In Vitro and in Vivo tissue harmonic images obtained with parallel transmit beamforming by means of orthogonal frequency division multiplexing [Correspondence] (original) (raw)
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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.
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).
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.
Second harmonic inversion for ultrasound contrast harmonic imaging
Physics in Medicine and Biology, 2011
Ultrasound contrast agents (UCAs) are small micro-bubbles that behave nonlinearly when exposed to an ultrasound wave. This nonlinear behavior can be observed through the generated higher harmonics in a back-scattered echo. In past years several techniques have been proposed to detect or image harmonics produced by UCAs. In these proposed works, the harmonics generated in the medium during the propagation of the ultrasound wave played an important role, since these harmonics compete with the harmonics generated by the micro-bubbles. We present a method for the reduction of the second harmonic generated during nonlinear-propagation-dubbed second harmonic inversion (SHI). A general expression for the suppression signals is also derived. The SHI technique uses two pulses, p' and p'', of the same frequency f0 and the same amplitude P0 to cancel out the second harmonic generated by nonlinearities of the medium. Simulations show that the second harmonic is reduced by 40 dB on a large axial range. Experimental SHI B-mode images, from a tissue-mimicking phantom and UCAs, show an improvement in the agent-to-tissue ratio (ATR) of 20 dB compared to standard second harmonic imaging and 13 dB of improvement in harmonic power Doppler.
Coded excitation for ultrasound tissue harmonic imaging
Ultrasonics, 2010
Coded excitation can improve the signal-to-noise ratio (SNR) in ultrasound tissue harmonic imaging (THI). However, it could suffer from the increased sidelobe artifact caused by incomplete pulse compression due to the spectral overlap between the fundamental and harmonic components of ultrasound signal after nonlinear propagation in tissues. In this paper, three coded tissue harmonic imaging (CTHI) techniques based on bandpass filtering, power modulation and pulse inversion (i.e., CTHI-BF, CTHI-PM, and CTHI-PI) were evaluated by measuring the peak range sidelobe level (PRSL) with varying frequency bandwidths. From simulation and in vitro studies, the CTHI-PI outperforms the CTHI-BF and CTHI-PM methods in terms of the PRSL, e.g., À43.5 dB vs. À24.8 dB and À23.0 dB, respectively.
Acoustical Science and Technology, 2001
Recently, harmonic imaging has been widely used for improving image quality in the field of ultrasonic diagnostic. In this research, the evaluation of the quality improvement of the ultrasonic Bmode images by tissue harmonic imaging was attempted by combining this technique with the numerical analysis method. The influence of the inhomogeneous intervening medium on the ultrasonic B-mode images was also considered. Also, the region of interest (ROI) on the B-mode images were compared with the surrounding region to quantify the contrast improvement based on the relative echo level. The image quality improvement of tissue harmonic imaging was also analyzed in consideration of the signalto-noise ratio (SNR).
Veterinary Radiology <html_ent glyph="@amp;" ascii="&"/> Ultrasound, 2002
Harmonic ultrasound is a technique based on the principle of transmitting at frequency f and receiving at frequency 2f (or 1/20. This technology has become available through the development of widebandwidth transducers. Microbubble contrast media produce a large amount of harmonic signal. Contrast harmonic ultrasound provides the opportunity to image patterns of high flow vasculature and overall perfusion. Regions of poor perfusion, including necrosis or infarction, can be identified with contrast harmonic ultrasound. While proportionately lower, tissues also produce harmonic signals. Tissue harmonic ultrasound sequences often improve subjective image quality compared to fundamental ultrasound in echocardiographic and abdominal examinations. This review will discuss the physical principles of harmonic ultrasound signal generation, medical and animal research applications, and an overview of current veterinary experiences.
Computer model for harmonic ultrasound imaging
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000
Harmonic ultrasound imaging has received great attention from ultrasound scanner manufacturers and researchers. In this paper, we present a computer model that can generate realistic harmonic images. In this model, the incident ultrasound is modeled after the "KZK" equation, and the echo signal is modeled using linear propagation theory because the echo signal is much weaker than the incident pulse. Both time domain and frequency domain numerical solutions to the "KZK" equation were studied. Realistic harmonic images of spherical lesion phantoms were generated for scans by a circular transducer. This model can be a very useful tool for studying the harmonic buildup and dissipation processes in a nonlinear medium, and it can be used to investigate a wide variety of topics related to Bmode harmonic imaging.
Broadband Reduction of the Second Harmonic Distortion During Nonlinear Ultrasound Wave Propagation
Ultrasound in Medicine and Biology, 2010
Ultrasound contrast harmonic imaging and detection techniques are hampered by the harmonic distortion of the ultrasound wave caused by the nonlinearities of the medium. To increase the discrimination between the tissue and ultrasound contrast agents at higher harmonics, we investigate a tissue harmonic suppression technique. The main attention of the research is the signal that is introduced at the source and is constructed out of several discrete frequency components from the second harmonic band. Therefore, this method was coined as the multiple component second harmonic reduction signal or multiple component SHRS. By adjusting the amplitude and phase of discrete components and simultaneously propagating multiple component SHRS with the imaging signal, the nonlinear distortion of the ultrasound waveform is considerably reduced. Using the numerical simulation, the optimal parameters for multiple component SRHS were deduced. The simulations results were corroborated in the water tank experiments and showed 40 dB reduction with respect to the fundamental, covering up to 75% of the entire second harmonic band. In the other series of experiments with the clinically used contrast agent, the uniform increase in agent-to-tissue ratio of 7.4 dB over a relatively large region of imaging was observed. The use of the proposed method in the everyday clinical practice can improve discrimination between the tissue and the contrast agent in harmonic imaging. (