Anatomical characteristics of thalamus-cortical sensory tract in the human brain using diffusion tensor tractography at 3.0 tesla scanner – Pham Thanh Nguyen

Journal of military pharmaco-medicine n 0 6-2018 129 ANATOMICAL CHARACTERISTICS OF THALAMUS-CORTICAL SENSORY TRACT IN THE HUMAN BRAIN USING DIFFUSION TENSOR TRACTOGRAPHY AT 3.0 TESLA SCANNER Pham Thanh Nguyen*; Lam Khanh**; Nguyen Duy Bac*** SUMMARY Objectives: To study characteristics of thalamocortical tract according to the cerebral origin. Using diffusion tensor tractography at 3.0 Tesla scanner, we attempted to characterize the morphology of thalamocortical tract in the human brain. Subjects and methods: 50 healthy subjects were enrolled in this study. Reconstructed images of thalamocortical tract in the human brain using diffusion tensor tractography at 3.0 Tesla scanner. Results: The median length of the right thalamocortical tract was 130.64 mm and the left was 123.14 mm, the average of two sides was 126.34 mm. The difference between two sides was statistically significance. The median fiber number of the right thalamuscortical tract was 401.50 and the left was 315.00 fibers, and the average of two sides was 365.50 fibers. There was a diverse branch of thalamuscortical tract: two branches (5%); three branches (25%); four branches (42%); five branches (16%); six branches (12%); in which contralateral branch for the right was 50%, equal to the left (50%). Conclusion: Using the diffusion tensor images and 3D image reconstruction technique allows to build the intuitive and accurate image of sensory thalamocortical tract, which helps to identify the morphological characteristics of the thalamus-cortical tract of healthy people without invasion. * Keywords: Sensory thalamocortical tract, Diffusion tensor tractography. INTRODUCTION Understanding the connection in a region and between regions within the brain helps us to know the functional activities and coordinate activity role of those regions (Passingham, Stephan et al, 2002). The nervous tract within the human brain can be determined by injecting fluorescent pigments after autopsy; however, the distance for observing only about 10 mm (Mufson, Brady et al, 1990). For further distance can be determined by dissection of the large conduction bundle, or by degradation after a local injury (Van Buren, 1972). However, they are invasive methods and impossible to identify and visualize the neural tract in the live human brain. Studying about the conduction bundle by non-invasive methods was almost handled on animals (Barbas and Pandya, 1987; Scannell, Burns et al, 1999) [2], the researchers on human brain did not use this method much. * Haiphong University of Medicine and Pharmacy ** 108 Military Central Hospital *** Vietnam Military Medical University Corresponding author: Nguyen Duy Bac (bac_hvqy@yahoo.com) Date received: 11/04/2018 Date accepted: 20/06/2018 Journal of military pharmaco-medicine n 0 6-2018 130 The diffusion tensor imaging (DTI) based on the diffusion anisotropy of the water molecules in the axons (Basser, Mattiello et al, 1994 [3, 4]). DTI is a new technique, which helps to determine the neural tracts, mostly in the living human brain. The anatomical images of sensory tract connected from the thalamus to other regions throughout brain are important for clinical practice. However, it has not been studied much, especially in Vietnam. We carried out the research: To investigate the characteristics of thalamus-cortical sensory tract according to the cerebral origin in the living human brain by using DTI and tractography. SUBJECTS AND METHODS 1. Subjects. 50 healthy subjects ≥ 18 years old with no previous history of neurological, psychiatric, or physical illness were enrolled into this study. All subjects understood the purpose of the study. The study protocol was approved by 108 Military Central Hospital. 2. Methods. * Diffusion tensor image: DTI data were obtained by using Phillips Achieva 3.0 T, SENSE NV 16 coil channels. Make the sections from background to top of the skull with the basic pulse chain T1W, T2W, FLAIR. Imaging parameters were as follows: acquisition matrix 128 x 128, FOV 230 x 230 mm2, TR: 10,172 ms, 93 ms, EPI factor b0 and b 1,000 s/mm2, section thickness of 2 mm (acquired isotropic voxel size, 1.8 x 1.8 x 2 mm3). * Fiber tracking: Diffusion-weighted image and DTI data were analyzed using software Philips Extended MR Workspace 2.6.3.1. Figure 1: The seed regions of interests (ROI). Construction 2D color map of fractional anisotropy (FA) was used to seed ROI. A B C Journal of military pharmaco-medicine n 0 6-2018 131 Construction 2D color map of fractional anisotropy (FA) has used to seed regions of interest (ROI) according to know anatomy (Akter, Hirai et al, 2011) [1]. The first ROI placed in the Commissuracerebelli, dark blue region on the FA 2D map (fig.1A); the second ROI placed in the thalamus (fig.1B); the third ROI placed in the posterior of capsulainterna, dark blue area on the the FA 2D map (fig.1C). The software to reconstruct 3D image of sensory thalamocortical tract was used to analyze the length, number of tract, and morphology. * Statistical analysis: The statistical package for the social sciences software (version 15.0; SPSS, Chicago, Illinois) was used for data analysis. The independent t-test was used to determine the difference in values of length, volume of sensory thalamocortical tract between sexes and two hemispheres. The significance level was set as p < 0.05. The distribution of ages, sexes and morphology of sensory thalamocortical tract were shown as the percentages. RESULTS 1. Characteristics of the subjects. Table 1: Age and gender of the subjects. Age groups, n (%) 18 - 39 40 - 59 ≥ 60 Total Male 9 (18%) 14 (28%) 3 (6%) 26 (52%) Female 12 (24%) 9 (18%) 3 (6%) 24 (48%) Both genders 21 (42%) 23 (46%) 6 (12%) 50 (100%) In this study, subjects distributed mostly in young and middle-age (18 - 39 years old) accounted for 42%; 40 - 49 years old accounted for 46% and ≥ 60 years old accounted for 15%. The percentage of two genders was similar with male (52%) and female (48%). 