High frequency chirp coded excitation ultrasound imaging system

An increase of imaging frequency enhances the performance in spatial resolution of an ultrasound scanner while sacrificing echo signal to noise ratio (eSNR) because of a rise in the amount of attenuation. As solutions to raise the eSNR level while maintaining the enhanced spatial resolution, both fundamental and harmonic coded excitation imaging methods have been proposed. For this purpose, ultrasound bio-microscopes (UBM) capable of chirp coded excitations were implemented on both a linear and a sector mechanical scanning system. A custom-designed broadband (5 MHz – 140 MHz) linear power amplifier was designed as a part of a low noise arbitrary pulse generator to replace a commercial bench-top power amplifier in the linear UBM. The modified imaging system exhibited a better eSNR of 7 dB than the system with a commercial power amplifier while maintaining the spatial resolution in a wire target measurement. In-vivo imaging was carried on pig eye and zebrafish embryo using a 40 MHz and a 100 MHz single element transducer respectively. For high frame rate coded excitation imaging, a standalone frontend system for a sector UBM was implemented. The custom-designed system consisting of a transmitter, a receiver, a motor controller and a motor position interpreter achieved an eSNR of 66 dB utilizing chirp coded excitation for wire target imaging. Moreover, contrast to noise ratio (CNR) was improved from 2.92 to 3.18 with coded excitation. This modified scanner allowed contraction of cardiac chambers of both zebrafish and mouse hearts to be clearly visualized. As an effort to enhance the spatial resolution, pulse inversion chirp coded tissue harmonic imaging (PI-CTHI) was programmed into the custom-designed frontend system. In a wire target study using a 40 MHz single element transducer, lateral resolution was found to be 110 μm, which was narrower than fundamental imaging at153 μm. CNR was found to improve by 34 % when chirp coded excitation was applied to harmonic imaging. This imaging mode was shown to better delineate the clot formation in adult zebrafish heart imaging when the heart was amputated and allowed to regenerate.

成像频率的提升可改善超声扫描仪的空间分辨率性能，但会因衰减量增加而降低回波信噪比（echo signal to noise ratio, eSNR）。为在保持提升后的空间分辨率的同时提高回波信噪比水平，学界已提出基波编码激发成像与谐波编码激发成像两种方案。为此，研究人员将具备啁啾编码激发能力的超声生物显微镜（ultrasound bio-microscopes, UBM）集成到线性机械扫描系统与扇形机械扫描系统中。针对线性超声生物显微镜，研究人员设计了一款定制化宽带（5 MHz – 140 MHz）线性功率放大器，将其作为低噪声任意脉冲发生器的组成部分，以替代商用台式功率放大器。经改造的成像系统在金属丝靶标测试中保持了空间分辨率的同时，回波信噪比相较搭载商用功率放大器的系统提升了7 dB。研究人员分别采用40 MHz与100 MHz的单阵元换能器，对猪眼及斑马鱼胚胎开展了活体成像实验。针对高帧率编码激发成像，研究人员搭建了一套用于扇形扫描超声生物显微镜的独立前端系统。这套定制化系统包含发射单元、接收单元、电机控制器与电机位置解析模块，在金属丝靶标成像实验中采用啁啾编码激发时，回波信噪比可达66 dB。此外，采用编码激发可使对比度信噪比（contrast to noise ratio, CNR）从2.92提升至3.18。经改造的扫描仪可清晰可视化斑马鱼与小鼠心脏的心室收缩过程。为进一步提升空间分辨率，研究人员将脉冲反转啁啾编码组织谐波成像（pulse inversion chirp coded tissue harmonic imaging, PI-CTHI）功能编入这套定制化前端系统。在采用40 MHz单阵元换能器的金属丝靶标测试中，侧向分辨率可达110 μm，优于基波成像的153 μm。在谐波成像中采用啁啾编码激发时，对比度信噪比可提升34%。该成像模式可在成年斑马鱼心脏截肢后再生过程的成像中，更清晰地勾勒出血栓形成的形态。