OCTA Quantitatively Detecting The Lesion Structure Of Port Wine Stains And Its Application In Vascular-targeted Photodynamic Therapy

BackgroundPort wine stain(PWS)is a skin disease due to congenital and superficial cutaneous vascular malformations.Vascular-targeted photodynamic therapy(V-PDT)for the treatment of PWS is the gold standard method among the field of Chinese laser medicine.It has the advantages over high selectivity and outstanding curative effect.However,at present,the clinical diagnosis of PWS and the judge of V-PDT efficacy are mainly based on the physician’s visual judgment based on the appearance of the lesion area.There is a lack of non-invasive in vivo detection methods for acquiring the structural characteristics of PWS lesions and an objective quantitative evaluation method for assessing V-PDT efficacy,which limit the accurate objective diagnosis and optimization of V-PDT effect.Optical Coherence Tomography Angiography(OCTA)is an optical technology that can perform non-invasive,real-time,and high-precision imaging of the superficial layer of the skin and the structure of the microvascular network.At present,the application of OCTA in the skin field is still in the preliminary exploration stage,and there is no mature algorithm to quantify and describe the structural characteristics of PWS lesions.It is urgent to develop an OCTA system suitable for objective quantitative assessment of the structural characteristics of PWS lesions.PurposeThrough establishing the quantitative extraction algorithm for PWS lesion structure based on OCTA images,and analyzing the relationship between PWS lesion structure and the color of the lesions,the efficacy of V-PDT,to provide an objective method for preoperative V-PDT diagnosis,developing V-PDT plan,postoperative V-PDT efficacy evaluation.Method(1)The OCTA system which based on optical micro-angiography(OMAG)was used to detect various morphology of blood vessels:the ear skin of Balb/c mice,the skin of Laiheng chicken comb,and the skin of PWS lesion.The detection sites were respectively taken for routine histopathological examination.Compare the structure on HE-stained tissue sections and the OCTA images.(2)The refined epidermal thickness algorithm was built based on the vertical gradient algorithm through OCTA cross-sectional images(skin superficial structure,which added the horizontal component;MATLAB platform was used to create OCTA binarized images from OCTA en face images(3D microvascular reconstruction and projection on the skin surface),which used adaptive threshold and filtering and noise reduction;Compare the result of the epidermal thickness extracted by the refined epidermal thickness extraction algorithm and manual extraction method.Pearson correlation analysis was conducted to verify the accuracy of the algorithm;Five characteristic vessels were randomly selected from OCTA en face images and binarized images,respectively,and manually measured the diameter by two people respectively.Compared the results from two people and conducted Pearson correlation analysis to verify the accuracy of the algorithm;Based on OCTA binarized images to design the algorithm which can describe the PWS vascular characteristics——PWS vascular OCTA characteristics,PVOC.(3)OCTA was used to detect the diseased skin and the contralateral normal area of 134PWS patients.Each examination was repeated 3-5 times.Obtain OCTA cross-sectional images and OCTA en face images.Epidermal thickness and parameters describing vascular characteristics were extracted from refined epidermal thickness algorithm and PVOC.The relationship between PWS lesion structure and different color(pink,red,purple)of the lesion was analyzed.(4)Before and immediately after V-PDT,OCTA was used to scan the skin of the same part of 80 patients for 3-5 times.Obtain OCTA cross-sectional images and OCTA en face images.The efficacy was evaluated colorimetrically 3 to 6 months after V-PDT.The relationship between PWS lesion structure and V-PDT efficacy was analyzed.The lesion structural factors of PWS lesions affecting the prognosis of V-PDT were analyzed using a multi-factor binary Logistic regression model.Results(1)OCTA cross-sectional images and HE-stained tissue sections under light microscope could show the superficial skin structure of mice ear,cockscomb,PWS skin.The thickness of mice ear,diameter of mice arteriovenous,width of comb nipple,microvascular diameter of cockscomb,the epidermal thickness and the diameter and depth of PWS vessels in PWS were extracted from OCTA cross-sectional images and OCTA en face images,HE-stained tissue sections,compared the results from OCTA images and tissue sections.There was no statistic difference between them(P>0.05).