K-space model of motion artifacts in synthetic transmit ultrasound imaging

Nikolov, Svetoslav Ivanov; Jensen, Jørgen Arendt

doi:10.1109/ultsym.2003.1293268

Cited by 8 publications

(10 citation statements)

References 6 publications

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“…Tissue motion and motion artifacts are nevertheless not completely destructive to SA imaging. The susceptibility to motion of SA imaging has been investigated by several authors [22][23][24][25][26][27][28][29][30], and techniques to address the problems with tissue motion have been demonstrated.…”

Section: Two Stage Sequential Beamformingmentioning

confidence: 99%

Sequential beamforming for synthetic aperture imaging

2013

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a b s t r a c tSynthetic aperture sequential beamforming (SASB) is a novel technique which allows to implement synthetic aperture beamforming on a system with a restricted complexity, and without storing RF-data. The objective is to improve lateral resolution and obtain a more depth independent resolution compared to conventional ultrasound imaging. SASB is a two-stage procedure using two separate beamformers. The initial step is to construct and store a set of B-mode image lines using a single focal point in both transmit and receive. The focal points are considered virtual sources and virtual receivers making up a virtual array. The second stage applies the focused image lines from the first stage as input data, and take advantage of the virtual array in the delay and sum beamforming. The size of the virtual array is dynamically expanded and the image is dynamically focused in both transmit and receive and a range independent lateral resolution is obtained. The SASB method has been investigated using simulations in Field II and by off-line processing of data acquired with a commercial scanner. The lateral resolution increases with a decreasing F#. Grating lobes appear if F# 6 2 for a linear array with k-pitch. The performance of SASB with the virtual source at 20 mm and F# = 1.5 is compared with conventional dynamic receive focusing (DRF). The axial resolution is the same for the two methods. For the lateral resolution there is improvement in FWHM of at least a factor of 2 and the improvement at À40 dB is at least a factor of 3. With SASB the resolution is almost constant throughout the range. For DRF the FWHM increases almost linearly with range and the resolution at À40 dB is fluctuating with range. The theoretical potential improvement in SNR of SASB over DRF has been estimated. An improvement is attained at the entire range, and at a depth of 80 mm the improvement is 8 dB.

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Section: Two Stage Sequential Beamformingmentioning

confidence: 99%

Sequential beamforming for synthetic aperture imaging

2013

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“…3, the border line for inequality (10) is plotted as the dashed line. Notice that when the amplitude of the signals are the same k = 1, the phase difference ∆φ should not exceed a quarter of a period, and that when the signals are in phase ∆φ = 0, the sum of amplitudes must exceed…”

Section: A Continuous Wavementioning

confidence: 99%

“…The effects of tissue motion in synthetic aperture ultrasound have been studied by various authors [6]- [10]. Trahey and Nock investigated motion effects in a synthetic receive aperture system in [6] and showed that motion along the axial direction has a far larger effect on the resolution than lateral movement.…”

mentioning

confidence: 99%

Effects Influencing Focusing in Synthetic Aperture Vector Flow Imaging

Oddershede

Jensen

2007

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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Previously, a synthetic aperture vector velocity estimation method was proposed. Data are beamformed at different directions through a point, where the velocity is estimated. The flow direction is estimated by a search for the direction where the normalized cross-correlation peaks and the velocity magnitude along this direction are found.In this paper, different effects that influence the focusing in this method are investigated. These include the effect of phase errors in the emitted spherical waves, motion effects, and the effect of various interpolation methods in beamforming.A model based on amplitude drop and phase error for spherical waves created using the virtual source concept is derived. This model can be used to determine the opening angle of a virtual source. Simulations for different virtual source placements are made, and it is recommended that the virtual sources be placed behind the aperture when shallow structures are imaged, and when deeper-lying structures are imaged the virtual sources be placed in front of the aperture.Synthetic aperture methods involve summation of data from numerous emissions. Motion between these emissions results in incoherence and affects resolution, contrast, and the signal-to-noise ratio. The effects of motion on the synthetic aperture vector velocity estimation method are investigated, and it is shown that for both axial and lateral motion, the contrast and signal-to-noise ratio can be seriously affected. A compensation method using the previous vector velocity estimate, when new data are beamformed, is implemented and tested. It is shown from a number of flow phantom experiments that a significant improvement with respect to bias and standard deviation of the velocity estimates can be obtained by using this compensation. Increased performance is gained at the expense of computation time.Different interpolation methods can be used for beamforming the data. In this paper, the velocity estimation performance using various more complex interpolation schemes are compared to that using linear interpolation. No significant difference in the performance of the method is seen when other interpolation methods are used.

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“…By applying prior knowledge of the expected velocity range, the search range can be limited by only evaluating the cross correlation function (5) in lags corresponding to the expected velocity range.…”

Section: Synthetic Aperture Velocity Estimationmentioning

confidence: 99%

“…The effects of tissue motion in synthetic aperture ultrasound have been studied by various authors [1], [2], [3], [4], [5]. Trahey and Nock investigated motion effects in a synthetic receive aperture system in [1] and showed that motion along the axial direction has a far larger effect on the resolution than lateral movement.…”

Section: Introductionmentioning

confidence: 99%

P3C-4 Motion Compensated Beamforming in Synthetic Aperture Vector Flow Imaging

Jensen

Oddershede

2006

2006 IEEE Ultrasonics Symposium

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Abstract-In synthetic aperture imaging the beamformed data from a number of emissions are summed to create dynamic focusing in transmit. This makes the method susceptible to motion, which is especially the case for the synthetic aperture flow estimation method, where large movements are expected. In this paper, these motion effects are considered.A number of Field II simulations of a single scatterer moving at different velocities are performed both for axial and lateral velocities from 0 to 1 m/s. Data are simulated at a pulse repetition frequency of 5 kHz. The signal-to-noise ratio (SNR) of the beamformed response from the scatterer at all velocities is compared to that of a stationary scatterer. For lateral movement, the SNR drops almost linearly with velocity to -4 dB at 1 m/s, while for axial movement the SNR drop is largest, when the scatterer moves a quarter of a wavelength between emissions. Here the SNR is -10 dB compared to the stationary scatterer.A 2D motion compensation method for synthetic aperture vector flow imaging is proposed, where the former vector velocity estimate is used for compensating the beamforming of new data. This method is tested on data from an experimental flow rig acquired using our RASMUS experimental ultrasound scanner and a 5.5 MHz linear array transducer. A 11.25 µs non-linear chirp is used as excitation and the data from 128 emissions is used for estimating the flow direction and magnitude at a profile across the tube.The measurement was conducted at a flow angle of 60• with respect to the axial direction and a peak velocity of 0.1 m/s sampled at a pulse repetition frequency of 1 kHz. The mean bias across the profile was -8.4 % with respect to the peak velocity and the mean standard deviation was 12.2 % prior to compensation. When the proposed compensation was applied a mean bias of -3.6 % and a mean standard deviation of 2.8 % was seen.

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K-space model of motion artifacts in synthetic transmit ultrasound imaging

Cited by 8 publications

References 6 publications

Sequential beamforming for synthetic aperture imaging

Sequential beamforming for synthetic aperture imaging

Effects Influencing Focusing in Synthetic Aperture Vector Flow Imaging

P3C-4 Motion Compensated Beamforming in Synthetic Aperture Vector Flow Imaging

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