Helping the NHS reduce pressure ulcers

Christopher Kennedy, a young entrepreneur from Purley, has just established a business, Imago Care, that procures the latest medical technology to distribute to the NHS, hospices, nursing homes, and individual community based customers.

His flagship product, Parafricta, a frictionless fabric is the first proven answer to the key nursing goal identified by EPUAP (European Pressure Ulcer Advisory Board), namely to "protect against the adverse effects of external mechanical forces: pressure, friction and shear on skin".The 25 yr old explained: "It is wonderful to be a part of a product that will revolutionalize the way to prevent pressure ulcers, treat dry skin conditions like eczema, keep wound dressings in place that are dislodged due to friction and to help gain these sufferers a better quality of life."

"Pressure ulcers cost the NHS around 2 billion every year and now there is a product that can reduce this cost dramatically. The fabric boasts properties that have already gain recognition by London's Science Museum. It has a coefficient of friction close to that of ice, almost as strong as steel, breathable, inert and can be washed up to 160 degrees with out losing any of its properties. "Parafricta™ Fabric products have been evaluated by more than 15 NHS sites in the UK including Great Ormond Street, where trials were conducted on children with fragile skin due to Epidermolysis Bullosa.

The results have confirmed that the garments and bedclothes prevent skin breakdown and progression to clinically detrimental pressure ulcers.Imago Care has also procured other leading products that aid in the treatment of chronic and acute wounds. For more information please call 0208 668 6084 or visit www.imagocare.com.

Vascular Wound Assessment (Getting to the Heart of the Matter)

Vascular Wound Assessment (Getting to the Heart of the Matter)

January 13, 2009 — Matthew Livingston R.N. C.W.S.

I came across this very insightful post that I thought I would direct your attention to.

VASCULAR ASSESSMENT

The vascular assessment will answer the question “Does the wound have enough blood supply to heal?”
Healthy tissue is bright, beefy red, shiny, and granular with a velvety appearance. Tissue with poor
vascular supply is pale pink or blanched to dull, dusky red color.

Physical vascular assessment includes: peripheral pulses, temperature, presence or absence of hair,
mild to severe pain, rest pain, edema, and gangrene. The vascular assessment should also include:

Pallor: White, pale, blanched color of a limb when in the upright position.

Rubor: Dark purple to bright red color of a limb when in a dependent position.

Intermittent claudication: Cramping or fatigue of major muscle groups in one or both lower extremities that is reproducible upon walking a specific distance. This suggests intermittent claudication and is caused by muscle ischemia.

Mottling or mottled skin: Irregular patchy skin coloring. Refers specifically related to blood
vessel changes in the skin which cause the patchy appearance. This may indicate
vascular insufficiency.

Capillary refill: The measurement of the rate of blood refill in empty capillaries . Measured
by pressing a nail bed or area of tissue until it turns white and then timing until the
return of color once the pressure is released. Normal refill time is less than 2 seconds.

Diagnostic studies for vascular assessment:
Transcutaneous oxygen measurement (TCOM)
Ankle brachial index (ABI)
Arterial duplex scan
Arteriogram
Magnetic Resonance Arteriogram (MRA)

WITA Wound Assessment - Chronic Wounds

A chronic wound is a wound that does not heal in an orderly set of stages and in a predictable amount of time the way most wounds do; wounds that do not heal within three months are often considered chronic. Chronic wounds seem to be detained in one or more of the phases of wound healing. For example, chronic wounds often remain in the inflammatory stage for too long. In acute wounds, there is a precise balance between production and degradation of molecules such as collagen; in chronic wounds this balance is lost and degradation plays too large a role.

Chronic wounds may never heal or may take years to do so.

Encyclopedia

A chronic wound is a wound that does not heal in an orderly set of stages and in a predictable amount of time the way most wounds do; wounds that do not heal within three months are often considered chronic. Chronic wounds seem to be detained in one or more of the phases of wound healing. For example, chronic wounds often remain in the inflammatory stage for too long. In acute wounds, there is a precise balance between production and degradation of molecules such as collagen; in chronic wounds this balance is lost and degradation plays too large a role.

Chronic wounds may never heal or may take years to do so. These wounds cause patients severe emotional and physical stress as well as creating a significant financial burden on patients and the whole healthcare system.

