High Frame Rate Imaging Research Articles

Range-Doppler Based Moving Target Image Trace Analysis Method in Circular SAR

The single channel Circular Synthetic Aperture Radar (CSAR) has the advantage of continuous surveillance of a fixed scene of interest, which can provide high frame rate image sequences to detect ground moving targets. Recent image-sequence-based CSAR moving target detection methods utilize the fact that the target signal moves fast in the image sequence. Knowledge of the target’s image trace(moving trace in the image sequence, which is equal to a target signature’s morphology in a full aperture CSAR image) can help design better detection methods. However, previous signature morphology studies are based on linear track geometry assumptions, which cannot handle CSAR’s nonlinear track. Hence, this paper proposes a new image trace method based on the range-Doppler principle. The proposed method can deduct the exact analytic function of an arbitrary moving target’s image trace in CSAR. The method assumes radar operates in side-looking mode and that the target moves on the ground plane. It combines the range-Doppler equations(i.e., iso-range and iso-Doppler relation) and Cartesian transformation between the ground and radar coordinate system to obtain the parametric functions of the image trace. Based on the method, three types of target motion (including linear and nonlinear motion) are analyzed. The proposed method is validated with both simulated and real data.

Improved Coherent Plane-Wave Compounding Using Sign Coherence Factor Weighting for Frequency-Domain Beamforming.

This study proposes a novel modified sign coherence factor (SCF) weighting adapted to the frequency-domain (FD) beamforming for ultrasound plane-wave imaging to achieve a high frame rate and better image quality. First, before beamforming, the sign components were extracted from the radiofrequency signals of aperture data. Second, the modified SCF was established using the FD beamformed sign components. Finally, the FD beamformed image was weighted by the modified SCF. To assess the performance of the proposed modified SCF for FD beamforming, the resolution, contrast, computation complexity and execution time of the generated images were evaluated. The results revealed that the FD-SCF could significantly improve the computational load compared with the classic delay-and-sum SCF on the premise of equal image quality improvement. Therefore, high image quality and low computational load have been successfully combined under the proposed weighting method.

3-D High Frame Rate Imaging With Motion Compensation (3-D HFR With MoCo): An Experimental Evaluation

3-D High Frame Rate Imaging With Motion Compensation (3-D HFR With MoCo): An Experimental Evaluation

Assessment of bubble activity generated by histotripsy combined with echogenic liposomes

Objective. Histotripsy is a form of focused ultrasound therapy that uses the mechanical activity of bubbles to ablate tissue. While histotripsy alone degrades the cellular content of tissue, recent studies have demonstrated it effectively disrupts the extracellular structure of pathologic conditions such as venous thrombosis when combined with a thrombolytic drug. Rather than relying on standard administration methods, associating thrombolytic drugs with an ultrasound-triggered echogenic liposome vesicle will enable targeted, systemic drug delivery. To date, histotripsy has primarily relied on nano-nuclei inherent to the medium for bubble cloud generation, and microbubbles associated with echogenic liposomes may alter the histotripsy bubble dynamics. The objective of this work was to investigate the interaction of histotripsy pulse with echogenic liposomes. Approach. Bubble clouds were generated using a focused source in an in vitro model of venous flow. Acoustic emissions generated during the insonation were passively acquired to assess the mechanical activity of the bubble cloud. High frame rate, pulse inversion imaging was used to track the change in echogenicity of the liposomes following histotripsy exposure. Main results. For peak negative pressures less than 20 MPa, acoustic emissions indicative of stable and inertial bubble activity were observed. As the peak negative pressure of the histotripsy excitation increased, harmonics of the excitation were observed in OFP t-ELIP solutions and plasma alone. Additional observations with high frame rate imaging indicated a transition of bubble behavior as the pulse pressure transitioned to shock wave formation. Significance. These observations suggest that a complex interaction between histotripsy pulses and echogenic liposomes that may be exploited for combination treatment approaches.

