A non-invasive means to determine lesion depth (I.e. Breslow Thickness) and an indirect, lesion-specific assessment of cellular morphology could substantially improve the efficacy of melanoma screening. Such applications would be of great benefit in aiding diagnosis, reducing the number of unnecessary biopsies, and improving treatment options for patients. Using Spatial Frequency Domain Imaging (SFDI), we have developed a spectral method to isolate depth-specific scattering properties and hence, differentiate pigmented lesion volumes from underlying tissue by its structural morphology. This method was evaluated on solid phantoms that emulate the optical properties of suspect pigmented lesions over multiple thicknesses.
Partial thickness burn wounds extend partially through the dermis, leaving many pain receptors intact and making the injuries very painful. Due to the painfulness, quick assessment of the burn depth is important to not delay surgery of the wound if needed. Laser speckle imaging (LSI) of skin blood flow can be helpful in finding severe coagulation zones with impaired blood flow. However, LSI measurements are typically too superficial to properly reach the full depth of adult dermis and cannot resolve the flow in depth. Diffuse correlation spectroscopy (DCS) uses varying source-detector separations to allow differentiation of flow depths but requires time-consuming 2D scanning to form an image of the burn area. We here present a prototype for a hybrid DCS and LSI technique called speckle contrast Diffuse Correlation Tomography (scDCT) with the novel approach of using a laser line as a source. This will allow for fast 1D scanning to perform 3D tomographic imaging, making quantitative estimates of the depth and area of the coagulation zone from burn wounds. Simulations and experimental results from a volumetric flow phantom show promise to differentiate flows at different depths. The aim is to create a system that will provide more quantitative estimates of coagulation depth in partial thickness burn wounds to better estimate when surgery is needed.
SignificanceSpatial frequency domain imaging (SFDI) and spatial frequency domain spectroscopy (SFDS) are emerging tools to non-invasively assess tissues. However, the presence of aberrations can complicate processing and interpretation.AimThis study develops a method to characterize optical aberrations when performing SFDI/S measurements. Additionally, we propose a post-processing method to compensate for these aberrations and recover arbitrary subsurface optical properties.ApproachUsing a custom SFDS system, we extract absorption and scattering coefficients from a reference phantom at 0 to 15 mm distances from the ideal focus. In post-processing, we characterize aberrations in terms of errors in absorption and scattering relative to the expected in-focus values. We subsequently evaluate a compensation approach in multi-distance measurements of phantoms with different optical properties and in multi-layer phantom constructs to mimic subsurface targets.ResultsCharacterizing depth-specific aberrations revealed a strong power law such as wavelength dependence from ∼40 to ∼10 % error in both scattering and absorption. When applying the compensation method, scattering remained within 1.3% (root-mean-square) of the ideal values, independent of depth or top layer thickness, and absorption remained within 3.8%.ConclusionsWe have developed a protocol that allows for instrument-specific characterization and compensation for the effects of defocus and chromatic aberrations on spatial frequency domain measurements.
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