Fluorescence spectroscopy of neoplastic and non-neoplastic tissues

Abstract

Fast and non-invasive, diagnostic techniques based on fluorescence spectroscopy have the potential to link the biochemical and morphologic properties of tissues to individual patient care. One of the most widely explored applications of fluorescence spectroscopy is the detection of endoscopically invisible, early neoplastic growth in epithelial tissue sites. Currently, there are no effective diagnostic techniques for these early tissue transformations. If fluorescence spectroscopy can be applied successfully as a diagnostic technique in this clinical context, it may increase the potential for curative treatment, and thus, reduce complications and health care costs. Steady-state, fluorescence measurements from small tissue regions as well as relatively large tissue fields have been performed. To a much lesser extent, time-resolved, fluorescence measurements have also been explored for tissue characterization. Furthermore, sources of both intrinsic (endogenous fluorophores) and extrinsic fluorescence (exogenous fluorophores) have been considered. The goal of the current report is to provide a comprehensive review on steady-state and time-resolved, fluorescence measurements of neoplastic and non-neoplastic, biologic systems of varying degrees of complexity. First, the principles and methodology of fluorescence spectroscopy are discussed. Next, the endogenous fluorescence properties of cells, frozen tissue sections and excised and intact bulk tissues are presented; fluorescence measurements from both animal and human tissue models are discussed. This is concluded with future perspectives.

Figure 1

Energy level diagram illustrating the phenomena of absorption and fluorescence.

Figure 2

Illustration of a fluorescence (a) emission spectrum, (b) excitation spectrum, (c) excitation-emission matrix (EEM) and (d) decay profile.

Figure 3

Schematic of the basic components of an instrument employed for fluorescence spectroscopy of biological media.

Figure 4

Fluorescence emission spectra of metastatic and non-metastatic human lung squamous cell carcinoma (SCC) cells and normal human epithelial cells at (a) 350 nm and (b) 310 nm excitation.

Figure 5

Fluorescence decay profile at 440 nm associated with the lamp profile (no fit curve) and those associated with the (A) non-metastatic and (B) metastatic human lung, squamous cell carcinoma (SCC) cells.

Figure 6

Fluorescence emission spectra from (a) a normal urothelial cell and (b) a poorly differentiated transitional cell carcinoma (TCC) at 488 nm excitation.

Figure 7

Typical fluorescence emission spectra, obtained at 370 nm excitation of the various fluorescent micro-structures found in the (a) normal lamina propria, (b) adenomatous lamina propria, (c) eosinophilic granules, (d)(e) normal submucosa, and (f) dysplastic crypt cell of colon tissue.

Figure 8

The computed fluorescence emission spectra of normal and adenomatous colon tissue versus the corresponding average fluorescence emission spectra collected in vivo.

Figure 9

(a) Fluorescence emission spectra obtained in vivo at 370 nm excitation from normal mucosa, a hyperplastic polyp and an adenomatous polyp from the colon of a typical patient and (b) the ratio of the mean adenomatous polyp fluorescence spectrum divided by the mean normal fluorescence spectrum.

Figure 10

(A) Representative fluorescence decay profiles of an adenomatous polyp and (B) the normalized profiles (to a peak intensity of one), which reveal identical fluorescence decays between two different measurements.