Dual-comb based time-stretch optical coherence tomography for large and segmental imaging depth

Optical coherence tomography based on time-stretch enables high frame rate and high-resolution imaging for the inertia-free wavelength-swept mechanism. The fundamental obstacle is still the acquisition bandwidth's restriction on imaging depth. By introducing dual-comb with slightly different repetition rates, the induced Vernier effect is found to be capable of relieving the problem. In our work, a dual-comb based time-stretch optical coherence tomography is proposed and experimentally demonstrated, achieving a 1.5-m imaging depth and 200-kHz A-scan rate. Moreover, about a 33.4-µm resolution and 25-µm accuracy are achieved. In addition, by adjusting the frequency detuning of the dual-comb, the A-scan rate can be further boosted to video-rate imaging. With enlarged imaging depth, this scheme is promising for a wide range of applications, including light detection and ranging.

A phase-shifting method for computation reduction for high-frame-rate imaging

High-frame rate (HFR) imaging using steered plane wave (SPW) or limited-diffraction beam has a high-temporal resolution and thus has found many applications. To further study the HFR imaging methods, computer simulations were performed. However, the simulations require a large number of computations, especially for 3D imaging with 2D array transducers for a large imaging volume. In this paper, a phase-shifting method was developed to reduce the number of computations. In the method, the grid points of the transmit and receive beams were calculated at 1-mm interval in the depth direction that is perpendicular to the transducer surface. The interval is much larger than the 1/4 of the 0.58-mm wavelength required for an accurate interpolation for millions of random scatterers in pulse-echo response without aliasing. Since the HFR imaging uses either SPW or LDB, the wave vectors of these beams are fixed at each frequency. Due to the fact that the amplitude of ultrasound beams changes very little over a couple of wavelengths, the interpolation in the depth direction was replaced with a phase shift. Results show that images reconstructed with the phase-shifting method removed the artifacts caused by aliasing when conventional tri-linear interpolations were used for 3D imaging.

High-frame-rate limited-diffraction beam imaging

Limited-diffraction beams such as Bessel beam, X wave, and array beam are a class of beams that in theory do not spread as they propagate to infinite distance. When realized with a finite aperture, these beams have a large depth of field. In this paper, limited-diffraction beams and their applications to high-frame rate imaging are reviewed and further studied. Using a limited-diffraction beams (in either transmission or reception, or both, or with spatial Fourier transform of received signals), images can be reconstructed in Fourier domain. This significantly reduces the amount of computation in 3D imaging since FFT can be used. As the bandwidth of the transducer is increased, the image reconstructed can cover a larger field of view since a frequency in limited-diffraction beam corresponds to one angular direction of the beam (similar to the “frequency encoding” in the magnetic resonance imaging or MRI). Using the angular dependence with frequency, focused limited-diffraction beams can be used for high-frame-rate and high-resolution tissue property imaging. When limited-diffraction beams are used in transmissions, no time delay (only amplitude weighting) is needed, which simplifies imaging system hardware. Also, flow vector imaging can be obtained with limited-diffraction beams using sine and cosine (quadrature) aperture weighting.

High-Frame-Rate Speckle Tracking for Echocardiographic Stress Testing.

Stress echocardiography helps to diagnose cardiac diseases that cannot easily be detected or do not even manifest at rest. In clinical practice, assessment of the stress test is usually performed visually and, therefore, in a qualitative and subjective way. Although speckle tracking echocardiography (STE) has been proposed for the quantification of function during stress, its time resolution is inadequate at high heart rates. Recently, high-frame-rate (HFR) imaging approaches have been proposed together with dedicated STE algorithms capable of handling small interframe displacements. The aim of this study was to determine if HFR STE is effective in assessing strain and strain rate parameters during echocardiographic stress testing. Specifically, stress echocardiography, at four different workload intensities, was performed in 25 healthy volunteers. At each stress level, HFR images from the apical four-chamber view were recorded using the ULA-OP 256 experimental scanner. Then, the myocardium was tracked with HFR STE, and strain and strain rate biomarkers were extracted to further analyze systolic and diastolic (early and late) peaks, as well as a short-lived isovolumic relaxation peak during stress testing. The global systolic strain response was monophasic, revealing a significant (p < 0.001) increase at low stress but then reaching a plateau. In contrast, all strain rate indices linearly increased (p < 0.001) with increasing stress level. These findings are in line with those reported using tissue Doppler imaging and, thus, indicate that HFR STE can be a useful tool in assessing cardiac function during stress echocardiography.

