KEYWORDS: Ultrasonography, Computed tomography, Signal processing, Tomography, 3D image reconstruction, 3D image processing, Image transmission, Image quality, Computing systems
The ultrasound computed tomography system based on the ring probe adopts sequential single-slice scanning mode. The ring probe keeps stationary when the scan is in process; after the signals of one slice are captured, the ring probe steps along the elevation axis to scan the next slice. The scanning process needs to step and stop repeatedly, and the scanning time is relatively long. Also, the lack of signals between tomographic image slices may result in missed diagnosis. This paper proposes a new spiral synthetic aperture method for ultrasound tomographic volume imaging. The ring probe moves along the elevation axis at a certain speed, while the transmitting and receiving array elements are switched electronically. Therefore, “spiral” transmitting aperture and receiving aperture are formed, and continuous three-dimensional spatial spiral data are collected to directly reconstruct the three-dimensional volume image. Preliminary experimental result shows that this method can shorten the scanning time and improve image quality in the elevation direction.
In recent years, Ultrasound computed tomography (USCT) has important clinical application prospect in breast cancer screening and early diagnosis. In this paper, the biomedical image denoising technique based on variational mode decomposition (VMD) method for USCT is investigated. The VMD method allows decomposition of data into a finite number of intrinsic mode functions (IMFs) after a sifting pre-process. Removing the noise components and refactoring the remaining IMFs, the processed data can be used for USCT image reconstruction. It can provide images with less noises, higher resolution and better contrast compared to the traditional B-mode imaging method. The validation of VMD method for USCT is presented through the breast phantom experiment. The radio-frequency (RF) data of the breast phantom were captured by the USCT system developed in the Medical Ultrasound Laboratory. The main components of USCT system are data acquisition module and a 1024-element ring array with center frequency 2.5MHz. Graphics processing units (GPUs) have been highly applied to image reconstruction considering its high parallel computation ability. Experimental results show that the reconstructed image of breast phantom by the VMD method get the higher signal to noise ratio (SNR) and more homogeneous background compared to the delay and sum (DAS) method. The contrast ratio (CR) could be enhanced from 0.96 dB to 1.01dB and 88.38 dB to 99.53 dB at different regions of interest (ROI). The contrast to noise ratio (CNR) enhance from 0.09dB to 0.13dB at hypoechoic area and from 8.01 to 13.03 at hyperechoic area.
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.
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.
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.
Breast ultrasound tomography imaging (BUTI) is a new ultrasound imaging technique developed in recent years. In contrast to traditional ultrasound, BUTI uses a ring transducer to surround an object in a water tank and transmits the ultrasound echo from each element sequentially while receiving all the reflective and transmission signals from all elements. The tomography image is reconstructed using a similar reconstruction technique like x-ray computed tomography (X-CT) but much complicate due to the echo travelled along the curve instead of straight line like X ray. In this paper, with the objective of developing a breast ultrasound screening product, in vitro- and in vivo evaluation experiments were performed before proceeding to formal clinic trials. For the in vitro evaluation, a Breast Ultrasound Needle Biopsy Phantom from Supertech, IN, USA, was scanned by BUTIS (Breast ultrasound tomography imaging system) developed in HUST (Huazhong University of Science and Technology, Wuhan, China), MRI and traditional ultrasound scanner. Their image qualities were compared. In addition, the spatial resolution was estimated by using a nylon wire phantom. The results demonstrated that the spatial resolution of BUTIS is over 180 μm, which is almost 1 order higher than the traditional ultrasounds with the same frequency transducer. The in vivo evaluation was composed of a human arm and leg, the breast of a pregnant goat as well as human breasts from a female volunteer. The experimental results demonstrated that BUTIS can not only obtain exceptionally high contrast and high resolution images of soft tissue like the breast in vivo both for animal or human volunteer, but it can also be used to scan the subject with bones inside such as human arms and legs, which seems impossible for traditional ultrasounds. It illustrated that BUTIS will become a new efficient ultrasound imaging technique with wide potential applications in clinics.
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).
This paper presents a preliminary evaluation work on a pre-designed 3-D ultrasound imaging system. The system mainly consists of four parts, a 7.5MHz, 24×24 2-D array transducer, the transmit/receive circuit, power supply, data acquisition and real-time imaging module. The row-column addressing scheme is adopted for the transducer fabrication, which greatly reduces the number of active channels . The element area of the transducer is 4.6mm by 4.6mm. Four kinds of tests were carried out to evaluate the imaging performance, including the penetration depth range, axial and lateral resolution, positioning accuracy and 3-D imaging frame rate. Several strong reflection metal objects , fixed in a water tank, were selected for the purpose of imaging due to a low signal-to-noise ratio of the transducer. The distance between the transducer and the tested objects , the thickness of aluminum, and the seam width of the aluminum sheet were measured by a calibrated micrometer to evaluate the penetration depth, the axial and lateral resolution, respectively. The experiment al results showed that the imaging penetration depth range was from 1.0cm to 6.2cm, the axial and lateral resolution were 0.32mm and 1.37mm respectively, the imaging speed was up to 27 frames per second and the positioning accuracy was 9.2%.
This paper presents a work of real-time 3-D image reconstruction for a 7.5-MHz, 24×24 row-column addressing array transducer. The transducer works with a predesigned transmit/receive module. After the raw data are captured by the NI PXIe data acquisition (DAQ) module, the following processing procedures are performed: delay and sum (DAS), base-line calibration, envelope detection, logarithm compression, down-sampling, gray scale mapping and 3-D display. These procedures are optimized for obtaining real-time 3-D images. Fixed-point focusing scheme is applied in delay and sum (DAS) to obtain line data from channel data. Zero-phase high-pass filter is used to calibrate the base-line shift of echo. The classical Hilbert transformation is adopted to detect the envelopes of echo. Logarithm compression is implemented to enlarge the weak signals and narrow the gap from the strong ones. Down-sampling reduces the amount of data to improve the processing speed. Linear gray scale mapping is introduced that the weakest signal is mapped to 0 and the strongest signal 255. The real-time 3-D images are displayed with multi-planar mode, which shows three orthogonal sections (vertical section, coronal section, transverse section). A trigger signal is sent from the transmit/receive module to the DAQ module at the start of each volume data generation to ensure synchronization between these two modules. All procedures, include data acquisition (DAQ), signal processing and image display, are programmed on the platform of LabVIEW. 675MB raw echo data are acquired in one minute to generate 24×24×48, 27fps 3-D images. The experiment on the strong reflection object (aluminum slice) shows the feasibility of the whole process from raw data to real-time 3-D images.
KEYWORDS: Data acquisition, Ultrasonography, Transducers, Imaging systems, Field programmable gate arrays, 3D image processing, Analog electronics, Amplifiers, Electrodes, Image processing
This paper present a preliminary work on a pre-beamformed data acquisition ultrasound imaging system for a
3-MHz, 32×32 2-D array tranducer . The row-column addressing scheme is adopted for the transducer fabrication.
This scheme provides a simple interconnection, consisting of one top and one bottom single-layer flex circuits. The
designed system can acquire pre-beamformed data with 12-bit resolution at 40-MHz sampling rate. The digitized
data of all channels are first fed through FPGAs to deserialize and stored in a 4GB RAM buffer. The acquired data
can be transferred through a 1000 Mbps Ethernet link to a computer for off-line processing and analysis. The system
design is based on high-level commercial integrated circuits to obtain the maximum flexibility and minimum system
complexity. Partial beam summation have been performed to help finish the 3-D B-mode volumetric imaging.
Key words: ultrasound imaging system, 2-D array transducer, row-column addressing, off-line processing
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