Researchers have generated the first three-dimensional optical images of human breast cancer in patients based on tissue fluorescence.

The technology, fluorescence diffuse optical tomography (FDOT), relies on the presence of fluorophore molecules in tissue that re-radiate fluorescent light after illumination by excitation light of a different color. The reconstructed images demonstrated significant tumor contrast compared to typical endogenous optical contrast in breast tissue.

Tumor-to-normal tissue contrast based on FDOT with the fluorophore Indocyanine Green (ICG) dye was two-to-four-fold higher than contrast based on endogenous contrasts such as hemoglobin and scattering parameters obtained with traditional diffuse optical tomography (DOT).

With the continued development of molecularly-targeted exogenous fluorophores, the study, conducted by researchers at the University of Pennsylvania (Penn; Philadelphia, PA, USA), should help in the development of new diagnostic tools based on optics that will provide improved sensitivity and specificity between healthy and normal tissues.
Fluorophores are extremely sensitive to their local environment, and therefore, FDOT holds potential to provide information about tumor physiology, including tissue oxygen, tissue pH, and tissue calcium concentration levels.

“Previously, the FDOT technique was used for in-vivo imaging of animal tissues, but ours is the first successful demonstration of its use to detect cancer in deep-tissue, human breast imaging,” stated Dr. Arjun Yodh, professor of physics at Penn.

DOT uses near-infrared light to scan and provide cross-sectional and volumetric views of biologic tissue. It is promising as a tool to characterize lesions and monitor therapy; however, its resolution is not as high as other anatomically oriented imaging modalities, and contrast comes primarily from vasculature abnormalities.

In the current study utilizing FDOT, the intravenous addition of an exogenous molecular agent, ICG, was used to enhance tumor contrast. The vasculature of tumors delays ICG washout from the body and thereby increases its concentration in tumors relative to normal tissue.

“The potential uses of optical fluorophores bear close resemblance to the use of contrast agents in PET [positron emission tomography] and MRI [magnetic resonance imaging],” Dr. Yodh said. “Successful FDOT represents a critical first step towards application of molecular imaging probes such as dyes and molecular beacons that bind to tumor-specific receptors in deep tissue, a current direction for biomedical optics research.”

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