- 學位論文
微氣泡輔助之穴蝕效應與超音波治療之應用
Microbubble-assisted Cavitation and Its Application to Ultrasonic Therapy
摘要
穴蝕效應是超音波誘使氣泡形成至破裂的過程，此過程釋出之能量可能引起嚴重的生物效應，因此造影用超音波之強度和能量均受到嚴格監控，以避免對人體組織不當的損傷。但是若能侷限穴蝕效應於患部，利用釋出的能量破壞腫瘤細胞或輔助藥物傳遞，穴蝕效應有潛力成為專一性治療之工具，並且可以有效與現有之超音波影像系統結合。因此，本研究終極目標是結合超音波影像與治療，在造影安全規範下，藉由微氣泡的輔助，有效誘發穴蝕效應，達成腫瘤治療之目的。 本研究之主要工作如下：首先我們量化評比數種波形誘發之穴蝕效應劑量，在固定機械參數於0.06~0.79之範圍內，測試總脈衝周數為10周的1.5MHz、3MHz和串接波形誘發的慣性穴蝕劑量。結果顯示相同機械參數的三種波形可誘發不同程度的穴蝕效應，可能原因之一為機械參數主要是預測自由氣泡之破裂，而本實驗的氣泡皆是有殼氣泡；原因之二是機械參數代表穴蝕效應發生的門檻，卻無法預測穴蝕效應之程度。故機械參數或許並非評估此類氣泡之穴蝕效應的最佳指標，而單以機械參數作為穴蝕效應之安全規範亦有再檢討之必要。 完成定量分析之後，本研究進一步將此技術應用到離體實驗，觀察穴蝕效應破壞腫瘤細胞之能力。由於活體內穴蝕核數量少且分布不均，不利於掌控穴蝕效應，為了能夠降低穴蝕效應之門檻，並且針對患部做專一性治療，在離體實驗部分，本研究將使用實驗室自製微脂體做為穴蝕核。微脂體有諸多發展潛力，微脂體表面傳輸定位抗體及修飾標定可使微脂體具有靶向性，可與特定組織進行專一性結合，應用在治療上，積聚在靶區的微脂體可提供微氣泡，增強靶區穴蝕效應，達到靶向治療之功能；應用在造影方面，微脂體可作為高頻超音波影像之對比劑與分子探針，協助分子影像技術之開發。我們已經可以製作包覆空氣之微脂體，並且以影像亮度法定性分析微脂體輔助之穴蝕效應，以慣性穴蝕效應劑量方法定量分析穴蝕效應劑量，建立穴蝕效應劑量與微脂體濃度、發射聲壓與脈衝長度之關聯。我們更進一步將自製微脂體用於離體實驗測試，建立離體實驗之架構以誘發穴蝕效應，並觀察細胞死亡率之變化。 離體實驗中，我們針對MKN45細胞株測試穴蝕效應對癌症細胞的破壞，目前由於微脂體對於實驗干擾仍未去除，尚未觀察到穴蝕效應引發之顯著癌細胞破壞，未來將改良自製微脂體之配方與製程，增加有效穴蝕核數量並加強控制微脂體品質，期能輔助增強穴蝕效應。此外也將最佳化超音波參數，選定合適頻率以及設計特殊波形以增強穴蝕效應，改進破壞腫瘤細胞之能力。離體實驗之後，我們將展開活體實驗，以活體微透析探針與微光纖系統，非侵入式即時觀察腫瘤治療效果。
並列摘要
Cavitation is the phenomena where cavities form and rapidly collapse within a liquid under intense pressure changes. The energy emitted during the cavitation process is likely to induce tissue damage. Therefore, the safety regulations for diagnostic ultrasound have been carefully established to minimize the risk of cavitational bioeffects. Nevertheless, well-controlled acoustic cavitation can also be an effective tool for noninvasive cancer therapy. Our long-term goal is to integrate ultrasound diagnosis and therapy- to achieve localized cancer treatment by microbubble-assisted cavitation under safety regulations. This study is the first step to the long-term job. The inertial cavitation doses (ICDs) are measured and studied at a constant mechanical index (MI). The MIs vary from 0.06 to 0.79. The ICDs induced by 1.5-MHz signals, 3-MHz signals and a signal cascading a 3-MHz signal with a 1.5-MHz signal are not equal even if the three waveforms have the same MIs. It is believed that the is due to the fact that MI was defined on cavitation activities of free gas bubbles, but encapsulated bubbles were used in our experiments. Another reason is that MI is not directly related to the degree and amount of cavitation as ICD. As a result, MI may not be the best index to quantify acoustic cavitation. The use of MI as the only parameter to represent potential cavitation-induced tissue damage is also questionable and requires further investigation. The in-house liposome microbubbles were used in the in vitro study on cavitational bioeffects. The quantitative study of liposome-assisted cavitation was conducted. An experimental system was built for the observation of the cavitation-induced cell damage to the human gastric cancer cell line, MKN45. Current results did not indicate a significant cavitation-induced cell death after one-minute exposure to ultrasound. In the future, the ultrasound parameters need to be optimized and the recipe of the in-house liposome microbubbles also needs to be improved for higher stability and stronger ICD. The in vivo study will follow the in vitro experiments. A microdialysis perfusion system and a microlight-guide system will be used to monitor the efficacy of in vivo tumor treatment.