Sentinel lymph node biopsy is a primary mean of staging cancer; however, the time-intensive nature of standard pathology limits the volume of the node that can be assessed. As a result, micrometastases can be missed, which have been shown to affect treatment decisions and therefore clinical outcomes. Optical imaging offers a potential solution for improved sensitivity and larger tissue evaluation, but an understanding of optical properties is necessary because of the high scattering nature of biological tissue. Here, time-domain optical imaging and measures of transmittance are used to characterize the optical properties of porcine lymph nodes at 685 nm and 780 nm. Results demonstrated values comparable to that of other soft biological tissue (685 nm: μa = 0.09 ± 0.01cm-1 , μs’ = 2.60 ± 0.42 cm-1 , g = 0.95; 780 nm: μa = 0.24 ± 0.10cm-1 , μs’ = 3.35 ± 0.14 cm-1 , g = 0.92). Based on these coefficients, optical properties of TiO2 were investigated so that a protocol to fabricate a lymph node tissue-mimicking phantom could be defined.
Skull base tumors are particularly difficult to visualize and access for surgeons because of the crowded environment and close proximity of vital structures, such as cranial nerves. As a result, accidental nerve damage is a significant concern and the likelihood of tumor recurrence is increased because of more conservative resections that attempt to avoid injuring these structures. In this study, a paired-agent imaging method with direct administration of fluorophores is applied to enhance cranial nerve identification. Here, a control imaging agent (ICG) accounts for non-specific uptake of the nerve-targeting agent (Oxazine 4), and ratiometric data analysis is employed to approximate binding potential (BP, a surrogate of targeted biomolecule concentration). For clinical relevance, animal experiments and simulations were conducted to identify parameters for an optimized stain and rinse protocol using the developed paired-agent method. Numerical methods were used to model the diffusive and kinetic behavior of the imaging agents in tissue, and simulation results revealed that there are various combinations of stain time and rinse number that provide improved contrast of cranial nerves, as suggested by optimal measures of BP and contrast-to-noise ratio.
Nerve preservation during surgery is critical because damage can result in significant morbidity. This remains a challenge especially for skull base surgeries where cranial nerves (CNs) are involved because visualization and access are particularly poor in that location. We present a paired-agent imaging method to enhance identification of CNs using nerve-specific fluorophores. Two myelin-targeting imaging agents were evaluated, Oxazine 4 and Rhodamine 800, and coadministered with a control agent, indocyanine green, either intravenously or topically in rats. Fluorescence imaging was performed on excised brains ex vivo, and nerve contrast was evaluated via paired-agent ratiometric data analysis. Although contrast was improved among all experimental groups using paired-agent imaging compared to conventional, solely targeted imaging, Oxazine 4 applied directly exhibited the greatest enhancement, with a minimum 3 times improvement in CNs delineation. This work highlights the importance of accounting for nonspecific signal of targeted agents, and demonstrates that paired-agent imaging is one method capable of doing so. Although staining, rinsing, and imaging protocols need to be optimized, these findings serve as a demonstration for the potential use of paired-agent imaging to improve contrast of CNs, and consequently, surgical outcome.
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