在超声医学领域，谐波成像解决了病人因肥胖、肋间隙狭窄、腹壁厚等原因造成显像困难的问题，极大的提升了临床诊断的准确性。与传统超声成像相比，谐波成像对腹部脏器、心脏血管等组织的成像效果更好，提高了此类组织病变检查的准确率。目前，谐波成像作为超声图像诊断的高级成像模式之一，其相关研究比较欠缺，它的成像质量至今依然受限于设备系统性能的不足以及相关技术的不成熟。 本文在深入学习超声谐波成像技术的基础上，使用脉冲翻转叠加的方法消弱组织的基波信号，并通过增强造影剂微泡的次谐波信号来抑制组织基波的残余信号，提高谐波信号与组织信号的功率比(STR),从而提高图像分辨率。在脉冲翻转叠加法的基础上，通过分析与验证，采用了序列脉冲翻转叠加法，弥补了前者精确度不足的缺陷，消除组织基波信号的效果更加明显。通过实验的图像结果表明，序列脉冲翻转叠加法比普通脉冲翻转叠加法得到的图像分辨率更高。 本文设计的高频超声谐波成像系统，是以Cyclone V系列的5CGXFC7D7F31C8N型FPGA芯片为控制核心，实现了数字化信号处理。为了提高系统电路的稳定性和可靠性，电路采用小型化、集成化、低噪声的设计理念，FPGA高速并行数字信号处理的特点使系统的实时性得到提高。系统结构按照功能分为信号发射电路、回波信号接收与转换电路、信号采集与处理电路、数据传输模块。为了满足不同需求，软件算法采用模块化设计，易于升级和系统扩展。软件是使用VHDL语言编写的，嵌入在FPGA内部，包括信号激励模块、回波信号处理模块和USB3.0数据传输模块。 本文搭建了模拟血管内血液流动的实验平台，在基于FPGA所设计的高频超声谐波成像系统上进行实验。通过得到的血管内谐波图像证明脉冲翻转叠加法在消除组织基波信号方面有很好的效果，图像分辨率比以往有了很大的提高。同时验证了序列脉冲翻转叠加的方法可以得到更好的STR和信噪比，得到的图像分辨率有了进一步的提高。

In the field of ultrasonic medical, harmonic imaging solved the imaging problems caused by obesity, rib space narrowing, abdominal wall thickness of patients. It greatly improved the accuracy of clinical diagnosis. Compared with the traditional ultrasonic imaging, the imaging effect of harmonic imaging is better on abdominal viscera, cardiovascular tissue and improved the accuracy to check of such tissues. At present, the harmonic imaging as one of the advanced imaging models of ultrasound image diagnosis, its research is lacking, its imaging quality is still restricted to the shortage of the equipment system performance and the related technology is not mature. In this paper, on the basis of in-depth study of ultrasonic harmonic imaging technology, we use the method of pulse flip to weaken the tissue fundamental wave signal, and enhance the harmonic signal of ultrasound contrast agents micro-bubble to suppress the residual fundamental wave signal of tissue. It can improve harmonic and tissue signal power ratio (STR) to improve the image resolution. On the basis of pulse flip superposition method, through analysis and verification, it uses the sequence pulse flip superposition method, which makes up the defect of the former accuracy. It’s effect to eliminate the tissue fundamental wave signal is more obvious. Images through the experiment results show that the sequence pulse flip superposition method could get the higher resolution of the image than regular pulse flip superposition method. The design of high frequency ultrasound harmonic imaging system , uses Cyclone V series of 5CGXFC7D7F31C8N model FPGA chip as its core article to realize the digital signal processing. In order to improve the stability and reliability of the system circuit, it adopts the design concept of miniaturization, integration, low noise. The high-speed parallel digital signal processing characteristic of FPGA makes the system real-time performance improved. System structure according to the function is divided into signal transmitting circuit, echo signal receiving and converting circuit, signal acquisition and processing circuit, data transmission module. In order to meet the different needs, software algorithm adopts modular design to be easy to upgrade and system expansion. Software is written in VHDL language, embedded into the FPGA. The software system includes the signal driving module, echo signal processing module and the data transmission module. This study has set up an experimental platform for the simulation of intravascular blood flow. Experiments are operated with the high-frequency ultrasonic harmonic imaging system, whose design is based on FPGA. Through the harmonic image in blood vessels, it can prove pulse flip superposition method in eliminating the tissue fundamental wave signal has a very good result, which gets the better image resolution than ever before. At the same time, it also verifies the sequence pulse flip superposition method can get the better STR and signal-to-noise ratio, the image resolution has improved further.