Hynynen K
Arizona Cancer Center, University of Arizona, Tucson 85724.
Int J Hyperthermia. 1990 Nov-Dec;6(6):1005-12. doi: 10.3109/02656739009140983.
It is well known that ultrasound beams will be completely reflected at a soft-tissue-gas interface. The reflected beam is contributing to the power absorption at the tissue interface and may cause a hot spot which could prevent therapeutic temperatures at the treatment volume. In this study the temperature elevation caused by a reflected ultrasound beam at the skin surface has been investigated in dogs' thighs in vivo. The magnitude of the hot spot was quantified and the effect of entrance angle was also investigated. In addition, the possibility of eliminating the hot spot by coupling the beam out of the tissue was studied. The results showed that the temperature elevation can be up to four times larger at the skin-air surface than in resting muscle under similar exposure. The geometry of the reflecting surface had a significant effect on the temperature distribution. When the sound was coupled out of the tissue the magnitude of the temperature elevation at the skin reduced to less than half (depending on the geometry) but was still larger than temperatures measured in muscle. These results suggest the need for computerized treatment planning for scanned focused ultrasound treatments.
众所周知，超声束在软组织-气体界面会发生完全反射。反射束会导致组织界面处的功率吸收，并可能形成一个热点，这可能会阻止治疗体积内达到治疗温度。在本研究中，在犬大腿的体内研究了皮肤表面反射超声束引起的温度升高。对热点的大小进行了量化，并研究了入射角的影响。此外，还研究了通过将束耦合出组织来消除热点的可能性。结果表明，在类似暴露条件下，皮肤-空气表面的温度升高可比静息肌肉中的温度升高大四倍。反射表面的几何形状对温度分布有显著影响。当声音从组织中耦合出来时，皮肤处的温度升高幅度降至不到一半（取决于几何形状），但仍高于肌肉中测得的温度。这些结果表明，对于扫描聚焦超声治疗，需要进行计算机化的治疗计划。
