Doppler Angle Research Articles

Increasing the Maximum Detectable Flow Velocity in High-Frequency Ultrasound Vector Doppler Imaging.

High-frequency ultrasound (HFUS; >30 MHz) Doppler imaging has been widely used in the imaging of small animals and humans because of its high resolution. Vector Doppler imaging (VDI) has certain advantages for visualizing complex flow patterns independent of the Doppler angle. However, no commercial HFUS VDI system is currently available; therefore, several studies have connected an ultrasound research platform (Verasonics Vantage 256) with an HFUS array transducer for HFUS VDI. Unfortunately, the maximum frame rate of this system is only 10 kHz at an operational frequency of 40 MHz because of limitations related to data transmission hardware, thereby restricting the maximum detectable velocity of Doppler measurements. To address this drawback, in the present study, an electrocardiography (ECG)-gating-based HFUS VDI system was developed to avoid Doppler flow aliasing in data acquisition by ultrasound research platform at its maximum frame rate of 10 kHz. The developed method aligns all tilted plane waves with the ECG R-wave, which avoids the trade-off between frame rate and tilted angles number in conventional VDI. The performance of the proposed data acquisition method in HFUS VDI was verified using a steady-flow phantom, for which estimation errors were less than 10% under different flow settings. In animal studies, peak flow velocities in the carotid artery, left ventricle, and aortic arch of wild-type mice were measured (approximately 55, 655, and 765 mm/s, respectively). Also, the HFUS VDI from the mitral regurgitation mice model was obtained to present the complex flow patterns through the proposed method. In contrast to the conventional method, no Doppler aliasing occurs in the proposed method because the frame rate is sufficient. The experimental results indicate the developed HFUS VDI has the potential to become a useful tool for vector flow visualization in small animals, even under a high flow velocity.

Measurement of transcranial Doppler insonation angles from three-dimensional reconstructions of CT angiography scans.

Blood velocities measured by Transcranial Doppler (TCD) are dependent on the angle between the incident ultrasound beam and the direction of blood flow (known as the Doppler angle). However, when TCD examinations are performed without imaging the Doppler angle for each vessel segment is not known. We have measured Doppler angles in the basal cerebral arteries examined with TCD using three-dimensional (3D) vessel models generated from computed tomography angiography (CTA) scans. This approach produces angle statistics that are not accessible during non-imaging TCD studies. We created 3D models of the basal cerebral arteries for 24 vasospasm patients. Standard acoustic windows were mapped to the specific anatomy of each patient. Virtual ultrasound transmit beams were generated that originated from the acoustic window and intersected the centerline of each arterial segment. Doppler angle measurements were calculated and compiled for each vessel segment. Doppler angles were smallest for the middle cerebral artery M1 segment (median 24.6°) and ophthalmic artery (median 25.0°), and largest for the anterior cerebral artery A2 segment (median 76.4°) and posterior cerebral artery P2 segment (median 75.8°). The ophthalmic artery had the highest proportion of Doppler angles that were less than 60° (99%) while the anterior cerebral artery A2 segment had the lowest proportion of Doppler angles that were less than 60° (10%). These angle measurements indicate the expected deviation between measured and true velocities in the cerebral arteries, highlighting specific segments that may be prone to underestimation of velocity.

Photonic scheme for the simultaneous measurement of Doppler frequency shift and angle of arrival based on optical frequency shift heterodyne and power mapping.

A photonic-assisted scheme based on optical frequency shift heterodyne and low-frequency power mapping is proposed and experimentally demonstrated to measure the Doppler frequency shift (DFS) and Angle-of-arrival (AOA) of the microwave signals. In the proposed system, the optical signal is divided into two paths. The upper optical signal is injected into a dual-drive Mach-Zehnder modulator (DDMZM) and modulated by the two echo signals with a phase difference. The lower path optical signal is frequency-shifted by an acousto-optic modulator (AOM) and then modulated by the transmitted signal via a Mach-Zehnder modulator (MZM). After an optical filter, the two first-order sideband optical signals heterodyne in the photodetector. The DFS without direction ambiguity and AOA are mapped to the frequency shift and power of the low-frequency microwave signal. By adjusting the DC bias of the DDMZM, two power-phase mapping curves are obtained to eliminate phase ambiguity in AOA measurement. The measurement accuracy is enhanced by adjusting the identity of the two power mapping curves in different measurement ranges. A proof-of-concept experiment demonstrates a DFS measurement at 20 GHz with errors less than ± 8 Hz in the range of ±100 kHz and an AOA measurement from -62.5° to 62.5° with no more than ±2.5° errors.

