O'Brien William D, Yang Yan, Simpson Douglas G
Bioacoustics Research Laboratory, Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL 61801, USA.
Ultrasound Med Biol. 2004 Jul;30(7):965-72. doi: 10.1016/j.ultrasmedbio.2004.03.015.
The monopole-source solution was used to calculate the three-dimensional complex acoustic pressure field for one-dimensional focused rectangular apertures in a medium having homogeneous acoustic and thermal properties. For each of six frequencies (1, 3, 5, 7, 9 and 12 MHz) and three focuses (f/1, f/2 and f/4), 33 rectangular aperture cases were investigated, for a total of 594 cases. For these focused field geometries, the three-dimensional temperature distribution was calculated using the bioheat transfer equation in homogeneous perfused media (attenuation = absorption: 0.3 dB/cm-MHz; perfusion length: 1.0 cm). For each of the 594 cases, the acoustic field was normalized to the derated spatial-peak temporal-average intensity (ISPTA.3) of 720 mW/cm2, the maximum value condition allowed based on the U.S. Food and Drug Administration (FDA) regulatory limit for most diagnostic ultrasound (US) equipment. Using the normalized acoustic field, the axial temperature increase profiles and the maximum temperature increases (DeltaTmax) were determined for each case. Also, from the normalized acoustic field, the unscanned-mode soft-tissue thermal index (TIS) for the rectangular sources was determined according to the procedures of the Standard for Real-Time Display of Thermal and Mechanical Indices on Diagnostic Ultrasound Equipment, commonly called the output display standard, ODS. The DeltaTmax:TIS ratio of the 594 cases yielded a mean value of 0.22, a median value of 0.16, a maximum value of 1.04 and a minimum value of 0.039. For all but one of the cases, TIS was greater than DeltaTmax. Also, two new unscanned-mode soft-tissue thermal indices (denoted TIS(new1) and TIS(new2)) were proposed. For new model 1, the DeltaTmax: TIS(new1) ratio yielded a mean value of 1.02, a median value of 1.01, a maximum value of 1.83 and a minimum value of 0.44. For new model 2, the DeltaTmax: TIS(new2) ratio yielded a mean value of 1.04, a median value of 0.99, a maximum value of 2.31 and a minimum value of 0.34. Further, both new models fit more closely to DeltaTmax than does the ODS-determined TIS and have the potential of being easier for manufacturers to implement because only the source power and frequency need to be measured.
使用单极源解来计算具有均匀声学和热学特性的介质中一维聚焦矩形孔径的三维复声压场。对于六个频率（1、3、5、7、9和12 MHz）中的每一个以及三个焦距（f/1、f/2和f/4），研究了33个矩形孔径情况，总共594个情况。对于这些聚焦场几何形状，使用均匀灌注介质中的生物热传递方程（衰减 = 吸收：0.3 dB/cm-MHz；灌注长度：1.0 cm）计算三维温度分布。对于594个情况中的每一个，将声场归一化为720 mW/cm²的降额空间峰值时间平均强度（ISPTA.3），这是根据美国食品药品监督管理局（FDA）对大多数诊断超声（US）设备的监管限制所允许的最大值条件。使用归一化的声场，确定每个情况下的轴向温度升高曲线和最大温度升高（ΔTmax）。此外，根据诊断超声设备热学和力学指标实时显示标准（通常称为输出显示标准，ODS）的程序，从归一化声场中确定矩形源的未扫描模式软组织热指数（TIS）。594个情况的ΔTmax:TIS比值得出平均值为0.22，中位数为0.16，最大值为1.04，最小值为0.039。除了一个情况外，所有情况下TIS都大于ΔTmax。此外，还提出了两个新的未扫描模式软组织热指数（表示为TIS(new1)和TIS(new2)）。对于新模型1，ΔTmax:TIS(new1)比值得出平均值为1.02，中位数为1.01，最大值为1.83，最小值为0.44。对于新模型2，ΔTmax:TIS(new2)比值得出平均值为1.04，中位数为0.99，最大值为2.31，最小值为0.34。此外，与ODS确定的TIS相比，这两个新模型都更接近ΔTmax，并且由于只需要测量源功率和频率，制造商实施起来可能更容易。
