Jeri R. Payette

Near infrared spectroscopic assessment of hemodynamic changes in the early post-burn period

Near infrared reflectance spectroscopy and imaging was used to assess non-invasively the hemodynamic changes that occur in the early post-burn period in cutaneous burn injuries of varying depth. An acute porcine model was used to demonstrate the potential of near infrared spectroscopy and imaging to accurately determine the change in tissue oxygenation, blood volume and tissue water content following a thermal injury. Near infrared spectroscopy was used to monitor tissue at discrete locations, while spectroscopic imaging was able to survey large areas of tissue. Both methods were rapid and non-invasive. Tissue hemoglobin oxygen saturation, total hemoglobin and tissue water content were all affected by thermal injury and changed significantly over a 3 h post-burn monitoring period. Burns that ranged in severity between superficial and full thickness displayed a significantly different hemodynamic response. When the early post-burn profiles (1-3 h) of tissue hemoglobin oxygen saturation, total hemoglobin and tissue water content were considered jointly, injuries leading to superficial, intermediate partial thickness, deep partial thickness and full thickness burns could all be differentiated at high statistical significance. These results suggest that non-invasive hemodynamic monitoring in the early post-burn period using near infrared spectroscopy may be of value in the early assessment of burn injury.

Visualization of cutaneous hemoglobin oxygenation and skin hydration using near-infrared spectroscopic imaging.

Background/aims: The visualization of skin hemodynamics and tissue water content has important implications in a number of areas of dermatology, plastic surgery, and clinical skin evaluation. The aim of this study was to develop instrumentation and techniques for infrared spectroscopic imaging, and to evaluate whether they can be used to make objective assessments of skin health, perhaps even before clinical signs are evident.

Clinical utilization of near-infrared spectroscopy devices for burn depth assessment.

The diagnosis of burn depth is based on a visual assessment and can be subjective. Near‐infrared (NIR) spectroscopic devices were used preclinically with positive results. The purpose of this study was to test the devices in a clinical setting using easily identifiable burn wounds. Adult patients with acute superficial and full‐thickness burns were enrolled. NIR point spectroscopy and imaging devices were used to collect hemodynamic data from the burn site and an adjacent unburned control site. Oxy‐hemoglobin and deoxy‐hemoglobin concentrations were extracted from spectroscopic data and reported as oxygen saturation and total hemoglobin. Sixteen patients (n=16) were included in the study with equal numbers in both burn wound groups. Point spectroscopy data showed an increase in oxygen saturation (p<0.0095) and total hemoglobin (<0.0001) in comparison with the respective control areas for superficial burn wounds. The opposite was true for full‐thickness burns, which showed a decrease in oxygenation (p<0.0001) and total hemoglobin (p<0.0147) in comparison with control areas. NIR imaging technology provides an estimate of hemodynamic parameters and could easily distinguish superficial and full‐thickness burn wounds. These results confirm that NIR devices can successfully distinguish superficial and full‐thickness burn injuries.

Visible-Near Infrared Multispectral Imaging of the Rat Dorsal Skin Flap

Visible-near infrared multispectral reflectance image sets were acquired from the dorsal surface of rats both before and after elevation of reversed McFarlane skin flaps. Raw images were dominated by uneven surface illumination and shadowing along with the variation associated with instrument response. These interfering features obscured variation associated with a change in tissue reflectance, which is related to the degree of flap perfusion. Logarithmic residual preprocessing followed by principal component analysis of multispectral images could clearly detect a difference in the optical properties between the base and distal section of the flap. The difference in the reflectance properties correlates with the varying degree of tissue perfusion. Principal component analysis detected this optical difference between the well-perfused base of the skin flap and the compromised distal section of the flap immediately following surgery. The first visual signs of compromised tissue perfusion appeared only 6 or more hours after surgery. The results from this study indicate that the application of principal component analysis to discrete wavelength near infrared multispectral reflectance images of skin flaps can effectively distinguish reflectance changes related to the degree of tissue perfusion immediately following surgical elevation of the reversed McFarlane skin flap.

Tissue viability by multispectral near infrared imaging: a fuzzy C-means clustering analysis

Clinically, skin color, temperature, and capillary perfusion are used to assess tissue viability following microvascular tissue transfer. However, clinical signs that arise as a consequence of poor perfusion become evident only after several hours of compromised perfusion. This study demonstrates the potential usefulness of optical/infrared multispectral imaging in the prognosis of tissue viability immediately post-surgery. Multispectral images of a skin flap model acquired within 1 h of surgical elevation are analyzed in comparison to the final 72 h clinical outcome with a high degree of correlation. Regional changes in tissue perfusion and oxygenation present immediately following surgery are differentiated using fuzzy clustering and image processing algorithms. These methodologies reduce the intersubject variability inherent in infrared imaging methods such that the changes in perfusion are reproducible and clearly distinguishable across all subjects. Clinically, an early prognostic indicator of viability such as this would allow for a more timely intervention following surgery in the event of compromised microvasculature.

