**2. Optical technology applying on the skin** *in vivo*

Histology remains the most accurate method for wound healing assessment, including biopsy and chamber-embedding, re-epithelization, epithelial thickness index, granulation tissue thickness, remodeling, and scarring can be obtained by histological analysis. Moreover, visual inspection also can evaluate woundswhich is based on observations such as wound size, color, odor, and level of pain [48–51]. The limitations of the histological analysis method are mainly invasive and destructive, the method generates new wounds during the examination, which delays the time of wound healing and is not suitable for patients at high risk of wound infection, thus reducing the accuracy of wound assessment. Therefore, non-invasive monitoring techniques are a safer way to assess and monitor wound healing, which can help clinicians and researchers more objectively determine and assess whether healing is

*Integrated Optical Coherence Tomography and Deep Learning for Evaluating of the Injectable… DOI: http://dx.doi.org/10.5772/intechopen.106006*

improving or deteriorating [50–52]. DRS is a non-invasive technique, and the general configuration of a DRS system includes a light source, a photodetector, and a fiber optic probe for light transmission. The DRS can measure the characteristic diffuse reflectance spectrum of tissue in the visible to near-infrared wavelength range. The tissue structure was restored by diffuse reflectance using photon transmission model and least squares curve fitting algorithm. In addition, DRS can also obtain information such as chromophore concentration, absorption and scattering properties of tissues such as breast and skin [53–55]. OCT provides a non-invasive method for obtaining optical cross-sections of the superficial cortex [56, 57], which uses the light scattering characteristics of tissue to construct high-resolution subsurface images. OCT is based on the same echolocation principle as an ultrasound but uses light waves instead of acoustic waves. **Figure 6** shows schematic diagram of the DRS and OCT system.

## **2.1 Evaluation of skin scars and structure by DRS**

Hsu, Chao-Kai et al. assessed the severity of scarring by measuring the diffuse reflectance of the skin. **Figure 7a** shows the representative clinical pictures of keloid (KS, black solid circle) and normal scars (NS, red solid circle) of one of such patients. The uninjured skin located 3 cm away from the keloid (CKS, black dashed circle) and normal scars (CNS, red dashed circle) were used as control groups. It can be seen that in the range of 500–600 nm, the absorption rate of keloids is higher than that of normal scars and uninjured skin, and the magnitude of the reduced scattering spectrum of keloids is the lowest (**Figure 6b** and **c**) [53]. The results of this study demonstrate that the DRS system can not only quantify collagen concentration, water content,

#### **Figure 6.**

*Schematic diagram of the DRS and OCT system. SLD: Super-luminescent diodes, FC: Fiber coupler, GM: Galvo mirrors, OL: Objective lens, PC: Personal computer, BF: Bandpass filter, FOV: Field of view, SA: Salicylic acid, a: Azone. Reprinted with permission from reference [58].*

#### **Figure 7.**

*(a) The clinical picture of a keloid patient containing keloid scar (KS), normal scar (NS)the uninjured skin (CKS), and normal scars (CNS). (b) Typical absorption and (c) reduced scattering spectra in KS, NS, CNS and CKS, (d) DRS spectrum and (f) PPTR signal as obtained from the intact skin site near the bruise in subject a (solid orange curves) and the best-fitting model predictions (dashed lines). Reprinted with permission from reference [53, 59].*

and oxygen saturation, but also determine the alignment of collagen bundles in keloid scars. In another study, Bin Chen et al. developed a DRS-based inverse method to extract structural parameters of skin tissue. The model was experimentally validated by constructing a skin model and performing spectral measurements, which

## *Integrated Optical Coherence Tomography and Deep Learning for Evaluating of the Injectable… DOI: http://dx.doi.org/10.5772/intechopen.106006*

demonstrated the agreement between the measured and calculated spectral data [60]. Marin, Ana et al. combined diffuse reflectance spectroscopy and pulsed photothermal radiometry (PPTR) in the visible spectral range to examine the dynamic process of traumatic bruising recovery, while using a numerical model of light and heat transport in a four-layer model of human skin from data for both techniques. **Figure 6d** and **f** shows both DRS spectra and PPTR signals obtained from the bruised site display large differences with respect to the nearby intact site.We can see a significant reduction in diffuse reflectance can be seen throughout the presented spectral range, mainly due to the higher blood content in the dermis [59]. These tasks show that DRS should also be able to quantitatively evaluate the wound healing during the treatment of wounding gel, including the scar condition after wound healing, whether the wound ulcers occurs.

