Functional Brain Imaging Using Raman Spectroscopy

Image Credits Shutterstock/Sergey Nivens

Raman spectroscopy is a useful experimental tool that provides researchers with valuable information on the molecular vibrations of an element. By understanding these properties, researchers are able to identify, quantitate and provide qualitative information on the sample to be studied, which can be in the form of a solid, liquid, gas, gel, slurry or powder for the purposes of this analytical procedure.

In theory, Raman spectroscopy involves shining a laser, or similar monochromatic light source, onto a sample and measuring the amount of scattered light that bounces off the sample. While the majority of this light will be of the same frequency as the excitation source, a phenomenon that is also referred to as Rayleigh or elastic scattering, approximately 10-5 % of the incident scattered light will exhibit a differing frequency1.

This change in frequency of the incident light intensity is a result of the interactions that occur between the incident electromagnetic waves and the vibrational energy levels that are present within the molecules of the sample being analyzed. The Raman spectrum therefore is a plot of the intensity of this “shifted” light versus frequency.   

Raman spectroscopic analysis of samples provides a non-destructive, microscopic and chemical analysis that is useful in a variety of different applications. Some of the most common scientific applications of Raman spectroscopy include:

  • Geology
  • Mineralogy
  • Pharmaceuticals
  • Cosmetics
  • Carbon Materials
  • Semiconductors
  • Biomedical Sciences2

Raman Spectroscopy for Imaging

When applied for obtaining information on the chemical composition of cells and tissues, Raman spectroscopy does not require an exogenous label to be attached to molecules within the cell, thereby accelerating the imaging process at a reduced cost as compared to other currently used imaging techniques.

Additionally, by avoiding the application of fluorescent labels onto cellular molecules, researchers are able to prevent any potential interference between the epitope and the molecule being analyzed.

The use of Raman spectroscopy is a particularly advantageous tool for disease diagnosis, as it can adequately measure any molecular changes occurring at the tissue level. In fact, Raman spectroscopy has already been identified as a useful diagnostic tool for atherosclerosis and other vascular diseases, as well as cancers of the esophagus, breast, lung, bladder, skin and several other organs3.

Imaging Brain Ischemia with Raman Spectroscopy and Gold Nanoparticles

A specific subcategory of Raman spectroscopy known as surface-enhanced Raman scattering (SERS) has already been used for biomedical applications to provide molecular information on tissues without requiring the labeling of any molecules during the process.

In an effort to further advance this technology, researchers have attached both gold (Au) and silver (Ag) nanoparticles to reporter molecules during the imaging process to detect the redox potential, localized pH levels and hybridization of DNA within a single living cell.

Herein, a study published by Yamazo and colleagues (2014) utilized a self assembled nanostructure composed of boehmite to provide a stronger enhancement of Raman signals that arise when a metabolic derangement is detected in a living tissue.

For the purposes of the current study, the researchers found that the substrate, which they have termed as the ‘gold nanocoral’ (GNC) provided an accurate representation of the mouse ischemic brain following the adherence of the substrate to the damaged area4.

In Vivo Brain Cancer Imaging Using Raman Spectroscopy  

Current imaging techniques that are used for the diagnosis of most solid cancers include computer tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) and ultrasound (US) scans. While useful in their ability to accurately determine the location and anatomical relationship of the cancer to surrounding tissues, these imaging techniques are limited in their ability to characterize the molecular composition of tumors.

Therefore, physicians must often perform invasive procedures on patients to remove samples of the tumor in order to acquire this necessary information following histopathological analyses.

A recent study conducted by a group of researchers in Canada utilized a core needle biopsy tool that is integrated with Raman spectroscopy. Following the determination of the location of the tumor and the appropriate trajectory for probe insertion, the researchers inserted the core needle biopsy through a burr hole to take several Raman measurements at various different locations within the trajectory.

In addition to analyzing the Raman spectrum, the researchers also obtained a tissue sample of the tumor for further validation of this data by histopathological analysis5. The researchers of this study are hopeful that this technique could drastically reduce the rate of hemorrhages and infections that occur following needle insertion and tissue collection during related procedures.  

References

  1. “What is Raman Spectroscopy” – InPhotonics
  2. “What are the most common applications of Raman spectroscopy?” – Horiba Scientific
  3. Zhang, Y., Hong, H., & Cai, W. (2011). Imaging with Raman Spectroscopy. Current Pharmaceutical Biotechnology 11(6), 654-661. DOI:10.2174/138920110792246483.
  4. Yamazoe, S., Naya, M., Shiota, M., Morikawa, T., Kubo, A., Tani, T., et al. (2014). Large-area surface-enhanced Raman spectroscopy imaging of brain ischemia by gold nanoparticles grown on random nanoarrays of transparent boehmite. ACS Nano 8(6), 5622-5632. DOI: 10.1021/nn4065692.
  5. Desroches, J., Hermyn, M., Pinto, M., Picot, F., Tremblay, M., Obaid, S., et al. (2018). A new method for using Raman spectroscopy for in vivo targeted brain cancer tissue biopsy. Nature. DOI: 10.1038/s41598-018-20233-3.

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