Jon Cobb

Thermography and Thermometry in the Assessment of Diabetic Neuropathic Foot: A Case for Furthering the Role of Thermal Techniques

There are currently 3 established techniques employed routinely to determine the risk of foot ulceration in the patient with diabetes mellitus. These are the assessment of circulation, neuropathy, and foot pressure. These assessments are widely used clinically as well as in the research domain with an aim to prevent the onset of foot ulceration. Routine neuropathic evaluation includes the assessment of sensory loss in the plantar skin of the foot using both the Semmes Weinstein monofilament and the biothesiometer. Thermological measurements of the foot to assess responses to thermal stimuli and cutaneous thermal discrimination threshold are relatively uncommon. Indeed, there remains uncertainty regarding the importance of thermal changes in the development of foot ulcers. Applications of thermography and thermometry in lower extremity wounds, vascular complications, and neuropathic complications have progressed as a result of improved imaging software and transducer technology. However, the uncertainty associated with the specific thermal modality, the costs, and processing times render its adaptation to the clinic. Therefore, wider adoption of thermological measurements has been limited. This article reviews thermal measurement techniques specific to diabetic foot such as electrical contact thermometry, cutaneous thermal discrimination thresholds, infrared thermography, and liquid crystal thermography.

Transducers for foot pressure measurement: survey of recent developments

Recent advances in the development of transducers for the measurement of vertical and shear forces acting on the plantar surface of the foot are reviewed. Barefoot and in-shoe discrete and matrix transducers are reviewed in terms of structure, operation, performance and limitations. Examples of capacitive, piezoelectric, optical, conductive and resistive types of transducer are presented. Where available, the current clinical status is specified.

Noninvasive Measurement Techniques for Monitoring of Microvascular Function in the Diabetic Foot

There are, currently, 3 established clinical techniques routinely employed to determine the risk of ulceration in the diabetic foot. These are assessment of the circulation, the nervous control of sensation, and foot sensitivity to loading. Macrovascular measurements are used to assess sufficiency of the arterial supply to the foot. Evaluation of somatic neuropathy provides an indication of loss of plantar sensation. Skin pressure measurements indicate abnormalities in plantar loading. This combined approach is effective in allowing preventative measures to be applied prior to the onset of ulceration. In contrast, clinical measurement of microvascular function in the diabetic foot is uncommon. Indeed, there remains uncertainty regarding the importance of micro-vascular complications in the development of foot ulcers. This is in part due to the difficulty of making in vivo measurements of microvascular function. This article evaluates 3 noninvasive measurement techniques for routine micro-vascular assessment of the diabetic foot: transcutaneous oxygen tension, laser Doppler flowmetry, and near-infrared spectroscopy. These techniques can be used to obtain useful parameters of microvascular function including surface oxygen, blood flow, intracellular oxygenation, and cellular respiration. In principle, such measurements can be related to underlying pathophysiology, for example, microangiopathy or autonomic neuropathy. This article considers how these general techniques can be adapted to support routine clinical measurement of microvascular function, particularly in the neuropathic diabetic foot.

An in-shoe laser Doppler sensor for assessing plantar blood flow in the diabetic foot

Increased pressure due, to sensory neuropathy, is important in the development of plantar ulceration in type II diabetes. However, additional factors are thought to pre-dispose the skin tissue to ulceration. Autonomic neuropathy and microangiopathy are the basis for the capillary steal theory and the haemodynamic hypothesis, developed to explain the aetiology of this type of ulcer, in terms of microvascular complications. The aim of the present study was to develop a system to allow assessment of blood flow at prevalent sites of ulceration. Previous studies have been limited to assessment of the bare foot under rest conditions. The new system allows measurements to be made in-shoe, during static and dynamic loading. The system comprises a laser Doppler sensor, a load sensor, measurement shoe, instrumentation and analysis software. The measurement shoe was designed to minimise movement artefact and provide thermal insulation for the foot. A simple flow rig was used to characterise the sensor. The blood flux response was linear (<5% deviation from ideal) for particle concentrations up to 0.25% and for mean particle velocities up to 8mm s(-1). The worst case drift in the response over a six-month period was 3.7%. Device to device repeatability varied by 12.5% over five devices.

A novel approach to thermochromic liquid crystal calibration using neural networks

Liquid crystal thermography (LCT) is a common surface temperature measurement technique. Typically, the colour response is calibrated against temperature by building an analytical relation between the temperature and the hue of the colour. A suitable polynomial fit is then used to describe this relation after removing the discontinuity in the hue. The variability of hue at each calibration point determines the temperature resolution. However, this technique does not take into consideration the variability in R, G and B intensities used to determine the hue, leading to uncertainty in the measured temperature. This paper describes a novel technique using neural networks to calibrate thermochromic liquid crystal (TLC) material and compensate for high variability in RGB intensities along with other sources of noise in the data. A TLC-based temperature measurement system and calibration results are presented. In our measurements, the lighting intensity (8-bit mean intensity of black surface ± standard deviation) is changed from a minimum of 16.65 ± 2.30 to a maximum of 31.41 ± 3.85. The neural networks were trained on the steady-state TLC calibration system. The results indicate that the neural networks can cope with the variation in lighting by merging the shifted hue curves into a single curve determined by the regression analysis of the test data. Performance characteristics studied on various network configurations relevant to the analysis are described. This approach may be useful in developing liquid crystal thermography for various biomedical applications.

