基于超声平面波的功率多普勒成像方法研究

基于平面波的超声成像方法可实现超快速的帧频,有利于检测人体组织中快速变化的信号,已成为超声领域研究的热点之一。采用多角度平面波相干复合的方法可有效抑制旁瓣,改善单一平面波的成像质量,权衡帧频和信噪比,可将其应用于血流的功率多普勒成像中。实验证明发射十个以上不同角度的平面波进行相干复合波束形成,B超图像对比度约为40 d B,且帧频可达1000 Hz。利用该方法在低速血流模型中进行实验,可以有效滤除组织信号,提取血流信号,信号强度表征血容量等血液动力学参数,说明基于平面波的功率多普勒方法对低速血流的检测具有较高的敏感性。在此基础上,深入探讨了复合图像采样帧数、时间分辨率和多普勒信息的关系。选取不同数量的复合图像计算血流功率多普勒信号,其帧频大于传统功率多普勒成像方法,可达百赫兹。复合图像帧数增多,帧频和时间分辨率降低,多普勒信息增强;反之亦然。高时间分辨率有利于快速血流检测,而提高灵敏度有利于微细低速血流检测。因此,基于平面波的功率多普勒成像技术有可能为心血管疾病和脑部血流检测开辟一条新思路。

Study of Power Doppler Imaging Method with Ultrasonic Plane Wave

Emitting plane wave makes ultrasonic imaging enough fast so that it could detect variable blood signal in body, hence it becomes one of the most popular research interest. A new algorithm, multi-angle plane wave coherent compound imaging (MPWCCI) was realized to suppress side-lobe signal, improving the quality of ultrasonic image. Trading off frame rate and signal-noise-ratio (SNR), it could be used to image blood Power Doppler (PD). The contrast of B mode image could be up to 40 dB, and the frame rate to 1000Hz, using more than ten plane waves to compound. Test was accomplished in the slow-flow blood phantom, it shows that clutter signal could be eliminated and blood signal could be extracted effectively, and finally an image depicting hemodynamics was obtained. Result verifies that MPWCCI-PD has a fine sensitivity to slow flow. Furthermore, the effect of the ensemble size on image quality and temporal resolution was discussed. Calculating blood PDs in varying ensemble size data reveals that its frame rate exceeds that of conventional PD imaging, up to tens of Hertz, and the shorter the ensemble images are, the higher the temporal resolution and the better image, and vice versa. Higher temporal resolution is conducive to detecting fast blood flow and better sensitivity is good for the detection of small vessels. MPWCCI-PD may be helpful to imaging cases caused by angiocardiopathy, or brain small vessels.