Reliability and validity of quantifying absolute muscle hardness using ultrasound elastography

Area of Science:

• Biomechanics
• Medical Imaging
• Musculoskeletal Research

Background:

• Muscle hardness, a measure of transverse muscle stiffness, is crucial for understanding muscle function.
• Previous quantitative methods for muscle hardness using ultrasound elastography lacked complete reliability and validity verification.

Purpose of the Study:

• To rigorously verify the reliability and validity of a quantitative ultrasound elastography method for absolute human muscle hardness measurement.
• To assess the method's accuracy in both in vitro and in vivo settings.

Main Methods:

• Ultrasound elastography was used to quantify Young's moduli of tissue-mimicking materials (20-80 kPa) and the medial gastrocnemius muscle.
• A strain/Young's modulus ratio derived from two reference materials (7 and 30 kPa) was employed for calculations.
• Intra- and inter-investigator reliability was assessed using coefficient of variations and intraclass correlation coefficients.

Main Results:

• The method demonstrated high reliability with low coefficients of variation (≤6.9%) and high intraclass correlation coefficients (≥0.77).
• A strong correlation (0.996) was found between ultrasound elastography and mechanical methods for tissue-mimicking materials.
• In vivo measurements of medial gastrocnemius muscle Young's moduli aligned with previously reported magnetic resonance elastography values.

Conclusions:

• The reliability and validity of the quantitative ultrasound elastography method for absolute muscle hardness measurement are confirmed.
• This validated method offers a promising tool for non-invasive assessment of muscle mechanical properties.