Three-dimensional optical coherence tomography for optical biopsy of lymph nodes and assessment of metastatic disease

Abstract

Background: Numerous techniques have been developed for localizing lymph nodes before surgical resection and for their histological assessment. Nondestructive high-resolution transcapsule optical imaging of lymph nodes offers the potential for in situ assessment of metastatic involvement, potentially during surgical procedures.

Methods: Three-dimensional optical coherence tomography (3-D OCT) was used for imaging and assessing resected popliteal lymph nodes from a preclinical rat metastatic tumor model over a 9-day time-course study after tumor induction. The spectral-domain OCT system utilized a center wavelength of 800 nm, provided axial and transverse resolutions of 3 and 12 μm, respectively, and performed imaging at 10,000 axial scans per second.

Results: OCT is capable of providing high-resolution label-free images of intact lymph node microstructure based on intrinsic optical scattering properties with penetration depths of ~1-2 mm. The results demonstrate that OCT is capable of differentiating normal, reactive, and metastatic lymph nodes based on microstructural changes. The optical scattering and structural changes revealed by OCT from day 3 to day 9 after the injection of tumor cells into the lymphatic system correlate with inflammatory and immunological changes observed in the capsule, precortical regions, follicles, and germination centers found during histopathology.

Conclusions: We report for the first time a longitudinal study of 3-D transcapsule OCT imaging of intact lymph nodes demonstrating microstructural changes during metastatic infiltration. These results demonstrate the potential of OCT as a technique for intraoperative, real-time in situ 3-D optical biopsy of lymph nodes for the intraoperative staging of cancer.

FIG. 1

Three-dimensional OCT of a normal lymph node. Cross-sectional (y–z and x–z) and en face (x–y) images can be computationally extracted from the highly sampled 3-D data volumes as shown here, and in subsequent figures

FIG. 2

Normal lymph node (day 0). An en face OCT image plane (a) is matched to the corresponding histological section (c). The horizontal green line in (a) indicates the location of the cross-sectional OCT image in (b). The black-framed region in the histological section (c) is magnified in (d) to highlight a follicle and other structural features of the normal lymph node

FIG. 3

Popliteal lymph node imaged on day 3 after injection of tumor cells in the footpad of a preclinical rat metastatic tumor model. An en face OCT image is shown in (a). The cross-sectional OCT image in (b) was extracted at the position indicated by the horizontal green line on the en face OCT image in (a). The capsular structure is less distinct, and mild inflammation results in regions of lower optical scattering in the subcapsular region (yellow arrows). The histological section corresponding to the en face OCT image in (a) is shown in (c). Similar inflammation-related features are clearly visible on high magnification (d) of the area indicated by the black frame in the histology section (c)

FIG. 4

Lymph node imaged on day 5 after injection. A new heterogeneous low-scattering layer (yellow arrows) in the capsular and subcapsular region is prominent in both the en face (a) and cross-sectional (b) OCT images, and focal regions of higher scattering have become evident in the cortex (red arrows). The histological section corresponding to the en face OCT image is shown in (c). Infiltration of tumor cells and macrophages into the precortical region is visible in the magnified area (d) from the black-framed region shown on the histology section in (c)

FIG. 5

Lymph node imaged on day 7 after injection. An en face OCT (a) and corresponding histology image (d) are shown. Lowscattering subcapsular regions have extended deeper into the node, and a more homogeneous highly scattering cortex is evident, as shown in (b), where follicular structures are no longer visible, as confirmed by histology in (e). An adjacent area reveals decreased optical scattering (yellow arrows), as seen in (c), from a histologically verified region of inflammation with aggregates of macrophages but no tumor cells (f). The green and yellow frames around the crosssectional OCT images (b and c, respectively) correspond to the horizontal lines of the same color in (a), indicating the positions of these cross sections relative to the en face OCT image. The highlighted and magnified histology areas (e and f) correspond to the left and right black-framed areas, respectively, on the complete en face lymph node section in (d)

FIG. 6

Lymph node imaged on day 9 after injection. OCT reveals a relatively homogeneous scattering pattern across the lymph node in both en face (a) and cross-sectional (b) images, due to near-total effacement of normal nodal architecture, as shown in the corresponding histological section in (c). A thick low-scattering layer in the capsular and subcapsular region (yellow arrows) can be seen in the en face (a) and cross-sectional (b) OCT images, resulting from metastatic tumor invasion. This correlates to regions in the histology that show only few remaining lymphocytes in the node (d). The green-framed cross-sectional OCT image in (b) was extracted from the location of the horizontal green line shown on the en face imaging in (a). The magnified histological region in (d) is from the black-framed region in (c)