Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics
Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics
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具有线性调频编码激励的超谐波成像：过滤光谱重叠谐波
DOI：
10.1109/tuffc.2014.006424
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
S. Freear
中科院分区：
文献类型：
--
作者：
S. Harput;J. Mclaughlan;D. Cowell;S. Freear
超谐波成像利用组织中产生的高次谐波提高了空间分辨率。超谐波分量由三、四、五次谐波组合而成，其能量含量低，因此信噪比较差。本研究采用编码激励来提高激励能量。在接收端通过使用谐波匹配滤波器进行脉冲压缩来提高信噪比。编码信号的使用还引入了脉冲激励无法实现的新的滤波能力。这在使用宽带信号时尤为重要。对于窄带信号，谐波的频谱边界分离清楚，易于滤波；然而，可用的成像带宽没有得到充分利用。宽带激励更适合谐波成像应用，以保持轴向分辨率，但它产生频谱重叠的谐波，不可能在时域和频域过滤。脉冲压缩后，这种重叠增加了范围边瓣，这是成像伪影，降低了b模图像质量。在本研究中，利用扇形啁啾变换（FChT）在另一个域实现了高次谐波的隔离。为了显示激励带宽对超谐波成像的影响，采用线性调频啁啾激励进行测量，带宽为10%至50%。利用宽带啁啾激励对线体进行超谐波成像。通过比较空间分辨率和旁瓣电平，给出了应用FChT滤波技术和不应用FChT滤波技术的结果。宽带激励信号如预期的那样获得了更好的分辨率，然而，对于分数带宽为50%的啁啾激励的超谐波分量，观察到高达-23 dB的范围旁瓣。该滤波技术在不影响轴向分辨率的情况下实现了> ~ 50db范围的旁瓣抑制，提高了图像质量。
Superharmonic imaging improves the spatial resolution by using the higher order harmonics generated in tissue. The superharmonic component is formed by combining the third, fourth, and fifth harmonics, which have low energy content and therefore poor SNR. This study uses coded excitation to increase the excitation energy. The SNR improvement is achieved on the receiver side by performing pulse compression with harmonic matched filters. The use of coded signals also introduces new filtering capabilities that are not possible with pulsed excitation. This is especially important when using wideband signals. For narrowband signals, the spectral boundaries of the harmonics are clearly separated and thus easy to filter; however, the available imaging bandwidth is underused. Wideband excitation is preferable for harmonic imaging applications to preserve axial resolution, but it generates spectrally overlapping harmonics that are not possible to filter in time and frequency domains. After pulse compression, this overlap increases the range side lobes, which appear as imaging artifacts and reduce the Bmode image quality. In this study, the isolation of higher order harmonics was achieved in another domain by using the fan chirp transform (FChT). To show the effect of excitation bandwidth in superharmonic imaging, measurements were performed by using linear frequency modulated chirp excitation with varying bandwidths of 10% to 50%. Superharmonic imaging was performed on a wire phantom using a wideband chirp excitation. Results were presented with and without applying the FChT filtering technique by comparing the spatial resolution and side lobe levels. Wideband excitation signals achieved a better resolution as expected, however range side lobes as high as -23 dB were observed for the superharmonic component of chirp excitation with 50% fractional bandwidth. The proposed filtering technique achieved >50 dB range side lobe suppression and improved the image quality without affecting the axial resolution.
影响因子：
4.2
作者：
Park, Jinhyoung;Li, Xiang;Zhou, Qifa;Shung, K. Kirk
通讯作者：
Shung, K. Kirk