Role of Advanced MRI to Evaluate Structural and Functional Connectivity of Human Brain.

Role of Advance MRI to Evaluate structural and functional connectivity of Human Brain

The anatomy of human brain is the most sophisticated among all creatures. It is associated with human body movements, senses, human behavior, and intelligence. To properly understand brain, function a good understanding on structural and functional connectivity and associated brain networks is essential.

Structural Brain Connectivity: -Structural connectivity refers to anatomical connections by white matter fiber tracts that connect different parts of the brain. Structural connections can be understood as the underlying wiring of the Brain for signal transmission

Functional Brain Connectivity: -Structural connectivity refers to underlying wiring for signal transmission. But not all white matter tracts carry information all the time. Many functional networks in the brain have been identified where signal moves from one node to another. Functional connectivity can be explained based on the real time behavior of neuronal activity patterns which connect anatomically to different brain regions. It has been found that brain is active even in the resting state. Based on fMRI based studies a default mode network has been discovered that is found to be active even when the brain is in the resting state with no external stimuli.

Role of Magnetic Resonance Imaging (MRI): - Magnetic Resonance Imaging (MRI) provide high resolution tissue details in 3D image of the brain. MRI in particular has many modalities that provide a non-invasive and safe way to study many aspects of human brain. T1 and T2 images provide the brain structural details While Functional Magnetic Resonance Imaging (fMRI) provides information on brain activity in different parts of the brain, either as response to some stimuli or even in the resting state.  Diffusion Weighted Imaging (DWI) is highly useful imaging technique for research and diagnosis of the white matter related structures and their pathways as well connections. For mapping the white matter tracts in the brain, Diffusion Tensor Imaging (DTI) and Fiber Tractography play a vital role. DTI also helps in the quantitative analysis of brain diseases connected with white matter fibers.

Diffusion Tensor Imaging and Fiber Tracking: -Water in the brain diffuses faster along the neuronal fiber tracts than across them. This direction dependent diffusion is called anisotropic diffusion. In DTI whole water diffusion tensor is calculated at each voxel in the brain. This gives information about the fastest direction of diffusion in each voxel. Based on this information neuronal fiber Tractography can be performed which shows neuronal fibres as 3D curves on MRI images.

Functional MRI (fMRI) and Mapping of Brain Activity & Connectivity: - The blood flow changes during brain activity can create a MR contrast called the BOLD (Blood Oxygenation Level Dependent Contrast). Images acquired with BOLD contrast are called Functional MR Images.fMRI can be used to determine brain activation and functional connectivity. It permits images of brain activity to be acquired while a subject could be performing a task or even when the subject is resting.

So, we can evaluate structural and functional connectivity of different parts of brain which help us to understand various types of diseases based on functions of brain and structural study can help out diagnosis of anatomical details affected by diseases.

Keywords:

(Magnetic Resonance Imaging (MRI), Diffusion Weighted Imaging (DWI), Functional Magnetic Resonance Imaging (fMRI), Diffusion Tensor Imaging (DTI), BOLD (Blood Oxygenation Level Dependent Contrast).