Scanning in Situ Spectroscopy Pplatform for Imaging Surgical Breast Tissue Specimens

A non-contact localized spectroscopic imaging platform has been developed and optimized to scan 1 x 1 cm² square regions of surgically resected breast tissue specimens with ~150-micron resolution. A color corrected, image-space telecentric scanning design maintained a consistent sampling geometry and uniform spot size across the entire imaging field. Theoretical modeling in ZEMAX allowed estimation of the spot size, which is equal at both the center and extreme positions of the field with ~5% variation across the designed waveband, indicating excellent color correction. The spot sizes at the center and an extreme field position were also measured experimentally using the standard knife-edge technique and were found to be within ~8% of the theoretical predictions. Highly localized sampling offered inherent insensitivity to variations in background absorption allowing direct imaging of local scattering parameters, which was validated using a matrix of varying concentrations of Intralipid and blood in phantoms. Four representative, pathologically distinct lumpectomy tissue specimens were imaged, capturing natural variations in tissue scattering response within a given pathology. Variations as high as 60% were observed in the average reflectance and relative scattering power images, which must be taken into account for robust classification performance. Despite this variation, the preliminary data indicates discernible scatter power contrast between the benign vs malignant groups, but reliable discrimination of pathologies within these groups would require investigation into additional contrast mechanisms

Video-Rate Near Infrared Tomography to Image Pulsatile Absorption Properties in Thick Tissue

A high frame-rate near-infrared (NIR) tomography system was created to allow transmission imaging of thick tissues with spectral encoding for parallel source implementation. The design was created to maximize tissue penetration through up to 10 cm of tissue, allowing eventual use in human imaging. Eight temperature-controlled laser diodes (LD) are used in parallel with 1.5 nm shifts in their lasing wavelengths. Simultaneous detection is achieved with eight high-resolution, CCD-based spectrometers that were synchronized to detect the intensities and decode their source locations from the spectrum. Static and dynamic imaging is demonstrated through a 64 mm tissue-equivalent phantom, with acquisition rates up to 20 frames per second. Imaging of pulsatile absorption changes through a 72 mm phantom was demonstrated with a 0.5 Hz varying object having only 1% effect upon the transmitted signal. This subtle signal change was used to show that while reconstructing the signal changes in a tissue may not be possible, image-guided recovery of the pulsatile change in broad regions of tissue was possible. The ability to image thick tissue and the capacity to image periodic changes in absorption makes this design well suited for tracking thick tissue hemodynamics in vivo during MR or CT imaging

Anthropomorphic Breast Phantoms with Physiological Water, Lipid, and Hemoglobin Content for Near-Infrared Spectral Tomography

Breast mimicking tissue optical phantoms with sufficient structural integrity to be deployed as stand-alone imaging targets are developed and successfully constructed with biologically relevant concentrations of water, lipid, and blood. The results show excellent material homogeneity and reproducibility with inter- and intraphantom variability of 3.5 and 3.8%, respectively, for water and lipid concentrations ranging from 15 to 85%. The phantoms were long-lasting and exhibited water and lipid fractions that were consistent to within 5% of their original content when measured 2 weeks after creation. A breast-shaped three-compartment model of adipose, fibroglandular, and malignant tissues was created with water content ranging from 30% for the adipose simulant to 80% for the tumor. Mean measured water content ranged from 30% in simulated adipose to 73% in simulated tumor with the higher water localized to the tumor-like material. This novel heterogeneous phantom design is composed of physiologically relevant concentrations of the major optical absorbers in the breast in the near-infrared wavelengths that should significantly improve imaging system characterization and optimization because the materials have stand-alone structural integrity and can be readily molded into the sizes and shapes of tissues commensurate with clinical breast imaging

Calibration and Optimization of 3D Digital Breast Tomosynthesis Guided Near Infrared Spectral Tomography

Calibration of a three-dimensional multimodal digital breast tomosynthesis (DBT) x-ray and non-fiber based near infrared spectral tomography (NIRST) system is challenging but essential for clinical studies. Phantom imaging results yielded linear contrast recovery of total hemoglobin (HbT) concentration for cylindrical inclusions of 15 mm, 10 mm and 7 mm with a 3.5% decrease in the HbT estimate for each 1 cm increase in inclusion depth. A clinical exam of a patient\u27s breast containing both benign and malignant lesions was successfully imaged, with greater HbT was found in the malignancy relative to the benign abnormality and fibroglandular regions (11 μM vs. 9.5 μM). Tools developed improved imaging system characterization and optimization of signal quality, which will ultimately improve patient selection and subsequent clinical trial results

Sub-Diffusive Scattering Parameter Maps Recovered Using Wide-Field High-Frequency Structured Light Imaging