(2)The refined epidermal thickness extraction algorithm can accurately identify the air-epidermal and epidermal-dermal interfaces on OCTA cross-sectional images of PWS patients,and the extracted values of epidermal thickness were highly correlated with them obtained manually(r=0.9855,P<0.0001).The improved image binarization algorithm can also better extract the binarized images from the OCTA en face images of PWS patients,moreover,the vascular diameters measured from OCTA en face images and OCTA binarized image were high correlated(r=0.8963,P<0.0001).PVOC contained following six factors:average vascular density,average vascular diameter,the proportion of vessels of different diameters(divided every 30μm);vascular depth distribution(every 200μm below the epidermis-dermis interfaces,where one index was set as superficial/deep vessel density);proportion of vertical vessels;the changes of average vascular density before and after V-PDT.(3)OCTA results of 134 patients with PWS showed that the vascular diameter of lesions increased with the deepening of skin color(pink:50.2±11.7μm,red:74.2±25.0μm,purple:102.9±32.0μm);The depth of the vessels also increased with the deepening of the lesion color:the pink PWS mainly distributed in the dermis 0-200μm,the red PWS mainly distributed in the dermis 0-600μm,and the purple PWS mainly distributed in the dermis 200-800μm;The vascular density of red type was the highest(31.5±3.8%),pink type and purple type were 28.6±5.6%and 29.3±5.2%,respectively.As for red type,compared pink type,there was statistical difference(P<0.05),however,there was no statistical difference with purple type(P>0.05).There was no significant difference in the proportion of vertical vessels among pink,red and purple types(5.8±6.5%,10.0±17.8%,9.2±12.9%)(P>0.05).Moreover,some patients with same skin color,the lesion structure varied differently from above results.(4)Among the total 80 PWS patients who received V-PDT,22 were non-responders and58 got improved.Comparing the structure of PWS lesions in non-responders and improved patients,non-responders had a thicker epidermis(95.0±5.2μm vs 75.3±3.0μm,P=0.0012),and a higher proportion of 10-30μm vessels(9.43±0.49 vs 7.54±0.30mm/mm~2,P=0.0014),higher average density ratio between shallow(0-400μm)and deep layers(400-600μm)(1.7±0.1 vs1.4±0.1,P=0.0006),higher proportion of vertical vessels(15.84±4.33 vs 3.38±0.64%,P<0.0001),and no decrease of number of vessels immediately after V-PDT(χ2=8.945,P=0.002).A binary logistic regression model was constructed based on the above factors.The model was statistically significant,χ2=46.220,P<0.001,and the model prediction accuracy was86.1%.The proportion of vertical vessels(OR=-0.230,95%CI:0.673～0.937,P=0.006)and average vascular density ratio between shallow and deep layers(OR=-2.663,95%CI:0.007～0.669,P=0.021)were the key PWS structure factors for V-PDT efficacy.Conclusion(1)The OCTA system used in this study can present skin tissue structure from mice ear skin,superficial cockscomb skin,superficial PWS skin.Moreover,it can also accurately image the corresponding vessels with different morphology.The content of this part verifies the feasibility and reliability of OMAG-OCTA imaging skin structure and various morphological microvessels.(2)The refined epidermal thickness extraction algorithm and the binarization algorithm based on OCTA en face images can accurately extract data and binarize OCTA en face images;PVOC can describe the microvascular characteristics of PWS,and its clinical significance will be explored in subsequent studies.(3)With the deepening of lesion color,the diameter and distribution depth of lesion vessels were enlarged and deepened.The red type has the highest blood vessel density;There was no correlation between the proportion of vertical vessels and lesion color.There are significant individual differences in the structure of lesions.PVOC can quantitively obtain personalized PWS lesion structure and provide objective basis for V-PDT planning.(4)Multiple structural factors of PWS can significantly affect the efficacy of V-PDT.The Logistic regression model of V-PDT efficacy which based on these structural factors has high accuracy,and the proportion of vertical vessels and average vascular density ratio between shallow and deep layers are the crucial factor affecting the V-PDT prognosis.