Browsing by Subject "medical imaging"
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Item Automated Determination of Arterial Input Function Areas in Perfusion Analysis(2013-04-04) Liu, QunPerfusion in biological system refers to capillary-level blood flow in tissues, and is a critical parameter used for detecting physiological changes. Medical imaging provides an effective way to measure tissue perfusion. Quantitative analysis of perfusion studies requires the accurate determination of the arterial input function (AIF), which describes the delivery of intravascular tracers to tissues. Automating the process of finding the AIF can save operating time, remove the inter-operator variability, and correct the errors in the presence of the dispersion of the arterial system. Even though several methods are currently developed for automatically extracting an AIF, they are specific to a single modality and particular to a certain tissue. In this thesis, we developed an algorithm to automatically determine an AIF by classifying the characteristic parameters of image pixels' dynamic evaluation curves between blood feeding areas and tissues. This automated AIF determination can be used to facilitate the generation of parametric maps for perfusion studies based on various imaging modalities and covering a variety of tissues. Automatic AIF determination was accomplished by extracting characteristic parameters such as maximum slope, maximum enhancement, time to peak, time to wash-out, and wash-out slope. Multi-dimensional data containing the characteristic parameters were converted and reduced into two-dimensional (2-D) representations, which were presented as a plurality of 2-D plots. Then physiological phases were localized within the simplified representations. Automated segmentation of non-AIF tissues and determination of AIF areas were accomplished by automatically finding peaks and valleys of each physiological phase on the plurality of 2-D plots. The algorithm was tested in CT myocardial perfusion studies, in which a pig was used as a model of myocardial ischemia and perfusion. PET gastrointestinal (GI) perfusion studies were performed using this algorithm, in which GI perfusion was evaluated when cardiac outputs were controlled with four modes. This automated AIF determination study was compared with manual selection of AIF in PET imaging and microsphere studies to assess the effectiveness of this algorithm. In the CT myocardial perfusion study, the perfusion of infarcted myocardium was significantly lower than that of non-infarcted areas and lower than that when it was normal. In the PET abdominal perfusion study, PET imaging data gives lower value of standard deviation relative to the mean than that in microsphere results. In the manual AIF selection study, a slight change in selecting the AIF region caused a big influence on the result. On the contrary, the automated AIF selection remains consistent in the entire study and reduces inter-operator variation. A conclusion was made that this technique is applicable to several imaging modalities, such as PET, CT and MRI, and is effective on many tissues. In addition, this algorithm is straightforward and provides consistent results. More importantly, this automated AIF determination technique replaces the conventional spatial classification method with the functional classification method, taking more physiological considerations and explanations involved.Item Functional photoacoustic tomography of animal brains(Texas A&M University, 2005-11-01) Wang, XuedingThis research is primarily focused on laser-based non-invasive photoacoustic tomography of small animal brains. Photoacoustic tomography, a novel imaging modality, was applied to visualize the distribution of optical absorptions in small-animal brains through the skin and skull. This technique combines the high-contrast advantage of optical imaging with the high-resolution advantage of ultrasonic imaging. Based on the intrinsic optical contrast, this imaging system successfully visualized three-dimensional tissue structures in intact brains, including lesions and tumors in brain cerebral cortex. Physiological changes and functional activities in brains, including cerebral blood volume and blood oxygenation in addition to anatomical information, were also satisfactorily monitored. This technique successfully imaged the dynamic distributions of exogenous contrast agents in small-animal brains. Photoacoustic angiography in small-animal brains yielding high contrast and high spatial resolution was implemented noninvasively using intravenously injected absorbing dyes. In the appendix, the theory of Monte Carlo simulation of polarized light propagation in scattering media was briefly summarized.Item Photoacoustic and thermoacoustic tomography: system development for biomedical applications(Texas A&M University, 2006-04-12) Ku, GengPhotoacoustic tomography (PAT), as well as thermoacoustic tomography (TAT), utilize electromagnetic radiation in its visible, near infrared, microwave, and radiofrequency forms, respectively, to induce acoustic waves in biological tissues for imaging purposes. Combining the advantages of both the high image contrast that results from electromagnetic absorption and the high resolution of ultrasound imaging, these new imaging modalities could be the next successful imaging techniques in biomedical applications. Basic research on PAT and TAT, and the relevant physics, is presented in Chapter I. In Chapter II, we investigate the imaging mechanisms of TAT in terms of signal generation, propagation and detection. We present a theoretical analysis as well as simulations of such imaging characteristics as contrast and resolution, accompanied by experimental results from phantom and tissue samples. In Chapter III, we discuss the further application of TAT to the imaging of biological tissues. The microwave absorption difference in normal and cancerous breast tissues, as well as its influence on thermoacoustic wave generation and the resulting transducer response, is investigated over a wide range of electromagnetic frequencies and depths of tumor locations. In Chapter IV, we describe the mechanism of PAT and the algorithm used for image reconstruction. Because of the broad bandwidth of the laser-induced ultrasonic waves and the limited bandwidth of the single transducer, multiple ultrasonic transducers, each with a different central frequency, are employed for simultaneous detection. Chapter V further demonstrates PAT??s ability to image vascular structures in biological tissue based on blood??s strong light absorption capability. The photoacoustic images of rat brain tumors in this study clearly reveal the angiogenesis that is associated with tumors. In Chapter VI, we report on further developing PAT to image deeply embedded optical heterogeneity in biological tissues. The improved imaging ability is attributed to better penetration by NIR light, the use of the optical contrast agent ICG (indocyanine green) and a new detection scheme of a circular scanning configuration. Deep penetrating PAT, which is based on a tissue??s intrinsic contrast using laser light of 532 nm green light and 1.06 ??m near infrared light, is also presented.