非均質角譜法於穿顱聚焦式超音波之模擬

Abstract

聚焦式超音波是一種很有前途的腦部疾病治療方法，近年來越來越多的治療計劃需要透過實時的模擬來滿足，以協助臨床醫生做出治療計畫，因此快速且準確的模擬出超音波聲場聚焦分布成為一個重要課題。在我們的研究中，我們提出一種高計算效率的方式來模擬非均勻介質組織下的三維經顱聚焦式超音波聲場聚焦分布。我們將角譜法加入角度權重來模擬經顱聚焦分布的結果，並根據文獻中壓克力材料的設置來驗證本論文方法的精確度，最後透過真實離體顱骨比較模擬數據和測量數據之間的聲場聚焦分布差異。該模擬還與正在進行的臨床測試分析結合，以提供完整的治療計劃。我們開發的角譜法具有快速的計算能力，可以達到半實時的速度計算三維壓力場，範圍覆蓋整個顱內。在壓克力場域中模擬及量測的結果在位置差異上以及穿透率差異上分別小於0.5mm和5%。經顱實驗測量結果（5個真實顱骨中的129個位置）與本論文方法的模擬在相關度R2為 0.7233，平均位置差異為 2.424mm，正規化均方根誤差為 0.1390，根據上述的結果，本論文提出的方法對於經顱聚焦超音波治療的治療計劃具有顯著的效益。

Focused ultrasound is a promising methodology for the therapy of brain diseases. Nowadays, more and more demand has been requested to fulfill the need of delivering real-time treatment planning in order to assist treatment decision-making for clinicians. Rapid and accurate simulation of the ultrasound pressure becomes an important issue. In this study, we proposed the use of a high computational efficiency strategy to simulate a 3D transcranial focused ultrasound beam under heterogenetic tissue conditions. Angular Spectrum Method(ASM) algorithm was Improved by angle weight to simulate the transcranial focal beam deposition. The precision of the algorithm was calibrated via the PE material in vitro setting and then compared the pressure discrepancy between simulated and measured data through a trans-human-cadaver sample setup. The simulation also incorporates the analysis of ongoing clinical testing to provide treatment planning information. The developed ASM algorithm provided the efficient computational capability to calculate a 3D pressure field with a semi-real-time scale with the range to cover the entire brain cavity. The position discrepancy and magnitude between the simulated and measured PE in vitro phantoms were less than 0.5 mm and 5%, respectively. The correlation between the comparison of transcranial measurements (129 positions contributed from 5 human cadavers) as well as the ASM estimations was R2= 0.7233 , the position discrepancy was 2.424mm and NRMS error was 0.1390. This high computing efficient algorithm implementation may provide benefits to improve the treatment planning quality of the current transcranial focused ultrasound treatment.