Inked up

Molecular dyes, more well known as food colourants, have been used for magnetic resonance imaging (MRI)–guided near-infrared spectral tomography (NIRST) of resectioned breast tissue for women treated with breast-conserving cancer surgery.

In work supported by the National Cancer Institute and National Institutes of Health as part of an Academic Industry Partnership between Dartmouth College and PerkinElmer, investigators hope to improve breast cancer outcomes. The researchers at the Optics in Medicine Lab at Dartmouth's Thayer School of Engineering and Norris Cotton Cancer Center, led by Brian Pogue and Keith Paulsen, with graduate student David McClatchy III, have devised a new way to perform near infrared (NIR) optical measurements of resected breast tissue after the margins have had their traditional marking by the surgeon to preserve information about their orientation for potential follow-up surgeries. The team points out that approximately 1 in 4 women who have had breast-conserving surgery (BCS) require subsequent surgery to remove residual cancerous tissue left behind because of unclear margins. "This work is a significant step towards making NIR optical methods for intraoperative breast tumour margin assessment clinically feasible by not compromising the current surgical practice of inking resected specimens for margin orientation," explains McClatchy.

Optical clues

Writing in the Journal of Biomedical Optics, the team describes how only a small volume of non-malignant tissue around the tumour is removed surgically and that is an increasingly common choice among women diagnosed with localized breast cancer. Previously, complete mastectomy was the only surgical therapy. However, the surgeon will usually have some difficulty in locating and resecting the cancerous tissue completely around the core of the tumour, which means there will be clumps of residual cancer cells that will be seen in follow-up scans and these must also be removed to prevent the disease continuing to grow and spread.

The biomedical optics community, including the team at Dartmouth's Optics in Medicine Lab, has been focused on the development of a system that might be used during surgery, intraoperatively in other words, to determine whether or not the margins of resected breast specimens are free of cancer and so avoid the need for remedial resections later. The new approach is a practical solution for allowing surgeons to continue using their practice of inking the margins of the tumour but also allowing them to carry out quality imaging after the inking process is complete. The key to success was simply to swap food dyes, approved under the US Federal Food, Drug, and Cosmetic Act, FD&C food dyes, for the conventional surgical inks. The standard inks attenuate near-infrared signals making the resulting images useless whereas the food dyes do not lead to this problem and allow sharp intraoperative imaging to be carried out. After the required NIR images have been obtained, the surgeon can then use the standard inks to allow histopathological processing of samples to be carried out independently of the procedure.