The Age-related Changes Of Normal Adult Brain Structure And Leukoaraiosis: Studied With 3.0T MR DT1

Part One: The age-related changes of normal adult brain structure: DTI studyObjective: To investigate the fractional anisotropy (FA) and mean diffusivity (MD) of white matter fibers and gray matter nucleus of various age groups in order to reflect the brain microstructure changes with advancing age indirectly in diffusion tensor imaging with 3.0Tesla MR scanner.Materials and Methods: 80 normal adults (47 men, 33 women; age range 20～81 years; mean age 49.5 years) were divided into 3 groups according to their ages: younger group in 28 cases (20～39 years), middle age group in 30 cases (40～59 years) and older group in 22 cases (≥60 years). All subjects were without neurological diseases or disorders affecting the cental nervous system and were examined with GE Signa Excite 3.0T using 8 channels head coil. The sequence included T1 FLAIR, T2WI, FLAIR and diffusion-weighted imaging (DWI) partially, and diffusion tensor imagin with diffusion sensitive gradients applied in 25 directions, b value equal to 1000s/mm² . 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, anterior limb and posterior limb of internal capsule, frontal lobe white matter, centrum semiovale, head of caudate nucleus, thalamus 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. P 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 80 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 highest(0.784±0.049), from high to low, having genu of corpus callosum, posterior and anterior limb limb of internal capsule, centrum semiovale, frontal lobe white matter. The comparison between head of caudate nucleus and lentiform nucleus was not statistically significant. The MD of genu of corpus callosum was the highest, but the rest of brain structures were or were not statistically significant which had no obviously distribution rule.(3) FA and MD varied among different structures and different age groups in normal adult brain. The values were confined between maximum and minimum.2. The correlation of FA/MD in different structures with age(1) The FA of genu of corpus callosum, anterior limb and posterior limb of internal capsule, frontal lobe white matter and centrum semiovale showed significant negative correlation with age (P<0.05) . Surprisingly, the FA of thalamus and lentiform nucleus showed significant positive correlation with age (P<0.05) . The correlation of FA with age did not reach statistical significance in splenium of corpus callosum, posterior limb of internal capsule and head of caudate nucleus which showed a descending tendency (P>0.05 ) .(2) The MD of genu of corpus callosum, anterior limb and posterior limb of internal capsule, frontal lobe white matter, centrum semiovale, head of caudate nucleus, thalamus and lentiform nucleus demonstrated significant positive correlation with age. The correlation of MD with age did not reach statistical significance in splenium of corpus callosum which showed a rising tendency (P>0.05) .3. The comparison of FA and MD of different structures among age groups(1) The comparison of FA among groups: The difference of FA in genu of corpus callosum, anterior limb of internal capsule, frontal lobe white matter, centrum semiovale, thalamus, lentiform nucleus was statistically significant among 3 groups(P<0.05) . The FA of genu of corpus callosum in younger group was obviously bigger than that in middle age group (P<0.01) , the younger group bigger than older group (P<0.05) . The FA of anterior limb of internal capsule in younger group was obviously bigger than that in older group. The FA of frontal lobe white matter, centrum semiovale 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 obviously bigger than that in younger group, the older group bigger than middle age group, and lentiform nucleus in older group than younger group. Furthermore, posterior limb of internal capsule just showed the middle age group bigger than older group.(2) The comparison of MD among groups: The difference of MD in genu of corpus callosum, anterior limb and posterior limb of internal capsule, frontal lobe white matter, centrum semiovale, thalamus, head of caudate nucleus, lentiform nucleus was statistically significant among 3 groups (P<0.05) . The MD of genu of corpus callosum in middle age group was bigger than that in younger group (P<0.05), the older group obviously bigger than younger group (P<0.01). The MD of frontal lobe white matter in older group was obviously bigger than that in middle age group than younger group. The MD of other structures almost showed that the older group was bigger than younger group, the older group bigger than middle age group. The difference of MD in splenium of corpus callosum didn't show statistical significance among 3 groups.Conclusion: 1. Diffusion Tensor Imaging in 3.0Tesla MR can display the anatomy structures of cerebral white matter fibers more nicely, that could offer the condition in order to analyze the brain microstrucrure changes with an accurate positioning and quantification. Different brain structures have different diffusion and anisotropy characters. It could be in favor of clinical research and reference that we have received the normal threshold values of major anatomic sites for normal adult in various age groups with 3.0Tesla MR.2. The value of FA and MD can reflect brain microstrucrure in quantification. The anisotropy changes of normal brain structures were correlated with age which having a rule. The FA of mostly brain structures was descended and the MD be increased with age. Remarkably, the FA of thalamus and lentiform nucleus was rising with age, and the parameter values of splenium of corpus callosum showed no correlation with age.3. Among different age groups, the FA and MD of mostly brain structures showed the difference between older group and younger group or middle age group which demonstrated the notable change happened in the brain microstructures of normal elderly over 60 years old. These information was that routine MRI can not find and offer, and it helped to form a reference standard for comparison with neurodegenerative disorders.Part Two: A DTI study of leukoaraiosisObjective: To study leukoraiosis (LA) in diffusion tensor imaging with 3.0Tesla MR scanner, to investigate the diffusion and