Harmonic Imaging with Fresnel Beamforming in the Presence of Phase Aberration (original) (raw)
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Harmonic Beamforming: Performance Analysis and Imaging Results
IEEE Transactions on Instrumentation and Measurement, 2006
In this paper, harmonic beamforming (HB), a technique proposed by the authors to improve the quality of tissueharmonic imaging and contrast-agent imaging processes in medical echography, is briefly presented. It relies on a modification to the delays used in reception beamforming that notably reduces the echoes centered on the fundamental frequency while keeping the echoes centered on the second harmonic and preserving focusing quality. The HB is assessed in terms of its spectral and spatial characteristics, harmonic-to-fundamental ratio (HFR), and range resolution for different bandwidths of the insonifying pulse. The tuning of the parameters involved in HB and its effects are investigated in detail. The results are compared with those provided by traditional methods of harmonic imaging, clearly showing some advantages in the application of the proposed beamforming scheme. Such advantages are also confirmed by analyzing and comparing the results obtained in a simulated contrast-agent imaging task, where HB generated the most similar images to those yielded by the pulse-inversion approach. Therefore, HB is a very promising technique, also considering that it can be very easily incorporated in current ultrasound medical scanners without any hardware modification or frame-rate reduction.
Harmonic source wavefront aberration correction for ultrasound imaging
The Journal of the Acoustical Society of America, 2011
A method is proposed which uses a lower-frequency transmit to create a known harmonic acoustical source in tissue suitable for wavefront correction without a priori assumptions of the target or requiring a transponder. The measurement and imaging steps of this method were implemented on the Duke phased array system with a two-dimensional (2-D) array. The method was tested with multiple electronic aberrators [0.39p to 1.16p radians root-mean-square (rms) at 4.17 MHz] and with a physical aberrator 0.17p radians rms at 4.17 MHz) in a variety of imaging situations. Corrections were quantified in terms of peak beam amplitude compared to the unaberrated case, with restoration between 0.6 and 36.6 dB of peak amplitude with a single correction. Standard phantom images before and after correction were obtained and showed both visible improvement and 14 dB contrast improvement after correction. This method, when combined with previous phase correction methods, may be an important step that leads to improved clinical images.
2014 IEEE International Ultrasonics Symposium, 2014
In classic pulse echo ultrasound imaging, the data acquisition rate is limited by the speed of sound. To overcome this limitation, parallel beamforming techniques in transmit (PBT) and in receive mode (PBR) have been developed. To perform harmonic imaging, PBT techniques are preferable being capable of generating stronger harmonics thanks to the possibility to use focused beams in transmission. Recently, orthogonal frequency division multiplexing (OFDM) has been explored to perform PBT. To date, only numerical studies and in-vitro experiments in water have been performed, thus neglecting the effect of frequency dependent absorption. In this paper, PBT by means of OFDM tissue harmonic images are presented. A homemade agarose tissue mimicking phantom containing water filled cylindrical cavities was utilized as test object. The ULA-OP ultrasound open platform was used in combination with the linear array probe LA533 (Esaote Italy). Starting from the available transducer bandwidth, sub-bands were allocated to each beam transmitted in parallel. Three orthogonal sub-bands were used, improving the frame rate by a factor three. A classic B-mode tissue harmonic image was then obtained with the same setup for comparison. The contrast to noise ratio (CNR) and average background brightness inside the cavities were evaluated to provide an indirect measure of the influence of interbeam interference.
Clinical evaluation of Synthetic Aperture Sequential Beamforming and Tissue Harmonic Imaging
2014
This study determines if the data reduction achieved by the combination Synthetic Aperture Sequential Beamforming (SASB) and Tissue Harmonic Imaging (THI) affects image quality. SASB-THI was evaluated against the combination of Dynamic Received Focusing and Tissue Harmonic Imaging (DRF-THI). A BK medical UltraView 800 ultrasound scanner equipped with a research interface and an abdominal 3.5 MHz 3.5CL192-3ML convex array transducer was used and connected to a stand alone PC. SASB-THI and DRF-THI scan sequences were recorded interleaved and processed offline. Nineteen patients diagnosed with focal liver pathology were scanned to set a clinical condition, where ultrasonography is often performed. A total of 114 sequences were recorded and evaluated by five radiologists. The evaluators were blinded to the imaging technique, and each sequence was shown twice with different left-right positioning, resulting in 1140 evaluations. The program Image Quality Assessment Program (IQap) and a Visual Analog Scale (VAS) were applied for the evaluation. The scale ranged from-50 to 50, where positive values favored SASB-THI. SASB-THI and DRF-THI were evaluated alike in 49% of the evaluations, 28% favored SASB-THI and 23% favored DRF-THI. The average rating was 0.70 (Cl:-0.80 to 2.19). The statistical analysis, where the hypothesis of no differences between the techniques was tested, yielded a p-value of p=0.64, indicating no preference to any technique. This study demonstrates that SASB-THI and DRF-THI have equally good image quality although a data reduction of 64 times is achieved with SASB-THI.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2015
In classic pulse-echo ultrasound imaging, the data acquisition rate is limited by the speed of sound. To overcome this, parallel beamforming techniques in transmit (PBT) and in receive (PBR) mode have been proposed. In particular, PBT techniques, based on the transmission of focused beams, are more suitable for harmonic imaging because they are capable of generating stronger harmonics. Recently, orthogonal frequency division multiplexing (OFDM) has been investigated as a means to obtain parallel beamformed tissue harmonic images. To date, only numerical studies and experiments in water have been performed, hence neglecting the effect of frequencydependent absorption. Here we present the first in vitro and in vivo tissue harmonic images obtained with PBT by means of OFDM, and we compare the results with classic B-mode tissue harmonic imaging. The resulting contrast-to-noise ratio, here used as a performance metric, is comparable. A reduction by 2 dB is observed for the case in which three parallel lines are reconstructed. In conclusion, the applicability of this technique to ultrasonography as a means to improve the data acquisition rate is confirmed.
