Improvement In Spectral Quality Research Articles

Retrospective frequency drift correction of rosette MRSI data using spectral registration.

Frequency drift correction is an important postprocessing step in MRS that yields improvements in spectral quality and metabolite quantification. Although routinely applied in single-voxel MRS, drift correction is much more challenging in MRSI due to the presence of phase-encoding gradients. Thus, separately acquired navigator scans are normally required for drift estimation. In this work, we demonstrate the use of self-navigating rosette MRSI trajectories combined with time-domain spectral registration to enable retrospective frequency drift corrections without the need for separately acquired navigator echoes. A rosette MRSI sequence was implemented to acquire data from the brains of 5 healthy volunteers. FIDs from the center of k-space ( FIDs) were isolated from each shot of the rosette acquisition, and time-domain spectral registration was used to estimate the frequency offset of each FID relative to a reference scan (the first FID in the series). The estimated frequency offsets were then used to apply corrections throughout -space. Improvements in spectral quality were assessed before and after drift correction. Spectral registration resulted in significant improvements in signal-to-noise ratio(12.9%) and spectral linewidths (18.5%). Metabolite quantification was performed using LCModel, and the average Cramer-Rao lower bounds uncertainty estimates were reduced by 5.0% for all metabolites, following field drift correction. This study demonstrated the use of self-navigating rosette MRSI trajectories to retrospectively correct frequency drift errors in in vivo MRSI data. This correction yields meaningful improvements in spectral quality.

Integration of Satellite Data with High Resolution Ratio: Improvement of Spectral Quality with Preserving Spatial Details.

Commonly used image fusion techniques generally produce good results for images obtained from the same sensor, with a standard ratio of spatial resolution (1:4). However, an atypical high ratio of resolution reduces the effectiveness of fusion methods resulting in a decrease in the spectral or spatial quality of the sharpened image. An important issue is the development of a method that allows for maintaining simultaneous high spatial and spectral quality. The authors propose to strengthen the pan-sharpening methods through prior modification of the panchromatic image. Local statistics of the differences between the original panchromatic image and the intensity of the multispectral image are used to detect spatial details. The Euler’s number and the distance of each pixel from the nearest pixel classified as a spatial detail determine the weight of the information collected from each integrated image. The research was carried out for several pan-sharpening methods and for data sets with different levels of spectral matching. The proposed solution allows for a greater improvement in the quality of spectral fusion, while being able to identify the same spatial details for most pan-sharpening methods and is mainly dedicated to Intensity-Hue-Saturation based methods for which the following improvements in spectral quality were achieved: about 30% for the urbanized area and about 15% for the non-urbanized area.

Advanced processing and simulation of MRS data using the FID appliance (FID‐A)—An open source, MATLAB‐based toolkit

To introduce a new toolkit for simulation and processing of magnetic resonance spectroscopy (MRS) data, and to demonstrate some of its novel features. The FID appliance (FID-A) is an open-source, MATLAB-based software toolkit for simulation and processing of MRS data. The software is designed specifically for processing data with multiple dimensions (eg, multiple radiofrequency channels, averages, spectral editing dimensions). It is equipped with functions for importing data in the formats of most major MRI vendors (eg, Siemens, Philips, GE, Agilent) and for exporting data into the formats of several common processing software packages (eg, LCModel, jMRUI, Tarquin). This paper introduces the FID-A software toolkit and uses examples to demonstrate its novel features, namely 1) the use of a spectral registration algorithm to carry out useful processing routines automatically, 2) automatic detection and removal of motion-corrupted scans, and 3) the ability to perform several major aspects of the MRS computational workflow from a single piece of software. This latter feature is illustrated through both high-level processing of in vivo GABA-edited MEGA-PRESS MRS data, as well as detailed quantum mechanical simulations to generate an accurate LCModel basis set for analysis of the same data. All of the described processing steps resulted in a marked improvement in spectral quality compared with unprocessed data. Fitting of MEGA-PRESS data using a customized basis set resulted in improved fitting accuracy compared with a generic MEGA-PRESS basis set. The FID-A software toolkit enables high-level processing of MRS data and accurate simulation of in vivo MRS experiments. Magn Reson Med 77:23-33, 2017. © 2015 Wiley Periodicals, Inc.

