# Near Infrared Illumination Optimization for Vein Detection: Hardware and Software Approaches
## 3 Results and Discussion
### Evaluation of Near Infrared LEDs Wavelength and Arrangement
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \((\lambda)\) & **HPM9** & **CPM9** & **HPR8** & **CPR8** & **HAM9** & **CAM9** & **HAR8** & **CAR8** \\ \hline
**720 nm** & 1 & 1 & 1 & 1 & 0 & 0 & 0 & 0 \\
**760 nm** & 0 & 0 & 3 & 3 & 0 & 0 & 0 & 0 \\
**850 nm** & 7 & 8 & 7 & 8 & 3 & 3 & 3 & 3 \\
**900 nm** & 7 & 8 & 7 & 8 & 3 & 3 & 2 & 2 \\
**940 nm** & 7 & 8 & 6 & 5 & 3 & 3 & 1 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Vein counting on palm and arm areas at different incident wavelengths. and capillaries than the papillary layer and has a denser and thicker network. In many early investigations on skin optics, the epidermis and the dermis are treated as separate optical mediums. Since the epidermis lacks veins and capillaries, haemoglobin can only be found in the dermis. The third layer below the dermis is subcutaneous tissue. It is crucial to remember that it is not considered an additional skin layer. The average thickness of this layer is stated to be 4 to 9 mm [28]. NIR radiation enables the sight of veins 3-5 mm beneath the skin, commonly employed for catheterization or blood draws [14]. In the upper arm, the average thickness of the skin is 2.00 mm (2.14 mm in men and 1.84 mm in females) [29]. The epidermis of the human palm is the thickest (approximately 1.5 mm) [23]. The dermis (thin inner skin) contains fewer blood vessels than the arm [23]. In terms of NIR light penetration, the arm skin layer has a thicker dermis layer that is an excellent site for vein imaging. Figure 11 reveals that the total vein counting applying the HR (Hessian Ring LED) image processing technique for the palm area was higher than the HM (Hessian Square LED) arrangement as the number of vein counts on the image 760 nm was included. Furthermore, the image processing encounters an error to process the 760 nm images for the square LED arrangement, causing it to be omitted as the selected wavelength. The studied area produced the same findings for the contrast method, either square LED or ring LED arrangement on the palm. Figure 12 reveals that both HM (Hessian Square LED) and CM (Contrast Square LED) showed the same number of vein counts on the arm area. Figure 11: Number of vein counts vs LEDs arrangement for the palm area. Near-infrared radiation is able to penetrate human tissue [1]. Infrared radiation was focused on the palm and arm area for this current study. An increase in the penetration depth can be achieved using longer wavelengths of light [30]. However, the composition in blood vessels, such as water, oxyhaemoglobin and deoxyhaemoglobin affected the penetration and absorption processes in the vein. This is because epidermal energy absorption depends on the water content [31]. Furthermore, human skin absorbs light differentially where the absorption can be increased by the deoxygenated blood haemoglobin [32]. For the 850 nm wavelength, the composition of water is lower compared to the composition of deoxyhaemoglobin and oxyhaemoglobin. Therefore, it has a low affinity to water, causing the wavelength to be absorbed more by the vein. In terms of the LEDs arrangements, the ring LED arrangement creates a non-uniform light distribution and the center area of the region of interest was not illuminated enough. The result in the arm area shows the same result, whereas the square LED arrangement has shown a more promising result. The increase in the square LED is considered sufficiently significant, even if the number of vein counting is increased by one. Hence, the counting was focused on the arm area since it is commonly used for venepuncture. Different configurations are studied for the simplicity and accuracy of the illumination process. These configurations include ring LED and square LED arrangements for the light radiation source. While both of the presented arrangement configurations offer a good contrast in the region of interest, the results from the experiments suggested that the square LED arrangement LEDs provide better results in terms of radiation distribution and uniformity [33].