Nirlep A. Patel

Optical coherence tomographic elastography technique for measuring deformation and strain of atherosclerotic tissues

Objectives: To evaluate optical coherence tomographic elastography as a method for assessing the elastic properties of atherosclerotic plaque and the parameters that influence interpretation. Methods: Phantoms and aorta were examined in vitro to quantify speckle modulation and measure the displacement and strain maps. A correlation method was used as a speckle tracking technique for measuring axial and lateral displacement vectors and calculation of strain maps. The influence of correlation kernel size on accuracy of the method was evaluated. Results: In terms of a percentage error between calculated and measured displacements, the best results for phantoms were obtained with a 41 × 41 kernel (1.88% error). For both phantom and aorta images, it was found that, with the increasing size of cross correlation kernel, the axial and lateral displacement maps are less noisy and the displacement vectors are more clearly defined. However, the large kernels tend to average out the differences in displacements of small particles in phantoms and decrease the ability of speckle tracking to make microstructural assessments. Therefore, it is important to select kernel size carefully, based on the image features. Conclusions: Optical tomographic elastography can be used to assess the microstructural properties of atherosclerotic tissue at micrometre scale resolution, but preselected analysis criteria must be understood in a critical interpretation of the results.

Review of the ability of optical coherence tomography to characterize plaque, including a comparison with intravascular ultrasound.

Over the last 50 years the introduction of several imaging technologies have been pivotal in reducing mortality associated with coronary artery disease. However coronary disease continues to be the leading cause of mortality in the industrialized world. Optical coherence tomography (OCT) has recently been introduced for micron scale intravascular imaging. It is analogous to ultrasound, measuring the intensity of back-reflected infrared light instead of sound. Some of the advantages of OCT include its resolution, which is higher than any currently available imaging technology and acquisition rates are near video speed. Unlike ultrasound, OCT catheters consist of simple fiber optics and contain no transducers within their frame, thereby making imaging catheters both inexpensive and small. Currently, the smallest catheters have a cross-sectional diameter of 0.014”. OCT systems are compact and portable and can be combined with a range of spectroscopic techniques. We review the application of OCT to intracoronary imaging.

Monitoring osteoarthritis in the rat model using optical coherence tomography

A need exists for an animal model to assess therapeutics for osteoarthritis (OA) without sacrificing the animal. Our goal is to assess the progression of experimentally induced osteoarthritis in the rat knee joint by monitoring articular cartilage thickness, surface abnormalities, and collagen organization using a new technology known as optical coherence tomography (OCT). OA was generated in Wistar Hanover rats via injection of sodium iodoacetate into the left articular joint of the knee while normal saline was injected as a control in the contralateral right knee. Rats were sacrificed at 1-, 2-, 3-, 4-, and 8-week intervals and the knee joints were subsequently harvested and imaged using normal and polarization sensitive OCT (PS-OCT). Treated knees were compared to normal counterparts in the contralateral leg. Following imaging, knees underwent both routine histological processing and picrosirus staining for organized collagen. OCT images indicate that injection of sodium iodoacetate resulted in a progressive decrease in cartilage thickness and loss of the bone-cartilage interface which correlated with histology. In addition, PS-OCT was able to detect collagen disorganization, an early indicator of OA. The use of OCT in combination with the induction of OA in rats is a promising new animal model for assessing articular changes with the goal of monitoring therapeutics longitudinally. Future work will extend the model to in vivo assessments.

Guidance of aortic ablation using optical coherence tomography

Purpose: There is a significant need for an imaging modality that is capable of providing guidance for intravascular procedures, as current technologies suffer from significant limitations. In particular, laser ablation of in-stent restenosis, revascularization of chronic total occlusions, and pulmonary vein ablation could benefit from guidance. Optical coherence tomography (OCT), a recently introduced technology, is similar to ultrasound except that it measures the back-reflection of infrared light instead of sound. This study examines the ability of OCT to guide vascular laser ablation. Methods: Aorta samples underwent laser ablation using an argon laser at varying power outputs and were monitored with OCT collecting images at 4frames. Samples were compared to the corresponding histopathology. Results: Arterial layers could be differentiated in the images sequences. This allowed correlation of changes in the OCT image with power and duration in addition to histopathology. Conclusions: OCT provides real-time guidance of arterial ablation. At 4 frames, OCT was successfully able to show the microstructural changes in the vessel wall during laser ablation. Since current ablation procedures often injure surrounding tissue, the ability to minimize collateral damage to the adjoining tissue represents a useful advantage of this system. This study suggests a possible role for OCT in the guidance of intravascular procedures.

Imaging of cartilage degeneration in vivo using ultrahigh resolution OCT

Ultrahigh resolution OCT is used to visualize experimentally induced osteoarthritis in a rat knee model. Using a Cr4+:Forsterite laser, ultrahigh image resolutions of 5um are achieved in vivo. Progression of osteoarthritic remodeling and cartilage degeneration are quantified. The utility of OCT for the assessment of cartilage integrity is demonstrated.

Imaging of cartilage degeneration progression in vivo using ultrahigh-resolution OCT

Ultrahigh resolution OCT is used to visualize experimentally induced osteoarthritis in a rat knee model. Using a Cr4+:Forsterite laser, ultrahigh image resolutions of 5um are achieved. Progression of osteoarthritic remodeling and cartilage degeneration are quantified. The utility of OCT for the assessment of cartilage integrity is demonstrated.

OCT imaging of the musculoskeletal and cardiovascular systems

In this presentation, the application of optical coherence tomography (OCT) to the prevention of myocardial infarction and early identification of osteoarthritis is discussed. Myocardial infarction or a heart attack is the leading cause of death worldwide. It results from an acute loss of blood flow to a region of the heart resulting in death to that heart tissue. Most heart attacks are caused by small, thin walled lipid filled plaques which can not be detected by currently available imaging technologies. This paper outlines some of the advances demonstrating the potential of OCT for the identification of high risk plaque. Osteoarthritis is a major cause of mobility in the industrialized world. The hallmark of the disease is a degradation of articular cartilage. As new therapeutics have been shown to be effective in animal models, there effectiveness in humans remains unclear as there is no effective method for accurate monitoring changes in cartilage. In the second part of this manuscript, the effectiveness of OCT for monitoring articular cartilage is described.