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Published May 2010 | Published
Journal Article Open

Sentinel Lymph Nodes and Lymphatic Vessels: Noninvasive Dual-Modality in Vivo Mapping by Using Indocyanine Green in Rats—Volumetric Spectroscopic Photoacoustic Imaging and Planar Fluorescence Imaging

Abstract

Purpose: To noninvasively map sentinel lymph nodes (SLNs) and lymphatic vessels in rats in vivo by using dual-modality nonionizing imaging—volumetric spectroscopic photoacoustic imaging, which measures optical absorption, and planar fluorescence imaging, which measures fluorescent emission—of indocyanine green (ICG). Materials and Methods: Institutional animal care and use committee approval was obtained. Healthy Sprague-Dawley rats weighing 250−420 g (age range, 60−120 days) were imaged by using volumetric photoacoustic imaging (n = 5) and planar fluorescence imaging (n = 3) before and after injection of 1 mmol/L ICG. Student paired t tests based on a logarithmic scale were performed to evaluate the change in photoacoustic signal enhancement of SLNs and lymphatic vessels before and after ICG injection. The spatial resolutions of both imaging systems were compared at various imaging depths (2–8 mm) by layering additional biologic tissues on top of the rats in vivo. Spectroscopic photoacoustic imaging was applied to identify ICG-dyed SLNs. Results: In all five rats examined with photoacoustic imaging, SLNs were clearly visible, with a mean signal enhancement of 5.9 arbitrary units (AU) ± 1.8 (standard error of the mean) (P < .002) at 0.2 hour after injection, while lymphatic vessels were seen in four of the five rats, with a signal enhancement of 4.3 AU ± 0.6 (P = .001). In all three rats examined with fluorescence imaging, SLNs and lymphatic vessels were seen. The average full width at half maximum (FWHM) of the SLNs in the photoacoustic images at three imaging depths (2, 6, and 8 mm) was 2.0 mm ± 0.2 (standard deviation), comparable to the size of a dissected lymph node as measured with a caliper. However, the FWHM of the SLNs in fluorescence images widened from 8 to 22 mm as the imaging depth increased, owing to strong light scattering. SLNs were identified spectroscopically in photoacoustic images. Conclusion: These two modalities, when used together with ICG, have the potential to help map SLNs in axillary staging and to help evaluate tumor metastasis in patients with breast cancer.

Additional Information

© 2010 Radiological Society of North America. Green OA works will be published under a Creative Commons Attribution-NonCommerical-NoDerivatives 4.0 International License (CC BY-NC-ND), which allows users to share the authors' work as long as appropriate credit is given to the creator of the work; the material is not used for commercial purposes; and the material is not remixed, transformed, or built upon by the user. This research was supported by the National Institutes of Health (grants R01 EB000712, R01 EB008085, R01 NS46214, U54 CA136398). L.V.W. has a financial interest in Endra (Ann Arbor, Mich), which, however, did not support this work. Author contributions: Guarantors of integrity of entire study, C.K., L.V.W.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, C.K., K.H.S., L.V.W.; experimental studies, C.K., K.H.S., L.V.W.; statistical analysis, all authors; and manuscript editing, all authors.

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August 19, 2023
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