Acute and chronic wounds are at opposite ends of a spectrum of wound healing types that progress toward being healed at different rates.

Epidemiology

Chronic wounds mostly affect people over the age of 60. The incidence is 0.78% of the population and the prevalence ranges from 0.18 to 0.32%. As the population ages, the number of chronic wounds is expected to rise.

Types

The vast majority of chronic wounds can be classified into three categories: venous ulcers, diabetic, and pressure ulcers. A small number of wounds that do not fall into these categories may be due to causes such as radiation poisoning or ischemia.

Venous ulcers

Venous ulcers, which usually occur in the legs, account for about 70% to 90% of chronic wounds and mostly affect the elderly. They are thought to be due to venous hypertension caused by improper function of valves that exist in the veins to prevent blood from flowing backward. Ischemia results from the dysfunction and, combined with reperfusion injury, causes the tissue damage that leads to the wounds.

Diabetic ulcers

Another major cause of chronic wounds, diabetes, is increasing in prevalence. Diabetics have a 15% higher risk for amputation than the general population due to chronic ulcers. Diabetes causes neuropathy, which inhibits nociception and the perception of pain. Thus patients may not initially notice small wounds to legs and feet, and may therefore fail to prevent infection or repeated injury. Further, diabetes causes immune compromise and damage to small blood vessels, preventing adequate oxygenation of tissue, which can cause chronic wounds. Pressure also plays a role in the formation of diabetic ulcers.

Pressure ulcers

Another leading type of chronic wounds is pressure ulcers, which usually occur in people with conditions such as paralysis that inhibit movement of body parts that are commonly subjected to pressure such as the heels, shoulder blades, and sacrum. Pressure ulcers are caused by ischemia that occurs when pressure on the tissue is greater than the pressure in capillaries, and thus restricts blood flow into the area. Muscle tissue, which needs more oxygen and nutrients than skin does, shows the worst effects from prolonged pressure. As in other chronic ulcers, reperfusion injury damages tissue.

Pain and chronic wounds

Chronic wound patients often report pain as dominant in their lives. It is recommended that healthcare providers handle the pain related to chronic wounds as one of the main priorities in chronic wound management (together with addressing the cause). Six out of ten venous leg ulcer patients experience pain with their ulcer, and similar trends are observed for other chronic wounds.

Persistent pain (at night, at rest, and with activity) is the main problem for patients with chronic ulcers. Frustrations regarding ineffective analgesics and plans of care that they were unable to adhere to were also identified.

Contributing factors

In addition to poor circulation, neuropathy, and difficulty moving, factors that contribute to chronic wounds include systemic illnesses, age, and repeated trauma. Comorbid ailments that may contribute to the formation of chronic wounds include vasculitis (an inflammation of blood vessels), immune suppression, pyoderma gangrenosum, and diseases that cause ischemia. Immune suppression can be caused by illnesses or medical drugs used over a long period, for example steroids. Emotional stress can also negatively affect the healing of a wound, possibly by raising blood pressure and levels of cortisol, which lowers immunity.

What appears to be a chronic wound may also be a malignancy; for example, cancerous tissue can grow until blood cannot reach the cells and the tissue becomes an ulcer. Cancer, especially squamous cell carcinoma, may also form as the result of chronic wounds, probably due to repetitive tissue damage that stimulates rapid cell proliferation. Another factor that may contribute to chronic wounds is old age. The skin of older people is more easily damaged, and older cells do not proliferate as fast and may not have an adequate response to stress in terms of gene upregulation of stress-related proteins. In older cells, stress response genes are overexpressed when the cell is not stressed, but when it is, the expression of these proteins is not upregulated by as much as in younger cells.

Comorbid factors that can lead to ischemia are especially likely to contribute to chronic wounds. Such factors include chronic fibrosis, atherosclerosis, edema, sickle cell disease, and arterial insufficiency-related illnesses.

Repeated physical trauma plays a role in chronic wound formation by continually initiating the inflammatory cascade. The trauma may occur by accident, for example when a leg is repeatedly bumped against a wheelchair rest, or it may be due to intentional acts. Heroin users who lose venous access may resort to 'skin popping', or injecting the drug subcutaneously, which is highly damaging to tissue and frequently leads to chronic ulcers. Children who are repeatedly seen for a wound that does not heal are sometimes found to be victims of a parent with Munchausen syndrome by proxy, a disease in which the abuser may repeatedly inflict harm on the child in order to receive attention.

