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Pulse compression based excitation signals have been shown to improve signal quality in many active ranging applications without negatively impacting range resolution. Most prior work into using pulse compression presents the technique as if matched filtering is necessary to successfully achieve signal compression. Matched filtering against modulated excitation signals does result in useful information compression, however, it also suppresses information outside of the bandwidth of the transmission signal. This can distort or remove useful information in some applications, such as ultrasonic guided wave inspections, making the processing step unsuitable. In this paper, we show that when pulse compression with coded excitation is employed, a second filtering option is available for compressing the modulated information. The second option, which we have termed the sequence filter, utilises sequence elements as the template against which the filtering of coded excitation measurements is undertaken, thereby allowing compression to be achieved independent of received signal frequency content. We verify that sequence filtering successfully produces signal compression in two experimental ultrasound non-destructive testing applications where frequency modulated pulse compression was unsuitable. With both sequence filtering and matched filtering, we show signal-to-noise ratio gains in excess of 20 dB from using pulse compression. [ABSTRACT FROM AUTHOR]

Ultrasonic testing is an established method of non-destructive evaluation. The increasing complexity of material systems requires an extension of conventional methods. In related fields such as radar and medical ultrasound, signal optimisation and coded stimulation are successfully used and offer great potential for optimising state-of-the-art measurements and extending applications. In our work, we highlight the difference between using a coded sequence to stimulate an ultrasonic testing system and the actual performance of the digital code to motivate the exploration of inverse stimulation. In order to study inverse stimulation, a custom-built ultrasonic system was designed. As a first step, the transfer function was obtained by testing pulse and chirp stimulation. In the next step, inverse stimulation was performed based on the linear transfer function to engineer the ultrasonic echoes to have shapes similar to the target code. Finally, the auto-correlation function of the ultrasonic echoes resulting from the inverse stimulation is compared with the function of the original code sequence and the agreement of the recorded ultrasonic echo with the spectrally limited code sequence. With this work we propose an integrated, low-voltage, fully linear ultrasonic testing system where the recording of a linear transfer function allows echo engineering even for a binary coded excitation sequence. We have demonstrated that inverse stimulation enables the generation of binary ultrasonic echoes with performance equal to the digital code. • Single measurement transfer function acquisition for linear ultrasonic testing systems • Accurate prediction of coded excitation ultrasonic echoes • Inverse stimulation of a binary ultrasonic echoes equals the digital code performance • A 5 V only testing system can be built, covering small space and reducing material cost [ABSTRACT FROM AUTHOR]

Coded excitation (CE) has the ability to enhance image quality and penetration depth by improving the signal-to-noise ratio (SNR). Their usefulness has been extensively proven in the literature, however, there are very few publications that have discussed the practicality of using CEs, as they can increase the operating temperature of a transducer beyond the safety limits. In this paper, the potential for capacitive micromachined ultrasonic transducers (CMUTs) to handle CEs is investigated and compared to a geometrically similar Lead Zirconate Titanate (PZT) probe. It is hypothesized that CMUTs are comparatively advantageous for CE and can generate CE signals more effectively while operating within the safety limits of temperature specified by the International Electrotechnical Commission (IEC). Simple chirp signals were used for excitation and the temperature of the transducer assembly was measured under two different test conditions following the IEC standards. The still air test showed that at the pulse repetition frequency of 4 kHz and a signal duration of 8 μ s , the PZT probe reached the safe limit of 27 °C within 3 min of acquisition, whereas the CMUT probe showed an increase of only 4–5 °C over 30 min of scan time. The phantom experiments showed that for the maximum temperature rise allowed at the object-transducer interface by the IEC, the gain in SNR possible for the CMUT probe was 13–14 dB and the increase in penetration depth was 30 mm, whereas no gain in SNR and penetration depth was achieved for the PZT probe. The peak mechanical index and the derated spatial peak temporal averaged intensity were found to be less than half the FDA limits for both probes in all cases, proving temperature to be the first limiting factor when using CE. Therefore, the CMUT has shown to be thermally more efficient than the PZT probe and a good candidate for CE imaging. • Coded excitation boosts SNR but risks probe overheating. • Safety standards are set out by international authorities for safe use of ultrasound. • CMUTs are generally known to be thermally more efficient then PZT transducers. • CMUTs maintain safe temperature levels for longer than PZT probes during scans. • CMUT probe gains SNR and penetration depth with coded excitation, unlike PZT probe at similar temperature rise. [ABSTRACT FROM AUTHOR]

• Enriches the theory and methodology of coded excitation. • A method of multivariate coded excitation is proposed to compensate for the shortcomings of traditional binary coding modulation. • The combination of a multivariate coding technology and ultrasonic wave guide improves the excitation energy of the system and helps to identify rail fracture damage. • Simulations and experiments verify the feasibility and superiority of multivariate coded excitation for monitoring rail fracture. Steel lay the basis of railroad train traffic. Rail fracture is the most serious injury to the rail, which should be monitored in time. The conventional mono-pulse exciting ultrasonic guide wave (UGW) has low energy, the conventional Barker code has limited coding sequence length and the orthogonal complementary Golay code has the problem of low monitoring efficiency. This study proposes multivariate coded excitation (MCE) to excite UGW to monitor rail fracture, and the feasibility of coding and decoding the method is theoretically derived and verified. Ideally, the MCE generated based on the 3-bit Barker code (B 3 : 1,1, −1) and 4-bit orthogonal complementary Golay code ( GA 4 : 1,1,1, −1; GB 4 : 1,1, −1,1) is calculated to have a main-lobe power level (MPL) gain of 8.1020 dB, which is significantly higher than the MPL of Barker and Golay codes. For the proposed method, finite element modeling simulation and experimental study are carried out respectively. Analyze and process the data, and calculate the gain of the difference in amplitude (DIA) between the amplitude of echo caused by rail fracture and the amplitude in the healthy rail. The gain of the DIA of the echoes in the MCE is above 50 dB (experimental data, the value of simulation data is 5 dB) under different degrees of rail fracture, while the gain of the DIA of the echoes caused by the other three excitation methods is below 40 dB (experimental data, the value of simulation data is 1 dB). Simulation and experimental results show that the MCE makes up for the shortcomings of the conventional Barker code and Golay code, improves the excitation energy of the monitoring system, and the high gain of the DIA of the echoes is more conducive to the identification of rail fracture damage. [ABSTRACT FROM AUTHOR]

