Diffusion measurements in intracranial hematomas: Implications for MR imaging of acute stroke

BACKGROUND AND PURPOSE: The purpose of our study was to analyze the diffusi on properties of intracranial hematomas to understand the effects of hemato mas on diffusion-weighted MR images of patients with acute stroke and to fu rther our understanding of the evolution of signal intensities of hematomas on conventional MR images. We hypothesized that hematomas containing blood with intact RBC membranes (ie, early hematomas) have restricted diffusion compared with hematomas in which RBC membranes have lysed. METHODS: Seventeen proven intracranial hematomas were studied with conventi onal and diffusion MR imaging. Hematomas were characterized using conventio nal images to determine the stage of evolution and their putative biophysic al composition, as described in the literature. Apparent diffusion coeffici ent (ADC) measurements for each putative hematoma constituent (intracellula r oxyhemoglobin, intracellular deoxyhemoglobin, intracellular methemoglobin , and extracellular methemoglobin) were compared with each other and,vith n ormal white matter. RESULTS: Hematomas showing hemoglobin within intact RBCs by conventional MR criteria (n = 14) showed equivalent ADC values, which were reduced compare d with hematomas containing lysed RBCs (P = .0029 to, .024), Compared with white matter, hematomas containing lysed RBCs had higher ADC measurements ( P = .003), whereas hematomas containing intact RBCs had reduced ADC measure ments (P < .0001). CONCLUSION: Restricted diffusion is present in early intracranial hematomas in comparison with both late hematomas and normal white matter. Therefore, early hematomas would be displayed as identical to the signal intensity of acute infarction on ADC maps, despite obvious differences on conventional MR images. These data also are consistent with the biochemical composition that has been theorized in the stages of evolving intracranial hematomas an d provide further evidence that paramagnetic effects, rather than restricti on of water movement, are the dominant cause for their different intensity patterns on conventional MR images.