Abstract
A multimodal micro-computed tomography (CT) and multi-spectral structured light imaging (SLI) system is introduced and systematically analyzed to test its feasibility to aid in margin delineation during breast conserving surgery (BCS). Phantom analysis of the micro-CT yielded a signal-to-noise ratio of 34, a contrast of 1.64, and a minimum detectable resolution of 240 μm for a 1.2 min scan. The SLI system, spanning wavelengths 490 nm to 800 nm and spatial frequencies up to 1.37 , was evaluated with aqueous tissue simulating phantoms having variations in particle size distribution, scatter density, and blood volume fraction. The reduced scattering coefficient, and phase function parameter, γ, were accurately recovered over all wavelengths independent of blood volume fractions from 0% to 4%, assuming a flat sample geometry perpendicular to the imaging plane. The resolution of the optical system was tested with a step phantom, from which the modulation transfer function was calculated yielding a maximum resolution of 3.78 cycles per mm. The three dimensional spatial co-registration between the CT and optical imaging space was tested and shown to be accurate within 0.7 mm. A freshly resected breast specimen, with lobular carcinoma, fibrocystic disease, and adipose, was imaged with the system. The micro-CT provided visualization of the tumor mass and its spiculations, and SLI yielded superficial quantification of light scattering parameters for the malignant and benign tissue types. These results appear to be the first demonstration of SLI combined with standard medical tomography for imaging excised tumor specimens. While further investigations are needed to determine and test the spectral, spatial, and CT features required to classify tissue, this study demonstrates the ability of multimodal CT/SLI to quantify, visualize, and spatially navigate breast tumor specimens, which could potentially aid in the assessment of tumor margin status during BCS.
Highlights
Breast conserving surgery (BCS) is common treatment for localized breast cancer, being less invasive than a full breast removal and having similar long term survival rates when combined with radiation therapy (Fisher et al 2002)
The micro-computed tomography (CT) target phantom analysis resulted in the same minimum detectable objects (MDO) for the low and high energy scans, with only the smallest fiber and smallest speck cluster not clearly visible
A novel multimodal imaging system combining superficial structured light imaging (SLI) and volumetric micro-CT was systematically evaluated in phantoms, and as a proof-of-principle, a freshly excised human breast specimen was scanned
Summary
Breast conserving surgery (BCS) is common treatment for localized breast cancer, being less invasive than a full breast removal and having similar long term survival rates when combined with radiation therapy (Fisher et al 2002). A plethora of biomedical devices have been proposed for this task, including electrical impedence spectroscopy (Kaufman et al 2016), photoacoustic tomography (Wong et al 2017), optical coherence tomography (Erickson-Bhatt et al 2015), non-linear microscopy (Tao et al 2014), dark field-confocal microscopy (Laughney et al 2012), and Raman spectroscopy (Wang et al 2016), among others. All of these methods either require exogenous dyes, chemically processing or fixing of tissue, or combing through point sampling volumes with a probe. A recently demonstrated imaging method, broadly referred to as high spatial frequency structured light imaging (SLI), has shown label free sensitivity to changes in freshly resected breast morphology over a large field of view (FOV) (~ 100–2 cm2) (McClatchy et al 2016)
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