Noninvasive depth estimation using tissue optical properties and a dual-wavelength fluorescent molecular probe in vivo.

Jessica P Miller,Dolonchampa Maji,Samuel Achilefu,Bruce J Tromberg,Jesse Lam

doi:10.1364/boe.8.003095

Abstract

Translation of fluorescence imaging using molecularly targeted imaging agents for real-time assessment of surgical margins in the operating room requires a fast and reliable method to predict tumor depth from planar optical imaging. Here, we developed a dual-wavelength fluorescent molecular probe with distinct visible and near-infrared excitation and emission spectra for depth estimation in mice and a method to predict the optical properties of the imaging medium such that the technique is applicable to a range of medium types. Imaging was conducted at two wavelengths in a simulated blood vessel and an in vivo tumor model. Although the depth estimation method was insensitive to changes in the molecular probe concentration, it was responsive to the optical parameters of the medium. Results of the intra-tumor fluorescent probe injection showed that the average measured tumor sub-surface depths were 1.31 ± 0.442 mm, 1.07 ± 0.187 mm, and 1.42 ± 0.182 mm, and the average estimated sub-surface depths were 0.97 ± 0.308 mm, 1.11 ± 0.428 mm, 1.21 ± 0.492 mm, respectively. Intravenous injection of the molecular probe allowed for selective tumor accumulation, with measured tumor sub-surface depths of 1.28 ± 0.168 mm, and 1.50 ± 0.394 mm, and the estimated depths were 1.46 ± 0.314 mm, and 1.60 ± 0.409 mm, respectively. Expansion of our technique by using material optical properties and mouse skin optical parameters to estimate the sub-surface depth of a tumor demonstrated an agreement between measured and estimated depth within 0.38 mm and 0.63 mm for intra-tumor and intravenous dye injections, respectively. Our results demonstrate the feasibility of dual-wavelength imaging for determining the depth of blood vessels and characterizing the sub-surface depth of tumors in vivo.

Highlights

Using light to evaluate disease is increasingly common for both preclinical and clinical applications [1]
Fluorescein isothiocyanate (FITC) peak emission was at 518 nm (Fig. 1(c)) and cypate peak emission was at 812 nm (Fig. 1(d))
The presence of two distinct fluorescent peaks allowed for imaging at dual-wavelengths, which was used to calculate the depth of the fluorescent signal. 3.2 Simulation of in vitro tissue depth estimation Description of tumor depth involves multiple depths that are of clinical significance

Summary

Introduction

Using light to evaluate disease is increasingly common for both preclinical and clinical applications [1]. The expansion of the technology is due to advances in imaging methodologies and in fluorescent molecular probes that have diverse emission wavelengths and can bind to specific biological structures [2, 3]. Fluorescence methods allow for real-time imaging without the use of ionizing radiation and show promise in translational applications such as intraoperative imaging [4, 5]. Planar optical imaging is an attractive translational tool due to the versatility of imaging systems and the growing availability of targeted molecular dyes. Planar optical imaging relies on the intensity of the fluorescent signal to determine the extent of the pathology [6]. The ability to assess the extent of a biological structure, such as a tumor or blood vessels, using a fluorescent dye will improve disease detection and surveillance [7]

Methods

Results

Conclusion