3-D Quantitative Reconstruction for the Medical Sound Velocity Measurement of Biological Tissue with Ultrasonic Diffraction Tomography

本文提出了一种基于声波绕物体垂直轴的发射/接收数据，在多层水平面上获得切片生物速度图像的三维定量重建方法。首先，针对有限观测孔径下的三维重建问题，在数据采集量和硬件资源要求不高的情况下，提出了一种通过在垂直方向引入空间滤波处理，将散射波从二维水平切片中分离出来，从而将三维重建问题简化为多层二维层析重建问题的方法。结果，通过针对水平面内部的2D图像重构操作再现准3D声速参数图像。对于第二件事，物体的声音变化先前被限制在3%或4%的范围内，并且观察距离被限制在物体的紧邻处。为了解决这一问题，针对传统Rytov近似中弱散射假设所带来的限制，提出了后向传播Rytov近似。已经证实，即使当物体的声速在大约10%的范围内变化并且观察距离延长超过50个波长时，也可以再现声速图像，其精度高达平均误差在0.1%以内<plus-minus>。因此，我们期望能够再现定量的声速图像，以满足医学诊断的实际需要，如乳腺癌的筛查试验

In this study, 3D quantitative rconstruction method for obtaining the sliced biological velocity image on the multi-layred horizontal plane is proposed based on the transmission/receiving data of the sound wave around the vertical axis of the object. For the first thing, to comply with the 3D reconstruction problem compatible with the limited observation aperture and the moderate amount of the data collection and hardware resources, a method was proposed for reducing the original 3D reconstruction problem into the multi-layred 2D tomographic reconstruction by introducing the spatial filter processing in a vertical direction to discriminate the scattered wave from the 2D sliced horizontal surface. As a result, the quasi-3D sound velocity parameter images were reproduced by the 2D image reconstruction operation for the inside of the horizontal surface. For the second things, sound variation of the object was previously restricted to the range within 3 or 4% and observation distance to the immediate vicinity of the object. To resolve this problem, the backward propagation Rytov approximation was proposed aiming at the mitigation of the restriction caused by the weak scattering assumption in the conventional Rytov approximation. It was verified that sound velocity images could be reproduced to the extent of the accuracy as high as average error being within 0.1% even when the sound velocity of the object was varied in a range of approximately <plus-minus>10% and observation distance was prolonged over 50 wavelengths. Above all, its expected that quantitative sound velocity images can be reproduced to satisfy the practical requirement in the medical diagnosis such as for the human breast cancer screening tes