This study investigates the hypothesis that structured light reflectance imaging with high spatial frequency patterns (fx) can be used to quantitatively map the anisotropic scattering phase function distribution (P(θs)) in turbid media. Monte Carlo simulations were used in part to establish a semi-empirical model of demodulated reflectance (Rd) in terms of dimensionless scattering (μ′sf−1x) and γ, a metric of the first two moments of the P(θs) distribution. Experiments completed in tissue-simulating phantoms showed that simultaneous analysis of Rd spectra sampled at multiple fx in the frequency range [0.05-0.5] mm−1 allowed accurate estimation of both μ′s(λ) in the relevant tissue range [0.4-1.8] mm−1, and γ(λ) in the range [1.4-1.75]. Pilot measurements of a healthy volunteer exhibited γ-based contrast between scar tissue and surrounding normal skin, which was not as apparent in wide field diffuse imaging. These results represent the first wide-field maps to quantify sub-diffuse scattering parameters, which are sensitive to sub-microscopic tissue structures and composition, and therefore, offer potential for fast diagnostic imaging of ultrastructure on a size scale that is relevant to surgical applications

Quantitative Imaging of Scattering Changes Associated with Epithelial Proliferation, Necrosis and Fibrosis in Tumors Using Microsampling Reflectance Spectroscopy

Highly localized reflectance measurements can be used to directly quantify scatter changes in tissues. We present a microsampling approach that is used to raster scan tumors to extract parameters believed to be related to the tissue ultrastructure. A confocal reflectance imager was developed to examine scatter changes across pathologically distinct regions within tumor tissues. Tissue sections from two murine tumors, AsPC-1 pancreas tumor and the Mat-LyLu Dunning prostate tumor, were imaged. After imaging, histopathology-guided region-of-interest studies of the images allowed analysis of the variations in scattering resulting from differences in tissue ultra-structure. On average, the median scatter power of tumor cells with high proliferation index (HPI) was about 26% less compared to tumor cells with low proliferation index (LPI). Necrosis exhibited the lowest scatter power signature across all the tissue types considered, with about 55% lower median scatter power than LPI tumor cells. Additionally, the level and maturity of the tumor\u27s fibroplastic response was found to influence the scatter signal. This approach to scatter visualization of tissue ultrastructure in situ could provide a unique tool for guiding surgical resection, but this kind of interpretation into what the signal means relative to the pathology is required before proceeding to clinical studies

Optical assessment of pathology in surgically resected tissues

Multi-spectral spatially modulated light is used to guide localized spectroscopy of surgically resected tissues for cancer involvement. Modulated imaging rapidly quantifies near-infrared optical parameters with sub-millimeter resolution over the entire field for identification of residual disease in resected tissues. Suspicious lesions are further evaluated using a spectroscopy platform designed to image thick tissue samples at a spatial resolution sensitive to the diagnostic gold standard, pathology. MI employs a spatial frequency domain sampling and model-based analysis of the spatial modulation transfer function to interpret a tissue's absorption and scattering parameters at depth. The spectroscopy platform employs a scanning-beam, telecentric dark-field illumination and confocal detection to image fields up to 1cm2 with a broadband source (480:750nm). The sampling spot size (100μm lateral resolution) confines the volume of tissue probed to within a few transport pathlengths so that multiple-scattering effects are minimized and simple empirical models may be used to analyze spectra. Localized spectroscopy of Intralipid and hemoglobin phantoms demonstrate insensitivity of recovered scattering parameters to changes in absorption, but a non-linear dependence of scattering power on Intralipid concentration is observed due to the phase sensitivity of the measurement system. Both systems were validated independently in phantom and murine studies. Ongoing work focuses on assessing the combined utility of these systems to identify cancer involvement in vitro, particularly in the margins of resected breast tumors

A Digital X-Ray Tomosynthesis Coupled Near Infrared Spectral Tomography System for Dual-Modality Breast Imaging

A Near Infrared Spectral Tomography (NIRST) system has been developed and integrated into a commercial Digital Breast Tomosynthesis (DBT) scanner to allow structural and functional imaging of breast in vivo. The NIRST instrument uses an 8-wavelength continuous wave (CW) laser-based scanning source assembly and a 75-element silicon photodiode solid-state detector panel to produce dense spectral and spatial projection data from which spectrally constrained 3D tomographic images of tissue chromophores are produced. Integration of the optical imaging system into the DBT scanner allows direct co-registration of the optical and DBT images, while also facilitating the synergistic use of x-ray contrast as anatomical priors in optical image reconstruction. Currently, the total scan time for a combined NIRST-DBT exam is ~50s with data collection from 8 wavelengths in the optical scan requiring ~42s to complete. The system was tested in breast simulating phantoms constructed using intralipid and blood in an agarose matrix with a 3 cm x 2 cm cylindrical inclusion at 1 cm depth from the surface. Diffuse image reconstruction of total hemoglobin (HbT) concentration resulted in accurate recovery of the lateral size and position of the inclusion to within 6% and 8%, respectively. Use of DBT structural priors in the NIRST reconstruction process improved the quantitative accuracy of the HbT recovery, and led to linear changes in imaged versus actual contrast, underscoring the advantages of dual-modality optical imaging approaches. The quantitative accuracy of the system can be further improved with independent measurements of scattering properties through integration of frequency or time domain data