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Author: Dror Nir, PhD

Optical Coherence Tomography (‘OCT’), is a technique for obtaining 3D optical-image from 1-2 mm thick tissue samples. The key benefits of using OCT for medical applications is that it is not ionizing, therefore harmless to the patient and the image resolution ~10µm, almost the size of a human cell.

Commercially available OCT systems have been used in ophthalmology and in interventional cardiology for quite a while. Recently, new applications attempting to provide intraoperative histopathology appear as alternative solution to frozen-sections based histopathology.

I found this nice diagram explaining why OCT can be used for identifying presence of cancer intra-operatively in an article [1] I downloaded from the website of the American association for cancer research.

Figure 1. Diagnostic scattering spectroscopy. In this cartoon illustration of the underlying principles of the method described in the work of Laughney and colleagues (1), an excised tissue sample sits on a glass plate, with normal cells depicted schematically on the left and tumor cells on the right. In contrast with the normal cells, the tumor cells are represented as having enlarged nuclei, with increased granularity of the chromatin, and, perhaps, a disrupted cytoskeleton resulting in cellular disorder. Light, from a broadband source, and after manipulation through an optical system, is collimated (parallel rays) and impinges on the tissue at normal incidence. While most light is scattered in the near-forward direction, some of the light is scattered directly backward after one (in most cases) or a few scattering events and is collected to be analyzed by a spectrometer (not depicted). The spectrometer provides a backscattering spectrum that is representative of the tissue properties. The wavelength dependence of the probability for backscattering varies with changes in the sizes and densities of the dominant scattering centers, such that the backscattered light spectrum changes with pathology, as manifested in the mean cellular micromorphology. In this way, the recorded spectrum relates directly to some of the micromorphology features that a pathologist recognizes as indicative of pathology when looking at histology slides, but in a quantitative manner, without the need to generate an actual microscopic image and without requiring subjective interpretation. (Of course, this physicist’s simplification ignores many tissue components that also affect scattering, such as extracellular matrix and vasculature.

In that article, Laughney and colleagues reported on real-time assessment of resection margins during breast- conserving surgery using OCT technique.

At the Thirty-Fifth Annual CTRC-AACR Breast Cancer Symposium held on Dec 4-8, 2012 in San Antonio, TX, BC Wilson, MK Akens, and CJ Niu (University Health Network, Ontario Cancer Institute, Toronto, ON, Canada; Tornado Medical System, Toronto, ON, Canada) discussed the unmet clinical need and the cost saving impact related to the potential use of Optical Coherence Tomography for intraoperative breast tumour margin width estimation in a poster session:

“Total mastectomy and lumpectomy with radiation have been shown to have equivalent patient outcomes, which has likely contributed to the more widespread adoption of breast conserving surgery (BCS) procedures. Assessment of breast lumpectomy margin widths in both an accurate and timely manner is essential to successful breast conservation procedures. Current BCS methodologies have been reported to result in reoperation rates of up to 20–60%, which represents a significant and unmet need for improved margin assessment. High reoperation rates present both increased treatment risk to patients and increased burden on healthcare systems. In the USA alone, over 150,000 lumpectomies are performed per year at an average cost between $11,000 and $19,000 USD per procedure. Assuming a relatively modest average repeat operation rate of 25%, potentially preventable repeat surgeries represent an approximate cost to the US healthcare system of $500M (USD) annually.”

From the same meeting: An abstract presenting the design of an ongoing multi-center, randomized, blinded clinical study aimed at Intraoperative assessment of tumor margins with a new optical imaging technology using a specific implementation of an OCT based device.

At last RSNA I have visited the French pavilion were one of the companies, LLTech, presented an OCT based system designed facilitate the work of pathologists and save time and money by allowing fresh tissue processing and pathology examination instead of the traditionally frozen sections (intraoperative) and fixated specimens (at lab)

That could be used by a pathologist to perform in-situ histology in the OR.

To summarize; OCT based systems seem to be something to look for in the future of cancer patients’ management.

References

1. Laughney AM, Krishnaswamy V, Rizzo EJ, Schwab EM, Barth RJ, et al. Scatter spectroscopic imaging distinguishes between breast pathologies in tissues relevant to surgical margin assessment. Clin Cancer Res. 2012;18:6315–25.

Writen by: Dror Nir, PhD