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Significance Spatial 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. Aim This 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. Approach Using 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. Results Characterizing 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%. Conclusions We 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. Funding: Knut and Alice Wallenberg Foundations Center for Molecular Medicine at Linkoeping University (WCMM)

Significance: Tissue simulating phantoms are an important part of validating biomedical optical techniques. Tissue pathology in inflammation and oedema involves changes in both water and hemoglobin fractions. Aim: We present a method to create solid gelatin-based phantoms mimicking inflammation and oedema with adjustable water and hemoglobin fractions. Approach: One store-bought gelatin and one research grade gelatin were evaluated. Different water fractions were obtained by varying the water-to-gelatin ratio. Ferrous stabilized human hemoglobin or whole human blood was added as absorbers, and the stability and characteristics of each were compared. Intralipid® was used as the scatterer. All phantoms were characterized using spatial frequency domain spectroscopy. Results: The estimated water fraction varied linearly with expected values (R2 = 0.96 for the store-bought gelatin and R2 = 0.99 for the research grade gelatin). Phantoms including ferrous stabilized hemoglobin stayed stable up to one day but had methemoglobin present at day 0. The phantoms with whole blood remained stable up to 3 days using the store-bought gelatin. Conclusions: A range of physiological relevant water fractions was obtained for both gelatin types, with the stability of the phantoms including hemoglobin differing between the gelatin type and hemoglobin preparation. These low-cost phantoms can incorporate other water-based chromophores and be fabricated as thin sheets to form multilayered structures. Funding: This research was financially supported by Knut and Alice Wallenberg Foundation’s Center for Molecular Medicine at Linkoping University (WCMM) and Hudfonden’s Edvard Welander och Finsenstiftelsen.

Clinical studies have demonstrated that epidermal pigmentation level can affect cerebral oximetry measurements. To evaluate the robustness of these devices, we have developed a phantom-based test method that includes an epidermis-simulating layer with several melanin concentrations and a 3D-printed cerebrovascular module. Measurements were performed with neonatal, pediatric and adult sensors from two commercial oximeters, where neonatal probes had shorter source-detector separation distances. Referenced blood oxygenation levels ranged from 30 to 90%. Cerebral oximeter outputs exhibited a consistent decrease in saturation level with simulated melanin content; this effect was greatest at low saturation levels, producing a change of up to 15%. Dependence on pigmentation was strongest in a neonatal sensor, possibly due to its high reflectivity. Overall, our findings indicate that a modular channel-array phantom approach can provide a practical tool for assessing the impact of skin pigmentation on cerebral oximeter performance and that modifications to algorithms and/or instrumentation may be needed to mitigate pigmentation bias. Funding: FDA Office of Minority Health and Health Equity and FDA Perinatal Health Center of Excellence

Significance: For optical methods to accurately assess hemoglobin oxygen saturation in vivo, an independently verifiable tissue-like standard is required for validation. For this purpose, we propose three hemoglobin preparations and evaluate methods to characterize them. Aim: To spectrally characterize three different hemoglobin preparations using multiple spectroscopic methods and to compare their absorption spectra to commonly used reference spectra. Approach: Absorption spectra of three hemoglobin preparations in solution were characterized using spectroscopic collimated transmission: whole blood, lysed blood, and ferrous-stabilized hemoglobin. Tissue-mimicking phantoms composed of Intralipid, and the hemoglobin solutions were characterized using spatial frequency-domain spectroscopy (SFDS) and enhanced perfusion and oxygen saturation (EPOS) techniques while using yeast to deplete oxygen. Results: All hemoglobin preparations exhibited similar absorption spectra when accounting for methemoglobin and scattering in their oxyhemoglobin and deoxyhemoglobin forms, respectively. However, systematic differences were observed in the fitting depending on the reference spectra used. For the tissue-mimicking phantoms, SFDS measurements at the surface of the phantom were affected by oxygen diffusion at the interface with air, associated with higher values than for the EPOS system. Conclusions: We show the validity of different blood phantoms and what considerations need to be addressed in each case to utilize them equivalently. Funding: This research was financially supported by VINNOVA grants via the Swelife and MedTech4Health programs (Grant Nos. 2016-02211, 2017-01435, and 2019-01522) and the Knut and Alice Wallenberg Foundation’s Center for Molecular Medicine at Linköping University (WCMM).

Autologous keratinocytes or stem cell based therapies are modern approaches for the treatment of skin loss in burn victims and chronic wound patients. The aim of this study is to identify depth-resolved structural changes in treated burn wounds using Spatial Frequency Domain Imaging (SFDI). When altering the investigated depth into tissue via the spatial frequency used in our calculations, we found changes in the scattering parameters for the treated samples. These scattering changes are correlated with histology, indicating a potential means to monitor re-epithelization and collagen formation during the treatment process across the entire wound area.

Detection of scattering and absorption properties in both visible and near-infrared regions are crucial to quantify multiple functional responses in tissue. We developed a compact, clinical spatial frequency domain imaging (SFDI) system around a custom, nine wavelength, compound-eye camera, spanning ~450-1000nm. In addition to the characterization and validation of this device, we performed a preliminary in-vivo investigation to evaluate the imager’s ability to characterize dermal response under a noxious heating protocol. Increases in hemoglobin and water concentration are detected as well as slight alterations in the reduced scattering spectrum that maybe correlated with cellular and extra-cellular reactivity.

Significance: Assessment of disease using optical coherence tomography is an actively investigated problem, owing to many unresolved challenges in early disease detection, diagnosis, and treatment response monitoring. The early manifestation of disease or precancer is typically associated with subtle alterations in the tissue dielectric and ultrastructural morphology. In addition, biological tissue is known to have ultrastructural multifractality. Aim: Detection and characterization of nanosensitive structural morphology and multifractality in the tissue submicron structure. Quantification of nanosensitive multifractality and its alteration in progression of tumor. Approach: We have developed a label free nanosensitive multifractal detrended fluctuation analysis(nsMFDFA) technique in combination with multifractal analysis and nanosensitive optical coherence tomography (nsOCT). The proposed method deployed for extraction and quantification of nanosensitive multifractal parameters in mammary fat pad (MFP). Results: Initially, the nsOCT approach is numerically validated on synthetic submicron axial structures. The nsOCT technique was applied to pathologically characterized MFP of murine breast tissue to extract depth-resolved nanosensitive submicron structures. Subsequently, two-dimensional MFDFA were deployed on submicron structural en face images to extract nanosensitive tissue multifractality. We found that nanosensitive multifractality increases in transition from healthy to tumor. Conclusions: This method for extraction of nanosensitive tissue multifractality promises to provide a noninvasive diagnostic tool for early disease detection and monitoring treatment response. The novel ability to delineate the dominant submicron scale nanosensitive multifractal properties may also prove useful for characterizing a wide variety of complex scattering media of non-biological origin.

