Soren D. Konecky

Quantitative optical tomography of sub-surface heterogeneities using spatially modulated structured light

We present a wide-field method for obtaining three-dimensional images of turbid media. By projecting patterns of light of varying spatial frequencies on a sample, we reconstruct quantitative, depth resolved images of absorption contrast. Images are reconstructed using a fast analytic inversion formula and a novel correction to the diffusion approximation for increased accuracy near boundaries. The method provides more accurate quantification of optical absorption and higher resolution than standard diffuse reflectance measurements.

Spatial frequency domain tomography of protoporphyrin IX fluorescence in preclinical glioma models

Multifrequency (0 to 0.3u2009 mm(-1)), multiwavelength (633, 680, 720, 800, and 820 nm) spatial frequency domain imaging (SFDI) of 5-aminolevulinic acid-induced protoporphyrin IX (PpIX) was used to recover absorption, scattering, and fluorescence properties of glioblastoma multiforme spheroids in tissue-simulating phantoms and in vivo in a mouse model. Three-dimensional tomographic reconstructions of the frequency-dependent remitted light localized the depths of the spheroids within 500 μm, and the total amount of PpIX in the reconstructed images was constant to within 30% when spheroid depth was varied. In vivo tumor-to-normal contrast was greater than ∼1.5 in reduced scattering coefficient for all wavelengths and was ∼1.3 for the tissue concentration of deoxyhemoglobin (ctHb). The study demonstrates the feasibility of SFDI for providing enhanced image guidance during surgical resection of brain tumors.

Visible spatial frequency domain imaging with a digital light microprojector

Abstract. There is a need for cost effective, quantitative tissue spectroscopy and imaging systems in clinical diagnostics and pre-clinical biomedical research. A platform that utilizes a commercially available light-emitting diode (LED) based projector, cameras, and scaled Monte Carlo model for calculating tissue optical properties is presented. These components are put together to perform spatial frequency domain imaging (SFDI), a model-based reflectance technique that measures and maps absorption coefficients (μa) and reduced scattering coefficients (μs′) in thick tissue such as skin or brain. We validate the performance of the flexible LED and modulation element (FLaME) system at 460, 530, and 632 nm across a range of physiologically relevant μa values (0.07 to 1.5u2009u2009mm−1) in tissue-simulating intralipid phantoms, showing an overall accuracy within 11% of spectrophotometer values for μa and 3% for μs′. Comparison of oxy- and total hemoglobin fits between the FLaME system and a spectrophotometer (450 to 1000 nm) is differed by 3%. Finally, we acquire optical property maps of a mouse brain in vivo with and without an overlying saline well. These results demonstrate the potential of FLaME to perform tissue optical property mapping in visible spectral regions and highlight how the optical clearing effect of saline is correlated to a decrease in μs′ of the skull.

Imaging scattering orientation with spatial frequency domain imaging

Optical imaging techniques based on multiple light scattering generally have poor sensitivity to the orientation and direction of microscopic light scattering structures. In order to address this limitation, we introduce a spatial frequency domain method for imaging contrast from oriented scattering structures by measuring the angular-dependence of structured light reflectance. The measurement is made by projecting sinusoidal patterns of light intensity on a sample, and measuring the degree to which the patterns are blurred as a function of the projection angle. We derive a spatial Fourier domain solution to an anisotropic diffusion model. This solution predicts the effects of bulk scattering orientation on the amplitude and phase of the projected patterns. We introduce a new contrast function based on a scattering orientation index (SOI) which is sensitive to the degree to which light scattering is directionally dependent. We validate the technique using tissue simulating phantoms, and ex vivo samples of muscle and brain. Our results show that SOI is independent of the overall amount of bulk light scattering and absorption, and that isotropic versus oriented scattering structures can be clearly distinguished. We determine the orientation of subsurface microscopic scattering structures located up to 600 μm beneath highly scattering (μ() (s) = 1.5 mm(-1)) material.

Determination of the effect of source intensity profile on speckle contrast using coherent spatial frequency domain imaging

Laser Speckle Imaging (LSI) is fast, noninvasive technique to image particle dynamics in scattering media such as biological tissue. While LSI measurements are independent of the overall intensity of the laser source, we find that spatial variations in the laser source profile can impact measured flow rates. This occurs due to differences in average photon path length across the profile, and is of significant concern because all lasers have some degree of natural Gaussian profile in addition to artifacts potentially caused by projecting optics. Two in vivo measurement are performed to show that flow rates differ based on location with respect to the beam profile. A quantitative analysis is then done through a speckle contrast forward model generated within a coherent Spatial Frequency Domain Imaging (cSFDI) formalism. The model predicts remitted speckle contrast as a function of spatial frequency, optical properties, and scattering dynamics. Comparison with experimental speckle contrast images were done using liquid phantoms with known optical properties for three common beam shapes. cSFDI is found to accurately predict speckle contrast for all beam shapes to within 5% root mean square error. Suggestions for improving beam homogeneity are given, including a widening of the natural beam Gaussian, proper diffusing glass spreading, and flat top shaping using microlens arrays.

Spectrally-resolved imaging of dynamic turbid media

We present a rapid, noncontact imaging technique which can obtain the spectrally- and spatially-resolved scattering and absorption coefficients of a turbid medium. The measurement involves combining a spatially modulated illumination pattern with a snapshot imaging spectrometer for measurement. After capture of an (x, y, λ) datacube, an image demodulation scheme is applied in post-processing to obtain the spatial maps of diffuse reflectance, absorption coefficient, and reduced scattering coefficient. The resulting system is used to dynamic maps (in 1 s intervals) of the brains intrinsic optical signal.

Hyperspectral optical tomography of intrinsic signals in the rat cortex

Abstract. We introduce a tomographic approach for three-dimensional imaging of evoked hemodynamic activity, using broadband illumination and diffuse optical tomography (DOT) image reconstruction. Changes in diffuse reflectance in the rat somatosensory cortex due to stimulation of a single whisker were imaged at a frame rate of 5 Hz using a hyperspectral image mapping spectrometer. In each frame, images in 38 wavelength bands from 484 to 652 nm were acquired simultaneously. For data analysis, we developed a hyperspectral DOT algorithm that used the Rytov approximation to quantify changes in tissue concentration of oxyhemoglobin (ctHbO2) and deoxyhemoglobin (ctHb) in three dimensions. Using this algorithm, the maximum changes in ctHbO2 and ctHb were found to occur at 0.29±0.02 and 0.66±0.04u2009u2009mm beneath the surface of the cortex, respectively. Rytov tomographic reconstructions revealed maximal spatially localized increases and decreases in ctHbO2 and ctHb of 321±53 and 555±96u2009u2009nM, respectively, with these maximum changes occurring at 4±0.2u2009u2009s poststimulus. The localized optical signals from the Rytov approximation were greater than those from modified Beer–Lambert, likely due in part to the inability of planar reflectance to account for partial volume effects.

Fluorescence Optical Tomography of Preclinical Glioma Models Using Spatial Frequency Domain Imaging

Spatial frequency domain imaging of 5-aminolevulinic acid induced protoporphyrin IX was used to recover absorption, scattering, and fluorescence properties of glioblastoma multiforme in tissue-simulating phantoms and in vivo in a mouse model.