Near infrared diffuse optical tomography: improving the quality of care in chronic wounds of patients with diabetes

Biophotonics methods for functional monitoring of complications of diabetes mellitus

The prevalence of diabetes complications is a significant public health problem with a considerable economic cost. Thus, the timely diagnosis of complications and prevention of their development will contribute to increasing the length and quality of patient life, and reducing the economic costs of their treatment. This article aims to review the current state-of-the-art biophotonics technologies used to identify the complications of diabetes mellitus and assess the quality of their treatment. Additionally, these technologies assess the structural and functional properties of biological tissues, and they include capillaroscopy, laser Doppler flowmetry and hyperspectral imaging, laser speckle contrast imaging, diffuse reflectance spectroscopy and imaging, fluorescence spectroscopy and imaging, optical coherence tomography, optoacoustic imaging and confocal microscopy. Recent advances in the field of optical noninvasive diagnosis suggest a wider introduction of biophotonics technologies into clinical practice and, in particular, in diabetes care units.

Hyperspectral imaging as a novel diagnostic tool in microcirculation of wounds

Monitoring of perfusion is a cornerstone in surgery, phlebology and basic science to proof wound healing by interventions. In chronic wound management it is of utmost importance to realize and parametrize wound bed perfusion to verify actual, and plan further treatment by noninvasive diagnostics. Up to now monitoring is based on visual inspection of wounds as conventionally practiced over more than decades. The main problems of visual inspection are the lack of standardization and comparability because of interindividual variations. Therefore technical performance with contact free probes based on standardized perfusion measuring is strongly needed. Hyperspectral imaging (HSI) was investigated to overcome manual and visual wound inspection in monitoring of wound healing. HSI works noninvasive, and imaging of relevant perfusion parameters is possible without the need of contrast enhancing drugs.

METHODS

HSI technology uses imaging spectroscopic analysis in visual and near infrared spectrum to get information on imaged tissue in less than 10 s. Tissue is radiated by broad spectrum light and the following parameters are calculated from remitted spectra: the grade of oxygenation and the volume proportion of hemoglobin (in superficial and also deeper (8 mm) tissues. The calculated data comprise the "Tissue hemoglobin oxygen saturation" (StO2) as percental oxygenation index to assess superficial perfusion (VIS-spectrum), the "Near infrared perfusion" (NIR) to assess deeper perfusion (near infrared spectrum) and the "Tissue hemoglobin index" (THI) to measure the percental volume of hemoglobin of surface perfusion (VIS-spectrum). The measurements of these parameters are calculated as false color-coded perfusion results on screen.We investigated different kind of wounds (combustion, infection, ulcer wounds, wounds in immune disorders, trauma wounds) determining superficial and deeper oxygen saturation, hemoglobin distribution and water content using hyperspectral imaging with TIVITA™ Tissue system.

RESULTS

Hyperspectral Imaging allowed easy real time determination and visualization of hemodynamically relevant parameters- superficial and deeper oxygen saturation, total hemoglobin and tissue water content. In the patient with scleroderma, acral lesions with decreased perfusion correlated well with necrotic skin aspects.HSI clearly revealed macroscopic conspicuous suture wounds after Dupuytren surgery, infected soft tissue wounds with strong inflammatory hyperemia, edema in burn injuries, spatial geometry of abscess formation and chronic ulcer wounds. All measurements influenced further surveillance decisions. Hyperspectral imaging seems suitable for routine diagnostics and monitoring of skin and soft tissue lesions like acute and chronic wounds. It allows surveillance of postoperative suture wounds and burn wounds. Special indications may be transplant surveillance and monitoring of therapeutical interventions.