Pathophysiology

Chronic wounds may affect only the epidermis and dermis, or they may affect tissues all the way to the fascia. They may be formed originally by the same things that cause acute ones, such as surgery or accidental trauma, or they may form as the result of systemic infection, vascular, immune, or nerve insufficiency, or comorbidities such as neoplasias or metabolic disorders. The reason a wound becomes chronic is that the body’s ability to deal with the damage is overwhelmed by factors such as repeated trauma, continued pressure, ischemia, or illness.

Though much progress has been accomplished in the study of chronic wounds lately, advances in the study of their healing have lagged behind expectations. This is partly because animal studies are difficult because animals do not get chronic wounds, since they usually have loose skin that quickly contracts, and they normally do not get old enough or have contributing diseases such as neuropathy or chronic debilitating illnesses. Nonetheless, current researchers now understand some of the major factors that lead to chronic wounds, among which are ischemia, reperfusion injury, and bacterial colonization.

Ischemia

Ischemia is an important factor in the formation and persistence of wounds, especially when it occurs repetitively (as it usually does) or when combined with a patient’s old age. Ischemia causes tissue to become inflamed and cells to release factors that attract neutrophils such as interleukins, chemokines, leukotrienes, and complement factors.

While they fight pathogens, neutrophils also release inflammatory cytokines and enzymes that damage cells. One of their important jobs is to produce ROS to kill bacteria, for which they use an enzyme called myeloperoxidase. The enzymes and ROS produced by neutrophils and other leukocytes damage cells and prevent cell proliferation and wound closure by damaging DNA, lipids, proteins, the ECM, and cytokines that speed healing. Neutrophils remain in chronic wounds for longer than they do in acute wounds, and contribute to the fact that chronic wounds have higher levels of inflammatory cytokines and ROS. Since wound fluid from chronic wounds has an excess of proteases and ROS, the fluid itself can inhibit healing by inhibiting cell growth and breaking down growth factors and proteins in the ECM.

Bacterial colonization

Since more oxygen in the wound environment allows white blood cells to produce ROS to kill bacteria, patients with inadequate tissue oxygenation, for example those who suffered hypothermia during surgery, are at higher risk for infection. The host’s immune response to the presence of bacteria prolongs inflammation, delays healing, and damages tissue. Infection can lead not only to chronic wounds but also to gangrene, loss of the infected limb, and death of the patient.

Like ischemia, bacterial colonization and infection damage tissue by causing a greater number of neutrophils to enter the wound site. In patients with chronic wounds, bacteria with resistances to antibiotics may have time to develop. In addition, patients that carry drug resistant bacterial strains such as methicillin-resistant Staphylococcus aureus (MRSA) have more chronic wounds.

Growth factors and proteolytic enzymes

Chronic wounds also differ in makeup from acute wounds in that their levels of proteolytic enzymes such as elastase. and matrix metalloproteinases (MMPs) are higher, while their concentrations of growth factors such as Platelet-derived growth factor and Keratinocyte Growth Factor are lower.

Since growth factors (GFs) are imperative in timely wound healing, inadequate GF levels may be an important factor in chronic wound formation. In chronic wounds, the formation and release of growth factors may be prevented, the factors may be sequestered and unable to perform their metabolic roles, or degraded in excess by cellular or bacterial proteases.

Chronic wounds such as diabetic and venous ulcers are also caused by a failure of fibroblasts to produce adequate ECM proteins and by keratinocytes to epithelialize the wound. Fibroblast gene expression is different in chronic wounds than in acute wounds.

Though all wounds require a certain level of elastase and proteases for proper healing, too high a concentration is damaging. Leukocytes in the wound area release elastase, which increases inflammation, destroys tissue, proteoglycans, and collagen, and damages growth factors, fibronectin, and factors that inhibit proteases. The activity of elastase is increased by human serum albumin, which is the most abundant protein found in chronic wounds. However, chronic wounds with inadequate albumin are especially unlikely to heal, so regulating the wound's levels of that protein may in the future prove helpful in healing chronic wounds.