Chemo-enzymatic synthesis of site-specific isotopically labeled nucleotides for use in NMR resonance assignment, dynamics and structural characterizations

Stable isotope labeling is central to NMR studies of nucleic acids. Development of methods that incorporate labels at specific atomic positions within each nucleotide promises to expand the size range of RNAs that can be studied by NMR. Using recombinantly expressed enzymes and chemically synthesized ribose and nucleobase, we have developed an inexpensive, rapid chemo-enzymatic method to label ATP and GTP site specifically and in high yields of up to 90%. We incorporated these nucleotides into RNAs with sizes ranging from 27 to 59 nucleotides using in vitro transcription: A-Site (27 nt), the iron responsive elements (29 nt), a fluoride riboswitch from Bacillus anthracis (48 nt), and a frame-shifting element from a human corona virus (59 nt). Finally, we showcase the improvement in spectral quality arising from reduced crowding and narrowed linewidths, and accurate analysis of NMR relaxation dispersion (CPMG) and TROSY-based CEST experiments to measure μs-ms time scale motions, and an improved NOESY strategy for resonance assignment. Applications of this selective labeling technology promises to reduce difficulties associated with chemical shift overlap and rapid signal decay that have made it challenging to study the structure and dynamics of large RNAs beyond the 50 nt median size found in the PDB.

Retrofitting the Electric Lighting and Daylighting Systems to Reduce Energy Use in Buildings: A Literature Review

This paper presents a literature review about energy-efficient retrofit of electric lighting and daylighting systems in buildings. The review, which covers around 160 research articles, addresses the following themes: 1) retrofitting electric lighting in buildings, 2) electric lighting energy use and saving potential and 3) lighting retrofit strategies. The retrofit strategies covered in the review are: replacement of lamp, ballast or luminaire; use of task-ambient lighting design; improvement in maintenance; reduction of maintained illuminance levels; improvement in spectral quality of light sources; improvement in occupant behavior; use of control systems; and use of daylighting systems. The review indicates that existing general knowledge about lighting retrofit is currently very limited and that there is a significant lack of information concerning the actual energy performance of lighting systems installed in the existing building stock. The resulting key directions for future research highlights issues for which a better understanding is required for the spread and development of lighting retrofit. (Less)

A Comparison of Alternating Current and Direct Current Electrospray Ionization for Mass Spectrometry

A series of studies comparing the performance of alternating current electrospray ionization (AC ESI) mass spectrometry (MS) and direct current electrospray ionization (DC ESI) MS have been conducted, exploring the absolute signal intensity and signal-to-background ratios produced by both methods using caffeine and a model peptide as targets. Because the high-voltage AC signal was more susceptible to generating gas discharges, the operating voltage range of AC ESI was significantly smaller than that for DC ESI, such that the absolute signal intensities produced by DC ESI at peak voltages were one to two orders of magnitude greater than those for AC ESI. Using an electronegative nebulizing gas, sulfur hexafluoride (SF6), instead of nitrogen (N2) increased the operating range of AC ESI by ~50%, but did not appreciably improve signal intensities. While DC ESI generated far greater signal intensities, both ionization methods produced comparable signal-to-background noise, with AC ESI spectra appearing qualitatively cleaner. A quantitative calibration analysis was performed for two analytes, caffeine and the peptide MRFA. AC ESI utilizing SF6 outperforms all other techniques for the detection of MRFA, producing chromatographic limits of detection nearly one order of magnitude lower than that of DC ESI utilizing N2, and one-half that of DC ESI utilizing SF6. However, DC ESI outperforms AC ESI for the analysis of caffeine, indicating that improvements in spectral quality may benefit certain compounds or classes of compounds, on an individual basis.

Chemo-enzymatic synthesis of selectively ¹³C/¹⁵N-labeled RNA for NMR structural and dynamics studies.

