The Value Of Swi In The Experimental Intracerebral Microbleeds In The Rats

Background and Purpose:Recently,accompany with the development of the MR device,Susceptibility-weighted imaging(SWI) is an new imaging technique that was developed by Haacke et al.in 2004 based on T₂^*-gradient echo sequence,which is a high-spatial-resolution 3D gradient-echo MR imaging technique with long echo time and flow compensation applied in 3 directions,so the character of it is high resolution,3D,high signal-noise-ratio,and the magnitude image is multiplited several times by the phase mask imaging in this technique,which is generated by filtering the phase imaging,it become very sensitive to the nonhomogenuous of magnetic field generated by the different magnetic susceptibilitys,so SWI has dramatically improved the visualization not only hemorrhage and ferrugination,but also of venous structures, permitting smaller bleeding lesions to be depicted.The cerebral microbleeds get to the new level because of it and become one of the hots.Cerebral microbleeds as called as intracerebral patechial hemorrhage were first described after the clinical use of GRE in 1994 and are usually defined as rounded foci of＜5mm in size.We often ignore them because the person has them is not present syndrome,and no edema induced by microbleeds.Many study indicates cerebral microbleeds are the macker of the microvascular diseases,which have documented in healthy populations,patients with ischemic cerebrovascular disease,cerebral hemorrhage,intracerebral amyloid angiopathy,cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy,leukoencephalopathy and so on.Cerebral microbleeds have important clinical application because they can predict the recurrent of intracerebrl hemorrhage and hemorrhage after anticoagulant therapy.The research is to(1) compare with routine sequence of MR and SWI,to assess the susceptibility of SWI in cerebral microbleeds(2) compared by histopathological hematoma volume,figure out the amplification ratio of SWI.Materials and methods:1.Experiment materials:This study used 54 male Sprague-Dawley rats weighting from 210-240g,provided by experimental animal center of Zhengzhou university. Divided into control group(n=9) and experimental group(n=45).The rats of control group underwent intracranial needle insertion but without blood injection,the rats of control group underwent intracranial needle insertion anf blood injection.At 0.5h,3h,12h,24h,48h,72h,1w,2w,4w after operation,all the rats were scaned by MRI,And then the rats were sacrificed,the brain tissue were moved from skull for histopathology.2.Production of cerebral microbleed:The rat was placed in a stereotactic frame,and a cranial drill was introduced through a burr hole(1mm) into the right striatum(3mm lateral to midline,0.4mm anterior to bregma,6mm below the surface of the skull. Each rat received a 20μL injection of fresh blood(over 2 min).The blood used for injection was taken from a femoral vein.The injection cannula was slowly withdrawn 10 min after injection,and the burr hole was sealed with bone wax,the wound was sutured,and the animal was immediately transferred to the magnet.Control group was underwent intracranial needle insertion but without blood injection.3.MR scan:ALL rats underwent the T₁WI,T₂WI,T₂^*WI and SWI with SIEMENS Trio Tim 3.0T MR scanner.Choose the Loop 4 coil.The T₁WI(TSE):12ms TE,430ms TR,256×256 matrix,70×70mm FOV,2mm slicethickness,0.2mm slicethickness insertion,20 sclices;T₂WI(TSE):98ms TE,5990ms TR,256×256 matrix,70×70mm FOV,2mm slicethickness,0.2mm slicethickness insertion,20 sclices;T₂^*WI(GRE): 20ms TE 500ms,TR 256×256 matrix,70×70mm FOV 2mm slicethickness 0.2mm slicethickness insertion 20,sclices 20,Flip angle;SWI:20ms TE,29ms TR,256×256 matrix,70×70mm FOV,0.6mm slicethickness,0.12mm slicethickness insertion,20 sclices,15 Flip angle.ALL process were on the Syno VE27 workshop to calculate the volumes of microblees on T2WI and SWI.The volume was equal to half of sclicethickness and insertion.4.Test of neurological behavior:according to Zea Longa neurological deficit score to assessed whether have the damaged degree of neurological function after produce cerebral microbleed model or not.5.HistopathologyAfter scan and test of neurological behavior,rats were sacrificed,the brain tissues were quickly moved from the skull,and 2mm thick sections were cut in the coronal plane through the needle,Brain slices were dehydrated and embedded in the paraffin wax and stained with Prussian blue.6.Statistical analysisStatistical analysis was performed with SPSS 11.0 software;statistical methods were t-test and analysis of variance.Result1.In 45 experimental rats,39 microbleeds are apperence on T₁WI and T₂WI which detection ratio is 86.7%;all of microbleeds are apperence on SWI which detection ratio is 100%;2.39 microbleeds are found on T₂WI,the average volume of the lesions is 0.830±0.416 (×10^-3mm³);45 microbleeds are found on SWI,the average volume of the lesions is 1.271±0.530(×10^-3mm³);the average volume of the lesions in histopathology is 0.967±0.764(×10^-3mm³)3.Compared with SWI(MNIP mapping),T₂WI and histopathology,There were not statistically differences between volumes in T₂WI and histopathology(P=0.285＞0.05) but were tatistically differences between volumes in histopathology and SWI(MNIP mapping).The T₂WI and histological volumes were in close numerical agreement.By contrast,the SWI lesion volume overestimated the histological volume by 2.152±1.500; 4.Volume of the lesions is decreased from 0.5h to 4w on T₂WI,SWI and histology,but amplification ratio of SWI is the largest in 1w and the smallest in 0.5hConclusions1.According to experiment,SWI is prior to the routine sequence to find out microbleeds2.According to the volumes computed from SWI(MNIP mapping),T₂WI and histopathology,we find the T₂WI and histological volumes were in close numerical agreement.By contrast,the SWI lesion volume overestimated the histological volume by 2.152±1.500.3.SWI could be served as an effective method for diagnosing cerebral microbleeds.