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Spatial frequency domain imaging (SFDI) is a wide-field diffuse optical imaging technique for separately quantifying tissue reduced scattering (μs ' ) and absorption (μa) coefficients at multiple wavelengths, providing wide potential utility for clinical applications such as burn wound characterization and cancer detection. However, measured μs ' and μa can be confounded by absorption from melanin in patients with highly pigmented skin. This issue arises because epidermal melanin is highly absorbing for visible wavelengths and standard homogeneous light-tissue interaction models do not properly account for this complexity. Tristimulus colorimetry (which quantifies pigmentation using the L * "lightness" parameter) can provide a point of comparison between μa, μs ' , and skin pigmentation.We systematically compare SFDI and colorimetry parameters to quantify confounding effects of pigmentation on measured skin μs ' and μa. We assess the correlation between SFDI and colorimetry parameters as a function of wavelength.μs ' and μa from the palm and ventral forearm were measured for 15 healthy subjects with a wide range of skin pigmentation levels (Fitzpatrick types I to VI) using a Reflect RS® (Modulim, Inc., Irvine, California) SFDI instrument (eight wavelengths, 471 to 851 nm). L * was measured using a Chroma Meter CR-400 (Konica Minolta Sensing, Inc., Tokyo). Linear correlation coefficients were calculated between L * and μs ' and between L * and μa at all wavelengths.For the ventral forearm, strong linear correlations between measured L * and μs ' values were observed at shorter wavelengths (R 0.92 at ≤659 nm), where absorption from melanin confounded the measured μs ' . These correlations were weaker for the palm (R 0.59 at ≤659 nm), which has less melanin than the forearm. Similar relationships were observed between L * and μa.We quantified the effects of epidermal melanin on skin μs ' and μa measured with SFDI. This information may help characterize and correct pigmentation-related inaccuracies in SFDI skin measurements.

Background Burns are devastating injuries, carry significant morbidity, and require long-term treatment or multiple reconstructive procedures. Wound healing and secondary insults caused by burn wound conversion are amendable to therapeutic intervention, where ischemia has been cited as one of the major factors (Dermatol Surg. 2008;34:1159-1169). Halting injury progression in the zone of stasis is crucial as conversion creates increased burn surface area and depth, leading to local and systemic consequences (J Burns Wounds. 2006;5:e2). Oxygen-carrying micro/nanobubbles, MNB(O2), offer a novel technology that can be used to effectively deliver oxygen to burn wounds and potentially counteract burn wound ischemia. Methods Topical irrigation with MNB(O2) of full-thickness burn wounds on a rodent model (n = 3) was compared against saline-treated controls (n = 3). Tissue structure (reduced scattering coefficient, μs'), oxyhemoglobin concentration (cHbO2), and tissue perfusion were quantified over the course of 28 days through spatial frequency domain imaging and laser speckle imaging. Histological samples taken at the end of the experiment were examined for evidence of wound healing. Results Findings in this preliminary study showed hastened healing with significant differences in spatial frequency domain imaging-measured μs' during wound healing (days 11-28) in MNB(O2) group. The healing "tipping point" seemed to occur at days 9 to 11 with increased collagen organization and increased cHbO2 occurring around that period confirming the gross healing improvements observed. In addition, histological evidence indicated that only the MNB(O2) burns had reached the remodeling phase by the end of 28-day study period. Conclusions These preliminary findings propose the potential of MNB(O2) as a topical method for improving burn wound healing.

