探討多個長條曲面超音波換能器於肝腫瘤熱治療之應用

Abstract

現今肝腫瘤高溫熱治療手術，如射頻、雷射、微波等，為低侵入式手術，超音波做為肝腫瘤治療的最大優勢為非侵入式手術。而以往超音波肝腫瘤臨床手術上遇到的問題為肋骨聲窗口的限制與腫瘤的移動以及治療時間過長。 此研究的目的，為利用多個長條曲面超音波換能器，曲率半徑15cm，圓弧長度17.7cm，寬度1cm，利用共焦加熱策略，探討在皮膚下3、6、9公分處的聲壓情形，並且在腫瘤正常呼吸末區段移動以及腫瘤靜態情形下，在五次單元加熱達到約1cm3~5 cm3熱劑量累積。 在皮下9公分處，考慮被肋骨限制的擺放方式，由五個換能器個別相隔15o進行共焦，在模擬方面假設為無肋骨組織影響聚焦情形，並且以擬反矩陣(pseudo inverse)方法，找到互補的聚焦模式並且進行切換加熱，結果可以在腫瘤正常呼吸末區段移動以及腫瘤靜態情形下，形成呼吸移動方向上(X方向)的連續熱劑量累積，再藉由換能器另一個方向上(Y方向)的自由移動，可以形成熱劑量的疊加，五次的疊加體積約1cm3。而皮下3、6公分處，擺放方式受到肋骨影響，換能器數量減少，仍以共焦的方法取得高功率強度場，並且利用擬反矩陣方法，找到其他的互補性聚焦，並且在五次單元加熱下熱劑量可達約5cm3。從以上的結果來看，熱劑量可以在深度(Z方向)3到9公分處造成累積。

The high temperature treatment for liver tumor, such as radiofrequency(RF) ablation、laser ablation、microwave ablation, are minimally invasive surgery. The advantage of focused ultrasound for liver tumor surgery is noninvasive. However, there are some problems of clinical surgery: the narrow ultrasound window due to ribs, the motion of tumor due to breath, and the long period of surgery time. This study used multiple concaved strip-shaped ultrasound transducers with a radius of curvature of 15 cm, arc length of 17.7 cm, and width of 1 cm to arrange the foci at the same point. The sound pressure was investigated at the depth of 3, 6, and 9 cm below the skin. In the situation of end-of-exhale and breath hold, the thermal dose accumulated to a volume of about 1cm3 ~5cm3 after five thermal ablations with shifts of the focus location. For a target region at the depth of 9 cm, five transducers were used. To avoid the ribs from obstructing the ultrasound beam path, the transducers were placed 15o apart from each other. Thus the computer simulation didn’t considered the effect of ribs on sound pressure. The pseudo inverse method was applied to obtain complementary sound pressure patterns. These patterns was switched to ablate the target region with a frequency of 10Hz. The results showed that the thermal dose accumulated along the motion direction caused by the breath (X direction). Multiple heating with the transducers moved in the Y direction, the thermal lesion up to 1cm3 could be formed for both situations of end-of-exhale and breath hold. When the target regions were at the depth of 3 cm or 6 cm, the number of transducers reduced, so that the ribs did not block the beam path. The transducers were placed to form a focus at the desired depth. High intensity sound pressure was obtained. The pseudo inverse method was used to obtain complementary sound pressure and the thermal dose accumulated to a volume of about 5cm3 after five thermal ablations with shifts of the focus location. The simulation results, demonstrated that the thermal lesion can be accumulated at different depths from 3cm to 9cm by using appropriate number of transducers and sonication modes.