Propagation of High Intensity Focused Ultrasound through a Patient-specific Ribcage Model

  • Rui Cao

    Student thesis: Doctoral ThesisDoctor of Philosophy


    A method of 3D modelling of high intensity focused ultrasound (HIFU) treatment through ribcage using patient data is described. This is further tested experimentally to derive at various parameters which could be indirectly useful in defining amount of energy and alteration needed in treatment protocols for the upper abdominal pathologies covered under ribcage.
    In the last ten years, feasibility and safety of HIFU treatment have been tested in a growing number of clinical studies. However, there are still challenges, such as the treatment through the ribcage. HIFU propagates through the ribs could lead to insufficient energy delivery to the focal target and heat deposition at the ribs may lead to surrounding soft tissue damage due to the bones properties of absorption and reflection to the ultrasound wave. Current research has not involved the physical human anatomical structures into the experimental study of the HIFU treatment through the ribcage. Therefore, our aim was to build a patient-specific physical ribcage model that possesses human anatomical structures to investigate its effect on HIFU treatment.
    Ribcage model was reconstructed based on patient data. This prototyping model possessed human anatomical structures and provided useful information in the treatment planning by applying HIFU sonication on tissue mimicking phantoms. In order to determine the optimal phantoms for medical imaging and HIFU application, the properties of tissue mimicking materials (TMMs) were characterised, including acoustic, thermal and elastic properties. Acoustic pressure distribution, acoustic power delivery and focus splitting were investigated with and without the presence of ribcage model in the focused ultrasound field.
    Multi-channel phased array transducer was applied to investigate the changes in temperature at focus and temperature was monitored by magnetic resonance imaging (MRI) thermometry. Sonications on phantom with varied focal lengths and ribcage locations using robotic arm were performed. Thermometry revealed that heating at focus can be controlled either by changing power or duration of application in order to achieve optimal results. Focal temperature change related to the shadow area on the transducer elements caused by the ribcage model in HIFU beam path. The experimental data based on the patient-specific ribcage model may contribute to design and optimise the sonication protocol in pre-clinical planning stage. It is believed that the HIFU sonication experiments using realistic phantoms based on patient data would be a step towards translation of this technology into more widespread clinical practice.
    Date of Award2014
    Original languageEnglish
    SponsorsChina Scholarship Council
    SupervisorZhihong Huang (Supervisor), Ghulam Nabi (Supervisor) & Andreas Melzer (Supervisor)

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