Significance: Spatial frequency domain imaging (SFDI) is a quantitative imaging method to measure absorption and scattering of tissue, from which several chromophore concentrations (e.g., oxy-/deoxy-/meth-hemoglobin, melanin, and carotenoids) can be calculated. Employing a method to extract additional spectral bands from RGB components (that we named cross-channels), we designed a handheld SFDI device to account for these pigments, using low-cost, consumer-grade components for its implementation and characterization. Aim: With only three broad spectral bands (red, green, blue, or RGB), consumer-grade devices are often too limited. We present a methodology to increase the number of spectral bands in SFDI devices that use RGB components without hardware modification. Approach: We developed a compact low-cost RGB spectral imager using a color CMOS camera and LED-based mini projector. The components’ spectral properties were characterized and additional cross-channel bands were calculated. An alternative characterization procedure was also developed that makes use of low-cost equipment, and its results were compared. The device performance was evaluated by measurements on tissue-simulating optical phantoms and in-vivo tissue. The measurements were compared with another quantitative spectroscopy method: spatial frequency domain spectroscopy (SFDS). Results: Out of six possible cross-channel bands, two were evaluated to be suitable for our application and were fully characterized (520 ± 20 nm; 556 ± 18 nm). The other four cross-channels presented a too low signal-to-noise ratio for this implementation. In estimating the optical properties of optical phantoms, the SFDI data have a strong linear correlation with the SFDS data (R2 = 0.987, RMSE = 0.006 for μa, R2 = 0.994, RMSE = 0.078 for μs′). Conclusions: We extracted two additional spectral bands from a commercial RGB system at no cost. There was good agreement between our device and the research-grade SFDS system. The alternative characterization procedure we have presented allowed us to measure the spectral features of the system with an accuracy comparable to standard laboratory equipment. Funding agencies: Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation

We have optimized our prior phantom-based test method for cerebral oximetry performance using a new 3D-printed cerebrovascular module (CVM). In addition, we have and added a surrogate for a thin perfused scalp layer to evaluate perfusion- related confounding factors. The new CVM’s optical properties better represented biological tissue and also incorporated a water-mimicking dye. The modular phantom also included biologically relevant scalp/skull and cerebrospinal fluid (CSF) layers. Performance testing of two commercially available clinical oximeters with the modified CVM over a range of oxygen saturation levels illustrates the utility of our solid phantom-based approach for standardized cerebral oximeter performance assessment.

Spatial Frequency Domain Imaging (SFDI) is a quantitative imaging method that measures optical properties of tissue. We present the design of a compact spectral imager to perform SFDI in low resource settings, which exploits a low-cost color CMOS camera and mini-projector. These devices are usually limited to three broad spectral bands (RGB). We have developed a novel method to extrapolate two additional wavelengths without hardware modifications, improving the spectral resolution of the device, allowing to account for additional sources of skin pigmentation. Our device performance was evaluated on tissue-simulating phantoms. In-vivo measurements were compared to a commercial probe-based system (EPOS).

Micro-projection array patches (MAPs) are an alternative approach to deliver vaccine without using needles and syringe. MAPs achieve improved vaccination efficiency by introducing a microtrauma in the skin, but a comprehensive understanding of all mechanisms behind this response remains elusive. Spatial frequency domain spectroscopy (SFDS) was used to quantify skin reactivity. This optical technique enables characterization of the skin response by identifying (1) functional tissue parameters, (2) changes in tissue structure and (3) measures of tissue damage. In a preliminary investigation, measurements were performed on 12 subjects in whom the MAP was applied on the lower forearm.

Assessment of disease using OCT is an actively investigated problem, owing to many unresolved challenges in early disease detection, diagnosis and treatment response monitoring. The spatial scale to which the information can be obtained from the scattered light is limited by the diffraction limit (~λ/2; λ = wavelength of light is typically in the micron level) and the axial resolution of OCT systems is limited by the inverse of spectral bandwidth. Yet, onset or progression of disease /precancer is typically associated with subtle alterations in the tissue dielectric and its ultra-structural morphology. On the other hand, biological tissue is known to have ultra-structural multifractality. For both the fundamental study of biological processes and early diagnosis of pathological processes, information on the nanoscale in the tissue sub-micron structural morphology is crucial. Therefore, we have developed a novel spectroscopic and label-free 3D OCT system with nanoscale sensitivity in combination of multifractal analysis for extraction and quantification of tissue ultra-structural multifractal parameters. This present approach demonstrated its capability to measure nano-sensitive tissue ultra-structural multifractality. In an initial study, we found that nano-sensitive sub-micron structural multifractality changes in transition from healthy to tumor in pathologically characterized fresh tissue samples. This novel method for extraction of nanosensitive tissue multifractality promises to develop a non-invasive diagnosis tool for early cancer detection.

Obesity leads to a higher risk of diabetes and cardiovascular diseases. Wearable devices can be used to manage and promote the healthy lifestyle among the obese by measuring heart rate, heart rate variability, perfusion, and pressure pulse-wave velocities. While operational challenges are common in wearable devices using electrical or thermal sensors, those with optical sensors are more robust. Current optical sensors rely on fluctuations in light intensity due to spatio-temporal variations in tissue absorption. The thick layer of adipose tissue in high body mass index (BMI) individuals strongly scatters light, reducing the optical contrast and signal to noise ratio. Moreover, higher BMI alters chemical concentrations— like water, oxygenation, and blood volume in the dermal layer— and thus the optical properties (OP). Although OP of the skin exists in literature, no study has strictly recorded the effect and magnitude of a higher BMI on them. In this study, we combine the spatial frequency domain spectroscopy (SFDS) with a multi-sensor blood flow imaging device (PulseCam) to characterize the OPs and monitor the vascularization in the obese. The effects of skin morphology and physiology on the performance of optical sensor are preliminarily investigated.

