| Palpation is a standard screening procedure for the detection of several superficial cancers including breast, thyroid, prostate, and liver tumors through both self and clinical examination. This is because solid masses typically have distinct stiffnesses compared to their surrounding normal tissue. Conventional imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI), and mammography can provide morphological characteristics however, these modalities do not provide the information elicited upon palpation. Accurate depiction of tissue elasticity for accurately and efficiently detecting tumors is therefore needed.The mechanical response of soft tissue to the oscillatory acoustic radiation force is investigated using a finite-element model (FEM) of elastic, homogenous gels and stiff inclusion gels. The HMI experiments in gelatin and polyacrylamide tissue-mimicking gels were performed to validate mechanical responses in FEM. FEM and gel HMI studies demonstrate that the tissue dynamics, in response to an oscillatory force occur at the same frequency, and that the size and stiffness of the inclusions affect the dynamic tissue response. HMI has also been demonstrated to accurately map 17 post-surgical breast specimens (i.e., normal, benign, and malignant tissues) and reliably differentiate benign from malignant human breast tumors (p = 0.008) based on their distinct oscillatory displacements.Since HMI uses a highly focused beam, it can be easily integrated with ultrasound thermal therapy for the monitoring of the latter, aimed at regionally and thermally treating the detected tumors. The resulting integration of imaging and therapy into the HMI for Focused Ultrasound (HMIFU) system can be used as an image guidance tool for visualization of the targeted tissue (e.g. tumor), and generation and monitoring of the relative tissue stiffness changes during heating through the successful detection of the ablation onset. HMIFU is applied in 7 in vitro and 5 ex vivo liver tissues as well as 11 transgenic mice of breast cancer in vivo. The results show that the HMIFU system could follow the tissue stiffness change during heating and indicate the onset of coagulation necrosis so that the treatment procedure can be performed in a time-efficient manner.In conclusion, the dissertation study presented herein demonstrates that HMI can combine imaging and therapeutics for cancer treatment into a single, all-ultrasound, fully-integrated system. HMI may thus constitute a non-ionizing, a cost-efficient, and a reliable alternative method for detection of tumor and real-time monitoring of tumor thermal treatment.The work presented in this dissertation investigates a novel elasticity imaging technique, namely Harmonic Motion Imaging (HMI). HMI is an ultrasound based technique for tumor detection and classification. It uses a focused ultrasound (FUS) transducer to generate an oscillatory acoustic radiation force for an internal, non-contact palpation to internally estimate relative tissue hardness. HMI is unique among other elasticity imaging techniques in the sense that it provides a spatially localized distribution of an oscillatory acoustic radiation force that can be applied across a wide range of frequencies. The dynamic tissue response at the interrogated region can be related to the underlying tissue mechanical properties, which may differentiate healthy from diseased tissue. |
