| BackgroundCutaneous squamous cell carcinoma(cSCC),a non-melanoma skin cancer with a high incidence,causes distant metastasis and life-threatening.Therefore,early diagnosis and taking effective intervention measures for cSCC and its precancerous lesions,such as actinic keratosis(AK)can prevent the occurrence of cSCC and reduce the lethality of cSCC further.Clinically,the method to make sure the diagnosis of skin diseases is pathology.However,biopsy will not only bring the feelings of pain to patients,but also may cause wound bleeding,infection,and the formation scar.Therefore,early,noninvasive and accurate diagnostic techniques need to be developed and applied.Dermascopy,reflective confocal laser microscopy(RCM)and skin ultrasound have been applied for clinical diagnosis of skin diseases.However,these techniques may mot balance pathological results,imaging depth or resolution well.The imaging resolution of optical coherence tomography(OCT)in skin tissue is about 10um,and the imaging depth is about 2 mm.OCT imaging enables to show the longitudinal microstructure of skin tissue with a high resolution,and continuously perform the change of epidermal thickness and the shape change of dermo-epidermal junction(DEJ)located in the basal layer.The results of OCT imaging can be better matched with histopathology.In previous studies,there have been no experimental reports using OCT to continuously and periodically track the occurrence and development of cSCC.ObjectiveIn this study,the OCT was used to evaluate the changes in skin structure characteristics during the evolution of mice normal skin into AK or even cSCC,and to use OCT to evaluate the structural characteristics of human cSCC in vitro.Preliminarily explore the feasibility of OCT in diagnosing AK and cSCC.MethodFemale and hairless SKH-1 mice were received ultraviolet radiation for 5 days a week.The initial minimal erythema dose(MED)of mice is 160 m J/cm~2 of UVB.The first and second weeks were irradiated with exploratory dose,the power density was 90%MED,and the irradiation time was 1 minute.The subsequent irradiation time was increased by5 seconds every 2 weeks.Take 1 cage of mice each time(5 mice per cage)and expose them to the above light source.The back is 30 cm away from the light source.At 24 weeks of exposure,the SKH-1 mouse skin squamous cell carcinoma model was established.At two-week intervals each time,a digital camera was used to take general photographs of the mice;a dermoscopy was used to record the changes in the skin of the mice;and the OCT was used to perform real-time in vivo imaging of the skin structure of the mice.Finally,the mouse skin was cut for histopathological examination.Clinical human normal skin,pigmented nevus,seborrheic keratosis(SK)and cSCC isolated tissues were collected.The OCT was used to image the isolated tissue to show the structural characteristics of different skin tissues,and finally perform histopathological examination to verify the above experimental results.Image J software was used to analyze the thickness of the mouse epidermis and the changes in the signal intensity of each layer.The Graph Pad Prism 7 was applied to make the charts and analyze the research data.We used mean±standard deviation to show epidermal thickness and signal intensity data.The linear regression analysis was used to display the relationship for lighting time and epidermal thickness.The R~2 was used to show the correlation between OCT and histopathology methods measuring the epidermal thickness.Student’s t-test was also taken for the analysis.And statistical significance was defined as P<0.05.ResultBefore the mice were exposed to UVR,the skin was smooth and pink.When ultraviolet rays were irradiated to the 14th week,needle-like papules appeared on the skin.Subsequently,the size of the papules gradually increased and the number gradually increased.At the 24th week,growths of varying sizes were seen on the back skin of mice,and the larger ones showed cauliflower-like damage.Dermoscopy revealed that the skin was exposed to UVR and the background under the microscopy was consistent,and normal subcutaneous vascular structures were visible.In the 14th week of UVR,a large number of hair follicle mouth plugs were seen under dermoscopy,and a white strawberry sign was visible locally.At the 24th week,red growths were visible under dermoscopy,yellow-white keratinocytes were visible on the surface,and dots,hairpins,and a large number of irregular linear blood vessels were visible on the edges.In the OCT image,before UVR exposure,the structure of each layer of the mouse skin is evenly distributed and clearly distinguishable.When the ultraviolet rays were irradiated to the 14th week,the DEJ evolved into a wave shape,towards the dermis layer;the epidermis layer thickened.At the 24th week,the normal layered structure of the mouse skin disappeared.Before receiving UVR,the pathology of mouse skin tissue showed that the skin DEJ was flat and parallel to the skin surface.At the 14th week,DEJ showed bud-like proliferation changes,extending to the superficial dermis;the thickness of the epidermis increased significantly.At the 24th week,a large number of abnormal cells can be seen to break through the basement membrane to reach the dermis,and a keratinized bead structure appears.In the OCT images of normal skin tissue in vitro,the skin layer structure was complete,and the reflected signals of each layer were uniform.In cSCC in vitro tissues,obvious keratinization and discontinuous surface structure were found at skin surface,thickened stratum corneum,and no DEJ structure could been seen.The histopathological results of normal skin in vitro showed that the structure of the epidermis and dermis was complete,the cells of each layer were evenly distributed and the DEJ was clear.For SK,scattered,hollow-like low-reflective signal structures could be found.For cSCC tissues,the skin surface was keratinized obviously,no DEJ structure was seen,and low-reflective signal structure areas could be found.ConclusionOCT could be used to assess the structural characteristics of AK and cSCC,and the results were consistent with histopathology.It was suggested that OCT can be used for non-invasive diagnosis of cSCC and AK. |
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