High wavenumber Raman spectroscopy for intraoperative assessment of breast tumour margins.

Optimal oncological results and patient outcomes are achieved in surgery for early breast cancer with breast conserving surgery (BCS) where this is appropriate. A limitation of BCS occurs when cancer is present at, or close, to the resection margin - termed a 'positive' margin - and re-excision is recommended to reduce recurrence rate. This is occurs in 17% of BCS in the UK and there is therefore a critical need for a way to assess margin status intraoperatively to ensure complete excision with adequate margins at the first operation. This study presents the potential of high wavenumber (HWN) Raman spectroscopy to address this. Freshly excised specimens from thirty patients undergoing surgery for breast cancer were measured using a surface Raman probe, and a multivariate classification model to predict normal versus tumour was developed from the data. This model achieved 77.1% sensitivity and 90.8% specificity following leave one patient out cross validation, with the defining features being differences in water content and lipid versus protein content. This demonstrates the feasibility of HWN Raman spectroscopy to facilitate future intraoperative margin assessment at specific locations. Clinical utility of the approach will require further research.

Spatially offset Raman spectroscopy for biomedical applications.

In recent years, Raman spectroscopy has undergone major advancements in its ability to probe deeply through turbid media such as biological tissues. This progress has been facilitated by the advent of a range of specialist techniques based around spatially offset Raman spectroscopy (SORS) to enable non-invasive probing of living tissue through depths of up to 5 cm. This represents an improvement in depth penetration of up to two orders of magnitude compared to what can be achieved with conventional Raman methods. In combination with the inherently high molecular specificity of Raman spectroscopy, this has therefore opened up entirely new prospects for a range of new analytical applications across multiple fields including medical diagnosis and disease monitoring. This article discusses SORS and related variants of deep Raman spectroscopy such as transmission Raman spectroscopy (TRS), micro-SORS and surface enhanced spatially offset Raman spectroscopy (SESORS), and reviews the progress made in this field during the past 5 years including advances in non-invasive cancer diagnosis, monitoring of neurotransmitters, and assessment of bone disease.

Spatially Offset Raman Spectroscopy-How Deep?

Spatially offset Raman spectroscopy (SORS) is a technique for interrogating the subsurface composition of turbid samples noninvasively. This study generically addresses a fundamental question relevant to a wide range of SORS studies, which is how deep SORS probes for any specific spatial offset when analyzing a turbid sample or, in turn, what magnitude of spatial offset one should select to probe a specific depth. This issue is addressed by using Monte Carlo simulations, under the assumption of negligible absorption, which establishes that the key parameter governing the extent of the probed zone for a point-like illumination and point-like collection SORS geometry is the reduced scattering coefficient of the medium. This can either be deduced from literature data or directly estimated from a SORS measurement by evaluating the Raman intensity profile from multiple spatial offsets. Once this is known, the extent of the probed zone can be determined for any specific SORS spatial offset using the Monte Carlo simulation results presented here. The proposed method was tested using experimental data on stratified samples by analyzing the signal detected from a thin layer that was moved through a stack of layers using both non-absorbing and absorbing samples. The proposed simple methodology provides important additional information on SORS measurements with direct relevance to a wide range of SORS applications including biomedical, pharmaceutical, security, forensics, and cultural heritage.

Estimating the Reduced Scattering Coefficient of Turbid Media Using Spatially Offset Raman Spectroscopy.

We propose a new method for estimating the reduced scattering coefficient, µs', of turbid homogeneous samples using Spatially Offset Raman Spectroscopy (SORS). The concept is based around the variation of Raman signal with SORS spatial offset that is strongly µs'-dependent, as such, permitting the determination of µs'. The evaluation is carried out under the assumptions that absorption is negligible at the laser and Raman wavelengths and µs' is approximately the same for those two wavelengths. These conditions are often satisfied for samples analyzed in the NIR region of the spectrum where SORS is traditionally deployed. Through a calibration procedure on a PTFE model sample, it was possible to estimate the µs' coefficient of different turbid samples with an error (RMSEP) below 18%. The knowledge of µs' in the NIR range is highly valuable for facilitating accurate numerical simulations to optimize illumination and collection geometries in SORS, to derive in-depth information about the properties of SORS measurements or in other photon applications, dependent on photon propagation in turbid media with general impact across fields such as biomedical, pharmaceutical, security, forensic, and cultural sciences.

