Anatomical characteristics of thalamus cortical sensory tract in the human brain using diffusion tensor tractography at 3.0 tesla scanner

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.

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)

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

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 (%)

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

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)

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)

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 (%)

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

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 It was also the basis for the assessment, detection of functional area

of brain and understanding the mechanics

of some diseases related to brain injury

and nerve conduction clinically such as:

stroke, degenerative myelin, diffuse axonal

injury, Wallerian degeneration The study

also opened up a new direction in DTI

applications to study neurotransmitter

activity about physiological conditions and

diseases and understand the function of

neural activity in clinical applications

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