Tissue characterization using high wave number Raman spectroscopy

Abstract

Raman spectroscopy is a powerful diagnostic tool, enabling tissue identification and classification. Mostly, the so-called fingerprint (approximately 400-1800 cm(-1)) spectral region is used. In vivo application often requires small flexible fiber-optic probes, and is hindered by the intense Raman signal that is generated in the fused silica core of the fiber. This necessitates filtering of laser light, which is guided to the tissue, and of the scattered light collected from the tissue, leading to complex and expensive designs. Fused silica has no Raman signal in the high wave number region (2400-3800 cm(-1)). This enables the use of a single unfiltered fiber to guide laser light to the tissue and to collect scattered light in this spectral region. We show, by means of a comparison of in vitro Raman microspectroscopic maps of thin tissue sections (brain tumors, bladder), measured both in the high wave number region and in the fingerprint region, that essentially the same diagnostic information is obtained in the two wave number regions. This suggests that for many clinical applications the technological hurdle of designing and constructing suitable fiber-optic probes may be eliminated by using the high wave number region and a simple piece of standard optical fiber.

Fiberoptic Resonance Raman Spectroscopy to Measure Carotenoid Oxidative Breakdown in Live Tissues

“…2). Confounding Raman signals arising from the probe fiber usually preclude using a single fiber for Raman endoscopy in this wave number range (16)(17)(18), but in our case, these obstructing signals are out of resonance and/or out of the analysis window and thus cause no interference. The isolated 1,525 cm −1 C=C resonance Raman carotenoid peak is further characterized using a Lorentzian line shape, and the peak attributes are reported.…”

“…Investigative groups are exploring the use of a single fiberoptic mode of delivering and collecting Raman measurements (16)(17)(18), but systems that monitor a broad bandwidth are easily overwhelmed by background fluorescence obscuring relatively weak Raman signals. Our single-fiber resonance-enhanced Raman system able to provide both illumination and collection is made possible by the relative ease by which our software and optics can eliminate background fluorescence within a relatively narrow bandwidth of interest for carotenoids.…”

Developing fibre optic Raman probes for applications in clinical spectroscopy

“…Thus indicating simple fibre optics and the high wavenumber region may be sufficient for many applications. 64 The first in vivo bladder Raman studies using an Emvision probe based around a filtered six collection fibres around one illumination fibre. 79 They used the fingerprint region and 785nm illumination.…”

In vivo optical monitoring of tissue pathologies and diseases with vibrational contrast

“…On the other hand, spectroscopic techniques provide very high information content with typically low spatial sampling (a few points). Raman spectroscopy has a demonstrated diagnostic potential in oncology in vivo or ex vivo for a number of organs such as the colon [1], esophagus [2], stomach [3], breast [4,5], cervix [6,7], skin [8], bladder [9] and brain [10,11] to name only a few. The importance of such results are not only limited to the development of in vivo tools, but may also prove useful to improve the diagnostic accuracy of current methods, reduce inter-observer variability [12] and augment our understanding of carcinogenesis processes.…”

“…For tissue spectroscopy, information in the fingerprint region is mostly extracted from the position and height of the lines, whereas in the high wave number region information comes from the lineshape of the vibrations, as was shown by Puppels' group [9]. For tissue diagnosis applications, the use of statistical methods for the classification of the spectral data is required, and sufficient, to extract the necessary information (for a review, see [13]).…”