WASHINGTON, April 13 - By combining two techniques, magnetic resonance imaging (MRI) and near-infrared optics, researchers at Dartmouth College and Dartmouth Medical School may have devised a new, potentially more accurate method for diagnosing breast cancer. Their pilot study, demonstrating the feasibility of the concept, is published in the April 15 issue of the journal Optics Letters, published by the Optical Society of America.
The new technique utilizes MRI to produce an image of the breast, yielding information on its structure, including shape and composition. The near-infrared light technique provides information on how the tissue is functioning, for example, whether a region contains a large amount of blood and is rapidly consuming oxygen as early cancers typically do. The researchers are hoping this dual-procedure approach will be a key to learning which tissues are malignant before performing a biopsy.
The pilot study involved a 29-year-old woman with a ductal carcinoma, a very common breast cancer, in her left breast. A contrast MRI procedure was performed, where MRI was done before and after the contrasting agent gadolinium was injected. The area enhanced by the contrasting agent was targeted for the optical technique, known as near-infrared spectroscopy (NIRS). The results showed the area's hemoglobin level was high, oxygen saturation was low and water content was high, all indicators of cancerous tissue.
Recent advancements in medical imaging systems have focused on increasing the detail of anatomical images, but there has also been a growing interest in devices that provide information on tissue function. One of the difficulties with functional imaging has been that most of these devices have low spatial resolution. The structural information from the MR image helps guide the NIRS technique to the regions of interest so that the two can together create high-resolution, functional images of breast cancer.
The American Cancer Society recently recommended MRI screening for patients at high risk of developing breast cancer in their lifetimes. Researchers believe that this new dual-procedure technique may potentially aid in cancer diagnosis.
Screening for breast cancer typically begins with X-ray mammography to look for tumors and cysts in women without any symptoms. Mammograms are much less expensive than MRI, but because they compress the breast to show all of the information in one view, they are a less effective tool, especially when the breast is dense. MRI provides multiple slices of high-resolution images of breast tissue, creating a three-dimensional picture. Unlike mammography, the NIRS technique does not generate images directly from the data acquired by the machine. It records the spectrum of near-infrared light that is absorbed or scattered (bounced around) in the tissue. One of the most challenging aspects of the Dartmouth team's work was developing the software to reconstruct and display the information so it could be compared with the MR image.
The dual-procedure scanning approach should not be much more expensive than current MRI, said Dartmouth College researcher Keith Paulsen. The machines used for MRI can cost millions of dollars, but the additional equipment for NIRS would be a fraction of that amount and could be used in conjunction with existing MRI machines. If larger studies prove to be successful and the procedure is deemed valuable enough for insurance reimbursement by the FDA, Paulsen said this new method could become more widely available within the next five years.
The Dartmouth researchers have been working on the project for about four years, receiving several hundred thousand dollars a year from the National Cancer Institute, a component of the National Institutes of Health.
The next step will be to perform a larger number of case studies. The researchers will use volunteers who have breast abnormalities that have been recommended for biopsy. Employing the new dual-procedure approach, they will image the subjects before the biopsy and compare their results to the findings from the biopsy. Dartmouth aims to complete approximately 50 such cases over the next several years.
Paper: "Image-guided optical spectroscopy provides molecular-specific information in vivo: MRI-guided spectroscopy of breast cancer hemoglobin, water, and scatterer size," Colin M. Carpenter et al., Optics Letters, Vol. 32, No. 8, April 15, p. 933-935; abstract at http://www.
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