Review of near-infrared methods for wound assessment

Dual-mode nanoprobe strategy integrating ultrasound and near-infrared light for targeted and synergistic arterial thrombolysis

Efficient thrombolysis in time is crucial for prognostic improvement of patients with acute arterial thromboembolic disease, while limitations and complications still exist in conventional thrombolytic treatment methods. Herein, our study sought to investigate a novel dual-mode strategy that integrated ultrasound (US) and near-infrared light (NIR) with establishment of hollow mesoporous silica nanoprobe (HMSN) which contains Arginine-glycine-aspartate (RGD) peptide (thrombus targeting), perfluoropentane (PFP) (thrombolysis with phase-change and stable cavitation) and indocyanine green (ICG) (thrombolysis with photothermal conversion). HMSN is used as the carrier, the surface is coupled with targeted RGD to achieve high targeting and permeability of thrombus, PFP and ICG are loaded to achieve the collaborative diagnosis and treatment of thrombus by US and NIR, so as to provide a new strategy for the integration of diagnosis and treatment of arterial thrombus. From the in vitro and in vivo evaluation, RGD/ICG/PFP@HMSN can aggregate and penetrate at the site of thrombus, and finally establish the dual-mode directional development and thrombolytic treatment under the synergistic effect of US and NIR, providing strong technical support for the accurate diagnosis and treatment of arterial thrombosis.

Layer-by-Layer Microneedle-Mediated rhEGF Transdermal Delivery for Enhanced Wound Epidermal Regeneration and Angiogenesis

Appropriate treatments for acute traumas tend to avoid hemorrhages, vascular damage, and infections. However, in the homeostasis-imbalanced wound microenvironment, currently developed therapies could not precisely and controllably deliver biomacromolecular drugs, which are confronted with challenges due to large molecular weight, poor biomembrane permeability, low dosage, rapid degradation, and bioactivity loss. To conquer this, we construct a simple and effective layer-by-layer (LBL) self-assembly transdermal delivery patch, bearing microneedles (MN) coated with recombinant human epidermal growth factor (LBL MN-rhEGF) for a sustained release to wound bed driven by typical electrostatic force. Pyramidal LBL MN-rhEGF patches hold so enough mechanical strength to penetrate the stratum corneum, and generated microchannels allow rhEGF direct delivery in situ. The administrable delivery of biomacromolecular rhEGF through hierarchically coated MN arrays follows the diffusion mechanism of Fick's second law. Numerous efforts further have illustrated that finger-pressing LBL MN-rhEGF patches could not only promote cell proliferation of normal human dermal fibroblasts (NHDF) and human umbilical vein endothelial cells (HUVEC) in vitro but also take significant effects (regenerative epidermis: ∼144 μm; pro-angiogenesis: higher CD31 expression) in accelerating wound healing of mechanically injured rats, compared to the traditional dressing, which relies on passive diffusion. Our proof-of-concept features novel LBL biomacromolecular drug-delivery systems and self-administrated precision medicine modes at the point of care.

Compact and ultracompact spectral imagers: technology and applications in biomedical imaging

Significance

Spectral imaging, which includes hyperspectral and multispectral imaging, can provide images in numerous wavelength bands within and beyond the visible light spectrum. Emerging technologies that enable compact, portable spectral imaging cameras can facilitate new applications in biomedical imaging.

Aim

With this review paper, researchers will (1) understand the technological trends of upcoming spectral cameras, (2) understand new specific applications that portable spectral imaging unlocked, and (3) evaluate proper spectral imaging systems for their specific applications.

Approach

We performed a comprehensive literature review in three databases (Scopus, PubMed, and Web of Science). We included only fully realized systems with definable dimensions. To best accommodate many different definitions of "compact," we included a table of dimensions and weights for systems that met our definition.

Results

There is a wide variety of contributions from industry, academic, and hobbyist spaces. A variety of new engineering approaches, such as Fabry-Perot interferometers, spectrally resolved detector array (mosaic array), microelectro-mechanical systems, 3D printing, light-emitting diodes, and smartphones, were used in the construction of compact spectral imaging cameras. In bioimaging applications, these compact devices were used for in vivo and ex vivo diagnosis and surgical settings.

Conclusions

Compact and ultracompact spectral imagers are the future of spectral imaging systems. Researchers in the bioimaging fields are building systems that are low-cost, fast in acquisition time, and mobile enough to be handheld.

Arterial spin labeling magnetic resonance imaging quantifies tissue perfusion around foot ulcers

Objective

Tools that quantify tissue perfusion of the foot are deficient, contributing to the uncertainty in predicting ulcer healing potential. This pilot study aims to quantify peri-wound foot perfusion at various tissue depths using a novel application of pseudo-continuous arterial spin labeling magnetic resonance imaging.

