Purpose: Intervertebral disc degeneration (IVDD), resulting in the depletion of hydrophilic glycosaminoglycans (GAGs) located in the nucleus pulposus (NP), can lead to debilitating neck and back pain. Magnetic Resonance Imaging (MRI) is a promising means of IVD assessment due to the sensitivity of MRI tissue relaxation properties to matrix composition. Furthermore, anomalous (i.e. non-monoexponential) relaxation models have shown higher sensitivity to specific matrix components compared to conventional monoexponential models. Here, we extend the use of the stretched exponential model, an anomalous relaxation model, to IVD relaxometry data. Theory and Methods: T1ρ and T2 relaxation data were measured in the cervical IVDs of healthy volunteers and IVDs adjacent to cervical fusion, and analyzed using both conventional and stretched-exponential (SE) models. Model differences were evaluated via goodness of fit in the healthy data. Normalized histograms of the resultant quantitative MRI (qMRI) maps were described using stable distributions, and data were compared across adjacent disc segments. Results: In the healthy IVDs, we found lower mean squared error in the SE relaxation model fitting behavior compared to monoexponential models, supporting anomalous relaxation behavior in healthy IVDs. SE model parameter αT1ρ increased level-wise in the caudal direction, especially in the nucleus pulposus, while conventional T1ρ and T2 monoexponential measures did not vary. For IVDs adjacent to cervical fusion, SE parameters deviated near the fusion site compared with those in the healthy population. Conclusion: SE modeling of T1ρ relaxation provides greater sensitivity to level-wise variation in IVD matrix properties compared with conventional relaxation modeling, and could provide improved sensitivity to early stages of IVD degeneration. The improved model fit and correlation between the SE αT1ρ parameter with IVD level suggests SE modeling may be a more sensitive method for detection of GAG content variation.

中文翻译：

---

椎间盘体内异常T1ρ和T2弛豫的拉伸指数模型

目的：椎间盘退变（IVDD），导致位于髓核（NP）内的亲水性糖胺聚糖（GAG）耗竭，可导致颈背疼痛和衰弱。由于MRI组织松弛特性对基质成分的敏感性，磁共振成像（MRI）是一种有前途的IVD评估方法。此外，与常规的单指数模型相比，异常（即非单指数）松弛模型显示出对特定矩阵成分的更高灵敏度。在这里，我们将拉伸指数模型（异常弛豫模型）的使用扩展到IVD弛豫测量数据。理论与方法：测量健康志愿者的宫颈IVD和邻近颈椎融合的IVD中的T1ρ和T2弛豫数据，并使用常规模型和扩展指数（SE）模型进行了分析。通过健康数据的拟合优度来评估模型差异。使用稳定的分布描述了所得定量MRI（qMRI）图的标准化直方图，并在相邻的椎间盘段之间比较了数据。结果：在健康的IVD中，我们发现SE松弛模型拟合行为的均方误差低于单指数模型，这支持了健康的IVD中异常的松弛行为。SE模型参数αT1ρ沿尾部方向逐级增加，特别是在髓核上，而常规的T1ρ和T2单指数度量没有变化。对于与宫颈融合术相邻的IVD，与健康人群相比，SE参数在融合部位附近偏离。结论：与常规弛豫建模相比，T1ρ弛豫的SE建模对IVD矩阵特性的逐级变化具有更高的敏感性，并且可以提高对IVD退化早期的敏感性。改进的模型拟合以及SEαT1ρ参数与IVD水平之间的相关性表明SE建模可能是检测GAG含量变化的更灵敏方法。