Significance: Spatial frequency domain imaging (SFDI) is a wide-field imaging technique that provides quantitative maps of tissue optical properties. We describe a compact SFDI imager that employs a multispectral compound-eye camera. This design enables simultaneous image acquisition at multiple wavelengths. Such a device has potential for application for quantitative evaluation of superficial tissues by nonspecialists in low-resource settings. Aim: The aim of this work was to develop a compact SFDI imager for widefield imaging of in-vivo tissue optical properties and verify its ability to measure optical properties of tissue-simulating phantoms and in a preclinical model of burn wounds. Approach: This compound-eye imager was constructed using a CMOS sensor subdivided into multiple regions, each having a bandpass filter and objective lens. The ability of the instrument to image optical properties was compared with (1) a commercial SFDI imager and (2) a laboratory-based system. Initial validation of ability to accurately characterize optical properties was performed using a tissue-simulating optical phantom. It was then applied to an established murine model of thermal contact burn severity. In-vivo measurements of the optical properties of rat skin were performed before and after the application of burns. Histology was used to verify burn severity. Results: Measurements of the tissue-simulating phantom optical properties made using the compound-eye imager agree with measurements made using the two comparison SFDI devices. For the murine burn model, the burns showed a decrease in the reduced scattering coefficient at all measurement wavelengths compared with preburn measurements at the same locations. This is consistent with previously reported changes in scattering that occur in full-thickness burns. Conclusion: We demonstrate the potential for SFDI to be translated into compact form factor using a compound-eye camera that is capable of obtaining multiple wavelengths channels simultaneously.

While clinical examination is needed for burn severity diagnosis, several emerging technologies aim to quantify this process for added objectivity. Accurate assessments become easier after burn progression, but earlier assessments of partial thickness burn depth could lead to earlier excision and grafting and subsequent improved healing times, reduced rates of scarring/infection, and shorter hospital stays. Spatial Frequency Domain Imaging (SFDI), Laser Speckle Imaging (LSI) and thermal imaging are three non-invasive imaging modalities that have some diagnostic ability for noninvasive assessment of burn severity, but have not been compared in a controlled experiment. Here we tested the ability of these imaging techniques to assess the severity of histologically confirmed graded burns in a swine model. Controlled, graded burn wounds, 3 cm in diameter were created on the dorsum of Yorkshire pigs (n=3, 45–55kg) using a custom-made burn tool that ensures consistent pressure has been employed by various burn research groups. For each pig, a total of 16 burn wounds were created on the dorsal side. Biopsies were taken for histological analysis to verify the severity of the burn. Clinical analysis, SFDI, LSI and thermal imaging were performed at 24 and 72 hours after burn to assess the accuracy of each imaging technique. In terms of diagnostic accuracy, using histology as a reference, SFDI (85%) and clinical analysis (83%) performed significantly better that LSI (75%) and thermography (73%) 24 hours after the burn. There was no statistically significant improvement from 24 to 72 hours across the different imaging modalities. These data indicate that these imaging modalities, and specifically SFDI, can be added to the burn clinicians’ toolbox to aid in early assessment of burn severity.

While visual clinical impression is the standard of care for burn severity assessment, accuracy improves after the injury progresses, leading to patients waiting days for a diagnosis. Spatial Frequency Domain Imaging (SFDI) has shown the potential to assess burn grade as early as 24 hours post-burn. Here, we compared SFDI and Laser Speckle Imaging (LSI) at 24 and 72 hours after burn injury to clinical burn severity diagnosis. Three patients with burns ranging in severity were imaged. Both techniques showed an ability to categorize burn severity 24 hours after the initial injury, well before the outcome was determined by a clinician at 72 hours or later.

Spatial frequency domain imaging (SFDI) is a wide-field imaging technique that provides quantitative tissue optical property maps. We describe a compact, multi-aperture SFDI imager for burn severity evaluation. This was constructed using a CMOS sensor subdivided into multiple regions, each having a bandpass filter and objective lens. This compound-eye design enables simultaneous image acquisition at multiple wavelengths. The imager was evaluated using a rat burn model and compared to conventional SFDI devices that acquire wavelength data sequentially. The burns showed a decrease in the reduced scattering coefficient that is consistent with previously reported changes in full thickness burns.

