Port wine stains is a congenital vascular malformation disease, which occurs mostly on the face and neck. Photodynamic therapy is an effective treatment for port wine stains, which utilizes photodynamic reaction between light, photosensitizer and oxygen in the tissue to produce phototoxic substance singlet oxygen to destroy the lesion. However, the irradiance dose is simply described by the irradiance on a specific plane instead of the irradiance on the lesion with curve shape. The clinician has little knowledge about the effective irradiance value on the lesion, which limits the understanding between the effect and the dosage. To get the effective irradiance on the lesion, a two-steps algorithm is proposed in this paper. Firstly, the point cloud data of lesion are constructed, and the normal vector of each point of the point cloud is calculated based on the least square method. Secondly, according to the first and second laws of irradiance, the effective irradiance on the lesion can be obtained when the parameters of the light source are available. Several typical port wine stains lesions are used to verify the difference between the irradiance on the plane and the lesion. The algorithm can not only help the clinician to make the preoperative planning of photodynamic therapy, but also provide a method for the study on the relationship between the effective irradiance dose on the lesions and the treatment effect of photodynamic therapy for port wine stains.
Dose control is one of the key factors of clinical treatment for port wine stains (PWS) under vasculature-targeted photodynamic therapy. A skin simulation model was proposed to show the PDT Type II reaction around the microcapillaries, and to establish the optimal PDT protocol such as light modulation for different PWS vascular types. A simplified two-dimensional cross section of PWS vascular composed of a single superficial epidermal layer, a deeper dermal layer, and a microcapillaries was used. A series of capillary diameters of 40, 70, 100 and 130 micrometers were used to model typical PWS lesions with different blood flow rates. Oxygen and photosensitizers (PS) are pumped from the microartery at heartbeat frequency and exit the vasculature from the microvein, and a PDT type II reaction occurs near the vessel wall: PS excited by light absorption combines with free oxygen, which leads to a reactive singlet state of oxygen (SSO) that in turn causes direct endothelial cell damage. The mathematical simulation model equations are composed of light transmission, oxygen diffusion, photosensitizer diffusion, singlet oxygen generation and photobleaching, which were solved by finite element method. With the drug diffusion and optical absorption properties of human skin, the photon consumption, drugs and oxygen diffusion and photochemical processes within the vessel wall can be simulated. This simulation can provide a quantitative method to optimize the light and drug dose for clinical treatment of PWS.
Quantification evaluation and outcomes analysis of photodynamic therapy for port-wine stains (PWS) is usually rely on the clinician subjective assessment. The aim of this study is focused on an objective assessment model for port-wine stains during the successive treatment sessions of photodynamic therapy. The assessments of the outcome were assessed in the clearance of the lesion area before and after treatment and the trace of the lesion across the entire color space in this paper. Firstly, 3D point clouds containing the lesion coordinates and color was achieved. Then, the obtained unorganized point cloud is projected onto a specified plane to generate an organized grid, and the depth image on that plane can be also obtained. Thirdly, the lesion region is separated by using the SLIC superpixel segmentation combined with the color feature of the lesion, and the lesion was re-projected to the original three-dimensional point cloud. In the end, depending on the color and location information of the 3D lesion skin points, triangulation reconstruction was performed by the greedy projection triangulation algorithm to calculate the irregular surface area of the lesion skin. The result show that the lesion skin area based on three-dimensional space are stable and reliable regardless of the scanning angle or distance difference and the chromaticity distribution in the color space can show the recovery trend of the lesion skin at different treatment stages, so three-dimensional scanning of patients can be an approach to monitor the progress of an individual’s PWS following treatments accurately and objectively.
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