Author(s): Ponticorvo, Adrien; Burmeister, David M; Rowland, Rebecca; Baldado, Melissa; Kennedy, Gordon T; Saager, Rolf; Bernal, Nicole; Choi, Bernard; Durkin, Anthony J | Abstract: The current standard for diagnosis of burn severity and subsequent wound healing is through clinical examination, which is highly subjective. Several new technologies are shifting focus to burn care in an attempt to help quantify not only burn depth but also the progress of healing. While accurate early assessment of partial thickness burns is critical for dictating the course of treatment, the ability to quantitatively monitor wound status over time is critical for understanding treatment efficacy. SFDI and LSI are both non-invasive imaging modalities that have been shown to have great diagnostic value for burn severity, but have yet to be tested over the course of wound healing.In this study, a hairless rat model (n = 6, 300-450 g) was used with a four pronged comb to create four identical partial thickness burns (superficial n = 3 and deep n = 3) that were used to monitor wound healing over a 28 days period. Weekly biopsies were taken for histological analysis to verify wound progression. Both SFDI and LSI were performed weekly to track the evolution of hemodynamic (blood flow and oxygen saturation) and structural (reduced scattering coefficient) properties for the burns.LSI showed significant changes in blood flow from baseline to 220% in superficial and 165% in deep burns by day 7. In superficial burns, blood flow returned to baseline levels by day 28, but not for deep burns where blood flow remained elevated. Smaller increases in blood flow were also observed in the surrounding tissue over the same time period. Oxygen saturation values measured with SFDI showed a progressive increase from baseline values of 66-74% in superficial burns and 72% in deep burns by day 28. Additionally, SFDI showed significant decreases in the reduced scattering coefficient shortly after the burns were created. The scattering coefficient progressively decreased in the wound area, but returned towards baseline conditions at the end of the 28 days period. Scattering changes in the surrounding tissue remained constant despite the presence of hemodynamic changes.Here, we show that LSI and SFDI are capable of monitoring changes in hemodynamic and scattering properties in burn wounds over a 28 days period. These results highlight the potential insights that can be gained by using non-invasive imaging technologies to study wound healing. Further development of these technologies could be revolutionary for wound monitoring and studying the efficacy of different treatments. Lasers Surg. Med. 49:293-304, 2017. © 2017 Wiley Periodicals, Inc.

Significance: Spatial frequency domain imaging (SFDI) is a diffuse optical measurement technique that can quantify tissue optical absorption (μa) and reduced scattering (μ0 s) on a pixelby-pixel basis. Measurements of μa at different wavelengths enable the extraction of molar concentrations of tissue chromophores over a wide field, providing a noncontact and label-free means to assess tissue viability, oxygenation, microarchitecture, and molecular content. We present here openSFDI: an open-source guide for building a low-cost, small-footprint, threewavelength SFDI system capable of quantifying μa and μ0 s as well as oxyhemoglobin and deoxyhemoglobin concentrations in biological tissue. The companion website provides a complete parts list along with detailed instructions for assembling the openSFDI system. Aim: We describe the design of openSFDI and report on the accuracy and precision of optical property extractions for three different systems fabricated according to the instructions on the openSFDI website. Approach: Accuracy was assessed by measuring nine tissue-simulating optical phantoms with a physiologically relevant range of μa and μ0 s with the openSFDI systems and a commercial SFDI device. Precision was assessed by repeatedly measuring the same phantom over 1 h. Results: The openSFDI systems had an error of 0 6% in μa and −2 3% in μ0 s, compared to a commercial SFDI system. Bland–Altman analysis revealed the limits of agreement between the two systems to be 0.004 mm−1 for μa and −0.06 to 0.1 mm−1 for μ0 s. The openSFDI system had low drift with an average standard deviation of 0.0007 mm−1 and 0.05 mm−1 in μa and μ0 s, respectively. Conclusion: The openSFDI provides a customizable hardware platform for research groups seeking to utilize SFDI for quantitative diffuse optical imaging. Funding agencies: U.S. Department of Defense (DoD)United States Department of Defense [W81XWH-15-1-0070]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; European Research Council under the European UnionEuropean Research Council (ERC) [715737]; Fre

The aim of this study was to determine the optical absorption and scattering properties in a large Swedish cohort including 1765 subjects. The study was performed in the Linkoping site within the national multicenter Swedish CArdioPulmonary bioImage Study (SCAPIS), a world unique study including detailed imaging and functional analysis of heart, vessels and lungs in 30 000 men and women in Sweden to predict and prevent cardiovascular disease and chronic obstructive pulmonary disease. The subjects, men and women between 50 and 64 years old, were randomly selected and recruited from the population registry in Sweden. Measurements on the volar forearm were performed at baseline and during a systolic occlusion provocation with an integrated system, including spatially resolved diffuse reflectance spectroscopy and laser Doppler flowmetry. Data were analyzed with an inverse Monte Carlo algorithm, accounting for both scattering, geometrical and absorbing properties of the tissue. The absorption coefficient was assumed to differ between the epidermis and the two dermis layers, while the reduced scattering coefficient was equal in all layers. The reduced scattering coefficient (@ 650 nm) was (M ± SD) = 1.68 ± 0.34 mm-1. Gender was found to significant change the fraction of small scattering particles and the reduced scattering coefficient. The absorption coefficient (@ 650 nm) for the dermis layers was 0.010 ± 0.005 mm-1. This large study on optical properties of skin can serve as reference values and provide new knowledge on how factors like gender, age, BMI etc. affect the optical properties.