Methods

Ten diabetic patients with neuropathic wounds and 20 healthy volunteers without wounds were recruited. Wounds were graded according to the Wound, Ischemia, Foot Infection (WIfI) system. All subjects underwent a noncontrasted ASL MRI of the foot for perfusion measurements. For healthy volunteers, perfusion was compared at rest and during sustained toe flexion between four regions: lateral plantar, medial plantar, lateral calcaneal, and medial calcaneal. Evaluations of diabetic volunteers compared perfusion between four zones: wound, near border, far border, and remote. Remote zone perfusion in diabetics was compared with perfusion in the plantar foot of healthy volunteers.

Results

There were 11 wounds, which were located over the metatarsal heads in five, the stump of a transmetatarsal amputation in three, the heel in two, and the mid foot in one. The median WIfI stage was 2. One patient had a WIfI ischemia grade of 1; the remaining patients' grades were 0. The mean ankle-brachial index was 1.0 ± 0.3. There were two patients with a WIfI foot infection grade of 1; the remaining patients' grades were 0. In healthy volunteers, plantar foot perfusion with sustained toe flexion was 43.9 ± 1.7 mL/100g/min and significantly higher than perfusion at rest (27.3 ± 2.7 mL/100g/min; P < .001). In diabetic patients, perfusion at the wound, near border, far border, and remote regions was 96.1 ± 10.7, 92.7 ± 9.4, 73.4 ± 8.2, and 62.8 ± 2.7 mL/100g/min. Although this perfusion pattern persisted throughout the depth of the wound, perfusion decreased with tissue depth. In the near border, perfusion at 20% of the wound depth was 124.0 ± 35.6 mL/100g/min and 69.9 ± 10.1 mL/100g/min at 100% (P = .006). Lastly, remote perfusion in diabetics was 2.3 times the plantar perfusion in healthy volunteers (27.3 ± 2.7 mL/100g/min; P < .001).

Conclusions

The pattern of resting tissue perfusion around nonischemic diabetic foot ulcers was successfully quantified with arterial spin labeling magnetic resonance imaging. Diabetic patients with wounds were hyperemic compared with healthy volunteers. There was a 1.5-fold increase in peri-wound tissue perfusion relative to the rest of the foot. This study is the first step in developing a tool to assess the perfusion deficit in ischemic wounds.

Wound Size Imaging: Ready for Smart Assessment and Monitoring

Significance: We introduce and evaluate emerging devices and modalities for wound size imaging and also promising image processing tools for smart wound assessment and monitoring. Recent Advances: Some commercial devices are available for optical wound assessment but with limited possibilities compared to the power of multimodal imaging. With new low-cost devices and machine learning, wound assessment has become more robust and accurate. Wound size imaging not only provides area and volume but also the proportion of each tissue on the wound bed. Near-infrared and thermal spectral bands also enhance the classical visual assessment. Critical Issues: The ability to embed advanced imaging technology in portable devices such as smartphones and tablets with tissue analysis software tools will significantly improve wound care. As wound care and measurement are performed by nurses, the equipment needs to remain user-friendly, enable quick measurements, provide advanced monitoring, and be connected to the patient data management system. Future Directions: Combining several image modalities and machine learning, optical wound assessment will be smart enough to enable real wound monitoring, to provide clinicians with relevant indications to adapt the treatments and to improve healing rates and speed. Sharing the wound care histories of a number of patients on databases and through telemedicine practice could induce a better knowledge of the healing process and thus a better efficiency when the recorded clinical experience has been converted into knowledge through deep learning.

Oxygen-Sensing Biomaterial Construct for Clinical Monitoring of Wound Healing

OBJECTIVE

Oxygen is essential to wound healing; therefore, accurate monitoring can guide clinical decisions. Clinical wound assessment is often subjective, and tools to monitor wound oxygen are typically expensive, indirect, and highly variable. This study demonstrates the utility of a novel, low-cost oxygen-sensing thin film for serial assessment of wound oxygenation.

DESIGN

Dual-layer films were fabricated with boron oxygen-sensing nanoparticles (BNPs) impregnated into a chitosan-polycaprolactone layer for direct wound bed contact with a relatively oxygen impermeable calcium alginate surface layer. The BNPs are a dual-emissive difluoroboron β-diketonate dye incorporated into poly(lactic acid) nanoparticles. Under UV excitation, the BNPs emit fluorescence based on concentration and oxygen-sensitive phosphorescence. The fluorescence/phosphorescence ratio is directly proportional to oxygen concentration.

