Researchers combine optical, x-ray tomo techniques to better ID breast cancer

November 15, 2010
Rebekah Moan

Combining digital breast tomosynthesis and a laser-based technique called diffuse optical tomography, radiologists may be better able to distinguish malignant from benign lesions in the breast, according to a new study.

Combining digital breast tomosynthesis and a laser-based technique called diffuse optical tomography, radiologists may be better able to distinguish malignant from benign lesions in the breast, according to a new study published in Radiology.

Diffuse optical tomography measures levels of hemoglobin concentration, oxygen saturation, and other cellular characteristics based on how light from a near-infrared laser is absorbed and scattered within tissue.

"Optical imaging provides information that is not available on the mammogram," said Dr. Daniel Kopans, a professor of radiology and a senior radiologist in the breast imaging division at Massachusetts General Hospital. Kopans is leading the ongoing research with David Boas, Ph.D., an associate professor at Harvard.

Cancers tend to have higher concentrations of hemoglobin due to the nests of blood vessels that develop around them, and they tend to deoxygenate blood faster than normal tissues, he said. Unlike MRI, optical imaging does not require intravenous injection of a contrast agent to see metabolism of the tissues. Optical imaging's drawback is that it is low in spatial resolution.

In their research, Kopans and colleagues combine digital breast tomosynthesis and optical imaging to evaluate the breast without moving the patient. "By not moving the breast between studies, we can use the high-resolution, three-dimensional information from (breast tomosynthesis) to ‘constrain' the optical information," he said. "This allows us to refine the optical information and make better use of it to help differentiate benign from malignant tissues."

The study, which was funded by the National Institutes of Health, combined breast tomosynthesis and optical tomography to examine 189 breasts from 125 women with an average age of 56. Optical source and detector probes were attached to a breast tomo unit and, with the breast compressed, used to acquire optical data. The optical probes were then removed without altering the breast compression and a breast tomo scan was performed.

Of the 189 imaging studies, 138 were negative and 51 showed evidence of lesions. The researchers found 26 malignant and 25 benign lesions, which were confirmed on biopsy.

In the 26 malignant tumors, total hemoglobin concentration (HbT) was significantly greater than in the normal glandular tissue of the same breast. Solid benign lesions and cysts had significantly lower HbT contrast compared with the malignant lesions.

"By providing additional differentiation of malignant and benign lesions, combined optical and x-ray imaging could potentially reduce unnecessary biopsies," said lead author Qianqian Fang, Ph.D., a radiology instructor at Harvard.

Oxygen saturation levels were significantly lower in cysts compared with those in malignant and solid benign lesions and glandular breast tissue.

"Although cysts are easy to diagnose using ultrasound, distinguishing cysts from malignant or benign lesions during a mammogram would save women the anxiety and costs associated with a second procedure," Fang said. "We are hopeful that this combined system may help improve the efficiency and diagnostic accuracy of breast screening."

The researchers are still developing the combination strategy, but the preliminary results are quite encouraging, according to Kopans.

"We have clearly shown proof of concept. We are working to establish the clinical value of the combined techniques to improve our ability to detect and diagnose breast cancer earlier," he said. "We have made tremendous progress in our goal to develop a clinically valuable device to help further decrease the death rate from breast cancer."

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