi pools, tentatively intra and extracellular pools, can be resolved at 11.7 T, and that only the intracellular Pi signal varies with progressive saturation, while the extracellular Pi signal remains constant. Not resolving this extracellular Pi can cause a significant bias in the estimation of the forward constant rate of ATP synthesis.

Ladislav Valkovic^1,2,3,4, Marek Chmelík^1,2, Martin Meyerspeer^1,5, Borjan Gagoski⁶, Martin Krššák^1,2,7, Christopher T Rodgers⁴, Ivan Frollo³, Ovidiu C Andronesi⁸, Siegfried Trattnig^1,2,9, and Wolfgang Bogner^1,2
1High-field MR Centre, Medical University of Vienna, Vienna, Austria, ²Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria, ³Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Bratislava, Slovakia, ⁴Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, Oxford, United Kingdom, ⁵Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria, ⁶Fetal Neonatal Neuroimaging and Developmental Science Center, Boston Children's Hospital, Boston, MA, United States, ⁷Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria, ⁸Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States, ⁹Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna, Austria

Typically, only rough localization by the sensitive volume of the surface coil is used for dynamic ³¹P-MRS. However, such localization often mixes signals from several muscle groups. Available single-muscle localization techniques (e.g., semi-LASER or DRESS) provide only limited coverage and current ³¹P-MRSI techniques suffer from slow acquisition. To overcome the low temporal resolution of the standard ³¹P-MRSI, caused by slow Cartesian readout, we have developed, and tested in healthy subjects at 7T, a ³¹P-MRSI sequence using spiral readout trajectory. This sequence enables spatially resolved quantification of mitochondrial capacity in several investigated muscles (e.g., GM, GL and SOL) simultaneously at 7T.