RNAs are an important class of cellular regulatory elements, and they are well characterized by X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy in their folded or bound states. However, the apo or unfolded states are more difficult to characterize by either method. Particularly, effective NMR spectroscopy studies of RNAs in the past were hampered by chemical shift overlap of resonances and associated rapid signal loss due to line broadening for RNAs larger than the median size found in the PDB (~25 nt); most functional riboswitches are bigger than this median size. Incorporation of selective site-specific (13)C/(15)N-labeled nucleotides into RNAs promises to overcome this NMR size limitation. Unlike previous isotopic enrichment methods such as phosphoramidite, de novo, uniform-labeling, and selective-biomass approaches, this newer chemical-enzymatic selective method presents a number of advantages for producing labeled nucleotides over these other methods. For example, total chemical synthesis of nucleotides, followed by solid-phase synthesis of RNA using phosphoramidite chemistry, while versatile in incorporating isotope labels into RNA at any desired position, faces problems of low yields (<10%) that drop precipitously for oligonucleotides larger than 50 nt. The alternative method of de novo pyrimidine biosynthesis of NTPs is also a robust technique, with modest yields of up to 45%, but it comes at the cost of using 16 enzymes, expensive substrates, and difficulty in making some needed labeling patterns such as selective labeling of the ribose C1' and C5' and the pyrimidine nucleobase C2, C4, C5, or C6. Biomass-produced, uniformly or selectively labeled NTPs offer a third method, but suffer from low overall yield per labeled input metabolite and isotopic scrambling with only modest suppression of (13)C-(13)C couplings. In contrast to these four methods, our current chemo-enzymatic approach overcomes most of these shortcomings and allows for the synthesis of gram quantities of nucleotides with >80% yields while using a limited number of enzymes, six at most. The unavailability of selectively labeled ribose and base precursors had prevented the effective use of this versatile method until now. Recently, we combined an improved organic synthetic approach that selectively places (13)C/(15)N labels in the pyrimidine nucleobase (either (15)N1, (15)N3, (13)C2, (13)C4, (13)C5, or (13)C6 or any combination) with a very efficient enzymatic method to couple ribose with uracil to produce previously unattainable labeling patterns (Alvarado et al., 2014). Herein we provide detailed steps of both our chemo-enzymatic synthesis of custom nucleotides and their incorporation into RNAs with sizes ranging from 29 to 155 nt and showcase the dramatic improvement in spectral quality of reduced crowding and narrow linewidths. Applications of this selective labeling technology should prove valuable in overcoming two major obstacles, chemical shift overlap of resonances and associated rapid signal loss due to line broadening, that have impeded studying the structure and dynamics of large RNAs such as full-length riboswitches larger than the ~25 nt median size of RNA NMR structures found in the PDB.

Expression, purification and preliminary NMR characterization of isotopically labeled wild-type human heterotrimeric G protein αi1

Molecular-level investigation of proteins is increasingly important to researchers trying to understand the mechanisms of signal transmission. Heterotrimeric G proteins control the activation of many critical signal transmission cascades and are also implicated in numerous diseases. As part of a longer-term investigation of intramolecular motions in RGS and Gα proteins in their apo and complexed forms, we have successfully developed a protocol for preparing milligram quantities of highly purified, isotopically labeled wild-type human Gαi1 (hGαi1) subunit for NMR studies. High levels of expression in Escherichia coli can be attributed to the use of the SUMO fusion protein system, a bacterial strain that produces rare codons, supplementation of minimal medium with small quantities of isotopically labeled rich medium and a lowered induction temperature. Purification of hGαi1 utilized affinity and size exclusion chromatography, and protein activity was confirmed using fluorescence-based GTP-binding studies. Preliminary NMR analysis of hGαi1 has shown that high-quality spectra can be obtained at near-physiological temperatures, whereas lower temperature spectra display numerous weak and broadened peaks, providing preliminary evidence for widespread μs-ms timescale exchange. In an effort to further optimize the NMR spectra we prepared a truncated form of hGαi1 (hGαi1-Δ31) in which the 31-residue unstructured N-terminus was removed. This resulted in further improvements in spectral quality by eliminating high-intensity peaks that obscured resonances from structured segments of the protein. We plan to use hGαi1-Δ31 in future investigations of protein dynamics by NMR spectroscopy to gain insight into the role of these motions in RGS/Gα binding selectivity.

