Baker A C
School of Physics, University of Bath, UK.
Phys Med Biol. 1991 Nov;36(11):1457-64. doi: 10.1088/0031-9155/36/11/005.
There is a well established requirement for making output measurements on medical ultrasound equipment, in particular for safety and calibration purposes. In addition there is a need for non-linear propagation models to allow predictions to be made for in vivo pressure fields of systems ranging from lithotripters to diagnostic imaging sets. In the past it has been shown that good agreement can be found between experiment and theory for transducers that behave as perfect pistons but little work has been published on comparisons for 'real' medical ultrasound systems. This paper compares experiment with theory for a medical ultrasound system operating in water. Pressure field measurements are presented for a Philips 3.5 MHz, 13 mm diameter, 'long internal focus' (LIF) transducer. The measurements were made using a membrane hydrophone in water. Initially the transducer was driven continuously with a function generator at low amplitude so that the effective aperture radius and focal length could be determined. The transducer was then driven by a Philips 'sono-Diagnost B' imaging system which produced a short finite amplitude pulse. The results are compared with a finite difference model based on the parabolic approximation to the non-linear wave equation. Reasonable agreement (typically 10-15%) is shown for spectral magnitudes although some difficulty was encountered in accurately characterizing the transducer in terms of its geometry and drive waveform.
对医学超声设备进行输出测量有既定要求，特别是出于安全和校准目的。此外，还需要非线性传播模型，以便对从碎石机到诊断成像设备等系统的体内压力场进行预测。过去已经表明，对于表现为理想活塞的换能器，实验和理论之间可以达成良好的一致性，但关于“实际”医学超声系统比较的研究发表得很少。本文对在水中运行的医学超声系统进行了实验与理论的比较。给出了飞利浦3.5MHz、直径13mm、“长内聚焦”（LIF）换能器的压力场测量结果。测量是在水中使用膜式水听器进行的。最初，用函数发生器以低幅度连续驱动换能器，以便确定有效孔径半径和焦距。然后，用飞利浦“sono-Diagnost B”成像系统驱动换能器，该系统产生一个短的有限幅度脉冲。将结果与基于非线性波动方程抛物线近似的有限差分模型进行比较。尽管在根据换能器的几何形状和驱动波形准确表征换能器方面遇到了一些困难，但频谱幅度显示出合理的一致性（通常为10 - 15%）。