Spatial Frequency Domain Imaging (SFDI) is a non-invasive diffuse optical imaging technology that quantifies tissue optical properties by projecting spatially modulated light onto a region of interest. By detecting and fitting the diffuse reflectance to a light transport model, tissue absorption (μa) and scattering (μs') coefficients are calculated. However, when measuring skin, bulk μa and μs' from a homogeneous light transport model may not correspond with the actual properties of individual skin layers, especially for highly pigmented skin. To obtain physiologically accurate skin optical property values, we propose an iterative method based on a two- layered Monte Carlo model. We initially assume that μs' in darker skin is the same as that in lighter skin, and set the epidermal a as the free parameter when fitting the diffuse reflectance. To test this algorithm, we analyzed data from the forearms of 6 subjects having various levels of pigmentation, at 8 visible-to-near-infrared wavelengths. We compared the measured reflectance to both the homogeneous model and our layered model to quantify fit accuracy. At 471 nm and 526 nm for patients of Fitzpatrick skin types IV-VI (relatively dark skin), the two-layered model provided a 10-20% improvement in fit to the AC reflectance as a function of spatial frequency, compared to the homogeneous model. These improved fits yielded epidermal absorption coefficients that were notably higher than the bulk μa from the homogeneous model. Fitting the extracted epidermal μa to a melanin extinction spectrum1 enabled estimation of the melanin concentration in the epidermis.

Adequate resuscitation is critical for burn wound patients where the affected total body surface area (TBSA) exceeds 20%, as fluid loss leads to organ failure, shock, and patient mortality. Protocols have been developed to combat fluid loss, however excess fluids can also lead to compartment syndromes. Here, we used spatial frequency domain imaging (SFDI), a non-contact wide field imaging technique to measure in-vivo water changes in a 40 % TBSA porcine burn model. In this pilot study one pig received intravenous fluids according to the Parkland formula on top of enteral fluid resuscitation, while a second pig received no fluids during the experiment. Unburned regions of skin were imaged with SFDI from 3 to 22 hours post-burn. This imaging technique uses structured illumination, projected at multiple spatial frequencies and wavelengths, to measure tissue reflectance, which is used to obtain the reduced scattering and absorption coefficients. Water fraction is based upon absorption in the near-infrared spectrum at 971 nm, where water has a high extinction coefficient. SFDI measurements of superficial tissue hydration showed increased water fraction for the pig that received fluid resuscitation (+17%), and a decrease for the pig that received no fluids (-5%). Analysis showed decreased scattering measured in the pig that received fluids (+13%), suggesting increased interstitial water pressure. These preliminary results are consistent with systemic hydration, as estimated based on CT-measured subcutaneous fat thickness. SFDI may, therefore offer the possibility of non-invasively monitoring fluid resuscitation of large TBSA patients.

Significance: Spatial frequency domain imaging (SFDI), a noncontact wide-field imaging technique using patterned illumination with multiple wavelengths, has been used to quantitatively measure structural and functional parameters of in vivo tissue. Using SFDI in a porcine model, we previously found that scattering changes in skin could potentially be used to noninvasively assess burn severity and monitor wound healing. Translating these findings to human subjects necessitates a better understanding of the variation in “baseline” human skin scattering properties across skin types and anatomical locations. Aim: Using SFDI, we aim to characterize the variation in the reduced scattering coefficient (μs′) for skin across a range of pigmentation and anatomic sites (including common burn locations) for normal human subjects. These measurements are expected to characterize baseline human skin properties to inform our use of SFDI for clinical burn severity and wound healing assessments. Approach: SFDI was used to measure μs′ in the visible- and near-infrared regime (471 to 851 nm) in 15 subjects at 10 anatomical locations. Subjects varied in age, gender, and Fitzpatrick skin type. Results: For all anatomical locations, the coefficient of variation in measured μs′ decreased with increasing wavelength. High intersubject variation in μs′ at visible wavelengths coincided with large values of the melanin extinction coefficient at those wavelengths. At 851 nm, where intersubject variation in μs′ was smallest for all anatomical locations and absorption from melanin is minimal, significant intrasubject differences in μs′ were observed at the different anatomical locations. Conclusions: Our study is the first report of wide-field mapping of human skin scattering properties across multiple skin types and anatomical locations using SFDI. Measured μs′ values varied notably between skin types at wavelengths where absorption from melanin was prominent. Additionally, μs′ varied considerably across different anatomical locations at 851 nm, where the confounding effects from melanin absorption are minimized.