Multiphoton imaging and Raman spectroscopy of the bovine vertebral endplate.

The interface between the intervertebral disc and the vertebral body is important to the discs' biomechanics and physiology, and is widely implicated in its pathology. This study aimed to explore biochemically and structurally the bony endplate, cartilage endplate and intervertebral disc, below the nucleus and below the annulus in healthy bovine tails. Multiphoton imaging and spontaneous Raman spectroscopy were employed. Raman spectroscopy provided relative quantification of mineral and matrix components across the vertebral endplate and its adjacent areas with microscopic spatial resolution. Microscopy utilising second-harmonic generation (SHG) and two-photon fluorescence (TPF) allowed for the structural identification of distinct endplate regions. The cartilage endplate was revealed as structurally distinct from both the bone and disc, supporting its biomechanical function as a transition zone between the soft and hard tissue components. The collagen fibres were continuous across the tidemark which defines the interface between the mineralised and non-mineralised regions of the endplate. Raman spectroscopy revealed gradients in phosphate and carbonate content through the depth of the endplate and also differences beneath the nucleus and annulus consistent with a higher rate of remodelling under the annulus.

Characterization of colorectal mucus using infrared spectroscopy: a potential target for bowel cancer screening and diagnosis.

Biological materials presenting early signs of cancer would be beneficial for cancer screening/diagnosis. In this respect, the suitability of potentially exploiting mucus in colorectal cancer was tested using infrared spectroscopy in combination with statistical modeling. Twenty-six paraffinized colon tissue biopsy sections containing mucus regions from 20 individuals (10 normal and 16 cancerous) were measured using mid-infrared spectroscopic imaging. A digital de-paraffinization, followed by cluster analysis driven digital color-coded multi-staining segmented the infrared images into various histopathological features such as epithelium, connective tissue, stroma, and mucus regions within the tissue sections. Principal component analysis followed by supervised linear discriminant analysis was carried out on pure mucus and epithelial spectra from normal and cancerous regions of the tissue. For the mucus-based classification, a sensitivity of 96%, a specificity of 83%, and an area under the curve performance of 95% was obtained. For the epithelial tissue-based classification, a sensitivity of 72%, a specificity of 88%, and an area under the curve performance of 89% was obtained. The mucus spectral profiles further showed contributions indicative of glycans including that of sialic acid changes between these pathology groups. The study demonstrates that infrared spectroscopic analysis of mucus discriminates colorectal cancers with high sensitivity. This concept could be exploited to develop screening/diagnostic approaches complementary to histopathology.

Non-invasive depth determination of inclusion in biological tissues using spatially offset Raman spectroscopy with external calibration.

Spatially offset Raman spectroscopy (SORS) allows chemical characterisation of biological tissues at depths of up to two orders of magnitude greater than conventional Raman spectroscopy. In this study, we demonstrate the use of SORS for the non-invasive prediction of depth of an inclusion within turbid media (e.g. biological tissues) using only external calibration data sets, thus extending our previous approach that required internal calibration. As with the previous methodology, the concept is based on relative changes in Raman band intensities of the inclusion that are directly related to the path length of Raman photons travelling through the medium thereby encoding the information of depth of the inclusion. However, here the calibration model is created using data only from external measurements performed at the tissue surface. This new approach facilitates a fully non-invasive methodology applicable potentially to in vivo medical diagnosis without any a priori knowledge. Monte Carlo simulations of photon propagation have been used to provide insight into the relationship between the spatial offset and the photon path lengths inside the tissues enabling one to derive a general scaling factor permitting the use of spatial offset measurements for the depth prediction. The approach was validated by predicting the depth of surface-enhanced Raman scattering (SERS) labelled nanoparticles (NPs) acting as inclusions inside a slab of ex vivo porcine tissue yielding an average root mean square error of prediction of 7.3% with respect to the overall tissue thickness. Our results pave the way for future non-invasive deep Raman spectroscopy in vivo by enabling, for example, the localisation of cancer lesions or cancer biomarkers in early disease diagnosis and targeted treatments.

Direct monitoring of light mediated hyperthermia induced within mammalian tissues using surface enhanced spatially offset Raman spectroscopy (T-SESORS).

