Abstract 4246: Multispectral open-air fluorescence-guided imaging and detection of tumors using a hands-free translational platform with liquid crystal tunable filters (LCTF)
Authors: Behrooz Ali , Vasquez Kristine , Waterman Peter , Meganck Jeff , Peterson Jeffrey , Miller Peter , Kempner Joshua , Yared Wael 
Published: July 2016

Abstract
Intraoperative identification and resection of tumors currently relies on the ability of the surgeon to visually detect or palpate the tumors and residual malignant tissue. As such, minuscule tumor nodules can go undetected or be inadequately removed, with such cases often resulting in the need for secondary treatment or additional surgical intervention. The Solaris™ platform is an open-air fluorescent imaging instrument designed for large animal fluorescence-guided surgery, with the advantage of real-time acquisition of fluorescence images/video under surgical light conditions. Solaris supports four fixed fluorescent channels ranging from visible to near infrared (NIR), and a multispectral channel where a liquid crystal tunable filter (LCTF) is used to acquire spectral data by sweeping across the green-to-red portion of the visible spectrum. This range of imaging channels allows for single-wavelength and multispectral imaging of widely used reagents (e.g. indocyanine green [ICG] and Fluorescein isothiocyanate [FITC]) and unique NIR fluorescent dyes used for detecting and labeling tumors.
While fluorescent imaging using NIR imaging agents (680, 750, 800 nm) offered effective tumor detection, identification of tumors implanted in nude mice or rats using visible (400-650 nm) reagents such as FITC presented challenges considering the presence of auto-fluorescence originating from tissue and food (alfalfa). For these reagents, Solaris acquired multispectral images using the LCTF under ambient light conditions, and an automated spectral unmixing algorithm was applied to the multispectral data, after background correction and ambient light removal, to separate tissue and food auto-fluorescence from the reagent fluorescent signal. The algorithm used vertex component analysis to automatically extract the primary pure spectra present in the multispectral images and unmix the reagent fluorescent signal by non-negative least squares fitting. To test the spectral unmixing capabilities of Solaris, in vivo experiments were performed using small amounts of locally injected FITC in mice and rats. In the absence of unmixing, it was not possible to accurately detect sites of FITC signal, but with unmixing the labeled regions were well defined. Additional studies in tumor-bearing mice and rats substantiated the ability to spectrally unmix FITC agent signal in deep tumor masses imaged under ambient light, enhancing the ability to surgically resect them. To further validate this concept, bioluminescent tumor cell lines were implanted in mice. After image-guided tumor resection, both the residual tumor bed and the resected tumors were imaged to confirm complete removal. These data demonstrate that intraoperative image-guided resection of fluorescent-labeled tumors can be achieved using LCTF-based open-air multispectral imaging on the Solaris.
Citation Format: Ali Behrooz, Kristine Vasquez, Peter Waterman, Jeff Meganck, Jeffrey Peterson, Peter Miller, Joshua Kempner, Wael Yared. Multispectral open-air fluorescence-guided imaging and detection of tumors using a hands-free translational platform with liquid crystal tunable filters (LCTF). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4246.