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978-3-8439-0564-0, Reihe Elektrotechnik
Quantitative Molecular Ultrasound Imaging
208 Seiten, Dissertation Ruhr-Universität Bochum (2012), Softcover, A5
Ultrasound contrast agents commonly consist of encapsulated gas bubbles with diameters in the micrometer range. These microbubbles can be coated with ligands that bind to disease specific receptors in the vasculature. The imaging of the adherent microbubbles allows the assessment of the disease on a molecular level.
The specific challenge in molecular ultrasound imaging is to separate the microbubble response from the surrounding tissue in the ultrasound echo. Furthermore, the assessment of the efficiency of treatments, e.g. anti-angiogenic therapy, requires a quantification of the number of retained microbubbles. To detect therapeutic effects at an early stage, the quantification technique must be sensitive to very small changes in the microbubble concentration. The aim of this thesis is therefore to develop concepts for the precise quantification of microbubble concentrations with ultrasound.
In the first part the optimization of microbubble size to maximize acoustic backscatter is discussed. Then the feasibility of quantification by counting single microbubbles is investigated. A statistical model to estimate microbubble counts from Doppler images is derived. As Doppler is prone to motion and flow artifacts, a novel technique for the detection of microbubble destruction is then introduced which is based on the variance of the phase shifts of consecutive ultrasound echoes. This technique is finally implemented on a small animal imaging system, to demonstrate the detection of single microbubbles with the proposed method in vivo.