Preclinicalapplication of laser speckle imaging and development of multimodal optical imaging system

Abstract

Monitoring of subcutaneous blood flow is of high importance for fundamental studies, clinical diagnoses, and intraoperative procedures because it provides critical information on the condition of biological tissues and the various disorders in human organs. Laser speckle contrast imaging (LSCI) provides two dimensional (2D) images of blood flow velocity in biological tissue and has been widely used due to its simplicity, real-time feedback, and negligible motion artifacts. However, to the best of our knowledge, there is a paucity of imaging studies of the vasculature and blood flow in deep tissue layers due to tissue turbidity. A physicochemical tissue optical clearing (PCTOC) method effective for reducing light scattering in tissue was applied to enhance the contrast of LSCI of vasculature in deep tissue layers, which cannot be clearly observed by the naked eye. The mice femoral artery region was selected as a sample. The results showed that the PCTOC method enhanced the contrast of LSCI and the vasculature could be clearly observed after the application of PCTOC.OCAs have been studied to solve the light scattering problem in tissue. The OCA method is based on several known mechanisms such as dehydration, reduction of refractive index mismatch between collagen and surrounding medium, collagen dissociation, and thus the reduction of light scattering coefficient. However, the mechanisms of the OTC method have not been clearly understood. There are many studies focused on enhancing OCA performance in practical optical imaging methods. Nevertheless, none of these studies has evaluated certain fundamental parameters such as concentration and application time of OCAs simultaneously. Therefore, in this work all aspects of OCAs were examined to explore the correlation between various parameters for optimal OTC effects. Ex-vivo porcine skin samples were implemented to determine the optimal concentration of glycerol. The efficacy of the optical clearing effect was evaluated as a function of glycerol concentration with optical coherence tomography (OCT) and ultrasound images. OCT was used to evaluate the reduction of light scattering. Ultrasound imaging was used to qualitatively evaluate collagen density, which may be related to the degree of collagen dissociation. The 70% glycerol concentration showed the most effective optical clearing effect 60 min after application.Intense pulsed light (IPL) therapy is an important treatment for vascular lesions. The goal of treating vascular lesions with IPL is to raise the blood vessel temperature enough to cause coagulation, leading to the destruction of lesions and their replacement by fibrous granulation tissue. Despite the advantages of IPL treatment, reported side effects include temporary erythema, superficial blistering, hypopigmentation, and hyperpigmentation. These side effects are caused by high doses of energy applied directly to the skin. An optical clearing agent (OCA) is used to reduce side effects and consequently enhance the IPL effect. IPL was applied to the highly vascular distributed region of a rabbit ear. OCA was used with IPL and the changes in blood vessels were observed. The alteration of the blood vessel was imaged using the laser speckle contrast imaging (LSCI) modality and a transillumination image system. When IPL was applied with OCA to a blood vessel, vasodilation and angiogenesis were observed and these alterations were maintained over time.Arthritis is a leading cause of disability and associated with a substantial limitation in daily activity, work disability, low quality of life, and high health care costs. Although arthritis is a serious and common condition with the potential for injury, no appropriate evaluation method has been established due to the absence of cost-effective, accurate joint imaging modalities. Here, the feasibility of optical imaging in evaluating arthritis using an animal model was investigated. In particular, after inducing arthritis in mice, optical images of mouse feet were obtained. Two experiments were conducted: arthritis severity evaluation and early stage arthritis evaluation. LSCI was used for severity experiments and the results were compared with a visual inspection by a trained expert. Early stage arthritis was evaluated using LSCI and erythema index imaging and the results were compared with histological results. LSCI succeeded in properly evaluating early stage arthritis from other stages of arthritis and from a sample without arthritis.Generally, optical imaging techniques offer a number of important advantages for objective and quantitative diagnosis. Optical imaging can also provide real-time and high resolution microscopic and macroscopic information for rapid and accurate diagnosis. The recent advances in a wide range of optical technologies enable the miniaturization of optical imaging platforms and integrated multimodal imaging. These advances have also allowed for functional (molecular) and structural (anatomical) information about the object to be obtained from a single instrument. In this dissertation, a multimodal optical imaging system was developed with the following functionality: real time laser speckle imaging, color imaging including polarization imaging, erythema imaging, and melanin and fluorescence imaging. The developed system was evaluated by obtaining various optical images from human skin.