METHODS

A series of in vitro oxygen challenges and in vivo murine and porcine wound healing models were used to validate the utility of the film in sensing wound oxygenation.

MAIN RESULTS

In vitro testing demonstrated the oxygen-sensing capability of the BNP film and its ability to shield ambient oxygen to isolate wound oxygen. In vivo testing demonstrated the ability of the film to accurately monitor relative oxygen changes in a murine wound over time, measuring a 22% fluorescence/phosphorescence increase during acute healing.

CONCLUSIONS

This study presents a low-cost, noninvasive, direct, and serial oxygen mapping technology to detect spatial differences in wound oxygenation. Clinical use of the films has the potential to monitor wound healing trajectories and guide wound care decisions.

Hyperspectral imaging in wound care: A systematic review

Multispectral and hyperspectral imaging (HSI) are emerging imaging techniques with the potential to transform the way patients with wounds are cared for, but it is not clear whether current systems are capable of delivering real-time tissue characterisation and treatment guidance. We conducted a systematic review of HSI systems that have been assessed in patients, published over the past 32 years. We analysed 140 studies, including 10 different HSI systems. Current in vivo HSI systems generate a tissue oxygenation map. Tissue oxygenation measurements may help to predict those patients at risk of wound formation or delayed healing. No safety concerns were reported in any studies. A small number of studies have demonstrated the capabilities of in vivo label-free HSI, but further work is needed to fully integrate it into the current clinical workflow for different wound aetiologies. As an emerging imaging modality for medical applications, HSI offers great potential for non-invasive disease diagnosis and guidance when treating patients with both acute and chronic wounds.

Quantifying dermal microcirculatory changes of neuropathic and neuroischemic diabetic foot ulcers using spatial frequency domain imaging: a shade of things to come?

INTRODUCTION

The use of non-invasive vascular and perfusion diagnostics are an important part of assessing lower extremity ulceration and amputation risk in patients with diabetes mellitus. Methods for detecting impaired microvascular vasodilatory function in patients with diabetes may have the potential to identify sites at risk of ulceration prior to clinically identifiable signs. Spatial frequency domain imaging (SFDI) uses patterned near-infrared and visible light spectroscopy to determine tissue oxygen saturation and hemoglobin distribution within the superficial and deep dermis, showing distinct microcirculatory and oxygenation changes that occur prior to neuropathic and neuroischemic ulceration.

RESEARCH DESIGNS AND METHODS

35 patients with diabetes mellitus and a history of diabetic foot ulceration were recruited for monthly imaging with SFDI. Two patients who ulcerated during the year-long longitudinal study were selected for presentation of their clinical course alongside the dermal microcirculation biomarkers from SFDI.

RESULTS

Patient 1 developed a neuropathic ulcer portended by a focal increase in tissue oxygen saturation and decrease in superficial papillary hemoglobin concentration 3 months prior. Patient 2 developed bilateral neuroischemic ulcers showing decreased tissue oxygen saturation and increased superficial papillary and deep dermal reticular hemoglobin concentrations.

CONCLUSIONS

Wounds of different etiology show unique dermal microcirculatory changes prior to gross ulceration. Before predictive models can be developed from SFDI, biomarker data must be correlated with the clinical course of patients who ulcerate while being followed longitudinally.

TRIAL REGISTRATION NUMBER

NCT03341559.

Hyperspectral imaging in wound care: A systematic review

Multispectral and hyperspectral imaging (HSI) are emerging imaging techniques with the potential to transform the way patients with wounds are cared for, but it is not clear whether current systems are capable of delivering real-time tissue characterisation and treatment guidance. We conducted a systematic review of HSI systems that have been assessed in patients, published over the past 32 years. We analysed 140 studies, including 10 different HSI systems. Current in vivo HSI systems generate a tissue oxygenation map. Tissue oxygenation measurements may help to predict those patients at risk of wound formation or delayed healing. No safety concerns were reported in any studies. A small number of studies have demonstrated the capabilities of in vivo label-free HSI, but further work is needed to fully integrate it into the current clinical workflow for different wound aetiologies. As an emerging imaging modality for medical applications, HSI offers great potential for non-invasive disease diagnosis and guidance when treating patients with both acute and chronic wounds.

[Hyperspectral imaging for postoperative flap monitoring of pedicled flaps]

BACKGROUND

Since pedicle flaps were first described by the Indian physician Sushruta Samhita in the 6th century B. C., they have become an integral part of reconstructive surgery. As more and more research has been conducted into the underlying physical principles, flap monitoring has developed steadily in the last few decades. Hyperspectral Imaging (HSI) is a new quantitative measuring method for assessing the perfusion of the underlying tissue.

