NIH Resource on Medical Ultrasonic Transducer Technology, Department of Biomedical Engineering, University of Southern California, Los Angeles, CA 90089, USA.
Ultrasonics. 2013 Feb;53(2):369-76. doi: 10.1016/j.ultras.2012.07.003. Epub 2012 Jul 21.
The application of chirp coded excitation to pulse inversion tissue harmonic imaging can increase signal to noise ratio. On the other hand, the elevation of range side lobe level, caused by leakages of the fundamental signal, has been problematic in mechanical scanners which are still the most prevalent in high frequency intravascular ultrasound imaging. Fundamental chirp coded excitation imaging can achieve range side lobe levels lower than -60dB with Hanning window, but it yields higher side lobes level than pulse inversion chirp coded tissue harmonic imaging (PI-CTHI). Therefore, in this paper a combined pulse inversion chirp coded tissue harmonic and fundamental imaging mode (CPI-CTHI) is proposed to retain the advantages of both chirp coded harmonic and fundamental imaging modes by demonstrating 20-60MHz phantom and ex vivo results. A simulation study shows that the range side lobe level of CPI-CTHI is 16dB lower than PI-CTHI, assuming that the transducer translates incident positions by 50μm when two beamlines of pulse inversion pair are acquired. CPI-CTHI is implemented for a proto-typed intravascular ultrasound scanner capable of combined data acquisition in real-time. A wire phantom study shows that CPI-CTHI has a 12dB lower range side lobe level and a 7dB higher echo signal to noise ratio than PI-CTHI, while the lateral resolution and side lobe level are 50μm finer and -3dB less than fundamental chirp coded excitation imaging respectively. Ex vivo scanning of a rabbit trachea demonstrates that CPI-CTHI is capable of visualizing blood vessels as small as 200μm in diameter with 6dB better tissue contrast than either PI-CTHI or fundamental chirp coded excitation imaging. These results clearly indicate that CPI-CTHI may enhance tissue contrast with less range side lobe level than PI-CTHI.
啁啾编码激励在脉冲反转组织谐波成象中的应用可以提高信噪比值。另一方面，由于基波信号的泄漏，在机械扫描器中，旁瓣电平的提高一直是个问题，而机械扫描器在高频血管内超声成象中仍然最为普遍。基本啁啾编码激励成象可以用汉宁窗达到低于-60dB 的旁瓣电平，但它产生的旁瓣电平比脉冲反转啁啾编码组织谐波成象（PI-CTHI）高。因此，在本文中，提出了一种组合的脉冲反转啁啾编码组织谐波和基本成象模式（CPI-CTHI），通过对 20-60MHz 的仿体和离体结果进行演示，保留了啁啾编码谐波和基本成象模式的优点。模拟研究表明，CPI-CTHI 的旁瓣电平比 PI-CTHI 低 16dB，假设当两个脉冲反转对的波束线采集时，换能器将入射位置移动 50μm。CPI-CTHI 已在原型血管内超声扫描仪中实现，能够实时进行组合数据采集。线阵实验表明，CPI-CTHI 的旁瓣电平比 PI-CTHI 低 12dB，回波信号比噪比高 7dB，而横向分辨率和旁瓣电平分别比基本啁啾编码激励成象精细 50μm，低 3dB。对一只兔子气管的离体扫描表明，CPI-CTHI 能够显示直径小至 200μm 的血管，组织对比比 PI-CTHI 或基本啁啾编码激励成象分别高 6dB。这些结果清楚地表明，CPI-CTHI 可以在比 PI-CTHI 更低的旁瓣电平下增强组织对比度。