Predominant determinants for evaluation of right parasternal approach in transthoracic echocardiography in aortic stenosis: a study based on three-dimensional cardiac computed tomography analysis.

The maximum blood flow velocity through the aortic valve (AVmax) using Doppler transthoracic echocardiography (TTE) is important in assessing the severity of aortic stenosis (AS). The right parasternal (RP) approach has been reported to be more useful than the apical approach, but the anatomical rationale has not been studied. We aimed to clarify the influence of the angle formed by the ascending aorta and left ventricle on Doppler analysis by TTE (Sep-Ao angle) and three-dimensional multidetector computed tomography (3D-MDCT) in patients with AS. A total of 151 patients evaluated using the RP approach and 3D-MDCT were included in this study. The Sep-Ao angle determined using TTE was compared with that determined using 3D-MDCT analysis. In MDCT analysis, the left ventricular (LV) axis was measured in two ways and the calcification score was calculated simultaneously. The Sep-Ao angle on TTE was consistent with that measured using 3D-MDCT. In patients with an acute Sep-Ao angle, the Doppler angle in the apical approach was larger, potentially underestimating AVmax. Multivariate analysis revealed that an acute Sep-Ao angle, large Doppler angle in the apical approach, smaller Doppler angle in the RP approach, and low aortic valve calcification were independently associated with a higher AVmax in the RP approach than in the apical approach. The Sep-Ao angle measured using TTE reflected the 3D anatomical angle. In addition to measurements using the RP approach, technical adjustments to minimize the Doppler angle to avoid bulky calcification should always be noted for accurate assessment.

Technical Note: Impact of Linear Array Transducer Doppler Aperture Location on Spectral Peak Velocity Measurements - A Phantom Study

ObjectiveUltrasound beams sometimes need to be steered from the edge of linear array transducers to reach the sample volume with a desired Doppler angle in vascular exams. This phantom study aims to evaluate the impact of apertures located at the array edge on peak velocity (PV) measurements. MethodsThree ultrasound scanner systems equipped with eight transducers from 3 major ultrasound vendors were tested using a flow phantom with a horizontal tube. Five spectral Doppler measurements with the aperture positioned at one edge of the array and 5 with the aperture at the center of the array were obtained using all available scanner-transducer combinations while maintaining all scan parameters and the sample volume in the same tube location. Differences in PVs between center and edge apertures were compared across 4 constant flow rates. ResultsThe averaged PVs for all phantom flow rates ranged from 24.4 cm/s to 138.2 cm/s from the array center. The averaged PVs from the center aperture were significantly greater than the corresponding measurements from the edge aperture for each flow rate (all p < 0.001). The relative PV differences ranged from 6.7% to 19.4% across all transducers and flow rates. ConclusionSignificantly lower PVs were consistently shown with the Doppler beam aperture at the array edge compared to center among all tested systems. This may be due to a narrower aperture width, shifted central axis, and less intrinsic spectral broadening error at the array edge. Controlling variations in Doppler aperture location is important in clinical applications which depend on consistent velocity measurements.

Photonic architecture for remote multi-parameter measurement and transmission of microwave signals

A photonic architecture for remote multi-parameter measurement and transmission of microwave signals is proposed and demonstrated, which utilizes a dual-parallel dual-drive Mach-Zehnder modulator (DP-DDMZM) in the antenna unit and a dual-drive Mach-Zehnder modulator (DDMZM) in the processing unit. Doppler frequency shift (DFS) and angle of arrival (AOA) can be determined by analyzing the down-converted intermediate frequency signals. Introducing a reference signal in the processing unit ensures DFS measurement without directional ambiguity. The proposed architecture can also be applied for instantaneous frequency measurement based on down-conversion. Due to the use of optical single sideband modulation, long-distance transmission of radio frequency (RF) signals without dispersion-induced power fading can be achieved. Experiments for accurate and stable DFS and AOA measurement as well as long-distance RF signal transmission with dispersion-induced power fading are presented. The approach avoids the use of optical filters and polarization-related devices, facilitating wideband and stable operation, which is highly desirable. The proposed architecture is a potential solution for microwave photonic antenna remoting, offering support for both remote transmission and multi-parameter measurement.

