Lu Jian-Yu, Cheng Jiqi, Wang Jing
Ultrasound Laboratory, Department of Bioengineering, The University of Toledo, Toledo, OH 43606, USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2006 Oct;53(10):1796-812. doi: 10.1109/tuffc.2006.112.
A general-purpose high frame rate (HFR) medical imaging system has been developed. This system has 128 independent linear transmitters, each of which is capable of producing an arbitrary broadband (about 0.05-10 MHz) waveform of up to +/- 144 V peak voltage on a 75-ohm resistive load using a 12-bit/40-MHz digital-to-analog converter. The system also has 128 independent, broadband (about 0.25-10 MHz), and time-variable-gain receiver channels, each of which has a 12-bit/40-MHz analog-to-digital converter and up to 512 MB of memory. The system is controlled by a personal computer (PC), and radio frequency echo data of each channel are transferred to the same PC via a standard USB 2.0 port for image reconstructions. Using the HFR imaging system, we have developed a new limited-diffraction array beam imaging method with square-wave aperture voltage weightings. With this method, in principle, only one or two transmitters are required to excite a fully populated two-dimensional (2-D) array transducer to achieve an equivalent dynamic focusing in both transmission and reception to reconstruct a high-quality three-dimensional image without the need of the time delays of traditional beam focusing and steering, potentially simplifying the transmitter subsystem of an imager. To validate the method, for simplicity, 2-D imaging experiments were performed using the system. In the in vitro experiment, a custom-made, 128-element, 0.32-mm pitch, 3.5-MHz center frequency linear array transducer with about 50% fractional bandwidth was used to reconstruct images of an ATS 539 tissue-mimicking phantom at an axial distance of 130 mm with a field of view of more than 90 degrees. In the in vivo experiment of a human heart, images with a field of view of more than 90 degrees at 120-mm axial distance were obtained with a 128-element, 2.5-MHz center frequency, 0.15-mm pitch Acuson V2 phased array. To ensure that the system was operated under the limits set by the U.S. Food and Drug Administration, the mechanical index, thermal index, and acoustic output were measured. Results show that higher-quality images can be reconstructed with the square-wave aperture weighting method due to an increased penetration depth as compared to the exact weighting method developed previously, and a frame rate of 486 per second was achieved at a pulse repetition frequency of about 5348 Hz for the human heart.
已开发出一种通用的高帧率（HFR）医学成像系统。该系统有128个独立的线性发射器，每个发射器能够使用12位/40兆赫兹数模转换器在75欧姆电阻负载上产生高达±144伏峰值电压的任意宽带（约0.05 - 10兆赫兹）波形。该系统还有128个独立的、宽带（约0.25 - 10兆赫兹）且可变增益的接收通道，每个通道都有一个12位/40兆赫兹模数转换器以及高达512兆字节的内存。该系统由个人计算机（PC）控制，每个通道的射频回波数据通过标准USB 2.0端口传输到同一台PC进行图像重建。利用HFR成像系统，我们开发了一种具有方波孔径电压加权的新型有限衍射阵列波束成像方法。使用这种方法，原则上只需一两个发射器就能激励一个满阵二维（2-D）阵列换能器，在发射和接收时实现等效动态聚焦，从而无需传统波束聚焦和转向的时间延迟来重建高质量三维图像，这有可能简化成像仪的发射器子系统。为验证该方法，为简单起见，使用该系统进行了二维成像实验。在体外实验中，使用了定制的、128阵元、间距0.32毫米、中心频率3.5兆赫兹且分数带宽约为50%的线性阵列换能器，在轴向距离130毫米、视野超过90度的情况下重建ATS 539组织模拟体模的图像。在人体心脏的体内实验中，使用128阵元、中心频率2.5兆赫兹、间距0.15毫米的Acuson V2相控阵在轴向距离120毫米处获得了视野超过90度的图像。为确保系统在美国食品药品监督管理局规定的限制范围内运行，测量了机械指数、热指数和声输出。结果表明，与之前开发的精确加权方法相比，由于穿透深度增加，采用方波孔径加权方法可以重建更高质量的图像，并且在人体心脏实验中，当脉冲重复频率约为5348赫兹时，实现了每秒486帧的帧率。
