Near-infrared spectroscopy

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Near-infrared spectrum
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Near-IR absorption spectrum of dichloromethane showing complicated overlapping overtones of mid IR absorption features.

Near-infrared spectroscopy (NIRS) is a

pharmaceutical, food and agrochemical quality control, atmospheric chemistry
, combustion research and knowledge.

Theory

Near-infrared spectroscopy is based on molecular overtone and combination vibrations. Such transitions are

molar absorptivity in the near-IR region is typically quite small.[3] (NIR absorption bands are typically 10–100 times weaker than the corresponding fundamental mid-IR absorption band.)[4] One advantage is that NIR can typically penetrate much further into a sample than mid infrared
radiation. Near-infrared spectroscopy is, therefore, not a particularly sensitive technique, but it can be very useful in probing bulk material with little or no sample preparation.

The molecular overtone and combination bands seen in the near-IR are typically very broad, leading to complex spectra; it can be difficult to assign specific features to specific chemical components.

artificial neural networks) are often employed to extract the desired chemical information. Careful development of a set of calibration samples and application of multivariate calibration techniques is essential for near-infrared analytical methods.[5]

History

Near-infrared spectrum of liquid ethanol.

The discovery of near-infrared energy is ascribed to William Herschel in the 19th century,[6] but the first industrial application began in the 1950s. In the first applications, NIRS was used only as an add-on unit to other optical devices that used other wavelengths such as ultraviolet (UV), visible (Vis), or mid-infrared (MIR) spectrometers. In the 1980s, a single-unit, stand-alone NIRS system was made available.

In the 1980s, Karl Norris (while working at the USDA Instrumentation Research Laboratory, Beltsville, USA) pioneered the use NIR spectroscopy for quality assessments of agricultural products. Since then, use has expanded from food and agricultural to chemical, polymer, and petroleum industries; pharmaceutical industry; biomedical sciences; and environmental analysis.[7]

With the introduction of light-

fiber optics in the mid-1980s and the monochromator-detector developments in the early 1990s, NIRS became a more powerful tool for scientific research. The method has been used in a number of fields of science including physics, physiology, or medicine. It is only in the last few decades that NIRS began to be used as a medical tool for monitoring patients, with the first clinical application of so-called fNIRS in 1994.[8]

Instrumentation

Instrumentation for near-IR (NIR) spectroscopy is similar to instruments for the UV-visible and mid-IR ranges. There is a source, a detector, and a dispersive element (such as a

interferometer
are also common, especially for wavelengths above ~1000 nm. Depending on the sample, the spectrum can be measured in either reflection or transmission.

Common

incandescent or quartz halogen light bulbs are most often used as broadband sources of near-infrared radiation for analytical applications. Light-emitting diodes (LEDs) can also be used. For high precision spectroscopy, wavelength-scanned lasers and frequency combs
have recently become powerful sources, albeit with sometimes longer acquisition timescales. When lasers are used, a single detector without any dispersive elements might be sufficient.

The type of detector used depends primarily on the range of wavelengths to be measured. Silicon-based

InGaAs and PbS
devices are more suitable and have higher quantum efficiency for wavelengths above 1100 nm. It is possible to combine silicon-based and InGaAs detectors in the same instrument. Such instruments can record both UV-visible and NIR spectra 'simultaneously'.

Instruments intended for

acousto-optic tunable filter. Multiple images may be recorded sequentially at different narrow wavelength bands.[9]

Many commercial instruments for UV/vis spectroscopy are capable of recording spectra in the NIR range (to perhaps ~900 nm). In the same way, the range of some mid-IR instruments may extend into the NIR. In these instruments, the detector used for the NIR wavelengths is often the same detector used for the instrument's "main" range of interest.

NIRS as an analytical technique

The use of NIR as an analytical technique did not come from extending the use of mid-IR into the near-IR range, but developed independently. A striking way this was exhibited is that, while mid-IR spectroscopists use wavenumbers (cm−1) when displaying spectra, NIR spectroscopists used wavelength (nm), as is used in ultraviolet–visible spectroscopy. The early practitioners of IR spectroscopy, who depended on assignment of absorption bands to specific bond types, were frustrated by the complexity of the region. However, as a quantitative tool, the lower molar absorption levels in the region tended to keep absorption maxima "on-scale", enabling quantitative work with little sample preparation. The techniques applied to extract the quantitative information from these complex spectra were unfamiliar to analytical chemists, and the technique was viewed with suspicion in academia.

Generally, a quantitative NIR analysis is accomplished by selecting a group of calibration samples, for which the concentration of the analyte of interest has been determined by a reference method, and finding a correlation between various spectral features and those concentrations using a chemometric tool. The calibration is then validated by using it to predict the analyte values for samples in a validation set, whose values have been determined by the reference method but have not been included in the calibration. A validated calibration is then used to predict the values of samples. The complexity of the spectra are overcome by the use of multivariate calibration. The two tools most often used a multi-wavelength linear regression and partial least squares.