Simple DFS and AOA simultaneous measurement scheme without directional ambiguity with co-frequency self-interference signal cancellation

A photonic method based on a dual-polarization dual-parallel Mach–Zehnder modulator (DPol-DPMZM) for the simultaneous measurement of the Doppler frequency shift (DFS) and angle of arrival (AOA) of microwave signals is proposed and demonstrated by simulation. The upper arm of each sub-DPMZM is driven by the echo and self-interference signals from the antenna, while the lower arm is driven by the reference signal 1 and reference signal 2. The phase and amplitude of the reference signal 1 are adjusted to match the interference signals for achieving the self-interference cancellation (SIC). At the central office (CO), the DFS and AOA can be acquired in real time without directional ambiguity by processing the two downconverted low-frequency tones in the photocurrent. The simulation results show that the presence of the SI signal will seriously interfere with the observation of the SOI frequency and waveform, and the self-interference cancellation depth of about 42 dB can be obtained after the SIC. The measurement errors of the DFS without direction ambiguity are within 0.2 Hz. After the Hilbert transformation of the intermediate frequency (IF) signal, the AOA can be measured from −87.31∘ to +87.31∘ with errors less than 3.9°. The system has a large bandwidth, excellent real-time performance, and better invisibility, and is expected to be used in modern electronic warfare systems.

A High-Precision Positioning Method for Autonomous Underwater Vehicles with Communication Delays

In underwater navigation of autonomous underwater vehicles (AUVs), communication delays frequently occur, leading to a reduction in positioning accuracy. To mitigate this challenge, this work introduces a novel method for relative angle correction, aiming to reconstruct measurement information. Initially, Doppler measurement data are assimilated into the reconstruction of measurement equations to determine the relative angle between the AUV and the observatory. Subsequently, the obtained angle information is integrated into the Extended Kalman Filter (EKF) for the reconstruction of measurement equations. The proposed method effectively reduces positioning errors caused by hydroacoustic communication delays, consequently enhancing AUV positioning accuracy. The efficacy of the proposed method is demonstrated through a simulation study. Simulation results reveal that the incorporation of Doppler angle correction in the reconstructed measurement information method significantly decreases the localization error by approximately 50% compared to EKF and by around 20% compared to the method lacking angle correction.

Wideband Anti-Interference Microwave Photonic Measurement for Doppler Frequency Shift and Angle of Arrival

Wideband Anti-Interference Microwave Photonic Measurement for Doppler Frequency Shift and Angle of Arrival

European Carotid Surgical Trial-based diameter measurement using B-mode ultrasound imaging to quantify low-grade carotid artery stenosis: the QUAMUS study

BackgroundIdentification of carotid atherosclerotic lesions with no hemodynamic effect on Doppler ultrasound examination is a common situation. Although the use of B-mode ultrasound examination has been recommended to assess this type of lesion, there is no validated examination procedure to date for quantifying low-grade carotid stenosis. MethodsWe conducted a single-center prospective study (QUAntification Morphologique en UltraSonographie [QUAMUS] study) to assess the reproducibility of B-mode ultrasound quantification of low-grade internal carotid artery stenosis using the European Carotid Surgical Trial (ECST) measurement method. We included consecutive patients with <50% North American Symptomatic Carotid Endarterectomy Trial carotid stenosis identified by the University of Washington duplex criteria (ie, maximum systolic velocity of <125 cm/second at a Doppler angle of 50°-60°). The examination was carried out and interpreted independently, blindly, and successively by two operators according to a precise methodology based on the measurement of cross-sectional diameter in B-mode and calculation of the stenosis percentage according to the ECST method. The primary objective was to assess the measurement concordance of the stenosis percentage for a difference not exceeding 10% between the two operators. The secondary objective was to assess concordance in relation to examination quality. ResultsAmong the 86 patients included, 159 atherosclerotic carotid arteries were eligible and 157 could be explored (feasibility of 98.74%). The conditions were considered as good by the two operators in 69.43% of cases and poor in 2.55%. The concordance of the stenosis percentage measurement for a maximum difference of 10% between the two operators was 89.17% (95% confidence interval, 83.23-93.56) with a Lin concordance correlation coefficient of 0.87 (95% confidence interval, 0.82-0.90). Under examination conditions estimated as good, average, and poor, the concordance was 95.37%, 78.95%, and 60.00%, respectively. ConclusionsOur study shows that ECST-based B-mode ultrasound measurement of low-grade carotid stenosis is reliable and can be performed in routine practice in most patients with a measurement variation of <10% using a simple standardized examination procedure.

