The effect of abdominal wall morphology on ultrasonic pulse distortion. Part I. Measurements
The effect of abdominal wall morphology on ultrasonic pulse distortion. Part I. Measurements
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DOI：
10.1121/1.423946
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发表时间：
1998-12-01
影响因子：
2.4
通讯作者：
Waag, RC
中科院分区：
文献类型：
--
作者：
Hinkelman, LM;Mast, TD;Waag, RC
通过直接测量，评估了人体腹壁脂肪层和肌肉层在产生超声波阵面畸变中的相对重要性。所用的标本包括6个完整的腹壁标本和12个通过将每个完整标本分成脂肪层和肌肉层而获得的部分标本。在所采用的测量技术中，半球形换能器通过组织切片发射3.75 MHz的超声脉冲。接收到的波前由线性阵列在仰角方向上平移以合成二维孔径来测量。还在每个样本的不同位置测量插入损耗。计算了测量波形和计算参考之间的到达时间和能量水平的差异，该差异考虑了几何延迟和扩展。在对几何效应进行校正后，对接收波形进行了综合聚焦。分析和比较了各试件产生的畸变特征和焦点质量。测量结果表明，肌肉产生的到达时间失真比脂肪更大，而脂肪产生的能量水平失真比肌肉更大，但整个腹壁产生的失真并不等同于层产生的失真效果的简单组合。结果还表明，脂肪层和肌肉层都对腹壁引起的超声束失真有显著影响。然而，由脂肪层和肌肉层产生的失真的空间特性实质上不同。由肌肉层产生的失真，以及由肌肉层引起的焦斑图像畸变，显示出与肌纤维取向相关的相当大的各向异性。由脂肪层产生的变形显示了较小尺度的颗粒状结构，与单个脂肪小叶周围隔膜的散射有关。厚的脂肪层可能预期由于散射和体吸收效应两者而导致差的图像质量，而厚的肌肉层可能预期由于大的到达时间波动而导致聚焦像差。使用时移补偿的像差焦点的校正示出了对于肌肉部分比对于脂肪部分更完全的校正;使得基于相位屏幕模型的校正方法可以比对于脂肪层更适合于肌肉层。(C)1998年美国声学学会。[S0001-4966（98）05911-6]。
The relative importance of the fat and muscle layers of the human abdominal wall in producing ultrasonic wavefront distortion was assessed by means of direct measurements. Specimens employed included six whole abdominal wall specimens and twelve partial specimens obtained by dividing each whole specimen into a fat and a muscle layer. In the measurement technique employed, a hemispheric transducer transmitted a 3.75-MHz ultrasonic pulse through a tissue section. The received wavefront was measured by a linear array translated in the elevation direction to synthesize a two-dimensional aperture. Insertion loss was also measured at various locations on each specimen. Differences in arrival time and energy level between the measured waveforms and computed references that account for geometric delay and spreading were calculated. After correction for the effects of geometry, the received waveforms were synthetically focused. The characteristics of the distortion produced by each specimen and the quality of the resulting focus were analyzed and compared. The measurements show that muscle produces greater arrival time distortion than fat while fat produces,greater energy level distortion than muscle, but that the distortion produced by the entire abdominal wall is not equivalent to a simple combination of distortion effects produced by the layers. The results also indicate that both fat and muscle layers contribute significantly to the distortion of ultrasonic beams by the abdominal wall. However, the spatial characteristics of the,distortion produced by fat and muscle layers differ substantially. Distortion produced by muscle layers, as well as focal images aberrated by muscle layers, show considerable anisotropy associated with muscle fiber orientation. Distortion produced by fat layers shows smaller-scale, granular structure associated with scattering from the septa surrounding individual fat lobules. Thick layers of fat may be expected to cause poor image quality due to both scattering and bulk absorption effects, while thick muscle layers may be expected to cause focus aberration due to large arrival time fluctuations. Correction of aberrated focuses using time-shift compensation shows more complete correction for muscle sections than for fat sections; so that correction methods based on phase screen models may be more appropriate for muscle layers than for fat layers. (C) 1998 Acoustical Society of America. [S0001-4966(98)05911-6].