Interest in the conservation of paintings grows year by year. Their periodic inspection is essential for their conservation over the time. Thermographic non-destructive inspection is one technique useful for paintings, but it is essential to be able to detect buried defects while minimising the level of thermal stimulus. This paper describes a pulse-compression infrared thermography technique whereby defect detection is optimized while minimising the rise in temperature. To accomplish this task, LED lamps driven by a coded waveform based on a linear frequency modulated chirp signal have been used on paintings on both a wooden panel and a canvas layer. These specimens contained artificially fabricated defects. Although the physical condition of each painting was different, the experimental results show that the proposed signal processing procedure is able to detect defects using a low temperature contrast. [ABSTRACT FROM AUTHOR]

Background Golay excitation can be utilized to improve the signal-to-noise ratio (SNR). However, its application in ultrasound Doppler detection is limited due to potential motion artifacts in conventional decoding process. In this study, the improved Golay decoding has been implemented in a commercial 40-MHz pre-clinical system and experimentally verified for its efficacy in color-flow imaging. Methods Based on the Doppler spectral difference of half pulse-repetition-frequency ( PRF ) between the main lobe and range side lobe components of Golay excitation, the slow-time decoding with a low-pass filter with cut-off frequency of PRF /4 can separate the desired main lobe from the side lobe interference. The Prospect ® system has been customized to generate the Golay transmit sequence in swept-scan mode and to perform the PRF /4 decoding for in-vivo evaluation of mouse blood flow. Results Results indicate that the PRF /4 decoding can effectively eliminate the range side lobe artifacts in phantom experiments for flow velocity not exceeding the limit of ± PRF /4 in Doppler frequency. For in-vivo imaging, the SNR improves by about 7 dB and the Doppler penetration increases from 13.5 mm to 14.2 mm in mouse kidney when the transmit is switched from un-coded to Golay excitation. In mouse abdominal aorta, the Golay transmit also increases the Doppler sensitivity. Conclusion Golay-encoded color-flow imaging has been established using the pre-clinical system to achieve SNR improvement in Doppler detection without suffering from the range side lobe artifacts. To guarantee the performance of PRF /4 decoding, the side lobe aliasing should be avoided by carefully selecting the PRF to the match the flow velocity. [ABSTRACT FROM AUTHOR]

Speed of sound (SoS) is an acoustic property that is highly sensitive to changes in tissues. SoS can be mapped non-invasively using ultrasonic through transmission wave tomography. This however, practically limits its clinical use to the breast. A pulse-echo-based method that has broader clinical use and that can reliably measure treatment-induced changes in SoS even under poor signal-to-noise ratio (SNR) is highly desirable. The aim of this study was to evaluate the implementation of coded excitations (CoEs) to improve pulse-echo monitoring of heat-induced changes in the SoS. In this study, a binary phase modulated Barker sequence and a linear frequency-modulated chirp were compared with a common Gaussian pulse transmission. The comparison was conducted using computer simulations, as well as transmissions in both agar-gelatin phantoms and ex vivo bovine liver. SoS changes were experimentally induced by heating the specimens with a therapeutic ultrasound system. The performance of each transmission signal was evaluated by correlating the relative echo shifts to the normalized SoS measured by through transmission. The computer simulations indicated that CoEs are beneficial at very low SNR. The Barker code performed better than both the chirp and Gaussian pulses, particularly at SNRs <10 dB (R2 = 0.81 ± 0.06, 0.68 ± 0.07 and 0.55 ± 0.08, respectively, at 0 dB). At high SNRs, the CoEs performed statistically on par with the Gaussian pulse. The experimental findings indicated that both Barker and chirp codes performed better than the Gaussian pulse on ex vivo liver (R2 = 0.80 ± 0.15, 0.79 ± 0.15 and 0.54 ± 0.17, respectively) and comparably on agar-gelatin phantoms. In conclusion, CoEs can be beneficial for assessing temperature-induced changes in the SoS using the pulse-echo method under poor SNR. [ABSTRACT FROM AUTHOR]

• Ultrasound therapy requires real-time monitoring during treatment. • The use of focused ultrasound (FUS) transducers for the purpose is limited due to their inability to provide high quality of images. • The proposed coded excitation and Wiener deconvolution can enhance the resolution, SNR, and CNR of images acquired by FUS transducers. • The performance of the proposed method was confirmed by imaging experiments. To enhance the effectiveness and safety of focused ultrasound (FUS) therapy, ultrasound image-based guidance and treatment monitoring are crucial. However, the use of FUS transducers for both therapy and imaging is impractical due to their low spatial resolution, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). To address this issue, we propose a new method that significantly improve the quality of images obtained by a FUS transducer. The proposed method employs coded excitation to enhance SNR and Wiener deconvolution to solve the problem of low axial resolution resulting from the narrow spectral bandwidth of FUS transducers. Specifically, the method eliminates the impulse response of a FUS transducer from received ultrasound signals using Wiener deconvolution, and pulse compression is performed using a mismatched filter. Simulation and commercial phantom experiments confirmed that the proposed method significantly improves the quality of images acquired by the FUS transducer. The −6 dB axial resolution was improved 1.27 mm to 0.37 mm that was similar to the resolution achieved by the imaging transducer, i.e., 0.33 mm. SNR and CNR also increased from 16.5 dB and 0.69 to 29.1 dB and 3.03, respectively, that were also similar to those by the imaging transducer (27.8 dB and 3.16). Based on the results, we believe that the proposed method has great potential to enhance the clinical utility of FUS transducers in ultrasound image-guided therapy. [ABSTRACT FROM AUTHOR]

Coded excitation was initially introduced to ultrasound imaging as a method for enhancing the signal-to-noise ratio (SNR). However, this method was also shown to be helpful in conjunction with synthetic aperture transmission for high frame rate imaging. Recently, we introduced two families of mismatched coded excitations based on frequency modulation chirp and combined frequency modulation and Golay code. Here “mismatched” indicates that the coded excitations generate very small cross-correlations among themselves while each has a very strong autocorrelation. Employing weakly correlated coded excitations enables performing simultaneous insonifications from several elements of the ultrasonic transducer and receiving distinguishable responses to each code. In this work, we propose and experimentally demonstrate another set of mismatched correlated coded excitations based on Golay codes. The generated phase codes share identical duration and center frequency which results in similar SNR and image resolution. [ABSTRACT FROM AUTHOR]

