Towards Non-invasive Ultrasonic Characterization of Carotid Atherosclerotic Plaque

Vulnerable atherosclerotic plaques are thought to be prone to rupture due to various compositional and morphological factors. One key characteristic is thought to be the presence of a soft, lipid rich core in the plaque. Acoustic radiation force impulse (ARFI) and thermal strain imaging (TSI) are non-invasive ultrasound-based imaging modalities. ARFI imaging measures the tissue response to an ultrasonically generated mechanical perturbation. In TSI, the tissue temperature is increased and image contrast is a result of the temperature and composition dependence of the speed of sound. Initial efforts to develop a TSI system utilized two separate ultrasound transducers for heating and imaging. We developed signal processing to improve estimates of thermal strain obtained from this system and showed that TSI could be used to detect lipids in ex vivo human arterial tissue samples. However, the translational obstacles encountered by this system outweighed the potential imaging utility. In order to address these challenges, we developed temporally interleaved multi-foci beamforming which could be implemented on a standard imaging array to generate a broad, homogeneous ultrasound beam for either ARFI pushing or TSI heating. We showed that this beamforming approach could enable simultaneous acquisition of ARFI and thermal strain data while substantially improving the frame rate for ARFI imaging. In order to better understand the factors that affect signal quality in TSI and ARFI imaging, we conducted separate phantom studies for each imaging modality. We showed that with a temperature rise <1oC, TSI could differentiate between phantoms with different lipid percentages. Additionally, we showed that pulse inversion harmonic imaging could be used to improve TSI signal quality in the presence of clutter. Finally, we showed that high frame rate ARFI imaging was able to achieve a 45-fold improvement in frame rate at the cost of increased estimation bias and jitter, and decreased image contrast. These studies indicate that multi-foci beamforming can be used to enable simultaneous TSI and ARFI imaging on current clinical systems. This imaging sequences developed in this dissertation facilitate non-invasive assessment of both the composition and mechanical properties of tissue which might be especially useful for characterization of vulnerable plaques

Multi-Foci Beamforming Using Curved Linear Array Transducer for Qualitative Identification of Lipids in Human Liver

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of liver chronic diseases in the U.S. and its prevalence is growing in the world. In the United States, it affects an estimate of 80 to 100 million people. In less than a decade, NAFLD will likely become the number one cause of liver transplants in the country. NAFLD cases have risen rapidly over the last three decades and is the most common liver disease in children. NAFLD encompasses a disease spectrum of a variety of liver conditions ranging from simple steatosis (SS) to nonalcoholic steatohepatitis (NASH). SS is a benign form of the disease, characterized by the accumulation of lipid in the liver. On the other hand, NASH is defined by hepatic steatosis with cell injury, hepatic ballooning and various degrees of fibrosis. NASH may further develop into cirrhosis, liver failure and hepatocellular carcinoma (HCC). A non-invasive, early detection and accurate staging of NAFLD may allow for a timely intervention and treatment to prevent the progression of the disease to cirrhosis and HCC. We hypothesized a new dual-modality ultrasound imaging combining acoustic radiation force impulse (ARFI) imaging and thermal strain imaging (TSI) implemented on a clinical ultrasound probe. ARFI imaging utilizes high intensity focused ultrasound to generate a push in a region of interest (ROI). The response of the tissue inside the region of excitation due to the acoustic radiation push is determined by estimating the displacement between the pre-push reference frames and the post-push tracking frames. TSI has been used in the field of medical imaging for detecting lipids in atherosclerotic plaques and quantification of liver fat in ob/ob mice. TSI is based on the fact that the speed of sound changes differently in respect to the increase in temperature for different tissue composition. Lipids register a decreasing sound speed with increasing temperature, whereas water-bearing tissue exhibit an increasing sound speed with increasing temperature. Development of the proposed multi-modality system will be a step towards a novel clinical system which would permit the creation of a single co-registered image featuring information regarding lipid content and liver stiffness

Identification of the Elastic Modulus of an Organ Model Using Reactive Force and Ultrasound Image

制度:新 ; 報告番号:甲3418号 ; 学位の種類:博士(工学) ; 授与年月日:2011/7/28 ; 早大学位記番号:新574

Effects of Aerobic Exercise on Cognitive and Cerebrovascular Function in Hypertensive Adults