Excess matrix metalloproteinases, which are released by leukocytes, may also cause wounds to become chronic. MMPs break down ECM molecules, growth factors, and protease inhibitors, and thus increase degradation while reducing construction, throwing the delicate compromise between production and degradation out of balance.

Treatment

Though treatment of the different chronic wound types varies slightly, appropriate treatment seeks to address the problems at the root of chronic wounds, including ischemia, bacterial load, and imbalance of proteases. Various methods exist to ameliorate these problems, including antibiotic and antibacterial use, debridement, irrigation, vacuum-assisted closure, warming, oxygenation, moist wound healing, removing mechanical stress, and adding cells or other materials to secrete or enhance levels of healing factors.

Preventing and treating infection


To lower the bacterial count in wounds, therapists may use topical antibiotics, which kill bacteria and can also help by keeping the wound environment moist, which is important for speeding the healing of chronic wounds. Some researchers have experimented with the use of tea tree oil, an antibacterial agent which also has anti-inflammatory effects. Disinfectants are contraindicated because they damage tissues and delay wound contraction. Further, they are rendered ineffective by organic matter in wounds like blood and exudate and are thus not useful in open wounds.

A greater amount of exudate and necrotic tissue in a wound increases likelihood of infection by serving as a medium for bacterial growth away from the host’s defenses. Since bacteria thrive on dead tissue, wounds are often surgically debrided to remove the devitalized tissue. Debridement and drainage of wound fluid are an especially important part of the treatment for diabetic ulcers, which may create the need for amputation if infection gets out of control. Mechanical removal of bacteria and devitalized tissue is also the idea behind wound irrigation, which is accomplished using pulsed lavage.

Removing necrotic or devitalzed tissue is also the aim of maggot therapy, the intentional introduction by a health care practitioner of live, disinfected maggots non-healing wounds. Maggots dissolve only necrotic, infected tissue; disinfect the wound by killing bacteria; and stimulate wound healing. Maggot therapy has been shown to accelerate debridement of necrotic wounds and reduce the bacterial load of the wound, leading to earlier healing, reduced wound odor and less pain. The combination and interactions of these actions make maggots an extremely potent tool in chronic wound care.

Negative pressure wound therapy (NPWT) is a treatment that improves ischemic tissues and removes wound fluid used by bacteria. This therapy, also known as vacuum-assisted closure, reduces swelling in tissues, which brings more blood and nutrients to the area, as does the negative pressure itself. The treatment also decompresses tissues and alters the shape of cells, causes them to express different mRNAs and to proliferate and produce ECM molecules.

Treating painful wounds

Persistent chronic pain associated with non-healing wounds is caused by tissue (nociceptive) or nerve (neuropathic) damage and is influenced by dressing changes and chronic inflammation. Chronic wounds take long time to heal and patients can suffer from chronic wounds for many years . Chronic wound healing may be compromised by coexisting underlying conditions, such as venous valve backflow, peripheral vascular disease, uncontrolled edema and diabetes mellitus.

If wound pain is not assessed and documented it may be ignored and/or not addressed properly. It is important to remember that increased wound pain may be an indicator of wound complications that need treatment, and therefore practitioners must constantly reassess the wound as well as the associated pain.

Optimal management of wounds requires holistic assessment. Documentation of the patient’s pain experience is critical and may range from the use of a patient diary, (which should be patient driven), to recording pain entirely by the healthcare professional or caregiver. Effective communication between the patient and the healthcare team is fundamental to this holistic approach. The more frequently healthcare professionals’ measure pain, the greater the likelihood of introducing or changing pain management practices.

At present there are few local options for the treatment of persistent pain, whilst managing the exudate levels present in many chronic wounds. Important properties of such local options are that they provide an optimal wound healing environment, while providing a constant local low dose release of ibuprofen during weartime.

If local treatment does not provide adequate pain reduction, it may be necessary for patients with chronic painful wounds to be prescribed additional systemic treatment for the physical component of their pain. Clinicians should consult with their prescribing colleagues referring to the WHO pain relief ladder of systemic treatment options for guidance. For every pharmacological intervention there are possible benefits and adverse events that the prescribing clinician will need to consider in conjunction with the wound care treatment team.

