Jin Xing, Li Changhui, Wang Lihong V
Department of Biomedical Engineering, Texas A&M University, 3120 TAMU, College Station, Texas 77843-3120, USA.
Med Phys. 2008 Jul;35(7):3205-14. doi: 10.1118/1.2938731.
The effects of acoustic heterogeneities on transcranial brain imaging with microwave-induced thermoacoustic tomography were studied. A numerical model for calculating the propagation of thermoacoustic waves through the skull was developed and experimentally examined. The model takes into account wave reflection and refraction at the skull surfaces and therefore provides improved accuracy for the reconstruction. To evaluate when the skull-induced effects could be ignored in reconstruction, the reconstructed images obtained by the proposed method were further compared with those obtained with the method based on homogeneous acoustic properties. From simulation and experimental results, it was found that when the target region is close to the center of the brain, the effects caused by the skull layer are minimal and both reconstruction methods work well. As the target region becomes closer to the interface between the skull and brain tissue, however, the skull-induced distortion becomes increasingly severe, and the reconstructed image would be strongly distorted without correcting those effects. In this case, the proposed numerical method can improve image quality by taking into consideration the wave refraction and mode conversion at the skull surfaces. This work is important for obtaining good brain images when the thickness of the skull cannot be ignored.
研究了声学不均匀性对微波诱导热声层析成像经颅脑成像的影响。建立了一个用于计算热声波在颅骨中传播的数值模型，并进行了实验验证。该模型考虑了颅骨表面的波反射和折射，因此提高了重建的精度。为了评估在重建过程中何时可以忽略颅骨引起的影响，将所提方法获得的重建图像与基于均匀声学特性的方法获得的重建图像进行了进一步比较。从模拟和实验结果发现，当目标区域靠近脑中心时，颅骨层引起的影响最小，两种重建方法都能很好地工作。然而，随着目标区域越来越靠近颅骨与脑组织的界面，颅骨引起的畸变变得越来越严重，并且如果不校正这些影响，重建图像将严重失真。在这种情况下，所提数值方法可以通过考虑颅骨表面的波折射和模式转换来提高图像质量。这项工作对于在颅骨厚度不可忽略时获得良好的脑部图像很重要。