Measure and Analysis of Carbon Nanotube Diffusion in 3D

Measuring carbon nanotube diffusion is complex in 3D liquid environments. Single molecule fluorescence microscopy commonly provides nanotube trajectories in the 2D imaging plane with nanometer precisions but assessing the third dimension is more challenging task. To this aim, We will present two strategies based on point-spread function (PSF) engineering [1] or self-interfering PSF [2]. Because nanotubes are not spherical objects, 3D angular diffusion of the nanotubes shall also be considered. We will show that using a high-frame rate imaging (kHz) of nanotube movements, the autocorrelation time of nanotube fluorescence intensity can be computed in order to measure the rotational diffusion coefficient of the nanotubes. This further allows to estimate the length of the nanotubes either from the rotational diffusion coefficients alone, or by combining translational and rotational diffusion coefficients which has the advantage to avoid the requirement of knowing the solution viscosity or the SWCNT hydrodynamic diameter [3].

A Convolutional Neural Network for Ultrasound Plane Wave Image Segmentation With a Small Amount of Phase Array Channel Data.

Single-angle plane wave has a huge potential in ultrasound high frame rate imaging, which, however, has a number of difficulties, such as low imaging quality and poor segmentation results. To overcome these difficulties, an end-to-end convolutional neural network (CNN) structure from single-angle channel data was proposed to segment images in this article. The network removed the traditional beamforming process and used raw radio frequency (RF) data as input to directly obtain segmented image. The signal features at each depth were extracted and concatenated to obtain the feature map by a special depth signal extraction module, and the feature map was then put into the residual encoder and decoder to obtain the output. A simulated hypoechoic cysts dataset of 2000 and an actual industrial defect dataset of 900 were used for training separately. Good results have been achieved in both simulated medical cysts segmentation and actual industrial defects segmentation. Experiments were conducted on both datasets with phase array sparse element data as input, and segmentation results were obtained for both. On the whole, this work achieved better quality segmented images with shorter processing time from single-angle plane wave channel data using CNNs; compared with other methods, our network has been greatly improved in intersection over union (IOU), F1 score, and processing time. Also, it indicated that the feasibility of applying deep learning in image segmentation can be improved using phase array sparse element data as input.

High-precision velocity measurement method based on high frame rate image processing

The traditional drop-weight impact velocity measurement is affected by the measurement distance of the sensor and the measurement environment, and the accuracy is difficult to guarantee. Aiming at this problem, this paper proposes a high-precision velocity measurement method based on high frame rate image. Firstly, a measurement scheme based on high frame rate image is designed, the position information is obtained by processing the image of the marked point, and the target impact velocity is obtained according to the time difference between frames; Then an error model is established, and the sources of errors and solutions are analyzed; Then by improving the subpixel edge and other methods to improve the feature extraction accuracy of the marking point image, thereby improving the velocity measurement accuracy. Finally, the measurement accuracy is verified by the actual drop-weight free-fall experiment. The experimental results show that the method proposed in this paper is better than 0.5% in the measurement of the impact velocity of the drop weight, which meets the needs of practical applications, and the measuring process is visualized and traceable, which has high application value.

Reconstruction for plane-wave ultrasound imaging using modified U-Net-based beamformer.

An image reconstruction method that can simultaneously provide high image quality and frame rate is necessary for diagnosis on cardiovascular imaging but is challenging for plane-wave ultrasound imaging. To overcome this challenge, an end-to-end ultrasound image reconstruction method is proposed for reconstructing a high-resolution B-mode image from radio frequency (RF) data. A modified U-Net architecture that adopts EfficientNet-B5 and U-Net as the encoder and decoder parts, respectively, is proposed as a deep learning beamformer. The training data comprise pairs of pre-beamformed RF data generated from random scatterers with random amplitudes and corresponding high-resolution target data generated from coherent plane-wave compounding (CPWC). To evaluate the performance of the proposed beamforming model, simulation and experimental data are used for various beamformers, such as delay-and-sum (DAS), CPWC, and other deep learning beamformers, including U-Net and EfficientNet-B0. Compared with single plane-wave imaging with DAS, the proposed beamforming model reduces the lateral full width at half maximum by 35% for simulation and 29.6% for experimental data and improves the contrast-to-noise ratio and peak signal-to-noise ratio, respectively, by 6.3 and 9.97dB for simulation, 2.38 and 3.01dB for experimental data, and 3.18 and 1.03dB for in vivo data. Furthermore, the computational complexity of the proposed beamforming model is four times less than that of the U-Net beamformer. The study results demonstrate that the proposed ultrasound image reconstruction method employing a deep learning beamformer, trained by the RF data from scatterers, can reconstruct a high-resolution image with a high frame rate for single plane-wave ultrasound imaging.

