Ahmad Fadzil M H, Ihtatho Dani, Mohd Affandi Azura, Hussein S H
Intelligent Signal and Image Processing, Department of Electrical and Electronic Engineering, Universiti Teknologi PETRONAS, Perak, Malaysia.
J Med Eng Technol. 2009;33(7):516-24. doi: 10.1080/07434610902744074.
Skin colour is vital information in dermatological diagnosis as it reflects the pathological condition beneath the skin. It is commonly used to indicate the extent of diseases such as psoriasis, which is indicated by the appearance of red plaques. Although there is no cure for psoriasis, there are many treatment modalities to help control the disease. To evaluate treatment efficacy, the current gold standard method, PASI (Psoriasis Area and Severity Index), is used to determine severity of psoriasis lesion. Erythema (redness) is one parameter in PASI and this condition is assessed visually, thus leading to subjective and inconsistent results. Current methods or instruments that assess erythema have limitations, such as being able to measure erythema well for low pigmented skin (fair skin) but not for highly pigmented skin (dark skin) or vice versa. In this work, we proposed an objective assessment of psoriasis erythema for PASI scoring for different (low to highly pigmented) skin types. The colour of psoriasis lesions are initially obtained by using a chromameter giving the values L*, a*, and b* of CIELAB colour space. The L* value is used to classify skin into three categories: low, medium and highly pigmented skin. The lightness difference (DeltaL*), hue difference (Deltah(ab)), chroma (DeltaC*(ab)) between lesions and the surrounding normal skin are calculated and analysed. It is found that the erythema score of a lesion can be distinguished by their Deltah(ab) value within a particular skin type group. References of lesion with different scores are obtained from the selected lesions by two dermatologists. Results based on 38 lesions from 22 patients with various level of skin pigmentation show that PASI erythema score for different skin types i.e. low (fair skin) to highly pigmented (dark skin) skin types can be determined objectively and consistent with dermatology scoring.
肤色是皮肤病诊断中的重要信息，因为它反映了皮肤下的病理状况。它通常用于指示诸如牛皮癣等疾病的程度，牛皮癣可通过红色斑块的出现来表明。虽然牛皮癣无法治愈，但有许多治疗方法可帮助控制该疾病。为了评估治疗效果，目前的金标准方法——银屑病面积和严重程度指数（PASI），用于确定牛皮癣病变的严重程度。红斑（发红）是PASI中的一个参数，这种情况通过视觉评估，从而导致主观且不一致的结果。目前评估红斑的方法或仪器存在局限性，例如能够很好地测量低色素皮肤（白皙皮肤）的红斑，但不适用于高色素皮肤（深色皮肤），反之亦然。在这项工作中，我们提出了一种针对不同（低色素到高色素）皮肤类型的PASI评分的牛皮癣红斑客观评估方法。牛皮癣病变的颜色最初通过使用色差仪获得CIELAB颜色空间的L*、a和b值。L值用于将皮肤分为三类：低色素、中等色素和高色素皮肤。计算并分析病变与周围正常皮肤之间的明度差异（ΔL）、色调差异（Δh(ab)）、色度（ΔC*(ab)）。发现在特定皮肤类型组内，病变的红斑评分可以通过其Δh(ab)值来区分。由两位皮肤科医生从选定的病变中获得不同评分的病变参考。基于22名不同皮肤色素沉着水平患者的38个病变的结果表明，不同皮肤类型（即低色素（白皙皮肤）到高色素（深色皮肤））的PASI红斑评分可以客观确定，并且与皮肤科评分一致。
