Table 2.

Advantages and limitations of the two different modalities (MRI and US), used in estimation of skeletal muscle mass (adapted from [55])

Technique	Advantages	Limitations
MRI	No radiation exposure	High equipment costs
	Good for imaging soft tissues	Time consuming
	Able to review images after scanning	Limited accessibility for frail community-based patients and those with cognitive impairment
	Thorough image acquisition	Confined space in scanner
	Body mass composition differentiation	Low availability
		No definite low muscle mass thresholds
	High spatial resolution	Cannot use if patient has metal work/some pacemakers
	Accuracy
	Suitable for long-term follow-up, progression monitoring	Requires interpretation by radiologist
	Capable of detecting changes in muscle structure	Lack of standardized assessment protocol
	Cross-sectional imaging	Longer image acquisition time, complex post-processing
	Muscle edema and myosteatosis detection	Lack of portability
		Complex post-processing
		Controindications
US	Extremely safe	Variety of probes required to achieve varying depth/resolution
	Low cost
	No radiation exposure	Limited use in obese patients
	Ability to perform dynamic testing	Operator skills required
	Portable	Low reproducibility
		Low accuracy
	Cost-effective	No criteria for diagnosis of low muscle mass
		Fixed anatomical landmarks needed
	Quick to perform (short image acquisition time)	Correlation with functional parameters still unclear
	Suitable in all patient groups	Results depending on the type of software used to interpret images
	Can be interpreted at bedside by a lay sonographer (real-time imaging)	Studies focused on elderly subjects are lacking