Partial Hadamard encoded synthetic transmit aperture for high frame rate imaging with minimal l 2-norm least squares method

Objective. Synthetic transmit aperture (STA) ultrasound imaging is well known for ideal focusing in the full field of view. However, it suffers from low signal-to-noise ratio (SNR) and low frame rate, because each transducer element must be activated individually. In our previous study, we encoded all the transducer elements with partial Hadamard matrix and reconstructed the complete STA dataset with compressed sensing (CS) algorithm (CS-STA). As all the elements are activated in each transmission and the number of transmissions is smaller than that of STA, this method can achieve higher SNR and higher frame rate. Its main drawback is the time-consuming CS reconstruction (∼hours). In this study, we propose to accelerate the complete STA dataset reconstruction with minimal l 2-norm least squares method. Approach. Partial Hadamard apodized plane wave (PW) transmissions were performed to acquire the PW dataset. Thereafter, the complete STA dataset can be reconstructed from the PW dataset with minimal l 2-norm least squares method. Due to the orthogonality of partial Hadamard matrix, the minimal l 2-norm least squares solution can be easily calculated. Main results. The proposed method is tested with simulation data and experimental phantom and in-vivo data. The results demonstrate that the proposed method achieves ∼5 × 103 times faster reconstruction speed than CS algorithm. The simulation results demonstrate that the proposed method is capable of achieving the same accuracy as the conventional CS-STA method for the STA dataset reconstruction. The simulations, phantom and in-vivo experiments show that the proposed method is capable of improving the generalized contrast-to-noise ratio (gCNR) and SNR with maintained spatial resolution and fewer transmissions, compared with STA. Significance. In conclusion, the improved image quality and reduced computational time of LS-STA pave the way for its real-time applications in the clinics.

Crosstalk optimization of 5 MHz linear array transducer based on PZT/epoxy piezoelectric composite

Array ultrasonic transducers using electronic scanning method can obtain high frame rate and high-accuracy images compared with single-element transducers. However, for array transducers, crosstalk is a common problem and has bad influence on imaging quality. In this work, a 5 MHz linear array transducer with low crosstalk level is developed using PZT/epoxy piezoelectric composite. This PZT/epoxy composite has higher thickness electromechanical coupling coefficient (65.1%) and lower acoustic impedance (19.4 MRayls) compared with PZT ceramics. The influence of the width and depth of kerf on crosstalk is simulated by PZFlex software and the optimized kerf sizes are width 0.3 mm and depth 0.1 mm. The linear array transducer is fabricated according to the simulation results and the crosstalk level is measured. The experimental results are consistent with simulation and the transducer with this optimized kerf size has smaller crosstalk level (−24.1 dB). The central frequency and − 6 dB bandwidth of fabricated linear array transducer measured by impulse-echo response method are 4.82 MHz and 60.2% respectively. Compared with transducers made of PZT ceramic, this linear array transducer made of PZT/epoxy composite has wider bandwidth. The 5 MHz linear array transducer fabricated in this work has good acoustic performance and low crosstalk level and it is expected to obtain high-quality images in medical ultrasound imaging.

Tunable spatiotemporal resolution photoacoustic microscopy by combining quasi-periodic scanning and register-fusion algorithm

Quasi-periodic scanning combined with a register-fusion algorithm is proposed to realize tunable spatiotemporal resolution photoacoustic microscopy. Quasi-periodic scanning involves an irrational number ratio for the periods of scanning signals in two directions. It can provide sub-pixel spatial sampling for each frame. The proposed method can adjust the temporal and spatial resolutions by changing the data length for image reconstruction. For moving targets, the method can obtain a series of low-resolution images with a high imaging frame rate. A high-spatial-resolution image can be fused from these images using the register-fusion algorithm. The proposed method can acquire both motion and structural details of moving targets.

