Department of Biomedical Engineering and NIH Transducer Resource Center, University of Southern California, Los Angeles, CA 90089, United States.
Ultrasonics. 2011 Dec;51(8):953-9. doi: 10.1016/j.ultras.2011.05.010. Epub 2011 May 27.
In order to improve the lateral resolution and extend the field of view of a previously reported 48 element 30 MHz ultrasound linear array and 16-channel digital imaging system, the development of a 256 element 30 MHz linear array and an ultrasound imaging system with increased channel count has been undertaken. This paper reports the design and testing of a 64 channel digital imaging system which consists of an analog front-end pulser/receiver, 64 channels of Time-Gain Compensation (TGC), 64 channels of high-speed digitizer as well as a beamformer. A Personal Computer (PC) is used as the user interface to display real-time images. This system is designed as a platform for the purpose of testing the performance of high frequency linear arrays that have been developed in house. Therefore conventional approaches were taken it its implementation. Flexibility and ease of use are of primary concern whereas consideration of cost-effectiveness and novelty in design are only secondary. Even so, there are many issues at higher frequencies but do not exist at lower frequencies need to be solved. The system provides 64 channels of excitation pulsers while receiving simultaneously at a 20-120 MHz sampling rate to 12-bits. The digitized data from all channels are first fed through Field Programmable Gate Arrays (FPGAs), and then stored in memories. These raw data are accessed by the beamforming processor to re-build the image or to be downloaded to the PC for further processing. The beamformer that applies delays to the echoes of each channel is implemented with the strategy that combines coarse (8.3 ns) and fine delays (2 ns). The coarse delays are integer multiples of the sampling clock rate and are achieved by controlling the write enable pin of the First-In-First-Out (FIFO) memory to obtain valid beamforming data. The fine delays are accomplished with interpolation filters. This system is capable of achieving a maximum frame rate of 50 frames per second. Wire phantom images acquired with this system show a spatial resolution of 146 μm (lateral) and 54 μm (axial). Images with excised rabbit and pig eyeball as well as mouse embryo were also acquired to demonstrate its imaging capability.
为了提高之前报道的 48 元件 30MHz 超声线阵和 16 通道数字成像系统的横向分辨率和扩展视场，我们开发了一种 256 元件 30MHz 线性阵列和一个具有更多通道数的超声成像系统。本文介绍了一个 64 通道数字成像系统的设计和测试，该系统由模拟前端脉冲发生器/接收器、64 路时增益补偿（TGC）、64 路高速数字化仪以及一个波束形成器组成。个人计算机（PC）用作显示实时图像的用户界面。该系统设计为一个平台，用于测试内部开发的高频线性阵列的性能。因此，在其实现中采用了传统的方法。灵活性和易用性是首要关注的问题，而成本效益和设计新颖性的考虑只是次要的。即便如此，在更高的频率下仍有许多问题，但在较低的频率下并不存在，这些问题需要解决。该系统提供 64 个激励脉冲通道，同时以 20-120MHz 的采样率以 12 位接收。所有通道的数字化数据首先通过现场可编程门阵列（FPGA），然后存储在存储器中。这些原始数据由波束形成处理器访问，以重建图像或下载到 PC 进行进一步处理。应用于每个通道回波的延迟的波束形成器是通过组合粗延迟（8.3ns）和细延迟（2ns）的策略来实现的。粗延迟是采样时钟速率的整数倍，通过控制先进先出（FIFO）存储器的写使能引脚来实现，以获得有效的波束形成数据。细延迟是通过插值滤波器完成的。该系统能够实现 50 帧/秒的最大帧率。使用该系统获得的线阵图像显示出 146μm（横向）和 54μm（轴向）的空间分辨率。还获得了切除的兔眼和猪眼以及鼠胚的图像，以证明其成像能力。
