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Muscle pain related to exertion is common and the severity and significance can be difficult to assess clinically. Before magnetic resonance imaging (MRI) was available, scintigraphy, ultrasound, and computed tomography (CT) were used to evaluate muscle trauma.1-7 MRI is now considered the primary imaging modality for detecting muscle injury and for determining the type of injury and degree of muscle involvement.8-10 It is highly sensitive to muscle edema and hemorrhage and can therefore be of aid in evaluating muscle injury. Because MRI is sensitive to tissue alteration not apparent clinically, it can also aid in optimal management of patients following trauma, and can be used to identify various sequelae.
TECHNICAL CONSIDERATIONS
Normal skeletal muscle is characterized by an intermediate to low signal intensity on MRI. This is due to an intermediate to long Tl relaxation time and a relatively short T2 relaxation time. MRI is sensitive to acute and chronic changes in muscle water content that occur with muscle injury.11-14 Various types of muscle injury, including necrosis, strain, and delayed onset muscle soreness (DOMS) are associated with an increase in T2 relaxation time and spin density,12,13,15,16 while Tl relaxation times can vary. Because of this, muscle injuries are more conspicuous on short tau inversion recovery (STIR) and T2-weighted MRI sequences, which optimize the contrast between processes such as edema or more acute stages of hemorrhage and intact muscle.
A short TR/TE sequence (Tl weighting) is useful for identifying and characterizing processes that have a short Tl relaxation time such as subacute hematoma (which contains methemoglobin), interstitial hemorrhage, and fatty infiltration. Tl weighting is also utilized for assessment of architectural distortion of muscle. Signal intensity may be slightly increased or decreased (if there is fibrosis) in injured muscle on Tl weighting. At times, the lesion is isointense with muscle on Tl weighting and is not detected.16
The body coil is used for examination of larger structures such as the upper thigh and when comparison with the opposite side is indicated. Comparison views aid in detecting both alterations in muscle size and signal intensity. For localized muscle injury in the extremities, an extremity coil is used. The added signal to noise allows for higher spatial resolution, which demonstrates fine detail in subtle lesions. If there is...