Here we demonstrate light mediated heating of nanoparticles confined deep inside mammalian tissue, whilst directly monitoring their temperature non-invasively using a form of deep Raman spectroscopy, T-SESORS. One of the main barriers to the introduction of photo-thermal therapies (PTT) has been recognised as the inability to directly monitor the local temperature deep within the tissue at the point of therapy. Here Au nanoparticles with a Raman reporter molecule (temperature reporters) are used in combination with Au nanoshells (heat mediators) to provide simultaneously heating under NIR illumination and direct spectroscopic monitoring of local temperature deep within mammalian tissues. The surface enhanced Raman signal was read out at the tissue surface using a transmission geometry in this example and the temperature of the tissue was ascertained from the anti-Stokes to Stokes Raman reporter. This approach opens the prospect of non-invasive hyperthermia treatments with direct temperature feedback from deep inside within tissue, where nanoparticles can be used to both provide localised heating and accurately monitor the local temperature.

Enhanced deep detection of Raman scattered light by wavefront shaping.

Light scattering limits the penetration depth of non-invasive Raman spectroscopy in biological media. While safe levels of irradiation may be adequate to analyze superficial tissue, scattering of the pump beam reduces the Raman signal to undetectable levels deeper within the tissue. Here we demonstrate how wavefront shaping techniques can significantly increase the Raman signal at depth, while keeping the total irradiance constant, thus increasing the amount of Raman signal available for detection.

Mid-infrared multispectral tissue imaging using a chalcogenide fiber supercontinuum source.

We present, to the best of our knowledge, the first demonstration of mid-infrared supercontinuum (SC) tissue imaging at wavelengths beyond 5 µm using a fiber-coupled SC source spanning 2-7.5 µm. The SC was generated in a tapered large-mode-area chalcogenide photonic crystal fiber in order to obtain broad bandwidth, high average power, and single-mode output for diffraction-limited imaging performance. Tissue imaging was demonstrated in transmission at selected wavelengths between 5.7 (1754 cm-1) and 7.3 µm (1370 cm-1) by point scanning over a sub-millimeter region of colon tissue, and the results were compared to images obtained from a commercial instrument.

Clinical applications of infrared and Raman spectroscopy: state of play and future challenges.

Vibrational spectroscopies, based on infrared absorption and/or Raman scattering provide a detailed fingerprint of a material, based on the chemical content. Diagnostic and prognostic tools based on these technologies have the potential to revolutionise our clinical systems leading to improved patient outcome, more efficient public services and significant economic savings. However, despite these strong drivers, there are many fundamental scientific and technological challenges which have limited the implementation of this technology in the clinical arena, although recent years have seen significant progress in addressing these challenges. This review examines (i) the state of the art of clinical applications of infrared absorption and Raman spectroscopy, and (ii) the outstanding challenges, and progress towards translation, highlighting specific examples in the areas of in vivo, ex vivo and in vitro applications. In addition, the requirements of instrumentation suitable for use in the clinic, strategies for pre-processing and statistical analysis in clinical spectroscopy and data sharing protocols, will be discussed. Emerging consensus recommendations are presented, and the future perspectives of the field are assessed, particularly in the context of national and international collaborative research initiatives, such as the UK EPSRC Clinical Infrared and Raman Spectroscopy Network, the EU COST Action Raman4Clinics, and the International Society for Clinical Spectroscopy.

Correction: Clinical applications of infrared and Raman spectroscopy: state of play and future challenges.

Correction for 'Clinical applications of infrared and Raman spectroscopy: state of play and future challenges' by Matthew J. Baker, et al., Analyst, 2018, DOI: 10.1039/c7an01871a.

Detection of Aß plaque-associated astrogliosis in Alzheimer's disease brain by spectroscopic imaging and immunohistochemistry.

Recent work using micro-Fourier transform infrared (µFTIR) imaging has revealed that a lipid-rich layer surrounds many plaques in post-mortem Alzheimer's brain. However, the origin of this lipid layer is not known, nor is its role in the pathogenesis of Alzheimer's disease (AD). Here, we studied the biochemistry of plaques in situ using a model of AD. We combined FTIR, Raman and immunofluorescence images, showing that astrocyte processes co-localise with the lipid ring surrounding many plaques. We used µFTIR imaging to rapidly measure chemical signatures of plaques over large fields of view, and selected plaques for higher resolution analysis with Raman microscopy. Raman maps showed similar lipid rings and dense protein cores as in FTIR images, but also revealed cell bodies. We confirmed the presence of plaques using amylo-glo staining, and detected astrocytes using immunohistochemistry, revealing astrocyte co-localisation with lipid rings. This work is important because it correlates biochemical changes surrounding the plaque with the biological process of astrogliosis.

