Fan X, Hynynen K
Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Ultrasound Med Biol. 1996;22(4):471-82. doi: 10.1016/0301-5629(96)00026-9.
The noninvasive surgery of a tumor by focused transducers or phased arrays with multiple sonications was simulated in this study. The effects of multiple sonications on near field heating were investigated by varying the delay time between consecutive pulses and the movement pattern of the transducer within the focal plane. To avoid normal tissue damage, sufficient delay time between consecutive pulses is necessary. It was found that the delay is dependent on acoustic power and pulse duration. The treatment time is often long when a strongly focused transducer is used to treat a large tumor, because the volume of necrosed tissue generated by the focused ultrasound beam is small requiring a large number of multiple sonications. To reduce treatment time, it is necessary to decrease the total number of pulses. This can be done by increasing the acoustic power and/or sonication time, Longer sonications induce a perfusion dependency on the temperature elevations. The acoustic power is limited by mammalian tissue temperatures which should not exceed 100 degrees C to avoid boiling and gas formation. An alternative way to increase the coagulated tissue volume is to modify the acoustic field such that a large tissue volume is exposed, while generating a more uniform temperature elevation to avoid high exposure limiting temperatures. This can be done effectively by using a phased array. This study demonstrated that phased arrays can offer significantly shorter treatment times than similar spherically curved transducers.
本研究模拟了使用聚焦换能器或相控阵通过多次超声处理对肿瘤进行非侵入性手术。通过改变连续脉冲之间的延迟时间以及换能器在焦平面内的移动模式，研究了多次超声处理对近场加热的影响。为避免正常组织损伤，连续脉冲之间需要足够的延迟时间。研究发现，延迟时间取决于声功率和脉冲持续时间。当使用强聚焦换能器治疗大肿瘤时，治疗时间通常较长，因为聚焦超声束产生的坏死组织体积较小，需要大量的多次超声处理。为了减少治疗时间，有必要减少脉冲总数。这可以通过增加声功率和/或超声处理时间来实现，较长时间的超声处理会导致温度升高对灌注产生依赖性。声功率受到哺乳动物组织温度的限制，组织温度不应超过100摄氏度，以避免沸腾和气体形成。增加凝固组织体积的另一种方法是改变声场，使更大的组织体积暴露，同时产生更均匀的温度升高，以避免出现高暴露极限温度。这可以通过使用相控阵有效地实现。本研究表明，与类似的球面弯曲换能器相比，相控阵可显著缩短治疗时间。
