Ultrasound computed tomography (USCT) is a 3D imaging tool, especially for breast screening. Sound-speed tomography as one imaging modal of USCT is widely studied by researchers because of its great clinical potential for early breast cancer detection. Sound-speed reconstruction methods include ray-based methods and wave-based methods. In this study, a ray-based method for sound speed reconstruction: Fresnel volume tomography (FVT) is implemented. We use Limitedmemory Broyden–Fletcher–Goldfarb–Shanno (L-BFGS) optimization algorithm to solve the large and sparse equation for the inversion step. Considering the great computation burden in the L-BFGS inversion process, two kinds of acceleration schemes: CPU parallel and GPU parallel schemes are used and evaluated by in vitro experiment. The corresponding acceleration ratios are 5.3 and 18.6 for the 512×512 sound speed image reconstruction, compared to CPU serial computation.
Ultrasound computed tomography his paper designs and implements a high throughout, extensible and flexible ultrasound excitation and data acquisition system that transmits sustained high-speed ultrasound data to the server by Ethernet technology. The system is mainly used for the second-generation ultrasound computed tomography system designed in the medical ultrasound lab, but can also be utilized by other types of ultrasound imaging systems. The system consists of one or more ultrasonic excitation and acquisition boards. Each board includes multiplexing switches, pulse generators with T/R switches, analog front ends, analog-to-digital converters, and an FPGA, and can be used to excite a 256-element probe to transmit and receive ultrasound signals. The peak and the average bandwidth of one single board are 44.8Gbps and 4Gbps, respectively. Potential users can combine several excitation and acquisition boards to build high-end ultrasound imaging systems. The system has been applied to upgrade our ultrasound computed tomography system.
In recent years, many research studies have been carried out on ultrasound computed tomography (USCT) for its application prospect in early detection of breast cancer. The synthetic aperture focusing technique (SAFT) widely used for the USCT image reconstruction is highly compute-intensive. Speeding up and optimizing the reconstruction algorithm on the graphics processing units (GPUs) have been highly applied to medical ultrasound imaging field. In this paper, we focus on accelerating the processing speed of SAFT with the GPU, considering its high parallel computation ability. The main computational features of SAFT are discussed to show the degree of computation parallelism. On the basis of the compute unified device architecture (CUDA) programming model and the Single Instruction Multiple Threads (SIMT) model, the optimization of SAFT parallel computation is performed. The proposed method was verified with the radio-frequency (RF) data of the breast phantom and the pig heart in vitro captured by the USCT system developed in the Medical Ultrasound Laboratory. Experimental results show that a 1024×1024 image reconstruction with a single NVIDIA GTX-1050 GPU could be 25 times faster than that with a 3.20-GHz Intel Core-i5 processor without image quality loss. The results also imply that with the increase of the image pixels, the acceleration effect is more notable.
In recent years, many research studies have been carried out on ultrasound computed tomography (USCT) for improving
the detection and management of breast cancer. This paper investigates a signal pre-processing method based on
frequency-shift low-pass filtering (FSLF) and least mean square adaptive filtering (LMSAF) for USCT image quality
enhancement (proposed in our previous work). FSLF is designed base on Zoom Fast Fourier Transform algorithm (ZFFT)
for processing the ultrasound signals in the frequency domain, while LMSAPF is based on the least mean square (LMS)
algorithm in the time domain. Through the combination of the two filters, the ultrasound image is expected to have less
noises and artifacts, and higher resolution and contrast. The proposed method was verified with the radio-frequency (RF)
data of the nylon threads and the breast phantom captured by the USCT system developed in the Medical Ultrasound
Laboratory. Experimental results show that the reconstructed images of nylon threads by the proposed method had
narrower main lobe width and lower side lobe level comparing to the delay-and-sum (DAS). The background noises and
artifacts could also be efficiently restrained. The reconstructed image of breast phantom by the proposed method had a
higher resolution and the contrast ratio (CR) could be enhanced for about 12dB to 18dB at different region of interest
(ROI).
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