Muscle Changes Detected with DTI after Long-Distance Running

Diffusion-tensor imaging (DTI) may help detect muscle changes over time that are not revealed by qualitative T2-weighted MR imaging with fat suppression, according to a recent study from the Netherlands.

The researchers developed a method for obtaining DTI 3-D measurements of the upper leg—from hip to knee and fully including the hamstring and other frequently injured muscles—in a single imaging session. The study was published in the February 2015 issue of Radiology.

"Our method revealed subtle changes in DTI-derived parameters of muscle that occurred during marathon running, which were still measurable after three weeks," said the study's lead author Martijn Froeling, Ph.D., a postdoctorate student at University Medical Center Utrecht at Utrecht University in the Netherlands. "The elevated mean diffusivity, which was still present after three weeks, might be related to the natural disease course of fatigue-induced muscle disorders."

Dr. Froeling and his colleagues performed a feasibility study with five male amateur long-distance runners who were evaluated one week before, two days after and three weeks after they participated in a marathon. The athletes underwent a 3-T MR examination of both upper legs at each time point. Data were acquired in three 40-section stacks with a five-section overlap by using a moving table approach without repositioning the coil. DTI data gave researchers the three tensor eigenvalues, the mean diffusivity and the decreased fractional anisotropy (FA).

Using T2-weighted images with fat suppression, a musculoskeletal radiologist graded signs of muscle injury. The injuries were graded as 0 (no abnormalities); 1 (mild swelling and edema with no discontinuities of the muscle tissue); 2 (partially ruptured muscle tissue); or 3 (complete disruption of the muscle tissue).

The radiologist also recorded the location, specific muscle, craniocaudal and axial length of the edema and/or hemorrhage. Six muscles in both upper legs were manually segmented based on the T1- and the T2-weighted images.

T2-weighted images revealed grade 1 muscle strains in nine of the 180 muscles investigated after the marathon. Two days after running, the biceps femoris muscle showed significant increases in all three diffusion eigenvalues and mean diffusivity. Mean diffusivity and two of the eigenvalues were significantly increased in the semitendinosus and the gracilis muscles when measured two days after the marathon.

"These findings might be related to a high risk for injury in biceps femoris and semitendinosus muscles during long-distance running," Dr. Froeling said. He added that researchers could visualize the change of diffusion parameters by projecting them on the 3-D fiber tractography results.

DTI Could Be Relevant in Sports Injury Prognosis and Treatment

"The increase of mean diffusivity and decrease of FA after the marathon indicate that water diffusion is less restricted, which can be related to interstitial edema, cell swelling or the disruption of diffusivity barriers from muscle injury, " said Aart Nederveen, Ph.D., a medical physicist at the Academic Medical Center at the University of Amsterdam, the Netherlands, who supervised the project.

"The invisible damage may be the early part of the continuum of muscle damage related to injury," Dr. Nederveen said. "We believe that DTI parameters will become diagnostically relevant for prognosis and treatment of sports-related muscle injury."

The researchers also learned that the combination of muscle fiber tractography, diffusion parameters and anatomic MR imaging provides insight into physiologic changes in muscle up to three weeks after running.

"DTI may eventually allow for design of personalized rehabilitation programs," Dr. Froeling said. "The method could be especially useful in longitudinally evaluating athletes after muscle injury and could give a better prognosis when affected muscle function is restored."

DTI protocol allowed investigators to evlaluate subclinical muscle changes in the upper legs of long-distance runners that were otherwise not detectable on conventional T2-weighted MRI.

"DTI may even serve as an imaging biomarker in tailoring training; however, for DTI to become a routine clinical tool for assessment of muscle injuries, reference values and prospective studies are needed," Dr. Nederveen said.