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Fast, non-invasive hyperspectral imaging tool for the diagnosis and management of complex foot and leg ulcers — part 1

This is the first of two articles examining a new hyperspectral imaging system (HSI). This non-invasive imaging system provides information about tissue oxygenation, tissue haemoglobin index, near-infrared and the tissue water index. The TIVITA® is a new compact camera that can be used in clinical practice by the patient’s bedside. The data are generated within 6.4 seconds and the pictures can be shown to the patient directly at the bedside, enabling the clinician to discuss the findings with the patient, as well as possible treatment options. Part one shows how HSI can be used to increase the patient’s adherence to treatment. Part two will provide a more extensive look at how HSI works and how it can be used to evaluate and monitor wound dressing, debridement and new technologies in the treatment of diabetic foot ulcers and other chronic wounds.

In 2019, the International Working Group on the Diabetic Foot (IWGDF) published new guidelines (Schaper et al, 2019). Every 20 seconds, somewhere in the world, a human with diabetes has an amputation (Schaper et al, 2019). That is a drastic increase in amputation rates compared to the previous guidelines, which highlighted that there were 30 seconds between amputations across the globe (Armstrong et al, 2007).
Patient-related factors can influence the outcomes, including comorbidities, severity of the underlying conditions and adherence (Atkin et al, 2019).

Poster and leaflet campaign to raise awareness about DFU-associated amputations
Fox and Smith-Burges (2018) reported a new educational approach for patients with diabetes and the possible improvement of their adherence. The Manchester Leg Circulation Service initiated a wide-ranging poster and leaflet campaign to increase the awareness of people with diabetic foot ulcers (DFUs) about their high mortality risks and support clinicians in discussing this issue with their patients. The posters should also help clinicians to focus on effective risk-reduction interventions, which is one option to consider when improving patient adherence.

Hyperspectral imaging for improving the treatment of patients with hard-to-heal wounds
Another option to improve patient adherence is the use of the TIVITA® Tissue hyperspectral imaging system (Diaspective Vision GmbH, Germany), (Figure 1; Wild et al, 2018). Hyperspectral imaging (HSI) is a non-invasive imaging technique in the visible and near-infrared spectral range. The TIVITA Tissue (Tissue Perfusion Imaging System) is a camera system used for wound documentation that can measure wound size, as well as tissue perfusion, e.g. in chronic wounds and flaps. The target fields for wound healing analyses are plastic surgery, wound diagnostics, dermatology, oral and head surgery, wound-healing centres and burns injury centres. Indications include DFUs, complex leg ulcers, oedema, flap diagnostics and monitoring, chronic wounds, postoperative wound-healing disorders, burn diagnostics, wounds caused by vascular disease and pressure ulcers. There are no known contraindications so far.
This system provides information about tissue oxygenation (StO2), the tissue haemoglobin index (THI), perfusion in the deeper layer of the tissue, near-infrared perfusion index (NIR) and the tissue water index (TWI).

How does this system work?
Tissue is a mixture of absorbers and stray particles. The main absorber is haemoglobin in the microcirculation and water of tissue cells. Light is reflected, remitted, transmitted or absorbed (Wild et al, 2018). Shortwave light in the structures and components of the wound or tissue can absorb and scatter irradiated light. These physical effects can be recorded with a camera, working like a push-broom imager (Tetschke et al, 2016). The TIVITA contains a spectrometer with a CMOS camera sensor, which is sensitive to a wavelength range of 500–1,000 nm, offering a spatial resolution of 640 x 480 and a spectral resolution of 5 nm. Rutkowski et al (2017) state: “Based on the spectral information, a three-dimensional (3D) data cube consisting of two spatial dimensions and one spectral dimension is generated which constitutes the basis for calculation of oxygen saturation at tissue surface (StO2 in [%]), as well as in deeper layers (NIR), 8 mm depth, calculated index (0–100) and haemoglobin contend (THI, calculated index (0-100)).” Figure 2 shows the parameter images generated by the HSI data within 6.4 seconds.

Shortwave light is strongly absorbed, resulting in low penetration depth. This provides the user with  information about the superficial part of the tissue. Long-wave light in the NIR range is slightly absorbed, resulting in higher penetration depth. This provides information on the deeper layer of the tissue (Wild et al, 2018).

For more detailed information about how the HSI system works, the author suggests reading the following papers: Rutkowski et al (2017), Tetschke et al (2016) and Wild et al (2018). Part 2 will provide a deeper look at how this system works and how it can help to monitor new dressings, to evaluate debridement methods and to monitor new treatment options, such as cold atmospheric plasma (CAP).