Assessing the Healing of Venous Leg Ulcers Using a Noncontact Near-Infrared Optical Imaging Approach

Objective: Venous leg ulcers (VLUs) are one of the most common complications in lower extremity wounds. To date, clinicians employ visual inspection of the wound site during its healing process by monitoring surface granulation and reduction in wound size across weeks of treatment. In this study, a handheld near-infrared optical scanner (NIROS) has been developed at the Optical Imaging Laboratory to differentiate healing from nonhealing VLUs based on differences in blood flow to the wound and its surroundings. Approach: Noncontact near-infrared (NIR) area imaging of 12 VLUs have been carried out at two podiatric clinics. Diffuse reflectance images of the wounds were used to quantify optical contrasts between the wound and its surroundings. The variability in imaging conditions, analysis, and operator dependency were assessed to determine the robustness of the imaging approach. Results: Optical contrast obtained from diffuse reflectance images of VLUs were distinctly different for healing (positive contrast) and nonhealing (negative contrast) wounds, independent of the varying imaging and data analysis conditions. Innovation: NIR imaging of wounds to differentiate healing from nonhealing VLUs using a noncontact wide-area imager has been demonstrated for the first time. Conclusion: The application of a portable handheld imager to assess the healing or nonhealing nature of VLUs during weekly clinical treatment is significant since physiological changes, as observed using NIROS, manifest before visual reduction in wound size during the healing process.

Design of a portable imager for near-infrared visualization of cutaneous wounds

A portable imager developed for real-time imaging of cutaneous wounds in research settings is described. The imager consists of a high-resolution near-infrared CCD camera capable of detecting both bioluminescence and fluorescence illuminated by an LED ring with a rotatable filter wheel. All external components are integrated into a compact camera attachment. The device is demonstrated to have competitive performance with a commercial animal imaging enclosure box setup in beam uniformity and sensitivity. Specifically, the device was used to visualize the bioluminescence associated with increased reactive oxygen species activity during the wound healing process in a cutaneous wound inflammation model. In addition, this device was employed to observe the fluorescence associated with the activity of matrix metalloproteinases in a mouse lipopolysaccharide-induced infection model. Our results support the use of the portable imager design as a noninvasive and real-time imaging tool to assess the extent of wound inflammation and infection.

Critical Review of Noninvasive Optical Technologies for Wound Imaging

Significance: Noninvasive imaging approaches can provide greater information about a wound than visual inspection during the wound healing and treatment process. This review article focuses on various optical imaging techniques developed to image different wound types (more specifically ulcers). Recent Advances: The noninvasive optical imaging approaches in this review include hyperspectral imaging, multispectral imaging, near-infrared spectroscopy (NIRS), diffuse reflectance spectroscopy, optical coherence tomography, laser Doppler imaging, laser speckle imaging, spatial frequency domain imaging, and fluorescence imaging. The various wounds imaged using these techniques include open wounds, chronic wounds, diabetic foot ulcers, decubitus ulcers, venous leg ulcers, and burns. Preliminary work in the development and implementation of a near-infrared optical scanner for wound imaging as a noncontact hand-held device is briefly described. The technology is based on NIRS and has demonstrated its potential to differentiate a healing from nonhealing wound region. Critical Issues: While most of the optical imaging techniques can penetrate few hundred microns to a 1-2 mm from the wound surface, NIRS has the potential to penetrate deeper, demonstrating the potential to image internal wounds. Future Directions: All the technologies are currently at various stages of translational efforts to the clinic, with NIRS holding a greater promise for physiological assessment of the wounds internal, beyond the gold-standard visual assessment.

Direct-current-based image reconstruction versus direct-current included or excluded frequency-domain reconstruction in diffuse optical tomography

We study the level of image artifacts in optical tomography associated with measurement uncertainty under three reconstruction configurations, namely, by using only direct-current (DC), DC-excluded frequency-domain, and DC-included frequency-domain data. Analytic and synthetic studies demonstrate that, at the same level of measurement uncertainty typical to optical tomography, the ratio of the standard deviation of mu(a) over mu(a) reconstructed by DC only is at least 1.4 times lower than that by frequency-domain methods. The ratio of standard deviations of D (or mu(s)') over D (or mu(s)') reconstructed by DC only are slightly lower than those by frequency-domain methods. Frequency-domain reconstruction including DC generally outperforms that excluding DC, but as the amount of measurements increases, the difference between the two diminishes. Under the condition of a priori structural information, the performances of three reconstruction configurations are seemingly equivalent.