Abstract
Purpose: T2 mapping and diffusion tensor imaging (DTI) enable the detection of changes in the skeletal muscle microenvironment. We assessed T2 relaxation times, DTI metrics, performed histological characterization of frostbite-induced skeletal muscle injury and repair, and provided diagnostic imaging biomarkers. Design and Methods: Thirty-six Sprague Dawley rats (200 ± 10 g) were obtained. Thirty rats were used for establishing a skeletal muscle frostbite model, and six were untreated controls. Functional MR sequences were performed on rats on days 0, 3, 5, 10, and 14 (n = 6 per time point). Rats were then sacrificed to obtain the quadriceps muscles. Tensor eigenvalues (λ1, λ2, and λ3), mean diffusivity (MD), fractional anisotropy (FA), and T2 values were compared between the frostbite model and control rats. ImageJ was used to measure the extracellular area fraction (EAF), muscle fiber cross-sectional area (fCSA), and skeletal muscle tumor necrosis factor α (TNF-α), and Myod1 expression. The correlation between the histological and imaging parameters of the frostbitten skeletal muscle was evaluated. Kolmogorov–Smirnoff test, Leven’s test, one-way ANOVA, and Spearman coefficient were used for analysis. Results: T2 relaxation time of frostbitten skeletal muscle was higher at all time points (p < 0.01). T2 relaxation time correlated with EAF, and TNF-α and Myod1 expression (r = 0.42, p < 0.05; r = 0.86, p < 0.01; r = 0.84, p < 0.01). The average tensor metrics (MD, λ1, λ2, and λ3) of skeletal muscle at 3 and 5 days of frostbite increased (p < 0.05), and fCSA correlated with λ1, λ2, and λ3, and MD (r = 0.65, p < 0.01; r = 0.48, p < 0.01; r = 0.52, p < 0.01; r = 0.62, p < 0.01). Conclusion: T2 mapping and DTI imaging detect frostbite-induced skeletal muscle injury early. This combined approach can quantitatively assess skeletal muscle repair and regeneration within 2 weeks of frostbite. Imaging biomarkers for the diagnosis of frostbite were suggested.
Highlights
MATERIALS AND METHODSThe classification of cold-exposure injuries is based on the depth of tissue involved in the injury, which is divided into four levels
The current study aimed to explore the value of T2 mapping and Diffusion tensor imaging (DTI) parameters for the noninvasive evaluation of skeletal muscle in a rat model of frostbite and to provide imaging biomarkers for the clinical diagnosis and treatment of patients with severe frostbite
There were more new muscle fibers in the remodeled skeletal muscle tissue, and these were irregular in shape
Summary
The classification of cold-exposure injuries is based on the depth of tissue involved in the injury, which is divided into four levels. Skeletal muscle frostbite belongs to grade 4 frostbite, which is the most serious form of frostbite (Ingram and Raymond, 2013). Frostbite-induced pathological changes, such as cellular edema, microcirculation disorders, and inflammation in skeletal muscle tissue can cause severe sensory dysfunction, amputation, or death. Muscle frostbite can lead to lifelong disability and even death, it does not attract as much academic interest as other muscle injuries. Clinicians lack precise diagnostic criteria for the extent and degree of frostbite in patients (Petrone et al, 2014). Surgeons may need weeks or months to wait for a clear boundary between living tissue and necrotic tissue to form before performing amputation (Woo et al, 2013)
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