Original ContributionQuantification of Muscle Volume by Echography: Comparison with MRI Data on Subjects in Long-Term Bed Rest
Introduction
Presently, muscle volume in humans is estimated by relatively simple and inaccurate anthropometric measurements (e.g., measuring the thigh perimeter at different levels) or with sophisticated, cumbersome and expensive magnetic resonance imaging (MRI) (Trappe et al. 2001b) or computed tomography (Radegran et al. 1999) methodologies. Quantifying muscle volume loss is critical for the treatment of sarcopenia (the age-related loss of muscle mass) and for assessing the recovery of muscle atrophy induced by immobilization after trauma or surgery. Accurate measurements of muscle volume are also important for humans travelling on long-duration space missions, such as on the International Space Station or future trips to the moon or other planets with reduced gravity. Our objective was to develop a new tool for assessing physiological and pathological changes in muscle volume that was accurate and could be used in the aforementioned populations more feasibly than the current approaches.
Because of its size, low cost and relative ease of use, echography could serve as such a tool to accurately measure human skeletal muscle volume. However, 3-D echographs do not have a sufficient scanning angle for insonating and measuring large parts of human muscles (i.e., muscle volume). Thus, we developed a mechanical probe holder that could move a 2-D probe along the muscles and measure muscle volume by scanning a dedicated part of the muscle. The system was validated on subjects in which muscle atrophy was induced by putting them in head-down bed rest (HDBR) for two months. The study was designed to mimic the undesirable effects of microgravity on the main physiological systems, including the cardiovascular and musculoskeletal systems, and to test exercise and nutritional countermeasures designed to prevent these effects.
Loss of muscle mass and function has been one of the hallmarks of exposure to real and simulated microgravity (Adams et al., 2003, Alkner and Tesch, 2004a, Alkner and Tesch, 2004b, Fitts et al., 2000, Fitts et al., 2001, Tesch et al., 2005, Trappe et al., 2001a). Muscle volume of the knee extensors decreases significantly after short and long-duration space flights (8 to 17 d: 5 to 15%; 112 to 196 d: 10%), despite exercise countermeasures and dietary control (caloric intake requirements). However, because of technical constraints, measurements (usually MRI) are restricted to before and after flight, with no “real time” indication of the efficacy of the prescribed countermeasures (LeBlanc et al. 2000). Ground-based studies show the knee extensor muscle volume loss approaches 20% over several months and can be partially or completely prevented with exercise countermeasures (Akima et al., 2001, Alkner and Tesch, 2004a, Alkner and Tesch, 2004b, Blottner et al., 2006, Gallagher et al., 2005, Tesch and Trieschmann, 2004, Trappe et al., 2004, Trappe et al., 2007).
The objective of this study was to determine the accuracy of an echographic method for measuring the change in leg muscle volume against the gold standard, MRI. Echographic and MRI measurements were performed on the same subjects before and at the end of two months of HDBR. Some of the subjects used exercise or nutritional countermeasures designed to reduce or prevent muscle atrophy.
Section snippets
Principle of the ultrasound muscle scanner
A conventional echographic probe (5 to 10 MHz sector array, Challenge 2000, Esaote, Firenze, Italy) was fixed on a probe holder fabricated by the investigators that moved continuously along two parallel metallic rails (25 cm long and 6 cm apart) via a small electric engine (Model: ESCAP, reference:26N58-216E1, brushed DC, 12v, 5.7w; by PORTESCAP Cie, La Chaux-de-Fonds Canton de Fribourg, Switzerland) (Fig. 1). The DC motor uses a rotor, of which the active part simply consists of a
Results
The system was tested in vitro on different soft materials (silicone cylinders and cubes, and pieces of beefsteak), and the error on the volume (100 to 500 cm3) was less than 3%. The volume of each piece was determined by measuring the water displacement caused by immersion and compared with the volume measured on the echographic views collected with the ultrasound scanner.
The VI and VM were investigated with the lowest part of the probe support in contact with the upper pole of the patella,
Discussion
The light probe holder (300 g) was easy to place and maintain on the thigh of the subjects during the scanning operation. One or two runs of the motorized probe holder were performed at high speed (5 cm/s) to confirm the muscle of interest was scanned appropriately, and one acquisition run (1.5 cm/s) was sufficient to collect the images for the muscle volume calculation. Automatic muscle edge detection significantly shortened the time required for measuring all of the muscle CSAs and ultimately
Conclusion
The muscle volume data measured by the echographic scanner confirmed the MRI data. That is, the echographic method tracked the muscle volume loss because of the bed rest, the prevention of muscle loss with the exercise countermeasure or the lack of influence of the nutrition countermeasure. The ultrasound scanner allowed the accurate evaluation of the volume change of various muscles by an easy and semi-automated method.
Acknowledgments
The study WISE-2005 was sponsored by the European Space Agency (ESA), the National Aeronautics and Space Administration of the USA (NASA), the Canadian Space Agency (CSA) and the French space agency “Centre National d'Études Spatiales” (CNES). The authors would like to thank the radiology staff at Rangueil Hospital (Virginie Lorite, Ghylene Enrique, Christine Mazars, Muriel Rogawski) for their efforts with this investigation and the sonographers of the Dept Med Nucl et Ultrasons (M. Porcher, V.
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