Working principle and relevant physical properties of the Swiss Liquid Jet Aesthesiometer for Corneal Sensitivity (SLACS) evaluation.

PurposeTo describe and evaluate relevant physical properties of the Swiss Liquid Jet Aesthesiometer for Corneal Sensitivity (SLACS) for ocular surface sensitivity measurement.MethodsCharacteristics of Liquid Jet (LJ) droplets (consisting of isotonic saline solution) were analysed: vertical and horizontal displacement and speed of LJ droplets were recorded with the aid of the High Speed Photron FASTCAM NOVA S6 camera (stimulus duration: 40 ms). Stimulus mass was assessed for 20 sets of 10 LJs with aid of a microbalance (pressure range of 100–1500 mbar).ResultsBecause continuous flow LJ disintegrated into droplets in the lower pressure range (<700 mbar), pulsed stimuli were applied in order to obtain similar stimulus characteristics across the applied pressure range. For all measurements, very little variability was observed. Vertical and horizontal displacement did not exceed 0.13 mm in either direction. The mass per shot showed an unexpected cubic dependency on pressure. Up to approximately 700 mbar, LJ speed showed an almost linear relationship. For the pressure range of >700–1500 mbar, variability increased and speed decreased compared to the expected in a linear manner. However, this may be caused by the difficulty of identifying pattern changes of LJ droplets from one high speed image frame to the next with increasing stimulus speed, when determining LJ speed via pixel count.ConclusionsSwiss Liquid Jet Aesthesiometer for Corneal Sensitivity was shown to deliver fine droplets with a pulsed stimulus mode, in a repeatable manner with precise localisation to the ocular surface. Very little variability was observed in LJ speed and mass for the typical pressure range required for clinical sensitivity measurements.

Detection of a diastolic heart sound in children and young adults using high-frame-rate echocardiography

Abstract Funding Acknowledgements Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Colin"s Kids, Inc. PO Box 93 Hopewell, NJ 08525 Introduction The auscultatory finding of a fourth heart sound (S4) is clinically associated with a pathologic decrease in left ventricular compliance, but may be seen in healthy children by phonocardiography. High-frame-rate difference imaging (HFRDI) has demonstrated several propagating myocardial phenomena in the left ventricular (LV) lateral wall throughout the cardiac cycle, including during diastole. We hypothesize that these visualized wave phenomena correlate with physiologic and pathologic heart sounds. Purpose Using HFRDI, we sought to define the characteristics of a LV lateral wall late diastolic wave in healthy children and young adults. Methods HFRDI was obtained from the apical 4-chamber view with synchronized electrocardiogram (ECG) on the T5 system (Phased Array Research Scanner) acquiring images for this study between 587 and 1174 frames per second (depending on participant imaging characteristics). In addition, tissue Doppler images were acquired with synchronized ECG and phonocardiography (PCG) on a commercial ultrasound machine (Figure 1). Timing events were measured from the QRS onset on the ECG tracing. An S4 wave correlate was defined by meeting the following criteria: 1) occurring after the P wave on ECG; 2) at or after the onset of a’ on TDI; 3) occurring during the PCG S4; and 4) occurring prior to the S1 wave complex. The timing of the S4 wave in HFRDI was measured from the onset of QRS to the first appearance of the wave, and the wave velocity was calculated by measuring the length of the lateral wall and counting temporally calibrated image frames while the wave was visible. Results Nine healthy volunteers completed the imaging protocol with a median age of 20 years (range 6 – 22 years). A single, distinct late diastolic HFRDI wave was seen in all participants propagating from apex to base of the lateral LV free wall. This wave met the defined criteria to be a visual correlate of S4 in all participants. Measurements of correlated events are presented in Table 1. S4 propagating velocity was 2.96 ± 1.8 m/sec and occurred 25 ± 18 msec prior to the QRS onset. There is a strong positive correlation between age and S4 velocity [r(7) = 0.76, p = 0.019]. Conclusion The S4 heart sound can be reliably visualized by high frame rate imaging and has similar characteristics in healthy children and young adults. Further definition of normal and abnormal S4 wave characteristics may lead to a novel tool in defining LV diastolic function. Abstract Table 1 Abstract Figure 1

An FPGA-Accelerated Parallel Digital Beamforming Core for Medical Ultrasound Sector Imaging.

