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All Together Now
Near-Infrared Spectral Tomography (NIR)
The premise: Location. Location. Location. It's important in real estate and in NIR, too. NIR uses an approach similar to the idea behind MIS and EIS. But because of near-infrared's location on the electromagnetic spectrum, this modality can measure hemoglobin concentration and oxygen saturation levels—key indicators of microvascularity. (Tumors are hungry little beasts that require a lot of tiny blood vessels to keep them fed.)
The NIR modality has the ability to operate in two environments—in a free-standing system that Thayer engineers built and in a smaller unit that functions inside an MRI scanner. "I have a very practical focus," says Brian Pogue, the NIR project leader. "We're not going to replace mammography or magnetic resonance." So his team is looking for ways that NIR can add useful information to mammography and magnetic resonance imaging.
In the free-standing unit, the researchers use NIR to monitor tumors that are being shrunk with chemotherapy prior to being removed surgically. In the MRI scanner, they use NIR to help diagnose abnormal tissue, with the goal of preventing unnecessary biopsies. MRI makes it possible to zoom in on the tumor, while NIR can categorize it, explains Subhadra Srinivasan, a research scientist at Thayer who works with Pogue. Her job is to figure out how to use the MRI data to produce better NIR images in a three-dimensional format. Pogue, Srinivasan, and several colleagues recently published some of their results in the journal Optics Letters.
Unlike the other modalities, NIR is being explored by several research teams elsewhere. But what sets the Dartmouth NIR work apart is the aspect of integrating it with MRI.
The procedure: NIR must be conducted in complete darkness. During a free-standing NIR procedure, the woman lies face down with one of her breasts positioned over an opening. A circle of optical fibers surrounds and touches the breast. Light is sent from one fiber and is
Sixteen sets of optical fibers (above) surround the breast during an NIR procedure (pictured on the bottom right), which must take place in complete darkness. The cables and circuitry (below left) that power the optical array are usually hidden from view underneath the exam table and behind a black curtain.
then picked up by all the others. The light is emitted in sequence from all the fibers, and several different wavelengths within the near-infrared spectrum are used.
The process in an MRI is roughly the same.