The presence of hypertension in middle-age is a major risk factor for later-life development of cognitive and cardiovascular disease. Exercise is widely recommended to combat vascular and brain aging in hypertension. We sought to compare the effects of a single bout of aerobic exercise on 1) arterial stiffness and cerebral hemodynamics and 2) cognitive function in middle-aged adults with controlled-hypertension and without hypertension. Vascular and cognitive measures were assessed pre and post 30-min of aerobic exercise at ≈55% maximal oxygen consumption. Arterial stiffness and cerebral hemodynamics were measured non-invasively. Cognitive function was measured using a computerized testing battery that included executive function and memory tasks. Acute aerobic exercise resulted in similar 1) increases in arterial stiffness and cerebral hemodynamic pulsatility, and 2) accelerated executive function and memory reaction time post-exercise in adults with and without hypertension. Based on these results, we investigated if adults with hypertension had differential vascular contributions to cognitive activity. We measured cerebrovascular hemodynamics non-invasively during cognitive activity as a measure of neurovascular coupling. Adults with and without hypertension exhibit similar increases in large artery stiffness and decreases in extracranial hemodynamic pulsatility during cognitive activity, indicating similar neurovascular coupling between groups. In conclusion, these data indicate that middle-aged adults with controlled-hypertension experience similar 1) vascular responses to acute exercise and cognitive activity, and 2) beneficial changes in cognitive function following acute exercise as their counterparts without hypertension. Our results will be interpreted and explored in the context of hypertension severity and underscore the importance of optimal blood pressure control

Investigation expérimentale des contraintes hémodynamiques d'un fantôme d'artère sténosée

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal

Diagnostic precision and sex differences in quantitative cardiovascular magnetic resonance

Correct medical treatment necessitates a correct diagnosis. Cardiac imaging aims to establish an accurate diagnosis without performing unnecessary invasive procedures. Cardiovascular magnetic resonance (CMR) has emerged as a valuable diagnostic tool in clinical cardiology because of its inherently good soft-tissue contrast, dynamic visualizations and the possibility to perform quantitative tissue characterization. However, diagnostic precision may be affected in quantitative imaging by several factors such as the presence of sex differences, or measurements errors. Therefore, the aim of this thesis was to identify parameters and sex differences that affect precision and accuracy, and to evaluate post-processing methods to increase diagnostic precision. We found that intramyocardial blood affects native myocardial T1 values in patients without focal abnormalities, and that native myocardial T1 values differ between the sexes. We developed a blood correction model that maintained an increase in diagnostic precision by 13% when applied to an independent patient cohort, which furthermore also eliminated sex differences in healthy volunteers in Study I. In Study II, we evaluated a post-processing method called stationary tissue background correction for increasing diagnostic precision in clinical blood flow measurements. We found that the number of patients with a pulmonaryto-systemic blood flow ratio (Qp/Qs) outside of the normal range decreased following stationary tissue background correction. In Study III, we investigated the presence of sex differences in a newly developed myocardial perfusion imaging sequence in healthy volunteers. We found that women have higher myocardial blood volume, myocardial perfusion and myocardial extracellular volume compared to men both at rest and during adenosine stress, which provide mechanistic insight into myocardial physiology. In Study IV, we investigated the clinical accuracy and precision of synthetic scar images (SynLGE) from post-contrast T1 maps compared to conventional scar images (LGE) for diagnosing focal myocardial fibrosis of any etiology. Compared to LGE, SynLGE yielded a sensitivity of 77%, a specificity of 98%, a positive predictive value of 97% and a negative predictive value of 86%. In conclusion, there are sex differences in several aspects of clinical quantitative CMR imaging that may affect diagnostic precision. Post-processing is a powerful tool to improve diagnostic precision both by increasing precision in native myocardial T1 values via blood correction, and in Qp/Qs via stationary tissue background correction. SynLGE can provide complementary confidence in the assessment of focal myocardial fibrosis in complement to conventional LGE, and thereby increase diagnostic accuracy and precision

Pathogenesis and Treatment of Periodontitis

Pathogenesis and Treatment of Periodontitis includes comprehensive reviews on etiopathogenic factors of periodontal tissue destruction related to microbial dental plaque and also host response components. Adjunctive treatment modalities are also addressed in the book. Topics covered range from microbial pathogenic factors of P. gingivalis to the relationship between metabolic syndrome and periodontal disease, and from management of open gingival embrasures to laser application in periodontal treatment

Washington University Senior Undergraduate Research Digest (WUURD), Spring 2018

From the Washington University Office of Undergraduate Research Digest (WUURD), Vol. 13, 05-01-2018. Published by the Office of Undergraduate Research. Joy Zalis Kiefer, Director of Undergraduate Research and Associate Dean in the College of Arts & Scienc