Cerebral oximetry based on near-infrared spectroscopy (NIRS) has seen increasing clinical use for monitoring of premature infants as well as during neonatal, pediatric and adult cardiac surgery. One key confounding factor and a likely contributor to observed inconsistency amongst commercial NIRS oximeters is skin pigmentation. Clinical studies have shown negative bias in oxygen saturation (StO2) with increasing melanin content. In prior work, we developed a cerebral oximetry phantom comprised of a 3D-printed channel array module representing brain tissue and molded silicone layers simulating extracranial regions. The purpose of the current study was to develop and test epidermis-simulating layers that exhibit realistic human pigmentation properties. Initially, we performed spectroscopic characterization of potential melanin simulating agents – including coffee, India ink, synthetic melanin, and water-soluble nigrosin – in a polydimethylsiloxane (PDMS) substrate. We determined that the NIR absorption spectrum of water-soluble nigrosin most accurately matched human melanin. Layers of 0.1 mm thickness were fabricated with different nigrosin concentrations to simulate epidermis with light, moderate, and dark pigmentation. The brain module channels were filled with bovine blood in the 30-100% oxygenation range and measurements performed with neonatal/pediatric probes from commercially available cerebral oximeters. We found that StO2 reported by the oximeters decreased monotonically with increasing pigmentation level. The magnitude of this impact increased with decreasing StO2, producing a maximum change in saturation of approximately 8%. The consistency of our results with prior clinical findings provides preliminary evidence of the utility of our approach for assessing the impact of epidermal melanin in phantom-based performance testing.

Spectroscopic imaging of human tissue analyzes backscattered light intensity separated by wavelength. We used a DLP-projector illuminating sinusoidal patterns with varying phase and varying spatial frequency on forearm skin. Detection was done with: 1) a snap-shot filter mosaic camera with 16 wide-band sensitive pixels; 2-3) a four cameras setup with narrow and wide bandwidth optical bandpass filters in the 450-700 nm range, respectively. The detected images were processed with a demodulation scheme, assessing tissue optical parameters, involving light absorption. Calibration was done using an optical phantom with known optical properties. From the absorption coefficient the concentration of skin blood and its oxygenation was determined. We will present results from forearm arterial occlusion and release experiments using the three setups above. Specifically, the effect of the filter bandwidth will be evaluated using data from the multi-camera setups. Furthermore, the snap-shot filter mosaic camera data may be explained by the calculation of modulation using an illumination and detector setup with a broad spectral transmission bandwidth, with considerable variation in μ_a of included chromophores. Approaches for either reducing the effective bandwidth of the filters or by including their characteristic in a light transport model for SFDI modulation, will be proposed.

Burn wounds and wound healing invoke several biological processes that may complicate the interpretation of spectral imaging data. Through analysis of spatial frequency domain spectroscopy data (450 to 1000nm) obtained from longitudinal investigations using a graded porcine burn wound healing model, we have identified features in the absorption spectrum that appear to suggest the presence of hemoglobin breakdown products, e.g., methemoglobin. Our results show that the calculated concentrations of methemoglobin directly correlate with burn severity, 24h after the injury. In addition, tissue parameters such as oxygenation (StO2) and water fraction may be underestimated by 20% and 78%, respectively, if methemoglobin is not included in the spectral analysis.

We introduce a method for quantitative hyperspectral optical imaging in the spatial frequency domain (hs-SFDI) to image tissue absorption (μa) and reduced scattering (μs') parameters over a broad spectral range. The hs-SFDI utilizes principles of spatial scanning of the spectrally dispersed output of a supercontinuum laser that is sinusoidally projected onto the tissue using a digital micromirror device. A scientific complementary metal-oxide-semiconductor camera is used for capturing images that are demodulated and analyzed using SFDI computational models. The hs-SFDI performance is validated using tissue-simulating phantoms over a range of μa and μs' values. Quantitative hs-SFDI images are obtained from an ex-vivo beef sample to spatially resolve concentrations of oxy-, deoxy-, and met-hemoglobin, as well as water and fat fractions. Our results demonstrate that the hs-SFDI can quantitatively image tissue optical properties with 1000 spectral bins in the 580- to 950-nm range over a wide, scalable field of view. With an average accuracy of 6.7% and 12.3% in μa and μs', respectively, compared to conventional methods, hs-SFDI offers a promising approach for quantitative hyperspectral tissue optical imaging. Funding agencies: National Institute of Health (NIH) NIBIB Biomedical Technology Research Center LAMMP [P41EB015890]; NIH [R21EB020953]; Military Medical Photonics Program: AFOSR [FA9550-17-1-0193]; Arnold and Mabel Beckman Foundation

We present a method to recover absorption and reduced scattering spectra for each layer of a two-layer turbid media from spatial frequency-domain spectroscopy data. We focus on systems in which the thickness of the top layer is less than the transport mean free path ( 0.1 − 0.8l * ) . We utilize an analytic forward solver, based upon the N’th-order spherical harmonic expansion with Fourier decomposition ( SHEFN ) method in conjunction with a multistage inverse solver. We test our method with data obtained using spatial frequency-domain spectroscopy with 32 evenly spaced wavelengths within λ = 450 to 1000 nm on six-layered tissue phantoms with distinct optical properties. We demonstrate that this approach can recover absorption and reduced scattering coefficient spectra for both layers with accuracy comparable with current Monte Carlo methods but with lower computational cost and potential flexibility to easily handle variations in parameters such as the scattering phase function or material refractive index. To our knowledge, this approach utilizes the most accurate deterministic forward solver used in such problems and can successfully recover properties from a two-layer media with superficial layer thicknesses.

