Center for Biomedical Imaging, Department of Radiology and Radiological Science, Medical University of South Carolina, 68 President Street, MSC 120, Charleston, SC 29425, USA.
Stroke. 2012 Nov;43(11):2968-73. doi: 10.1161/STROKEAHA.112.657742. Epub 2012 Aug 28.
Despite being the gold standard technique for stroke assessment, conventional diffusion MRI provides only partial information about tissue microstructure. Diffusional kurtosis imaging is an advanced diffusion MRI method that yields, in addition to conventional diffusion information, the diffusional kurtosis, which may help improve characterization of tissue microstructure. In particular, this additional information permits the description of white matter (WM) in terms of WM-specific diffusion metrics. The goal of this study is to elucidate possible biophysical mechanisms underlying ischemia using these new WM metrics.
We performed a retrospective review of clinical and diffusional kurtosis imaging data of 44 patients with acute/subacute ischemic stroke. Patients with a history of brain neoplasm or intracranial hemorrhages were excluded from this study. Region of interest analysis was performed to measure percent change of diffusion metrics in ischemic WM lesions compared with the contralateral hemisphere.
Kurtosis maps exhibit distinct ischemic lesion heterogeneity that is not apparent on apparent diffusion coefficient maps. Kurtosis metrics also have significantly higher absolute percent change than complementary conventional diffusion metrics. Our WM metrics reveal an increase in axonal density and a larger decrease in the intra-axonal (Da) compared with extra-axonal diffusion microenvironment of the ischemic WM lesion.
The well-known decrease in the apparent diffusion coefficient of WM after ischemia is found to be mainly driven by a significant drop in the intra-axonal diffusion microenvironment. Our results suggest that ischemia preferentially alters intra-axonal environment, consistent with a proposed mechanism of focal enlargement of axons known as axonal swelling or beading.
尽管常规弥散磁共振成像（DWI）是脑卒中评估的金标准技术，但它仅提供了关于组织微观结构的部分信息。弥散峰度成像是一种先进的 DWI 方法，除了常规的弥散信息外，还可以提供弥散峰度，这有助于改善组织微观结构的特征描述。特别是，这种额外的信息可以用特定于白质（WM）的弥散指标来描述 WM。本研究旨在利用这些新的 WM 指标阐明缺血的可能的生物物理机制。
我们对 44 例急性/亚急性缺血性脑卒中患者的临床和弥散峰度成像数据进行了回顾性分析。本研究排除了有脑肿瘤或颅内出血病史的患者。采用感兴趣区分析方法，测量缺血性 WM 病变与对侧半球相比弥散指标的百分比变化。
与表观弥散系数图相比，峰度图显示出明显的缺血性病变异质性。峰度指标的绝对值变化百分比也明显高于互补的常规弥散指标。我们的 WM 指标显示，缺血性 WM 病变的轴突密度增加，轴内（Da）扩散微环境的减少比轴外更为明显。
已知 WM 在缺血后表观弥散系数（ADC）的降低主要是由于轴内扩散微环境的显著下降所致。我们的结果表明，缺血优先改变轴内环境，与轴突肿胀或成珠（beading）的焦点扩大机制一致。
