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New ways to characterize breast tumors


In X-ray mammography benign breast tumors are often classified as highly suspicious lesions. Therefore, new or additional imaging techniques are required which offer an improved differentiation between benign and malignant breast tumors. Together with physicians from the Charité hospital Berlin, the department 8.3 of the PTB develops and proves an optical technique to detect the leakage of a contrast agent through the capillary walls of breast tumors, similar to contrast-enhanced magnetic resonance mammography. However, in contrast to conventional magnetic contrast agents, the optical contrast agent presently used (indocyanine green) shows high binding to proteins of blood plasma. Due to the resulting large particle size the molecules of the contrast agent cannot pass the capillary walls in benign tumors. On contrary, capillaries in malignant lesions have a higher permeability. Here, the contrast agent may extravasate and accumulates in the surrounding tissue. Hence, the new modality detects permeability of microvessels to differentiate malignant from benign tumors.

To detect the contrast agent in the breast, PTB has developed a novel system for sensitive optical imaging based on detection of fluorescence originating from the contrast agent after excitation by near infrared laser radiation. By measuring the fluorescence as well as the laser radiation transmitted through the breast at a time, at which the contrast agent has already been washed-out from the blood itself, one obtains an optical mammogram which shows the remaining contrast agent enriched in the extracellular space of the carcinoma. First investigations on patients have shown that the method allows for differentiation between benign and malignant lesions (figure).

Fig.: Left: Fluorescence mammogram with carcinoma visible as bright spot due to the local increase in fluorescence caused by the enrichment of the contrast agent, Right: fluorescence mammogram with a benign lesion in the left part of the image that does not show any noticeable fluorescence.



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