Tu Tsang-Wei, Williams Rashida A, Lescher Jacob D, Jikaria Neekita, Turtzo L Christine, Frank Joseph A
Frank Laboratory, Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda, MD.
Center for Neuroscience and Regenerative Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD.
Ann Neurol. 2016 Jun;79(6):907-20. doi: 10.1002/ana.24641. Epub 2016 Apr 18.
Metrics of diffusion tensor imaging (DTI) and magnetization transfer imaging (MTI) can detect diffuse axonal injury in traumatic brain injury (TBI). The relationship between the changes in these imaging measures and the underlying pathologies is still relatively unknown. This study investigated the radiological-pathological correlation between these imaging techniques and immunohistochemistry using a closed head rat model of TBI.
TBI was performed on female rats followed longitudinally by magnetic resonance imaging (MRI) out to 30 days postinjury, with a subset of animals selected for histopathological analyses. A MRI-based finite element analysis was generated to characterize the pattern of the mechanical insult and estimate the extent of brain injury to direct the pathological correlation with imaging findings.
DTI axial diffusivity and fractional anisotropy (FA) were sensitive to axonal integrity, whereas radial diffusivity showed significant correlation to the myelin compactness. FA was correlated with astrogliosis in the gray matter, whereas mean diffusivity was correlated with increased cellularity. Secondary inflammatory responses also partly affected the changes of these DTI metrics. The magnetization transfer ratio (MTR) at 3.5ppm demonstrated a strong correlation with both axon and myelin integrity. Decrease in MTR at 20ppm correlated with the extent of astrogliosis in both gray and white matter.
Although conventional T2-weighted MRI did not detect abnormalities following TBI, DTI and MTI afforded complementary insight into the underlying pathologies reflecting varying injury states over time, and thus may substitute for histology to reveal diffusive axonal injury pathologies in vivo. This correlation of MRI and histology furthers understanding of the microscopic pathology underlying DTI and MTI changes in TBI. Ann Neurol 2016;79:907-920.
扩散张量成像（DTI）和磁化传递成像（MTI）指标可检测创伤性脑损伤（TBI）中的弥漫性轴索损伤。这些成像测量变化与潜在病理之间的关系仍相对不明。本研究使用TBI闭合性颅脑大鼠模型，调查了这些成像技术与免疫组织化学之间的放射学-病理学相关性。
对雌性大鼠进行TBI，伤后纵向行磁共振成像（MRI）直至伤后30天，选取部分动物进行组织病理学分析。生成基于MRI的有限元分析，以表征机械性损伤模式并估计脑损伤范围，从而指导与成像结果的病理相关性研究。
DTI轴向扩散率和分数各向异性（FA）对轴索完整性敏感，而径向扩散率与髓鞘紧密性显著相关。FA与灰质中的星形胶质细胞增生相关，而平均扩散率与细胞增多相关。继发性炎症反应也部分影响了这些DTI指标的变化。3.5ppm处的磁化传递率（MTR）与轴突和髓鞘完整性均密切相关。20ppm处MTR的降低与灰质和白质中星形胶质细胞增生的程度相关。
尽管传统的T2加权MRI在TBI后未检测到异常，但DTI和MTI能对反映不同时间损伤状态的潜在病理提供互补性见解，因此可能替代组织学以在体内揭示弥漫性轴索损伤病理。MRI与组织学的这种相关性进一步加深了对TBI中DTI和MTI变化潜在微观病理的理解。《神经病学纪事》2016年；79：907 - 920。
