Extracerebral layers ( ECL ) thickness variation within a subject between subjects

Objectives: To characterize the variations in extracerebral layer (ECL) thickness that exists within a subject. Secondly, to compare these ECL thickness variations across a group of subjects at two standardized location (at the level of the anterior commissure (AC) & 20mm above the AC (AC+20mm)). Finally, the influence of these ECL variations on propagation of light using the Monte Carlo simulations was determined. Method: T2-weighted brain MRI images were acquired from five young healthy subjects and viewed by MRIcro. Anterior commissure was chosen as the reference location for all subjects. MRI images were exported in 2 transverse slices per one subject; one at the AC and other one 20mm above the AC. Brain MRI images were loaded onto ImageJ and the line tool and fill functions were used to define angles from 0 to 360 ̊ within each image, using the AC as the point of origin. The color picker function was used with pencil tool to make red color land markers at two different locations. Therefore, total ECL thickness measurements were done by moving a line tool at ∆10 ̊ increment with use of measurement function from ImageJ. Results: There were 5 young healthy subjects for each with two transverse slices of brain MRI images at two different locations, resulting in a total sample of 10 image slices. At AC, the thinnest mean ECL thickness was at back head (region III) with value of 14.2mm. While the thickest mean ECL thickness was found at left side of head (region II) with value of 15.7mm. However at AC above 20mm, the thinnest post was at forehead (region I) with value of 10.9mm. The thickest mean ECL thickness was at back head (region III) with value of 14.9mm. Conclusion: It was found from the above results that the thinnest mean ECL thickness was found at the forehead on the AC+20mm slice. Since the fraction of NIRS signal containing information from the brain tissue increases as ECL thickness decreases, more accurate cerebral blood flow (CBF) measurements can be recorded at this location.