Applications

Typical applications of NIR spectroscopy include the analysis of food products, pharmaceuticals, combustion products, and a major branch of astronomical spectroscopy.

Astronomical spectroscopy

Near-infrared

Doppler shift of the parent star due to the radial velocity of the planet around the star.[10][11]

Agriculture

Near-infrared

chicken breeding as the assay method for characteristics of fat composition.[17]

Remote monitoring

Techniques have been developed for NIR spectroscopic imaging. Hyperspectral imaging has been applied for a wide range of uses, including the remote investigation of plants and soils. Data can be collected from instruments on airplanes, satellites or unmanned aerial systems to assess ground cover and soil chemistry.

Remote monitoring or remote sensing from the NIR spectroscopic region can also be used to study the atmosphere. For example, measurements of atmospheric gases are made from NIR spectra measured by the OCO-2, GOSAT, and the TCCON.

Materials science

Techniques have been developed for NIR spectroscopy of microscopic sample areas for film thickness measurements, research into the optical characteristics of nanoparticles and optical coatings for the telecommunications industry.

Medical uses

The application of NIRS in medicine centres on its ability to provide information about the oxygen saturation of haemoglobin within the microcirculation.[18] Broadly speaking, it can be used to assess oxygenation and microvascular function in the brain (cerebral NIRS) or in the peripheral tissues (peripheral NIRS).

Cerebral NIRS

When a specific area of the brain is activated, the localized blood volume in that area changes quickly. Optical imaging can measure the location and activity of specific regions of the brain by continuously monitoring blood hemoglobin levels through the determination of optical absorption coefficients.[19]

Infrascanner 1000, a NIRS scanner used to detect intracranial bleeding.

NIRS can be used as a quick screening tool for possible

intracranial bleeding cases by placing the scanner on four locations on the head. In non-injured patients the brain absorbs the NIR light evenly. When there is an internal bleeding from an injury, the blood may be concentrated in one location causing the NIR light to be absorbed more than other locations, which the scanner detects.[20]

So-called

fMRI techniques.[21] NIRS can be used on infants, and NIRS is much more portable than fMRI machines, even wireless instrumentation is available, which enables investigations in freely moving subjects.[22][23] However, NIRS cannot fully replace fMRI because it can only be used to scan cortical tissue, whereas fMRI can be used to measure activation throughout the brain. Special public domain statistical toolboxes for analysis of stand alone and combined NIRS/MRI measurement have been developed[24] (NIRS-SPM
).

Example of data acquisition using fNIRS (Hitachi ETG-4000)

The application in functional mapping of the human cortex is called

functional NIRS (fNIRS) or diffuse optical tomography (DOT).[25] The term diffuse optical tomography is used for three-dimensional NIRS. The terms NIRS, NIRI, and DOT are often used interchangeably, but they have some distinctions. The most important difference between NIRS and DOT/NIRI is that DOT/NIRI is used mainly to detect changes in optical properties of tissue simultaneously from multiple measurement points and display the results in the form of a map or image over a specific area, whereas NIRS provides quantitative data in absolute terms on up to a few specific points. The latter is also used to investigate other tissues such as, e.g., muscle,[26] breast and tumors.[27] NIRS can be used to quantify blood flow, blood volume, oxygen consumption, reoxygenation rates and muscle recovery time in muscle.[26]

By employing several wavelengths and time resolved (frequency or time domain) and/or spatially resolved methods blood flow, volume and absolute tissue saturation ( or Tissue Saturation Index (TSI)) can be quantified.

brain-computer interface
, urology, the detection of illnesses that affect the blood circulation (e.g., peripheral vascular disease), the detection and assessment of breast tumors, and the optimization of training in sports medicine.

The use of NIRS in conjunction with a bolus injection of indocyanine green (ICG) has been used to measure cerebral blood flow[29][30] and cerebral metabolic rate of oxygen consumption (CMRO2).[31] It has also been shown that CMRO2 can be calculated with combined NIRS/MRI measurements.[32] Additionally metabolism can be interrogated by resolving an additional mitochondrial chromophore, cytochrome-c-oxidase, using broadband NIRS.[33]

NIRS is starting to be used in pediatric critical care, to help manage patients following cardiac surgery. Indeed, NIRS is able to measure venous oxygen saturation (SVO2), which is determined by the cardiac output, as well as other parameters (FiO2, hemoglobin, oxygen uptake). Therefore, examining the NIRS provides critical care physicians with an estimate of the cardiac output. NIRS is favoured by patients, because it is non-invasive, painless, and does not require ionizing radiation.

