Scanning in situ Spectroscopy platform for imaging surgical breast tissue specimens

Abstract

A non-contact localized spectroscopic imaging platform has been developed and optimized to scan 1x1cm 2 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.

Structured light scatteroscopy

“…Figure 1(e) shows the average reflectance at 0.5 mm −1 spatial frequency plotted as a function of intralipid concentration and indicates a linear relationship between the recovered reflectance and the scatter concentration, similar to observed trends from probe-based localized scattering response measurements. 5 This linearity is lost at lower intralipid concentrations, where the signal change due to scattering was too small to be reliably measured using the off-the-shelf, uncooled CCD camera used in this study. Increasing the modulation depth of the input spatial frequency patterns or using a low noise, cooled CCD camera could help mitigate this issue.…”

“…Direct measurement of light scattering signals using spatial and angular localization techniques has been proposed recently using a confocal and dark-field optical scheme. 5,6 However, a critical limitation of the approach is that the wide-field imaging (several centimeters) requires electro-optical or mechanical scanning, which is time consuming and cumbersome, and hence, impractical in many clinical applications.…”

“…In localized scattering spectroscopy, the wavelength dependence of the recovered scatter parameters varies with the probe size and numerical aperture. 5 This dependency often results in varying scatter responses within the same medium when light is collected from different interrogation volumes because of differences in how the scattering phase function is sampled and provides a means to sense ultrastructural variations in heterogeneous media, such as tissue, at multiple size scales. In SLS, the effective sampling volume decreases as the spatial frequency is increased, so varying the spatial frequencies could provide a similar means to probe ultrastructural variations at multiple size scales.…”

Scatter Spectroscopic Imaging Distinguishes between Breast Pathologies in Tissues Relevant to Surgical Margin Assessment

“…The challenge in this is to optimize sensitivity to discriminating tissue ultra-structure, while sampling sufficient tissue to account for known patient heterogeneity. To achieve this goal, a scanning-beam platform for both spectroscopy and wide-field imaging was designed to rapidly image localized scattering spectra from intact breast surgical specimens[6, 7], and then to explore textural patterns for discrimination between pathologies in situ . The motivation for this approach was two-fold: (1) to exploit optical scattering, which is exquisitely sensitive to microscopic pathology, here used as the diagnostic gold standard, and (2) to capture spatial-spectral signatures because morphological patterns are otherwise difficult to interpret.…”

Cancer Detection in Human Tissue Samples Using a Fiber-Tip pH Probe

“…These include methodology based on Raman spectroscopy (10,11), scanning in situ spectroscopy and mapping of whole specimens (12), combined diffuse reflectance spectroscopy and intrinsic autofluorescence (10,13), or multimodal optical imaging (14). These studies have been exploratory and have examined and mapped tissue distribution in whole excised specimens ex vivo.…”