Prodromos Parasoglou^1,2, Ding Xia^1,2, Jill M Slade^3,4, and Ravinder R Regatte^1,2
1Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, ²Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, NY, United States, ³Department of Radiology, Michigan State University, East Lansing, MI, United States, ⁴Biomedical Imaging Research Center, Michigan State University, East Lansing, MI, United States

Defects in muscle efficacy can result from reduced blood supply, tissue oxygenation, and/or mitochondrial dysfunction. Phosphorus (31P) MR can noninvasively assess skeletal muscle bioenergetics, whereas microvascular function in muscle can be measured using BOLD MRI. However, given the limited tissue coverage of most 31P-MR approaches, the two measurements are typically obtained from different regions of the muscle. In this study, we implemented a high-resolution 31P-MRI method and combined it with BOLD MRI to obtain co-localized post-contractile microvascular and bioenergetics information in muscles of the lower leg of healthy subjects following plantar flexion.

Benjamin Marty^1,2, Pierre-Yves Baudin³, Noura Azzabou^1,2, Ericky C.A. Araujo^1,2, Pierre G. Carlier^1,2, and Paulo Loureiro de Sousa^4
1NMR laboratory, Institute of Myology, Paris, France, ²NMR laboratory, CEA/I2BM/MIRCen, Paris, France, ³Consultants for Research in Imaging and Spectroscopy, Tournai, Belgium, ⁴Université de Strasbourg, CNRS, ICube, FMTS, Strasbourg, France

Muscle inflammation and fatty infiltrations are indicators of disease activity and progression in neuromuscular disorders. They can respectively be assessed by muscle T2 relaxometry and water/fat separation techniques. T2 is often derived from multiecho spin-echo acquisitions and mono-exponential fitting. However, MSME signal rarely displays a pure spin-echo decay as it is a mix of refocused echoes and stimulated echoes. Recently, it has been proposed to process MSME signal using the Extended Phase Graph (EPG) algorithm to take into account stimulated echo. Here, we implemented a multi-component EPG-fitting to simultaneously quantify the muscle water T2 and fat fraction from MSME acquisitions.

Catherine DeBrosse¹, Ravi Prakash Reddy Nanga¹, Neil Wilson¹, Kevin D'Aquilla¹, Mark Elliott¹, Hari Hariharan¹, Felicia Yan², Leat Perez², Sara Nguyen², Elizabeth McCormick³, Marni Falk^3,4, Shana McCormack^2,4, and Ravinder Reddy^1
1Center for Magnetic Resonance and Optical Imaging, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States,²Division of Endocrinology and Diabetes, The Children's Hospital of Philadelphia, Philadelphia, PA, United States, ³Division of Human Genetics, The Children's Hospital of Philadelphia, Philadelphia, PA, United States, ⁴Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States

Patients with metabolic myopathies experience exercise intolerance due to oxidative phosphorylation (OXPHOS) defects. OXPHOS capacity is proportional to the recovery of phosphocreatine (PCr) after exercise, measured with ³¹P magnetic resonance spectroscopy (MRS). To maintain ATP during exercise, creatine (Cr) levels increase in proportion to PCr depletion. Therefore, OXPHOS can also be measured using the rate of Cr recovery. We have implemented an imaging technique with high spatial resolution and improved sensitivity over ³¹P MRS to measure Cr recovery: creatine chemical exchange saturation transfer (CrCEST). Using CrCEST, we observed differences in resting Cr levels and post-exercise recovery rates in patients vs. healthy subjects.

Benjamin Marty^1,2, Teresa Gerhalter^1,2, Ericky C.A. Araujo^1,2, Eric Giacomini³, and Pierre G. Carlier^1,2
1NMR laboratory, Institute of Myology, Paris, France, ²NMR laboratory, CEA/I2BM/MIRCen, Paris, France, ³UNIRS, CEA/I2BM/NeuroSpin, Gif-Sur-Yvette, France

The sodium ion is involved in a vast number of functions at the cellular level. Changes in sodium intracellular concentration or volume fraction indicate disorders that alter cell function/integrity or that are responsible for metabolic changes. Inversion-recovery and triple quantum filtration (TQF) methods have been previously proposed to discriminate intra- and extracellular Na+ signals. Here, we proposed a ²³Na MRS protocol to characterize skeletal muscle tissues in reasonable acquisition times and evaluated the sensitivity of different parameters (FID signal, TQF signal, TQF/FID ratio, T1 value, short T2* fraction) to differentiate various intracellular volume fractions conditions.

Jonathan David Kasper¹, Anne Tonson¹, Mike Klingler¹, Joshua Hubert¹, Ronald Meyer², and Robert Wiseman^2
1Physiology, Michigan State University, East Lansing, Michigan, United States, ²Physiology and Radiology, Michigan State University, East Lansing, Michigan, United States

Skeletal muscle is a thermodynamic system and its energetic state is determined by the magnitude of the mitochondrial redox, proton motive force, and ΔGATP potentials. Pyruvate dehydrogenase (PDH) flux is directly linked to NADH production and influences mitochondrial redox potential. This study sought to evaluate the effect of PDH activation on muscle energetics. Pharmacological activation of PDH results in elevation of steady state ΔGATP at rest and during stimulation below the aerobic threshold of muscle contraction. This effect is attributed to elevation of steady state redox potential and implicates PDH as an important site of regulation for skeletal muscle energetics.

