Ultrasound parameters used in muscle assessment, with main advantages and limitations
| Parameter | Definition | Site of assessment | Advantages | Limitations |
|---|---|---|---|---|
| Muscle thickness (MT) | Distance between the superficial and deep muscle fascia | Every muscular compartment (most studies on upper leg muscles) | Simple to measure High validity and reliability | Requires standardisation and fixed anatomic landmarks |
| Anatomical crosssectional area (ACSA) | Area of the muscle perpendicular to its longitudinal axis at the point of the largest muscle diameter | Any muscle compartment which can be wholly visualised by ultrasound | Studies have shown high validity and reliability Demonstrated diagnostic accuracy of varying degrees for sarcopenia and low muscle mass | Requires standardisation and fixed anatomic landmarks |
| Physiological crosssectional area (PCSA) | Area of the muscle perpendicular to the course of its muscle fibers at the point of the largest muscle diameter | Muscle strength can be inferred from PCSA | ||
| Echo intensity (EI) | Median brightness of ultrasound image, expressed in gray scale (0–255) | Every muscle compartment | Provides information regarding the degree of intramuscular fatty infiltration | Requires standardisation Measurements may be influenced by various external factors (e.g. ultrasound image settings, probe tilt, patient rest duration, participant positioning, patient’s hydration status, subcutaneous adipose tissue etc) |
| Fascicle length (FL) | Length of the fascicular path between the insertions of the fascicle into the superficial and deep muscle aponeuroses | Pennate muscles (mostly of the lower limb) | Provides information regarding the maximum force and speed of muscle fiber contraction Related to the force generating capacity of the muscle and muscle function | Requires specific operator training Accuracy of measurements are highly dependent on correct measurement technique (e.g. joint position, muscle contraction during measurement, probe placement on the skin, probe orientation relative to the muscle fiber course etc. |
| Pennation angle (PA) | Angle of insertion of muscle fiber fascicles into the deep aponeurosis | |||
| Contrast enhanced ultrasound (CEUS) | Used to assess the degree of muscle vascularisation | Muscles of upper leg, most commonly quadriceps femoris | Provides information on changes of muscle vascularization, which has been shown to be a contributing factor in sarcopenia pathogenesis | Requires specific operator training and the use of contrast agents The utility of this method in the clinical setting is still unclear |