2. Characteristics of thalamus-cortical sensory tract. Figure 2: The 3D reconstructed images of sensory thalamocortical tract. Green showed the tract on the right hemisphere and the yellow illustrated for tract of the left hemisphere. Journal of military pharmaco-medicine n 0 6-2018 132 The 3D reconstructed images of sensory thalamocortical tract were built successfully based on diffusion tensor image and fiber tracking by using the dedicated software. Based on the clearly images, we can measure the length, and count the number of bunch in each hemisphere separately. Figure 3: Comparison of sensory thalamocortical tract length between right and left hemisphere. Values represent median (± SD); n = 50 for each side; *** represent p < 0.001 left side versus right side. The results showed that the median length of sensory of thalamocortical tract on the right hemisphere (130.64 mm) was statistically significance longer than the left one (123.14 mm). This suggested that there were differences in the anatomical characteristics of sensory thalamocortical tract length between the right and the left. Figure 4: Length comparison of right (A) and left (B) of the sensory of thalamocortical tract between sexes; values represent median (± SD); male (n = 26), female (n = 24). Journal of military pharmaco-medicine n 0 6-2018 133 We also investigated influence of gender on the length of sensory of thalamocortical tract by comparing the sexes. Results of statistical analysis showed that the length bunch of male tended to be longer than that of female; however, there were no significant differences between sexes. Figure 5: Comparison of number of sensory thalamocortical tract lines between right and left hemisphere. Values represent median (± SD); n = 50 for each side. We counted the number of lines of the sensory of thalamocortical tract on both sides of the hemisphere. The statistical analysis showed that the median number of right side (401.5) tended to be higher than the left (315.0). However, the difference was not statistically significant. Figure 6: Comparison of number of lines in right (A) and left (B) sensory of thalamocortical tract between two genders; values represent median (± SD); male (n = 26), female (n = 24). Journal of military pharmaco-medicine n 0 6-2018 134 The results of comparing the number of sensory thalamocortical tract lines between two genders showed that the lines of right side was equivalent in the two sexes, in the left side, the lines of male tended to be lower than female. However, the difference had no statistically significance. Figure 7: Branch morphology of the sensory thalamocortical tract. (A - E: The number of branches from 2 - 6; F: Branching into contralateral hemisphere) Based on the 3D reconstruction images of the sensory of thalamocortical tract and the number of branches, we classified the branch morphology as following: 2, 3, 4, 5, 6 or contralateral branches. Table 2: The branch morphological distribution of the sensory thalamocortical tract. Branch morphology, n (%) Right hemimsphere Left hemisphere Total 2 branches 3 (3%) 2 (2%) 5 (5%) 3 branches 14 (14%) 11 (11%) 25 (25%) 4 branches 22 (22%) 20 (20%) 42 (42%) 5 branches 6 (6%) 10 (10%) 16 (16%) 6 branches 5 (5%) 7 (7%) 12 (12%) Contralateral branches 6 (50%) 6 (50%) 12 (100%) The results showed that sensory thalamocortical tract was the polymorphic branch. The most abundant was 4 branches morphology; the other morphologies, including 3 branches, 5 branches, 6 branches, 2 branches morphology was the lowest. The obtained images showed the appearance of branch into the contralateral hemispheres, with the left and right ratio equal on each side. Journal of military pharmaco-medicine n 0 6-2018 135 DISCUSSION Our results showed that the length of sensory of thalamocortical tract on the right hemisphere (130.64 mm) was statistically significance longer than on the left hemisphere (123.14 mm). The study by Kamali et al (2009) [7] about the sensations in the brain stem did not show any differences in length between the right and left side. The differences between our results and the Kamali’s can be explained, the different anatomical locations could also lead to differences in the structure. Moreover, there are always differences in general function and sensory conduction, in particular, between the right and left side of brain (Kobayashi, Takeda et al, 2005 [8]), which may lead to differences in the length of sensory of thalamocortical tract between two sides. When we compared the length of sensory of thalamocortical tract between two sexes, the results showed that the one in male tended to be longer than in female, this may be due to the brain of male larger than female (Luders, Gaser et al, 2009 [9]). However, the differences were not statistically significant due to the amount of analysis may be not large enough. The number of the sensory thalamocortical tract lines showed in the right hemisphere (401.5) higher than that in the left hemisphere (315.0), although the difference was not statistically significant. This may be due to the majority of research subjects are right-handlers, which can make the sensory transduction differences between the right and left side of the body (Tan 1993; Patel and Mehta, 2012 [10,11]). To clarify this requires, it need to have an extensive research with the big enough number of research subjects. In the relationship between gender and number of the sensory thalamocortical tract lines, notably the numbers on the left side in male (295.5) were much lower than in female (347.0), although the difference was not statistically significant, while the number on the right side is almost equivalent between male (401.5) and female (398.5). These differences were quite interesting, though to assert that require larger studies to clarify these phenomena. Our results showed that the sensory thalamocortical tract was the polymorphic branch. The diversity of morphology may be related to the function and distribution of nerve conduction bundles, and also related to the diversity of subjects studied (gender, age). The DTI in studying the anatomical characteristics of the sensory thalamocortical tract was the new advanced techniques not only in Vietnam but also in the world, since it was established (1994), so far this was the ideal method for the study of white matter, designated the nerves and neurotransmitters on the non-invasive living body (Han, Ahn et al, 2008; Hong, Son et al, 2010 [5, 6]). CONCLUSIONS Our results were important to anatomical reference parameters for understanding normal function through the brain in sensory transduction from the thalamus to the cortex. 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