Spatial frequency domain imaging (SFDI) utilizes a digital light processing (DLP) projector for illuminating turbid media with sinusoidal patterns. The tissue absorption (μ a ) and reduced scattering coefficient (μ , s ) are calculated by analyzing the modulation transfer function for at least two spatial frequencies. We evaluated different illumination strategies with a red, green and blue light emitting diodes (LED) in the DLP, while imaging with a filter mosaic camera, XiSpec, with 16 different multi-wavelength sensitive pixels in the 470-630 nm wavelength range. Data were compared to SFDI by a multispectral camera setup (MSI) consisting of four cameras with bandpass filters centered at 475, 560, 580 and 650 nm. A pointwise system for comprehensive microcirculation analysis was used (EPOS) for comparison. A 5-min arterial occlusion and release protocol on the forearm of a Caucasian male with fair skin was analyzed by fitting the absorption spectra of the chromophores HbO 2 , Hb and melanin to the estimatedμ a . The tissue fractions of red blood cells ( f RBC), melanin (/mel) and the Hb oxygenation ( S 0 2 ) were calculated at baseline, end of occlusion, early after release and late after release. EPOS results showed a decrease in S 0 2 during the occlusion and hyperemia during release ( S 0 2 = 40%, 5%, 80% and 51%). The f RBC showed an increase during occlusion and release phases. The best MSI resemblance to the EPOS was for green LED illumination ( S 0 2 = 53%, 9%, 82%, 65%). Several illumination and analysis strategies using the XiSpec gave un-physiological results (e.g. negative S 0 2 ). XiSpec with green LED illumination gave the expected change in /RBC , while the dynamics in S 0 2 were less than those for EPOS. These results may be explained by the calculation of modulation using an illumination and detector setup with a broad spectral transmission bandwidth, with considerable variation in μ a of included chromophores. Approaches for either reducing the effective bandwidth of the XiSpec filters or by including their characteristic in a light transport model for SFDI modulation, are proposed.

Hyperspectral Imaging (HSI) is a growing field in tissue optics due to its ability to collect continuous spectral features of a sample without a contact probe. Spatial Frequency Domain Imaging (SFDI) is a non-contact wide-field spectral imaging technique that is used to quantitatively characterize tissue structure and chromophore concentration. In this study, we designed a Hyperspectral SFDI (H-SFDI) instrument which integrated a supercontinuum laser source to a wavelength tuning optical configuration and a sCMOS camera to extract spatial (Field of View: 2cm×2cm) and broadband spectral features (580nm-950nm). A preliminary experiment was also performed to integrate the hyperspectral projection unit to a compressed single pixel camera and Light Labeling (LiLa) technique.

With recent proliferation in compact and/or low-cost clinical multispectral imaging approaches and commercially available components, questions remain whether they adequately capture the requisite spectral content of their applications. We present a method to emulate the spectral range and resolution of a variety of multispectral imagers, based on in-vivo data acquired from spatial frequency domain spectroscopy (SFDS). This approach simulates spectral responses over 400 to 1100 nm. Comparing emulated data with full SFDS spectra of in-vivo tissue affords the opportunity to evaluate whether the sparse spectral content of these imagers can (1) account for all sources of optical contrast present (completeness) and (2) robustly separate and quantify sources of optical contrast (crosstalk). We validate the approach over a range of tissue-simulating phantoms, comparing the SFDS-based emulated spectra against measurements from an independently characterized multispectral imager. Emulated results match the imager across all phantoms ([Formula: see text] absorption, [Formula: see text] reduced scattering). In-vivo test cases (burn wounds and photoaging) illustrate how SFDS can be used to evaluate different multispectral imagers. This approach provides an in-vivo measurement method to evaluate the performance of multispectral imagers specific to their targeted clinical applications and can assist in the design and optimization of new spectral imaging devices.

© 2017 Author(s). Spatial Frequency Domain Spectroscopy (SFDS) is a technique for quantifying in-vivo tissue optical properties. SFDS employs structured light patterns that are projected onto tissues using a spatial light modulator, such as a digital micromirror device. In combination with appropriate models of light propagation, this technique can be used to quantify tissue optical properties (absorption, μa, and scattering, μs′, coefficients) and chromophore concentrations. Here we present a handheld implementation of an SFDS device that employs line (one dimensional) imaging. This instrument can measure 1088 spatial locations that span a 3 cm line as opposed to our original benchtop SFDS system that only collects a single 1 mm diameter spot. This imager, however, retains the spectral resolution (∼1 nm) and range (450-1000 nm) of our original benchtop SFDS device. In the context of homogeneous turbid media, we demonstrate that this new system matches the spectral response of our original system to within 1% across a typical range of spatial frequencies (0-0.35 mm-1). With the new form factor, the device has tremendously improved mobility and portability, allowing for greater ease of use in a clinical setting. A smaller size also enables access to different tissue locations, which increases the flexibility of the device. The design of this portable system not only enables SFDS to be used in clinical settings but also enables visualization of properties of layered tissues such as skin.

Tissue simulating phantoms provide a valuable platform for quantitative evaluation of the performance of diffuse optical devices. In this paper we report the development of a poly(dimethylsiloxane) (PDMS) tissue phantom that mimics the spectral characteristics of tissue water. We have developed these phantoms to mimic different water fractions in tissue for testing new devices within the context of clinical applications such as burn wound triage. Compared to liquid phantoms, PDMS phantoms are easier to transport and use, and have a longer usable life than gelatin based phantoms. The pthalocyanine dye 9606 was used to provide an absorption feature of in the vicinity of 970 nm. Scattering properties were independently determined by adding titanium dioxide powder to obtain reduced scattering coefficients similar to that of tissue in the near infrared. Phantom properties were characterized using the techniques of inverse adding doubling and spatial frequency domain imaging. Results presented here demonstrate that we can fabricate solid phantoms that can be used to simulate different water fractions.

A fiber probe-based device for assessing microcirculatory parameters, especially red blood cell (RBC) tissue fraction, their oxygen saturation and speed resolved perfusion, has been evaluated using state-of-the-art multi-layer tissue simulating phantoms. The device comprises both diffuse reflectance spectroscopy (DRS) at two source-detector separations (0.4 and 1.2 mm) and laser Doppler flowmetry (LDF) and use an inverse Monte Carlo method for identifying the parameters of a multi-layered tissue model. First, model parameters affecting scattering, absorption and geometrical parameters are fitted to measured DRS spectra, then speed parameters are fitted to LDF spectra. In this paper, the accuracy of the spectral parameters is evaluated. The measured spectral shapes at the two source-detector separations were in good agreement with forward calculated spectral shapes. In conclusion, the multi-layer skin model based on spectral features of the included chromophores, can reliably estimate the tissue fraction of RBC, its oxygen saturation and the reduced scattering coefficient spectrum of the tissue. Furthermore, it was concluded that some freedom in the relative intensity difference between the two DRS channels is necessary in order to compensate for non-modeled surface structure effects.

