KEYWORDS: Tissues, Skin, Temperature metrology, Blood, 3D modeling, Animal model studies, Injuries, Finite element methods, Thermal modeling, Blood circulation
Optical methods have been used to investigate electrical injury on animal models such as live mice, rats, and rabbits. Here we introduce a completely digital phantom of a mouse, with the aim of investigating electrical injury through spectroscopic imaging techniques. The basis of our phantom is a three-dimensional digital mouse reconstructed from co-registered computed tomographic images and cryosection by a different group. Image processing algorithms were applied to make the model suitable to Finite Element Analysis of thermal and electrical transport. Our digital model is capable of simulating temperature, voltage, current changes along the animal body during and after electrical shocks.
Skin perfusion and oxygenation is easily disrupted by imposed pressure. Fiber optics probes, particularly those spectroscopy or Doppler based, may relay misleading information about tissue microcirculation dynamics depending on external forces on the sensor. Such forces could be caused by something as simple as tape used to secure the fiber probe to the test subject, or as in our studies by the full weight of a patient with spinal cord injury (SCI) sitting on the probe. We are conducting a study on patients with SCI conducting pressure relief maneuvers in their wheelchairs. This study aims to provide experimental evidence of the optimal timing between pressure relief maneuvers. We have devised a wireless pressure-controlling device; a pressure sensor positioned on a compression aluminum plate reads the imposed pressure in real time and sends the information to a feedback system controlling two position actuators. The actuators move accordingly to maintain a preset value of pressure onto the sample. This apparatus was used to monitor the effect of increasing values of pressure on spectroscopic fiber probes built to monitor tissue oxygenation and Doppler probes used to assess tissue perfusion.
Clinician’s recommendations on wheelchair pressure reliefs in the context of the high prevalence of pressure ulcers that
occur in people with spinal cord injury is not supported by strong experimental evidence. Some data indicates that
altered tissue perfusion and oxygenation occurring under pressure loads, such as during sitting, induce various
pathophysiologic changes that may lead to pressure ulcers.
Pressure causes a cascade of responses, including initial tissue hypoxia, which leads to ischemia, vascular
leakage, tissue acidification, compensatory angiogenesis, thrombosis, and hyperemia, all of which may lead to tissue
damage. We have developed an advanced skin sensor that allows measurement of oxygenation in addition to perfusion,
and can be safely used during sitting. The sensor consists of a set of fiber optics probes, spectroscopic and Laser Doppler
techniques that are used to obtain parameters of interest. The overriding goal of this project is to develop the evidence
base for clinical recommendations on pressure reliefs.
In this paper we will illustrate the experimental apparatus as well as some preliminary results of a small clinical
trial conducted at the National Rehabilitation Hospital.
High voltage electrical injuries may lead to irreversible tissue damage or even death. Research on tissue injury following
high voltage shock is needed and may yield stage-appropriate therapy to reduce amputation rate. One of the mechanisms
by which electricity damages tissue is through Joule heating, with subsequent protein denaturation. Previous studies have
shown that blood flow had a significant effect on the cooling rate of heated subcutaneous tissue. To assess the thermal
damage in tissue, this study focused on monitoring changes of temperature and optical properties of skin next to high
voltage wounds. The burns were created between left fore limb and right hind limb extremities of adult male Sprague-Dawley rats by a 1000VDC delivery shock system. A thermal camera was utilized to record temperature variation during
the exposure. The experimental results were then validated using a thermal-electric finite element model (FEM).
Electrical injury is a devastating and hard to treat clinical lesion. Fully understanding the pathophysiology of electrical
trauma is still a challenge for clinicians and scientists. Further elucidating the natural history of this form of tissue injury
could be helpful in improving limb salvage and offering stage-appropriate therapy. Multi-spectral imaging technique is a
non-invasive technology that can be used to determine optical properties of tissues in and adjacent to injury. Images at
different wavelengths can provide essential information related to the pathophysiological condition of the tissue. To
promote the applicability of this technique in medical diagnosis, we built a complete experimental model of electrical
injury. In this model, electrical injuries were created by a reliable high-tension shock system at preset voltage or current.
A thermal camera recorded the change of skin temperature during the electrical shock. Then, a high-resolution spectral
imaging system based on structured illumination was used to capture images for post analysis to extrapolate optical
properties of the tissue. To test accuracy, this imaging system was calibrated by using a set of epoxy phantoms with
known optical properties. In this paper, the results of experiments conducted on rats and discussions on the systemic
changes in tissue optical properties before and after electrical shock are presented.
Patients with diabetic retinopathy (DR) may experience a reduction in retinal oxygen saturation (SO2). Close
monitoring with a fundus ophthalmoscope can help in the prediction of the progression of disease. In this paper we
present a noninvasive instrument based on structured illumination aimed at measuring the retina optical properties
including oxygen saturation. The instrument uses two wavelngths one in the NIR and one visible, a fast acquisition
camera, and a splitter system that allows for contemporaneous collection of images at two different wavelengths.
This scheme greatly reduces eye movement artifacts. Structured illumination was achieved in two different ways,
firstly several binary illumination masks fabricated using laser micro-machining were used, a near-sinusoidal
projection pattern is ultimately achieved at the image plane by appropriate positioning of the binary masks.
Secondarily a sinusoidal pattern printed on a thin plastic sheet was positioned at image plane of a fundus
ophthalmoscope. The system was calibrated using optical phantoms of known optical properties as well as an eye
phantom that included a 150μm capillary vessel containing different concentrations of oxygenated and deoxygenated hemoglobin.
Today it is still clinical practice to determine burns wounds and their depth by visual inspection. However, it was
recently shown that burns develop differently from their initial grade depending on the contact time of the source. As
this contact time varies it is difficult to assess the burn severity relaying only on a naked eye. Parameters such as oxygen
saturation, hematocrit, water presence, and perfusion, can offer a more quantitative approach to wound assessment hence
improving diagnosis and treatment. These parameters can be obtained with spectroscopic and flow sensitive techniques.
We propose a study of burns dynamic using a combination of spectroscopic and thermal imaging techniques. A spectral
camera based on a lenslet array architecture was used to obtain 18 images of the skin, each lenslet was interfaced with a
narrowband filter hence 18 spectrally sensitive images were obtained. In this paper the results of a preliminary electrical
burns study are presented.
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