Color-matched and fluorescence-labeled esophagus phantom and its applications

Abstract

We developed a stable, reproducible three-dimensional optical phantom for the evaluation of a wide-field endoscopic molecular imaging system. This phantom mimicked a human esophagus structure with flexibility to demonstrate body movements. At the same time, realistic visual appearance and diffuse spectral reflectance properties of the tissue were simulated by a color matching methodology. A photostable dye-in-polymer technology was applied to represent biomarker probed "hot-spot" locations. Furthermore, fluorescent target quantification of the phantom was demonstrated using a 1.2 mm ultrathin scanning fiber endoscope with concurrent fluorescence-reflectance imaging.

Fig. 1

(a) A cross-sectional graph illustrating the phantom design. (b) An overview of the resultant phantom.

Fig. 2

Schematic diagram of the experimental setup to quantify targets’ fluorescence.

Fig. 3

(a) Standard SFE RGB imaging; (b) SFE dual mode imaging, with the 532 nm blue photomultiplier tube (PMT) channel inactive.

Fig. 4

A summary diagram of the CIE color calculation methodology. Calculated color coordinates represent the visual appearance of a paint recipe viewed under illumination by the xenon Cermax lamp. Clinically BE is observed with an endoscope that incorporates a color CCD camera. The spectral response of modern endoscopic CCD cameras closely matches the ideal $\overline{x}$, $\overline{y}$, and $\overline{z}$ functions. Therefore, the calculated color coordinates correspond reasonably well to the clinically observed color of BE.

Fig. 5

CIE color calculations of: (a) Ref.  BE color, (b) simulated healthy esophagus mucosa color, (c) simulated BE color, and (d) Atlantic salmon fillet color.

Fig. 6

Diffuse spectra reflectance of simulated healthy esophagus and BE tissue from the phantom.

Fig. 7

Fluorol dye-in-polymer emission spectra under 444 nm laser excitation, measured by a calibrated spectrometer.

Fig. 8

Photo representations of dye-in-polymer. (a) $\sim 750\mu \mathrm{m}$ thin disks, (b) die-cut distinctive star shaped targets.

Fig. 9

(a) Fluorescent target emission intensity recorded with a spectrometer as a function of dye concentration. (b) Fluorescent target SFE image intensity as a function of dye concentration.

Fig. 10

Standard RGB SFE imaging of the phantom. (a) SFE images of the same phantom with with sphincter open (left) and sphincter closed (right). (b) Endoscope images of a human Barrett’s esophagus © 2004 by Mayo Foundation for Medical Education and Research.

Fig. 11

SFE fluorescence and red reflectance dual-modal imaging of the phantom. Dual-modal SFE imaging of the phantom with four $100\mu \mathrm{mol}/\mathrm{L}$ fluorescent targets. Left: sphincter open. Right: sphincter closed.

Fig. 12

Phantom application: the SFE distance compensation (DC) algorithm development. (a) Sphincter open mode; (b) sphincter closed mode; (1-a) before DC SFE dual-mode (reflectance-fluorescence) image; (1-b) before DC colormap of the fluorescence image from (1-a); (2) After DC colormap of the fluorescence image from (1-a).