Circle of Willis was thus classified as 1) complete (all component vessels of both anterior and posterior parts of the circle of Willis visible and ≥ 0.8 mm diameter) or 2) incomplete (either anterior or posterior parts of the circle of Willis incomplete).
The yellow circle indicates posterior area within 3 mm from the fovea and the outside of that was considered as the mid-periphery.
The arc angles of the elbow workspace range from 68.8° to 83.4° and are located at the lateral and posterior quadrant of the circle on which the elbow trajectories located.
The two configurations of the posterior part of the circle of Willis, the non-foetal configuration (diameter PCoA < diameter P1) and the foetal configuration (diameter PCoA > diameter P1), were analysed.
Although these variants in the anterior and posterior parts of the circle of Willis circulation account each for 2 10 % in the general population [ 15], the combination of these variants in a single individual most likely reflects a developmental abnormality.
In addition, two configurations of the posterior part of the circle of Willis can be distinguished: a non-foetal configuration, when the diameter of the PCoA is smaller than the diameter of the ipsilateral P1 segment of the posterior cerebral artery (P1), and a foetal configuration, when the diameter of the PCoA is larger than the diameter of the ipsilateral P1.
The correlation between the left and right halves of the posterior part of the circle of Willis, for the P1, the PCoA and the P1/PCoA ratio, shows us the relation between the blood supply of the left and the right hemispheres.
The data showed a correlation between the left and the right halves of the posterior part of the circle of Willis for the diameter of the P1 (R = 0.457, P = 0.002), the diameter of the PCoA (R = 0.554, P < 0.001) and for the P1/PCoA ratio (R = 0.462, P = 0.005).
Furthermore, a significant correlation was found between the diameter of the P1 and the diameter of the PCoA, and a significant correlation between the left and right halves of the posterior part of the circle of Willis for the diameter of the P1, the diameter of the PCoA and the P1/PCoA ratio.
