Magnetic Sensitive Imaging Technology For Depicting Tissue Magnetic Susceptibility In The Brain

Objective The deposition of paramagnetic iron,anti-magnetic calcification and white matter fiber bundle lesions in the brain have an effect on the magnetic susceptibility of tissue.Tissue magnetic susceptibility contrasts can be visualized on susceptibility weighted imaging（SWI）magnitude（SW-M）and SWI phase（SW-P）or on quantitative susceptibility mapping（QSM）.This study aims to compare their performances for depicting brain susceptibility structures.Methods（1）In the numerical simulation,in order to evaluate how to describe the susceptibility structure on SW-M,SW-P and QSM,we used the known susceptibility structure as the reference standard to simulate.The zero magnetization background and three groups of small spheres（radius=1mm）,two large spheres（radius=10 mm）and two cylinders（radius=5mm,length=50mm,perpendicular to B₀）containing paramagnetic substance and diamagnetic substance（±0.15ppm）were simulated by computer to simulate the substances with different sizes and magnetism in the brain.（2）In the clinical trial,the FLASH 16 slice CT machine was used to collect the brain CT images of 25 volunteers who had received brain CT examination,and the SWI sequence in 3.0T MRI was used to collect the brain SW-M and SW-P information of volunteers,and the post-processing software and SW-M and SW-P information were used to reconstruct the QSM information.According to the imaging findings of basal ganglia nuclei,veins,calcification and white matter tracts,the images of SW-M,SW-P and QSM were evaluated by Wilcoxon signed rank sum test.In order to quantify the calcification in choroid plexus,11 cases of choroid plexus calcification detected by CT were analyzed by linear regression analysis with SW-P and QSM.Results In the clinical trial,in displaying basal ganglia nuclei,QSM score was higher than SW-M（p=0.0001）and SW-P（p=0.008）,and SW-P was higher than SW-M（p=0.03）.In displaying veins,QSM score was higher than SW-M（p=0.003）,equivalent to SW-P（p=0.386）,and SW-P was higher than SW-M（p=0.005）.In displaying calcification,QSM score was higher than SW-M（p=0.00002）and SW-P（p=0.0005）,and SW-P was higher than SW-M（p=0.0001）.In displaying white matter tracts,QSM score was higher than SW-M（p=0.0002）and SW-P（p=0.0005）.The score was higher than that of SW-M（p=0.00002）and SW-P（p=0.00001）,and SW-P was higher than that of SW-M（p=0.0002）.For measurements at the choroid plexus,QSM vs CT linear regression had a higher coefficient of determinant than SW-P vs CT and SW-P vs QSM.Conclusion SW-M,SW-P and QSM can be generated from postprocessing the same multiecho gradient echo acquisition.For depicting magnetic susceptibility structures in the brain,QSM is scored to be equivalent or higher than SW-P,and SW-P is scored higher than SW-M.Magnetic susceptibility structures in the brain can be depicted on QSM and on SWI images.SWI phase images depict only edges of large susceptibility structures and show susceptibility sign consistently only for smallstructures contained in thick voxels.SWI magnitude images selectively enhance edges of susceptibility structures.QSM can faithfully depict the susceptibility spatial distribution including the edge and body of susceptibility structures.