Treating ischemia and hypoxia

Blood vessels constrict in tissue that becomes cold and dilate in warm tissue, altering blood flow to the area. Thus keeping the tissues warm is probably necessary to fight both infection and ischemia. Some healthcare professionals use ‘radiant bandages’ to keep the area warm, and care must be taken during surgery to prevent hypothermia, which increases rates of post-surgical infection.

Underlying ischemia may also be treated surgically by arterial revascularization, for example in diabetic ulcers, and patients with venous ulcers may undergo surgery to correct vein dysfunction.

Diabetics that are not candidates for surgery (and others) may also have their tissue oxygenation increased by Hyperbaric Oxygen Therapy, or HBOT, which can compensate for limitations of blood supply and correct hypoxia. In addition to killing bacteria, higher oxygen content in tissues speeds growth factor production, fibroblast growth, and angiogenesis. However, increased oxygen levels also means increased production of ROS. Antioxidants, molecules that can lose an electron to free radicals without themselves becoming radicals, can lower levels of oxidants in the body and have been used with some success in wound healing.

Low level laser therapy has been repeatedly shown to significantly reduce the size and severity of diabetic ulcers as well as other pressure ulcers.

Growth factors and hormones

Since chronic wounds underexpress growth factors necessary for healing tissue, chronic wound healing may be speeded by replacing or stimulating those factors and by preventing the excessive formation of proteases like elastase that break them down.

One way to increase growth factor concentrations in wounds is to apply the growth factors directly, though this takes many repetitions and requires large amounts of the factors. Another way is to spread onto the wound a gel of the patient’s own blood platelets, which then secrete growth factors such as vascular endothelial growth factor (VEGF), insulin-like growth factor 1–2 (IGF), PDGF, transforming growth factor-ß (TGF-ß), and epidermal growth factor (EGF). Other treatments include implanting cultured keratinocytes into the wound to reepithelialize it and culturing and implanting fibroblasts into wounds. Some patients are treated with artificial skin substitutes that have fibroblasts and keratinocytes in a matrix of collagen to replicate skin and release growth factors. In other cases, skin from cadavers is grafted onto wounds, providing a cover to keep out bacteria and preventing the buildup of too much granulation tissue, which can lead to excessive scarring. Though the allograft (skin transplanted from a member of the same species) is replaced by granulation tissue and is not actually incorporated into the healing wound, it encourages cellular proliferation and provides a structure for epithelial cells to crawl across. On the most difficult chronic wounds, allografts may not work, requiring skin grafts from elsewhere on the patient, which can cause pain and further stress on the patient’s system. Collagen dressings are another way to provide the matrix for cellular proliferation and migration, while also keeping the wound moist and absorbing exudate. Since levels of protease inhibitors are lowered in chronic wounds, some researchers are seeking ways to heal tissues by replacing these inhibitors in them. Secretory leukocyte protease inhibitor (SLPI), which inhibits not only proteases but also inflammation and microorganisms like viruses, bacteria, and fungi, may prove to be an effective treatment.

Research into hormones and wound healing has shown estrogen to speed wound healing in elderly humans and in animals that have had their ovaries removed, possibly by preventing excess neutrophils from entering the wound and releasing elastase. Thus the use of estrogen is a future possibility for treating chronic wounds.

WITA Wound Assessment & Care Management Software

WITA™ uses an advanced statistical pattern recognition algorithm to analyse wound images quickly, providing accurate tissue and dimension data, at the click of a button. WITA™ has a simple three step wound image analysis process that defines the percentage of granulated, fibrous and necrotic tissue, whilst automatically and accurately calculating the circumference, area, width and length of the wound.

Not convinced of WITA™ tissue analysis?

N.B. When analysing wounds it is important to take a clear photo in order to obtain the most accurate results from WITA™.

WITA™ is a clever solution and if you are not happy with the end results of your analysis, simply click on the 'Adjustment Tool', and manually define each of the tissue types to your satisfaction.