While visual assessment by a clinician is the standard of care for burn severity evaluations, new technologies at various stages of development are attempting to add objectivity to this practice by quantifying burn severity. Assessment accuracy generally improves after the burn injury has progressed, but early assessments that correctly identify superficial partial and deep partial burns have the potential to lead to more prompt treatments and shorter recovery times. To date, Spatial Frequency Domain Imaging (SFDI) has only been used in animal models of burns, but has shown the potential to categorize burns accurately at earlier time points. Here we examine the potential for SFDI to assess burn severity in clinical patients. We also utilize Laser Speckle Imaging (LSI), an FDA cleared non-invasive imaging technology that typically measures blood perfusion in order to evaluate burns in clinical patients. We present a case series of two patients, both with partial thickness burns of varying severity. Partial thickness burns are often difficult for clinicians to categorize based on visual appearance alone. SFDI and LSI were both performed on each patient at approximately 24 and 72 h after their respective burn incidents. Each technique was able to render spatially resolved information that enabled improved assessment accuracy for each burn. This represents the first publication of SFDI applied to clinical burn patients after being successfully utilized in animal models, and highlights the potential for SFDI as a feasible tool for the timely categorization of burn severity. Keywords: Burns, Clinical, Humans, Spatial Frequency Domain Imaging, Laser Speckle Imaging

Delayed graft function occurs in 40% of kidney transplantation cases, and is not apparent until after surgery has concluded. To understand changes in donor kidney tissue before transplantation, spatial frequency domain imaging (SFDI) was used to measure absorption and reduced scattering coefficients in excised porcine kidneys as they underwent a standard period of cold ischemic time (CIT). SFDI indicated an increase in reduced scattering and absorption. The scattering b parameter increased until 24 hours, then returned towards baseline. These results suggest that continued investigation may lead to the development of a noninvasive assessment for graft viability.

Spatial frequency domain imaging (SFDI), a noncontact imaging technique using structured illumination with multiple wavelengths, has proved feasible for characterizing burns of different severities induced in porcine dorsum. However, translation to human clinical subjects may be subject to variation in tissue optical properties due to different skin types or body parts. To interrogate this potential difference in optical properties, SFDI was used to measure the reduced scattering coefficient (μs’ ) in patients of varying Fitzpatrick skin type groups at 10 anatomical locations on the body. These scattering values were compared against previously measured average μs’ values for burns in a porcine model. At 851nm, superficial partialthickness burns had a 12.6% higher μs’ than unburned porcine dorsum. Deep partial-thickness and had 12.9% higher average μs’ than unburned porcine dorsum, while full-thickness burns had 2.5% higher average μs’ than unburned porcine dorsum. The variation seen in scattering values at 851nm at one anatomical location (dorsal forearm) for the different skin type groups showed a 6.3% lower average μs’ in group 3 (skin types VVI) compared to group 2 (skin types III-IV). Average scattering values were 3.8% lower in group 1 (skin types I-II) compared to group 2 (skin types III-IV). The variation of μs’ at 851nm across multiple anatomical locations for the same skin type group (Group 1) was a 23% difference from the anatomical location with the highest average μs’ at 851nm (forehead) to the lowest (shin). These findings indicate that further consideration of skin type and location will be integral to the translation of classification techniques based μs’ measurements of porcine dorsum to human patients.

