Two-photon induced fluorescence of artery tissue

Fluorescence spectroscopy has been explored as a promising technique for a minimally invasive, non-destructive medical diagnostic. Both cancerous and atherosclorotic tissue have been shown to be distinguishable from normal tissue using fluorescence techniques. However, due to the limitations of conventional fluorescence methods in tissue, further investigation is required to improve the technique before fluorescence becomes a viable alternative to current diagnostic methods. Two-photon induced fluorescence (TPF) has several advantages over conventional single photon fluorescence (SPF), particularly in the study of biological molecules and tissue. Although the potential advantages of TPF are substantial, the technique has not been well explored in native tissue, and has not been studied in artery tissue. Investigating fluorescence of native biological tissue using this technique is important as many medical applications require diagnostics on tissue that has not been chemically altered.; This investigation yielded results pertaining to both the feasibility and properties of measuring two-photon induced fluorescence of endogenous tissue. The main focus was to compare two-photon spectra to single-photon spectra, in order to examine the claimed advantages of TPF as a technique for optical biopsies of tissue.; As part of this thesis, a research system was designed that can induce and measure the weak TPF signals induced in native tissue. For the first time, single-color TPF was investigated experimentally in artery tissue and its primary fluorescent proteins. The observed difference between the SPF and TPF emission spectra of artery tissue, but not of its primary fluorophores, illustrate that TPF offers the potential to probe deeper into the artery wall. When used as an atherosclerosis diagnostic, in connection with an ablation device, this ability to section artery and to probe deep into the tissue is important to eliminate the diseased tissue while avoiding any arterial perforation. The maximum laser intensity that can be used without damaging the artery was also determined.; In order to better understand the capabilities of TPF, the interaction of laser light with tissue was investigated both analytically and with a Monte Carlo computer model. The results show that the perceived penetration advantages of TPF are significantly reduced by the high scattering coefficient of tissue. These conclusions can be used to guide the diagnostic use of TPF.