Automatic Quantitative Analysis of Healing Skin Wounds using Colour Digital Image Processing

Abstract

This article reviews the recently published research of image processing laboratories involved in colour image processing applied to skin wounds and lesions. The lack of non-invasive methods to evaluate wound repair is a major obstacle in acquiring quantitative data in clinical trials. The role of colour image processing as the most acceptable automatic method of objectively and reproducibly analysing skin lesions and wounds is explored. Image acquisition, digitisation and the use of various image processing algorithms in the analysis of wounds and lesions have been studied in this review. In conclusion, there is considerable scope for further research and development in this field.

Introduction

Colour image processing has many advantages over human assessment of wounds and skin lessions; digital image processing techniques are objective and reproducible. Colour image processing has significant potential, since the analysis and comparison of colour images is a task which humans find particularly difficult. With the current technological trends in computer hardware and scanners, computerised systems are becoming increasingly affordable.

There are two main applications of colour image processing in the field of skin imaging. They are the assessment of the healing of skin wounds or ulcers, and the diagnosis of pigmented skin lesions such as melanomas. The analysis of lesions involves more traditional image processing techniques such as edge detection and object identification, followed by an analysis of the size, shape, irregularity and colour of the segmented lesion. However, in wound analysis, although it is necessary to detect the wound border and to calculate its area, analysis of the colours within the wound site is often more important. In short, wounds generally have a non-uniform mixture of yellow slough, red granulation tissue and black necrotic tissue, and the proportions of each are an important determining factor in the healing state of the wound.

In the case of assessing skin lesions in the clinic, clinicians have to decide whether or not a skin lesion should be tested further, and analysis using colour image processing could provide additional information to aid such decisions. A very general review on digital imaging has been written by Perednia et al. [1] . Their review covers the basics of image analysis, transmission and storage on computer. One problem of storage is that image files can be very large. However this can be reduced to some extent by use of data compression techniques without significantly reducing the information content or quality of an image. One of the groups reviewed found that dermatologists were able to diagnose lesions with compressed digital images without significant change from their performance with the original digital image.

Colour Image Processing

There are relatively few research groups around the world involved in colour image processing of wounds or lesions. Fewer still have experimented with techniques for assessing skin wounds using colour image processing. Herbin et al. [2] [3] at the Department de Biostatistiques et Informatique Medicale, Hopital Cochin, Paris, France analysed RGB colour images digitised from Kodachrome colour slides of wounds, in order to quantitatively assess wound healing kinetics. They studied artificially created blister wounds on the forearms of eight volunteers over twelve days. The wounds were photographed with a 2mm white paper disk placed adjacent to the wound site, which served as both a colour and geometric reference. Each digitised slide image was corrected, using the white reference patch. They evaluated a simple colour index of healing for these uniformly coloured wounds and used an automated approach to determine the wound area. Although they have tackled the problem of automating wound analysis, their method was not as complex as would be necessary for the analysis of natural wounds which have a highly variegated colouring. Another group, Arnqvist et al.[4] at the Department of Scientific Computing, University of Uppsala, Sweden, experimented with a method for the semi-automatic classification of secondary healing ulcers. Color photographs were acquired with a 35mm still camera with ring flash. The photographs were then digitised into a 24-bit RGB image. Photographs were taken at an optimal angle of thirty degrees to the wound plane normal in order to reduce reflections from the flash. In each scene they placed a scale, calibrated in millimeters, to enable estimation of the wound area. The wound tissue types were divided into black necrotic eschar, yellow necrosis/fibrin (or slough), red granulation tissue, and a fourth class which contained the undesired reflections from glossy parts of the wound which were almost entirely white. Their method was only semi-automatic because a skilled operator had to use a mouse to track around the wound boundaries to define the region of interest (ROI). The operator then chose one wound classifier from a database of 16 which had been created using hundreds of photographs of different wounds taken under various lighting conditions. An algorithm then segmented the wound image into the three tissue types, the segmentation depending on the classifier chosen. Each classifier related to a type of wound. Finally, the operator-defined binary image and the segmentation performed by the classifier were combined to give an overall wound classification. Finally the areas of each of the three tissue type zones and the total wound area were computed using the scale.

