Ultrasound and magnetic resonance imaging are not interchangeable to assess the Achilles tendon cross-sectional-area
In the diagnosis of musculoskeletal disorders, there are several applications where both ultrasound and magnetic resonance imaging (MRI) may be considered viable alternatives. Because there are advantages and disadvantages to each imaging method, often it is unclear which should be considered for a specific indication. This article reviews this topic in the following manner. First, musculoskeletal applications where there are significant advantages for the use of ultrasound are discussed, which includes evaluation of soft tissue foreign bodies, peripheral nerves, pathologies that require dynamic imaging for diagnosis, and soft tissues adjacent to metal hardware. This is followed by a discussion of indications where both ultrasound and MRI may be considered, such as evaluation of a focal tendon abnormality, focal ligament abnormality, soft tissue fluid collection, and confirmation of a probable benign cyst, such as Baker's cyst and wrist ganglion. Musculoskeletal ultrasound should be viewed as an imaging method that complements MRI rather than one that competes with MRI in the evaluation of musculoskeletal abnormalities, as it can offer important information.