A critical need exists for a robust method that enables early discrimination between superficial-partial and deep-partial thickness burn wounds. In this study, we report on the use of laser speckle imaging (LSI), a simple, non-invasive, optical imaging modality, to measure acute blood flow dynamics in a preclinical burn model. We used a heated brass comb to induce burns of varying severity to nine rats and collected raw speckle reflectance images over the course of three hours after burn. We induced a total of 12 superficial-partial and 18 deep-partial thickness burn wounds. At 3h after burn we observed a 28% and 44% decrease in measured blood flow for superficial-partial and deep-partial thickness burns, respectively, and that these reductions were significantly different (p=0.00007). This preliminary data suggests the potential role of LSI in the clinical management of burn wounds.

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

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 (μs&') and absorption (μ_a) coefficients. The measured scattering b parameter increased until 24 h 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.

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.

Baseline optical properties are typically assumed in calculating the differential pathlength factor (DPF) of mouse brains, a value used in the modified Beer-Lambert law to characterize an evoked stimulus response. We used spatial frequency domain imaging to measure in vivo baseline optical properties in 20-month-old control ([Formula: see text]) and triple transgenic APP/PS1/tau (3xTg-AD) ([Formula: see text]) mouse brains. Average [Formula: see text] for control and 3xTg-AD mice was [Formula: see text] and [Formula: see text], respectively, at 460 nm; and [Formula: see text] and [Formula: see text], respectively, at 530 nm. Average [Formula: see text] for control and 3xTg-AD mice was [Formula: see text] and [Formula: see text], respectively, at 460 nm; and [Formula: see text] and [Formula: see text], respectively, at 530 nm. The calculated DPF for control and 3xTg-AD mice was [Formula: see text] and [Formula: see text] OD mm, respectively, at 460 nm; and [Formula: see text] and [Formula: see text] OD mm, respectively, at 530 nm. In hindpaw stimulation experiments, the hemodynamic increase in brain tissue concentration of oxyhemoglobin was threefold larger and two times longer in the control mice compared to 3xTg-AD mice. Furthermore, the washout of deoxyhemoglobin from increased brain perfusion was seven times larger in controls compared to 3xTg-AD mice ([Formula: see text]).

Significance

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.

Aim

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.

Approach

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.

Results

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.

Conclusions

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.

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, 3cm 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 72h 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%) 24h after the burn. There was no statistically significant improvement from 24 to 72h 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.

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.