Introduction While visual assessment is the standard for burn severity evaluation, new technologies are attempting to increase objectivity. Burn depth assessment accuracy improves over time as the appearance changes, but earlier diagnosis potentially leads to prompt treatment and shorter recovery. Laser Speckle Imaging (LSI), FDA approved for grading burns, is typically done 72hrs after injury. Spatial Frequency Domain Imaging (SFDI), a novel technology only tested in animal burn models, uses multiple wavelengths of patterned light to quantify tissue absorption (hemodynamics) and scattering (structure). SFDI has shown the potential to differentiate burns as early as 24hrs postburn by measuring scattering (µs’) changes due to collagen damage. Here, we examine SFDI burn severity assessment in clinical patients, and compare against LSI and clinical assessment. Methods 5 burn cases were imaged with LSI and SFDI approximately 24 and 72hrs postburn. The clinician was blinded to imaging results and made diagnoses on their standard of care. Results One patient received no surgical intervention, one received excision and xenograft, and two received excision and autograft. An autograft was recommended for one patient, but not performed due to preexisting conditions. SFDI measurements at 24hrs showed low µs’ values in regions that eventually required autografts, and high µs’ in burns that did not. While clinical decisions were made no earlier than 72hrs postburn, µs’ maps at 24hrs postburn were able to illustrate severity in these regions. In 2 of 3 autograft cases, LSI was unable to determine the severity until 72hrs postburn. Conclusions Here, we compared SFDI to LSI in a clinical setting to quantify burn wound severity. Similar to animal models, SFDI was demonstrated to accurately characterize severity earlier than the perfusion-based LSI. This is likely due to sensitivity of µs’ measured by SFDI to the structural changes in damaged collagen (i.e., zone of coagulation) that occur immediately postburn.

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.

There is a need for noninvasive, quantitative methods to characterize wound healing in the context of longitudinal investigations related to regenerative medicine. Such tools have the potential to inform the assessment of wound status and healing progression and aid the development of new treatments. We employed spatial frequency domain imaging (SFDI) to characterize the changes in optical properties of tissue during wound healing progression in a porcine model of split-thickness skin grafts and also in a model of burn wound healing with no graft intervention. Changes in the reduced scattering coefficient measured using SFDI correlated with structural changes reported by histology of biopsies taken concurrently. SFDI was able to measure spatial inhomogeneity in the wounds and predicted heterogeneous healing. In addition, we were able to visualize differences in healing rate, depending on whether a wound was debrided and grafted, versus not debrided and left to heal without intervention apart from topical burn wound care. Changes in the concentration of oxy- and deoxyhemoglobin were also quantified, giving insight into hemodynamic changes during healing.

Accurate assessment of burn severity is critical for wound care and the course of treatment. Delays in classification translate to delays in burn management, increasing the risk of scarring and infection. To this end, numerous imaging techniques have been used to examine tissue properties to infer burn severity. Spatial frequency-domain imaging (SFDI) has also been used to characterize burns based on the relationships between histologic observations and changes in tissue properties. Recently, machine learning has been used to classify burns by combining optical features from multispectral or hyperspectral imaging. Rather than employ models of light propagation to deduce tissue optical properties, we investigated the feasibility of using SFDI reflectance data at multiple spatial frequencies, with a support vector machine (SVM) classifier, to predict severity in a porcine model of graded burns. Calibrated reflectance images were collected using SFDI at eight wavelengths (471 to 851 nm) and five spatial frequencies (0 to 0.2 mm−1). Three models were built from subsets of this initial dataset. The first subset included data taken at all wavelengths with the planar (0 mm−1) spatial frequency, the second comprised data at all wavelengths and spatial frequencies, and the third used all collected data at values relative to unburned tissue. These data subsets were used to train and test cubic SVM models, and compared against burn status 28 days after injury. Model accuracy was established through leave-one-out cross-validation testing. The model based on images obtained at all wavelengths and spatial frequencies predicted burn severity at 24 h with 92.5% accuracy. The model composed of all values relative to unburned skin was 94.4% accurate. By comparison, the model that employed only planar illumination was 88.8% accurate. This investigation suggests that the combination of SFDI with machine learning has potential for accurately predicting burn severity.

