Dual-modality optical biopsy of glioblastomas multiforme with diffuse reflectance and fluorescence: ex vivo retrieval of optical properties

Abstract

Glioma itself accounts for 80% of all malignant primary brain tumors, and glioblastoma multiforme (GBM) accounts for 55% of such tumors. Diffuse reflectance and fluorescence spectroscopy have the potential to discriminate healthy tissues from abnormal tissues and therefore are promising noninvasive methods for improving the accuracy of brain tissue resection. Optical properties were retrieved using an experimentally evaluated inverse solution. On average, the scattering coefficient is 2.4 times higher in GBM than in low grade glioma (LGG), and the absorption coefficient is 48% higher. In addition, the ratio of fluorescence to diffuse reflectance at the emission peak of 460 nm is 2.6 times higher for LGG while reflectance at 650 nm is 2.7 times higher for GBM. The results reported also show that the combination of diffuse reflectance and fluorescence spectroscopy could achieve sensitivity of 100% and specificity of 90% in discriminating GBM from LGG during ex vivo measurements of 22 sites from seven glioma specimens. Therefore, the current technique might be a promising tool for aiding neurosurgeons in determining the extent of surgical resection of glioma and, thus, improving intraoperative tumor identification for guiding surgical intervention.

Calibration of Spectral Imaging Devices With Oxygenation-Controlled Phantoms: Introducing a Simple Gel-Based Hemoglobin Model

“…Therefore, longer aging is not considered when using the Presygen system. Nevertheless, the selected ranges of optical properties and oxygen saturation in the current phantom model are within literature for tissues and optical phantoms [7,21,22].…”

“…In all phantoms, the total absorption coefficient (µ a ) is calculated by applying Beer-Lambert law to the measured transmission from a spectrophotometer (Ultraspec 3,000, Pharmacia Biotech Inc., NJ) whereas µ s ' is calculated by applying Mie theory to 1-µm-diameter polystyrene microsphere [2,3,7]. The final volume of each phantom was 15 ml, and all phantoms were stored at 4 • C degrees.…”

“…In addition, a fitting approach was FIGURE 1 | Image of the commercial multispectral imaging system (Presygen TM /si-1). applied to fit the total absorption coefficient, µ a and to obtain the oxygen saturation value [4,7], such that: µ a (λ) = ln(10)·f 1 ·[f 2 ·ε HbO2 (λ) + (1 − f 2 )·ε Hb (λ)] + µ a,yeast (1) In Equation (1), µ a,yeast (cm −1 ) is the absorption coefficient of yeast in Agar gel solution, λ is wavelength, f 1 (mol.liter −1 ) is the total concentration of hemoglobin, f 2 (dimensionless) is oxygen saturation (StO2), and ε HbO2 (cm −1 .M −1 ) and ε Hb (cm −1 .M −1 ) are molar extinction coefficients of oxygenated and deoxygenated hemoglobin, respectively. To obtain f 2 , the least square fitting routine "fminsearch" in MATLAB R was used to fit the broadband measurement of µ a and µ a,yeast into Equation (1).…”

“…While hemoglobin (Hb) absorption represents a key source of crosstalk in optical properties extraction and distortion in collected signal [3,4], its optical signatures over a wide spectral range are the keys to non-invasive assessment of tissue oxygenation with multi-spectral imaging (MSI) systems [5,6]. Although powdered Hb (i.e., H0267, Sigma-Aldrich) has been widely used to fabricate phantoms for calibration of fiber-optics-based techniques [2][3][4]7], it is not an ideal material for varying and accurately controlling of oxygen saturation. This is due to the autoxidation of the present heme group leading to the formation of the ferric derivative (methemoglobin) over time in addition to the already existed small amount of methemoglobin in the powder.…”

Optimizing interstitial photodynamic therapy with custom cylindrical diffusers

“…The optical properties for each tissue type at the wavelengths shown in Table were extracted from the literature . Table shows the optical properties at the different wavelengths considered, where μ a , μ s , g and n are the absorption coefficient, scattering coefficient, anisotropy factor and the refractive index, respectively.…”