OBJECTIVE

This study aims to evaluate HSI as a monitoring method for pedicle flaps.

PATIENTS AND METHODS

In 16 patients who had undergone reconstructive surgery, oxygen saturation, haemoglobin and water concentration of the locoregional flap, necrotic flap areas as well as intact skin were measured on postoperative days 1 to 7. Subsequently, the data were statistically described and graphically illustrated.

RESULTS

HSI revealed increased haemoglobin concentration and decreased oxygen and water concentration in necrotic flap areas compared with the monitor island and healthy skin. The distribution of the values collected from the vital skin areas and the monitor island was almost identical.

CONCLUSION

HSI allows for safe, immediate, non-contact measurement of tissue perfusion of transferred tissue areas in patients after pedicle flap surgery. The use of HSI may improve postoperative flap monitoring.

A Systematic Review on Classification, Identification, and Healing Process of Burn Wound Healing

Because of the intrinsic complexity, the classification of wounds is important for the diagnosis, management, and choosing the correct treatment based on wound type. Generally, burn injuries are classified as a class of wounds in which injury is caused by heat, cold, electricity, chemicals, friction, or radiation. On the other hand, wound healing is a complex process, and understanding the biological trend of this process and differences in the healing process of different wounds could reduce the possible risk in many cases and greatly reduce the future damage to the injured tissue and other organs. The aim of this review is to provide a general perspective for the burn wound location among the other types of injuries and summarizing as well as highlighting the differences of these types of wounds with emphasizing on factors affecting thereof.

Extended Perfusion Parameter Estimation from Hyperspectral Imaging Data for Bedside Diagnostic in Medicine

Background: Hyperspectral Imaging (HSI) has a strong potential to be established as a new contact-free measuring method in medicine. Hyperspectral cameras and data processing have to fulfill requirements concerning practicability and validity to be integrated in clinical routine processes. Methods: Calculating physiological parameters which are of significant clinical value from recorded remission spectra is a complex challenge. We present a data processing method for HSI remission spectra based on a five-layer model of perfused tissue that generates perfusion parameters for every layer and presents them as depth profiles. The modeling of the radiation transport and the solution of the inverse problem are based on familiar approximations, but use partially heuristic methods for efficiency and to fulfill practical clinical requirements. Results: The parameter determination process is consistent, as the measured spectrum is practically completely reproducible by the modeling sequence; in other words, the whole spectral information is transformed into model parameters which are easily accessible for physiological interpretation. The method is flexible enough to be applicable on a wide spectrum of skin and wounds. Examples of advanced procedures utilizing extended perfusion representation in clinical application areas (flap control, burn diagnosis) are presented.

A compact hyperspectral camera for measurement of perfusion parameters in medicine

Worldwide, chronic wounds are still a major and increasing problem area in medicine with protracted suffering of patients and enormous costs. Beside conventional wound treatment, for instance kinds of oxygen therapy and cold plasma technology have been tested, providing an improvement in the perfusion of wounds and their healing potential, but these methods are unfortunately not sufficiently validated and accepted for clinical practice to date. Using hyperspectral imaging technology in the visible (VIS) and near infrared (NIR) region with high spectral and spatial resolution, perfusion parameters of tissue and wounds can be determined. We present a new compact hyperspectral camera which can be used in clinical practice. From hyperspectral data the hemoglobin oxygenation (StO2), the relative concentration of hemoglobin [tissue hemoglobin index (THI)] and the so-called NIR-perfusion index can be determined. The first two parameters are calculated from the VIS-part of the spectrum and represent the perfusion of superficial tissue layers, whereas the NIR-perfusion index is calculated from the NIR-part representing the perfusion in deeper layers. First clinical measurements of transplanted flaps and chronic ulcer wounds show, that the perfusion level can be determined quantitatively allowing sensitive evaluation and monitoring for an optimization of the wound treatment planning and for validation of new treatment methods.

A portable three-dimensional photoacoustic tomography system for imaging of chronic foot ulcers

Background

Chronic leg ulcers affect approximately 6.5 million Americans and the disorder is associated with a range of serious complications. Since many chronic ulcers have underlying vascular insufficiency, accurate assessment of tissue perfusion is critical to treatment planning and post-surgical monitoring. However, existing clinical tests fail to meet this need in practice due to their low sensitivity or accuracy.

