Radiofrequency (RF) and microwave ablation techniques are interstitial, focal ablative therapies that can be used in a percutaneous fashion. They permit in situ destruction of hepatic, renal and prostatic tumors. However, local recurrence rates after RF ablative therapy are as high as 34-55%, due in part to the inability to visualize the zone of necrosis (thermal lesion) after treatment under conventional ultrasound guidance. Elastography is a promising tool for visualizing the zone of necrosis in tissue resulting from RF ablation. The goal of this research is to develop and evaluate techniques for ultrasound-based in-vivo elastography for visualizing ablated regions during and after thermal therapy, and to determine whether elastographic images provide clinical information on the extent and viability of the treated region. The research plan develops and evaluates """"""""RF electrode displacement"""""""" elastography. Basic elastic modulus properties of normal liver, liver neoplasms and metastases, and ablated liver wjll first be measured using a precision mechanical testing device. Elastography phantoms using the Young's Modulus measured in liver tissue will also be used to determine the reliability of mapping out ablated regions. Special phantoms, including those that have complex shapes, will challenge electrode displacement elastography under realistic conditions. Finite element analysis (FEA) will be utilized to model tissue displacements induced by RF electrode displacements and to extrapolate and understand phantom results. In-vivo studies will be conducted to test electrode displacement elastography for in-vivo elastographic imaging both on a wood- chuck HCC cancer and Rabbit VX2 metastases model to evaluate the elastographic depiction of cancers before and after ablation therapy. Comparisons of the elastograms with histopathology using light microscopy of ablated tissue will be performed to determine if elastograms are able to differentiate ablated (necrotic) from unablated (regions with viable cancer cells) and normal tissue regions. Real-time implementation of electrode displacement elastography along with 2-D cross-correlation processing will be implemented on the Siemens Antares scanner. Finally, a pilot study will be performed using the real-time elastographic modality developed on the Siemens Antares scanner on both a larger porcine animal model and tumor model (both the primary HCC and metastases model) to evaluate the ability to monitor percutaneous RF ablation using elastography under actual imaging conditions Clinical application of in-vivo elastography to monitor the progression and outcome of ablative cancer treatments during the minimally invasive RF ablation procedure could benefit a large group of patients.
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