Steven Baete¹, Gene Cho^1,2, Jenny T. Bencardino³, and Eric E Sigmund^1
1Center for Biomedical Imaging, Dept. of Radiology, NYU Langone Medical Center, New York, New York, United States, ²Sackler Institute of Graduate Biomedical Sciences, NYU School of Medicine, New York, New York, United States, ³Department of Radiology, NYU Hospital for Joint Diseases, New York, New York, United States

The feasibility of dynamic single line acquisition of diffusion tensor parameters is demonstrated in a flow phantom and in in vivo skeletal muscle on a 3T clinical scanner. This method, Single Line Multiple Echo Diffusion Tensor Acquisition Technique SL-MEDITATE), encodes each of multiple echoes generated by five RF-pulses with different diffusion weighting. A single line is selected by orthogonal slice selective gradients. The resulting dynamic acquisition can be used to study the transient changes in diffusion tensor parameters, such as in muscle tissue following exercise, where traditional DTI methods lack temporal resolution.

Vaclav Brandejsky¹, Chris Boesch¹, and Roland Kreis^1
1Departments of Radiology and Clinical Research, University Bern, Bern, Switzerland

Purpose: To study apparent diffusivity and directionality for metabolites of skeletal muscle in humans by 1H-MRS. Methods: Diffusion tensors in tibialis anterior muscle oriented at the magic angle were determined at 3T using optimized methods including an adapted STEAM sequence and simultaneous fitting. Results: Apparent diffusivities and fractional anisotropies of taurine, creatine, trimethyl¬ammonium compounds, carnosine and water were estimated. The diffusivities of most metabolites and water were significantly different from each other. Diffusion was found to be anisotropic and the diffusion tensors to be essentially coaligned. Magnitudes of the diffusivities were largely ordered according to molecular weight.

Jae Mo Mo Park¹, Sonal Josan¹, Dirk Mayer², Ralph Hurd³, David Bendahan⁴, Daniel Spielman¹, and Thomas Jue^5
1Radiology, Stanford University, Stanford, CA, United States, ²Diagnostic Radiology and Nuclear Medicine, University of Maryland, Baltimore, MD, United States, ³GE Healthcare, Menlo Park, CA, United States, ⁴Centre de Resonance Magnetique Biologique et Medicale, Marseille, United States,⁵Biochemistry, UC Davis, Davis, CA, United States

In this study, we have directly followed hyperpolarized [1-13C]lactate in rat leg muscle in vivo to confirm that muscle can indeed metabolize exogenous lactate. Metabolic dynamics and 3D images were acquired at baseline and 1h after dichloroacetate. The fate of acetyl-CoA in mitochondria was further investigated using hyperpolarized [2-13C]pyruvate. The radically increased 13C-bicarbonate peak indicates pyruvate dehydrogenase (PDH) activation and a potential participation of lactate in the TCA cycle to support oxidative phosphorylation. Moreover, [2-13C]pyruvate experiment confirms that the up-regulated PDH activity results in increased pyruvate flow into the TCA cycle.

Andrew L Wentland¹, Emily J McWalter², Saikat Pal³, Scott L Delp³, and Garry E Gold^2,3
1Medical Physics, University of Wisconsin School of Medicine & Public Health, Madison, WI, United States, ²Radiology, Stanford University, Stanford, CA, United States, ³Bioengineering, Stanford University, Stanford, CA, United States

The purpose of this study was to create a novel tool for computing muscle forces non-invasively in vivo. Cross-sectional images of the forearms and lower legs of healthy volunteers were acquired with a fat/water separation technique as well as 2D phase contrast MRI during 1 Hz cycles of flexion/relaxation. Forces were derived from these images. Results indicate that this technique provides the ability to quantify inertial forces rather than applied forces. As a result, this technique provides the first known method for quantifying inertial forces. This analysis technique may be useful in evaluating muscle pathophysiology and further developing biomechanical models.

Prodromos Parasoglou¹, Ding Xia¹, and Ravinder R Regatte^1
1Radiology, NYU School of Medicine, New York, New York, United States

Phosphorus saturation transfer methods can assess the turnover rates of important metabolic reactions such as the adenosine triphosphate (ATP) synthesis/hydrolysis cycle. In this study, we focused on the development and implementation of an imaging method for simultaneously measuring the kinetics of ATP synthesis and the Pi-to-ATP fluxes in muscles of the lower leg. Mapping the kinetics of the ATP synthesis reaction and the Pi-to-ATP fluxes in several muscles of the leg using our imaging method could provide useful insights into the study of diseases such as insulin resistance and diabetes.

Kory W. Mathewson¹, Mark Haykowsky², and Richard B. Thompson^1
1Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada, ²Faculty of Rehabilitation, University of Alberta, Edmonton, Alberta, Canada

We propose a new imaging approach which interleaves complex-difference and susceptometry MRI acquisitions for real-time imaging of skeletal muscle blood flow (SMBF) and venous oxygen saturation (SvO2) for the calculation of skeletal muscle oxygen consumption (VO2). The goal of this study was to determine the reproducibility of this approach during sub-maximal knee-extensor exercise. The coefficient of variation from test/retest trials was 7.6%, 15.6% and 12.3% for SMBF, SvO2 and VO2, with mean values of 0.9±0.1L/min/kg, 43.2±13.5% and 95.7±18.0mL/min/kg respectively. To our knowledge, this is the first report of non-invasive skeletal muscle VO2 and its determinants (SMFB,SvO2) during dynamic exercise.

Rachel Bentley¹, Stuart R Gray², Christian Schwarzbauer¹, Dana Dawson³, Michael P Frenneaux³, and Jiabao He^1
1Aberdeen Biomedical Imaging Centre, University of Aberdeen, Aberdeen, Aberdeenshire, United Kingdom, ²Musculoskeletal Research Programme, University of Aberdeen, Aberdeen, Aberdeenshire, United Kingdom, ³Cardiovascular Research Programme, University of Aberdeen, Aberdeen, Aberdeenshire, United Kingdom

Dietary nitrate improves skeletal muscle metabolic efficiency, and might induce hypoxia dependent vasodilation and consequently augment oxygen delivery. We conducted dual echo gradient echo muscle fMRI study to evaluate tissue oxygenation during plantar flexion exercise at 15% and 25% maximum voluntary contraction (MVC). Significant decreases in maximal percentage change were found in soleus (p=0.004) and gastrocnemius (p=0.017) at 15% MVC, but not at 25% MVC. This reduction is primarily found in type 1 muscle groups at lower exercise intensity, indicating that dietary nitrate affects skeletal muscle via enhancements in mitochondrial function instead of vascular effects in young healthy subjects.