anisotropy characters of the lesions and normal-appearing white matter (NAWM) of LA, and compare them with the FA, MD of normal control group. To find the correlation between the FA, MD of LA and the degree of severity of LA and cognition function.Materials and Methods: 50 LA patients (33 men, 17 women; age range 52～82years; mean age 67.8 years) and 35 normal elderly (23 men, 12 women; age range 50～81 years; mean age 66.3 years) were divided into 2 groups: LA group and control group. All subjects were examined with routine MR, DWI and DTI scan being same as the parameter of part one. We proceeded the DTI data post processing. The FA and MD were measured in the lesion and NAWM around the lesion which is located in around the anterior, posterior part of the lateral ventricles and centrum semiovale been selected as regions of interest (ROIs). The FA and MD were measured in the corresponding white matter of normal group with 3 ROIs each other position, getting the mean value of every position for the following computation. All LA patients were divided into four grades according to their severity and were checked by neurologist with MMSE to diagnose dementia. The FA and MD were compared between the lesion and NAWM of LA, between NAWM and normal white matter of control group. The correlation of FA and MD of the lesion and NAWM with the severity grade of LA and cognition function respectively was evaluated. P value less than 0.05 was considered as statistical significance.Results: 1. The characters of anisotropy and diffusion about the lesion, NAWM of LA and the comparison of FA and MD among the lesion, NAWM of LA and normal white matter of control group(1) The signal appearances of the lesion in LA were different in FA and MD maps. The differences of FA/MD in symmetrical positions of both brain hemispheres in LA group and control group were not statistically significant (P>0.05) . The differences of FA, MD between lesion and NAWM (50 cases) in the corresponding positions were all statistically significant (P<0.05) . The FA of lesion was obviously lower than that of NAWM; on the contrary the MD of lesion was obviously higher than that of NAWM.(2) The differences of FA, MD between NAWM (50 cases) and normal white matter of control group (35 cases) in the corresponding positions (around the anterior part of the lateral ventricle and centrum semiovale) were statistically significant(P<0.05) . It demonstrated the FA of the former was obviously lower than that of the latter; however the MD of the former was higher than that of the latter (P<0.01). The parameters of the around the anterior part of the lateral ventricle showed obviously different. The differences of FA, MD between NAWM and normal white matter of control group in the around the posterior part of the lateral ventricle were not statistically significant (P>0.05) .(3) The differences of FA, MD among different positions in the lesions and NAWM were statistically significant (P<0.05) . The multiple comparison of FA/MD among different positions showed that in lesions the FA around the anterior part of the lateral ventricle was the lowest (0.205±0.056); in NAWM the FA around the anterior part of the lateral ventricle was the lowest and MD was the highest, respectively being 0.318±0.066, (0.926±0.067)×10^-3mm²/s.2. The correlation between FA, MD of the lesion/ NAWM and grade of LA(1) The FA showed significant negative correlation with grade of LA. The more serious of LA, the lower of FA. The correlation between the FA of the lesion around the anterior part of the lateral ventricle and grade of LA was the most obvious(P<0.05) ; however the FA of NAWM of centrum semiovale showed no significant correlation with grade of LA which just had a descending tendency (P>0.05) .(2) The MD showed significant positive correlation with grade of LA. The more serious of LA, the higher of MD. The correlation between the MD of the lesion and NAWM around the anterior part of the lateral ventricle and grade of LA was the most obvious (P<0.01); however the MD of NAWM around the posterior part of the lateral ventricle and of centrum semiovale showed no significant correlation with grade of LA which just had a rising tendency (P>0.05) .(3) There was no significant correlation between grade of LA and age.3. The correlation among grade of LA, FA and MD of lesion/ NAWM and cognition function (MMSE)(1) The grade of MMSE demonstrated significant negative correlation with grade of LA (r = -0.679, P=0.000). The more serious of LA, the lower grade of MMSE. The incidence of dementia showed significant positive correlation with grade of LA ( x²=19.958, P=0.000) . The more serious of LA, the higher incidence of dementia.(2) The FA, MD of lesion/ NAWM showed significant correlation with the count of MMSE. It showed the lower count of MMSE, the lower of FA, the higher of MD in which the MD of lesion and NAWM around the anterior of the lateral ventricle was the most obvious (P=0.000) .Conclusion: 1 . The technique of DTI could find the change of brain microstructure in LA routine MRI could not offer and the correlation among that and grade of LA and cognition function. The changes in FA, MD of lesion and NAWM were all characteristic which showed the former was descending; the latter was rising with different degree. The brain structure around the anterior part of the lateral ventricle was obviously influenced by LA.2. The DTI parameters of the lesions and NAWM could quantified response the severity degree of LA. Along with the grade of LA was more serious, the FA was lower and the MD was higher. The correlation between the appearances in DTI dof the lesion around the anterior part of the lateral ventricle and grade of LA was the most obvious. It could offer a helpful supervising fator for evaluating and deciding the grade of LA.3. The grade of LA demonstrated obviously correlation with the degree of cognition dysfunction which showed the more serious of LA, the higher incidence of dementia. The count of MMSE showed significant correlation with the MD of lesion and NAWM around the anterior of the lateral ventricle. DTI could observe the progressing of LA through supervising and measuring partial parameters which could be advantaged to make DTI being a significant evaluating instrument for retrospective research and clinical treatment of diseases.