Optical coherence tomography (OCT) is another NIR medical imaging technique capable of 3D imaging with high resolution on par with low-power microscopy. Using optical coherence to measure photon pathlength allows OCT to build images of live tissue and clear examinations of tissue morphology. Due to technique differences OCT is limited to imaging 1–2 mm below tissue surfaces, but despite this limitation OCT has become an established medical imaging technique especially for imaging of the retina and anterior segments of the eye, as well as coronaries.

A type of neurofeedback, hemoencephalography or HEG, uses NIR technology to measure brain activation, primarily of the frontal lobes, for the purpose of training cerebral activation of that region.

The instrumental development of NIRS/NIRI/DOT/OCT has proceeded tremendously during the last years and, in particular, in terms of quantification, imaging and miniaturization.[28]

Peripheral NIRS

Peripheral microvascular function can be assessed using NIRS. The oxygen saturation of haemoglobin in the tissue (StO2) can provide information about tissue perfusion. A vascular occlusion test (VOT) can be employed to assess microvascular function. Common sites for peripheral NIRS monitoring include the thenar eminence, forearm and calf muscles.

Particle measurement

NIR is often used in particle sizing in a range of different fields, including studying pharmaceutical and agricultural powders.

Industrial uses

As opposed to NIRS used in optical topography, general NIRS used in chemical assays does not provide imaging by mapping. For example, a clinical carbon dioxide analyzer requires reference techniques and calibration routines to be able to get accurate CO2 content change. In this case, calibration is performed by adjusting the zero control of the sample being tested after purposefully supplying 0% CO2 or another known amount of CO2 in the sample. Normal compressed gas from distributors contains about 95% O2 and 5% CO2, which can also be used to adjust %CO2 meter reading to be exactly 5% at initial calibration.[34]

See also

References

  1. ^ "An introduction to near infrared (NIR) spectroscopy | IM Publications Open". www.impopen.com. Retrieved 2022-06-01.
  2. PMID 30854368
    .
  3. ^ "Combination Bands, Overtones and Fermi Resonances". Chemistry LibreTexts. 2013-10-02. Retrieved 2022-06-03.
  4. ISBN 978-0-429-11957-6
    , retrieved 2022-06-03
  5. doi:10.1016/j.chemolab.2007.04.006
    .
  6. ^ "Herschel and the Puzzle of Infrared". American Scientist. 2017-02-06. Retrieved 2022-06-03.
  7. ISBN 9780128498835
    . Retrieved 2022-06-03.
  8. S2CID 18367840
    .
  9. S2CID 97322208
    .
  10. S2CID 13991155
    .
  11. S2CID 4422175
    .
  12. OCLC 49278168.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  13. OCLC 85784907.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  14. doi:10.1109/issc.2019.8904963
    .
  15. doi:10.1109/sensors47125.2020.9278647
    .
  16. ISBN 9781420007374
    .
  17. ^
    PMID 15852128
    .
  18. PMID 27876185
    .
  19. ISBN 978-3-540-68042-0
    .
  20. ^ Zeller, Jason S. (19 March 2013). "EM Innovations: New Technologies You Haven't Heard of Yet". Medscape. Retrieved 5 March 2015.
  21. PMID 11870923. Archived from the original
    (PDF) on 2012-07-17.
  22. PMID 18607442
    .
  23. doi:10.1155/2009/719604
    .
  24. S2CID 9269142. Archived from the original
    (PDF) on 2011-12-03.
  25. PMID 28422138
    .
  26. ^ a b van Beekvelt, MCP (2002). "Quantitative near-infrared spectroscopy in human skeletal muscle methodological issues and clinical application" (PDF). PhD Thesis, University of Nijmegen. Archived from the original (PDF) on 2013-10-16.
  27. PMID 10467293
    .
  28. ^
    S2CID 36520517. Archived from the original
    (PDF) on 2011-07-07.
  29. S2CID 206118964
    .
  30. PMID 11978878
    .
  31. PMID 16192991
    .
  32. S2CID 15513319
    .
  33. PMID 27170072
    .
  34. ^ "Archived copy" (PDF). Archived from the original (PDF) on 2014-01-25. Retrieved 2014-05-12.{{cite web}}: CS1 maint: archived copy as title (link)

Further reading

  • Kouli, M.: "Experimental investigations of non invasive measuring of cerebral blood flow in adult human using the near infrared spectroscopy." Dissertation, Technical University of Munich, December 2001.
  • Raghavachari, R., Editor. 2001. Near-Infrared Applications in Biotechnology, Marcel-Dekker, New York, NY.
  • Workman, J.; Weyer, L. 2007. Practical Guide to Interpretive Near-Infrared Spectroscopy, CRC Press-Taylor & Francis Group, Boca Raton, FL.

External links

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