| Objective: To investigate the imaging evolution of the ischemia stroke in the SWI, and evaluate the role of SWI in assessment of reperfusion after ischemia stroke.Materials and Methods: 54 patients (30 males, 24 females, age 20-85 years, average 67 years) with cerebral infarction were performed with conventional MRI and SWI. 9 cases of hyperacute infarction (<6 hours), 18 cases of acute infarction (7-24 hours), 18 cases of subacute infarction (1.5- 7days), 3 cases of stable stage (8-14days), and 6 cases of chronic infarction (>15days) were recruited in this study. 21 cases of large area infarction were followed up twice in this study. Furthermore, 54 healthy volunteers were selected to perform the same MR examination. Their ages and gender were almost matched to the patients group. MRI scanning was performed on GE Signa 1.5T echospeed MR/i scanner and 8-channel head coil were used.Scanning parameters: T1WI: TR 400 ms,TE 15 ms,slice thickness 6 mm,interval 1 mm(T1WI has the same slice thickness and interval with T2WI);T2WI:TR 3000 ms,TE102ms。DWI:TR 6000ms,TE 96.3ms,slice thickness 6mm,interval 1mm,b values: 0/1000s/mm2 , SWI:TR 50ms,TE 40ms,slice thickness 2.0mm,interval 0mm,field of view 24cm,matrix 320×320,NEX 0.75,Bandwidth 31.25,Flip angle 30°. The raw data of SWI were post-processed in GE Advantage workstation 4.3 and were used to generate the corrected phase image (CPI) and SWIminp images. Phase values of the infarction and the contralateral normal appearing white matter (NAWM) and the healthy volunteers NAWM were measured in the CPI. For the 21 patients with massive infarction, according the Adamas rules that the infarction diameters were bigger than 3cm2 and related to more than two main vascular territory, were followed up by SWI and FairPWI and 3DTOF-MRA. The presence of hemorrhage within the infarction, the extent of hemorrhage and microvascular changed around the ischemia area were observed in the follow-up images. The hemorrhagic area and the ratio of hemorrhagic area to maximum infarction area were measured by SPIN (Signal process in neuroimaging, Wayne State University provide) software, we took the average values measured three times in adjacent levels and defined the extent of hemorrhage as follow: the severe hemorrhage, which the ratio of hemorrhagic area to infarction area was greater than 30 percent with significant mass effect, the moderate hemorrhage, of which the rate of hemorrhage was greater than 10 percent, less than 30 percent with mild mass effect, the mild hemorrhage, of which the rate of hemorrhages was less than 10 percent without mass effect. We also counted the number of the microvessels around the infarction demonstrated in SWIminp images and defined the extent of microvessels showed as follow: the significantly showed, which the numbers of microvessels showed were greater than 10 and the diameters were greater or equal as the contralateral brain microvessels, the mildly showed were less than 10 and the diameters is almost same to the contralateral vessels. NIH Stroke Scale (NIHSS) scores in different stages were conducted by a neurologist or a senior neurology resident. The correlation between the extent of hemorrhage in the infarction region, the number of surrounding microvessels and the NIHSS changed was analyzed. All cases were read and measured by two doctors with double blind way. All patients were treated with nutrient vessels and nerves medicine, did not use thrombolytic therapy. Written informed consent was obtained from all participants.The statistic method is SPSS 16.o software. TO compare the average phase values between the ischemia lesion and the contralateral areas and the healthy volunteers normal white matters by Wilcoxon, and the correlation between the volume of the blood after reperfusion infarction and the microvessels numbers around the infarction with the clinical NIHSS scores changed is tested by Spearman. P value less than 0.05 indicated a statistically significant difference.Results:1. The phase values of hyperacute and acute infarcts were significantly higher than those of NAWM (p<0.001). However, for the cases of subacute , there was a little difference between the phase values of infarction and NAWM (P=0.04). In the stable and chronic stage, the phase values of the infarction were significantly lower than NAWM (p<0.001).2. With the time prolonged, the average phase values of the ischemia lesion gradually decreased and reached the lowest level in the chronic stage. There was a significant negative correlation between phase values and the time after ischemia stroke (r = -0.990, P=0.001).3. Hemorrhage was revealed by SWI in 16 out of 21 massive cerebral infarctions. However, T2WI and T1WI found only 5 and 4 cases. There was a significant positive correlation between the severe hemorrhage and the NIHSS scores (rs=0.765, P=0.001).4. Among the 21 cases of large area infarctions, increased microvessels were observed in 10 patients (47.6%). There was no significant correlation between the microvessels and the NIHSS scores changed (rs=0.408, P=0.066).Conclusions:1. SWI is useful in the staging of ischemia stroke. There is characteristic feature in changes of SWI Phase values of the stroke and Phase values can distinguish different stages of cerebral infarction.2. SWI is sensitive in detecting the microbleeds in the infarction, which can be used to predict the evolution of reperfusion injury after ischemia stroke.3. The microvascular changes reflected on SWI can be used to assess the reperfusion status after stroke, which is helpful in guiding the clinical treatment. |
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