| Objectives:1.To investigate the value of susceptibility weighted imaging in the rat hyperacute cerebral ischemia.2.To compare the application of susceptibility weighted imaging and perfusion weighted imaging in the rat hyperacute cerebral ischemia,and to evaluate the usefulness of susceptibility weighted imaging in the detection of ischemic penumbra.3.To evaluate the brain oxygen metabolism in patients of chronic middle cerebral artery stenosis or occlusion with susceptibility weighted imaging.4.To detect the ischemic penumbra of acute cerebral infarction with susceptibility weighted imaging and diffusion weighted imaging,and to explore the existing duration of ischemic penumbra.Materials and Methods:1.40 male healthy Wistar rats were enrolled in this study.The rat model of middle cerebral artery occlusion(MCAO)was performed according to the intraluminal filament technique.Susceptibility weighted imaging and diffusion weighted imaging were performed at 20 minutes and 2.5 hours respectively after MCAO model was successfully accomplished,and corrected phase images and ADC map were acquired through postprocessing.According to the DWI and ADC map of 2.5 hours after occlusion,the phase radians and SWI signal intensity values of the infarction core,peri-core area,and counterparts in the contralateral hemisphere were measured respectively,the phase radians and SWI signal intensity values in different ROIs and same ROI in different times were compared.2.20 male healthy Wistar rats were enrolled in this study.Susceptibility weighted imaging,perfusion weighted imaging and diffusion weighted imaging were performed at 2.5 hours after MCAO model was successfully accomplished.The area percent of abnormal signal and the core showed relative normal signal on SWI,the hypoperfusion area percent on PWI and hyperintensity area percent on DWI versus the whole brain area in the same slice were measured respectively. Finally the area percent of abnormal signal on SWI and the hypoperfusion area percent on PWI,the area percent of the core showed relative normal signal on SWI and the hyperintensity area percent on DWI,the hypointensity area percent on SWI and PWI/DWI mismatch area percent were compared and correlated respectively.3.11 patients with severe unilateral middle cerebral artery(MCA)chronic stenosis or occlusion and 10 healthy controls with matched gender and age were performed TOF-MRA and susceptibility weighted imaging,the phase radians and SWI signal intensity values of lesion side,normal side of patients and the two sides of controls were measured and compared.4.20 patients with acute cerebral infarction within 6-24 hours after onset of clinical symptoms were underwent susceptibility weighted imaging and diffusion weighted imaging,according to the DWI and ADC map,the phase radians and SWI signal intensity values of brain tissue around the infarction core were measured,to identify the presence of ischemic penumbra.Results:1.20 minutes after occlusion of MCA in rats,the phase radians of the infarction core,the peri-core area,and the counterparts in the contralateral hemisphere were -0.05060±0.03201,0.04508±0.02051,-0.03791±0.01735,0.04315±0.01740 respectively,the difference was significant(F=164.341,P=0.000).and the SWI signal intensity values were 201.66±59.86,289.72±55.51,203.48±47.19, 304.43±79.91 respectively,the difference was also significant(F=25.250, P=0.000).The phase radians and SWI signal intensity values of the infarction core,the peri-core area were lower than that of the counterparts in the contralateral hemisphere(P=0.000),but the infarction core and the peri-core area had no significant difference(P values were 0.279,0.906 respectively).2.5 hours after occlusion of MCA,the phase radians of the infarction core,the peri-core area,and the counterparts in the contralateral hemisphere were 0.04681±0.01689,0.04287±0.01906,-0.03866±0.01691,0.04596±0.01784 respectively,the difference was significant(F=180.038,P=0.000).and the SWI signal intensity values were 293.18±73.22,284.48±39.89,200.36±43.08, 308.14±59.53 respectively,the difference was also significant(F=24.323, P=0.000).The phase radians and SWI signal intensity values of the peri-core area were lower than that of infarction core and counterparts in the contralateral hemisphere(P=0.000),but that of infarction core and counterparts in the contralateral hemisphere had no significant difference(P>0.05).2.2.5 hours after occlusion of MCA in rats,the hypoperfusion area percent on PWI and the area percent of abnormal signal on SWI were 35.75±9.44(%),35.56±8.07(%)respectively,there was no significant difference(t=0.226,P=0.824). The hyperintensity area percent on DWI and the area percent of the core showed relative normal signal on SWI were 29.15±8.57(%),26.68±6.53(%),there was also no significant difference(t=2.007,P=0.062).The area percent of abnormal signal on SWI and the hypoperfusion area percent on PWI were well correlated(Pearson correlate coefficient is 0.932,P=0.000).The hyperintensity area percent on DWI and the area percent of the core showed relative normal signal on SWI were also well correlated(Pearson correlate coefficient is 0.807, P=0.000).3.The phase radians of lesion side,normal side of patients and the two sides of controls were 0.00600±0.00210,0.01166±0.00352,0.01208±0.00286, 0.01051±0.00230(F=13.476,P=0.000),and the SWI signal intensity values were 194.29±28.08,238.33±24.76,245.05±8.76,233.06±11.66(F=13.360, P=0.000),the difference were all significant.The phase radians and SWI signal intensity values of lesion side were all lower than that of normal side and two sides of controls(P＜0.05).4.In the 20 patients with acute cerebral infarction,6 lesions located at basal ganglia and hypothalamus region,14 lesions located at lobes.All the 6 lesions located at basal ganglia and hypothalamus region had no SWI penumbra,while 5 lesions at lobes had SWI penumbra,2 of the 5 lesions were smaller than 2.0cm,and other 3 lesions were equal to or larger than 2.0cm,the time after onset of clinical symptoms were 7,10,10,15,19 hours respectively.Conclusions:1.SWI can detect cerebral ischemia in rat as early as 20 minutes after occlusion of MCA,which demonstrate as decrease of the signal on SWI and phase radian. With the development of the ischemia,the signal of the infarction core may increase to relative normal signal on SWI,which signify irreversible infarction.2.SWI can reflect the hemodynamics and metabolism of ischemic penumbra in hyperacute infarction inderectly,so may substitute for MR perfusion weighted imaging to detect cerebral ischemic penumbra.3.SWI can reflect the increase of OEF and decrease of CBF in chronic cerebral ischemia indirectly,may substitute for CT or MR perfusion to evaluate the cerebral ischemia volume and extent in patients with MCA stenosis or occlusion, and guide to make a therapeutic plan.4.There is no absolute time window of ischemic penumbra,it's duration has individual differences.Ischemic penumbra can be detected in about 25%of patients with cerebral infarction within 6-24 hours after onset.SWI combined with DWI can detect ischemic penumbra sensitively and provide convincing imaging evidence for individual thrombolytic protocol.
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