At the University of Glamorgan, Wales, Jones and Plassmann [5] [6], of the Department of Computer Studies have developed an instrument, known as MAVIS (Measurement of Area and Volume InStrument), to measure the dimensions of skin wounds. It involves capturing two images of the wound in quick succession whilst the wound is illuminated with colour-coded structured light. This enabled phvolume measurements to be made. A colour CCD video camera with a 250 W tungsten halogen bulb was used for imaging the skin directly. MAVIS is capable of measuring the area phand volume of deep three-dimensional wounds. For each acquisition, a magnesium oxide chip, placed alongside the wound, was used as a white standard. The group have experimented with algorithms that use colour to segment an image into one of three tissue types: healthy skin, wound tissue and epithelialisation tissue. They found that epithelialisation tissue is often a darkened band around the wound, separating skin from wound. In all, they tried six measurement parameters: the R, G, and B intensities; Hue; Saturation; and gray-level intensity. The R, G and B intensities were only examined in isolation and they concluded that, `It is clear from inspection of Red, Green and Blue plane intensity-level histograms for the different tissue types that straightforward thresholding of these planes cannot produce a good segmentation which distinguishes between wound and skin or wound and surrounding connected tissue'. They conclude that in looking at such 1D histograms, segmentation is only partially achievable, but using a 3D RGB histogram space, volume clusters may be more widely separated.

One group has made some progress with such a 3D RGB colour histogram clustering technique. Mekkes et al.[7] at the Department of Dermatology, University of Amsterdam, The Netherlands, have been using colour images to assess the healing of wounds. They recognized that many of the enormous number of wound care materials that have been introduced into the market have not been properly tested in randomized, double-blind clinical trials. They pointed out that such trials are desperately needed to supply clinicians with information to guide them in their choice of wound care products. They compared a debriding product (Intrasite Gel) with an old form of treatment using saline soaked gauzes [8]. They found that for a proper evaluation of the cleansing effect of both treatments, colour aspects were more important than wound size. Their technique measured the shift from black to yellow necrotic tissue to red granulation tissue. Their aim is to create an automatic computerised method which can be used as a reference standard or `gold-standard' for colour wound analysis. In their system, images were acquired directly with an RGB video camera and framegrabber. They used two polarised filters to reduce unwanted reflections. A clinicians knowledge of the colours in secondary healing ulcers was used for calibration of the system. The computer had to be instructed in advance as to which colours can be encountered in the granulation region and which in the necrotic region of a wound. They found that clusters in RGB space for a given tissue type formed an irregularly shaped 3D cloud, and so simple thresholding along the R, G and B axes would not help to segment the image into these three tissue types. For this reason, large classification tables, of the colours present in each tissue type, were created semi-automatically by the computer with the aid of a clinician. One problem discovered was that although digital image analysis could detect the wound margins automatically, the colour differences between granulation tissue, surrounding skin and the thin partly transparent layer of newly formed epithelium were too small to allow automatic detection.

Finally, there are a few other groups that have done some work in colour image processing of wounds. El Gammal et al. [9] at the Dermatological clinic of Ruhr University, Germany, wrote a very short paper on the use of the black-yellow-red classification scheme to evaluate the debridement activity of wounds. Solomon et al. [10] at the University of Otago Medical School, New Zealand developed a simple and rapid technique to measure the size of skin wounds and ulceration using two-dimensional colour video images of ulcers. The images were stored on video cassette, thus rendering low image quality. The work did not involve the development of colour image processing algorithms, but a novel method to correct for limb convexity was presented. Smith et al.[11] at the University of Akron, Ohio, USA, evaluated wound repair in humans and animals using video images. Images were stored on VHS video tape, and only basic colour image processing techniques were applied to the digitised images.

Image Acquisition, Digitisation and Calibration

Some groups used photography to capture the original wound image, others decided to use a video camera and framegrabber for direct image capture and digitisation. If photography is used, then the type of film used will affect the image quality. Once the film has been processed then the slides need to be digitised and for this a colour slide scanner can give a very high spatial resolution, up to 2,700 dots per inch. Such a scanner can capture 95% of the information in a high resolution colour slide. For 35mm film, this means that a resolution of over 3000 pixels across the image is possible. Standard 35mm still cameras have the added advantage that they are highly portable, and can easily be used outside the laboratory or clinic, in the patient's home for instance. Care must be taken with the exposure setting on the camera. In considering just greyscale images, Hall et al. [12] discovered that different exposures of the film have a significant effect on the histogram of the image. This has many repercussions in image processing since histogram analysis is a major tool of the image processor.

