氣泡在高能聚焦超音波燒灼影響之研究

Ablation Effect of High Intensity Focal Ultrasound with Bubbles

范紋鳳(Wen-Feng Fan)

指導教授 ： 陳俊杉

國立臺灣大學/工學院/土木工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.03350

摘要

高強度聚焦型超音波(high intensity focused ultrasound, HIFU)治療的置入氣泡的角色扮演加熱機制為一個當前有趣的議題。在高頻率時，非線性傳播導致在毫秒之內產生汽化氣泡；在較低的頻率，空化氣泡可能透過黏性逸散、聲學輻射和熱傳導提高溫度。
在本研究中，旨在探討含氣泡與不含氣泡的仿體燒灼效果。快速多極法(fast multipole method, FMM)用於計算壓力場。溫度場的計算則以壓力場的結果代入生物熱傳導方程式中計算(bio-heat transfer equation, BHTE)。BHTE則是使用商用有限元素分析軟體ANSYS求解。此外，並架設一個研究觀察燒灼效果的必要實驗平台。實驗中變化換能器的趨動頻率及和輸出電功率研究氣泡的影響。
對於不含氣泡的仿體，紡錘形的焦斑在實驗可觀察並且模擬上可預測。對於含單一氣泡仿體，焦斑在氣泡之前積累並且形成蝌蚪形狀。而微小的空化氣泡在低頻率產生並且在模擬中能合理地被簡化作單一氣泡。我們發現單一氣泡的半徑愈大將導致更大的焦斑。本研究認為空化氣泡和汽化氣泡同樣重要，並且同時提高HIFU的焦斑大小和形狀。

關鍵字

氣泡 ； 高能聚焦超音波 ； 快速多集法

並列摘要

A current topic of interest for high intensity focused ultrasound (HIFU) treatments involves the role of bubbles as a heating mechanism. At high amplitudes, nonlinear propagation leads to the generation of boiling bubbles within milliseconds; at lower amplitudes, cavitation bubbles can enhance heating through viscous dissipation, acoustic radiation, and heat conduction.
In this study, ablation effects of phantom with and without bubbles were studied. The fast multipole method (FMM) was used to calculate the pressure field. The temperature field was calculated using a bio-heat transfer equation (BHTE) that took the pressure field as the input source. The BHTE was solved using ANSYS. In addition, an experimental platform was set up where critical experiments were conducted to study the ablation effects. Frequency of transducer and output electric power were varied to study the bubble effects.
For the cased without bubbles, a cigar-shaped was observed in experiments and predicted in simulation. For the case with a single bubble, lesion was accumulated before the bubble and formed a tadpole-shape. The tiny cavitation bubbles occurred at low frequency could be reasonably simplified as a single bubble in simulation. We found that a larger radius of a single bubble would produce a larger lesion size. We concluded that cavitation bubbles and boiling bubbles share important characteristics and both enhance the lesion size and shape for HIFU.

並列關鍵字

bubbles ； HIFU ； FMM

參考文獻

Bailey, M. R., L. N. Couret, et al. (2001). "Use of overpressure to assess the role of bubbles in focused ultrasound lesion shape in vitro." Ultrasound Med Biol 27(5): 695-708.

Clarke, R. L. and G. R. ter Haar (1997). "Temperature rise recorded during lesion formation by high-intensity focused ultrasound." Ultrasound Med Biol 23(2): 299-306.

Damianou, C., K. Hynynen, et al. (1993). Application of the thermal dose concept for predicting the necrosed tissue volume during ultrasound surgery. Ultrasonics Symposium, 1993. Proceedings., IEEE 1993.

Damianou, C. A., K. Hynynen, et al. (1995). "Evaluation of accuracy of a theoretical model for predicting the necrosed tissue volume during focused ultrasound surgery." Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions on 42(2): 182-187.

Gumerov, N. A. and R. Duraiswami (2002). "Computation of scattering from N spheres using multipole reexpansion." The Journal of the Acoustical Society of America 112(6): 2688-2701.