Pulse-compression infrared thermography is an emerging nondestructive testing and evaluation technique. An analysis of the main issues hampering the full exploitation of this technique is presented from both theoretical and experimental point of view and various strategies are introduced to overcome these problems and optimize the defect detection performance. A comparison between conventional pulse-compression thermography procedures and the proposed one is reported, using an LED modulated with a Barker sequence as coded excitation, and a carbon fibre composite benchmark sample containing artificial defects at different depths. The experimental results show that the suggested signal processing procedure assures a higher SNR and hence an improved defect detection capability. In addition, a time-analysis of such signals allows the correlation between the depth of defects and heat diffusion time to be more clearly identified. [ABSTRACT FROM AUTHOR]

When assessing ultrasonic measurements of material parameters, the signal processing is an important part of the inverse problem. Measurements of thickness, ultrasonic wave velocity and mass density are required for such assessments. This study investigates the feasibility and the robustness of a wavelet-based processing (WBP) method based on a Jaffard–Meyer algorithm for calculating these parameters simultaneously and independently, using one single ultrasonic signal in the reflection mode. The appropriate transmitted incident wave, correlated with the mathematical properties of the wavelet decomposition, was determined using a adapted identification procedure to build a mathematically equivalent model for the electro-acoustic system. The method was tested on three groups of samples (polyurethane resin, bone and wood) using one 1-MHz transducer. For thickness and velocity measurements, the WBP method gave a relative error lower than 1.5%. The relative errors in the mass density measurements ranged between 0.70% and 2.59%. Despite discrepancies between manufactured and biological samples, the results obtained on the three groups of samples using the WBP method in the reflection mode were remarkably consistent, indicating that it is a reliable and efficient means of simultaneously assessing the thickness and the velocity of the ultrasonic wave propagating in the medium, and the apparent mass density of material. [ABSTRACT FROM AUTHOR]

• Differential compression of Golay encoded ultrasound (DCGEU) imaging method is proposed. • Feasibility of slow blood flow imaging in small vessels with the DCGEU is demonstrated. • Complementary Golay coded sequences (CGCS) significantly improves the slow flow imaging. • Transducer bandwidth and high receiving channel noise level influence the slow flow imaging. In our research we present a new method of differential compression of the Golay encoded ultrasound (DCGEU) in the standard beamforming mode to visualize the slow (<1cm/s) blood mimicking fluid flow in small diameter tubes. The proposed DCGEU method is based on synthesis of several subsequent B-mode frames acquired with certain time intervals (30 ms in this study) followed by the visualization of differential beamformed radio frequency (RF) echoes, which yielded the images of the scatterers moving slowly in the vessel and suppressing the static echoes outside the vessel. In order to extract small backscattered echoes from the vessel area we took an advantage of improved sensitivity of the complementary Golay coded sequences (CGCS). The validation of the proposed DCGEU method was carried out in two stages. In the first one, we compared the flow images in small tubes with a diameter of 1 mm and 2.5 mm, reconstructed from numerically simulated acoustic data for the standard transmission of short pulses and 16-bits long CGCS signals. In the second stage of the research, the experimental data were acquired in a flow phantom with silicone tubes with an internal diameter of 1.5 mm and 4.5 mm and a fluid flow velocity of 0.9 cm/s. The experiments were carried out using preprogrammed Verasonics Vantage™ research ultrasound system equipped with ALT L12-5/50 mm MHz linear array transducer with 7.8 MHz center frequency. It was evidenced both in simulations and experiments that the DCGEU provided a good flow image along the entire length of tubing with virtually angle independent detection in comparison with the conventional short pulse interrogation. [ABSTRACT FROM AUTHOR]

Abstract: With the emergence of the mouse as the predominant model system for studying mammalian brain development, in utero imaging methods are urgently required to analyze the dynamics of brain growth and patterning in mouse embryos. To address this need, we combined synthetic focusing with a high-frequency (38-MHz) annular-array ultrasound imaging system for extended depth-of-field, coded excitation for improved penetration and respiratory-gated transmit/receive. This combination allowed non-invasive in utero acquisition of motion-free 3-D data from individual embryos in approximately 2 min, and data from four or more embryos in a pregnant mouse in less than 30 min. Data were acquired from 148 embryos spanning 5 d of early to mid-gestational stages of brain development. The results indicated that brain anatomy and cerebral vasculature can be imaged with this system and that quantitative analyses of segmented cerebral ventricles can be used to characterize volumetric changes associated with mouse brain development. [Copyright &y& Elsevier]

Abstract: We demonstrate two methods for vasa vasorum imaging using contrast-enhanced intravascular ultrasound, which can be performed using commercial catheters. Plaque neovascularization was recognized as an independent marker of coronary artery plaque vulnerability. IVUS-based methods to image the microvessels available to date require high bandwidth (−6 dB relative frequency bandwidth >70%), which are not routinely available commercially. We explored the potential of ultraharmonic imaging and chirp reversal imaging for vasa vasorum imaging. In vitro recordings were performed on a tissue-mimicking phantom using a commercial ultrasound contrast agent and a transducer with a center frequency of 34 MHz and a −6 dB relative bandwidth of 56%. Acoustic peak pressures <500 kPa were used. A tissue-mimicking phantom with channels down to 200 μm in diameter was successfully imaged by the two contrast detection sequences while the smallest channel stayed invisible in conventional intravascular ultrasound images. Ultraharmonic imaging provided the best contrast agent detection. [Copyright &y& Elsevier]