Framegrabbers, the digitiser boards in computers that connect to the video camera, do not have such high resolution. Typically framegrabbers digitise images to only 512 pixels by 512 pixels, and resolution does not meet up to the standards of photography or colour slide scanners. Colour resolution is also inferior for framegrabbers, typically a colour framegrabber has a colour resolution of 24-bits, corresponding to 16 million colours. Their advantage is that digitisation of the images takes place as they are acquired, and consequently no photographic processing time is incurred. However, although video cameras can be as compact as a still camera, and use of a laptop computer allows the system to be portable, such a system tends to be less versatile than using a 35mm still camera. This renders imaging outside the laboratory less suitable. The best solution would be to use a phdigital still camera, but these are still fairly new on the market and rather expensive. Still, costs are gradually falling and so they are becoming a viable option. They are quick, as no photographic processing is needed, digitisation occurs immediately, and they render high resolution images, comparable with slide scanners.

Calibration is a very important step and often overlooked by programmers since they often aim to improve results by writing more complex algorithms rather than aim to improve the quality of the original input image. By considering the nature of non-uniformities in an image acquisition system due to the non-linear response of electronic devices and non-uniform lighting, methods can be devised to measure these non-uniformities to enable corrections to be made at the pre-processing stage. The use of a pure white reference object in each scene, or better still a uniform greyscale, can be of great benefit in correcting for non-linearities between the red, green and blue channels as well as correcting for the non-linear reproduction of intensity by the system. In fact, Hall et al. [12] found that It is not sufficient to simply have a reference white and black in the image for calibration purposes, as this would assume a linear relationship for all shades of grey in between'. Such greyscale non-linearities are inherent in all imaging systems. Calibration can also be taken further, to ensure the correct reproduction of colour as well as intensity. Frey and Palus [13]. Others considered the measurement of a colour in a digital image processing system and explained a method for calibrating such a system. In particular, they state that greyscale linearisation of each of the three channels, R, G and B, is not enough to allow the system to reproduce colours or hues correctly. A further step of linearisation must be performed over the three channels together. This ensures that a pure red object which is twice as bright as another object of the exact same red hue, is represented as being twice as bright in the red channel only, rather than becoming marginally brighter in the red, green and blue channels for example. For this stage, a colour look-up table (LUT) must be created and used for each digitisation.

Conclusion

In conclusion it is found that for wound imaging in particular, the image processing functions and algorithms needed are not simple compared with the functions provided by the majority of image processing packages used by research laboratories and industry. Wound imaging requires the use of colour; effective results cannot be achieved with grey-scale images. This is not so true for lesion imaging though, and the use of greyscale processing algorithms is sometimes sufficient. Industry has yet to catch up with the latest colour image processing algorithms currently being developed by researchers. A lot of commercial image processing software packages have colour image processing operations/algorithms that are simply greyscale algorithms applied to the Red, Green and Blue signals separately. However, it is important to treat a colour pixel as a whole, and not to separate it into its three constituent components, in order to make full use of all the information available in a colour image resulting in a more successful algorithm.

Acknowledgement

The authors gratefully acknowledge the supply of the wound images by, and helpful discussions with, P.J.Phillips and Dr S.Thomas of the Surgical Materials Testing Laboratory, Bridgend General Hospital, Wales.

References

1. D A Perednia, What dermatologists should know about digital imaging, Journal of the American Academy of Dermatology, vol. 25, no. 1, pp. 89-108, 1991. PubMed Abstract:http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?uid=1880259&form=6&db=m&Dopt=r
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Wound Assessment - Consent for Wound Photograph

Photography is an important means of documenting wound assessment. But written or oral consent is an important yet neglected area of wound photography. Ideally, oral consent for routine wound photography should be given, and be documented as being given, on the wound assessment chart by nurses in the clinical environment. For medical photographers and specialist nurses who may use the photographs for other reasons such as teaching and publication, written signed consent should be required on a special consent form kept in the medical case notes by the photographer concerned.

WITA follows best practice techniques in wound assessment and have implemented steps and procedures that take patient photo consent into consideration.

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