Photonic Measurement for Doppler Frequency Shift and Angle of Arrival Based on Integrated Dual-Parallel Dual-Drive Modulator

A microwave photonic Doppler frequency shift (DFS) and angle of arrival (AOA) measurement method based on a dual-parallel dual-drive Mach–Zehnder modulator (DP-DDMZM) is proposed and demonstrated. A sawtooth wave signal is used to drive the DC port of the modulator to realize the optical frequency shift, and thus the direction discrimination of DFS is realized. Due to single-sideband modulation, the proposed system can avoid periodic power fading and the separation of the remote antenna unit (RAU) and central office (CO) can be achieved. In the experiment, the microwave DFS is estimated with a clear direction and a maximum measurement error of 0.25 Hz over an ultrawide operation frequency from 6 to 36 GHz. The experiment also proves that the phase error of AOA measurement is less than 1.5 degrees. Compared with the traditional electronic microwave measurement scheme, the proposed scheme has great competitive advantages in future broadband electronic applications due to the features of multifunction, large bandwidth and anti-interference.

Association between resistivity index of central retinal artery and severity of diabetic retinopathy.

Diabetic retinopathy (DR) is a leading cause of ocular morbidity. Its progression depends mainly on retinal vasculature and ocular blood flow. Color Doppler imaging (CDI) is a noninvasive imaging technique that measures blood flow velocity. The resistivity index (RI), calculated by the CDI, reflects the vascular resistance distal to the measuring location. RI is independent of the doppler angle and position of the patient, making it a reliable and reproducible parameter. To the best of our knowledge, there is only one study in literature studying the association between resistivity index (RI) of the central retinal artery (CRA) and severity of DR. To determine the association between RI of CRA and severity of DR. To determine the association between RI of CRA and spectral-domain optical coherence tomography (SD-OCT) biomarkers for DR. Type II diabetics visiting our OPD underwent DR screening and were graded into three categories according to ETDRS classification which include Group A-No diabetic retinopathy (No DR), Group B-Nonproliferative diabetic retinopathy (Moderate-Severe-Very Severe NPDR), and Group C-Proliferative diabetic retinopathy (PDR). SD-OCT was performed. Ultrasonic color doppler imaging was done. RI of the CRA was noted. It was compared between the three groups and its association with severity of DR and OCT biomarkers (central subfield thickness, cube average thickness and ellipsoid zone disruption) was studied. 56 eyes of 28 patients were included in our study with 20 in Group A,14 in Group B, and 22 in Group C. RI of CRA compared within groups showed statistically significant association with severity of DR (P < 0.001). The presenting BCVA (LogMar) showed positive correlation with RI in all groups. OCT biomarker central subfield thickness showed a positive correlation with RI in Groups A (P < 0.001) and B. Ellipsoid zone (EZ) disruption showed a statistically significant association with RI in Group C (P < 0.001). The RI of CRA is a reliable biomarker for the assessment of the severity of DR. Patients with high RI of CRA had higher chances of EZ disruption and presented with poor visual acuity.

Utility of renal resistive index measurement in juvenile systemic lupus erythematosus: a cross-sectional single-center study.

