Intra-operative imaging of surgical margins of canine soft tissue sarcoma using optical coherence tomography

Abstract

Optical coherence tomography (OCT) is a rapid non-invasive imaging technique that has shown high sensitivity for intra-operative surgical margin assessment in human breast cancer clinical trials. This promising technology has not been evaluated in veterinary medicine. The objective of this study was to correlate normal and abnormal histological features with OCT images for surgical margins from excised canine soft tissue sarcoma (STS) and to establish image evaluation criteria for identifying positive surgical margins. Fourteen client-owned dogs underwent surgical resection of a STS and OCT imaging of 2 to 4 areas of interest on the resected specimen were performed. Following imaging these areas were marked with surgical ink and trimmed for histopathology evaluation. Results showed that different tissue types had distinct characteristic appearances on OCT imaging. Adipose tissue exhibited a relatively low scattering and a honey-comb texture pattern. Skeletal muscle and sarcoma tissue were both dense and highly scattering. While sarcoma tissue was highly scattering, it did not have organized recognizable structure in contrast to muscle which showed clear fibre alignment patterns. In this investigation, we showed different tissue types had different and characteristic scattering and image texture appearances on OCT, which closely correlate with low-power histology images. Given the differentiation between tissue types the results support that OCT could be used to identify positive surgical margins immediately following resection of STS. Further research is needed to assess the diagnostic accuracy of this method for surgical margin assessment.

Keywords: dogs; margins of excision; surgical oncology.

FIGURE 1

Photograph illustrating resected soft tissue sarcoma prepared for the optical coherence tomography (OCT) imaging with the U-shaped marking of on area of interest (black and yellow coloured)

FIGURE 2

Correlation of histology properties of A, adipose; B, skeletal muscle; C, skin and D, soft tissue sarcoma with corresponding optical coherence tomography (OCT) images (E-H, respectively). The left-sided row (A-D) shows the haemotoxylin and eosin stained digitized histological images of the resected tissue and the right-sided row (E-H) shows the corresponding OCT images. The black and white scale bars across the bottom of images D and H represent 500 μm to show the scale of all histologic and OCT images shown

FIGURE 3

A-C, Examples of surgical specimens and corresponding optical coherence tomography (OCT) and histology images with sarcoma at surgical margins. On the left side, is a photograph of gross surgical specimen with incomplete boxes marked with surgical inks highlighting imaged areas. On the right side, the bottom row shows haemotoxylin and eosin stained digitized histological images, and the corresponding OCT images are shown in the top row. The white or black scale bars at the bottom of each OCT or histologic image represent 500 μm. A, Images for case 2, area 1 sample: The OCT and histological sections were taken from the area bounded by the U-shaped yellow surgical ink. The OCT images show layer of skeletal muscle with deeper high scattering area consistent with underlying sarcoma (white arrows). B, Images for case 8, area 1: The OCT and histological sections were taken from the area bounded by the U-shaped orange surgical ink. The OCT image shows a thin layer of tissue with low scattering areas consistent with the pseudocapsule with air bubbles (black linear structures, yellow arrow) overlying a high scattering tissue with no alignment patterns underlying consistent with sarcoma (white arrowheads). The imaging of the deeper tissues is attenuated by the overlying air bubbles. This result is consistent with sarcoma <1 mm from the deep surgical margin. C, Images for case 8, area 4: The OCT and histological sections were taken from the area bounded by the U-shaped yellow surgical ink. The OCT image shows a distinct and condense pseudocapsule immediately under the probe (red arrow) but with high scattering tissue consistent with sarcoma underlying. This result is consistent with sarcoma <1 mm from the deep tissue margins. Deeper tissue imaging of the tumour is seen in comparison to that seen in Figure 3B due to the lack of air attenuating light penetration