Development of Atherosclerotic Plaque Ultrasound Phantoms for the Investigation of Vulnerable Plaque Features

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Yau, Olivia
Plaque vulnerability , Plaque density , Echogenicity , Grayscale median , Ultrasound , Phantom , Pixel Distribution Analysis , Plaque heterogeneity , Plaque composition
As the burden of atherosclerotic cardiovascular disease (ACVD) continues to rise, increasing efforts are directed to innovate screening tools for the detection of vulnerable plaque and the vulnerable patient. Vulnerable plaque lesions are thought to be specific lesions responsible for the majority of cardiovascular events, and are generally characterized by a large lipid core and a thin fibrous cap. Recent advances in ultrasound offer novel techniques to characterize various aspects of plaque vulnerability. This study investigated two approaches for evaluating plaque vulnerability. Specifically, a density-based plaque phantom was developed for the evaluation of plaque echogenicity, a feature of plaque vulnerability that can be characterized by Grayscale Median (GSM) analysis. It was found that plaque density has a significant positive linear correlation with plaque echogenicity. Another phantom model of simulated heterogeneous plaque lesions was developed for the evaluation of plaque composition, a feature of plaque vulnerability that can be characterized by colourized Pixel Distribution Analysis (PDA), a novel tissue characterization technique. Two sets of GSM ranges associated with specific tissue types were established. Percentages of gray pixels identified in the correct tissue GSM range from colourized PDA were compared between the two sets of GSM ranges we established, and a previously reported set of tissue GSM ranges. Our tissue GSM ranges of: echolucent plastisol 0-4, muscle 68-86 (Neck muscle and leg muscle) and 104-108 (abdomen muscle), fat 87-100 (visceral fat) and bone 145-175, detected a greater percentage of pixels within the correct tissue type in comparison to the two other sets of ranges. It is anticipated that the phantoms developed will serve as an ex vivo platform for the optimization of vulnerable plaque imaging technologies, allowing for timely and cost-effective development of ultrasound probes, software, contrast agents, and drug delivery systems for the treatment of atherosclerosis. The research presented in this thesis has focused on developing ultrasound analysis techniques to better stratify patients by their risk of ACVD. Atherosclerotic plaque lesions, specifically vulnerable plaque lesions, may not be apparent by conventional diagnostic modalities. This research can improve diagnosis and treatment of cardiovascular diseases.
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