A Model of Pulsed Photothermal Radiation for the Laser Treatment of Dermatological Diseases

A theoretical model has been established to address the difficulties in measuring the internal temperature distribution and morphology of biological tissues during the laser treatment of dermatological diseases, as well as the problem of suboptimal therapeutic outcomes caused by doctors' selection of treatment parameters based on their experience. This model utilizes pulsed photo-thermal radiation (PPTR) to reconstruct the skin structure and enable intelligent laser parameter selection, thereby assisting in laser treatment. Three inverse algorithms, namely, truncated singular value decomposition (CTP-TSVD) with a custom truncated parameter selection method, Tikhonov regularization (L-Tikhonov) with the L-curve method for selecting the regularization parameter, and conjugate gradient with a predetermined number of iterations (GN1-CG) were used for simulation calculations. An error evaluation function was established to analyze and compare the reconstruction effects of varying epidermal layer thickness, lesion layer thickness, and depth under the three algorithms. Additionally, skin mimics were fabricated for ex vivo experiments. Based on these experiments, a study was conducted to explore the application of clinical treatment for nevus erythematosus. The results demonstrated that the comprehensive performance evaluation indices of the three algorithms, namely L-Tikhonov, GNI-CG, and CTP-TSVD, were 0.066, 0.082 and 0.126 respectively, in descending order. This finding confirms that the three inverse algorithms are capable of maintaining a high level of accuracy in reconstructing the vascular layer of nevus erythematosus within the typical depth range. The results of in vitro experiments and the clinical applications demonstrate that the PPTR model proposed in this study has the potential to address various aspects of the epidermis, lesion layer, and other tissues, including temperature rise distribution, thickness, and location. The accuracy of the reconstruction results can meet the treatment needs. These findings provide some quantitative guidance for the selection of parameters during laser treatment procedures. © 2024 Xi'an Jiaotong University. All rights reserved.