#### **2.2 Investigating the wound healing by OCT and OMAG**

In recent years, how to extract the blood flow information in tissue capillaries and image the microcirculation blood flow of tissue capillaries has become a hotspot in the field of OCT research. Compared with OCT, OCT microangiography (OMAG) is a novel technique that can provide microcirculatory imaging enabled by processing OCT data [61].

For this reason, OCT technology has been extended to develop OMAG. OMAG uses the structural imaging of OCT to extract tissue blood flow information through algorithms, so as to achieve non-invasive, non-contact, and no need for contrast agents to image blood flow in tissue capillaries [62, 63]. Wang et al. [64] used an imaging system that combined dual wavelength laser speckle imaging (DW-LSI) with DOMAG to image the ears of mouse, which monitored hemodynamic changes during acute wound healing. After the wound was created using the biopsy punch, the blood flow in the first-order branches of the affected arteries and veins in the laser speckle image was markedly reduced as can be seen from the orange circles in **Figure 8B**. In addition, detailed changes in axial blood flow velocity can be found in the DOMAG image (**Figure 8C**). 10 min after perforation, compared with the baseline image at the white circle in **Figure 8C** (b), the two venous branches of the involved vessel and its downstream disappeared. At the same time, the left collateral vein was significantly increased to compensate for blood flow (white arrows in **Figure 8C** (b). Finally, changes in blood flow were quantified by integrating the flow velocity in the projection plane to obtain arterial flow maps.

Furthermore, blood vessel images can be obtained by incorporating OMAG technique into PS-OCT instrument [65]. Both Jung-Taek Oh and Kwan S Park used PS-OCT for quantitative assessment and monitoring of wound healing. Epidermis (E) and dermis layers (D), blood vessel (V), and cartilage (C) in the tissue of the pinna is observable in the reflectivity images. And blood vessels can be separately visualized in the blood vessel images by OMAG technique (**Figure 8D**) [65, 66]. The phase retardation image represents cumulative phase retardation due to the birefringence inside the tissue because the difference in phase shift between two characteristic polarization states of backscattered light from the tissue is altered by the tissue birefringence. Therefore, PS-OCT can characterize the amount of collagen by measuring the polarization parameters of the sample, such as phase retardation and degree of polarization (DOP), which will help us to observe the growth direction and recovery of the wound [67].

#### **Figure 8.**

*(a) Schematic of the bulk-type PS-OCT system. (b) Images acquired from the laser speckle imaging system showing the large-scale blood flow changes of the mouse ear following a punch biopsy. (a) Baseline image of the mouse ear before punch; (b)-(f) are images taken at 10 s, 5 min, 10 min, 25 min, and 55 min after punch, respectively. Scale bar: 1 mm. (c) Changes in blood flow velocity and direction of the mouse ear following a punch biopsy. (a) Baseline DOMAG image of the mouse ear; (b), (c) and (d) are DOMAG images taken at before punch, 10 min, 25 min and 55 min after the punch, respectively. (e) and (f) are skeletonized arterial network at baseline and at 10 min after he punch, respectively. 1–6 denote the blood vessel segments that have shown significant blood flow changes, A-E denote the five main arterial branches. Scale bar: 1 mm. (D) Multifunctional PS-OCT imaging of the punch biopsy wound model of a mouse. Reprinted with permission from reference [64–66].*

*Integrated Optical Coherence Tomography and Deep Learning for Evaluating of the Injectable… DOI: http://dx.doi.org/10.5772/intechopen.106006*
