Diffusion tensor imaging study of brain precentral gyrus and postcentral gyrus during normal brain aging process

Abstract Objective To study the changes of white matter tracts in precentral gyrus and postcentral gyrus during normal brain aging process by analyzing fractional anisotropy (FA) values obtained from diffusion tensor imaging (DTI) technology. Methods Magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) were conducted on 120 healthy right‐handed subjects. The subjects were separated into four age groups, namely Young Male/Female (<45 years old) and Senior Male/Female (>45 years old). Each subject undertakes routine MRI and DTI scans. Left/right precentral and left/right postcentral gyrus are automatically detected on the image. The area for region of interest (ROI) is set to be 18 ± 2 mm2. Results For each age group, the FA values of white matter in precentral gyrus and postcentral gyrus are statistically different (p < .05) in both left and right sides of the brain across different age groups and genders. Additionally, the FA values are statistically different (p < .05) between two young and senior age groups across different genders, brain regions, and hemispheres. Conclusion The FA values of precentral gyrus and postcentral gyrus are statistically different across genders, age groups, and hemispheres. Additionally, the FA values of both precentral gyrus and postcentral gyrus decrease over time, which is a strong indication of aging.

obtained from DTI studies. These parameters include mean diffusivity (MD), fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD) (Landman et al., 2007). One of the most commonly utilized parameter is FA (Sorensen, Wu, & Copen, 1999). To be specific, FA values refer to the percentage of water molecules that diffuse along the axon as compared to other directions. The closer FA value is to 1, the more anisotropic the white matter is, and the better the integrity of the white matter is preserved (Büchel et al., 2004). precentral gyrus and postcentral gyrus are the sites where primary motor cortex and primary somatosensory cortex are located, respectively. Although there are numerous reports on the DTI study of white matter (Madden, Bennett, & Song 2009;Madden et al., 2012), the majority of them were focused on diseases models such as ischemic stroke (Kunimatsu et al., 2003), ALS (Bowen, Pattany, & Bradley, 2000), schizophrenia, and (Kubicki, Park, & Westin, 2005) Alzheimer's Disease (Douaud, Jbabdi, & Behrens, 2011). To the best of our knowledge, there is no report on the changes of the microscopic structure and function of precentral gyrus and postcentral gyrus during normal aging process.
Given there is an increasingly medical need for the treatment/preventing of motor and sensation impairment among the senior population (Seidler, Bernard, & Burutolu, 2010), the present study is focused on structural changes of precentral gyrus and postcentral gyrus during normal aging process by using DTI as a tool. and Female (n = 30), with the age ranging from 20 to 44, average age = 35; Senior Male (n = 30) and Female (n = 30), with the age from 45 to 81, average age = 59.

| Inclusion criteria
1. Right-handed; 2. Mini-mental State Examination score > 27; 3. no symptoms of neurological diseases; 4. no history of brain surgery or traumatic brain injury, hypertension, diabetes, or cardiovascular diseases; 5. no history of alcohol abuse, smoking addiction, or drug addiction; 6. no MRI contraindication; 7. no history of epilepsy or meningitis; 8. no history of cerebral anoxia or chronic hypoglycemia; and 9. no lesions observed during routine MRI.

| Data acquisition
Diffusion tensor imaging was performed on subjects who meet the abovementioned criteria, and the images were further processed to eliminate artifacts and to exclude low-quality images. All subjects have signed consent forms.
MRI and DTI data were collected on an HDXT 1.5 T scanner (General Electric Health Care) with 8-channel head coil. The scanning protocol includes axial DTI with echo planar imaging (EPI) sequence: TR/TE = 8000/98.3 ms, slice thickness = 4.0 mm, slice gap = 0.0 mm, FOV = 22 × 22 cm, and NEX = 2; the scan was performed from the lower edge of corpus callosum to the top edge of the brain with a total of 18 slices. In addition to the DTI acquirement, which was used for the analysis here, the scanning protocol included structural sequences to rule out any impairment. The duration of the scan is 4 min 24 s.

| Image processing
Diffusion tensor imaging data were processed on an ADW 4.5 workstation equipped with Functool software to generate images. The precentral gyrus and postcentral gyrus on one side of the brain are identified by an experienced radiologist, and a region of interest (ROI) with an area of (18 ± 2) mm 2 was manually selected on this side. Subsequently, by using the auto-detection function of the program, precentral gyrus and postcentral gyrus on the opposite site of the brain are detected automatically (Figure 1) with the same area of ROI, (18 ± 2) mm 2 . Depending on the size and shape of the precentral gyrus and postcentral gyrus, minor modifications were adopted based on the automated selection of ROI for each specific

| Statistical analysis
The statistical analysis was conducted with commercial software SPSS 21 for t test. All results were shown in average with a standard deviation. p value was calculated to determine whether there is significant difference between the two brain regions that are studied (i.e., precentral gyrus and postcentral gyrus).

| RE SULTS
The FA values obtained from DTI scanning showed a significant difference between precentral gyrus and postcentral gyrus in all age groups comparing the same side of the brain. The data are summarized in Tables 1 and 2. For example, as shown in Table 1

| D ISCUSS I ON
The significant difference of FA value between the precentral gyrus and postcentral gyrus reflects that their microscopic structures are distinct from each other due to different roles they plan in motion control and body sensation. The distinct functionalities of precentral gyrus and postcentral gyrus are consistent with the observed difference of FA values between these two brain regions for all age groups. As summarized in Tables 1 and 2, the FA values of precentral  (Lebel, Caverhill-Godkewitsch, & Beaulieu, 2010;Meyer et al., 1996;Michielse, Coupland, & Camicioli, 2010;Sullivan, Adalsteinsson, & Pfefferbaum, 2005). Our study revealed that although FA values follow the trend of decreasing over time, the FA value of precentral gyrus on the posterior side is greater than that of postcentral gyrus on the anterior side. In addition, it was reported that precentral gyrus has a greater volume than the postcentral gyrus, which is called wide belt sign (Damoiseaux, Smith, & Witter, 2009 (Wei, Luo, & Li, 2009). It is possible to delay the onset of brain aging by physical training.
It is worthwhile to note that Male Group (Young and Senior) tends to have slightly higher FA values than Female Group (Young and Senior). The difference across the two genders also possibly arises from the difference in the amount of acquired physical training that helps slow down the rate of brain aging. In addition, as shown in Tables 1 and 2, FA values on the left side of the brain are generally higher than those on the right side. Since all subjects

| CON CLUS ION
Our study analyzed the FA values of both brain regions in different age groups using DTI scanning and discovered the microscopic environment in brain white matter changes over time for both precen-

CO N FLI C T O F I NTE R E S T
The authors declare there is no conflict of interest.

AUTH O R CO NTR I B UTI O N
Ling Zhou and Zuo-Jun Geng contributed to the conception and design of the study. All authors participated in the clinical practice, including diagnosis, treatment, consultation, and follow-up of patients.

PE E R R E V I E W
The peer review history for this article is available at https://publo ns.com/publo n/10.1002/brb3.1758.

DATA AVA I L A B I L I T Y S TAT E M E N T
The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.