Calibration and analysis of a multimodal micro-CT and structured light imaging system for the evaluation of excised breast tissue

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 (SNR) 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 mm−1, was evaluated with aqueous tissue simulating phantoms having variations in particle size distribution, scatter density, and blood volume fraction. The reduced scattering coefficient, μs′ 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 (MTF) was calculated yielding a maximum resolution of 3.78 cycles per mm. The three dimensional (3D) 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.

Review of methods for intraoperative margin detection for breast conserving surgery

“…49,50 Micro-CT has also been combined with other types of imaging systems such as spatial frequency domain imaging (SFDI) to create multidimensional data that may offer accurate specimen margin assessments. 51 A recent study of fresh lumpectomy specimens was able to identify the correct margin status on 25 out of 29 patients that were able to be analyzed. There were four false negative results which lead to a sensitivity of 56% and a specificity of 100%.…”

Context-free hyperspectral image enhancement for wide-field optical biomarker visualization

“…While this sort of behavior is not necessarily fundamentally flawed (this is the expected behavior of the algorithm), for in vivo imaging this implies that contrast will fluctuate as different sorts of spectra are presented to the camera in various proportions. For example, in the case of margin delineation, tumors may be accentuated if surrounded by adipose tissue, or darkened if surrounded by normal or connective tissue (adipose and normal tissue can present lower and higher scattering coefficients and average reflectance than malignant tissue, respectively) [15,34]. These inconsistencies may be problematic in a clinical setting, explaining the motivation behind this desired improvement, and providing an insight on how these techniques cannot be exploited for specific applications unless the dependency with the SVD is avoided.…”

Structured light imaging for breast-conserving surgery, part I: optical scatter and color analysis

“…Its performance was quantified experimentally, as described in detail previously. 12 The SLI system demonstrated a maximum spatial resolution of 3.78 cycles∕mm at the highest illumination spatial frequency (f x ) of 1.37 mm −1 and at the shortest source wavelength (λ) of 490 nm. Optical scattering properties were recovered accurately with ratios of μ 0 s ∕μ a as low as 0.8.…”

“…The system imaged tissue specimens with four illumination spatial frequencies (f x ¼ 0.00, 0.15, 0.60, and 1.37 mm −1 ) at four source wavelengths (λ ¼ 490, 550, 600, 700 nm). 12 It acquired a lateral cone beam μCT scan. The analysis presented here is focused solely on the SLI data.…”

“…Optical properties were calculated for 120 RoIs spanning 10 breast tissue pathologies based on a subdiffusive SFDI (sd-SFDI) model described in detail previously. 9,12,15,16 This dataset represents one of the most complete descriptions of optical properties of breast tissue morphologies reported to date. For each RoI, the reduced scattering coefficient (μ 0 s ), the absorption coefficient (μ a ), and the anisotropic scatter phase function parameter (γ) were found at each wavelength based on the sd-SFDI model.…”