Ali Basiri

Use of a multi-spectral camera in the characterization of skin wounds

Skin breakdown is a prevalent and costly medical condition worldwide, with the etiologic and healing processes being complex and multifactorial. Quantitative assessment of wound healing is challenging due to the subjective measurement of wound size and related characteristics. We propose that in vivo spectral reflectance measurements can serve as valuable clinical monitoring tool/device in the study of wound healing. We have designed a multi spectral camera able to acquire 18 wavelength sensitive images in a single snapshot. A lenslets array in front of a digital camera is combined with narrowband filters (bandwidth 10 nm) ranging from 460 to 886 nm. Images taken with the spectroscopic camera are composed of 18 identical sub-images, each carrying different spectral information, that can be used in the assessment of skin chromophores. A clinical trial based on a repeated measures design was conducted at the National Rehabilitation Hospital on 15 individuals to assess whether Poly Carboxy Methyl Glucose Sulfate (PCMGS, CACIPLIQ20), a bio-engineered component of the extracellular matrix of the skin, is effective at promoting healing of a variety of wounds. Multi spectral images collected at different wavelengths combined with optical skin models were used to quantify skin oxygen saturation and its relation to the traditional measures of wound healing.

Measuring the retina optical properties using a structured illumination imaging system

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.

Detection of familial adenomatous polyposis with polarized spectroscopic imaging and oral vascular density

Familial Adenomatous Polyposis (FAP) is an autosomal dominant disease characterized by the development of multiple colonic polyps at younger age with a near 100% lifetime risk of colorectal cancer in later years. The determination of FAP is made after extensive clinical evaluation and genetic testing of at risk individuals. Genetic testing is expensive and in some cases deleterious mutations are not found in all patients with a clinical diagnosis of FAP. As such, the early identification of affected individuals could substantially eliminate associated morbidity and mortality. We investigated a novel spectro-polarimetric imaging system to capture images of the oral mucosa at different wavelengths in an attempt to distinguish patients with FAP from controls. Total diffused oral mucosal reflectance (OMR) and oral mucosal vascular density (OMVD) were calculated from spectral data collected from 33 patients with gene positive FAP, 5 patients who tested negative for FAP, and 45 controls. A statistically significant difference in OMVD (p < 0.001) was observed between individuals with FAP and controls. Analysis of OMR showed no significant difference between the two subject groups.

Assessment of electrical burn injury using structured illumination in an in-vivo electrical injury model

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.

An Imaging Pulse Oximeter Based on a Multi-Aperture Camera

This paper presents an imaging arterial pulse oximeter based on the acquisition of two images respectively at the peak and trough a local arterial pulse. Spectroscopic sensitive images are obtained using a multi-aperture system synchronized to a point pulse oximeter. Each acquired image consists of 16 spectroscopic images of the same field of view. By subtracting the images obtained at the peak and trough of the arterial pulse one is able to eliminate common absorbers and scatterers and ultimately focus only on the metric of interest.

A Novel Model of Skin Electrical Injury

High voltage electrical burns can cause devastating third and fourth degree burns. The pathophysiology of electrical injury is not well understood. We have developed an Electrical Burn Delivery System (EBDS) capable of reliably delivering pre-set voltages and currents to biological specimens in order to accurately simulate the damage from high-tension electrical contact. In addition to the high voltage delivery the system can also measure skin impedance before and after shock. Two different imaging techniques were used for non-invasive assessment of skin damage pre and post shock. A thermal camera was used to monitor the extent of thermal damage due to the electrical shock, while hyper-spectral imaging was used to monitor wavelength dependent differences in total reflectance. We present results of experiments conducted on freshly excised human skin samples as well as porcine skin samples.

Imaging spectroscopy of thermal and electrical burs

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.

Imaging spectroscopy with a multi-aperture camera

A new type of spectroscopic sensitive camera was used in a clinical trial at the National Rehabilitation Hospital aimed at monitoring the healing process of several types of skin wounds. Results showed significant increase in oxygen saturation related to a decrease in wound size.