Raman spectroscopy and multivariate analysis for the non invasive diagnosis of clinically inconclusive vulval lichen sclerosus.

Vulval lichen sclerosus (LS) is a common inflammatory condition associated with an increased risk of developing vulval carcinoma. Diagnosis is usually clinical although biopsy is necessary if the diagnosis is uncertain or if there is a failure to respond to adequate initial treatment. Raman spectroscopy has the potential to be applied in vivo for near real time objective non-invasive optical diagnosis, avoiding the need for invasive tissue biopsies. The aim of this study was to evaluate the diagnostic performance of Raman spectroscopy for differentiating LS from other vulval conditions in fresh vulval biopsies. Biopsies were analysed from 27 women with suspected LS in whom the attending gynaecologist could not establish the diagnosis on clinical presentation alone. Spectral variance was explored using principal component analysis and in conjunction with the histological diagnoses was used to develop and test a multivariate linear discriminant classification model. This model was validated with leave one sample out cross validation and the diagnostic performance of the technique assessed in comparison with the pathology gold standard. After cross validation the technique was able to correctly differentiate LS from other inflammatory vulval conditions with a sensitivity of 91% and specificity of 80%. This study demonstrates Raman spectroscopy has potential as a technique for in vivo non-invasive diagnosis of vulval skin conditions. Applied in the clinical setting this technique may reduce the need for invasive tissue biopsy. Further in vivo study is needed to assess the ability of Raman spectroscopy to diagnose other vulval conditions before clinical application.

Developing fibre optic Raman probes for applications in clinical spectroscopy.

Raman spectroscopy has been shown by various groups over the last two decades to have significant capability in discriminating disease states in bodily fluids, cells and tissues. Recent development in instrumentation, optics and manufacturing approaches has facilitated the design and demonstration of various novel in vivo probes, which have applicability for myriad of applications. This review focusses on key considerations and recommendations for application specific clinical Raman probe design and construction. Raman probes can be utilised as clinical tools able to provide rapid, non-invasive, real-time molecular analysis of disease specific changes in tissues. Clearly the target tissue location, the significance of spectral changes with disease and the possible access routes to the region of interest will vary for each clinical application considered. This review provides insight into design and construction considerations, including suitable probe designs and manufacturing materials compatible with Raman spectroscopy.

High-resolution FTIR imaging of colon tissues for elucidation of individual cellular and histopathological features.

Novel technologies that could complement current histopathology based cancer diagnostic methods are under examination. In this endeavour mid-infrared spectroscopic imaging is a promising candidate that can provide valuable bio-molecular information from unstained cells and tissues in a rapid and a non-destructive manner. With this imaging technique, the biochemical information obtained from smaller areas of the tissues can be of clinical significance and hence the measured pixel size. Until recently it was difficult to obtain spectral data from pixels below around 5 microns square. High NA objectives have been utilised to reduce the ideal diffraction limit, enabling for the first time elucidation of subcellular features. In this context, the ability of high-resolution imaging, obtained using novel high-magnification optics retro-fitted onto a bench top FTIR imaging system, to characterise histopathological features in colonic tissues has been tested. Formalin fixed paraffin embedded colon tissues from three different pathologies were imaged directly using the conventional and the high-magnification imaging set-ups. To circumvent chemical de-paraffinization protocols, an extended multiplicative signal correction (EMSC) based electronic de-paraffinization was carried out on all the infrared images. Multivariate analysis of the high-magnification infrared imaging data showed a detailed information of the histological features of the colon tissue in comparison to conventional imaging. Furthermore, high-magnification imaging has enabled a label-free characterization of the mucin rich goblet cell features in an unprecedented manner. The current study demonstrates the applicability of high-magnification FTIR imaging to characterise complex tissues on a smaller scale that could be of clinical significance.

Spectropathology for the next generation: quo vadis?

Although the potential of vibrational spectroscopy for biomedical applications has been well demonstrated, translation into clinical practice has been relatively slow. This Editorial assesses the challenges facing the field and the potential way forward. While many technological challenges have been addressed to date, considerable effort is still required to gain acceptance of the techniques among the medical community, standardise protocols, extend to a clinically relevant scale, and ultimately assess the health economics underlying clinical deployment. National and international research networks can contribute much to technology development and standardisation. Ultimately, large-scale funding is required to engage in clinical trials and instrument development.

