Table 1. Methods to assess skeletal muscle mass and muscle imaging.

	Method	Advantages	Limitations
Golden Standard	Magnetic resonance imaging (MRI)	High resolution Cross-sectional measurement of lean and fat mass areas in a specific part of the body Assessment of muscle quality	High cost Time-consuming image analysis High space requirements Technically difficult to perform
	Computerized tomography (CT)	Cross-sectional measurement of lean and fat mass areas in a specific part of the body Assessment of muscle quality	Exposure to radiations Time-consuming image analysis High space requirements Technically difficult to perform
	Creatinine excretion	Measure directly related to total body muscle mass	Time-consuming Diet restrictions the days before the urine collection Results not immediately available Complicated procedure Daily variation of creatinine excretion
Widely Used Measures	Dual energy X-ray absorptiometry (DEXA)	Low cost Widely available Sensitive and accurate method Estimates of lean, fat, and bone tissues in the entire body or in specific parts of it Does not require highly trained personnel	No information about muscle quality Space requirements Exposure to low dose radiation Possible biased results due to limited differentiation between water and bone-free lean tissue
	Bioelectrical impedance analysis (BIA)	Low cost Minimal maintenance Portable Results immediately available Does not require highly trained personnel	Results based on body resistance No measure of muscle quality Affected by hydration status Lower accuracy compared to other methods (i.e., MRI, CT, DEXA)
	Anthropometry	Low cost Easy to assess	Very limited accuracy No information about muscle quality Nutritional status and comorbidities can easily bias the results
Other Measures	Peripheral quantitative computerized tomography (pQCT)	Cross-sectional measurement of lean and fat mass areas in a specific part of the body Assessment of muscle quality Portable Does not require highly trained personnel	Images of a body part which may not be applicable to different body districts Limited accuracy compared to MRI or CT Originally designed to evaluate bone parameters, it has lower application on muscle Exposure to low dose radiation
	Ultrasound	Low cost Can assess specific muscles Valid and reliable	Needs trained personnel Difficulties assessing muscle quality Does not assess total body skeletal muscle mass
	Neutron activation	Estimate of overall skeletal muscle mass	High cost Limited validity Exposure to radiations Technically difficult to perform No information about muscle quality No information about specific body districts (e.g., limbs)