Quantitative Ultrashort Echo Time MRI for Evaluation of Sciatic Nerve Degeneration and Regeneration in Rat Models

Background Evaluating peripheral nerve response after injury or repair remains a critical clinical challenge. Current medical imaging approaches provide limited insight into the degenerative or regenerative environment of affected nerves. Purpose To assess the efficacy of ultrashort echo time (UTE) quantitative MRI (qMRI) for evaluating peripheral nerve degeneration and regeneration in rat models of sciatic nerve injury and to assess correlations between UTE qMRI parameters and histologic findings. Materials and Methods In this animal study conducted from November 2022 to December 2023, four experimental groups were created in 6-8-week-old male Lewis rats: (a) sham injury (n = 16), where the sciatic nerve was exposed bilaterally at midthigh level but not transected; (b) injury/early autograft repair (n = 15), where a 10-mm nerve segment was excised, flipped, and resutured into the nerve gap; (c) injury/delayed isograft repair (n = 13), where nerves were transected, capped to prevent spontaneous regeneration, and repaired with a 10-mm isograft 2 months after injury; and (d) no repair, where nerves were capped after excising a 5-mm segment (n = 15). Rats underwent UTE qMRI with a 3-T scanner 1-3 months after surgery or repair. UTE magnetization transfer ratio (MTR), UTE T2*, and UTE T1 were compared using analysis of variance. Correlation analysis evaluated relationships between UTE qMRI-derived parameters and immunohistochemical outcomes. Results UTE MTR (P < .001), UTE T2* (P < .001), and UTE T1 (P < .001) showed lower values in early and delayed repair groups versus the sham group. UTE MTR showed excellent performance in distinguishing the sham group from early and delayed repair groups (mean area under the receiver operating characteristic curve, 0.93 ± 0.03). Histologic analysis demonstrated a moderate positive correlation between myelin area fraction and UTE MTR (r = 0.46; P = .007) and a weak negative correlation between collagen area fraction and UTE MTR (r = -0.38; P = .04). Conclusion UTE MRI-derived MTR effectively distinguished among rat models of peripheral nerve injury and repair and correlated with histologic findings. © RSNA, 2025 Supplemental material is available for this article. See also the editorial by Tan and Argentieri in this issue.