Robust Reconstruction of MRSI Data Using a Sparse Spectral Model and High Resolution MRI Priors

We introduce a novel algorithm to address the challenges in magnetic resonance (MR) spectroscopic imaging. In contrast to classical sequential data processing schemes, the proposed method combines the reconstruction and postprocessing steps into a unified algorithm. This integrated approach enables us to inject a range of prior information into the data processing scheme, thus constraining the reconstructions. We use high resolution, 3-D estimate of the magnetic field inhomogeneity map to generate an accurate forward model, while a high resolution estimate of the fat/water boundary is used to minimize spectral leakage artifacts. We parameterize the spectrum at each voxel as a sparse linear combination of spikes and polynomials to capture the metabolite and baseline components, respectively. The constrained model makes the problem better conditioned in regions with significant field inhomogeneity, thus enabling the recovery even in regions with high field map variations. To exploit the high resolution MR information, we formulate the problem as an anatomically constrained total variation optimization scheme on a grid with the same spacing as the magnetic resonance imaging data. We analyze the performance of the proposed scheme using phantom and human subjects. Quantitative and qualitative comparisons indicate a significant improvement in spectral quality and lower leakage artifacts.

Hepatic lipid profiling in chronic hepatitis C: An in vitro and in vivo proton magnetic resonance spectroscopy study

Hepatic steatosis is an important factor in pathogenesis, progression and response to treatment in hepatitis C. We aimed to investigate differences in hepatic lipid composition in liver biopsies from patients with chronic hepatitis C using proton magnetic resonance spectroscopy ((1)H MRS) and to translate these findings to the in vivo clinical setting. Two cohorts of patients with histologically defined chronic hepatitis C were studied. High-resolution MR spectra were obtained from 47 liver biopsy samples. These data were used to derive biologically relevant prior knowledge for the assignment and interpretation of lower-resolution in vivo hepatic MRS data acquired at 1.5T from a second cohort of 59 patients. MRS data were obtained both in vitro and in vivo from a subset of 11 patients. Multivariate factor analysis demonstrated characteristic MR spectral differences by fibrosis stage and genotype. Total lipid increased with fibrosis stage (r=0.43, p=0.003) and was higher in genotype 3 compared to genotype 1 (p=0.03), while lipid polyunsaturation decreased with increasing fibrosis stage (r=-0.55, p<0.0005) and, independently, with increasing steatosis. Non-invasive assessment using in vivo hepatic (1)H MRS corroborated in vitro findings, but the signal-to-noise ratio was insufficient for reliable assessment of lipid polyunsaturation in vivo. Hepatic lipid composition was analysed using MRS in patients with chronic hepatitis C in vitro and in vivo, demonstrating significant differences in indices by disease severity. High-resolution data informed the analysis and interpretation of in vivo spectra, but further improvements in spectral quality in vivo are required.

Combined MRI and MRS in Prostate Cancer: Improvement of Spectral Quality by Susceptibility Matching

Local magnetic field inhomogeneity caused by susceptibility artifacts due to air in the endorectal coil substantially degrades the quality of 3D MR spectroscopic imaging (3D-MRSI). Perflubron (PFB) has magnetic susceptibility similar to that of human tissue. We prospectively assessed the effect of susceptibility matching using PFB on in vivo prostate (1)H-3D-MRSI. Ninety-one consecutive patients referred for 3D-MRSI were examined using air and PFB as the filling agent for endorectal coils at 1.5T with an identically placed PRESS box and sat bands. Solely auto-shim without additional manual shimming was used. The full width at half maximum (FWHM) of the water peak was statistically compared with a paired t-test. The spectral quality was visually evaluated for the definition of metabolite peaks and for the citrate peak split (duplet). The MR image quality was rated on a five-point scale. FWHM was significantly less (p < 0.001) using PFB (mean 9.0 +/- 3.3, range 3 - 20) than air (mean 14.9 +/- 4.2, range 6 - 26) in 85/91 patients (93%). The spectral quality markedly improved using PFB and frequently the duplet of the citrate peak was able to be identified. Image quality ratings were similar (mean rating PFB 4.2, air 4.3 points). Omitting manual shimming led to a time savings of 4 min. per study. 3D-MRSI using PFB for susceptibility matching benefits from significantly better local field homogeneity, thus providing improved spectra quality. Combined with a substantial time savings in data acquisition, this may increase the clinical utilization of 3D-MRSI in patients with prostate cancer.