How can this hyperspectral imaging system contribute to the treatment of patients with DFU?
HSI is a new method for wounds and surgery (Köhler et al, 2019; Marotz et al, 2019). As it is contactless, HSI is ideal for conducting bedside diagnostics. Beside calculating the already mentioned parameters, the wound area can also be measured (Figure 3) and markers can be set for analysing different tissue areas (Figure 4).

Case report
The patient is male and was born in 1960. He presented with a DFU on the right forefoot (Wagner 3/Armstrong D). The ulcer was 11 cm long and 7 cm wide. The big toe on the right foot was missing; it was amputated in November 2017 at another hospital. Since this time, the patient developed a DFU. In 2017, he underwent a thromboendarterectomy in the groin at the same hospital.

Peripheral arterial disease (PAD) was also present. He was admitted to the author’s hospital through the outpatient diabetic foot clinic. The skin on the right leg was macerated due to chronic oedema. The leg was swollen, red and very painful (Figures 5, 6 & 7). Due to the pain, which was present when he lay in bed, he mostly sat on the bedside or in his wheelchair. He was a heavy smoker, thus he was outside with the wheelchair more than inside the room. The patient slept sitting on the bedside. He was very uncooperative to the treatment options and did not want compression therapy because of the pain. The patient did not trust the clinicians at  Kreiskliniken Reutlingen, as the previous hospital had already taken into consideration a potential amputation of his right leg. The first picture taken with the HSI system (Figure 8) showed oedema in the wound bed and in the leg as a whole (Figure 9). He also had a swollen left leg (Figure 10).

A biopsy was taken of the wound. Five different bacteria species were found to be present in the wound (serratia marcescens, citrobacter koseri, morganella morganii ssp. Morganii, comamonas testosterone and enterococcus faecium). The patient was treated with intravenous antibiotics, and the wound was subjected to surgical debridement and larval therapy (maggots). The wound was then treated with a DACC dressing (Cutimed® Sorbact, Essity) and a dressing with capillary action (Vacutex™, Protex healthcare) and a superabsorbent dressing (Zetuvit®, Paul Hartmann Ag).
The PAD was treated with a percutaneous transluminal angioplasty (PTA) of the arteria tibialis anterior and the arteria fibularis in the right leg in the author’s hospital 7 days after admission.

The hospital’s pain department was involved in the treatment of the patient’s pain. After discussion with the patient, two nerve blocks were inserted in the right leg (DIC/saphenous). Additionally, continuous 24-hour medication was applied.
A picture was taken with the HSI (Figure 9) showing the presence of oedema in the right leg. Clinicians at the author’s hospital discussed the different treatment options with the patient. Suggestions included manual lymphatic drainage, skin care and mild compression therapy (Todd, 2017). The patient was against this idea for two reasons: firstly, the pain; and secondly, his poor experience with his previous hospital. The images of the HSI were shown to the patient and the clinicians involved in his care continually explained to him the importance of compression therapy and manual lymphatic drainage (Figure 10). After 2 days, the patient was convinced to use a mild compression therapy on the left leg with adhesive compression bandages (UrgoK2 lite, Urgo Medical) (Figure 11).

After he recognised the positive impact of the compression therapy on the left leg, the patient was then convinced to try a velcro wrap system on his right leg (Figure 12, 13 & 14).

After a 75-day stay in the author’s hospital, the patient was released and looked after through the diabetic foot outpatient centre. Four weeks later, the patient underwent a skin graft on the right forefoot (Figure 15). No oedema was present in the left leg (Figure 16) nor in the right leg (Figure 17). As the skin graft healed, he was discharged after 4 weeks. He visited the diabetic foot outpatient centre once a week until complete wound healing was achieved (Figure 18). In June 2019, he had an appointment in our diabetic foot outpatient centre. The wound was still healed

Conclusion
HSI is a bedside diagnostic tool that is helpful in  the monitoring of the treatment of patients with chronic wounds. As the images can be shown directly at the patient’s bedside, it is also a useful tool to improve patient adherence to treatment.

HSI can be used to control the success of different therapeutic strategies, such as compression therapy. Another possible use is the evaluation of the mode of actions of different types of wound dressings directly on the wound bed/surface. This also applies for the different types of debridement.

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Atkin L, Bucko Z, Condo Montero E et al (2019) Implementing TIMERS: the race against hard-to-heal wounds. J Wound Care 23(Sup3a): S1–S50
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Schaper NC, van Netten JJ, Apelqvist J et al (2019) IWGDF Guidelines on the Prevention and Management of Diabetic Foot Disease. Available at: https://iwgdfguidelines.org/wp-contenthttps://www.diabetesonthenet.com/uploads/2019/05/IWGDF-Guidelines-2019.pdf (accessed 08.06.2020)
Tetschke F, Markgraf W, Gransow M et al (2016) Hyperspectral imaging for monitoring oxygen saturation levels during normothermic kidney perfusion. J Sensors and Sensor Systems 5: 313–8
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