Autofluorescence imaging endoscopy for identification and assessment of inflammatory ulcerative colitis

Abstract

Aim: To validate the clinical relevance of autofluorescence imaging (AFI) endoscopy for the assessment of inflammatory ulcerative colitis (UC).

Methods: A total of 572 endoscopic images were selected from 42 UC patients: 286 taken with white light imaging (WLI) and 286 with AFI from the same sites. WLI images were assessed for overall mucosal inflammation according to Mayo endoscopic subscore (MES), and for seven characteristic endoscopic features. Likewise, AFI photographs were scored according to relative abundance of red, green and blue color components within each image based on an RGB additive color model. WLI and AFI endoscopic scores from the same sites were compared. Histological evaluation of biopsies was according to the Riley Index.

Results: Relative to red (r = 0.52, P < 0.01) or blue (r = 0.56, P < 0.01) color component, the green color component of AFI (r = -0.62, P < 0.01) corresponded more closely with mucosal inflammation sites. There were significant differences in green color components between MES-0 (0.396 ± 0.043) and MES-1 (0.340 ± 0.035) (P < 0.01), and between MES-1 and ≥ MES-2 (0.318 ± 0.037) (P < 0.01). The WLI scores for "vascular patterns" (r = -0.65, P < 0.01), "edema" (r = -0.62, P < 0.01), histology scores for "polymorphonuclear cells in the lamina propria" (r = -0.51, P < 0.01) and "crypt architectural irregularities" (r = -0.51, P < 0.01) showed correlation with the green color component of AFI. There were significant differences in green color components between limited (0.399 ± 0.042) and extensive (0.375 ± 0.044) (P = 0.014) polymorphonuclear cell infiltration within MES-0. As the severity of the mucosal inflammation increased, the green color component of AFI decreased. The AFI green color component was well correlated with the characteristic endoscopic and histological inflammatory features of UC.

Conclusion: AFI has application in detecting inflammatory lesions, including microscopic activity in the colonic mucosa of UC patients, based on the green color component of images.

Keywords: Autofluorescence imaging endoscopy; Endoscopic activity; Green color component; Histological activity; Microscopic inflammation.

Figures

Figure 1

Endoscopic photograph by autofluorescence imaging showing the actual counts of red, green and blue colors based on the RGB additive model in different mucosal areas. The actual counts of red, green and blue colors varied depending on the brightness of the examined area, but the abundance of the actual counts, in parentheses, was approximately constant in the same picture.

Figure 2

Representative endoscopic photographs of ulcerative colitis using white light imaging (upper row) and autofluorescence imaging (lower row) at the same sites according to the level of endoscopic ulcerative colitis activity (inactive, mild, moderate and severe). The color of the large intestinal mucosa on the autofluorescence imaging (AFI) changes by degrees, from green to grayish and magenta color. WLI: White light imaging.

Figure 3

Comparison of overall mucosal inflammation on white light imaging and the abundance of RGB color components on autofluorescence imaging. A: The green color component corresponds most often with sites of mucosal inflammation in different colonoscopy images (according to Spearman rank correlation coefficient); B: There are significant differences in the green color component values between Mayo endoscopic subscore (MES)-0 and MES-1 (bP < 0.01), between MES-0 and MES-2 (bP < 0.01), between MES-0 and MES-3 (bP < 0.01), between MES-1 and MES-3 (aP < 0.05), between MES-0 and ≥ MES-2 (bP < 0.01) and between MES-1 and ≥ MES-2 (aP < 0.05), but not between MES-1 and MES-2 or between MES-2 and MES-3 (Tukey-Kramer multiple comparison test). WLI: White light imaging.

Figure 4

Comparison of seven endoscopic ulcerative colitis features on white light imaging and the green color component on autofluorescence imaging. The green color component on autofluorescence imaging is well correlated with vascular pattern (r = -0.65, P < 0.01) and edema (r = -0.62, P < 0.01) scores on WLI, but not with the ulcer score (r = -0.23, P < 0.01) (Spearman rank correlation coefficient). WLI: White light imaging.

Figure 5

Comparison of histology scores, six histological characteristic ulcerative colitis features and the green color component on autofluorescence imaging. The autofluorescence imaging green color component is relatively well correlated with the scores for polymorphonuclear cells in the lamina propria (r = -0.51, P < 0.01) and crypt architectural irregularities (r = -0.51, P < 0.01), but not with the scores for crypt abscesses (r = -0.30, P < 0.01), and mucin depletion (r = -0.26, P < 0.01) based on Spearman rank correlation coefficient.

Figure 6

Comparison of limited (combined grades 0 and 1) and extensive (combined grades 2 and 3) polymorphonuclear cell infiltration of the green color components in Mayo endoscopic subscore-0. The mean number of green color components for images classified into the amount of polymorphonuclear cell infiltration in Mayo endoscopic subscore (MES)-0 is 0.399 ± 0.042 for limited and 0.375 ± 0.044 for extensive infiltration. There are significant differences in green color component values between limited and extensive polymorphonuclear cell infiltration in MES-0 (P = 0.014, by Student’s t-test).