Raman Scattering Helps Evaluate Laser Ablation

Raman spectroscopy can be used to differentiate squamous cell carcinoma (SCC) from normal skin following treatment with high-powered lasers, according to a new study.

Researchers at Florida Atlantic University (FAU; Boca Raton, USA) obtained 25 tissue samples from 11 patients undergoing Mohs micrographic surgery for the removal of non-melanoma skin cancer (NMSC). Laser treatment was performed using a fractional CO2 laser emitting at 10.6 μm. Treatment levels ranged from 20 mJ to 1200 mJ total energy delivered per laser treatment spot. Raman spectra were collected from both untreated and CO2 laser-treated samples, using a 785 nm diode laser. The researchers then classified spectra as originating from either normal or NMSC tissue, and from treated or untreated tissue.

The results showed that partial laser ablation did not adversely affect the ability of Raman spectroscopy to differentiate normal from cancerous residual tissue, with the spectral classification model correctly identifying SCC tissue with 95% sensitivity and 100% specificity following partial laser ablation, compared with 92% sensitivity and 60% selectivity for untreated NMSC tissue. The main biochemical difference identified between normal and NMSC tissue was high levels of collagen in the normal tissue, which was lacking in the NMSC tissue.

The researchers concluded a Raman-based technique for skin cancer diagnosis and treatment, although not yet fully developed, could one day obviate the need for a more costly and time-consuming treatment method like Mohs micrographic surgery, at least in some, if not all, clinical cases, since CO2 laser treatment does not hinder the ability of Raman spectroscopy to differentiate normal from diseased tissue. The study was published in the December 2014 issue of Lasers in Surgery and Medicine.

“Successful clinical implementation of the proposed surgical method could greatly enhance the speed and effectiveness of skin cancer treatment, especially if real-time analysis of the process were developed,” said lead author associate Professor of Chemistry and Biochemistry Andrew Terentis, PhD, of the FAU Charles E. Schmidt College of Science. “It demonstrates the feasibility of a potentially much faster and more accurate mode of skin cancer treatment based entirely on laser technology.”

Raman spectroscopy is a form of molecular spectroscopy based on Raman scattering. When a beam of light interacts with a material, part of it is transmitted, part it is reflected, and part of it is scattered; over 99% of the scattered radiation has the same frequency as the incident beam, but a small portion has frequencies different from that of the incident beam. This scattered radiation contains information on the particular atoms or ions that comprise the molecule, the chemical bonds connect them, the symmetry of their molecule structure, and the physicochemical environment where they reside.

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