# Feasibility of LED-Assisted CMOS Camera: Contrast Estimation for Laser Tattoo Treatment
## 1 Introduction  
Owing to the characteristics of a tattoo (i.e., body location, size, depth, age, and pigment color) [1; 2; 3; 4; 5], a number of tattoo removal techniques are in use, including surgical excision, cryosurgery, chemical destruction, and laser removal [3; 6; 7; 8; 9]. Currently, laser tattoo removal is considered to be one of the most efficient techniques owing to the selective treatment of the tattoo pigments. Unlike surgical excision, the laser removal method delivers various wavelengths, selectively targets the particular tattoo pigments, and then fragments the pigment into small particles using short pulsed laser light [10; 11; 12]. These fragments are then removed from the skin through the lymphatic system or trans-epidermal elimination [13; 14]. In addition, the targeted tattoo pigments specifically absorb laser light with no or minimal injury to the surrounding healthy tissue. Thus, the method can reduce pain, treatment time, and complications [2; 8; 13].  
Typically, laser treatment requires many sessions to completely remove the tattoo from the skin. Thus, the quantification of the amount of tattoo clearance after each treatment can be critical in optimizing treatment parameters such as fluence and repetition rate to minimize the number of the sessions for the complete tattoo removal. Recently, various qualitative assessments have been studiedto identify the residual tatto concentration after a laser treatment, including histology, invisible radiation photography, optical coherence tomography (OCT) [15; 16], and two-photon microscopy (TPM) [17]. However, most assessment methods are costly and time consuming (or non-real-time). In particular, OCT can determine the degree of tattoo distribution in the skin after the treatment owing to the absorption/scattering responses of the tattoo in the infrared (IR) spectra. The tattoo can be detected by variations in the contrast between the tattoo pigmented area and the normal skin area with an OCT image [15; 16]. However, the limitation of this method is that certain inks can be undetectable because of the high transmission in the IR range [15].  
In the current study, we developed a simple imaging device to detect the relative variations in the tattooed skin after laser treatment. Owing to its cost-effectiveness and simple operation, a complementary metal-oxide-semiconductor (CMOS) camera was chosen to acquire the images of the tattooed skin. To minimize external exposure factors (i.e., environmental illumination, intensity, exposure time, etc.), light emitting diodes (LEDs) were used to irradiate the tattoed area in a dark room during image acquisition. In particular, LEDs are a less expensive light source and can emit various wavelengths (e.g., blue, green, and red) with narrow bandwidths and low intensities [18; 19; 20; 21]. Thus, it was hypothesized that a CMOS camera with cost-effective and small-sized LED sources could be a feasible imaging tool to estimate the contrast variations in the tattooed skin after a laser treatment [20; 21]. Furthermore, because the laser-treated tattoo can be removed through the lymphatic system or trans-epidermal elimination [13; 14], the current study evaluated the proposed device in vivo to emulate clinical conditions.