Purpose To confirm the interest of 3-dimensional ultrashort echo-time (3D-UTE) sequences to assess morphologic aspects in normal and pathological Achilles entheses in a rat model of spondyloarthropathy (SpA) with histological correlations, in comparison with conventional RARE T2 Fat-Sat sequences, and, furthermore, to evaluate the feasibility of a 3D multiecho UTE sequence performed before and after the intravenous injection of ultrasmall superparamagnetic iron oxide (USPIO) particles to assess macrophagic involvement in the Achilles enthesis in the same rat model of SpA. Materials and Methods Fourteen rats underwent in vivo MRI of the ankle at 4.7 T, including a 3D RARE T2 Fat-Sat sequence and a 3D ultrashort echo-time (UTE) sequence for morphologic assessment at baseline and day 3 after induction of an SpA model, leading to Achilles enthesopathy in the left paw (right paw serving as a control). A 3D multiecho UTE sequence was also performed at day 3 before and then 24 (4 rats) and 48 (2 rats) hours after intravenous injection of USPIO. Visual analysis and signal intensity measurements of all images were performed at different locations of the Achilles enthesis and preinsertional area. Visual analysis and T2∗ measurements were performed before and after USPIO injection, on the 3D multiecho UTE sequence in the same locations. Normal and pathological values were compared by Wilcoxon signed-rank tests. MR findings were compared against histological data. Results 3D-UTE sequences enabled morphologic identification of the anterior fibrocartilage and posterior collagenic areas of the Achilles enthesis. Visual analysis and signal intensity measurements distinguished SpA-affected entheses from healthy ones at day 3 (P=0.02). After administration of USPIO, no differences in signals were detected. Similarly, both visual analysis and signal T2∗ measurements in the enthesis were unable to distinguish the SpA-affected tendons from healthy ones (P=0.914). Neither the normal anatomy of the enthesis nor its pathological pattern could be distinguished using the standard RARE sequence. Histology confirmed the absence of USPIO in Achilles entheses, despite marked signs of inflammation. Conclusion Unlike conventional RARE T2 Fat-Sat sequences, 3D-UTE sequences enable morphologic assessment of normal enthesis anatomy and early detection of abnormalities in pathological conditions. However, 3D multiecho UTE sequences combined with USPIO injections with T2∗ measurements were unable to detect macrophagic involvement in these pathological conditions.

中文翻译：

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脊柱关节病小鼠模型中的早期跟腱附着：巨噬细胞检测中超短回波时间序列的形态成像和超小超顺磁性氧化铁 (USPIO) 颗粒评估。

目的 与传统的 RARE T2 Fat- 相比，确认 3 维超短回波时间 (3D-UTE) 序列对评估脊柱关节病 (SpA) 大鼠模型中正常和病理性跟腱附着点形态学方面的兴趣，并具有组织学相关性。 Sat 序列，此外，评估静脉注射超小超顺磁性氧化铁 (USPIO) 颗粒之前和之后进行的 3D 多回声 UTE 序列的可行性，以评估同一 SpA 大鼠模型中跟腱附着点的巨噬细胞参与情况。材料和方法 14 只大鼠在 4.7 T 下接受踝关节体内 MRI，包括 3D RARE T2 Fat-Sat 序列和 3D 超短回波时间 (UTE) 序列，用于基线和诱导 SpA 模型后第 3 天的形态学评估，导致左爪跟腱附着病（右爪作为对照）。还在静脉注射 USPIO 之前第 3 天以及静脉注射 USPIO 后第 24 小时（4 只大鼠）和 48 小时（2 只大鼠）进行 3D 多回波 UTE 序列。所有图像的视觉分析和信号强度测量均在跟腱附着点和插入前区域的不同位置进行。在注射 USPIO 之前和之后，对相同位置的 3D 多回波 UTE 序列进行视觉分析和 T2* 测量。通过 Wilcoxon 符号秩检验比较正常值和病理值。将 MR 结果与组织学数据进行比较。结果 3D-UTE 序列能够对跟腱附着点的前纤维软骨和后胶原区域进行形态学识别。第 3 天时，视觉分析和信号强度测量将受 SpA 影响的附着点与健康附着点区分开来（P=0.02）。施用 USPIO 后，未检测到信号差异。同样，视觉分析和附着点信号 T2* 测量都无法区分受 SpA 影响的肌腱和健康肌腱 (P=0.914)。使用标准 RARE 序列无法区分附着点的正常解剖结构及其病理模式。尽管有明显的炎症迹象，但组织学证实跟腱附着处不存在 USPIO。结论 与传统的 RARE T2 Fat-Sat 序列不同，3D-UTE 序列能够对正常附着点解剖结构进行形态学评估，并早期检测病理状况的异常。然而，3D 多回波 UTE 序列与 USPIO 注射和 T2* 测量相结合，无法检测到这些病理条件下巨噬细胞的参与。