Nucleus pulposus structure and function assessed in shear using magnetic resonance elastography, quantitative MRI, and rheometry

IF 3.4 3区医学 Q1 ORTHOPEDICS

JOR Spine Pub Date : 2024-05-13 DOI:10.1002/jsp2.1335

Megan Co, Brian Raterman, Brett Klamer, Arunark Kolipaka, Benjamin Walter

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Abstract

Background

In vivo quantification of the structure–function relationship of the intervertebral disc (IVD) via quantitative MRI has the potential to aid objective stratification of disease and evaluation of restorative therapies. Magnetic resonance elastography (MRE) is an imaging technique that assesses tissue shear properties and combined with quantitative MRI metrics reflective of composition can inform structure–function of the IVD. The objectives of this study were to (1) compare MRE- and rheometry-derived shear modulus in agarose gels and nucleus pulposus (NP) tissue and (2) correlate MRE and rheological measures of NP tissue with composition and quantitative MRI.

Method

MRE and MRI assessment (i.e., T1ρ and T2 mapping) of agarose samples (2%, 3%, and 4% (w/v); n = 3–4/%) and of bovine caudal IVDs after equilibrium dialysis in 5% or 25% PEG (n = 13/PEG%) was conducted. Subsequently, agarose and NP tissue underwent torsional mechanical testing consisting of a frequency sweep from 1 to 100 Hz at a rotational strain of 0.05%. NP tissue was additionally evaluated under creep and stress relaxation conditions. Linear mixed-effects models and univariate regression analyses evaluated the effects of testing method, %agarose or %PEG, and frequency, as well as correlations between parameters.

Results

MRE- and rheometry-derived shear moduli were greater at 100 Hz than at 80 Hz in all agarose and NP tissue samples. Additionally, all samples with lower water content had higher complex shear moduli. There was a significant correlation between MRE- and rheometry-derived modulus values for homogenous agarose samples. T1ρ and T2 relaxation times for agarose and tissue were negatively correlated with complex shear modulus derived from both techniques. For NP tissue, shear modulus was positively correlated with GAG/wet-weight and negatively correlated with %water content.

Conclusion

This work demonstrates that MRE can assess hydration-induced changes in IVD shear properties and further highlights the structure–function relationship between composition and shear mechanical behaviors of NP tissue.

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利用磁共振弹性成像、定量磁共振成像和流变仪评估剪切力作用下的髓核结构和功能

背景通过定量磁共振成像（MRI）对椎间盘（IVD）的结构-功能关系进行活体量化，有可能有助于对疾病进行客观分层和评估修复疗法。磁共振弹性成像（MRE）是一种评估组织剪切特性的成像技术，它与反映成分的定量 MRI 指标相结合，可为 IVD 的结构-功能提供信息。本研究的目的是：(1) 比较琼脂糖凝胶和髓核（NP）组织中的 MRE 和流变学衍生剪切模量；(2) 将 NP 组织的 MRE 和流变学测量与成分和定量 MRI 相关联。方法对琼脂糖样品（2%、3% 和 4% (w/v)；n = 3-4/%）和在 5% 或 25% PEG（n = 13/PEG%）中平衡透析后的牛尾 IVD 进行 MRE 和 MRI 评估（即 T1ρ 和 T2 映像）。随后，对琼脂糖和 NP 组织进行了扭转机械测试，包括在 0.05% 的旋转应变下进行 1 到 100 Hz 的频率扫描。此外，还在蠕变和应力松弛条件下对 NP 组织进行了评估。线性混合效应模型和单变量回归分析评估了测试方法、琼脂糖或聚乙二醇百分比和频率的影响以及参数之间的相关性。结果在所有琼脂糖和 NP 组织样本中，MRE 和流变仪得出的剪切模量在 100 Hz 时均大于 80 Hz。此外，所有含水量较低的样本都具有较高的复合剪切模量。对于均质琼脂糖样品，MRE 和流变仪得出的模量值之间存在明显的相关性。琼脂糖和组织的 T1ρ 和 T2 松弛时间与这两种技术得出的复合剪切模量呈负相关。对于 NP 组织，剪切模量与凝胶体/湿重呈正相关，与含水率呈负相关。结论这项研究表明，MRE 可以评估水合引起的 IVD 剪切特性的变化，并进一步强调了 NP 组织的组成和剪切机械行为之间的结构-功能关系。

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