Quantitative Optical Spectroscopy for Tissue Diagnosis

Abstract

The interaction of light within tissue has been used to recognize disease since the mid-1800s. The recent developments of small light sources, detectors, and fiber optic probes provide opportunities to quantitatively measure these interactions, which yield information for diagnosis at the biochemical, structural, or (patho)physiological level within intact tissues. However, because of the strong scattering properties of tissues, the reemitted optical signal is often influenced by changes in biochemistry (as detected by these spectroscopic approaches) and by physiological and pathophysiological changes in tissue scattering. One challenge of biomedical optics is to uncouple the signals influenced by biochemistry, which themselves provide specificity for identifying diseased states, from those influenced by tissue scattering, which are typically unspecific to a pathology. In this review, we describe optical interactions pursued for biomedical applications (fluorescence, fluorescence lifetime, phosphorescence, and Raman from cells, cultures, and tissues) and then provide a descriptive framework for light interaction based upon tissue absorption and scattering properties. Finally, we review important endogenous and exogenous biological chromophores and describe current work to employ these signals for detection and diagnosis of disease.

Simulated hypogravity impairs the angiogenic response of endothelium by up-regulating apoptotic signals

“…It is known that membrane damage causes the leakage of coenzyme molecules, as NAD(P)H and flavins from mitochondria, and their diffusion in all the parts of the cell, nucleus included [11,23]. Under 365 nm excitation, the visible autofluorescence is mainly due to NAD(P)H, blue component, and oxidized flavins, yellow-green component [15]. The accumulation of these molecular species highlights a condition of metabolic impairment, due to the dysfunction of mitochondrial electron transport [24].…”

“…The emission of these endogenous fluorophores is called autofluorescence to distinguish it from the fluorescence obtained by adding exogenous markers. The most important endogenous fluorophores are proteins containing aromatic amino acids, the reduced form of pyridine nucleotides, flavins, and lipopigments [15,16]. Cells previously exposed to hypogravity and control condition were detached and plated on glass coverslips at the density of 5 · 10 4 cells/ cm 2 .…”

Laryngeal preneoplastic lesions and cancer: challenging diagnosis. Qualitative literature review and meta-analysis.

“…Since some energy has already been released as heat, the emitted light is of lower energy and longer wavelength than that of the illuminating light (112). Fluorophores are present at different concentrations in healthy and neoplastic laryngeal mucosa; for example, nicotinamide adenine dinucleotide (NADH) predominates within neoplastic cells in its dehydrogenated nonfluorescent form (113,114). Several fluorophores are normally found within laryngeal mucosa including prophyrins, elastin, collagen, and NADH (115,116).…”

Time-domain fluorescence lifetime imaging applied to biological tissue

“…References [37] and [38] provide recent reviews of tissue spectroscopy. Although intensity and spectrally resolved imaging have been widely applied to tissue autofluorescence, the origin of observed fluorescence contrast is still not fully understood and, to date, there has been relatively little FLIM of tissue autofluorescence.…”