Differences in tissue heating rates between ultrasound transducers have been well documented; however, comparative analysis between ultrasound fields to determine why tissue heating rates may differ is lacking. We selected three transducers from the same manufacturer with similar effective radiating area, output power, effective intensity and beam nonuniformity ratio [as defined by the FDA, 21 CFR Chap. 1, part 1,050 (10)], but markedly different Schlieren images. Each transducer was utilized to heat tissue with a standardized ultrasound application to determine whether Schlieren analysis may be useful in understanding variability in tissue heating rates. Thermocouples were inserted into the left triceps surae of 12 volunteers at a depth of 1.5 cm below one half the measured skin fold thickness (estimated average depth of the thermocouple was 1.99 +/- 0.27 cm). Each subject received one treatment from each transducer in a single session (n = 3); 3 MHz at 1.2 W/cm(2) for 8 min with a 100% duty cycle. Each transducer increased the IM temperature over time (p < 0.0001). IM temperatures were not significantly different between transducers from time zero to the fourth minute of treatment. After the fourth min, transducers B and C generated significantly higher tissue temperatures (p < 0.01). Transducer A, B and C increased IM temperature from 34.9 +/- 0.5 to 41.2 +/- 1.3 degrees C, 34.9 +/- 0.6 to 42.5 +/- 1.4 degrees C and 34.9 +/- 0.5 to 42.7 +/- 1.7 degrees C, respectively. Interestingly, transducer C emitted 22% lower output power but heated 24% higher than transducer A and our Schlieren images demonstrate that transducers B and C produced a more concentrated field compared with transducer A. The data we present here supports the general contention that a more concentrated field will heat to a higher temperature than a more disperse field, however, technical challenges in estimating output power, ERA and Schlieren analysis remain an issue.

译文

超声换能器之间的组织加热速率差异已得到充分记录; 但是,缺乏超声场之间的比较分析以确定为什么组织加热速率可能不同。我们从同一制造商中选择了三个换能器,它们具有相似的有效辐射面积,输出功率,有效强度和光束不均匀性比 [由FDA,21 CFR第1章,第1,050 (10) 部分定义],但明显不同的Schlieren图像。利用每个换能器通过标准化的超声应用来加热组织,以确定Schlieren分析是否有助于理解组织加热速率的变异性。将热电偶插入到12名志愿者的左肱三头肌中,深度1.5厘米低于测得的皮肤褶皱厚度的一半 (热电偶的估计平均深度为1.99 +/-0.27厘米)。每个受试者在单个会话 (n = 3) 中从每个换能器接受一次治疗; 在1.2 W/cm(2) 下3 MHz,持续8分钟,具有100% 的占空比。每个换能器随时间增加IM温度 (p <0.0001)。从零点到治疗的第四分钟,换能器之间的IM温度没有显着差异。在第四分钟后,换能器B和C产生明显更高的组织温度 (p <0.01)。换能器A、B和C分别将IM温度从34.9 +/- 0.5增加到41.2 +/- 1.3 ℃,34.9 +/- 0.6到42.5 +/- 1.4 ℃,34.9 +/- 0.5到42.7 +/- 1.7 ℃。有趣的是,与换能器A相比,换能器C发射22% 更低的输出功率,但加热的24% 更高,并且我们的Schlieren图像表明,与换能器a相比,换能器B和C产生了更集中的场。我们在这里提供的数据支持了一个普遍的论点,即更集中的场将比更分散的场加热到更高的温度,但是,估计输出功率,ERA和Schlieren分析的技术挑战仍然是一个问题。

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