KEYWORDS: Image quality, Acoustics, Wavelets, Ultrasonography, Denoising, Image transmission, Signal to noise ratio, Data acquisition, Fetus, Signal processing
High-speed acquisition of ultrasound volume data is needed for fetal cardiac diagnosis. The heartbeat of healthy fetus is 120-160 times per second. Therefore, the acquiring method based on plane wave compounding has been developed to achieve both volume rate and image quality. However, in the conventional plane wave compounding method, the sufficient image quality couldn’t be obtained when the acquiring speed is about 150 volumes per second. Compressed Sensing has been applied to improve the image quality and reduce the number of compounding in the previous work [1], but huge memory (458GB) is required. In this paper, we propose a method to acquire high quality volume image at high-speed with reasonable hardware resources. The basic concept is to improve the image quality of each plane wave image before compounding by simple signal processing. Generally, the acoustic noise of plane wave image generated by the diffraction depends on the steering angle. In our method, the acoustic noise is adaptively reduced depending on the steering angle, and the wavelet shrinkage [2] is used as a basic noise reduction algorithm. In the experimental results, the acoustic noise is reduced by 22dB with only 20MB memory usage for radio frequency simulation data. As a result, we achieved high-speed data acquisition of 167 volumes per second.
To diagnose heart valve incompetence, i.e., one of the most serious cardiac dysfunctions, it is essential to obtain images of fast-moving valves at high spatial and temporal resolution. Ultrasound synthetic transmit aperture (STA) imaging has the potential to achieve high spatial resolution by synthesizing multiple pre-beamformed images obtained with corresponding multiple transmissions. However, applying STA to fast-moving targets is difficult due to serious target deformation. We propose a high-frame-rate STA (fast STA) imaging method that uses a reduced number of transmission events needed for each image. Fast STA is expected to suppress deformation of moving targets; however, it may result in deteriorated spatial resolution. In this study, we conducted a simulation study to evaluate fast STA. We quantitatively evaluated the reduction in deformation and deterioration of spatial resolution with a model involving a radially moving valve at the maximum speed of 0.5 m/s. The simulated raw channel data of the valve phantom was processed with offline beamforming programs. We compared B-mode images obtained through single received-line in a transmission (SRT) method, STA, and fast STA. The results show that fast STA with four-times-reduced events is superior in reconstructing the original shape of the moving valve to other methods. The accuracy of valve location is 97 and 100% better than those with SRT and STA, respectively. The resolution deterioration was found to be below the annoyance threshold considering the improved performance of the shape reconstruction. The obtained results are promising for providing more precise diagnostic information on cardiovascular diseases.
KEYWORDS: Ultrasonography, Image quality, 3D image processing, Data acquisition, Beam steering, Image resolution, Spatial resolution, Signal processing, Signal to noise ratio, Terbium, Tantalum, Image processing
In recent clinical practice of ultrasound imaging, the importance of high-frame-rate imaging is growing. Simultaneous multiple transmission is one way to increase frame rate while maintaining a spatial resolution and signal-to-noise ratio. However, this technique has an inherent issue in that "cross-talk artifacts" appear between the multiple transmitted pulses. In this study, a novel method providing higher-frame-rate ultrasound imaging with reduced cross-talk by combining a synthetic aperture and spatial coded excitation is proposed. In the proposed method, two coded transmission beams are simultaneously excited during beam steering in the lateral direction. Parallel receive beamforming is then performed in the region around individual transmission beams. Decoding is carried out by using two beamformed signals from a region where laterally neighboring transmission beams overlap. All decoded beamformed signals are then synthesized coherently. The proposed method was evaluated using a simulated phantom image under the assumption of imaging with a general sector probe. Results showed that the method achieved twice the frame rate while maintaining image resolution (105%) and reducing cross-talk artifacts from −37 dB to less than −57 dB.
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