Plane-wave transmission followed by parallel receive beamforming is popular among high frame rate (HFR) ultrasound (US) imaging methods. However, due to technological limitations, HFR imaging is not widely successful in clinical US. The proposed work aims to design a field-programmable gate array (FPGA)-accelerated parallel beamforming core for medical US sector imaging systems. This architecture supports up to 128 channels and forms 28 beams per plane wave transmission in parallel. A block random access memories (BRAMs)-based, 28-read one-write (28R1W) multi-ported delay line architecture is actualized to realize the delay line. In addition, to optimize the FPGA memory, the required beam focusing delays are stored in an external static random access memory (SRAM) and are loaded into the internal delay line registers by a cycle stealing direct memory access (DMA). The FPGA prototype validation and verification are performed on the custom-designed Xilinx-Kintex-7 XC7C410T FPGA-based US imaging platform. The results showed that for a field of view (FOV) of 90° with 0.5° resolution, 640×480 imaging size, a ft/s of 714 is achieved. The performance of the proposed parallel beamformer architecture is compared with existing development works and concluded that the architecture is superior due to its occupancy of FPGA hardware resources and the processing speed.

Moving Target Detection Using GNSS-Based Passive Bistatic Radar

GNSS (global navigation satellite system)-based passive bi-static radar (PBR) has many advantages benefiting from the bi-static configuration and the excellent properties of the GNSS signals. In this paper, the possibility of moving target indication (MTI) using a GNSS-based PBR is analyzed and illustrated by experiments. The power budget is firstly evaluated to investigate the capabilities and limitations of the GNSS-based PBR. Due to the low power density of GNSS signals, long-time integration is required to achieve long-range surveillance. In our previous work, a Radon Fourier Transform (RFT)-based long-time integration algorithm has been proposed for GNSS-based PBR. However, the RFT-based methods are computationally inefficient. In this paper, a novel MTI algorithm based on high frame rate image sequence (HFRIS) is introduced to the GNSS-based PBR. Benefiting from the avoiding of the iterative multi-dimensional parameter searching, it has a higher computational efficiency than the RFT-based methods. At the same time, the possibility of multi-static positioning for moving targets using the GNSS-based PBR is analyzed. It is shown that the absolute position of the target in three dimensions could be determined if at least 3 satellites are utilized to measure the range delay of the target return. To confirm our analysis, experiments are conducted which detects the airplanes using the GPS signals as illuminators of opportunity. The collected data are processed by both the RFT-based method and the HFRIS-based method. Both methods have successfully detected the airplane target at a distance of about 5km, and the HFRIS-based method shows a far better performance in terms of processing efficiency. The multi-static positioning experiment is also conducted, and the estimated position of the target is well consistent with the values acquired by the flight record, which shows the potential of the GNSS-based PBR on multi-static operations.

Three-Dimensional Shear Wave Elastography Using a 2D Row Column Addressing (RCA) Array.

Objective. To develop a 3D shear wave elastography (SWE) technique using a 2D row column addressing (RCA) array, with either external vibration or acoustic radiation force (ARF) as the shear wave source. Impact Statement. The proposed method paves the way for clinical translation of 3D SWE based on the 2D RCA, providing a low-cost and high volume rate solution that is compatible with existing clinical systems. Introduction. SWE is an established ultrasound imaging modality that provides a direct and quantitative assessment of tissue stiffness, which is significant for a wide range of clinical applications including cancer and liver fibrosis. SWE requires high frame rate imaging for robust shear wave tracking. Due to the technical challenges associated with high volume rate imaging in 3D, current SWE techniques are typically confined to 2D. Advancing SWE from 2D to 3D is significant because of the heterogeneous nature of tissue, which demands 3D imaging for accurate and comprehensive evaluation. Methods. A 3D SWE method using a RCA array was developed with a volume rate up to 2000 Hz. The performance of the proposed method was systematically evaluated on tissue-mimicking elasticity phantoms and in an in vivo case study. Results. 3D shear wave motion induced by either external vibration or ARF was successfully detected with the proposed method. Robust 3D shear wave speed maps were reconstructed for phantoms and in vivo. Conclusion. The high volume rate 3D imaging provided by the 2D RCA array provides a robust and practical solution for 3D SWE with a clear pathway for future clinical translation.