Dutch researchers have developed an mpMRI protocol that found significant changes in mean diffusivity and other key measurements in both whole and localized muscle evaluations immediately after the long-distance run, which indicated micro muscle damage. Those changes, however, returned to normal two weeks after the event.
"Because we found that changes were more pronounced in specific muscles and muscle parts, it indicates that muscle trauma is not homogeneously distributed along the muscle length," said lead author Melissa Hooijmans, PhD, from the Amsterdam University Medical Centers. "It is something we would assume since muscles are not used homogeneously along the length of the muscle."
Musculoskeletal injuries are the most prevalent in recreational and elite sports. One of the most common types of damage is acute trauma caused by a single adverse event with clear clinical symptoms. The other type of injury is repetitive microtrauma, also known as an overuse injury, which results from the frequent use of muscles.
Generally, conventional T2-weighted MR images are used to diagnose muscle injuries. However, that approach often cannot detect micro muscle nor can it effectively monitor recovery.
"Quantitative methods, such as diffusion-tensor imaging (DTI) and T2-weighted quantification (qT2), have shown promise for the detection of muscle microtrauma and phases of muscle recovery," Hooijmans told ISMRM attendees. "However, both of these techniques are sensitive to a wide variety of processes, and using a single readout is not sufficient to correctly diagnose muscle injury."
Given those deficiencies, the researchers set out to develop and test a quantitative mpMRI approach to characterize exercise-induced microtrauma and recovery in individual upper leg muscles.
Hooijmans and colleagues enrolled 11 marathon runners (mean age, 51 years; range 50 to 56 years) in the study who underwent 3-tesla MRI scans (Ingenia, Philips Healthcare) with a 16-channel anterior and 12-channel posterior receiver coil. The exams were performed at three different time points: one week before the marathon, 24 to 48 hours after the run, and two weeks after the event.
The mpMRI protocol included a multi-echo spin-echo (MSE) sequence, a spin-echo diffusion-weighted MR imaging (DWI) sequence, a four-point Dixon sequence for anatomical reference, and a T2-weighted spectral presaturation with inversion recovery (SPIR) sequence.
While analyses were performed on eight main upper leg muscles, the researchers particularly focused on the biceps femoris long head, which is most frequently injured in such cases, and the vastus medialis, which is often spared in these types of injuries. The two muscles were divided into five equal segments to better assess the extent of localized damage. Muscles with insufficient signal-to-noise ratios or that showed overt injury were excluded from further analysis.
In the whole muscle analysis of the MRI data, the researchers found that mean diffusivity significantly increased right after the marathon but returned to baseline values at the two-week follow-up (range, 0 mm2/s to 3 mm2/s; p < 0.001). The biceps femoris long head, semitendinosus, and all quadriceps muscles contributed most significantly to the changes. In addition, qT2 values remained significantly lower after the marathon and at the two-week follow-up (p = 0.002).
The localized muscle assessment of mean diffusivity and qT2 values showed more pronounced effects immediately after the marathon, increasing as much as 15%, compared with baseline numbers and whole volume measurements.
For example, the researchers noted a significant mean diffusivity time effect in all five vastus medialis segments (p < 0.003) and in two of five biceps femoris long head muscle segments (p < 0.001). By comparison, they found a significant time effect for qT2 values in only one of five biceps femoris long head muscle segments (p < 0.003).
"Importantly, absence of clear T2 or perfusion effects suggests that [mean] diffusion parameters are more sensitive to detect muscle damage," the researchers wrote in their abstract. "It indicates that the changes in diffusion parameters post-marathon reflect changes in muscle microstructure rather than edema or perfusion."
In conclusion, Hooijmans and colleagues noted that this mpMRI approach is "essential to understand the underlying pathophysiology of muscle injury and recovery and could prove valuable for improved outcome prediction and risk assessment of sports-related injuries.