Browsing by Author "Liu, Peiying"
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Item Evaluating Bone by Ultrasound(2008-05-13) Liu, Peiying; Antich, Peter P.Bone fractures associated with osteoporosis, a major bone disease characterized by low density and high fracture risk, are common causes of disability and large medical care expenses around the world. Considering its low cost, high portability, and non-ionizing nature, non-invasive ultrasound techniques have been investigated as tools for evaluating bone quality and biomechanical competence. Quantitative ultrasound has been used clinically as a surrogate for the current gold standard measure in osteoporosis diagnosis - Bone Mineral Densitometry (BMD), which unfortunately utilizes ionizing radiation. This study proposes the application of a reflection ultrasound method to evaluate non-BMD properties of cancellous bone, including porosity and the microstructure of the trabecular network, all of which are directly related to bone morphological changes caused by osteoporosis and could result in better predictions of fracture risk. Computer simulations and phantom studies were adopted to guide the measurement of bone properties. In the computer simulations, the cellular model and the wire model of cancellous bone predict the backscattering dependence on porosity from two different perspectives, but reach the same result. This leads to the first conclusion that reflection ultrasound is not sensitive to the shape of a scatterer of wavelength size but to the spacing between scatterers. The in vitro cancellous bone study demonstrated that the average porosity is correlated with the density, while the local porosity depends upon the heterogeneity of the cancellous bone. The average porosity of cancellous bone can be directly determined from ultrasound signals reflected from the bone. Results of the ex vivo and in vivo short bone studies in patella are in agreement with that of Ultrasound Critical-angle Reflectometry (UCR). Thus, the second conclusion of this dissertation is that reflection ultrasound can be an effective tool for assessing bone properties in vivo. During the short bone-mimicking phantom study, the first critical angle detected by UCR was shown to correspond to the solid ultrasound velocity and is independent of porosity, but its amplitude is strongly related to porosity; the second critical angle, corresponding to bulk ultrasound velocity, is strongly related to porosity, but the correlation between its amplitude and the porosity is weak.Item A Multi-Parametric Investigation of Vascular Alterations in Elderly with Hypertension(2015-01-26) Sheffield, Adam; Sheng, Min; King, Kevin; Ravi, Harshan; Peng, Shin-lei; Liu, Peiying; German, Zohre; Lu, HanzhangBACKGROUND: Along with aging comes many cardiovascular and cerebral changes that impact a person's health. These changes manifest as variances in blood pressure, brain volume, cerebral blood flow (CBF), oxygen metabolism, and neurological functioning. OBJECTIVE: The purpose of this study is to provide evidence to support new or previously known biomarkers for declining cerebrovascular health, such as cerebral arterial stiffness, reduced vessel capacity, and thickening of the extracellular matrix. METHODS: 45 participants ranging from the ages of 61 to 79 with a mean of 67 were studied using a 3 Tesla MRI. Several MRI techniques were employed to acquire and analyze data. Phase-contrast (PC) MRI was used for acquiring images of moving fluid, so that arteries containing blood flow to the brain could be isolated in order to calculate total CBF. Blood-oxygen-level dependent contrast images and end-tidal CO2 and O2 measurements were also obtained using MRI after the participants were given a different sequence of gases to breathe containing varying amounts of oxygen, carbon dioxide, and nitrogen. This allowed the cerebrovascular reactivity (CVR) and venous cerebral volume (vCBV) of the vessels to be determined. Venous oxygenation (Yv) was assessed using T2-relaxation-under-spin-tagging (TRUST) MRI technique. Linear regressions were performed to account for age, sex, and blood pressure. Data were also analyzed by putting participants with a systolic blood pressure greater than 140 into a hypertensive category for comparison. Other data acquired during or immediately prior to the MRI scans include systolic and diastolic blood pressure, brain volume, and the oxygen saturation level of venous and arterial blood. RESULTS: A p-value of <0.05 was used to determine significance. The CVR for the hypertensive group was lower than that of the non-hypertensive group (p<0.01) and CVR decreased as systolic blood pressure increased (p=0.02). CVR also decreased with increasing age (p=0.02) and was higher in males than in females (p<0.01). CBF increased with systolic blood pressure (p=0.03) and was higher in females (p=0.03). Yv also increased with systolic blood pressure (p=0.02) and correlated strongly with CBF values (p<0.001). CONCLUSION: These results support certain relationships between blood pressure and the vascular markers within the brain, which may appear before cognitive decline or clinical symptoms emerge. This study is an early step on the path to discovering easily identifiable precursors to neurological changes that take place as normal aging processes occur.