Ball lens coupled fiber-optic probe for depth-resolved spectroscopy of epithelial tissue

Abstract

A ball lens coupled fiber-optic probe design is described for depth-resolved measurements of the fluorescence and reflectance properties of epithelial tissue. A reflectance target, fluorescence targets, and a two-layer tissue phantom consisting of fluorescent microspheres suspended in collagen are used to characterize the performance of the probe. Localization of the signal to within 300 microm of the probe tip is observed by use of reflectance and fluorescence targets in air. Differential enhancement of the fluorescence signal from the top layer of the two-layer tissue phantom is observed.

Fig. 1

(a) Ball lens coupled probe, showing illumination ray paths (solid lines) and collection region (dashed lines). A typical epithelial thickness of 300 µm is shown for reference. (b) Angular deviation of a ray incident parallel to the probe axis.

Fig. 2

Photograph of the ball lens coupled probe illuminating a cuvette containing the fluorescent dye Rhodamine.

Fig. 3

Normalized reflectance signal as a function of probe-to-target distance. Source–detector separation and illumination wavelength are noted. Half-maximum intensity occurs at an average distance of 136 µm (for 750-µm separation) or 340 µm (for 500-µm separation).

Fig. 4

Two-layer tissue phantom fluorescence data: straight fiber probe at a minimum source–detector separation (250 µm), corrected for excitation energy.

Fig. 5

Two-layer tissue phantom fluorescence data: ball lens coupled probe with a 2-mm-diameter ball lens and 750-µm source–detector separation, corrected for excitation energy.