| Objective:In this study, we assessed the changes of regional susceptibility in the normal SD rats’ brain in vivo by examining the developmental and ageing process from 1 to 24 months of age, to evaluate the correlation of magnetic susceptibility between age and both the gray and white matter over this lifespan.Materials and methods:Animal preparation:The experimental animal used in this study were purchased from Beijing Weitong Lihua Experimental Animal Technology Co., ltd., the experimental animal quality certificate and license number was: SCXK(Beijing 2012-0001). Healthy male SD rats were feeding in SPF environment:(24 + 2) ℃, 12 h light / dark, 7:00am to light, food and water were provided to the dam ad libitum. Animals were divided into 6 groups of 15 rats in each group, which respectively 1, 3, 6, 10, 13, and 24 months of age(including 24-month-old D- galactose aging animal model establishmented.), in 15 patients randomly selected 10 cases of animal experiments.Brain MR Imaging:The subjects were scanned at the US GE MR750 3.0T magnetic resonance scanner, brain scans of SD rats were experimental special coil.With pentobarbital sodium 300mg/kg weight of intramuscular injection of SD in rats after anesthesia prone fixed, and then local warming. Positioning of the scanning level was reference to rat brain stereotaxic atlas,bilateral lugs on the line and central line as the axial positioning point.To obtain magnetic susceptibility maps, the specimens were scanned with a 3D gradient echo sequence. TE = 7.8 ms, TR = 151.9 ms, FOV =5 × 5 cm, flip angle 12°, The whole acquisition time of QSM was 6min18 s.The Collected data was transmitted to the post processing and thendid data analysis of magnetic susceptibility in the work. The regions of interest of bilateral white matter and deep gray matter nuclei were outlined manually and the susceptibility was measured by Signal Processingin Nuclear Magnetic Resonance(SPIN) software. Regions-of-interest(ROI) in two white matter structures were corpus callosum(CC) and internal capsule(IC),the major brain nuclei included caudate putamen(CPu)、globus pallidus(GP)、substantia nigra(SN)and red nuclei(RN).Pearson correlation analysis was used to calculate the correlation between the susceptibility of white matter and deep brain gray nucleus and age. P value less than 0.05 indicated a statistically significant difference.Results:1 In the healthy subjects,the susceptibility of globus pallidus was 0.086083 ppm,it was the highest in the brain;the second was substantia nigra, susceptibility was 0.066416ppm;the least susceptibility was seen incaudate putamen, susceptibility was 0.037755 ppm, showed that the maximum iron content in brain was globus pallidus in which the lowest wascaudate putamen.2 In the globus pallidus, substantia nigra, red nucleus and caudate putamen, paired t test of Pvalue in the left and right sides of the magnetic susceptibility values were 0.155, 0.217, 0.287, 0.910, P<0.05,no statistical significance, showed that no significant differences exist in the globus pallidus, substantia nigra, red nucleus and caudate putamen susceptibility values between the right and left sides.3 There was a positive correlation between age and susceptibility of bilateral globus pallidus, substantia nigra, red nucleus and caudate putamen, the R values of left were 0.671, 0.742, 0.724 and 0.731; the R values of the right were 0.665, 0.736, 0.682, 0.764,(P<0.05); the mean susceptibility of these nucleus also had a positive correlation with age,theR values were 0.691, 0.749, 0.712 and 0.771,(P<0.05), with statistical significance.4 In the deep brain gray nucleus, magnetic susceptibility values of globus pallidus, substantia nigra, red nucleus, caudate putamen increasedwith age,magnetic susceptibility values started to increase gradually since 3-month- old with growth, and stabled at 13-month old.5 In the white matter, the magnetic susceptibility values of internalcapsule(IC) and corpus callosum(CC) decreased rapidly from the age of1-3months old, then gradually slowed down, and reached its minimum at around an age in the late 3-month old,and increased monotonically with the age growth. An initial decrease followed by a subsequent increase in magnetic susceptibility was observed, which could be fitted by a Poisson curve, and the Poisson trajectories in the susceptibility of white matter are consistent with the known characteristics of brain myelinationduring brain maturation and ageing.ConclusionIn this study, profound changes in magnetic susceptibility were observed in both the brain white matter and the gray matter. The Poisson trajectories in the susceptibility of white matter are consistent with the known characteristics of brain myelination during brain maturation and ageing. The growth of susceptibility contrast in gray matter is also in goodagreement with the known characteristics of iron deposition. The results suggest that susceptibility imaging may provide a promising and comprehensive tool for noninvasive assessment of myelination and iron content. In turn, an improved understanding of the spatial and temporal patterns of myelination and iron deposition during brain maturation and ageing may result in better utilization of susceptibility contrast for clinical evaluations of various neurological diseases. |
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