When molecules in cells are stimulated by light, they respond by becoming excited and re-emitting light of varying colors (fluorescence) that can be captured and measured by highly sensitive optical equipment.
Now, researchers at Cedars-Sinai Medical Center and the University of Southern California are developing miniaturized spectroscopic instruments and computer software to take a real-time look at biochemical, functional and structural changes occurring within the cells and tissue of the brain. If the technology continues to progress as anticipated, neurosurgeons will be able to shine a light during surgery to diagnose brain tumors instantaneously and they will be able to discern the borders of tumors with greater precision than ever.
Early studies appear to support these possibilities. The researchers report in the July/August issue of Photochemistry and Photobiology that the techniques and device they have developed are able to quickly and accurately discriminate between brain tumor and normal tissue.
Glioblastoma multiforme (GBM), the most common and deadly type of brain tumor, was the subject of the study. Because these tumors grow quickly and invade healthy tissue rapidly, patient survival rates usually are measured in weeks or months despite aggressive treatment with traditional surgery, chemotherapy and radiation. When “image complete” resection is accomplished – no remaining tumor is visible with high-resolution imaging techniques – patients have a median survival of about 70 weeks.
But complete removal is nearly impossible because the tumors aggressively infiltrate neighboring tissue and are irregularly shaped with poorly defined borders. Also, tumor cells tend to migrate away to establish satellites in other parts of the brain. When surgical removal is less than image complete, median survival is less than 19 weeks.
“Although our surgical goal is to remove as much tumor as possible without damaging healthy brain, distinguishing between the two is extremely difficult,” said Keith L. Black, MD, neurosurgeon, director of the Maxine Dunitz Neurosurgical Institute, the Division of Neurosurgery and the Comprehensive Brain Tumor Program.
“Fluorescence spectroscopy is one of several innovative imaging techniques in development, and I think the evolution of this capability comes at a critical time because we are beginning to see encouraging results in several therapeutic approaches,” continued Dr. Black, who holds the Ruth and Lawrence Harvey Chair in Neuroscience at Cedars-Sinai and is one of the journal article’s authors. “The clarity that fluorescence technology appears to offer may provide greater precision in surgery and also help us target cancer cells with a combination of new, highly focused therapies.”
The ability to immediately analyze cells revolves around the fact that different metabolic states and biochemical components emit light differently. Just as a prism splits white light into a full spectrum of color, laser light focused on tissue is re-emitted in colors determined by the properties of the molecules. Analyzing the colors in space and time provides information about the types of molecules present and their conformation.
“With time-resolved laser-induced fluorescence spectroscopy we measure both the wavelength of the emission and the time that molecules stay in the excited state before returning to the ground state. This provides information about the chemical composition of the tissue, about molecular and biochemical changes, as a function of the stages of disease,” said Laura Marcu, PhD, director of the Biophotonics Research and Technology Development Laboratory at Cedars-Sinai.
A research associate professor of electrical and biomedical engineering at USC’s Viterbi School of Engineering, Dr. Marcu is directing several USC graduate students and postdoctoral fellows in the creation of the optical imaging devices, hardware and software. She is working in conjunction with the neurosurgeons and researchers at the Maxine Dunitz Neurosurgical Institute to adapt the system’s clinical applications to central nervous system tissue, and is collaborating with cardiologists to pursue spectroscopic detection of atherosclerosis.
According to Dr. Marcu, first author of the article, the researchers found that high-grade gliomas are characterized by fluorescence emissions of longer duration overall, compared to those of normal tissue. Furthermore, gliomas can be distinguished by fluorescence lifetimes that differ at various wavelengths: glioma fluorescence is long-lived at certain short wavelengths but short-lived at some longer wavelengths. Analyzing the tissue in terms of both fluorescence intensity and fluorescence lifetime provides information that translates into a high level of diagnostic specificity.
Currently, the spectroscopic system consists of an optical instrument about the size of a ballpoint pen that is connected by a fiber-optic cable to a computer. Through a lens at the tip, the probe provides light and magnification for surgeons. Light from a nitrogen laser can be used to stimulate the molecules within cells and the light emitted from the cells is sent back to the data processing system.
The equipment is enabling the research teams to acquire accurate, repeatable measurements in living tissue and is serving as a prototype for future diagnostic technology. Dr. Marcu, a biomedical engineer specialized in optical spectroscopy and imaging, said a number of technological challenges are being addressed.
“Most of the earlier investigations were done in my laboratory on the optical table,” she said. “Now we’re in a new stage in which we have put together optical instrumentation that can go onto a standard endoscopic cart in the operating room.”
Before fluorescence spectroscopy can become routine in the operating room, the equipment must be miniaturized and fine-tuned, and the information displayed must be simplified, said Dr. Marcu. “At present, we look at a computer screen that contains information about the tissue. But we hope to develop miniature systems that provide yes or no answers – perhaps a light that changes colors to show which tissue is healthy and which is diseased. It will recognize in real time the characteristics of the tissue.”
Cedars-Sinai’s Biophotonics Research Lab is affiliated with the Minimally Invasive Technologies Institute (MISTI) within the Department of Surgery. The MISTI brings together a scientific research group, a pre-clinical faculty and a clinical research team, all focusing on the development, testing and introduction of minimally invasive and noninvasive technologies into everyday surgical practice.