© 2017 SPIE. Here we present a handheld, implementation of Spatial Frequency Domain Spectroscopy (SFDS) that employs line imaging. The new instrument can measure 1088 spatial locations that span a 3 cm line as opposed to our benchtop system that only collects a single 1 mm diameter spot. This imager, however, retains the spectral resolution (∼ 1 nm) and range (450 to 1000 nm) of our benchtop system. The device also has tremendously improved mobility and portability, allowing for greater ease of use in clinical setting. A smaller size also enables access to different tissue locations, which increases the flexibility of the device. The design of this portable system not only enables SFDS to be used in clinical settings, but also enables visualization of properties of layered tissues such as skin.

Rationale and Objectives The treatment of nonmelanoma skin cancer (NMSC) is usually by surgical excision or Mohs micrographic surgery and alternatively may include photodynamic therapy (PDT). To guide surgery and to optimize PDT, information about the tumor structure, optical parameters, and vasculature is desired. Materials and Methods Spatial frequency domain imaging (SFDI) can map optical absorption, scattering, and fluorescence parameters that can enhance tumor contrast and quantify light and photosensitizer dose. High frequency ultrasound (HFUS) imaging can provide high-resolution tumor structure and depth, which is useful for both surgery and PDT planning. Results Here, we present preliminary results from our recently developed clinical instrument for patients with NMSC. We quantified optical absorption and scattering, blood oxygen saturation (StO 2 ), and total hemoglobin concentration (THC) with SFDI and lesion thickness with ultrasound. These results were compared to histological thickness of excised tumor sections. Conclusions SFDI quantified optical parameters with high precision, and multiwavelength analysis enabled 2D mappings of tissue StO 2 and THC. HFUS quantified tumor thickness that correlated well with histology. The results demonstrate the feasibility of the instrument for noninvasive mapping of optical, physiological, and ultrasound contrasts in human skin tumors for surgery guidance and therapy planning.

IntroductionThe current standard for diagnosis of burn severity and subsequent wound healing is through clinical examination, which is highly subjective. Several new technologies focus on burn care ...

Background: Photodynamic therapy (PDT) offers the potential for enhanced treatment of nonmelanoma skin cancer (NMSC) with minimal scarring. Yet, PDT has not achieved consistent long term effectiveness to gain widespread clinical acceptance for treatment of skin cancer. Therapeutic response varies between practitioners, patients and lesions. One important contributing factor is theabsence of quantitative toolsto performin vivo dosimetry. To this end, we have developed a new quantitativeimaging devicethatcanbeused toinvestigate parameters related to optimizing dosimetry. Methods: We present a spatial frequency domain imaging (SFDI) based device designed to: (1) determine the optical properties at the therapeutic wavelength, which can inform variations in light penetration depth and (2) measure the spatially resolved oxygen saturation of the skin cancer lesions and surrounding tissue. We have applied this system to a preliminary clinical study of nine skin cancer lesions. Results: Optical properties vary greatly both spatially [101%, 48% for absorption and reduced scattering, respectively] and across patients [102%, 57%]. Blood volume maps determined using visible wavelengths (460, 525, and 630 nm) represent tissue volumes within � 1m m in tissue (1.17 � 0.3 mm). Here the average total hemoglobin concentration is approximately three times greater in the lesion than that detected in normal tissue, reflecting increased vasculature typically associated with tumors. Data acquired at near infrared wavelengths (730 and 850 nm) reports tissue blood concentrations and oxygenations from the underlying dermal microvasculature (volumes reaching 4.36 � 1.32 mm into tissue). Conclusions: SFDI can be used to quantitatively characterize in vivo tissue optical properties that could be useful for better informing PDT treatment parameters. Specifically, this information provides spatially resolved insight into light delivery into tissue and local tissue oxygenation, thereby providing more quantitative and controlled dosimetry specific to the lesion. Ultimately, by optimizing the execution of PDT, this instrument has the potentialtopositivelyimprovetreatmentoutcomes.Lasers Surg. Med. 45:207–215. 2013 Wiley Periodicals, Inc.

Background and Objective: Generalized argyria is a blue-gray hyperpigmentation of the skin resulting from ingestion or application of silver compounds, such as silver colloid. Case reports have noted improvement after Q-Switched Neodymium–Yttrium Aluminum Garnet laser (1,064 nm QS Nd:YAG) laser treatment to small surface areas. No reports have objectively monitored laser treatment of generalized argyria over large areas of skin, nor have long-term outcomes been evaluated. Study Design/Materials and Methods: An incremental treatment plan was developed for a subject suffering from argyria. A quantitative near infrared spectroscopic measurement technique was employed to non-invasively analyze tissue-pigment characteristics pre- and post-laser treatment. Post-treatment measurements were collected at weeks 1, 2, 3, and 4, and again at 1 year. Results: Immediate apparent removal of pigment was observed with 1 Q-switched 1,064 nm Nd:YAG laser treatment (3–6 mm spot; 0.8–2 J/cm 2 ) per area. Entire face, neck, upper chest, and arms were treated over multiple sessions. Treatments were very painful and general anesthesia was utilized in order to treat large areas. Near-infrared spectroscopy was used to characterize and quantify the concentration of silver particles in the dermis based on the absorption features of the silver particles as well as the optical scattering effects they impart. We were able to estimate that there was, on average, 0.042 mg/ml concentration of silver prior to treatment and that these levels went below the minimum detectable limit of the instrument post-treatment. There was no recurrence of discoloration over the 1-year study period. Conclusion: QS 1,064 nm laser treatment of argyria is a viable method to restore normal skin pigmentation with no evidence of recurrence over study period. Quantitative spectroscopic measurements: (1) confirmed dyspigmentation was due to silver, (2) validated our clinical assessment of no recurrence up to 1-year post-treatment, and (3) indicated no collateral tissue damage with treatments. Lasers Surg. Med. 2013 Wiley Periodicals, Inc.