Abstract: Coded tissue harmonic imaging with pulse inversion (CTHI-PI) based on a linear chirp signal can improve the signal-to-noise ratio with minimizing the peak range sidelobe level (PRSL), which is the main advantage over CTHI with bandpass filtering (CTHI-BF). However, the CTHI-PI technique could suffer from motion artifacts due to decreasing frame rate caused by two firings of opposite phase signals for each scanline. In this paper, a new CTHI method based on a nonlinear chirp signal (CTHI-NC) is presented, which can improve the separation of fundamental and harmonic components without sacrificing frame rate. The nonlinear chirp signal is designed to minimize the PRSL value by optimizing its frequency sweep rate and time duration. The performance of the CTHI-NC method was evaluated by measuring the PRSL and mainlobe width after compression. From the in vitro experiments, the CTHI-NC provided the PRSL of −40.6dB and the mainlobe width of 2.1μs for the transmit quadratic nonlinear chirp signal with the center frequency of 2.1MHz, the fractional bandwidth at −6dB of 0.6 and the time duration of 15μs. These results indicate that the proposed method could be used for improving frame rates in CTHI while providing comparable image quality to CTHI-PI. [ABSTRACT FROM AUTHOR]

Abstract: Through-transmitted ultrasonic waves can be used for computed projection imaging of the breast. The goal of this research was to analyze the acoustic properties changes associated with the propagation of ultrasonic waves through media before and after ultrasound contrast agent (UCA) injection and to study the feasibility of a new imaging method combining projection imaging and UCA. Two transmission techniques were examined: Gaussian pulses and pulse inversion. In the latter, three different double inverted pulses were studied: double Gaussian, double square and double sine. A computerized automatic ultrasonic scanning system was used for imaging. To simulate blood vessels, a phantom, consisting of a latex tube through which saline was circulated, was assembled. The phantom was placed within the scanner and sets of acoustic projection images were acquired. Then, a suspension of the UCA Definity™ was added to the saline and a new set of images was obtained. The pre and postcontrast images were quantitatively compared in terms of amplitude and time-of-flight (TOF). In addition, nonlinearity was evaluated by comparing the relative alteration of the positive and negative parts of the signal. Statistically significant (p < 0.001) changes in the projection images resulting from the UCA injection were observed in wave amplitude (22% ± 13%), TOF (7.9 ns ± 6.3 ns) and nonlinear properties (35% ± 32% and 56% ± 17% for Gausian pulses and pulse inversion, respectively). One in vivo study of a female breast is also presented and its preliminary outcomes discussed. Together, these results indicate the technical feasibility of the suggested method and its potential to detect breast tumors. (E-mail:haim@bm.technion.ac.il) [Copyright &y& Elsevier]

Abstract: In ultrasound harmonic imaging with chirp-coded excitation, a harmonic matched filter (HMF) is typically used on the received signal to perform pulse compression of the second harmonic component (SHC) to recover signal axial resolution. Designing the HMF for the compression of the SHC is a problematic issue because it requires optimal window selection. In the compressed second harmonic signal, the sidelobe level may increase and the mainlobe width (MLW) widen under a mismatched condition, resulting in loss of axial resolution. We propose the use of the fractional Fourier transform (FrFT) as an alternative tool to perform compression of the chirp-coded SHC generated as a result of the nonlinear propagation of an ultrasound signal. Two methods are used to experimentally assess the performance benefits of the FrFT technique over the HMF techniques. The first method uses chirp excitation with central frequency of 2.25 MHz and bandwidth of 1 MHz. The second method uses chirp excitation with pulse inversion to increase the bandwidth to 2 MHz. In this study, experiments were performed in a water tank with a single-element transducer mounted coaxially with a hydrophone in a pitch-catch configuration. Results are presented that indicate that the FrFT can perform pulse compression of the second harmonic chirp component, with a 14% reduction in the MLW of the compressed signal when compared with the HMF. Also, the FrFT provides at least 23% reduction in the MLW of the compressed signal when compared with the harmonic mismatched filter (HMMF). The FrFT maintains comparable peak and integrated sidelobe levels when compared with the HMF and HMMF techniques. (E-mail: elma@leeds.ac.uk) [Copyright &y& Elsevier]

Abstract: 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., −43.5dB vs. −24.8dB and −23.0dB, respectively. [Copyright &y& Elsevier]

Abstract: High-frequency ultrasound (HFU, >15 MHz) is a rapidly developing field. HFU is currently used and investigated for ophthalmologic, dermatologic, intravascular, and small-animal imaging. HFU offers a non-invasive means to investigate tissue at the microscopic level with resolutions often better than 100 μm. However, fine resolution is only obtained over the limited depth-of-field (∼1 mm) of single-element spherically-focused transducers typically used for HFU applications. Another limitation is penetration depth because most biological tissues have large attenuation at high frequencies. In this study, two 5-element annular arrays with center frequencies of 17 and 34 MHz were fabricated and methods were developed to obtain images with increased penetration depth and depth-of-field. These methods were used in ophthalmologic and small-animal imaging studies. Improved blood sensitivity was obtained when a phantom mimicking a vitreous hemorrhage was imaged. Central-nervous systems of 12.5-day-old mouse embryos were imaged in utero and in three dimensions for the first time. [Copyright &y& Elsevier]

Abstract: Most of the literature on coded excitation describes the signal-to-noise ratio gain of a coded waveform in terms of the time-bandwidth product. We have shown that in the context of ultrasound imaging, the expression for the SNR gain provided by matched filtering a coded waveform, can be reduced to the total number of chips in the transmit signal. Hence, the SNR gain is independent of both the bandwidth and the duration of a single-chip. This concept is described in detail, clarifying this seeming contradiction. The impact of bandwidth and pulse duration on the SNR, SNR gain and axial resolution is described. Bandwidth requirements and the impact of regulatory peak-power limitations are also addressed. [Copyright &y& Elsevier]

• Chirp signal has been used in combination with TMRs array eddy current probe. • Time analysis has been enabled via pulse-compression algorithm. • Quantitative/qualitative comparison of frequency and time domains analyses is shown. • Benefits of the proposed approach are discussed. Eddy current testing (ECT) is a widely used non-destructive testing (NDT) method in many industrial applications, which has been developed and advanced significantly in the past few decades. However, there are still challenges to overcome, such as the need for scanning and imaging large surfaces, improving the defect detection and classification capability. In this work, these have been addressed using tunnelling magnetoresistance (TMR) sensor array and a swept-frequency chirp excitation signal, together with the pulse-compression algorithm. Conventionally, time domain analysis is used in pulsed eddy current to gather info about any defects. Here the time domain analysis is implemented on the output of the pulse-compression procedure applied to the swept-frequency chirp response, which is also processed via frequency domain analysis. The results showed larger SNR values for time domain images and a better clustering of the SNR values compared to the frequency domain, facilitating the defect depth estimation and classification. [ABSTRACT FROM AUTHOR]

Abstract: In present research, Barker-coded excitation is applied to improve the sensitivity of emboli detection in transcranial Doppler (TCD) ultrasound systems. A 13-chip Barker code with a base pulse sequence that comprises two cycles at 2 MHz is used to compare with a 20-cycle pulse in both simulation studies and in vitro experiments. The results show that the system using coded excitation gains a 2.78-dB improvement in measured embolus-to-blood ratio (MEBR) while keeping a similar signal-to-noise ratio (SNR). The simulation results also indicate that the MEBR of the emboli are related to their velocities—a fast embolus has lower MEBR compared with a slow one with the same backscatter amplitudes, which makes fast emboli more difficult to detect. TCD system using coded excitation is more sensitive for faster and smaller emboli, which is significant for early diagnosis of stroke. (E-mail: xianglei00@mails.tsinghua.edu.cn) [Copyright &y& Elsevier]

Abstract: Averaging is frequently employed for waveform measurements in order to reduce the additive noise, but it becomes inaccurate if the averaged records are not coherent. This incoherence can be reduced if the waveform excitations and its acquisitions are clocked from the same source enabling synchronous digital averaging (SDA). Various aspects of an SDA instrument design are discussed in this paper: Architectures that perform averaging “on the fly”; impact of the master clock instability on the remaining incoherence; design of the mixed signal excitation stage; practical limitations on the number of averages, and how remaining incoherence of separate records is reduced as a result of averaging. Theoretical considerations are complemented by experimental results that show good agreement. [Copyright &y& Elsevier]

Abstract: Real-time visualization of microbubbles in the microvasculature of deep tissues remains a challenge for existing nonlinear microbubble imaging techniques. A technique with high sensitivity to nonlinear signals is required to compensate for the effects of limited power used to avoid bubble destruction and the high attenuation of the overlying tissues for deeper targets. The use of coded pulses in ultrasound imaging is well established as a means of improving the signal-to-noise ratio (SNR) within B-mode ultrasound imaging, but the feasibility of this approach for detecting microbubbles has not been well studied. In this work we investigate the use of binary phase encoding together with phase and amplitude modulation (PIAM) for the detection of nonlinear signals from microbubbles. A series of simulation experiments were conducted using a modified Rayleigh-Plesset model together with Golay and Barker coding techniques to investigate (i) the ability of binary encoded PIAM to detect nonlinear signals, (ii) the effect of the SNR and insonating pressure on the detection process, (iii) the sensitivity of different pulse encoding approaches and (iv) the effects of bubble resonance behavior on the detection process. The results show that the binary encoding approach combined with PIAM is able to detect nonlinear signals from microbubbles. It was found that nonlinear scattering from the microbubbles degrades the sensitivity of the binary encoded approach such that at high SNR there is no advantage in using these pulses over existing short-pulse PIAM. However, at lower SNR (<20 dB) the increased pulse length provides improved sensitivity without significant loss of spatial resolution, even under conditions in which the detection failed completely for existing approaches. The results also show that both the insonating acoustic pressure and resonance behavior of bubbles have an effect on the detection sensitivity and spatial resolution for the binary encoded approach. (E-mail: r.eckersley@imperial.ac.uk) [Copyright &y& Elsevier]

Abstract: The radiofrequency (RF) signal from a transcranial Doppler (TCD) ultrasound system allows us to track the motion of an embolus in a 2-D space of time and depth. The technique is limited by the narrow bandwidth (long duration) of the transmitted pulse because this provides poor axial resolution. This study aimed to assess whether implementing coded excitation and pulse compression in a TCD system would be a feasible means of increasing the bandwidth and hence improving the axial resolution, without the need for reducing the pulse length and increasing peak power levels. Embolic signals were collected in vitro from a flow phantom using a TCD system, which alternately transmitted coded and noncoded pulses. This allowed the same event to be investigated using the two different types of processing. Quantitative and qualitative measures were used to compare the two processing methods. The in vitro results were promising. They showed that the axial resolution could be improved, on average, by a factor of 6.6, using a pulse length of 13 μs and a chirp bandwidth of 0.8 MHz. This was reduced to a factor of 6 when a temporal bone sample was placed between the transducer and the flow phantom. Qualitatively the journey of an embolus was easier to track using the pulse compressed signal. Sonograms could be generated from smaller receive gates using the pulse compressed signal while still achieving an adequate signal-to-noise ratio. We found that it is both feasible and beneficial to implement coded excitation and pulse compression in a TCD system. (E-mail: dhe@le.ac.uk) [Copyright &y& Elsevier]

Abstract: The compression error of post-compression based coded excitation techniques increases with decreasing f-number, which causes the elevation of side-lobe levels. In this paper, a post-compression based coded excitation technique with reduced compression errors through dynamic aperture control is proposed. To improve the near-field resolution with no frame rate reduction, the proposed method performs simultaneous transmit multi-zone focusing using two mutually orthogonal complementary Golay codes. In the proposed method, the two mutually orthogonal sequences of length 16 are simultaneously transmitted toward two different focal depths, which are separately compressed into two short pulses on receive after dynamic focusing is performed. After carrying out the same transmit-receive operation for the same scan line with the complementary set of the orthogonal Golay codes, a single scan line with two transmit foci is obtained.The computer simulation results using a linear array with a center frequency of 7.5MHz and 60% 6dB bandwidth show that the range side-lobe level can be suppressed below −50dB, when f-number is maintained not smaller than 3. The performance of the proposed scheme for a smaller f-number of 2 was also verified through actual experiments using a 3.85MHz curved linear array with 60% 6dB bandwidth. Both the simulation and experimental results show that the proposed method provides improved lateral resolution compared to the conventional pre-compressed and post-compression based coded excitation imaging using Golay codes. [Copyright &y& Elsevier]

Abstract: Velocity measurement is a challenge for a variety of remote sensing systems such as ultrasonic and radar scanners. However, current Doppler-based techniques require a comparatively long data acquisition time. It has been suggested to use coded signals, such as linear frequency-modulated signals (chirp), for ultrasonic velocity estimation by extracting the needed information from a set of several sequential coded pulses. In this study, a method for velocity estimation using a single linear frequency-modulated chirp transmission is presented and implemented for ultrasonic measurements. The complex cross-correlation function between the transmitted and reflected signals is initially calculated. The velocity is then calculated from the phase of the peak of the envelope of this cross-correlation function. The suggested method was verified using computer simulations and experimental measurements in an ultrasonic system. Applying linear regression to the data has yielded very good correlation (r = 0.989). With the suggested technique, higher frame rates of velocity mapping can be potentially achieved relative to current techniques. Also, the same data can be utilized for both velocity mapping and image reconstruction. (E-mail: haim@bm.technion.ac.il) [Copyright &y& Elsevier]

Abstract: Coded ultrasonography is intensively studied in many laboratories due to its remarkable properties, particularly increased penetration depth and signal-to-noise ratio (SNR). However, no data on the spatial behavior of the pressure field generated by coded bursts transmissions in the tissue were yet reported. This paper reports the results of investigations of the field structure in water, in degassed beef liver and in pork tissue using four different excitations signals, two and 16 periods sine bursts and sinusoidal sequences with phase modulation using 13-bits Barker code and 16-bits Golay complementary codes. The results of measured pressure field distributions before and after compression were compared with those recorded using short pulse excitation. (E-mail: jlitn@ippt.gov.pl) [Copyright &y& Elsevier]

Abstract: The ways in which ultrasound is used in medical diagnosis are reviewed, with particular emphasis on the ultrasound source (probe) and implications for acoustic exposure. A brief discussion of the choice of optimum frequency for various target depths is followed by a description of the general features of diagnostic ultrasound probes, including endo-probes. The different modes of diagnostic scanning are then discussed in turn: A-mode, M-mode, B-mode, three-dimensional (3D) and 4D scanning, continuous wave (CW) Doppler, pulse-wave spectral Doppler and Doppler imaging. Under the general heading of B-mode imaging, there are individual descriptions of the principles of chirps and binary codes, B-flow, tissue harmonic imaging and ultrasound contrast agent-specific techniques. Techniques for improving image quality within the constraints of real-time operation are discussed, including write zoom, parallel beam forming, spatial compounding and multiple zone transmission focusing, along with methods for reducing slice thickness. At the end of each section there is a summarising comment on the basic features of the acoustic output and its consequences for patient safety. [Copyright &y& Elsevier]

Abstract: A field programmable gate array (FPGA) based hardware platform that is used to implement a digital, multi-gate pulsed Doppler ultrasound system for transcranial Doppler (TCD) use is described. The Doppler audio signal is extracted from the digitised radio-frequency signal by matched filtering and suitable sampling. The system was configured to acquire Doppler signals from 16 depth locations and to display Doppler signal power versus depth as well as a sonogram from a user specified depth. The signal-to-noise performance of the system was comparable with that of a commercially available TCD unit for equivalent pulse repetition frequency and sample volume settings. The flexibility of the platform was used to demonstrate the feasibility of using coded transducer excitation and pulse compression techniques to improve axial resolution compared to a non-coded implementation. The axial resolution improvement was demonstrated using a flow phantom and measured using a vibrating wire phantom. The measured resolutions were 9.1 and 2.4mm for the conventional and coded implementations, respectively. The reduction in signal-to-noise ratio of approximately 5dB associated with the configuration using coded excitation was attributable to the frequency response characteristics of the transducer rather than the processing technique used. This work demonstrates both the flexibility associated with an FPGA implementation of a Doppler ultrasound system and the potential for coded excitation to improve axial resolution in TCD systems. [Copyright &y& Elsevier]

Abstract: A modified Rayleigh-Plesset model was used to investigate the nonlinear acoustic response of ultrasound contrast microbubbles to multipulse phase and amplitude modulated, chirp encoded sequences. Trade-offs between the signal-to-noise ratio (SNR) and axial resolution were quantified for differing chirp time-bandwidth products and methods for minimising the artifacts formed in the postprocessing stages were developed. It was found that the chirp length can be increased and bandwidth reduced to improve SNR, though resolution is sacrificed. Results from the simulated chirp, pulse inverted, amplitude modulated (chirp PIAM) sequences were also compared with equivalent short pulse PIAM sequences and it was found that the chirp sequences preserve their extra energy after scattering, which translates to an improved SNR after processing. Compression artifacts were reduced by using chirps with a centre frequency and bandwidth tuned to the frequency response of the microbubble and reversing the frequency sweep of one chirp in the sequence. (E-mail: r.eckersley@imperial.ac.uk) [Copyright &y& Elsevier]

Abstract: A scheme of using phase-coded excitation and mismatched filter compression for high-frequency ultrasound imaging is presented in this paper. Biphase-coded pulses were constructed to excite the transducer. Received signals were compressed with mismatched filters optimized by minimizing peak-sidelobe-level (PSL). Both simulation and experiments were carried out to demonstrate the advantage of this technique. The simulation results demonstrated a possible sidelobe reduction (<−90dB) with a slightly decrease of the signal-to-noise ratio of less than 1dB compared with the compression using matched filters alone. The experimental results showed about 14dB SNR improvement as well as −40dB sidelobe level when the Barker-13 code excitation with 3-cycle sinusoidal wave carrier was used. [Copyright &y& Elsevier]

A linear array imaging system with coded excitation is considered, where the proposed excitation/compression scheme maximizes the signal-to-noise ratio (SNR) and minimizes sidelobes at the output of the compression filter. A pulse with linear frequency modulation (LFM) is used for coded excitation. The excitation/compression scheme is based on the fast digital mismatched filtering. The parameter optimization of the excitation/compression scheme includes (i) choice of an optimal filtering function for the mismatched filtering; (ii) choice of an optimal window function for tapering of the chirp amplitude; (iii) optimization of a chirp-to-transducer bandwidth ratio; (iv) choice of an appropriate n-bit quantizer. The simulation results show that the excitation/compression scheme can be implemented as a Dolph–Chebyshev filter including amplitude tapering of the chirp with a Lanczos window. An example of such an optimized system is given where the chirp bandwidth is chosen to be 2.5 times the transducer bandwidth and equals 6 MHz: The sidelobes are suppressed to -80 dB, for a central frequency of 4 MHz, and to -94 dB, for a central frequency of 8 MHz. The corresponding improvement of the SNR is 18 and 21 dB, respectively, when compared to a conventional short pulse imaging system. Simulation of B-mode images demonstrates the advantage of coded excitation systems of detecting regions with low contrast. [Copyright &y& Elsevier]

Previously, we have shown that for a single bubble, using chirps as the excitation signal improves both the linear and the non-linear response. Computer simulations of randomly distributed contrast agent bubbles show an increase of 10–13 dB in response when comparing pulse excitations with chirp excitations that have equal bandwidths and peak amplitudes. Second harmonic compression of simulated bubble echoes with chirp excitation shows low side-lobe levels and limited loss of axial resolution when compared to pulse excitation. Experimental results from water tank measurements with SonoVue™ contrast agent are in agreement with computer simulations showing increased signal-to-noise ratio and an increase of ∼12 dB at the second harmonic when comparing pulse and chirp excitation. [Copyright &y& Elsevier]

Clinical ultrasound imaging is the most frequently used imaging modality in the world accounting for almost 25% of all imaging studies performed. Hence, manufacturers of commercial ultrasound equipment are committing significant engineering resources to advance the technology behind the modality and to improve the diagnostic capabilities of ultrasound imaging. Consequently, new imaging technologies are constantly being introduced to the market under a host of different trademarked names. Hence, this paper will review many of the recent advances in ultrasound imaging and try to differentiate between developments aimed at marketing and those providing real clinical improvements. In particular, we will describe the technologies behind concepts such as coded ultrasound imaging, real time spatial compounding, tissue harmonic imaging, extended field of view imaging as well as 3D and 4D (i.e., real time 3D) imaging. Some of the latest advances in blood flow imaging e.g., B-flow, advanced dynamic flow (ADF) and automatic optimization methods will also be described. [Copyright &y& Elsevier]

Despite the enormous development in medical ultrasound (US) imaging over the last decades, penetration depth with satisfying image quality is often a problem in clinical practice. Coded excitation, used for years in radar techniques to increase signal-to-noise ratio (SNR), has recently been introduced in medical US scanning. In the present study, coded excitation using frequency-modulated US signals is implemented and evaluated in vivo.A total of nine male volunteers were scanned in three different abdominal locations, using both conventional pulsed and coded excitation. A modified scanner (B-K Medical model 3535) with transmitter and receiver boards developed in our group and a mechanical 4 MHz transducer were used. The system acquired coded and conventional US image frames interleaved, yielding identical acquisitions with the two techniques. Cine-loop sequences were evaluated by three experienced sonographers estimating penetration depth and scoring image quality of both conventional and coded imaging.The results showed a significant (p < 0.001) increase in penetration depth around 2 cm. Image quality was significantly (p < 0.001) better using codes at full usable depth and slightly, but also significantly (p < 0.05), better above depths, where the effect of coded excitation was noticeable to the sonographers.We conclude that the higher SNR offered by coded excitation gives improved image quality and provides increased penetration in medical US imaging. This increased SNR can, alternatively, be used to allow imaging at higher frequencies and thereby increase spatial resolution without any loss of penetration. [Copyright &y& Elsevier]

Coded excitation with compression on receive is used in medical ultrasound (US) imaging to increase signal-to-noise ratio (SNR) and penetration depth. We performed a computer simulation study to investigate if chirped pulse excitation can be applied in US contrast agent imaging to increase SNR and contrast-to-tissue ratio (CTR) and, thus, reduce contrast agent destruction and tissue harmonics. A new nonlinear compression technique is proposed that selectively compresses the second harmonic component of the response. We compared a chirp of 9.4-μs duration, 2-MHz centre frequency, 45% relative bandwidth to a Gaussian pulse with equal centre frequency and bandwidth. For peak pressures between 50 and 300 kPa, we found for resonant bubbles an increase in response between 10 and 13 dB. Moreover, the axial resolution after compression was comparable to axial resolution of conventional imaging. This effect was relatively insensitive to peak excitation pressure and was largest for bubbles having resonance frequency around the centre frequency of the excitation. (E-mail: borsboom@tch.fgg.eur.nl) [Copyright &y& Elsevier]

Frame rate in ultrasound imaging can be dramatically increased by using sparse synthetic transmit aperture (STA) beamforming techniques. The two main drawbacks of the method are the low signal-to-noise ratio (SNR) and the motion artifacts, that degrade the image quality.In this paper we propose a spatio-temporal encoding for STA imaging based on simultaneous transmission of two quasi-orthogonal tapered linear FM signals. The excitation signals are an up- and a down-chirp with frequency division and a cross-talk of −55 dB. The received signals are first cross-correlated with the appropriate code, then spatially decoded and finally beamformed for each code, yielding two images per emission. The spatial encoding is a Hadamard encoding previously suggested by Chiao et al. [in: Proceedings of the IEEE Ultrasonics Symposium, 1997, p. 1679]. The Hadamard matrix has half the size of the transmit element groups, due to the orthogonality of the temporal encoded wavefronts. Thus, with this method, the frame rate is doubled compared to previous systems. Another advantage is the utilization of temporal codes which are more robust to attenuation.With the proposed technique it is possible to obtain images dynamically focused in both transmit and receive with only two firings. This reduces the problem of motion artifacts. The method has been tested with extensive simulations using Field II. Resolution and SNR are compared with uncoded STA imaging and conventional phased-array imaging. The range resolution remains the same for coded STA imaging with four emissions and is slightly degraded for STA imaging with two emissions due to the −55 dB cross-talk between the signals. The additional proposed temporal encoding adds more than 15 dB on the SNR gain, yielding a SNR at the same order as in phased-array imaging. [Copyright &y& Elsevier]

Objective: To investigate if US-visualisation of the needle tip echo during US-guided punctures could be improved by use of new technological applications. Method: an US-guided 18 G Trocar needle was inserted into targets of a puncture phantom. The punctures were performed in series of 10 using different settings of the US-scanner (GE Logic 700 Expert). At 7-cm of puncture depth the quality of the echo was tested using four different settings; normal (N), N+automatic tissue optimising (ATO), coded harmonic imaging (CHI), CHI+ATO and at 13-cm of puncture depths six different settings; N, N+ATO, coded excitation (CE), CE+ATO, CHI, CHI+ATO. In total 100 (40+60) images were randomly numbered and read independently by three radiologists with regard to scoring of the quality of the echoes from the needle tip, needle shaft and the target. Results: US visualisation of the needle tip was significantly (P<0.005) improved as compared to normal settings (N) when the settings of ATO and CE were used. CHI resulted in the lowest score. A high agreement between observers was registered. Similar results were registered with regard to scorings from the needle shaft and target. Conclusion: Not only changes of needle designs and puncture techniques can enhance echoes from the needle but also changes in the settings of the US-scanner with the use of new technological applications can improve visualisation of the needle echo. [Copyright &y& Elsevier]

• Mutually Orthogonal Golay Complementary sequences (MOGCS) were studied. • Simultaneous Synthetic Transmit Aperture method proposed increases the frame rate. • Transmission of MOGCS does not compromise B-mode image quality. • MOGCS maintain axial resolution similar to the short pulse transmission. Complementary Golay coded sequences (CGCS) have several advantages over conventional short pulse transmitted signals. Specifically, CGCS allow the signal-to-noise ratio (SNR) to be increased. Moreover, due to matched filtering and compression, echoes resembling the short pulse waveform with substantially higher amplitude can be obtained. However, CGCS require two subsequent transmissions to obtain a single compressed signal. This decreases the data acquisition rate and the frame rate of ultrasound imaging by two-fold. To alleviate this problem, mutually orthogonal Golay complementary sequences (MOGCS) can be used. MOGCS allow the simultaneous transmission of two CGCS pairs to be implemented, yielding the acoustic data for two image frames in one data acquisition cycle. The main objective of this work was an experimental study of the most crucial parameters of the received acoustic signals, e.g. the signal-to-noise ratio (SNR), the side-lobes level (SLL) of the signal and the axial resolution, obtained from simultaneous transmission of two pairs of CGCS comprising a MOGCS set to demonstrate their feasibility of being used in ultrasonography. For this purpose, a simultaneous synthetic transmit aperture method (SSTA) was proposed. The SSTA is based on MOGCS transmission and simultaneous reconstruction of two image frames from a single data acquisition cycle. This doubles the image reconstruction rate in comparison with conventional CGCS signals. In this paper, the ultrasound data from a perfect reflector, commercial phantoms and in vivo measurements were analysed. Two 16-bit long CGCS pairs comprising the MOGCS set were programmed and transmitted using the Verasonics Vantage™ research ultrasound system equipped with a Philips ATL L7-4 linear array ultrasound probe. It was shown that the signal parameters and overall quality of reconstructed B-mode images did not deteriorate when using the MOGCS in comparison to the conventional CGCS and short pulse signals explored so far. [ABSTRACT FROM AUTHOR]

• The frequency coded excitation is used to generate the MA signal. This result has not been reported in other literatures. • We compared the characteristics of the compressed MA signals under the Chirp signal and the m-sequence coded excitation. • The parameters to evaluate the effect of SNR improvement are proposed, including considering processing time and pulse width. • We combine the waveform averaging and coded excitation methods to get better image quality. Magnetoacoustic imaging provides valuable information for monitoring bioelectricity and early tumor diagnosis. However, the low signal-to-noise ratio (SNR) of the magnetoacoustic signal, resulting from the single pulsed excitation, limits the imaging quality. A signal processing method of frequency coding excitation is proposed to increase the SNR of the magnetoacoustic signal. Chirp signal frequency coding is studied by simulation. M -sequence phase coding and wave averaging are also adopted in the studies. The experiments are conducted using a phantom of beef and fat with embedded copper rings. Two evaluation parameters, SNR improvement per unit pulse duration and SNR improvement per unit pulse duration per unit time, as well as the processing speed, are proposed to evaluate the SNR improvement. The results show that the frequency coding approach can rapidly improve the SNR of the magnetoacoustic signal as well as phase coding excitation, compared with the wave averaging approach. A method of combining the coding and waveform averaging to improve the SNR of magnetoacoustic signal has been developed. A higher SNR improvement in the magnetoacoustic signal, up to 235×, with a short processing time of 0.867 s, can be obtained. This study provides an effective method to improve the SNR in magnetoacoustic imaging. [ABSTRACT FROM AUTHOR]

• Complementary Golay coded sequence were applied for attenuation assessment. • Attenuation assessment depths was increased compared to short pulse burst. • Increase in attenuation assessment depth gets larger with attenuation growth. Accurate evaluation of ultrasonic wave attenuation is important in many medical applications of ultrasound. The aim of this work is to present a thorough analysis of the effectiveness of using complementary Golay coded sequences (CGCS) during the evaluation of ultrasound attenuation in tissue-like materials, especially at greater depths or at high attenuation. In order to compare the results of the attenuation measurement with the use of CGCS transmission and a short two sine cycles pulse, ultrasound backscattered from medium with predefined attenuation of 0.3, 0.7 and 2 dB/[MHz × cm] were simulated. Also for the same transmission signals, measurements of ultrasound echoes scattered in the tissue phantom with an attenuation of 0.5 dB/[MHz × cm] were performed. In the case of numerically simulated data, for the CGCS excitation, the maximum depth for which the attenuation was correctly determined increased from 55 mm to 80 mm for the 0.7 dB/[MHz × cm] phantom and from 20 mm to 50 mm for the 2 dB/[MHz × cm] phantom compared to excitation of the transducer with a short two sine cycles pulse. When the measurement data obtained using the tissue phantom was used to estimate the attenuation coefficient, the relative error was determined to be 6% and 16% for the depths of 10 mm and 40 mm for the short two sine cycles pulse excitation, respectively. Corresponding values for CGCS excitation and considered depths were 2% and 4%. The use of CGSC sequence during attenuation measurements increases measurement accuracy and can improve medical diagnostic techniques. [ABSTRACT FROM AUTHOR]