Muscle matters: Transforming the care of intensive care unit acquired sarcopenia and myosteatosis

Table 1 Imaging modalities for intensive care unit muscle assessment

Technique	Parameters measured	Advantages	Limitations	Clinical utility
CT scan	Skeletal muscle CSA; muscle attenuation (density)	Accurately quantifies muscle/adipose tissue, visualizes muscle quality, and serves as the reference standard for sarcopenia diagnosis	Requires radiation and ICU transport, unsuitable for frequent reassessments, costly, and limited to opportunistic snapshots	Baseline risk stratification using CT-derived low muscle mass predicts worse outcomes and has been correlated with mortality and ICU length of stay
Ultrasound	Muscle thickness; CSA; echo-intensity (grayscale)	Bedside, portable, radiation-free, low-cost, repeatable for monitoring, and assesses limb and respiratory muscles in real time	Operator-dependent, limited to specific muscles, and affected by edema or obesity	Enables monitoring of muscle wasting, early detection of ICU-acquired loss, and assessment of diaphragm and peripheral muscles to guide rehabilitation
Magnetic resonance imaging	Muscle volume; detailed anatomy and composition	Provides highly accurate muscle volume and fat measurement without radiation	Infeasible in critically ill due to transport, time, cost, and contraindications with ICU devices or instability	Used in research to study muscle architecture; rarely applied clinically in ICU due to logistical constraints
Dual-energy X-ray absorptiometry scan	Lean body mass; appendicular muscle mass via dual X-ray absorption	Gold standard for body composition and precise in diagnosing chronic sarcopenia	Requires transport, affected by fluid shifts, involves low radiation, and unsuitable for ICU monitoring	Useful for nutritional assessment post-ICU or in research; impractical during acute ICU stay
Bioelectrical impedance analysis	Total body water, estimated fat-free mass (via electrical impedance)	Bedside, quick, non-invasive, and portable	Assumes normal hydration; inaccurate with fluid imbalance, vasopressors, edema, or position changes	Limited in ICU; useful for trend tracking by nutrition teams but confounded by fluid shifts

CT: Computed tomography; CSA: Cross-sectional area; ICU: Intensive care unit.