Abstract
This study reports the optical characterization and quantitative oximetry of human breast cancer using spectrally-resolved images collected with a broadband, continuous-wave optical mammography instrument. On twenty-six cancer patients, we collected two-dimensional optical mammograms and created maps of the concentrations of hemoglobin, water, and lipids, as well as the oxygen saturation of hemoglobin. For each cancerous breast, we analyzed the difference between the tumor region (as identified by x-ray and optical mammography) and the remainder of breast tissue. With respect to the surrounding tissue, we found that cancer regions have significantly higher concentrations of total hemoglobin (+2.4±0.4 μM) and water (+7±1% v/v), and significantly lower lipid concentration (8±2% v/v) and oxygen saturation of hemoglobin (5±1%). We also found a significant correlation between the tumor optical contrast and the grade of breast cancer as quantified by the Nottingham histologic score; this demonstrates how optical signatures may be representative of metabolic and morphological features, as well as the aggressive potential of the tumor.
Highlights
This study focuses on an additional near-infrared spectroscopy (NIRS) measured parameter, the oxygen saturation of hemoglobin, which is referred to as tissue saturation and hemoglobin saturation in the diffuse optics field
Despite the low optical signal at 925 nm for patient data, we found that the relative insensitivity of μeff to optical heterogeneities at this wavelength results in a robust method for optical estimation of breast tissue thickness [see Fig. 3(A)]
If there is a region of the breast where the chromophore concentrations differ from the reference point, the 925 nm range will experience less of an attenuation change compared to shorter wavelengths, where hemoglobin is the dominant absorber
Summary
Experimental setupWe have developed a broadband continuous-wave optical mammography system described in detail elsewhere [21]. Imaging of the breast is performed in a parallel plate geometry where the breast is mildly compressed between two polycarbonate plates. This mild compression is intended to maintain tissue stability during the scan while ensuring that the patient experiences no discomfort. A broadband light source (Xenon arc lamp, Model No 6258, Newport Corporation, Irvine, CA), with spectral filters in place to eliminate ultraviolet (below 400 nm) and infrared (above 950 nm) wavelengths, is used to illuminate the breast tissue. Illumination and detection optical fibers (3 and 4 mm in diameter, respectively) scan collinearly, and data are captured every 2 mm in the x- and y- directions of the plates (see Fig. 1 for coordinate system). Spectral data is acquired from 650 nm to 950 nm, with an 8 nm wavelength resolution
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