The small iron-independent component R2', as compared with that of R2, is consistent with the hypothesis that R2' has higher iron-related specificity.

In this paper a new method is presented for the relative assessment of brain iron concentrations based on the evaluation of T2 and T2*-weighted images. A multiecho sequence is employed for rapid measurement of T2 and T2*, enabling calculation of the line broadening effect (T2'). Several groups have failed to show a correlation between T2 and brain iron content. However, quantification of T2', and the associated relaxation rate R2', may provide a more specific relative measure of brain iron concentration. This may find application in the study of brain diseases, which cause associated changes in brain iron levels. A new method of field inhomogeneity correction is presented that allows the separation of global and local field inhomogeneities, leading to more accurate T2* measurements and hence, T2' values. The combination of T2*, and T2-weighted MRI methods enables the differentiation of Parkinson's disease patients from normal age-matched controls based on differences in iron content within the substantia nigra.

The blood-to-brain transfer rate constant (K i ) of Gd-DTPA was determined in MRI studies of a rat model of transient cerebral ischemia. The longitudinal relaxation rate, R 1 , was estimated using repeated Look-Locker measurements. A model-independent analysis of ⌬R 1 , the Patlak plot, produced maps of K i for Gd-DTPA and the distribution volume of the mobile protons (V p ) with intravascular-Gd changed R 1 's. The K i 's of Gd-DTPA were estimated in regions of interest with blood-brain barrier (BBB) opening (regions of interest, ROIs) and compared to those of 14 C-sucrose determined shortly thereafter by quantitative autoradiography. The K i 's for both Gd-DTPA and sucrose were much higher than normal within the ROIs (n ‫؍‬ 7); linear regression of K i for Gd-DTPA vs. K i for sucrose yielded a slope of 0.43 ؎ 0.11 and r 2 ‫؍‬ 0.72 (P ‫؍‬ 0.01). Thus, K i for Gd-DTPA varied in parallel with, but was less than, K i for sucrose. In the ROIs, mean V p was 0.071 ml g -1 and much higher than mean vascular volume estimated by dynamic-contrast-enhancement (0.013 ml g

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Background and Purpose This study was performed to document the progression of ischemic brain damage after middle cerebral artery occlusion in the rat using magnetic resonance imaging and histopathologic methods.Methods Cerebral ischemia was induced through permanent tandem occlusion of ipsilateral middle cerebral and common carotid arteries. The evolution of magnetic resonance imaging and histopathologic parameter changes was studied, both short term (1.5 to 8 hours) and long term (24 to 168 hours), in five specific brain regions within the middle cerebral artery territory.Results Significant changes in proton nuclear magnetic resonance spin-lattice and spin-spin relaxation times and the "apparent" diffusion coefficient of water could be detected within hours after the onset of permanent focal cerebral ischemia, whereas significant alterations in proton spin-density ratios were not apparent until approximately 48 hours. Histological changes were evident within 12 hours, with a significant loss of neurons seen in the most severely damaged regions at