Classification of burn injuries using near-infrared spectroscopy

Early surgical management of those burn injuries that will not heal spontaneously is critical. The decision to excise and graft is based on a visual assessment that is often inaccurate but yet continues to be the primary means of grading the injury. Superficial and intermediate partial-thickness injuries generally heal with appropriate wound care while deep partial- and full-thickness injuries generally require surgery. This study explores the possibility of using near-infrared spectroscopy to provide an objective and accurate means of distinguishing shallow injuries from deeper burns that require surgery. Twenty burn injuries are studied in five animals, with burns covering <1% of the total body surface area. Carefully controlled superficial, intermediate, and deep partial-thickness injuries as well as full-thickness injuries could be studied with this model. Near-infrared reflectance spectroscopy was used to evaluate these injuries 1 to 3 hours after the insult. A probabilistic model employing partial least-squares logistic regression was used to determine the degree of injury, shallow (superficial or intermediate partial) from deep (deep partial and full thickness), based on the reflectance spectrum of the wound. A leave-animal-out cross-validation strategy was used to test the predictive ability of a 2-latent variable, partial least-squares logistic regression model to distinguish deep burn injuries from shallow injuries. The model displayed reasonable ranking quality as summarized by the area under the receiver operator characteristics curve, AUC = 0.879. Fixing the threshold for the class boundaries at 0.5 probability, the model sensitivity (true positive fraction) to separate deep from shallow burns was 0.90, while model specificity (true negative fraction) was 0.83. Using an acute porcine model of thermal burn injuries, the potential of near-infrared spectroscopy to distinguish between shallow healing burns and deeper burn injuries was demonstrated. While these results should be considered as preliminary and require clinical validation, a probabilistic model capable of differentiating these classes of burns would be a significant aid to the burn specialist.

Detecting intestinal ischemia using near infrared spectroscopy

Blood supply to the intestine can suddenly be interrupted. Acute mesenteric intestinal ischemia often requires invasive surgery to restore blood supply to the intestine. Early correction of vascular insufficiency is the most important factor in improving patient survival when confronted with acute mesenteric intestinal ischemia. A prolonged loss of blood flow results in irreversible damage to the intestine that can lead to death. It is also imperative that dead segments of the intestines be removed. Several subjective criteria are relied upon to differentiate viable from non-viable tissue, unfortunately, these criteria can lead to an inaccurate assessment. A porcine model of intestinal ischemia was used to determine the efficacy of using near infrared (NIR) spectroscopy to find ischemic segments of the intestine and detect the onset of reperfusion following resolution of vascular occlusion. Nine segments of intestine were identified and six were assigned to three treatment groups; (1) segments undergoing no vascular manipulations, (2) segments undergoing arterial/venous occlusion and (3) segments undergoing arterial/venous occlusion followed by reperfusion. The remaining segments were used as spacers and interposed between each of the ischemia segments. A classification model, using partial least square discriminant analysis, was built on the spectra collected from the segments with no vascular manipulations and the segments that were solely subjected to arterial/venous occlusion. The spectra collected from the intestinal segments that experienced both occlusion and reperfusion were used to test the classification model. The model was able to detect and distinguish ischemic intestinal tissue with a specificity and sensitivity exceeding 80% with an overall classification accuracy of 89%. The method appears to be well suited as an intra-operative assessment method when intestinal ischemia is a concern.

Evaluating the health of compromised tissues using a near-infrared spectroscopic imaging system in clinical settings: lessons learned

The present and accepted standard for determining the status of tissue relies on visual inspection of the tissue. Based on the surface appearance of the tissue, medical personnel will make an assessment of the tissue and proceed to a course of action or treatment. Visual inspection of tissue is central to many areas of clinical medicine, and remains a cornerstone of dermatology, reconstructive plastic surgery, and in the management of chronic wounds, and burn injuries. Near infrared spectroscopic imaging holds the promise of being able to monitor the dynamics of tissue physiology in real-time and detect pathology in living tissue. The continuous measurement of metabolic, physiological, or structural changes in tissue is of primary concern in many clinical and biomedical domains. A near infrared hyperspectral imaging system was constructed for the assessment of burn injuries and skin flaps or skin grafts. This device merged basic science with engineering and integrated manufacturing to develop a device suitable to detect ischemic tissue. This device has the potential of providing measures of tissue physiology, oxygen delivery and tissue hydration during patient screening, in the operating room or during therapy and post-operative/treatment monitoring. Results from a pre-clinical burn injury study will be presented.

Hemodynamic Information Obtained by Statistical Analysis of Near-IR Spectroscopic Images

The probability of transplanted skin remaining viable is often difficult to assess visually. The adverse circulatory changes following the surgical elevation of a skin flap limits the supply of oxygen to the flap tissue. Regions of tissue which experience prolonged and severe deprivation of oxygen will not survive. A dorsal rat skin flap model was used to demonstrate the potential of visible/near IR multispectral imaging to detect tissues under hypoxic stress. Images were acquired before and immediately after surgery. Image pre-processing methods were used to enhance tissue contrast and eliminate image artifacts. Principal component analysis of these images further enhanced contrast along the length of the flap while varimax rotation simplified data interpretation. Significant hemodynamic changes were detected (i) between pre- and post-operative images, and (ii) within the post-elevation flap image itself. K-means and fuzzy C-means image segmentation methods were applied to the post-operative multispectral images and proved to be reliable means of predicting regions of tissue that would go on to become visibly necrotic after a 72 h monitoring period. The result suggest that statistical analysis of visible/near IR multispectral images can be used to extract clinically relevant information pertaining to tissue hemodynamics following reconstructive surgery.

Assessment of Tissue Viability by Near-IR Spectroscopy and Imaging

Near IR diffuse reflectance spectroscopy and imaging are used to assess tissue status following reconstructive surgery. Utilizing the differential absorption of oxy- and deoxy-hemoglobin between 670-1100 nm, tissue hemoglobin oxygen saturation changes were monitored in reverse McFarlane dorsal rat skin flaps. Significant changes in these parameters were observed upon surgical elevation of the skin flap. A significant regional variation along the skin flap was also observed. The magnitude of the drop is tissue oxygen saturation, as observed immediately following surgery, correlated with the final clinical outcome of the flap tissue. These results indicate the potential of near IR spectroscopy and imaging to monitor tissue oxygenation status and assess tissue viability following reconstructive surgery.