Systemic lupus erythematosus (SLE) is a multisystemic autoimmune disease with a complex etiopathogenesis. Renal involvement is the most common and devastating complication of the disease. Renal resistive index (RRI) was suggested as a noninvasive biomarker for lupus nephritis in previous studies. This is the first study to investigate the role of RRI measurement in juvenile SLE patients. This cross-sectional study included 25 juvenile SLE patients and 25 healthy controls. Demographic and clinical features were recruited from the medical files of the patients. RRI measurements were performed with color Doppler ultrasonography from intrarenal arteries when Doppler angles were 30-60 in right and left kidneys. Of 25 (19 female, 6 male) SLE patients, nineteen (76%) patients had urinary abnormalities during follow-up, and renal biopsy was performed in 14 patients, of which 9 (64.3%) had class 2 and 5 (35.7%) had class 4 lupus nephritis. RRI was found significantly higher in SLE group than healthy controls. RRI did not differ between SLE patients, grouped according to the presence of renal involvement and class IV lupus nephritis. RRI did not correlate with serum creatinine, GFR, spot urine protein/creatinine, and albumin/creatinine ratio. Although RRI was found significantly higher in juvenile SLE, it is not affected by GFR, proteinuria level, or the renal biopsy results, even the presence of proliferative nephritis. The underlying pathogenetic mechanisms of increased RRI in SLE should be clarified in further studies. Key Points • Renal resistive index (RRI) is a parameter derived from renal Doppler ultrasound imaging and shows the intrarenal arterial resistance. • This study reveals that RRI is increased in juvenile systemic lupus erythematosus. • RRI was previously related with renal involvement, particularly class 4 lupus nephritis in adults. However, RRI was not affected by the presence or degree of renal involvement in juvenile SLE patients in our study.

Photonic system for Doppler-frequency-shift and Angle-of-arrival simultaneous measurement using dual-parallel Mach–Zehnder modulator

A simple photonic system is proposed to measure the Doppler frequency shift (DFS) and Angle of arrival (AOA) of microwave signals simultaneously. The echo signals received by the two antennas are fed into two sub-MZM of a dual-parallel Mach–Zehnder modulator (DPMZM) respectively, and the reference signals are sent into one of the sub-MZM. The introduction of reference signals makes it easier to determine the direction of DFS. After the reference signal and echo signal pass through the low-speed PD, the beating signal is obtained. The value and direction of the DFS can be derived from the frequency of the down-converted signal. And the measurement of AOA can be calculated from the power of the output signal. The experimental results show that the echo signal measurement errors of DFS are less than ±0.5 Hz in the operating frequency range of 20 GHz, and the power sensitivity is less than -40 dBm. AOA has measurement errors of less than ±1.5° in the range of 0 to 90°. In addition, by adding only one test branch, the system can achieve the unambiguous measurement of AOA in the range of ±90°.

Photonics-Based Simultaneous DFS and AOA Measurement System without Direction Ambiguity

A novel scheme that can simultaneously measure the Doppler frequency shift (DFS) and angle of arrival (AOA) of microwave signals based on a single photonic system is proposed. At the signal receiving unit (SRU), two echo signals and the reference signal are modulated by a Sagnac loop structure and sent to the central station (CS) for processing. At the CS, two low-frequency electrical signals are generated after polarization control and photoelectric conversion. The DFS without direction ambiguity and wide AOA measurement can be real-time acquired by monitoring the frequency and power of the two low-frequency electrical signals. In the simulation, an unambiguous DFS measurement with errors of ±3 × 10-3 Hz and a -90° to 90° AOA measurement range with errors of less than ±0.5° are successfully realized simultaneously. It is compact and cost-effective, as well as has enhanced system stability and improved robustness for modern electronic warfare systems.

Simultaneous and unambiguous identification of DFS and AOA without dependence on echo signal power.

We present a photonics-based method of estimating Doppler frequency shift (DFS) and angle of arrival (AOA). The proposed identification method for the DFS and AOA is simultaneous and unambiguous. A reference radio frequency signal is introduced to realize the frequency downconversion. By monitoring the frequency of the downconverted signals generated after the photodetection, the direction ambiguity of the DFS is canceled out. The AOA can be instantaneously calculated through two downconverted signals via a Hilbert transform. Experimental results verify that a -77.90° to 77.90° AOA measurement with errors of less than ±1° is implemented, and a DFS measurement with errors of no more than ±3.1 Hz is also realized. Our proposed method not only removes the direction ambiguities of both DFS and AOA, but also avoids the dependence on echo signal power in AOA measurement, which largely increases the feasibility in realistic applications.