Eric Edward Sigmund^1,2, Steven H. Baete^1,2, Thomas Luo², Karan Patel², Mary Bruno^1,2, David Mossa^1,2, David Stoffel^1,2, Alisa Femia³, Sarika Ramachandran³, Andrew Franks³, and Jenny Bencardino^4
1Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, NYU School of Medicine, NY, NY, United States, ²Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, NY, NY, United States, ³Department of Dermatology, NYU School of Medicine, NY, NY, United States, ⁴Department of Radiology, NYU School of Medicine, NY, NY, United States

Dermatomyositis (DM) is a degenerative condition needing diagnostic/prognostic biomarkers, which diffusion imaging may provide. We collected anatomic, Dixon, and static diffusion imaging (DTI, IVIM) at rest, and dynamic DTI (MEDITATE) before and after leg-lift exercise, in thigh muscles of DM patients and controls at 3 T. Static imaging reveals higher fat fraction in patients than controls, and in hamstrings, elevated diffusion metrics in patients vs. controls; however, regional heterogeneity exists. Dynamic imaging shows significantly larger exercise response of radial diffusion in patients than controls, with slower return to equilibrium. These markers may enhance diagnosis and predict treatment response in DM.

Hanne Hakkarainen¹, Galina Wirth¹, Petra Korpisalo-Pirinen¹, Seppo Ylä-Herttuala¹, and Timo Liimatainen^1,2
1University of Eastern Finland, A.I. Virtanen Institute for Molecular Sciences, Kuopio, Finland, ²Imaging Center, Kuopio University Hospital, Kuopio, Finland

T₂ and T_1ρ relaxation time constants were applied to differentiate areas of early regeneration in a mouse hind limb ischemia model. Percentages of areas having early signs of regeneration and areas of other tissue morphologies were determined based on T₂ and T_1ρ of the ischemic muscle cross section and correlations between histology derived percentages were calculated. Both T₂ and T_1ρ were able to detect the early regenerative areas making them potential markers of activation of regeneration of skeletal muscle tissue after ischemia.

Christopher D J Sinclair¹, Jasper M Morrow¹, Robert L Janiczek², Matthew R M Evans¹, Elham Rawah¹, Sachit Shah¹, Michael G Hanna¹, Mary M Reilly¹, Tarek A Yousry¹, and John S Thornton^1
1Institute of Neurology, University College London, London, London, United Kingdom, ²Experimental Medicine Imaging, GlaxoSmithKline, Uxbridge, Middlesex, United Kingdom

Measuring muscle-water T2 (T2w) independently of fat is increasingly important for detecting potentially reversible disease changes in imminent clinical trials. The IDEAL-CPMG sequence combines chemical-shift fat-fraction (f.f.) quantification with spin-echo T2 relaxometry in a single acquisition to determine T2w. Here we measured the scan-rescan reproducibility of IDEAL-CPMG T2w and f.f. in healthy individuals and applied it in a group of neuromuscular patients with periodic paralysis to determine the association between T2w and f.f.. Reproducibility was excellent and IDEAL-CPMG was sensitive to subtle T2w changes. There was a weak association between T2w and f.f., likely reflecting concurrent water and fat pathologies in this patient group.

Chengyan Wang¹, Rui Zhang², Xiaodong Zhang³, He Wang⁴, Kai Zhao³, Jue Zhang^1,2, Xiaoying Wang^1,3, and Jing Fang^1,2
1Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, Beijing, China, ²College of Enigneering, Peking University, Beijing, China,³Department of Radiology, Peking University First Hospital, Beijing, China, ⁴Philips Research China, Shanghai, Shanghai, China

The tissue oxygen extraction fraction (OEF) is an important physiological quantity, particularly in organs such as skeletal muscle, in which oxygen delivery and use are tightly coupled. The purpose of this study was to develop a reliable method to directly quantify regional skeletal muscle OEF at rest and during ischemia. The tissue oxygen extraction fraction (OEF) is an important physiological quantity, particularly in organs such as skeletal muscle, in which oxygen delivery and use are tightly coupled. The purpose of this study was to develop a reliable method to directly quantify regional skeletal muscle OEF at rest and during ischemia.

Ping Wang¹, Charles Nockowski², and John C Gore^1
1Vanderbilt University Institute of Imaging Science, Nashville, TN, United States, ²Philips Healthcare Technical Support at Vanderbilt, Nashville, TN, United States

In this study, we used an optimized GRE sequence to measure tissue sodium T1 and T2 in human calf muscle in vivo at 3T. The measured sodium T1 in calf is ¡Ö15.1ms, whereas the sodium short T2 component is ¡Ö1.8ms, and long T2 component ¡Ö28.7ms, which are in accord with literature reported values. These data permit the absolute determination of muscle sodium levels on a voxel by voxel basis in vivo.