2015
Parallel beamforming in transmit (PBT) by means of orthogonal frequency division multiplexing (OFDM) was recently applied to increase the frame rate of ultrasound tissue harmonic imaging. OFDM-PBT improves the data acquisition rate by generating, for each transmission event, multiple beams that are allocated to a specific portion of the available transducer bandwidth. Improving the frame rate is however not the only possible application of an increased data acquisition rate. In this paper, OFDM-PBT is exploited to perform multi-focus tissue harmonic imaging for improving the penetration depth and signal to noise ratio (SNR) without affecting the frame rate. Tissue harmonic images of a tissue mimicking phantom were obtained with OFDM-PBT and standard B-mode imaging. Results present improved penetration depth and SNR for OFDM-PBT as compared to standard B-mode. We estimated an improvement of 6 dB of the average SNR, at the expenses of a reduction of the axial resolution (0.7 vs 1.1 mm).
Aberration and second harmonic imaging
IEEE Ultrasonics Symposium, 2005., 2005
Simulations are presented which indicate that imaging at the second-harmonic frequency does not solve the problem of ultrasonic wave aberration. The nonlinearity of acoustic wave propagation in biological tissue is routinely exploited in medical imaging, since the larger signal-to-noise ratio leads to better image quality in many applications. The major sources of noise in ultrasound images are aberration and multiple reflections between the transducer and tissue structures (reverberations), both of which are the result of large spatial variations in the acoustic properties of the tissue. These variations mainly occur close to the body surface, i.e. the body wall. As a result, the nonlinearly-generated second-harmonic is believed to alleviate both reverberations and aberrations. However, in the case of aberration, the second-harmonic is generated by an aberrated pulse. Thus, the second-harmonic will experience considerable aberration even if it is generated at a greater depth. Propagation of the acoustic backscatter through the body wall will expose the pulse to further aberration, equivalent to that of linear fundamental imaging.
P3G-11 Generation and Aberration of Second-Harmonic Ultrasound Beams in Heterogeneous Tissue
2006 IEEE Ultrasonics Symposium, 2006
A simulation study with different f-numbers shows results concerning generation and aberration of threedimensional second-harmonic beams using a constant aperture. The second-harmonic is compared to the transmit firstharmonic and a same frequency fundamental. Heterogeneity was implemented as a 20 mm body wall model using a series of delay screens designed to match human abdominal body wall characteristics. Transmit pressures for the simulations are estimated using a constant MI of 1.1. The amount of secondharmonic generated increases for high f-numbers improving the signal-to-noise-ratio of the second-harmonic. A substantial part of the aberrated second-harmonic total energy at the focal point is generated beyond the body wall. Aberration reduces the amount of second-harmonic energy generated by 30-50% compared to the homogeneous case. The second-harmonic transmit beam is nonetheless aberrated. Comparison of aberrated transmit beam profiles shows that the side-lobe level of the second-harmonic is lower than for the fundamental beam, and about the same as the first-harmonic. The shape of the second-harmonic beam profiles resembles the first-harmonic more and more for an increasing fnumber. Thus, second-harmonic imaging improves image quality for deeper organs due to the improved signal-to-noise-ratio and lower side-lobe level for both a homogeneous and a heterogeneous case.
Fresnel Beamforming for Compact Portable Ultrasound Array System
This paper presents a new beamforming method that may reduce the size and cost of the system with minimized image quality tradeoffs. Applying optical Fresnel principles in ultrasound imaging, a system with 4 transmit and 2 receive channels can be used to steer and focus an array with 64 to 128 elements. The spatial resolution and contrast-to-noise ratios obtained from simulation and experiment show that the spatial resolution using an 8-phase Fresnel beamforming method is comparable to those values obtained from traditional delay-andsum beamforming.