Analysis Of Microbleeds And Brain Nucleus By Using Susceptibility Weighted Imaging

Background and Purpose:Susceptibility Weighted Imaging (SWI), which employs phase information induced by tissues with various susceptibilities to improve the image contrast, is well known for its superior ability in detection of hemorrhage, microbleeds and even iron deposition in human brain diseases. In this study we use SWI (1) to detect the distribution and prevalence of cerebral microbleedings (CMBs) in rats after acute ischemic stroke; and (2) to find out the correlations of presence and distribution of CMBs with biphasic blood-brain barrier (BBB) opening.Materials and Method:MRI at3.0Tesla MR scanner was performed on9middle cerebral artery occlusion (MCAO) rats at the time point of4h and24h after ischemia respectively, as BBB opening is supposed to take place at the two time points. T2-weighted images (T2WI), T2maps and diffusion-weighted images (DWI) were generated to estimate the onset and severity of brain ischemia. Phase images and minimum intensity projection (mIP) images of SWI were used to analyze the number, size and distribution of CMBs.Result:At24h after ischemia, the number of CMBs increased to thirteen were found in7of9rats (one CMB in4rats, two CMBs in1rat, three CMBs in1rat, and four CMBs in lrat, respectively), whereas only two CMBs found in1of9rats at4h after ischemia. All visible CMBs found in SWI images were located on the ischemic lateral cortex, with the diameters from0.2mm to0.5mm. At4h after ischemia, two CMBs were found to be located at the edge area of T2hyperintensity; at24h, eight CMBs were found to be located within the areas of T2hyperintensity, four CMBs outside areas of T2hyperintensity and one CMB at the edge of areas of T2hyperintensity. However, all those CMBs were located inside areas of DWI/ADC abnormal intensity at both time points. In addition, widening vessels around the CMBs in the ischemic hemisphere were found in7rats at4h and the same widening vessels were found in6rats at24h from SWI mlPs, which were not found in the symmetrical regions Conclusion:The technique of SWI is capable of in vivo detecting CMBs and widening vessels at BBB opening time in cerebral ischemia model of rats, which is not only helpful for better understanding the pathophysiological mechanism of acute stroke, but also helpful for providing more information to the diagnosis and treatment of ischemic stroke, in case of improper thrombolysis which may lead to intracerebral hemorrhage (ICH). Background and Purpose:Iron in brain has a metabolic pathway of "cerebellum-brain stem-basal ganglia". However, iron deposition in the deep brain nucleus will take place, when the iron metabolic pathway is affected by cerebral lesion. Susceptibility weighted imaging (SWI) is superior in detection of iron deposition for its paramagnetism dephasing effect from background tissues, which is characterized of the phase images are high-pass-filtered. The goal of this study is to determine the iron deposition in brain nucleus from normal aging by using SWI.Materials and Methods:20healthy young people were recruited (10males and10females,22-24yr of age) for this study. The whole brain traversal MRI scannings were performed on all people at Siemens3.0T MRI scanner. T1WI and T2WI were used to evaluate structural lesion of the brain. The phase value of cerebrospinal fluid (CSF) was chosen as baseline of iron content estimate in order to exclude the inhomogeneous distribution of iron. SWI phase images were used to estimate the iron content in red nucleus (RN), substantia nigra (SN), putamen (PUT), globus pallidus (GP), head of caudate nucleus (HCN), dentate nucleus (DN) and dorsal thalamus (DT).Result:High-resolution brain nucleus phase images were acquired from SWI sequence, in which paramagnetic iron displayed as hypointensity, which was obviously different from the background tissues. For the healthy young people, the iron content in the nucleus of both sides had no significant difference (p>0.05). The mean phase value of GP (-0.087±0.029radians), SN (-0.083±0.014radians), DN (-0.062±0.014radians), RN (-0.052±0.015radians) and HCN (-0.051±0.009radians) was much higher than that of PUT (-0.043±0.013radians) and DT (-0.023±0.008radians).Conclusion:The enhanced contrast SWI sequence is capable of estimating the iron content in brain by using its phase information. The iron contents in brain deep nucleus are different and inhomogeneous, which is in consistent with the iron metabolic rules in brain.