Normal Aging In The Central Nervous System: Quantitative MR Diffusion-tensor Analysis

Objective To investigate the characteristics of diffusivity of white matter fibers and gray nucleus and to elucidate changes in mean diffusivity (ADC) and fractional anisotropy (FA) using MR diffusion tensor imaging (DTI) in the central nervous system during normal aging. Quantitative diffusion tensor analysis correlation with normal aging and may help in assessing normal age-related changes and serve as a standard for comparison with neurodegenerative disorders.Method MRI data were acquired in a group of 94 healthy subjects (42 males,52 females, range=20-80 years, all right handed) We tested for linear and nonlinear relationships between brain structure and age (see below) and also performed subgroup analyses for which we divided subjects into young adults (YA) (n=40,range=20-40years), middle aged (MA) (n=38, range=41-60years), and older adults (OA) (n=1, range=61-80years). All subjects were without neurological were examined with GE Signa Excite 3.0 T using 8 channels head coil. We received FA map and MD map using Functool software processing DTI data on AW 4.2 offered by GE Company. For each subject, genu and splenium of corpus callosum,posterior limb of internal capsule,frontal lobe white matter,centrum semiovale thalamus,hippocampus and lentiform nucleus were selected as regions of interest(ROIs). The values of fractional anisotropy(FA)and mean diffusivity(MD) of each ROI were measured. Then the FA/MD of different brain structures of normal adults were compared multiply. They also were correlated with the age respectively and compared among the 3 groups. Value less than 0.05 was considered as statistical significance.Results 1. The characters of anisotropy and diffusion about different brain structures(1)The differences of FA/MD in symmetrical positions of both brain hemispheres, the differences of FA/MD in the same structures of different gender were not statistically significant(P>0.05). The FA/MD of different brain structures of normal adults in 94 cases were received.(2)The multiple comparison of FA/MD of different brain structures showed that the FA of brain white matter was higher than grey matter. The FA of splenium of corpus callosum was the higllest(0.853±0.019), from high to low,having genu of corpus callosum, posterior of internal capsule, centrum semiovale, frontal lobe white matter. The thalamus is higher than lentiform nucleus and hippocampus in gray matter. The MD of brain structures were or were not statistically significant which had no obviously distribution rule.2. The correlation of FA/MD in different structures with age(1).The FA of genu of corpus callosum, frontal lobe white matter,hippocampus and centrum semiovale showed significant negative correlation with age(P<0.05). Surprisingly,the FA of thalamus of internal capsule, showed significant positive correlation with age(P<0.05). The correlation of FA with age did not reach statistical significance in lentiform nucleus and splenium of corpus callosum (P>0.05).(2)The MD of most structures we selected demonstrated significant positive correlation with age.3. The comparison of FA and MD of different structures among age groups(1)The comparison of FA among groups:The FA of genu of corpus callosum in younger group was obviously bigger than that in middle age group(P<0.05), the younger group bigger than older group(P<0.05).The FA of frontal lobe white matter,centrum semiovale and hippocampus in younger group was obviously bigger than that in older group, the middle age group bigger than older group. Differently,the FA of thalamus in older group was bigger than that in younger group, the older group bigger than middle age group.(2)The comparison of MD among groups:The difference of MD in the structres was statistically significant among 3 groups(P<0.05)except splenium of corpus callosum and lentiform nucleus.Conclusion:1. Diffusion Tensor Imaging in 3. OTesla MR can display the anatomy structures of cerebral white matter fibers more nicely,that could offer the condition in order to analyze the brain microstructure changes with an accurate positioning and quantification.2. The value of FA and MD can reflect brain microstructure in quantification. The anisotropy changes of normal brain structures were correlated with age which having a rule.3,The FA of mostly brain structures was descended and the MD be increased with age.3. These information was that routine MRI can not find and offer,and it helped to form a reference standard for comparison with neurodeg enerative disorders.