Application of machine vision to assess involved surface in patients with psoriasis

Abstract

An objective method is still lacking in the quantitative assessment of psoriasis severity. The purpose of this study was to examine whether computer image analysis (CIA) by a new colour segmentation method can be used as an objective method of estimating involved surface area in patients with psoriasis. Involved surface area in psoriasis was assessed from colour photographs covering the same areas as the psoriasis area and severity index (PASI) scores of 26 patients by human observers from different medical professional groups and by CIA. The reliability of CIA was tested with reference analysis by colouring manually the involved areas in the images with the aid of projected slides. The surface area estimates by the different methods were compared with each other and the resulting effects on the PASI score were assessed. The agreement between the reference analysis and the image analysis was high, especially on trunk areas, but the cylindrical shape of the limbs resulted in some difficulties in assessing involved skin area. The human eye estimates differed from the image analysis ones in almost one-third of the cases and mostly when psoriasis affected under 30% of the skin surface area. Both over- and underestimates emerged, but overestimates were more common. Error estimates had a significant effect on the PASI score. The CIA method seems to be reliable and practicable in estimating the actual surface of psoriasis. The method has the disadvantage of being time-consuming (photographing, processing of pictures) and technically demanding. Further development of this method should make it faster in the future.

Method of assessing involved facial areas: rule of fours

“…The present study demonstrates that global assessments tended to overestimate involved facial areas vs. image analysis findings, which concurs with previously published results 1,17,20 …”

Objective assessment of involved surface area in patients with psoriasis

“…The measurement of the involved area of psoriasis showed the need for an objective assessment that could overcome the difference between the observers, which was statistically significant in the study ( P <0.05, Kruskal–Wallis test). The percentages of the involved areas measured by the visual grading method were significantly higher than those from image analysis on the trunk, upper and lower limbs, and the total involved body area ( P <0.05, Wilcoxon signed rank test) (8, 9). On the other hand, the measurements of the head area were not statistically different ( P >0.05, Wilcoxon signed rank test), showing that it was difficult to observe the involved area present on the head and to estimate these lesions accurately because of the smaller size of the lesion (8).…”

“…In addition, we could measure the involved surface areas of patients with psoriasis whose lesional areas were less than 4% of the total surface area using the image analysis system, but not with the visual grading method. These results suggest that more accurate and objective data can be obtained from image analysis (9).…”

Validation of Psoriasis Clinical Severity and Outcome Measures

“…[1][2][3] However, several studies have demonstrated a tendency for clinicians to overestimate the affected area, especially in mild disease [2][3][4][5][6][7] and to lack sensitivity in evaluating responsiveness to therapy. While interrater reliability for BSA has been shown to be somewhat variable, intrarater reliability is excellent.…”