Johns Lennart D, Demchak Timothy J, Straub Stephen J, Howard Samuel M
Department of Physical Therapy, Quinnipiac University, Hamden, CT 06518, USA.
Ultrasound Med Biol. 2007 Dec;33(12):1911-7. doi: 10.1016/j.ultrasmedbio.2007.06.012. Epub 2007 Aug 15.
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.
超声换能器之间组织加热速率的差异已有充分记录；然而，缺乏对超声场进行比较分析以确定组织加热速率为何可能不同的研究。我们从同一制造商处挑选了三个换能器，它们具有相似的有效辐射面积、输出功率、有效强度和波束不均匀率[如美国食品药品监督管理局（FDA）在《联邦法规汇编》第21卷第1章第1050部分（10）中所定义]，但纹影图像明显不同。每个换能器都用于通过标准化的超声应用来加热组织，以确定纹影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12名志愿者左小腿三头肌中，深度为测量的皮肤褶皱厚度一半以下1.5厘米处（热电偶的估计平均深度为1.99±0.27厘米）。每个受试者在单次治疗中接受每个换能器的一次治疗（n = 3）；以1.2W/cm²的功率、100%的占空比进行3MHz、8分钟的治疗。每个换能器随时间升高了肌肉内（IM）温度（p < 0.0001）。在治疗的从零分钟到第四分钟期间，各换能器之间的IM温度无显著差异。第四分钟后，换能器B和C产生的组织温度显著更高（p < 0.01）。换能器A、B和C分别将IM温度从34.9±0.5升高到41.2±1.3摄氏度、从34.9±0.6升高到42.5±1.4摄氏度以及从34.9±0.5升高到42.7±1.7摄氏度。有趣的是，换能器C的输出功率低22%，但加热效果比换能器A高24%，并且我们的纹影图像表明，与换能器A相比，换能器B和C产生的场更集中。我们在此呈现的数据支持这样一个普遍观点，即更集中的场比更分散的场加热到更高的温度，然而，在估计输出功率、有效辐射面积和纹影分析方面的技术挑战仍然是一个问题。