Infrared micro-spectroscopy for cyto-pathological classification of esophageal cells.

We report results from a study utilizing infrared spectral cytopathology (SCP) to detect abnormalities in exfoliated esophageal cells. SCP has been developed over the past decade as an ancillary tool to classical cytopathology. In SCP, the biochemical composition of individual cells is probed by collecting infrared absorption spectra from each individual, unstained cell, and correlating the observed spectral patterns, and the variations therein, against classical diagnostic methods to obtain an objective, machine-based classification of cells. In the past, SCP has been applied to the analysis and classification of cells exfoliated from the cervix and the oral cavity. In these studies, it was established that SCP can distinguish normal and abnormal cell types. Furthermore, SCP can differentiate between truly normal cells, and cells with normal morphology from the vicinity of abnormalities. Thus, SCP may be a valuable tool for the screening of early stages of dysplasia and pre-cancer.

Characterisation of a fibre optic Raman probe within a hypodermic needle.

We demonstrate the first use of a multifibre Raman probe that fits inside the bore of a hypodermic needle. A Raman probe containing multiple collection fibres provides improved signal collection efficiency in biological samples compared with a previous two-fibre design. Furthermore, probe performance (signal-to-noise ratios) compared favourably with the performance achieved in previous Raman microscope experiments able to distinguish between benign lymph nodes, primary malignancies in lymph nodes and secondary malignancies in lymph nodes. The experimental measurements presented here give an indication of the sampling volume of the Raman needle probe in lymphoid tissues. Liquid tissue phantoms were used that contained scattering medium encompassing a range of scattering properties similar to those of a variety of tissue types, including lymph node tissues. To validate the appropriateness of the phantoms, the sampling depth of the probe was also measured in excised lymph node tissue. More than 50 % of Raman photons collected were found to originate from between the tip of the needle and a depth of 500 µm into the tissue. The needle probe presented here achieves spectral quality comparable to that in numerous studies previously demonstrating Raman disease discrimination. It is expected that this approach could achieve targeted subcutaneous tissue measurements and be viable for use for the in vivo Raman diagnostics of solid organs located within a few centimetres below the skin's surface. Graphical Abstract Schematic of multi-fibre Raman needle probe with disposible tips and proximal optical filtration.

Endoscopic Raman spectroscopy enables objective diagnosis of dysplasia in Barrett's esophagus.

BACKGROUND: Early detection and targeted endoscopic resection of Barrett's esophagus-associated high-grade dysplasia (HGD) can prevent progression to invasive esophageal malignancy. Raman spectroscopy, a highly sophisticated analytical technique, has been translated into an endoscopic tool to facilitate rapid, objective diagnosis of dysplasia in the esophagus. OBJECTIVE: To evaluate the ability of endoscopic Raman spectroscopy (ERS) to objectively detect esophageal HGD and adenocarcinoma. DESIGN: A total of 798 one-second spectra were measured from 673 ex vivo esophageal tissue samples, collected from patients with Barrett's esophagus by using a novel endoscopic Raman probe. Spectra were correlated with consensus histopathology. Multivariate analysis was used to evaluate the classification accuracy of ERS ex vivo. SETTING: Probe measurements were conducted in the laboratory. Tissue specimens were collected from the operating theatre and endoscopy unit. PATIENTS: Tissue from 62 patients was included in the study. INTERVENTIONS: Endoscopic biopsy/resection or esophagectomy was performed where indicated clinically. MAIN OUTCOME MEASUREMENT: Diagnostic performance of ERS for detection of HGD and esophageal adenocarcinoma. RESULTS: ERS demonstrated a sensitivity of 86% and a specificity of 88% for detecting HGD and adenocarcinoma. The ability to grade dysplasia and differentiate intestinal metaplasia from nonintestinal metaplasia columnar-lined esophagus was also demonstrated. Diagnostic classification was based on objective measurement of the biochemical profile of different tissue types. The potential for combination ERS and narrow-band imaging was also demonstrated. LIMITATIONS: Measurements were taken from ex vivo tissue. CONCLUSION: ERS enables rapid, accurate, objective diagnosis of superficial esophageal disease (metaplasia, dysplasia, intramucosal cancer) in clinically applicable time scales.