Magnetic Resonance Compatible Knee Extension Ergometer.

Area of Science:

• Biomedical Engineering
• Musculoskeletal Physiology
• Magnetic Resonance Imaging

Background:

• Studying muscle metabolism noninvasively requires precise mechanical measurements during contractions.
• Existing MR-compatible ergometers lack adequate torque and velocity control for accurate isotonic and isokinetic assessments.
• Integrating precise control mechanisms with MR compatibility presents a significant engineering challenge.

Purpose of the Study:

• To design and evaluate a novel MR-compatible ergometer capable of precise torque and velocity control.
• To enable accurate metabolic energy measurements in contracting lower limb muscles using MR spectroscopy.
• To overcome the limitations of current ergometers in providing controlled mechanical conditions within a 3 Tesla magnetic field.

Main Methods:

• Development of an MR-compatible ergometer with a passive, non-ferrous component inside the scanner bore and an active, external component outside the magnetic field.
• Utilizing a waveguide to transmit control signals and power between the external active component and the internal passive component.
• Implementing torque and velocity controllers for knee joint movements, operating up to 420 N·m and 270°/s, respectively.
• System and human subject evaluations to assess mechanical performance under controlled conditions.

Main Results:

• The developed ergometer operates effectively within a 3 Tesla magnetic field.
• Mechanical performance evaluations demonstrated high accuracy, with mean percent errors below 9% for isotonic contractions.
• Human subject evaluations showed excellent precision, with mean percent errors below 2% for isokinetic contractions.
• The design successfully separates active electronics from the MR environment, maintaining compatibility.

Conclusions:

• The novel MR-compatible ergometer provides precise torque and velocity control for studying muscle metabolism.
• This device facilitates accurate isotonic and isokinetic measurements during MR spectroscopy, enhancing muscle physiology research.
• The design overcomes previous limitations, offering a valuable tool for noninvasive muscle energy assessment in advanced MR environments.