# Feasibility of LED-Assisted CMOS Camera: Contrast Estimation for Laser Tattoo Treatment
## 2 Materials and Methods  
All animal experimental procedures were implemented in accordance with the guidelines of the Korean National Institute of Health and were approved by the committee on animal care and use at the Pukyong National University (Permit Number: 2016-30). Six Asian mice (150-200 g; eight weeks old) were used as the animal model for the current study. The mice were fed in an individual 108 cm\({}^{2}\) cage (temperature = 22 \({}^{\circ}\)C and humidity = 55%). Prior to tattooing, each mouse was anesthetized with a 0.3-mL solution of Zoletil and Rompun (3:1 ratio). Two commercially available tattoo inks were used for the tests: black (E02-1, Eternal Tattoo Supply, Brighton, MI, USA) and red inks (Odyssey red, D&H Company, Seoul, Korea). Each ink was tattooed on the back of a mouse after its hair was shaved completely, and three mice were tested for each color. The tattoo ink was injected approximately 1 mm below the skin using a reciprocating vibrator-driven needle. Two 1-cm-long tattoo bands (0.2-cm thick and 1 cm apart) of each color were created on the back of each animal (Figure 1a). After the tattoo areas had completely healed (14 days), each mouse received a laser tattoo treatment under anesthesia. Owing to the different characteristics of light absorption [5; 11; 13], the black and red  
Figure 1: Experimental setups of (**a**) in vivo laser tattoo treatment and (**b**) analysis of tattoo contrast with LED-assisted CMOS camera. tattoos were removed using Q-switched 1064-nm and 532-nm wavelengths, respectively (Iris, Bluecore Company, Busan, Korea). The laser conditions for the tattoo treatment included a spot size of 5 mm on the skin, a pulse duration of 8-10 ns, and a repetition rate of 1 Hz. For comparison purposes, one-half of each tattoo band was removed by the laser treatment (i.e., 0.5 cm on the left side), and the other half remained intact. The aiming beam was precisely aligned and positioned on half of the tattoo band prior to the treatment. Based on the previous in vivo studies [5; 11; 13], fluences of 1.5 J/cm\({}^{2}\) and 0.5 J/cm\({}^{2}\) were selected for removing the black and red tattoos, respectively. Table 1 shows a summary of the laser parameters used for the current study. To estimate the relative variations in the tattoo contrast after a laser treatment, a CMOS camera was utilized with the assistance of multicolor LEDs. According to Figure 1b, the customized imaging device consisted of a 25-mm focal lens (66-895, Edmund Optics, Barrington, NJ, USA), a monochromatic CMOS camera (DMK AFUX236-M12, The Imaging Source, Taipei City, Taiwan) with a high resolution (1920 \(\times\) 1200), a frame rate of up to 54 fps, and three different LEDs (SLTRGB35066N, Samsung, Suwon, Korea). Both the CMOS camera and LEDs were vertically positioned above each sample, as shown in Figure 1b. The LEDs were able to selectively irradiate three different light colors (red, green, and blue lights) in a predetermined manner using an LED controller. According to the manufacturer, the central wavelengths of the red, green, and blue lights (i.e., RGB lights) correspond to 635, 530, and 450 nm, respectively. During the irradiation, each LED was measured to generate a luminous intensity of 300 mcd. Each tattooed area was then captured pre and post treatment by exploiting the customized imaging device under the irradiation of various LED colors. A total of six images were acquired for each tattoo. All the post-treatment images were captured two weeks after the laser treatment, which corresponds to the time required for the complete tissue healing [11; 13]. Both the non-treated and the treated areas on the tattoo band were detected from the acquired images.