The ability to accurately assess burn wound severity in a timely manner is a critical component of wound management as it dictates the course of treatment. While full thickness and superficial burns can be easily diagnosed through visual inspection, burns that fall in between these categories are difficult to classify. Additionally, the ability to better quantify different stages of wound healing from a burn of any severity would be important for evaluating the efficacy of different treatment options. Here we present a longitudinal (28 day) study that employs spatial frequency domain imaging (SFDI) and laser speckle imaging (LSI) as non-invasive technologies to characterize in-vivo burn wounds and healing in a murine model. Burn wounds were created using an established technique of a brass comb heated to a given temperature and applied for a set amount of time. They were imaged immediately after the initial injury and then at 2, 4, 7, 14, 21, and 28 days following the injury. Biopsies were taken on the day of the injury in order to verify the extent of the burn damage as well as at different time points after the injury in order to visualize different stages of inflammation and healing. The results of this study suggest that the reduced scattering coefficient measured using SFDI and blood flow as measured using LSI have the potential to provide useful metrics for quantifying the severity of burn injuries as well as track the different stages associated with wound healing progression.

Tissue-simulating phantoms provide the opportunity to evaluate the performance of optical and spectroscopic instruments under controlled experimental conditions. Recent efforts have advanced phantom fabrication methods to provide more tissue realistic phantoms, both in terms of a) incorporating absorbing agents that more faithfully mimic in vivo tissue chromophores spanning visible and near infrared regimes and b) accounting for multi-layer tissue structures with distinct optical properties. The spectral scattering properties in these phantoms, however, are typically based only on a single scattering agent, thereby locking the spectral scattering properties to a single particle size distribution. However, in both healthy tissue as well as pathologic tissue, regions of distinct and differentiated scattering may be present. With differing mean size and distribution of scattering objects in these tissue regions, the relative wavelength-dependent scattering spectra may vary. For example, partial thickness burns exhibit significant cellular damage and collagen denaturation that will significantly alter the wavelength-dependent scattering properties resembling large Mie-like scatterer distributions in both visible and near infrared regimes. We present a low-cost method to fabricate silicone tissue-simulating phantoms with tunable scattering spectra properties that span visible and near infrared wavelengths. We use optical polishing agents (white aluminum oxides powders) at various grit sizes to approximate Mie scattering across multiple mean particle sizes. Mean particle sizes used in this study range from 17-3 micron. The optical properties of these phantoms are verified using an integrating sphere in combination with inverse adding-doubling methods. The tolerances of this fabrication method will be discussed.

Polydimethylsiloxane (PDMS) has been a popular medium to fabricate tissue simulating optical phantoms. Recently, its use has significantly expanded in instrument calibration and performance testing, validation of advanced models of light transport of complex tissue geometries and evaluation of novel measurement modalities. To meet these demands, fabrication methods of these optical phantoms have become more refined and its structure and constituent components (i.e. dyes and scattering agents) have evolved to better mimic optical properties of tissue spanning both visible and near infrared regimes. We present efforts at the Beckman Laser Institute that address these challenges through PDMS phantoms.

Author(s): Yafi, Amr; Vetter, Thomas S; Scholz, Thomas; Patel, Sarin; Saager, Rolf B; Cuccia, David J; Evans, Gregory R; Durkin, Anthony J | Abstract: BackgroundThe purpose of this study was to investigate the capabilities of a novel optical wide-field imaging technology known as spatial frequency domain imaging to quantitatively assess reconstructive tissue status.MethodsTwenty-two cutaneous pedicle flaps were created on 11 rats based on the inferior epigastric vessels. After baseline measurement, all flaps underwent vascular ischemia, induced by clamping the supporting vessels for 2 hours (either arteriovenous or selective venous occlusions); normal saline was injected into the control flap and hypertonic-hyperoncotic saline solution was injected into the experimental flap. Flaps were monitored for 2 hours after reperfusion. The spatial frequency domain imaging system was used for quantitative assessment of flap status over the duration of the experiment.ResultsAll flaps demonstrated a significant decline in oxyhemoglobin and tissue oxygen saturation in response to occlusion. Total hemoglobin and deoxyhemoglobin were increased markedly in the selective venous occlusion group. After reperfusion and the administration of solutions, oxyhemoglobin and tissue oxygen saturation in those flaps that survived gradually returned to baseline levels. However, flaps for which oxyhemoglobin and tissue oxygen saturation did not show any signs of recovery appeared to be compromised and eventually became necrotic within 24 to 48 hours in both occlusion groups.ConclusionsSpatial frequency domain imaging technology provides a quantitative, objective method of assessing tissue status. This study demonstrates the potential of this optical technology to assess tissue perfusion in a very precise and quantitative way, enabling wide-field visualization of physiologic parameters. The results of this study suggest that spatial frequency domain imaging may provide a means for prospectively identifying dysfunctional flaps well in advance of failure.

We present a method for low-cost fabrication of polydimethylsiloxane (PDMS) tissue simulating phantoms with tunable scattering spectra, spanning visible, and near-infrared regimes. These phantoms use optical polishing agents (aluminum oxide powders) at various grit sizes to approximate in vivo tissue scattering particles across multiple size distributions (range: 17 to 3 μm). This class of tunable scattering phantoms is used to mimic distinct changes in wavelength-dependent scattering properties observed in tissue pathologies such as partial thickness burns. Described by a power-law dependence on wavelength, the scattering magnitude of these phantoms scale linearly with particle concentration over a physiologic range [μ's=(0.5 to 2.0 mm−1)] whereas the scattering spectra, specific to each particle size distribution, correlate to distinct exponential coefficients (range: 0.007 to 0.32). Aluminum oxide powders used in this investigation did not detectably contribute to the absorption properties of these phantoms. The optical properties of these phantoms are verified through inverse adding-doubling methods and the tolerances of this fabrication method are discussed.

