Novel MRI-Guided Ultrasound Equations for Whole-Body Muscle Mass in Caucasian Adults.

A cohort of 211 healthy Caucasian adults was enrolled for whole-body MRI and ultrasound examinations to develop and validate muscle mass estimation equations.

• Participants had a median age of 42.0 years (interquartile range 29.0–58.0) and were 52% female.
• Eight muscle thicknesses and seven cross-sectional areas (CSAs) were assessed across the right arm, trunk, and leg.
• The sample was divided into a development group (two-thirds) and a cross-validation group (one-third).
• Stepwise multiple regression was used to establish ultrasound equations in the development group, which were then cross-validated.

The most accurate ultrasound equation for estimating whole-body muscle mass achieved an adjusted R2 of 0.942 and a standard error of estimate (SEE) of 1.7 kg.

• This model included ultrasound muscle thickness measurements of the forearm extensor, rectus abdominis, rectus femoris, biceps femoris, and tibialis anterior muscles.
• CSA measurements of the triceps brachii and tibialis anterior muscles were also included.
• Additional predictors in the model were sex, weight, and BMI.
• MRI served as the reference standard for whole-body muscle mass.

A more practical, simplified ultrasound equation was developed that requires fewer measurements while still providing good predictive accuracy.

• This simplified model achieved an adjusted R2 of 0.927 and an SEE of 2.0 kg.
• The practical equation focused on ultrasound muscle thickness and CSA of select arm, abdominal, and leg muscles, combined with sex and height.
• The authors described this model as offering 'a good balance between accuracy and measurement burden.'
• The trade-off compared to the most accurate model was a reduction in adjusted R2 from 0.942 to 0.927 and an increase in SEE from 1.7 kg to 2.0 kg.

Models combining muscle thickness and CSA measurements demonstrated improved prediction accuracy compared to models using muscle thickness alone.

• Combined models showed higher adjusted R2 values and lower SEE compared to thickness-only models.
• The authors concluded that this finding supports the inclusion of CSA in future applications of ultrasound-based muscle mass estimation.
• Seven CSAs were assessed across the right arm, trunk, and leg alongside the eight muscle thickness measurements.

Ultrasound was investigated as a cost-effective, non-invasive alternative to MRI for assessing surrogates of muscle mass, including muscle thickness and cross-sectional area.

• Accurate measurement of muscle mass was identified as challenging despite its importance as a critical indicator of health and functionality.
• MRI was used as the reference standard for whole-body muscle mass throughout the study.
• The study population was restricted to healthy Caucasian adults, which defines the intended applicability of the developed equations.