While most superficial (first degree) burns and full thickness (third degree) burns are easily diagnosed through standard clinical inspection, burns that fall between these extremes are challenging to accurately classify based on clinical appearance alone. Accurate early assessments have the potential to enable earlier debridement and grafting, thereby reducing complication rates, healing times, and chances for infection. To this end, several emerging technologies aim to objectively and non-invasively quantify burn severity, including Spatial Frequency Domain Imaging (SFDI), Laser Speckle Imaging (LSI), and infrared thermal imaging (IR). While these imaging modalities have some diagnostic ability for in-vivo assessment of burn severity, they have not been directly compared in a controlled experiment. Here we compare the ability of these techniques to assess the severity of graded burns in a porcine model (n=96 burns, 6 pigs). Biopsies were taken for histological analysis to verify burn severity. Clinical assessment, SFDI, LSI and thermal imaging were performed for all graded burns at 24 and 72 hours post-burn. In terms of accuracy of burn severity assessment, using histology as a reference, SFDI (85%) and clinical analysis (83%) performed significantly better that LSI (75%) and thermography (73%) at the 24 hour post-burn time point. There was no statistically significant improvement in assessment accuracy at the 72 hour post-burn time point, across the imaging modalities. These data indicate that SFDI may provide valuable information to clinicians in future clinical trials. This information can be obtained early in the process, which may hasten surgical intervention and reduce complications.

Assessment of burn severity is critical for wound treatment. Spatial frequency domain imaging (SFDI) has been previously used to characterize burns based on the relationships between histology and tissue optical properties. Recently, multispectral and hyperspectral imaging optical features have been combined with machine learning to classify burn severity. Here, we investigated the use of SFDI reflectance data at multiple wavelengths and spatial frequencies, with a support vector machine (SVM), to predict severity in a porcine model of graded burns. Burn severity predictions using SVM were compared to burn grade determined using histology techniques. Results suggest that the combination of spatial frequency data with machine learning models has the potential for accurately predicting burn severity at the 24 hr postburn time point.

Spatial frequency domain imaging (SFDI) is a wide-field imaging technique that enables quantification of in vivo tissue optical properties. SFDI was employed to evaluate burn wounds in pigs where incomplete debridement resulted in skin graft failure. We observed increase in the magnitude of the reduced-scattering coefficient in the wound beds after debridement, prior to grafting in wounds that failed compared to the reduced scattering measured in the wound beds that did not fail. We anticipate that SFDI may be a useful means for determining appropriate debridement prior to grafting.

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.

The ability to predict success or failure of wound healing strategies in burns has the potential to enable customized treatments tailored for the individual patient that would ultimately shorten recovery times, reduce the need for repeated grafting, and aid in achieving full rehabilitation. To this end, we are investigating the potential for spatial frequency domain imaging (SFDI) to non-invasively assess wound severity and healing status. SFDI is a wide-field diffuse optical imaging technique that enables non-invasive quantitative determination of in vivo tissue optical properties associated with physiologic structure and function. We have employed SFDI in a longitudinal study of wound healing using a controlled porcine burn model. Regions of wound repair using split thickness skin grafts were imaged using SFDI at multiple time points over a period of 60 days. The reduced scattering and absorption coefficients were determined at nine wavelengths spanning 470–970 nm, enabling determination of oxy- and deoxy-hemoglobin concentration, total hemoglobin concentration, oxygen saturation, and water fraction. These values obtained were compared to unburned control regions, undebrided burns, and debrided regions without treatment by grafting. Changes in the reduced scattering associated with structural changes in tissue correlate with histology as the wound heals. Compared to unburned tissue, the reduced scattering coefficient associated with repaired wounds is depressed and is spatially heterogeneous immediately following grafting. Over the course of healing, the scattering values increase and converge toward values of normal tissue and become more spatially homogeneous. Variations in chromophore concentrations are also characterized.

