MEDICAL DIAGNOSTICS: LIBS spots cancer in vivo
Researchers from Mississippi State University (MSU; Starkville, MS) believe they can diagnose and classify cancer in vivo by determining the intensity ratio of trace elements in normal and cancerous material.
Researchers from Mississippi State University (MSU; Starkville, MS) believe they can diagnose and classify cancer in vivo by determining the intensity ratio of trace elements in normal and cancerous material. Headed by Jagdish Singh of the Diagnostic Instrumentation and Analysis Laboratory at MSU, the team is using laser-induced-breakdown spectroscopy (LIBS) to distinguish between normal and malignant tumor cells in tissue samples.1 By applying LIBS to normal and cancerous canine liver samples, the researchers discovered that the intensity ratios of calcium to potassium and sodium to potassium were significantly higher in the malignant-tissue spectra.
Two years ago the research team began analyzing animal tissue to determine the differences in the elemental composition of benign and malignant tissue samples, according to Fang-Yu Yueh, principal investigator on the project. Partnering with the college of veterinary medicine at MSU, the researchers analyzed the surface of liver and lung tissue.
“Cancer diagnosis and classification, which can be extremely complicated, often rely upon subjective interpretation of biopsy material,” said Singh. “These labor-intensive methods could produce different results, depending on the histopathologist doing the examination. Automated real-time diagnostic procedures would make the procedure easier and the results more accurate.”
Laser-induced-breakdown spectra were taken of normal (top) and malignant (bottom) liver tissue of a dog. Intensity ratios of some peaks can be used to check for cancer.
Laser-induced-breakdown spectroscopy involves firing a high-energy laser pulse at a target to form a microplasma at the surface of the sample. Using a spectrometer, scientists analyze the light emitted from the microplasma to reveal the elemental composition of the target. While LIBS has been a known technology since the 1960s, it has been considered difficult to perform. But in recent years the development of compact, high-performance optical equipment such as Q-switched Nd:YAG lasers that emit millijoule pulses and high-resolution broadband spectrometers has made it possible to perform field analysis with LIBS. Benefits of LIBS, according to Singh, include high sensitivity, speed, and elimination of sample preparation.
For the LIBS cancer-analysis procedure at MSU, the researchers use a frequency-doubled Nd:YAG laser operated at a repetition rate of 10 Hz and with a pulse width of 5 ns at 532 nm. A UV fused-silica lens focuses the laser beam down to a spot size of 40 µm and collects light emitted from the laser-induced plasma. Two UV-grade quartz lenses couple the LIBS signal to an optical fiber, which links the setup to an echelle optical spectrograph and an intensified CCD camera. The echelle analyzer detects the entire UV and visible wavelength range simultaneously, controls external radiation sources such as lasers, and provides time-correlated measurement of the radiation for measurement of complex spectra with a high spectral resolution and simultaneous multi-element analysis.
“We found that the concentration of trace elements in normal and tumor cells was significantly different,” said Singh. For comparison, the tissue samples were also analyzed by an inductively coupled plasma-emission-spectroscopy (ICPES) system. The results from the LIBS measurement and ICPES analysis were in good agreement.
Although the result in this study is preliminary, it demonstrates the potential of LIBS for development as an in vivo diagnostic tool for cancer detection and classification, he added, noting that further development in this area is needed to obtain quantitative results for practical applications.
- Akshaya Kumar et al., Applied Optics 43(28) (Oct. 1, 2004).
ILENE SCHNEIDER is a freelance writer living in Irvine, CA; e-mail: firstname.lastname@example.org.