Sub-diffusion flow velocimetry with number fluctuation optical coherence tomography.

We have implemented number fluctuation dynamic light scattering optical coherence tomography (OCT) for measuring extremely slow, sub-diffusion flows of dilute particle suspensions using the second-order autocovariance function. Our method has a lower minimum measurable velocity than conventional correlation-based OCT or phase-resolved Doppler OCT, as the velocity estimation is not affected by the particle diffusion. Similar to non-dilute correlation-based OCT, our technique works for any Doppler angle. With our analysis we can quantitatively determine the concentration of particles under flow. Finally, we demonstrate 2D sub-diffusion flow imaging with a scanning OCT system at high rate by performing number fluctuation correlation analysis on subsequent B-scans.

A Simple Photonic System for DFS and AOA Simultaneous Measurement

A simple photonics-based dual-channel system is proposed to simultaneously measure the Doppler frequency shift (DFS) and angle of arrival (AOA) of microwave signals. The system applies two parallel push–pull Mach–Zehnder modulators (MZMs) for carrier suppression dual-sideband (CS-DSB) modulation. The introduction of the reference signal results in a DFS measurement without direction ambiguity. The DFS can be determined by measuring the frequency of the down-converted intermediate frequency (IF) signal, and the AOA can be calculated by comparing the phase shift of the two channels. A proof-of-concept experiment shows that the DFS measurement error is less than 0.4 Hz during ±100 kHz, and the AOA measurement error is within 1.5° in a range of 0–70°.

MmGesture: Semi-supervised gesture recognition system using mmWave radar

Gesture recognition has found versatile applications in natural human–computer interaction (HCI). Compared with traditional camera-based or wearable sensors-based solutions, gesture recognition using the millimeter wave (mmWave) radar has attracted growing attention for its characteristics of contact-free, privacy-preserving and less environment-dependence. Recently, most of studies adopted one of the Range Doppler Image (RDI), Range Angle Image (RAI), Doppler Angle Image (DAI) or Micro-Doppler Spectrogram extracted from the raw radar signal as the input of a deep neural network to realize gesture recognition. However, the effectiveness of these four inputs in gesture recognition has attracted little attention so far. Moreover, the lack of large amounts of labeled data restricts the performance of traditional supervised learning network. In this paper, we first conducted extensive experiments to compare the effectiveness of these four inputs in the gesture recognition, respectively. Then we proposed a semi-supervised leaning framework by utilizing few labeled data in the source domain and large amounts of unlabeled data in the target domain. Specially, we combine the ∏-model and some specific data augmentation tricks on the mmWave signal to realize the domain-independent gesture recognition. Extensive experiments on a public mmWave gesture dataset demonstrate the superior effectiveness of the proposed system.

Photonic Measurement for Doppler Frequency Shift and Angle of Arrival Based on a Dual-Polarization Dual-Drive Mach–Zehnder Modulator

A novel photonic-assisted system for realizing the simultaneous measurement of Doppler frequency shift (DFS) and angle of arrival (AOA) is proposed. It is a simplified structure that is based on a dual-polarization dual-drive Mach–Zehnder modulator (DPol-DDMZM). The DFS direction can be accurately determined by comparing the phase relationship between the upper and lower low-frequency signal waveforms. An amplitude comparison function (ACF), which constructs a one-to-one mapping between the power ratio and the phase difference of echo microwave signals, can reduce the AOA measurement errors. The simulation results show that the simulated ACFs agree well with the theoretical ACFs, and the measurement errors of AOA are less than ±2.8° in a range of 0° to 78°. Moreover, the DFS can be realized by analyzing the spectrum of the low-frequency electrical signal with a measurement error of less than ±0.05 Hz. The system structure is compact and cost-effective, which provides an alternative solution for modern radar and electronic warfare receivers.