利用超高场（7T）Z 谱 MRI 检测大鼠骨髓脂肪含量随年龄的早期变化。
Early detection of increased marrow adiposity with age in rats using Z-spectral MRI at ultra-high field (7 T).
机构信息
School of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China.
Guangdong Provincial Key Laboratory of Medical Image Processing, Southern Medical University, Guangzhou, Guangdong, China.
出版信息
NMR Biomed. 2022 Feb;35(2):e4633. doi: 10.1002/nbm.4633. Epub 2021 Oct 18.
BACKGROUND
Nowadays, the drive towards high-field MRI is fueled by the pursuit of higher signal-to-noise ratio, spatial resolution, and imaging speed. However, high field strength is associated with field inhomogeneity, acceleration of T * decay, and increased chemical shift, which may pose challenges to conventional MRI for fat quantification in complex tissues such as bone marrow. With proton MRI spectroscopy ( H-MRS), on the other hand, it is difficult to produce high resolution. As a novel alternative fat quantification method, high-resolution Z-spectral MRI (ZS-MRI) can achieve fat quantification by acquiring direct saturated images of both fat and water under the same T , which may be less affected by T * decay and field inhomogeneity.
PURPOSE
To demonstrate ZS-MRI for marrow adipose tissue (MAT) quantification in rat's lumbar spine and the early detection of MAT changes with age.
METHODS
The accuracy of ZS-MRI for fat quantification at ultra-high-field MRI (7 T) was verified with MRS and conventional Dixon MRI in water-oil mixed phantoms with varying fat fraction (FF). Dixon MRI data were processed with iterative decomposition of water and fat with echo asymmetry and least-squares estimation. ZS-MRI was then used to longitudinally monitor the adiposity in the lumbar spine of young healthy rats at 13, 17, and 21 weeks to detect the early changes of FF with age in MAT. Hematoxylin-eosin staining of lumbar spines from separated rat groups was performed for verification.
RESULTS
In ex vivo phantom experiments, both Dixon MRI and ZS-MRI were well correlated with H-MRS for the quantification of FF at 7 T (R > 0.99). Compared with Dixon MRI, ZS-MRI showed reduced image artifacts due to field inhomogeneity and presented better agreement with H-MRS for the early detection of increased MAT due to age at 7 T (ZS-MRI R = 0.78 versus Dixon MRI R = 0.34). The increased MAT FF due to age was confirmed by histology.
CONCLUSION
ZS-MRI proves itself as an alternative fat quantification method for bone marrow in rats at 7 T.
背景
如今，追求更高的信噪比、空间分辨率和成像速度推动了高场 MRI 的发展。然而，高强度磁场与磁场不均匀性、T衰减加速和化学位移增加有关，这可能对骨髓等复杂组织的常规 MRI 脂肪定量构成挑战。另一方面，质子 MRI 波谱（H-MRS）很难产生高分辨率。作为一种新的替代脂肪定量方法，高分辨率 Z 谱 MRI（ZS-MRI）可以通过在相同 T 下获取脂肪和水的直接饱和图像来实现脂肪定量，这可能受 T衰减和磁场不均匀性的影响较小。
目的
证明 ZS-MRI 可用于大鼠腰椎骨髓脂肪组织（MAT）的定量，并早期检测随年龄变化的 MAT 变化。
方法
使用 MRS 和水油混合体模在不同脂肪分数（FF）下验证超高场 MRI（7T）下 ZS-MRI 进行脂肪定量的准确性。Dixon MRI 数据采用水脂分离的迭代分解、回声不对称和最小二乘法估计进行处理。然后，使用 ZS-MRI 对 13、17 和 21 周龄健康年轻大鼠的腰椎脂肪含量进行纵向监测，以检测 MAT 随年龄变化的 FF 早期变化。对分离的大鼠组的腰椎进行苏木精-伊红染色进行验证。
结果
在离体体模实验中，Dixon MRI 和 ZS-MRI 与 7T 下的 H-MRS 均对 FF 的定量具有很好的相关性（R>0.99）。与 Dixon MRI 相比，ZS-MRI 由于磁场不均匀性导致的图像伪影减少，并且在 7T 下对年龄引起的 MAT 增加的早期检测与 H-MRS 的一致性更好（ZS-MRI R=0.78 与 Dixon MRI R=0.34）。年龄引起的 MAT FF 的增加通过组织学得到证实。
结论
ZS-MRI 证明了其在 7T 下作为大鼠骨髓的替代脂肪定量方法的可行性。
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