© 2016 SPIE. We have developed a multimode dermoscope (SkinSpect™) capable of illuminating human skin samples in-vivo with spectrally-programmable linearly-polarized light at 33 wavelengths between 468nm and 857 nm. Diffusely reflected photons are separated into collinear and cross-polarized image paths and images captured for each illumination wavelength. In vivo human skin nevi (N = 20) were evaluated with the multimode dermoscope and melanin and hemoglobin concentrations were compared with Spatially Modulated Quantitative Spectroscopy (SMoQS) measurements. Both systems show low correlation between their melanin and hemoglobin concentrations, demonstrating the ability of the SkinSpectTMto separate these molecular signatures and thus act as a biologically plausible device capable of early onset melanoma detection.

© 2015 The Authors. The combined use of nonlinear optical microscopy and broadband reflectance techniques to assess melanin concentration and distribution thickness in vivo over the full range of Fitzpatrick skin types is presented. Twelve patients were measured using multiphoton microscopy (MPM) and spatial frequency domain spectroscopy (SFDS) on both dorsal forearm and volar arm, which are generally sun-exposed and non-sun-exposed areas, respectively. Both MPM and SFDS measured melanin volume fractions between ∼5% (skin type I non-sun-exposed) and 20% (skin type VI sun exposed). MPM measured epidermal (anatomical) thickness values ∼30.65 μm, while SFDS measured melanin distribution thickness based on diffuse optical path length. There was a strong correlation between melanin concentration and melanin distribution (epidermal) thickness measurements obtained using the two techniques. While SFDS does not have the ability to match the spatial resolution of MPM, this study demonstrates that melanin content as quantified using SFDS is linearly correlated with epidermal melanin as measured using MPM (R2 = 0.8895). SFDS melanin distribution thickness is correlated to MPM values (R2 = 0.8131). These techniques can be used individually and/or in combination to advance our understanding and guide therapies for pigmentation-related conditions as well as light-based treatments across a full range of skin types.

© 2015 Optical Society of America. The dosimetry of light-based therapies critically depends on both optical and vascular parameters. We utilized spatial frequency domain imaging to quantify optical and vascular parameters, as well as estimated light penetration depth from 17 nonmelanoma skin cancer patients. Our data indicates that there exist substantial spatial variations in these parameters. Characterization of these parameters may inform understanding and optimization of the clinical response of light-based therapies.

A polarization-sensitive hyperspectral imaging system (SkinSpect) has been built and evaluated using two-layer tissue phantoms, fabricated to mimic the optical properties of melanin in different epidermal thickness and hemoglobin in dermal layers. Multiple tissue-mimicking phantoms with varying top layer thicknesses were measured for optical system calibration and performance testing. Phantom properties were characterized and validated using SkinSpect. The resulting analysis shows that the proposed system is capable of distinguishing and differentiating the layer-dependent absorption spectra and the depths at which this absorption occurs.

© 2015 Society of Photo-Optical Instrumentation Engineers (SPIE). Fluorescence microscopy is commonly used to investigate disease progression in biological tissues. Biological tissues, however, are strongly scattering in the visible wavelengths, limiting the application of fluorescence microscopy to superficial (

A fiber-optic probe-based instrument, designed for assessment of parameters related to microcirculation, red blood cell tissue fraction (fRBC), oxygen saturation (SO2), and speed resolved perfusion, has been evaluated using state-of-the-art tissue phantoms. The probe integrates diffuse reflectance spectroscopy (DRS) at two source-detector separations and laser Doppler flowmetry, using an inverse Monte Carlo method for identifying the parameters of a multilayered tissue model. Here, we characterize the accuracy of the DRS aspect of the instrument using (1)liquid blood phantoms containing yeast and (2)epidermis-dermis mimicking solid-layered phantoms fabricated from polydimethylsiloxane, titanium oxide, hemoglobin, and coffee. The root-mean-square (RMS) deviations for fRBC for the two liquid phantoms were 11% and 5.3%, respectively, and 11% for the solid phantoms with highest hemoglobin signatures. The RMS deviation for SO2 was 5.2% and 2.9%, respectively, for the liquid phantoms, and 2.9% for the solid phantoms. RMS deviation for the reduced scattering coefficient (μs'), for the solid phantoms was 15% (475 to 850nm). For the liquid phantoms, the RMS deviation in average vessel diameter (D) was 1 μm. In conclusion, the skin microcirculation parameters fRBC and SO2, as well as, μs' and D are estimated with reasonable accuracy.

Tissue simulating phantoms can provide a valuable platform for quantitative evaluation of the performance of diffuse optical devices. While solid phantoms have been developed for applications related to characterizing exogenous fluorescence and intrinsic chromophores such as hemoglobin and melanin, we report the development of a poly(dimethylsiloxane) (PDMS) tissue phantom that mimics the spectral characteristics of tissue water. We have developed these phantoms to mimic different water fractions in tissue, with the purpose of testing new devices within the context of clinical applications such as burn wound triage. Compared to liquid phantoms, cured PDMS phantoms are easier to transport and use and have a longer usable life than gelatin-based phantoms. As silicone is hydrophobic, 9606 dye was used to mimic the optical absorption feature of water in the vicinity of 970 nm. Scattering properties are determined by adding titanium dioxide, which yields a wavelength-dependent scattering coefficient similar to that observed in tissue in the near-infrared. Phantom properties were characterized and validated using the techniques of inverse adding-doubling and spatial frequency domain imaging. Results presented here demonstrate that we can fabricate solid phantoms that can be used to simulate different water fractions.

Detailed interferometric measurements of the induced thermal distortions due to laser-diode and xenon flashlamp pumping of Nd:LiYF/sub 4/ are presented. The thermal distortions are quantified in terms of the primary aberrations of defocus, astigmatism, coma, and spherical. Defocus and astigmatism are shown to dominate the thermal aberrations. The measured defocus and astigmatism are converted to the conventional thermal-focal lengths in two perpendicular directions with respect to the Nd:YLF crystalline c axis for each of the two polarization states /spl sigma/ and /spl pi/. A comparison of the thermal-focal lengths measured with our xenon flashlamp and laser-diode-pumped rods is given when the rods are pumped to the same small signal gain. We calculate effective dioptric-power coefficients from our data for comparison to those reported in the literature for krypton-flashlamp pumping. A thermal time constant of 1.5 s is measured for our laser-diode-pumped Nd:YLF laser rod.