Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
Ultrasonics. 2011 Aug;51(6):689-96. doi: 10.1016/j.ultras.2011.02.001. Epub 2011 Feb 13.
Vibro-acoustography is an ultrasound based imaging modality that can visualize normal and abnormal soft tissue through mapping the acoustic response of the object to a harmonic radiation force at frequency Δf induced by focused ultrasound. In this method, the ultrasound energy is converted from high ultrasound frequencies to a low acoustic frequency (acoustic emission) that is often two orders of magnitude smaller than the ultrasound frequency. The acoustic emission is normally detected by a hydrophone. Depending on the setup, this low frequency sound may reverberate by object boundaries or other structures present in the acoustic paths before it reaches the hydrophone. This effect produces an artifact in the image in the form of gradual variations in image intensity that may compromise image quality. The use of tonebursts with finite length yields acoustic emission at Δf and at sidebands centered about Δf. Multiple images are formed by selectively applying bandpass filters on the acoustic emission at Δf and the associated sidebands. The data at these multiple frequencies are compounded through both coherent and incoherent processes to reduce the acoustic emission reverberation artifacts. Experimental results from a urethane breast phantom are described. The coherent and incoherent compounding of multifrequency data show, both qualitatively and quantitatively, the efficacy of this reverberation reduction method. This paper presents theory describing the physical origin of this artifact and use of image data created using multifrequency vibro-acoustography for reducing reverberation artifacts.
振动声学成像是一种基于超声的成像方式,通过将物体对聚焦超声在频率 Δf 处产生的谐波辐射力的声响应映射到图像上来可视化正常和异常的软组织。在这种方法中,超声能量从高超声频率转换为低声频率(声发射),通常比超声频率小两个数量级。声发射通常由水听器检测。根据设置的不同,这种低频声音可能会在到达水听器之前通过物体边界或声路径中存在的其他结构进行反射。这种效应会在图像中产生以图像强度逐渐变化形式出现的伪影,从而可能影响图像质量。使用有限长度的啁啾脉冲会在 Δf 处产生声发射,并在其中心产生关于 Δf 的边带。通过在 Δf 处的声发射和相关边带选择性地应用带通滤波器来形成多个图像。通过相干和非相干过程对这些多个频率的数据进行复合,以减少声发射的反射伪影。描述了来自聚氨酯乳房模型的实验结果。多频数据的相干和非相干复合,从定性和定量两方面都证明了这种反射减少方法的有效性。本文介绍了描述这种伪影的物理起源的理论,并使用多频振动声学成像创建的图像数据来减少反射伪影。