Methods

In this paper, we introduce a portable photoacoustic tomography (PAT) system for wound assessment. Since hemoglobin serves as the major endogenous contrast at near-infrared wavelengths, PAT provides label-free, three-dimensional (3D) imaging of hemoglobin distribution, which is closely related to blood perfusion. The proposed system consists of a 128-element linear transducer array, a data acquisition (DAQ) system, and a pulsed Nd:YAG laser source, all mounted on a portable cart for easy clinical testing.

Results

We validated our system through both phantom and human imaging studies. The phantom imaging results indicate that the system's spatial resolution ranges from 0.5 mm along the axial direction to 1.3 mm along the elevational direction. The healthy volunteer result shows clear foot vasculature, indicating good perfusion. The preliminary patient imaging results agree very well with the clinical test, demonstrating that PAT has a high potential for assessing the circulation around the wound.

Conclusions

We believe that our technique will be a valuable tool for assessing tissue perfusion and guiding wound treatment in vascular clinics.

Near-instant noninvasive optical imaging of tissue perfusion for vascular assessment

BACKGROUND

Noninvasive vascular tests are critical for identifying patients who may benefit from surgical revascularization, but current tests have significant limitations in people with diabetes. This study aimed to evaluate the ability of spatial frequency domain imaging (SFDI), an optical imaging method capable of measuring tissue oxygen saturation (StO₂) and tissue hemoglobin, to assess lower extremity blood supply.

METHODS

Ankle-brachial index, toe-brachial index, pedal Doppler waveforms, and SFDI images were prospectively evaluated in 47 consecutive patients with and without diabetes in whom there was concern for peripheral artery disease (PAD). SFDI is a noncontact optical imaging technology that uses structured illumination to quantify subsurface (2-3 mm in depth) StO₂ and tissue hemoglobin in the dermal microcirculation (HbT₁) and macrocirculation (HbT₂) over a large field of view (15 × 20 cm) within 10 seconds.

RESULTS

This demonstrates the ability of SFDI to capture reliable clinical measurements of perfusion in plantar aspects of the feet. SFDI StO₂ values differentiate nondiabetic patients with and without arterial disease, defined as ankle-brachial index <0.9 (P = .06), but are limited in those with diabetes (P = .43). An elevated StO₂ and reduced HbT₁ are observed in people with diabetes compared with nondiabetic patients (P < .05). An SFDI-derived HbT₂/HbT₁ index differentiates diabetics with PAD vs no PAD (P < .01) using toe-brachial index <0.7 as a cutoff for PAD in diabetes.

CONCLUSIONS

SFDI is a feasible, rapid, and easy to use widefield measurement of perfusion in a clinical setting. This first-of-use study suggests that the technology has potential to evaluate lower extremity perfusion in people with and without diabetes. Further studies with increased numbers of patients and end points including wound healing will need to be designed to fully evaluate the applicability of this new technology.

Preclosure spectroscopic differences between healed and dehisced traumatic wounds

BACKGROUND

The complexity and severity of traumatic wounds in military and civilian trauma demands improved wound assessment, before, during, and after treatment. Here, we explore the potential of 3 charge-coupled device (3CCD) imaging values to distinguish between traumatic wounds that heal following closure and those that fail. Previous studies demonstrate that normalized 3CCD imaging values exhibit a high correlation with oxygen saturation and allow for comparison of values between diverse clinical settings, including utilizing different equipment and lighting.

METHODS

We screened 119 patients at Walter Reed National Military Medical Center and at Grady Memorial Hospital with at least one traumatic extremity wound of ≥ 75 cm2. We collected images of each wound during each débridement surgery for a total of 66 patients. An in-house written computer application selected a region of interest in the images, separated the pixel color values, calculated relative values, and normalized them. We followed patients until the enrolled wounds were surgically closed, quantifying the number of wounds that dehisced (defined as wound failure or infection requiring return to the operating room after closure) or healed.

RESULTS

Wound failure occurred in 20% (19 of 96) of traumatic wounds. Normalized intensity values for patients with wounds that healed successfully were, on average, significantly different from values for patients with wounds that failed (p ≤ 0.05). Simple thresholding models and partial least squares discriminant analysis models performed poorly. However, a hierarchical cluster analysis model created with 17 variables including 3CCD data, wound surface area, and time from injury predicts wound failure with 76.9% sensitivity, 76.5% specificity, 76.6% accuracy, and a diagnostic odds ratio of 10.8 (95% confidence interval: 2.6-45.9).

CONCLUSIONS

Imaging using 3CCD technology may provide a non-invasive and cost-effective method of aiding surgeons in deciding if wounds are ready for closure and could potentially decrease the number of required débridements and hospital days. The process may be automated to provide real-time feedback in the operating room and clinic. The low cost and small size of the cameras makes this technology attractive for austere and shipboard environments where space and weight are at a premium.