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.

Burn wounds are often characterized by injury depth, which then dictates wound management strategy. While most superficial burns and full thickness burns can be diagnosed through visual inspection, clinicians experience difficulty with accurate diagnosis of burns that fall between these extremes. Accurately diagnosing burn severity in a timely manner is critical for starting the appropriate treatment plan at the earliest time points to improve patient outcomes. To address this challenge, research groups have studied the use of commercial laser Doppler imaging (LDI) systems to provide objective characterization of burn-wound severity. Despite initial promising findings, LDI systems are not commonplace in part due to long acquisition times that can suffer from artifacts in moving patients. Commercial LDI systems are being phased out in favor of laser speckle imaging (LSI) systems that can provide similar information with faster acquisition speeds. To better understand the accuracy and usefulness of commercial LSI systems in burn-oriented research, we studied the performance of a commercial LSI system in three different sample systems and compared its results to a research-grade LSI system in the same environments. The first sample system involved laboratory measurements of intralipid (1%) flowing through a tissue simulating phantom, the second preclinical measurements in a controlled burn study in which wounds of graded severity were created on a Yorkshire pig, and the third clinical measurements involving a small sample of clinical patients. In addition to the commercial LSI system, a research grade LSI system that was designed and fabricated in our labs was used to quantitatively compare the performance of both systems and also to better understand the “Perfusion Unit” output of commercial systems.

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 ...

Author(s): Rowland, Rebecca; Ponticorvo, Adrien; Jarrin Lopez, Alberto; Li, Shiri; Li, Xiaodong; Ichii, Hirohito; Durkin, Anthony | Abstract: Transplantation of kidneys results in delayed graft function in as many as 40% of cases. During the organ transplantation process, donor kidneys undergo a period of cold ischemic time (CIT), where the organ is preserved with a cold storage solution to maintain tissue viability. Some complications observed after grafting may be due to damage sustained to the kidney during CIT. However, the effects due to this damage are not apparent until well after transplant surgery has concluded. To this end, we have used spatial frequency domain imaging (SFDI) to measure spatially resolved optical properties of porcine kidneys over the course of 80-h CIT. During this time, we observed an increase in both reduced scattering (μsa') and absorption (μa) coefficients. The measured scattering b parameter increased until 24nh of CIT, then returned toward baseline during the remaining duration of the imaging sequence. These results show that the optical properties of kidney tissue change with increasing CIT and suggest that continued investigation into the application of SFDI to kidneys under CIT may lead to the development of a noninvasive method for assessing graft viability.

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.

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.

Extending the wavelength range of spatial frequency domain imaging (SFDI) into the short-wave infra- red (SWIR) has the potential to provide enhanced sensitivity to chromophores such as water and lipids that have prominent absorption features in the SWIR region. Here, we present, for the first time, a method combining SFDI with unstructured (zero spatial frequency) illumination to extract tissue absorption and scattering properties over a wavelength range (850 to 1800 nm) largely unexplored by previous tissue optics techniques. To obtain images over this wavelength range, we employ a SWIR camera in conjunction with an SFDI system. We use SFDI to obtain in vivo tissue reduced scattering coefficients at the wavelengths from 850 to 1050 nm, and then use unstructured wide-field illumination and an extrapolated power-law fit to this scattering spectrum to extract the absorption spectrum from 850 to 1800 nm. Our proof-of-principle experiment in a rat burn model illustrates that the combination of multispectral SWIR imaging, SFDI, and unstructured illumination can characterize in vivo changes in skin optical properties over a greatly expanded wavelength range. In the rat burn experiment, these changes (relative to normal, unburned skin) included increased absorption and increased scattering amplitude and slope, consistent with changes that we previously reported in the near-infrared using SFDI. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires