Tissue Harmonic Imaging Research Articles

Nonlinearity in a Medical Ultrasound Probe Under High Excitation Voltage

Tissue harmonic imaging is often the preferred ultrasound imaging modality due to its ability to suppress reverberations. The method requires good control of the transmit stage of the ultrasound scanner, as harmonics in the transmitted ultrasound pulses will interfere with the harmonics generated in the tissue during nonlinear propagation, degrading image quality. In this study, a medical ultrasound probe used in tissue harmonic imaging was experimentally characterized for transmitted second-harmonic distortion to identify and compare the sources of nonlinear distortion in the probe and transmit electronics. The system was tested up to amplitudes above what is found during conventional operation, pushing the system to the limits in order to investigate the phenomenon. Under these conditions, second-harmonic levels up to -20 dB relative to the fundamental frequency were found in the ultrasound pulses transmitted from the probe. The transmit stage consists of high-voltage transmit electronics, cable, tuning inductors, and the acoustic stack. The contribution from the different stages in the ultrasound transmit chain was quantified by separating and measuring at different positions. Nonlinearities in the acoustic transducer stack were identified as the dominating source for second harmonics in the transmitted ultrasound pulses. Contribution from other components, e.g., transmit electronics and cable and tuning circuitry, were found to be negligible compared with that from the acoustic stack. Investigation of the stack's electrical impedance at different driving voltages revealed that the impedance changes significantly as a function of excitation voltage. The second-harmonic peak in the transmitted pulses can be explained by this nonlinear electrical impedance distorting the driving voltage and current.

Interleaved Array Transducer with Polarization Inversion Technique to Implement Ultrasound Tissue Harmonic Imaging.

In ultrasound tissue harmonic imaging (THI), it is preferred that the bandwidth of the array transducer covers at least the fundamental frequency f0 for transmission and the second harmonic frequency 2f0 for reception. However, it is challenging to develop an array transducer with a broad bandwidth due to the single resonance characteristics of piezoelectric materials. In this study, we present an improved interleaved array transducer suitable for THI and a dedicated transducer fabrication scheme. The proposed array transducer has a novel structure in which conventional elements exhibiting f0 resonant frequency and polarization-inverted elements exhibiting 2f0 resonant frequency are alternately located, and the thicknesses of all piezoelectric elements are identical. The performance of the proposed method was demonstrated by finite element analysis (FEA) simulations and experiments using a fabricated prototype array transducer. Using the proposed technique, f0 and 2f0 frequency ultrasounds can be efficiently transmitted and received, respectively, resulting in a 90% broad bandwidth feature of the transducer. Thus, the proposed technique can be one of the potential ways to implement high resolution THI.

Diagnosis of Biliary Tract Disease Based on Ultrasound Tissue Harmonic Imaging

With the deepening of ultrasound imaging research, studying nonlinear phenomena in medical ultrasound will help people to further improve the existing diagnostic level. Harmonic imaging technology generated in recent years is an effective new technology for nonlinear acoustics in ultrasonic diagnosis. Patients with biliary tract lesions generally have few symptoms, which are often detected by chance during physical examination. Ultrasonography is currently the preferred diagnostic method for biliary tract disease. The application of tissue harmonic imaging (THI) can effectively eliminate many near-field misdiagnosed images, enhance the tissue echo of deep tissues or organs, and significantly improve signal-to-noise ratio and resolution. At the same time, it can better display the subtle features of biliary diseases, thereby reducing the rate of missed diagnosis and improving the accuracy of diagnosis. Therefore, this study aimed to observe the changes of ultrasound images in the lesions and surrounding tissues of several biliary lesions by ultrasound tissue harmonic imaging technology, and realized the diagnosis in the early stage of the disease by means of tissue harmonic imaging technology, then provided objective quantitative indicators for the diagnosis of biliary diseases. Also, this study confirmed that tissue harmonic imaging technology can significantly improve the ultrasound image resolution of biliary tract disease, clearly showing the sub-acute gallbladder wall, gallbladder wall, gallbladder cavity in the acute and chronic inflammation and the presence of subtle changes in the tumor. This can provide a rich diagnostic value for the clinic and has practical significance for clinical treatment.

Adaptive Ultrasound Tissue Harmonic Imaging Based on an Improved Ensemble Empirical Mode Decomposition Algorithm

Complete and accurate separation of harmonic components from the ultrasonic radio frequency (RF) echo signals is essential to improve the quality of harmonic imaging. There are limitations in the existing two commonly used separation methods, that is, the subjectivity for the high-pass filtering (S_HPF) method and motion artifacts for the pulse inversion (S_PI) method. A novel separation method called S_CEEMDAN, based on the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) algorithm, is proposed to adaptively separate the second harmonic components for ultrasound tissue harmonic imaging. First, the ensemble size of the CEEMDAN algorithm is calculated adaptively according to the standard deviation of the added white noise. A set of intrinsic mode functions (IMFs) is then obtained by the CEEMDAN algorithm from the ultrasonic RF echo signals. According to the IMF spectra, the IMFs that contain both fundamental and harmonic components are further decomposed. The separation process is performed until all the obtained IMFs have been divided into either fundamental or harmonic categories. Finally, the fundamental and harmonic RF echo signals are obtained from the accumulations of signals from these two categories, respectively. In simulation experiments based on CREANUIS, the S_CEEMDAN-based results are similar to the S_HPF-based results, but better than the S_PI-based results. For the dynamic carotid artery measurements, the contrasts, contrast-to-noise ratios (CNRs), and tissue-to-clutter ratios (TCRs) of the harmonic images based on the S_CEEMDAN are averagely increased by 31.43% and 50.82%, 18.96% and 10.83%, as well as 34.23% and 44.18%, respectively, compared with those based on the S_HPF and S_PI methods. In conclusion, the S_CEEMDAN method provides improved harmonic images owing to its good adaptivity and lower motion artifacts, and is thus a potential alternative to the current methods for ultrasonic harmonic imaging.

Sonographic visibility of the main posterior ankle ligaments and para-ligamentous structures in 15 healthy subjects.

The present article describes the ultrasound (US) appearance of ligaments and paraligamentous structures which are not included in standard US imaging of the ankle: the posterior inferior tibiofibular ligament (PITFL), the transverse tibiofibular ligament (TTFL), the posterior talofibular ligament (PTFL), the posterior intermalleolar ligament (PIL), the synovial recess (SR) of the posterior joint and the os trigonum (OT). Two skilled operators examined 15 ankles in 15 healthy volunteers. Correlation between thickness of the main ligaments and body mass index (BMI) was also analyzed. Compound and tissue harmonic imaging (THI) were carried out using 12-, 6-15- and 9-MHz linear probes. Exploration of the posterior ankle ligament complex is accurately described including correct ankle position, echogenicity, shape, direction and thickness. Both operators identified and measured the main ligaments (PITFL, TTFL and PTFL) in all volunteers (Intraclass Correlation Coefficient ranged from 0.8 to 1); both operators also detected SR and OT in 2/15 ankles and posterior intermalleolar ligament (PIL) in 5/15 ankles. Pearson's test showed a significant correlation (< 0.05) between TTFL thickness and BMI. Also, a dynamic study was carried out showing tension of the PTFL during dorsiflexion in 7/15 subjects. Our results highlight the potential role of accurate US imaging in detecting posterior ankle ligament involvement in acute and chronic traumas. To our knowledge, there are no previous articles in the literature dealing with this topic providing an accurate description of the US procedure, and in particular, no study has been carried out to identify OT.

Application of 14-MHz Ultrasonography with Tissue Harmonic Imaging to Determine Posterior Capsule Integrity in Traumatic Cataract.

Purpose To report the application of 14-MHz ultrasonography with tissue harmonic imaging (14 MHz + THI) to determine the integrity of the posterior capsule (PC) in traumatic cataract (TC). Methods Patients with TC who were scheduled to undergo cataract extraction and whose PC could not be observed by slit lamp examination were included in the study. The status of the PC was determined by 14 MHz + THI before cataract extraction and confirmed during surgery. The results regarding PC integrity obtained from 14 MHz + THI and intraoperative direct observation were compared. Result The study enrolled 52 eyes of 52 patients (49 men and 3 women), with a mean age of 42.15 years ± 11.23 (SD). The nature of the trauma was blunt (3 eyes) or sharp (49 eyes). The 14 MHz + THI method showed 21 PCs to be intact and 31 to have ruptured before cataract surgery. During surgery, 23 PCs were observed to be intact, while 29 PCs were ruptured. 27 PCs were ruptured and 19 were intact, as determined by the two methods. The 14 MHz + THI observations were consistent with the intraoperative observations of the PC (kappa = 0.764), with no significant difference between the two methods (P=0.687). The sensitivity, specificity, and accuracy of 14 MHz + THI for observation of the PC were 93.10%, 82.60%, and 88.46%, respectively. Conclusion The 14 MHz + THI method can accurately reveal the integrity of the PC in TC. It has important clinical value in the selection of cataract surgery methods and the prediction of complications during TC surgery.

Single-Chip 3072-Element-Channel Transceiver/128-Subarray-Channel 2-D Array IC With Analog RX and All-Digital TX Beamformer for Echocardiography

This paper presents a single-chip 3072-element-channel (ECh) transceiver/128-subarray-channel (SCh) 2-D array IC with analog receiver (RX) and all-digital transmitter (TX) beamformer for echocardiography. The proposed IC integrates 3072-ECh transceivers that are composed of a low-power tunable amplitude three-level pulser (TA3LP), zero-power-TX-and-RX- isolation switch (ZTRSW), programmable gain-and-input-impedance low-noise amplifier (PGZLNA), bidirectional dynamically reconfigurable switched-capacitor delayer (BDR- SCD), and 24-ECh-to-1-SCh charge-domain adder (CDADD). It also has 128-SCh low-noise cable buffers (LNCBUFs) and all the related peripheral circuits, including control and interface circuits. It has an all-digital TX architecture with a digital beamformer (TX-DBF) that is free from the waveform distortion and timing error caused by long cable propagation between the main instrument unit and the IC. The TA3LP launches the three-level bipolar signals that are necessary for tissue harmonic imaging (THI). The BDR-SCD can delay 2-bit TX digital signals or an RX analog signal; 24 RX signals in an SCh are coherently delayed using BDR-SCDs, summed in the charge domain with a CDADD without signal headroom concerns, and converted into an SCh signal. The proposed IC is fabricated with a $0.18-\mu \text{m}$ high-voltage silicon-on-insulator (HV SOI) CMOS process. Each ECh transceiver occupies only a $300 ~\mu \text{m}\,\,\times 300 ~\mu \text{m}$ silicon area while having a greater than 85-dB dynamic range, 25-ns resolution, 750-ns maximum time delay, and $138-{V}_{\textrm {pp}}$ output capabilities. The total die size is 417 mm2. An ultrasound system was also made to visualize 2-D/3-D phantom images with 0.74-mW/ECh power consumption in the B-mode.

Modeling of the Acoustic Field Produced by Diagnostic Ultrasound Arrays in Plane and Diverging Wave Modes.

Recent advances in ultrafast contrast imaging have facilitated innovations, such as superresolution imaging and ultrafast contrast-enhanced Doppler imaging. Combining plane and diverging wave imaging (PWI/DWI) with tissue harmonic imaging (THI) may offer improvements in image quality in applications such as 3-D THI and harmonic color flow. However, no studies have reported simulations of the nonlinear acoustic fields produced by diagnostic arrays in either plane or diverging wave mode. The aim of this study is to model three typical diagnostic arrays that are used in clinical practice and research, Verasonics L11-4v linear array, C5-2v convex array, and P4-2v phased array with the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation. We have two specific objectives: first, to investigate whether there is increased bubble destruction due to the nature of the plane and diverging fields in contrast imaging; and second, to investigate the feasibility of combining PWI/DWI and THI by quantifying the second harmonic generated by these fields. We showed in linear simulations that using such arrays for ultrafast contrast imaging produced pressures that are greater in the near field and lower in the far field than those of focused beams and thus may induce more near-field bubble destruction. In nonlinear simulations, the second harmonic produced by ultrafast THI was found to be 2-16 dB lower than that of focused beams for all arrays considered when operated at the same MI. This moderate difference of the second harmonic between PWI/DWI and focused ultrasound suggests that it is feasible to combine PWI/DWI and THI.

Interpretability and generalizability of a one-dimensional convolutional neural network method for hepatic steatosis characterization

Nonalcoholic fatty liver disease (NAFLD) affects 25% of the population globally. We developed a one-dimensional convolutional neural network (1-D CNN) method for the ultrasound tissue characterization using radio-frequency (RF) data and demonstrated its potential for the liver fat classification and quantification. We investigate herein the interpretability and generalizability of the method to understand why it works, and whether the performance is affected by settings, transducers, and platforms. We studied under various conditions the performances of 1-D CNN for predicting steatosis using magnetic resonance imaging-estimated proton density fat fraction (MRI-PDFF) as reference (steatosis: PDFF > 5%). Three datasets were used, each containing ultrasound RF data acquired from adults and same-day MRI-PDFF estimates: (1) 200 normal and NAFLD participants scanned using the Siemens S2000 ultrasound system with the 4C1 transducer (1–4 MHz); (2) 87 participants with known/suspected NAFLD scanned using Siemens S3000 with the 4C1 and/or 6C1HD transducers (1.5–6 MHz); and (3) 46 participants with known/suspected NAFLD scanned using GE Logiq e9 with the C1-6 transducer (1–6 MHz). The 1-D CNN method is generalizable among various instrumentation settings (e.g., focal depth, time gain compensation), betweentransducers of similar frequencies, between platforms, but not between the fundamental and tissue harmonic image modes. [Work supported by R01DK106419.] Nonalcoholic fatty liver disease (NAFLD) affects 25% of the population globally. We developed a one-dimensional convolutional neural network (1-D CNN) method for the ultrasound tissue characterization using radio-frequency (RF) data and demonstrated its potential for the liver fat classification and quantification. We investigate herein the interpretability and generalizability of the method to understand why it works, and whether the performance is affected by settings, transducers, and platforms. We studied under various conditions the performances of 1-D CNN for predicting steatosis using magnetic resonance imaging-estimated proton density fat fraction (MRI-PDFF) as reference (steatosis: PDFF > 5%). Three datasets were used, each containing ultrasound RF data acquired from adults and same-day MRI-PDFF estimates: (1) 200 normal and NAFLD participants scanned using the Siemens S2000 ultrasound system with the 4C1 transducer (1–4 MHz); (2) 87 participants with known/suspected NAFLD scanned using Siemens ...

Dual-Element Intravascular Ultrasound Transducer for Tissue Harmonic Imaging and Frequency Compounding: Development and Imaging Performance Assessment.

For accurate diagnosis of atherosclerosis, the high spatial and contrast resolutions of intravascular ultrasound (IVUS) images are a key requirement. Increasing the center frequency of IVUS is a simple solution to meet this requirement. However, this leads to a reduction in imaging depth due to the frequency-dependent attenuation of ultrasound. Here, we report a recently developed dual-element IVUS transducer for tissue harmonic imaging (THI) and frequency compounding to increase the spatial and contrast resolutions of IVUS images, while maintaining the imaging depth to assess the overall morphological change of blood vessels. One 35-MHz element is used for producing general IVUS images and the other 70-MHz element is for receiving the second harmonic signals induced by the 35-MHz ultrasound. The fundamental and second harmonic signals can also be used for frequency compound imaging to further improve contrast resolution. The spatial and contrast resolutions achieved by the developed transducer were evaluated through wire and tissue-mimicking phantom imaging tests. Additionally, the images of a stent deployed in a tissue-mimicking phantom and an excised pig artery were acquired to assess clinical usefulness of the transducer. The results demonstrated that the developed IVUS transducer enables us to simultaneously examine the overall morphological change of blood vessels by the 35-MHz ultrasound images and the near vessel layers such as the intima, the media, and the adventitia by either THI or compound images with high spatial and contrast resolutions. In addition, the developed transducer facilitates the simultaneous acquisition of 35- and 70-MHz fundamental images when needed. The developed dual-element IVUS transducer makes it possible to fully realize the potential benefits of IVUS in the diagnosis of atherosclerosis.

Ultrasound machine ‘knobology’

Being a ‘real time’ imaging modality, ultrasound images are almost always interpreted by the operator at the time of examination. Obtaining optimal image quality throughout the scan is therefore essential to maximise the clinical information that can be obtained. This article aims to discuss the main control features that are likely to be present on most machines, such as gain, depth and focal points, as well as some other options that may be available to the operator, such as tissue harmonic imaging and speckle reduction. Examples of different settings are shown, with reference to how they may be optimised to obtain the best possible image quality.

Improved Visualization in Difficult-to-Image Stress Echocardiography Patients Using Real-Time Harmonic Spatial Coherence Imaging.

Stress echocardiography is used to detect myocardial ischemia by evaluating cardiovascular function both at rest and at elevated heart rates. Stress echocardiography requires excellent visualization of the left ventricle (LV) throughout the cardiac cycle. However, LV endocardial border visualization is often negatively impacted by high levels of clutter associated with patient obesity, which has risen dramatically worldwide in recent decades. Short-lag spatial coherence (SLSC) imaging has demonstrated reduced clutter in several applications. In this work, a computationally efficient formulation of SLSC was implemented into an object-oriented graphics processing unit-based software beamformer, enabling real-time (>30 frames per second) SLSC echocardiography on a research ultrasound scanner. The system was then used to image 15 difficult-to-image stress echocardiography patients in a comparison study of tissue harmonic imaging (THI) and harmonic spatial coherence imaging (HSCI). Video clips of four standard stress echocardiography views acquired with either THI or HSCI were provided in random shuffled order to three experienced readers. Each reader rated the visibility of 17 LV segments as "invisible," "suboptimally visualized," or "well visualized," with the first two categories indicating a need for contrast agent. In a symmetry test unadjusted for patientwise clustering, HSCI demonstrated a clear superiority over THI ( ). When measured on a per-patient basis, the median total score significantly favored HSCI with . When collapsing the ratings to a two-level scale ("needs contrast" versus "well visualized"), HSCI once again showed an overall superiority over THI, with by McNemar test adjusted for clustering.

Comparing the image quality of tissue harmonic and conventional B-mode ultrasound of kidney in over-obese individuals.

BackgroundIncreased subcutaneous fat thickness and depth of target organs in over-obese patients, results in weak signals and inadequate images. Tissue harmonic imaging has been used widely in obese patients and is believed to result in higher quality images. This superiority is not proved in modern machines with improved image quality in conventional mode.ObjectiveTo compare the image quality between conventional and tissue harmonic ultrasound images.MethodsThis cross-sectional study was carried out from March 2015 to June 2016. Seventy-six over-obese patients referred to Ghaem Hospital (Mashhad, Iran) for weight-correction surgeries, were enrolled into the study. Conventional and tissue harmonic images of their kidneys were blinded and compared back-to-back by four expert radiologists. Data were analyzed by SPSS version 16, using Cochrane’s Q test.ResultsAll raters reported image quality to be better in tissue harmonic compared to fundamental frequency ultrasound (p=0.000, Cochrane’s Q test). Although better image quality in tissue harmonic mode was reported by the four raters, there was weak inter-observer agreement (p=0.081 for right kidney and p=0.21 for left kidney).ConclusionAdvances in ultrasound equipment and the introduction of tissue harmonic imaging can improve the diagnostic performance in over-obese patients and this mode of imaging should be used whenever evaluating over-obese subjects.

A 35 MHz/105 MHz Dual-Element Focused Transducer for Intravascular Ultrasound Tissue Imaging Using the Third Harmonic.

The superharmonic imaging of tissue has the potential for high spatial and contrast resolutions, compared to the fundamental and second harmonic imaging. For this technique, the spectral bandwidth of an ultrasound transducer is divided for transmission of ultrasound and reception of its superharmonics (i.e., higher than the second harmonic). Due to the spectral division for the transmission and reception, transmitted ultrasound energy is not sufficient to induce superharmonics in media without using contrast agents, and it is difficult that a transducer has a −6 dB fractional bandwidth of higher than 100%. For the superharmonic imaging of tissue, thus, multi-frequency array transducers are the best choice if available; transmit and receive elements are separate and have different center frequencies. However, the construction of a multi-frequency transducer for intravascular ultrasound (IVUS) imaging is particularly demanding because of its small size of less than 1 mm. Here, we report a recently developed dual-element focused IVUS transducer for the third harmonic imaging of tissue, which consists of a 35-MHz element for ultrasound transmission and a 105-MHz element for third harmonic reception. For high quality third harmonic imaging, both elements were fabricated to have the same focus at 2.5 mm. The results of tissue mimicking phantom tests demonstrated that the third harmonic images produced by the developed transducer had higher spatial resolution and deeper imaging depth than the fundamental images.

Abdominal Sonography: Evaluation of Image Quality in Patients with Varying BMI Using Tissue Harmonic Imaging and Standard Sonography

Abdominal Sonography: Evaluation of Image Quality in Patients with Varying BMI Using Tissue Harmonic Imaging and Standard Sonography

Development of Dual-Frequency Oblong-Shaped-Focused Transducers for Intravascular Ultrasound Tissue Harmonic Imaging.

Tissue harmonic imaging (THI), an essential mode of commercial ultrasound imaging scanners, can provide images with high spatial and contrast resolutions. For THI, the frequency spectrum of a transducer is generally divided for the transmission of fundamental signal and the reception of its second harmonic. Therefore, it is difficult to use the THI mode for intravascular ultrasound (IVUS) imaging because typical IVUS transducers have a narrow -6-dB fractional bandwidth of about 50%. Due to its small aperture (about 0.5 mm) and the strength of IVUS being too weak, it is difficult to construct a high-quality tissue harmonic image. In this paper, we report a recently developed dual-frequency oblong-shaped-focused IVUS transducer for high-quality intravascular THI; the transducer consists of three elements arranged side by side in the horizontal (i.e., elevation) direction. The two outer elements with a center frequency of 35 MHz are responsible for ultrasound transmission and the center element has a center frequency of 70 MHz for the reception of the second-harmonic signals. All three elements have a spherical shape with a radius of 3 mm to efficiently generate harmonics in the region of interest. This configuration of the developed IVUS transducer was determined to facilitate high-quality THI, which was based on the results of Field II simulation and finite-element analysis. The images of wires and a tissue-mimicking phantom indicated that the tissue harmonic images produced by the developed transducer have not only a high spatial resolution but also a deep imaging depth, compared to the 35- and 70-MHz fundamental images.

Tissue Harmonic Imaging Compared with Conventional BMode Ultrasound, Biphasic CECT and Tissue Diagnosis in Evaluation of Pancreatic Masses

Tissue Harmonic Imaging Compared with Conventional BMode Ultrasound, Biphasic CECT and Tissue Diagnosis in Evaluation of Pancreatic Masses

Comparison of total image quality in Tissue Harmonic Imaging as compared to conventional ultrasound technique in abdominal and pelvic ultrasonography

Comparison of total image quality in Tissue Harmonic Imaging as compared to conventional ultrasound technique in abdominal and pelvic ultrasonography

An Adaptive Synthetic Aperture Method Applied to Ultrasound Tissue Harmonic Imaging.

In recent years, the minimum variance (MV) beamformer has been highly regarded since it provides high resolution and contrast in B-mode ultrasound imaging compared with nonadaptive delay-and-sum (DAS) beamformer. However, the performance of MV beamformer is degraded in the presence of the noise due to inaccurate estimation of the covariance matrix resulting in low-quality images. The conventional tissue harmonic imaging (THI) offers multiple advantages over conventional pulse-echo ultrasound imaging, including enhanced contrast resolution and improved axial and lateral resolutions, but low signal-to-noise ratio (SNR) is a major problem facing this imaging method, which uses a fixed transmit focus and dynamic receive focusing (DRF). In this paper, a synthetic aperture method based on the virtual source, namely, bidirectional pixel-based focusing (BiPBF), has been combined with the MV beamformer and then applied to second-harmonic ultrasound imaging. The main objective is suppressing the noise level to enhance the performance of the MV beamformer in the harmonic imaging, especially in lower and deeper depths where the SNR is low. In addition, combining the BiPBF and MV weighting results in simultaneous improvement in imaging resolution and contrast, in comparison with the conventional methods: DRF (DAS), BiPBF (DAS), and DRF (MV). The performance of the proposed method is evaluated on simulated and experimental RF data. The THI is achieved using the pulse-inversion technique. The results of the simulated wire phantom demonstrate that the proposed beamformer can achieve the best lateral resolution, along different depths, compared with DRF (DAS), BiPBF (DAS), and DRF (MV) methods. The results of the simulated and experimental cyst phantoms show that the new beamformer improves the contrast ratio (CR) and contrast-to-noise ratio (CNR) of the resulting images. In results of simulated cyst phantom, in average, the new beamformer improves the CR and CNR of the cyst about (7.4 dB, 49%), (3.2 dB, 16%), and (5 dB, 26%) compared with DRF (DAS), BiPBF (DAS), and DRF (MV), respectively. In results of experimental cyst phantom, these relative improvements are about (4.2 dB, 22%), (1.7 dB, 7%), and (2.6 dB, 15%). In addition, BiPBF (MV) method offers improved edge definition of cysts in comparison with the other methods.

Experimental evaluation of ultrasound higher-order harmonic imaging with Filtered-Delay Multiply And Sum (F-DMAS) non-linear beamforming

Tissue Harmonic Imaging (THI) mode is currently one of the preferred choices by the clinicians for its ability to provide enhanced ultrasound images, thanks to the use of the second harmonic component of backscattered echoes. This paper aims at investigating whether the combination of THI with Filtered-Delay Multiply And Sum (F-DMAS) beamforming can provide further improvements in image quality. F-DMAS is a new non-linear beamformer, which, similarly to THI, is based on the use of the second harmonics of beamformed signals and is known to increase image contrast resolution and noise rejection. Thus, we have first compared the images obtained by using F-DMAS and the standard Delay And Sum (DAS) beamformers when only the second harmonics of the received signals was selected. Moreover, possible improvements brought about by other harmonic components generated by the combined use of the fundamental plus second harmonics and F-DMAS beamforming have been explored. Experimental results demonstrate that, as compared to standard harmonic imaging with DAS, THI and F-DMAS can be joined to improve the −20 dB lateral resolution up to 1 mm, the contrast ratio up to 12 dB on a cyst-phantom and up to 9 dB on in vivo images.