- 學位論文
應用於磁振導引聚焦超音波熱手術之量溫方法精進
Advancements in MR thermometry for MR-guided high intensity focused ultrasound therapy
摘要
磁振造影技術因為其對溫度變化的高偵測度、極高的軟組織分辨率以及其能夠顯 示出組織質變的能力而成為高能超音波熱治療手術中極為有用的工具，在此類手 術中常用來監控超音波聚焦位置及監控熱治療的溫度分佈。然而，將磁振造影技 術應用於高能聚焦超音波手術雖然看似方便好用，但目前還有一些磁振造影技術 問題可以再改善。首先，磁振造影測量溫度需要夠高的訊噪比以提高溫度量測準 確度，但一般臨床上因為缺少專用線圈，導致訊噪比偏低; 再者，若在治療過程 中將超音波燒灼設備進行位移，將會造成磁振影像溫度計算上的嚴重偏差，所以 在治療過程需要一段降溫時間以取得位移後新的溫度基準影像，但這樣會延長治 療時間，尤其是較大範圍的目標治療場合。最後，磁振造影掃描時間太長以致於 無法在手術當下即時取得完整器官的磁振溫度影像，現行的手術只好只收取器官 部分之磁振溫度影像以減短掃描時間達到即時溫度量測之目的，但這樣的策略還 是很有風險且不安全的。為了增進磁振影像導引之超音波熱治療手術於臨床的可 行性，本論文分為兩個部分來解決這些問題。第一部分，我們設計了一使用於磁 振造影儀之無線共振線圈來增進區域訊噪比，進而增加磁振造影之量溫準確度。 第二部分，我們發展了一套移除磁振影像背景組織相位訊號的演算法，稱為 APE 方法，APE 方法可用來處理在手術過程中移動超音波燒灼設備所造成之量溫偏差， 這樣燒灼點移動時不需等降溫後再取得新的溫度基準影像，因此可以減少治療時 間。總結，本篇論文提出以無線共振線圈、影像重建演算法及磁振造影掃描序列， 來提高磁振溫度量測的時間及空間解析度及溫度準確性，改善高能超音波熱治療 手術應用於臨床時所遇到的瓶頸。
並列摘要
Magnetic resonance imaging (MRI) is a promising tool to monitor focus localization and temperature distribution during high intensity focused ultrasound (HIFU) ablation treatment. This is due to its great sensitivity of temperature measurement, and attractive soft tissue contrast to clearly reveal protein denaturation and lesion formation. However, despite these attractive features, there are many challenges that limit its clinical application. For one thing, MR thermometry requires high signal-to-noise ratio (SNR) to achieve precise ablation measurements, but general SNR of clinical MR images is not sufficient to achieve this purpose. Second, repositioning of devices would lead to substantial temperature bias. Thus, arbitrary reposition the HIFU ablation devices during treatment is not feasibility. This limitation restrains the surgical planning, especially when the target is large area. Finally, MR scanning time is too long to acquire the thermal mapping of whole organs in real-time. Therefore, current MRgHIFU treatment used to acquire thermal mapping of a partial organ to achieve real-time MR thermometry, but this strategy comes with a high risk and insecurities. To facilitate MRgHIFU treatment for clinical use, this dissertation is divided into two parts to address these issues. First, we design a wireless inductively coupled surface coil (WICS coil) used in MR thermometry to increase temperature measurement accuracy by improving local SNR. Second, we develop a novel background tissue phase removing algorithm, called anatomical phase extraction (APE) method, to circumvent the detrimental effects of HIFU ablation devices repositioning. In summary, we successfully solved these issues which limit the clinical application of MRgHIFU treatment. First, we demonstrated the capability of the WICS coil for improving local SNR and enhancing temperature measurement accuracy. Additionally, HIFU ablation devices can reposition arbitrarily during treatment without temperature measurement bias by using the proposed APE method.