Research On Ultrasound Thermal Imaging And Strain Imaging

Cancer as a worldwide major public health problem affects people's lifestyle and even is life threatening.Several noninvasive or minimally invasive thermal ablation methods such as focused ultrasound therapy and radio-frequency ablation are available for assisting cancer treatment.The key point of the thermal treatment is to monitor temperature to ensure an accurate and appropriate thermal dose.The ultrasound-based temperature monitoring method is attracting more and more attention for its advantage of noninvasive,nonionizing radiation,low cost and real-time.The tissue thermal expansion and change in the speed of sound due to tissue temperature change result in an echo-time shifts,thus the temperature could be measured according to the echo shift.However such temperature estimation method needs to know the tissue thermal coefficients and the sound speed in advance,meanwhile,the problem of tissue motion which affect the echo shift should be corrected.On the other hand,change in the backscattered energy(CBE)could also be used to evaluate temperature change to reconstruct a CBE-based temperature map.The necessity of the method is to define a proper scatterer and the temperature image reconstructed could not visualize the temperature distribution in tissues.This thesis conducted high-intensity focused ultrasound(HIFU)exposure experiment with graphite phantom and established thermal maps basing on time-echoshift and change in backscattered-energy,which proved feasibility and disadvantages of both ultrasound-based thermal reconstruction methods.Paramount to the success of thermal therapy is that the ablation region adequately covers the entire tumor to ensure a complete destruction of cancer cells.Ultrasound elastography provides reliable images for monitoring the ablation region.In this thesis,electrode-displacement elastography is established and RFA tests on in-vitro liver tissues is conducted.The results revealed that the boundaries of ablation lesions could be well detected using electrode-displacement elastography when the electrode displacement was 1 mm,the imaging angle was low and the electrode length was different.