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Objective Assessment of Area and Erythema of Psoriasis Lesion Using Digital Imaging and Colourimetry

Psoriasis is a non-contagious skin disease which typically consists of red plaques covered by silvery-white scales. It affects about 3% of world population. During treatment, dermatologists monitor the extent of psoriasis continuously to ascertain treatment efficacy. Psoriasis Area and Severity I...

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Main Author: Ihtatho, Dani
Format: Thesis
Language:English
Published: 2008
Subjects:
TK Electrical engineering. Electronics Nuclear engineering
Online Access:http://utpedia.utp.edu.my/id/eprint/8543/1/2008%20Master%20-%20Objective%20Assessment%20of%20Area%20and%20Erythema%20of%20Psoriasis%20Lesion%20Using%20Digital%20Imaging.pdf
http://utpedia.utp.edu.my/id/eprint/8543/
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spelling oai:utpedia.utp.edu.my:85432023-05-15T03:56:37Z http://utpedia.utp.edu.my/id/eprint/8543/ Objective Assessment of Area and Erythema of Psoriasis Lesion Using Digital Imaging and Colourimetry Ihtatho, Dani TK Electrical engineering. Electronics Nuclear engineering Psoriasis is a non-contagious skin disease which typically consists of red plaques covered by silvery-white scales. It affects about 3% of world population. During treatment, dermatologists monitor the extent of psoriasis continuously to ascertain treatment efficacy. Psoriasis Area and Severity Index (PAS!) is the current gold standard method used to assess the extent of psoriasis. In PAS!, there are four parameters to be scored i.e., the surface area affected, erythema (redness), thickness and scaliness of the plaques. Determining PAS! score is a tedious task and thus it is not used in daily clinical practice. In addition, the PAS! parameters are visually determined and may result in intra-observer and inter-observer variations, even by experienced dermatologists. Objective methods in assessing area and erythema of psoriasis lesion have been developed in this thesis. Psoriasis lesion can be recognized by its colour dissimilarity with normal skin. Colour dissimilarity is represented by colour difference in CIELAB colour space, a widely used colour space to measure colour dissimilarity. Each pixel in CIELAB colour space can be represented by its lightness (L'), hue (hob), and chroma (Cab). Colour difference between psoriasis lesion and normal skin is analyzed in hue-chroma plane of CIELAB colour space. Centroids of normal skin and lesion in hue-chroma space are obtained from selected samples. Euclidean distances between all pixels with these two centroids are then calculated. Each pixel is assigned to the class of the nearest centroid. The erythema of psoriasis lesion is affected by degree of severity and skin pigmentation. In order to assess the erythema objectively, patients are grouped according to their skin pigmentation level. The L* value of normal skin which represents skin pigmentation level is utilized to group the patient into the three skin types namely fair, brown and dark skin types. Light difference (t.L*), hue difference (t.hab), and chroma difference (t.C'ab) of CIELAB colour space between reference lesions and the surrounding normal skin are analyzed. It is found that the erythema score of a lesion can be determined by their hue difference (t.hab) value within a particular skin type group. Out of 30 body regions, the proposed method is able to give the same PAS! area score as reference for 28 body regions. The proposed method is able to determine PAS! erythema score of 82 lesions obtained from 22 patients objectively without being influenced by other characteristic of the lesion such as area, pattern, and boundary. 2008-08 Thesis NonPeerReviewed application/pdf en http://utpedia.utp.edu.my/id/eprint/8543/1/2008%20Master%20-%20Objective%20Assessment%20of%20Area%20and%20Erythema%20of%20Psoriasis%20Lesion%20Using%20Digital%20Imaging.pdf Ihtatho, Dani (2008) Objective Assessment of Area and Erythema of Psoriasis Lesion Using Digital Imaging and Colourimetry. Masters thesis, Universiti Teknologi Petronas.
institution Universiti Teknologi Petronas
building UTP Resource Centre
collection Institutional Repository
continent Asia
country Malaysia
content_provider Universiti Teknologi Petronas
content_source UTP Electronic and Digitized Intellectual Asset
url_provider http://utpedia.utp.edu.my/
language English
topic TK Electrical engineering. Electronics Nuclear engineering
spellingShingle TK Electrical engineering. Electronics Nuclear engineering
Ihtatho, Dani
Objective Assessment of Area and Erythema of Psoriasis Lesion Using Digital Imaging and Colourimetry
description Psoriasis is a non-contagious skin disease which typically consists of red plaques covered by silvery-white scales. It affects about 3% of world population. During treatment, dermatologists monitor the extent of psoriasis continuously to ascertain treatment efficacy. Psoriasis Area and Severity Index (PAS!) is the current gold standard method used to assess the extent of psoriasis. In PAS!, there are four parameters to be scored i.e., the surface area affected, erythema (redness), thickness and scaliness of the plaques. Determining PAS! score is a tedious task and thus it is not used in daily clinical practice. In addition, the PAS! parameters are visually determined and may result in intra-observer and inter-observer variations, even by experienced dermatologists. Objective methods in assessing area and erythema of psoriasis lesion have been developed in this thesis. Psoriasis lesion can be recognized by its colour dissimilarity with normal skin. Colour dissimilarity is represented by colour difference in CIELAB colour space, a widely used colour space to measure colour dissimilarity. Each pixel in CIELAB colour space can be represented by its lightness (L'), hue (hob), and chroma (Cab). Colour difference between psoriasis lesion and normal skin is analyzed in hue-chroma plane of CIELAB colour space. Centroids of normal skin and lesion in hue-chroma space are obtained from selected samples. Euclidean distances between all pixels with these two centroids are then calculated. Each pixel is assigned to the class of the nearest centroid. The erythema of psoriasis lesion is affected by degree of severity and skin pigmentation. In order to assess the erythema objectively, patients are grouped according to their skin pigmentation level. The L* value of normal skin which represents skin pigmentation level is utilized to group the patient into the three skin types namely fair, brown and dark skin types. Light difference (t.L*), hue difference (t.hab), and chroma difference (t.C'ab) of CIELAB colour space between reference lesions and the surrounding normal skin are analyzed. It is found that the erythema score of a lesion can be determined by their hue difference (t.hab) value within a particular skin type group. Out of 30 body regions, the proposed method is able to give the same PAS! area score as reference for 28 body regions. The proposed method is able to determine PAS! erythema score of 82 lesions obtained from 22 patients objectively without being influenced by other characteristic of the lesion such as area, pattern, and boundary.
format Thesis
author Ihtatho, Dani
author_facet Ihtatho, Dani
author_sort Ihtatho, Dani
title Objective Assessment of Area and Erythema of Psoriasis Lesion Using Digital Imaging and Colourimetry
title_short Objective Assessment of Area and Erythema of Psoriasis Lesion Using Digital Imaging and Colourimetry
title_full Objective Assessment of Area and Erythema of Psoriasis Lesion Using Digital Imaging and Colourimetry
title_fullStr Objective Assessment of Area and Erythema of Psoriasis Lesion Using Digital Imaging and Colourimetry
title_full_unstemmed Objective Assessment of Area and Erythema of Psoriasis Lesion Using Digital Imaging and Colourimetry
title_sort objective assessment of area and erythema of psoriasis lesion using digital imaging and colourimetry
publishDate 2008
url http://utpedia.utp.edu.my/id/eprint/8543/1/2008%20Master%20-%20Objective%20Assessment%20of%20Area%20and%20Erythema%20of%20Psoriasis%20Lesion%20Using%20Digital%20Imaging.pdf
http://utpedia.utp.edu.my/id/eprint/8543/
_version_ 1768010122069540864
score 13.244413

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