Development of an automated in situ fracture stage for a ToF‐SIMS system

AbstractThe design philosophy and implementation of an ultra high vacuum (UHV), PC controlled, automated in situ fracture stage for a surface analysis system is described. ToF‐SIMS spectra are shown to illustrate the improvement in spectral quality obtained from micro‐compact tension (CT) tests of polymer matrix fracture surfaces produced using the fracture stage in UHV compared to those obtained from a sample tested at air. This system is flexible in that by changing the capacity of the load cell it is possible to reduce or increase maximum loads as the specimen type and material demands. The stage has been designed with instrumental flexibility in mind, utilising commercial SEM‐stub type sample mounts, and can thus be used for AES/SAM and XPS investigations, as well as ToF‐SIMS analysis, in the authors' laboratory. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Enhanced NMR signal detection of imino protons in RNA molecules containing 3′ dangling nucleotides

We present a method for improving the quality of nuclear magnetic resonance (NMR) spectra involving exchangeable protons near the base of the stem of RNA hairpin molecules. NMR spectra of five different RNA hairpins were compared. These hairpins consisted of a native RNA structure and four molecules each having different unpaired, or dangling, nucleotides at the 3' end. NMR experiments were acquired in water for each construct and the quality of the imino proton spectral regions were examined. The imino resonances near the base of the stem of the wild type RNA structure were not observed due to breathing motions. However, a significant increase in spectral quality for molecules with dangling 3' adenosine or guanosine nucleotides was observed, with imino protons detected in these constructs that were not observed in the wild type construct. A modest improvement in spectral quality was seen for the construct with a 3' unpaired uridine, whereas no significant improvement was observed for a 3' unpaired cytidine. This improvement in NMR spectral quality mirrors the increased thermodynamic stability observed for 3' unpaired nucleotides which is dependant on the stacking interactions of these nucleotides against the base of the stem. The use of a dangling 3' adenosine nucleotide represents an easy method to significantly improve the quality of NMR spectra of RNA molecules.

Selective excitation of overlapping multiplets; the application of doubly selective and chemical shift filter experiments to complex NMR spectra

Standard 1D TOCSY and NOE experiments have limitations where signals are severely overlapped. Here, two recently published selective excitation methods are evaluated, the first of which uses a chemical shift selective filter to select a single resonance based on its chemical shift, and the second of which is a doubly selective experiment comprising a 1D TOCSY preparation step and subsequent 1D NOE. We also demonstrate the improvement in spectral quality obtained by the use of the zero quantum filter, which is incorporated into both of these experiments. The application of these different methods of selectively exciting overlapped multiplets, to different types of samples is considered.

Raman spectroscopy and UV pulsed laser: an excellent symbiosis?

AbstractThe fundamental idea of the present work concerns photon technology performance. On the one hand, in order to improve the Raman spectral quality when pigment analysis is carried out, we use UV pulsed laser radiation (266 nm) and its non‐thermal photoablation‐induced effect. In this way, the unwanted superficial layers (old varnishes, for example, in easel paintings) can be locally removed and so a reduction of the total fluorescence in the spectrum of the analyzed zone is achieved. On the other hand, for the purpose of analyzing the quality of the process, we employ Raman spectroscopy to obtain molecular information about the previous and later compositions of the surface irradiated with UV pulses. The fluorescence reduction of the Raman spectra and its consequent spectral quality improvement are quantified by a proposed figure of merit (signal‐to‐noise ratio) which is calculated in a suitable spectral range. The UV pulses are obtained starting an Nd:YAG pulsed laser (1064 nm) in combination with non‐linear optical crystals, and the Raman system used in the analytical measurements is a Jobin Yvon Induram with optical fiber technology and an HeNe continuous laser (632.8 nm). A Haas shutter guarantees the spatial focusing of the optical pulses over a concrete point of the irradiated sample. Based on the experimental results, two conclusions can be established: first, non‐thermal photoablation is very effective at removing small areas of the superficial varnished layers; second, Raman spectroscopy and the proposed figure of merit are very useful for measuring the resulting improvement in spectral quality. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Cascaded z-filters for efficient single-scan suppression of zero-quantum coherence

A simple and robust method to suppress zero-quantum coherence (ZQC) in NMR experiments, in a single scan and with very high suppression ratio, is described. It is an appreciable improvement on a previous technique by Thrippleton and Keeler [Angew. Chem. Int. Ed. 42 (2003) 3938]. The method, called a z-filter cascade, preserves longitudinal, or z-magnetization, with high efficiency. Losses depend mostly on T 1 relaxation but not T 2 relaxation mechanisms. At the same time, suppression of ZQC can be essentially complete in a single scan. The time duration of the z-filter cascade scales inversely to representative chemical shift differences between the coupled spins, and is typically a few tens of milliseconds. The high efficiency of the zero-quantum suppression and excellent retention of the desired z-magnetization, in a single scan without resort to phase cycling or difference spectroscopy, makes the z-filter cascade a useful new pulse sequence building block for a whole range of NMR experiments. In cases where unwanted residual ZQC may have previously contributed to baseline “ t 1-noise” in two-dimensional NMR spectra, the z-filter cascade can deliver a noteworthy improvement in spectral quality.

