Raman spectroscopy could enable inflammatory bowel disease detection during colonoscopy

Knowing that current diagnostic and treatment procedures for inflammatory bowel disease (IBD) are inaccurate and rely largely on trial and error, researchers at Vanderbilt University (Nashville, TN) have developed a sensor that objectively identifies IBD and distinguishes between its two subtypes. The device represents a substantial achievement toward a more personalized approach to diagnosing and treating IBD.

Related: ATR-FTIR spectroscopy could be effective for detecting ulcerative colitis

The research team conducted a pilot study of a custom-developed endoscope that uses Raman spectroscopy (a chemical-fingerprinting technique) to detect molecular markers of IBD in the colon. The sensor is designed as a minimally invasive probe that can be easily integrated into a routine colonoscopy exam. After further refining, the researchers say doctors could use the device to help diagnose IBD and evaluate a patient's response to treatment.

"With current methods, ultimately the diagnosis is dependent on how the patient responds to therapy over time, and you often don’t know the diagnosis until it’s been a few years," says Anita Mahadevan-Jansen, senior author of the paper describing the work, who initiated the project after a personal experience with IBD. "That's why we decided to use a light-based method to probe the biochemistry of what’s going on in the colon. Our goal is to use Raman spectroscopy to look at the actual inflammatory signals."

IBD occurs in two subtypes: ulcerative colitis (UC), which is typically confined to the colon, and Crohn's disease, which can occur in any part of the gastrointestinal tract. They can cause similar symptoms such as severe diarrhea, pain, fatigue, and weight loss, yet the two types respond differently to available treatments, which include drugs, dietary interventions, and surgery. Doctors currently use a combination of clinical, radiologic, and pathological methods to diagnose a patient's IBD subtype and guide treatment decisions, but these methods detect symptoms rather than the underlying source of disease. As a result, up to 15% of patients are diagnosed with indeterminate colitis, meaning the subtype is unknown, and an additional 5–14% have their IBD reclassified based on how they respond to treatment.

Previous research conducted in tissue samples from people with IBD showed that UC and Crohn's disease have different molecular signatures. The new probe detects these signatures to glean information about not only disease subtype, but also the current degree of inflammation and even early indicators of IBD that occur before observable changes in the intestinal tissue.

To develop the probe, the researchers first used tissue samples and animal models to identify preliminary biomarkers and spectral signatures consistent with IBD. They then custom-built a portable Raman spectroscopy system with a 785 nm diode laser and fiber-optic probe that delivers 80 mW to the surface of the colon. Raman spectroscopy has been previously applied in the gastrointestinal tract for cancer detection, but using it to measure markers of inflammation poses some unique challenges because the signals are far more subtle. This necessitated special engineering, for example, to include filters that eliminate the Raman signature produced by the components of the probe itself.

In their pilot study, the researchers used the device in 15 patients with an existing diagnosis of Crohn's disease, eight patients with UC, and eight healthy volunteers. In general, the results suggest high sensitivity (the ability to detect IBD) but poor specificity (the ability to differentiate between subtypes), though results vary depending on the degree of inflammation and where the measurement was taken. When measuring the right colon in patients with active inflammation, the device detected Crohn's disease with 90% sensitivity and 75% specificity, compared to 86% and 39%, respectively, when results are averaged across all disease states, inflammation levels, and locations within the colon.

The researchers are now focused on refining a set of algorithms that help doctors interpret test results for a given patient. To improve the test's specificity, the team is analyzing data from an expanded cohort of patients to discern how factors such as gender, diet, demographics, and treatment regimen influence the Raman signature. Ultimately, they envision a system that combines key information about the patient with Raman spectra to deliver, in a matter of seconds, tailored results that can inform a diagnosis or help track a patient's response to treatment.

The researchers are also pursuing studies in animal models to further understand the sources of various molecular signals, identify the types of changes that can be expected as a result of treatment, and determine whether the device could be used to detect IBD or risk factors at even earlier stages.

Full details of the work appear in the journal Biomedical Optics Express; for more information, please visit http://dx.doi.org/10.1364/boe.8.000524.