Egolf D P, Nelson D K, Howell H C, Larson V D
Auditory and Electroacoustics Research Group, Palatine, Illinois 60067.
J Acoust Soc Am. 1993 May;93(5):2809-19. doi: 10.1121/1.405802.
Several audiological tests require knowledge of the sound-pressure spectrum at the eardrum. However, microphone readings are typically made at another, more-accessible position in the auditory canal. Recordings are then "adjusted" to the plane of the eardrum via mathematical models of the ear canal and eardrum. As bandwidths of audiological instruments have increased, ear-canal models have, by necessity, become more precise geometrically. Reported herein is a noninvasive procedure for acquiring geometry of the ear canal in fine detail. The method employs a computer-assisted tomographic (CAT) scanner in two steps to make radiographic images of parasagittal cross sections at uniform intervals along the lateral length of the canal. Accuracy was evaluated by comparing areas of cross sections appearing in radiographic images of a cadaver ear canal to cross sectional areas of corresponding michrotome slices of an injection mold of the same canal. Percent differences between these two areas had a mean value of 9.65% for 26 different cross sections of the one ear canal studied. Ear canal volume estimated from the CAT images was 6.12% different from the estimated volume of the injection mold: an improvement over the reported 39% maximum error of conventional acoustic volume measurements.
多项听力学测试需要了解鼓膜处的声压谱。然而，麦克风读数通常是在耳道内另一个更易到达的位置进行的。然后通过耳道和鼓膜的数学模型将记录“调整”到鼓膜平面。随着听力学仪器带宽的增加，耳道模型在几何形状上必然变得更加精确。本文报道了一种用于详细获取耳道几何形状的非侵入性方法。该方法分两步使用计算机辅助断层扫描（CAT）扫描仪，沿耳道的横向长度以均匀间隔制作矢状旁截面的射线图像。通过将尸体耳道射线图像中出现的横截面面积与同一耳道注射模具相应切片的横截面面积进行比较来评估准确性。对于所研究的一个耳道的26个不同横截面，这两个面积之间的百分比差异平均值为9.65%。从CAT图像估计的耳道体积与注射模具估计体积相差6.12%：比报道的传统声学体积测量的最大误差39%有所改进。
