How Does Water Diffusion in Human White Matter Change Following Ischemic Stroke?

Abstract

Purpose: Temporal evolution of the water apparent diŠusion coe‹cients (ADC) parallel (ADC¿) and perpendicular (ADC¥) to the human white matter tract following ischemia has not been investigated systematically. We attempted to quantify the evolution of ADC¿ and ADC¥ and examine whether it can be interpreted by a model of ischemic edema.Methods: We retrospectively selected 53 patients with ischemic lesions involving the posterior limb of the internal capsule (PLIC) and placed regions of interest in the right and left PLIC on ADC maps. We performed regression analysis of lesion-to-contralateral ratios of ADC¿ and ADC¥against the time (t＝1-1600 h) from onset. We thenˆtted the estimated time courses of ADC¿ and ADC¥obtained from the analysis to a model of nerve tissue composed of cylinders (axons) and spheres corresponding to isotropic structures, particularly focal cytoplasmic swellings of glial cells and axons seen in ischemic white matter.Results: The evolution of ADC¥ and ADC¿ diŠered. The estimated time course of ADC¿ in mm 2 ･ms -1 was 0.64＋0.88 exp (-0.24t) for 1ºtº54 h and 0.00059t＋0.61 for tAE54 h (contralateral normal value, 1.52). That of ADC¥ was 0.19-0.063 exp (-0.24t) for 1ºtº54 h and 0.00040t＋0.17 for tAE54 h (normal value 0.22). The modelˆtted to these values showed that the volume of the cylinders decreased, that of the spheres increased, and extracellular volume changed little from one hour to approximately one day after stroke onset.Conclusion: In the human PLIC, ADC¿ continued to decrease from one hour to a few days after stroke onset, and ADC¥tended to increase. The temporal evolution could be interpreted by progression of the focal cytoplasmic swelling of glial cells and axons previously observed in animal studies.Keywords: cytotoxic edema, glia, intracellular space, vasogenic edema Introduction DiŠusion-weighted (DW) magnetic resonance (MR) imaging enables noninvasive measurement of the diŠusivity of water molecules in the human brain. Prompt reduction of the apparent diŠusion coe‹cient (ADC) in ischemic tissue causes hyperintensity on DW images, which aids detection of early changes in the brain after onset of ischemic stroke. [1][2][3] ADC measurement may also be useful in characterizing ischemic damage and selecting therapeutic procedure. 4 Many studies have demonstrated temporal evolution of the mean diŠusivity (<ADC>, trace/3 of the diŠusion tensor) in patients with stroke. 5-13Follow-122 122 H. Tamura et al. Magnetic Resonance in Medical Sciencesing acute reduction of <ADC> after the onset of cerebral ischemia, <ADC> decreases slightly over 24 hours in many cases, [5][6][7][8][9] reaches a minimum, gradually increases to a normal value (pseudonormalization) between several days and one month, and continues to increase. Although the decrease is generally attributed to cellular edema and the increase to vasogenic edema and degradation of membrane structure, 1,[10][11][12] the exact mechanisms of these changes in <ADC> remain unclear.Human and animal studies show a decline in diŠusion anisot...

Progressive Assessment of Ischemic Injury to White Matter Using Diffusion Tensor Imaging: A Preliminary Study of a Macaque Model of Stroke

“…Obviously, the MD reduction in white matter was gradual and couple hours lagged behind the MD decreasing in grey matter, suggesting the resistance to ischemia is higher in white matter than that in the grey matter [ 35 ]. In addition, the MD changes of white matter in stroke macaques are in agreement with Tamura et al’s report in stroke patients [ 21 ].…”

“…Most MR imaging studies focus on grey matter injury of acute stroke, and the temporal evolution of DTI indices are well studied and the findings are generally consistent. A few DTI studies have been performed to characterize white matter injury during hyperacute and acute stroke in rats with MCA occlusion [ 8 , 20 ], stroke patients [ 21 ], and r-tPA treated patients [ 22 ]. The temporal changes of fractional anisotropy (FA) and diffusivity indices in cortex and ipsilesional corpus callosum in rats are well demonstrated from 2 hours to 6 or 8 weeks after transient MCA occlusion.…”

Preliminary observations of increased diffusional kurtosis in human brain following recent cerebral infarction

“…Similar orientation-dependent diffusion coefficient changes in white matter have been reported previously by Tamura et al . (27). …”

White matter injury in ischemic stroke

“…From one hour to a few days after stroke onset, there is a decline in ADC parallel with the WM fibers, while there is an increase in ADC perpendicular to the fiber bundles. This phenomenon might be attributed to the progression of the focal intracellular edema in glial cells and axons (Tamura et al, 2009). …”