Stroke Assessment With Diffusional Kurtosis Imaging

Abstract

Background and Purpose Despite being the gold standard technique for stroke assessment, conventional diffusion magnetic resonance imaging (dMRI) provides only partial information about tissue microstructure. Diffusional kurtosis imaging (DKI) is an advanced dMRI method that yields, in addition to conventional diffusion information, the diffusional kurtosis (K), 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 (WMM). The goal of this study is to elucidate possible biophysical mechanisms underlying ischemia using these new WMM. Methods We performed a retrospective review of clinical and DKI data of forty-four acute/subacute ischemic stroke patients. Patients with a history of brain neoplasm or intracranial hemorrhages were excluded from this study. ROI analysis was performed to measure percent change of diffusion metrics in ischemic WM lesions compared to the contralateral hemisphere. Results K maps exhibit distinct ischemic lesion heterogeneity that is not apparent on apparent diffusion coefficient (ADC) maps. K metrics also have significantly higher absolute percent change than complementary conventional diffusion metrics. Our WMM reveal an increase in axonal density and a larger decrease in the intra-axonal (Da) compared to extra-axonal (De) diffusion microenvironment of the ischemic WM lesion. Conclusions The well-known decrease in the ADC of WM following ischemia is found to be mainly driven by a significant drop in Da. 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.

Abnormalities in Diffusional Kurtosis Metrics Related to Head Impact Exposure in a Season of High School Varsity Football

“…axonal beading). 38 In our study, we observed a significant relationship between cumulative exposure metrics and many of the DKI-derived and WMM metrics. These results indicate a variety of changes and injury types that may be occurring within the white matter, including axonal swelling, axonal beading, ischemia, and astrogliosis.…”

“…Similar changes have been seen previously in ischemic regions of stroke patients. 38,39 The significant increase in MK also has been demonstrated in axonal injury and astrogliosis.…”

“…Similar changes have been seen previously in ischemic regions of stroke patients. 38,39 The significant increase in MK also has been demonstrated in axonal injury and astrogliosis.25 Astrogliosis is the increase of reactive astrocytes due to the destruction of nearby neurons. This abnormal increase in astrocytes increases the microcellular complexity and has been shown to significantly elevate the measured MK in animal models.…”

“…The trending decrease in D a , in conjunction with the increase in AWF, follows a model of ischemia and is consistent with axonal beading. 38 The increases in D a with decreases in D e radial suggest areas of cytotoxic edema, causing water to shift from extrato intra-axonal regions. In contrast, the increases in D e axial and radial may be due to areas of extra-axonal inflammation or vasogenic edema.…”

Cerebrovascular Reactivity in the Brain White Matter: Magnitude, Temporal Characteristics, and Age Effects

“…2 and the arrows indicate that CO 2 generated by tissue is cleared through blood vessels. (B) When the hypercapnic blood first arrives, arterial CO 2 concentration will increase, delivering extra CO 2 to the tissue.…”