In-shoe measurement of plantar blood flow in diabetic subjects: results of a preliminary clinical evaluation

The findings of clinical pilot study (n = 9 subjects) using a new laser Doppler sensor for assessing blood flux in plantar skin tissue are described. Cutaneous blood perfusion was recorded under the first metatarsal head (right foot) in standing and walking. The sensor was located in a measurement shoe custom made for each test subject. The test group comprised diabetic patients (type II) with vascular (n = 3) or neuropathic (n = 3) complications and three controls. All subjects were Caucasian males and in the age range considered particularly at risk of diabetic foot problems (mean 61 years, 51-72 years). Following static loading for 2, 3 and 4 min the blood.flux response increased rapidly in the control (mean = 10 s) and neuropathic (mean = 18 s) groups to a well-defined, peak blood flow. For the vascular group. the blood flux response was typically a slower rise (mean = 30 s) to a poorly defined peak blood flow value. Due to movement artifact a reliable signal could only be obtained for the swing phase of gait during which blood flux was observed to increase linearly. This was interpreted as reperfusion of the tissue following unloading. The rates of reperfusion expressed in arbitrary units (of blood flux) per millisecond (au ms(-1)) were 6.1-7.9 au ms(-1) for the control, 4-6.2 au ms- for the vascular and 2.3-4.5 au ms(-1) for the neuropathic groups. The feasibility of assessing the microcirculation of the plantar skin under conditions of static and dynamic loading, with the foot in-shoe, has been demonstrated for the first time. The results suggest that abnormal responses may be obtained from asymptomatic feet of diabetic patients with vascular and/or neuropathic complications. This method of assessment could be of use in predicting the occurrence of ulceration in the diabetic foot.

Linear Acceleration Measurement Utilizing Inter-Instrument Synchronization: A Comparison between Accelerometers and Motion-Based Tracking Approaches

Where as video cameras are a reliable and established technology for the measurement of kinematic parameters, accelerometers are increasingly being employed for this type of measurement due to their ease of use, performance, and comparatively low cost. However, the majority of accelerometer-based studies involve a single channel due to the difficulty associated with synchronizing multiple accelerometer channels. The authors of this article outline a method to synchronize multiple accelerometers using a maxima detection method. Results are presented that demonstrate the effectiveness of the new synchronization method with 52 of 54 recorded data sets showing no time lag error and two tests showing an error of .04 sec. Inter-instrument and instrument-video correlations are all greater than r = .94 (p < .01), with inter-instrument precision (Root Mean Square Error; RMSE) ≈ .1ms−2, demonstrating the efficacy of the technique. In conclusion, the new technique offers a robust solution, giving further support to the movement toward wider adoption of accelerometer-based performance measurement systems in sports science.

Upper limb functional electrical stimulation devices and their man-machine interfaces.

Abstract Functional Electrical Stimulation (FES) is a technique that uses electricity to activate the nerves of a muscle that is paralysed due to hemiplegia, multiple sclerosis, Parkinson’s disease or spinal cord injury (SCI). FES has been widely used to restore upper limb functions in people with hemiplegia and C5–C7 tetraplegia and has improved their ability to perform their activities of daily living (ADL). At the time of writing, a detailed literature review of the existing upper limb FES devices and their man–machine interfaces (MMI) showed that only the NESS H200 was commercially available. However, the rigid arm splint doesn’t fit everyone and prevents the use of a tenodesis grip. Hence, a robust and versatile upper limb FES device that can be used by a wider group of people is required.

A distributed three-channel wireless Functional Electrical Stimulation system for automated triggering of stimulation to enable coordinated task execution by patients with neurological disease

Abstract Functional Electrical Stimulation (FES) is a technique used to improve mobility and function for patients suffering some neurological related diseases such us Multiple Sclerosis (MS) and stroke. Some patients might require FES applied in more than one location depending on the extent of the neurological condition. Currently, this can be achieved using multi-channel FES systems. However, these systems can be bulky and impractical in daily usage. This research investigates using a wireless distributed FES system to overcome some of the limitations of the current multi-channel systems. A prototype of a three-channel FES system was built and tested. The prototype is used for drop foot stimulation and reciprocal arm swing stimulation while the user is walking, and for elbow extension and wrist/fingers opening stimulation if triggered while standing or sitting. A pilot study was designed to evaluate the reliability and repeatability of the system with 11 healthy volunteers without applying stimulation. This was followed by a case study with a hemiplegic person. The results indicate that the system can successfully detect and generate output responses appropriate to the input signals from the body sensors.

Characterisation and calibration of three physical forms of thermochromic liquid crystals

Abstract Liquid crystal thermography (LCT) provides a colour response proportional to the temperature of a heated surface in contact with the crystals. Thermochromic liquid crystals (TLC) are offered in the form of an emulsion, polymer sheet or latex support. Wider adoption of this technology has been limited due to response time, pressure sensitivity and imaging equipment. It is important to characterise TLC based on their chemical composition, colour play interval, spatial density and repeatability. This paper presents results for three forms of TLC material in terms of the effects of incident lighting, pressure sensitivity and hysteresis. Data are presented in the form of hue versus temperature calibration curves. Hue versus temperature curve shifts towards higher hue values for the identical temperature producing a maximum change of 15–20% in hue when the lighting intensity is changed from minimum to maximum. Hysteresis in the calibration curve occurred when the liquid crystals were heated above the colour play range producing a maximum temperature change of 1°C for R25C5W TLC sheet. This hysteresis was not permanent. The authors recommend using liquid crystals within their colour bandwidth to overcome hysteresis effects. The results may be helpful in developing LCT for various biomedical applications.