Macroscopic optical imaging technique for wide-field estimation of fluorescence depth in optically turbid media for application in brain tumor surgical guidance

Abstract

Abstract. A diffuse imaging method is presented that enables wide-field estimation of the depth of fluorescent molecular markers in turbid media by quantifying the deformation of the detected fluorescence spectra due to the wavelength-dependent light attenuation by overlying tissue. This is achieved by measuring the ratio of the fluorescence at two wavelengths in combination with normalization techniques based on diffuse reflectance measurements to evaluate tissue attenuation variations for different depths. It is demonstrated that fluorescence topography can be achieved up to a 5 mm depth using a near-infrared dye with millimeter depth accuracy in turbid media having optical properties representative of normal brain tissue. Wide-field depth estimates are made using optical technology integrated onto a commercial surgical microscope, making this approach feasible for real-world applications.

Fluorescence depth estimation from wide-field optical imaging data for guiding brain tumor resection: a multi-inclusion phantom study

“…In previous work, the depth of a single fluorescent source was accurately estimated when located up to 6mm below the surface based on linear relationships between fluorescence intensity ratio and fluorophore depth derived from analytical expressions [14]. However, the performance of this depth estimation strategy when multiple fluorescent sources are present in various sizes, separations and depths has not been investigated or characterized.…”

“…In previous work, we reported that depth estimation relies on the ability to acquire zero-depth data on a fluorescent inclusion, and calculation of the slope, m [14], of the linear relationship between the dual-wave fluorescence intensity ratio (DWFR), and the depth of the fluorescence emission [19]. A summary of the techniques and expressions for finding m are summarized in Table 1 [14].…”

“…A summary of the techniques and expressions for finding m are summarized in Table 1 [14]. For our tests, zero-depth data was measured with no intervening bulk media between the imaging system and each of the different AF647 inclusions used.…”

“…A commercially available surgical microscope (Carl Zeiss Meditec) previously adapted for PpIX fluorescence imaging was used [14]. A variable-intensity bright-field tungsten-halogen lamp served as a broadband white light source for reflectance measurements.…”

“…A phantom preparation method previously described [14] was optimized for the current study. Two identical inclusions of 1 cm diameter and 1 mm wall thickness were prepared.…”