Spatial offset

S. C. Park, M. Kim, J. Noh, H. Chung, Y. Woo, J. Lee and M.S. Kemper, Reliable and fast quantitative analysis of active ingredient in pharmaceutical suspension using Raman spechoscopy, Aruil. Chim. Acta, 593,46-53 (2007). P. Matousek, I.P. Clark, E.R.C. Draper, et al.. Subsurface probing in diffusely scattering media using spatially offset Raman spechoscopy, Appl. Spectrosc., 59, 393 00 (2005). 

P. Matousek, Inverse spatially offset Raman spechoscopy for deep noninvasive probing of turbid media, Appl. Spectrosc., 60, 1341-1347 (2006). 

C. Ricci, C. Eliasson, N.A. MacLeod, P.N. Newton, P. Matousek and S.G. Kazarian, Characterization of genuine and fake artesunate anti-malarial tablets using Fourier transform infrared imaging and spatially offset Raman spectroscopy through blister packs. Anal. Bioanal. Chem., 389, 1525-1532 (2007). 

C. Eliasson and P. Matousek, Noninvasive authentication of pharmaceutical products through packaging using spatially offset Raman spectroscopy, Arml Chem., 79, 1696-1701 (2007). 

SORS spatially offset Raman system WEA window factor analysis... 

Characterisation of Deep Layers of Tissue and Powders Spatially Offset Raman and Transmission Raman Spectroscopy... 

The SORS concept was first demonstrated (see Fig. 3.3a) on a two-layer sample composed of a 1mm thick PMMA powder layer on top of a trans-stilbene powder sublayer [18]. The Raman spectra obtained at different spatial offsets are illustrated in Fig. 3.4. The conventional Raman spectrum is that obtained with zero spatial offset. The introduction of a non-zero spatial offset led to a more rapid decrease of the surface-generated Raman signal (PMMA)... 

Fig. 3.4. A set of SORS spectra collected from a two-layer system consisting of 1 mm thick layer of PMMA made of 20 im diameter spheres followed by a 2 mm layer of trans-stilbene powder measured using 514 nm as the probe wavelength. The spectra are shown for different spatial offsets. The top and bottom spectra are those of the individual layers obtained in separate measurements. The spectra are offset for clarity. The acquisition time was 100 s for each spectrum and the average laser power 12 mW (reprinted with permission from [18]. Copyright (2005) The Society for Applied Spectroscopy)...

The fixed nature of the collection fibres in a conventional SORS experiment limits the range of spatial offsets available. An alternative approach (inverse SORS) swaps the laser and collection fibre geometries Raman light is collected through a group of fibres (arranged in a disc shape) contained within the centre of a probed area defined by a ring-shaped laser beam (see Fig. 3.5). 

Recently Eliasson and Matousek [26, 62] demonstrated that SORS can provide a chemical signature of the internal content of opaque plastic containers. This is demonstrated in Fig. 3.11 for aspirin tablets held inside an opaque (white) plastic pharmaceutical bottle (1.3mm thick). The conventional Raman signal is overwhelmed by the Raman component originating from the container wall and is consequently ineffective in determining the contents of the bottle. In contrast, the SORS method using a scaled subtraction of two SORS spectra measured at different spatial offsets yields a clean Raman spectrum of the tablets inside the bottle. SORS has also been used in the detection of counterfeit anti-malarial tablets by Ricci et al. [63] the chemical specificity of Raman spectroscopy readily distinguished between genuine and fake tablets and identified the content of the counterfeit tablets. 

This section will outline the developments of deep Raman spectroscopy from the use of time gating to spatially offset Raman spectroscopy to transmission Raman a sequence of increasing practical probing depth as advances have been made. This is counterbalanced by a reduction in depth selectivity with each new technique. An exploration of the potential use of deep Raman for breast cancer diagnostics will be used to illustrate the potential here. 

Spatially Offset Raman Spectroscopy (SORS) for Deep Probing of Calcifications... 

N. Stone, R. Baker, K.D. Rogers, A.W. Parker, P. Matousek, Future possibilities in the diagnosis of breast cancer by subsurface probing of calcifications with spatially offset Raman spectroscopy (SORS). Analyst 132, 899-905 (2007)... 

Transcutaneous Raman spectroscopic measurements using spatially offset optical fibers were reported less than a year later [59, 60]. The test systems were chicken tibiae and the humeri of human cadavers. The use of cadaveric and ex vivo specimens allowed validation of the measurements by comparison to exposed bone tissue. In these measurements a depth of 3-4 mm below the skin was reached. In vivo measurements began with a report of the Raman spectrum of a phalange of a human volunteer [61]. The periosteal surface was probably 1-2 mm below the skin and the mineral phosphate Vi was accurately reproduced, although incomplete separation of mineral and matrix spectra introduced errors in other bands. 

The corresponding screws cut against one another through a spatial curve. Therefore, the effective clearance orientated to the spatial curve is relevant as it is in view of the selfwiping effect and the product stress. The result is the spatial offset with the aforementioned advantages. ... 

Spatially offset Raman spectroscopy (SORS) Conventional Raman Spectroscopy is limited to the near-surface of diffusely scattering objects and to the first few hundred micrometers depth of surface material. Spatially Offset Raman Spectroscopy (SORS) is a variant of Raman Spectroscopy that allows highly accurate chemical analysis of objects beneath obscuring surfaces. This is done by making at least two Raman measurements one at the surface and one at an offset position of t3q>ically a few millimeters away. To do this without using an offset measurement would be severely restricted by photon shot noise generated... 

The zero-offset spectrum represents a conventional Raman spectrum. By increasing the spatial offset, the surface layer signal (PMMA) diminishes much more quickly that that of the sublayer (trons-stilbene) such that, at a spatial offset of >2 mm, an order of magnitude improvement in the intensity ratio is achieved. The same report also detailed improvements in the relative ratio between the Raman signals of the two layers by a factor of 19 at a 3.5 mm spatial offset. Interestingly, the quality of the spectra obtained in these measurements was substantially higher... 

Figure 12.4 A set of SORS spectra collected from a two-layer system consisting of a 1 mm-thick layer of PMMA made from 20pm-diameter spheres followed by a 2 mm-layer of frans-stilbene powder measured using 514nm as the probe wavelength. The spectra are shown for different spatial offsets. The top...

Figure 12.11 The estimates of pure Raman spectra of human bone in vivo measured transcutaneously at the distal phalanx of the thumb bones. Three different measurements are shown decomposed from the raw SORS spectra obtained at the zero and 3 mm spatial offsets. The spectra were obtained using a...

Although Raman spectroscopy does not employ absorption of infrared radiation as its fundamental principle of operation, it is combined with other infrared spectroscopies into a joint section. Results obtained with various Raman spectroscopies as described below cover vibrational properties of molecules at interfaces complementing infrared spectroscopy in many cases. A general overview of applications of laser Raman spectroscopy (LRS) as applied to electrochemical interfaces has been provided [342]. Spatially offset Raman spectroscopy (SORS) enables spatially resolved Raman spectroscopic investigations of multilayered systems based on the collection of scattered light from spatial regions of the samples offset from the point of illumination [343]. So far this technique has only been applied in various fields outside electrochemistry [344]. Fourth-order coherent Raman spectroscopy has been developed and applied to solid/liquid interfaces [345] applications in electrochemical systems have not been reported so far. 

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