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Physiological and Metabolic Interpretation of Diffusion‐Weighted Imaging Changes During Cerebral Ischemia
Author(s) -
Hilger Thomas,
Hoehn Mathias
Publication year - 2003
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1560/0bcg-d9vn-kgm9-hkfc
Subject(s) - ischemia , cerebral blood flow , chemistry , effective diffusion coefficient , diffusion mri , brain tissue , cardiology , neuroscience , magnetic resonance imaging , medicine , radiology , psychology
Diffusion‐weighted imaging (DWI) has become one of the most important imaging modalities for the characterization of acute stroke. In this review article the connection between DWI and independent non‐MR parameters is evaluated, thereby providing the background for the physiological and metabolic interpretation of DWI changes. The pathophysiological consequences reflected by DWI changes are determined by the duration and intensity of an ischemic event. Reversible changes in water diffusion of tissue are triggered at a cerebral blood flow decrease to approximately 35–40 mL/100g*min. More severe hemodynamic disturbances (<20 mL/100g*min) obviously result in irreversible tissue damage. Furthermore, a distinct relative decrease of the apparent diffusion coefficient (ADC) to 90% of control indicates tissue acidosis, and it has been shown that, under certain conditions, the ADC reflects the current energy state of the brain, as validated by the distribution of ATP. A close correlation between the depletion of ATP and an ADC decrease to 77% of control was found for the acute phase of both permanent and transient cerebral ischemia. The correlation of diffusion changes with final tissue damage revealed that ADC can reliably predict histopathological damage during the early acute phase of cerebral ischemia and after transient recovery. However, in the intermediate phase, while histology showed further cellular degeneration, ADC obviously does not reflect the tissue status. Depending on the individual situation, a moderate ADC decrease to ca. 70–80% of control must not necessarily result in irreversible tissue damage, whereas more severe decline to ca. 60% of control presumably transforms to necrosis.