Effects of chemical treatments on the quality and quantitative reliability of solid-state [formula omitted] NMR spectroscopy of mineral soils

Three mineral soils were treated by chemical methods traditionally used to increase cross polarization magic angle spinning technique (CP-MAS) 13 C nuclear magnetic resonance (NMR) spectral quality. Treatment with 2% HF/BF 3 produced the highest quality spectra followed by 4% sodium dithionite and 0.05 M tin(II) chloride, respectively. The improvement in spectral quality was due to both reduction in the paramagnetic character of the soils as well as an increase in the concentration of organic carbon. Surprisingly, removal of iron did not necessarily correlate with higher quality spectra. Dithionite selectively removed aliphatic material, most likely associated with iron, and 2% HF/BF 3 removed O-alkyl and carboxyl carbon. Relaxation rate constants (T 1H and T 1ρH) were shown to be a function of the treatment method employed rather than the paramagnetic content of the soil through use of proton spin relaxation editing (PSRE).

Spectral restoration from low signal-to-noise, distorted NMR signals: application to hyphenated capillary electrophoresis-NMR

In capillary electrophoresis separations coupled to NMR signal detection using small solenoidal coils, electrophoretic currents cause substantial distortion in the NMR spectral linewidths and peak heights, distortions which cannot be fully counteracted through shimming. The NMR spectra also have a low signal-to-noise ratio due to the small amounts of material, typically <1 nmol, associated with such microseparations. This study proposes a two-step, signal processing method to restore spectral lines from the distorted NMR spectrum. First, a reference signal is acquired to estimate the broadening function, as a combination of several Lorentzian functions, using a gradient descent method. Then multi-resolution wavelet analysis is applied to the distorted spectrum to determine an initial estimate of the frequencies of the spectral lines. Convergence to the final spectrum, a second set of Lorentzians, involves deconvolution with the estimated broadening function using a gradient descent method. Experimental CE-NMR data show that considerable improvements in spectral quality are possible using this approach, although fine splittings can not be resolved if the broadening function is large.

Gradient, high‐resolution, magic‐angle spinning nuclear magnetic resonance spectroscopy of human adipocyte tissue

The recently developed technique of gradient, high-resolution magic-angle spinning NMR (g-hr-MAS-NMR) spectroscopy was applied to the study of ex vivo human lipoma and liposarcoma tissue. Compared with conventional 1H-NMR, the g-hr-MAS method yielded a large improvement in spectral resolution and permitted the detection of metabolite resonance's in a well-differentiated liposarcoma that was not observed in spectra of similar samples obtained using nonspinning NMR methods. These findings suggest that g-hr-MAS-NMR spectroscopy provides a key improvement in spectral quality for ex vivo lipoma and liposarcoma tissue thereby permitting a more precise determination of tissue metabolite composition than conventional nonspinning NMR methods.

Vibrational spectroscopic studies of asbestos and comparison of suitability for remote analysis

Raman, mid-infrared (MIR) and near-infrared (NIR) spectroscopic methods have been applied to the analysis of fibrous (asbestos) and non-fibrous forms of serpentine and amphibole minerals. This paper describes the first application of NIR diffuse reflectance spectroscopy to the study of asbestos minerals. In addition, a more generally applicable Raman spectroscopic study, in terms of multiple excitation wavelengths and asbestos materials, than has previously been made is reported. Improvements in spectral quality (especially in the OH stretching region) over previously published MIR spectroscopic data are also reported. The results of this work indicate the NIR diffuse reflectance spectroscopy appears to be the preferred method for the remote analysis of asbestos due to the relatively simple spectra in the wavenumber range 7400-6900 cm −1, the high signal-to-noise ratio and spectral contrast of the spectra, the capability of using silica fiber-optics cables, and the time required to perform the analysis relative to the other vibrational spectroscopic techniques.