The Experts below are selected from a list of 6309 Experts worldwide ranked by ideXlab platform
Jørgen Arendt Jensen - One of the best experts on this subject based on the ideXlab platform.
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volumetric 3 d vector flow measurements using a 62 62 row column addressed array
Internaltional Ultrasonics Symposium, 2017Co-Authors: Simon Holbek, Matthias Bo Stuart, Jørgen Arendt JensenAbstract:Experimental results from volumetric 3-D vector flow measurements using a 62+62 row-column addressed (RCA) array are presented. A plane-by-plane steered transmit sequence and its post processing steps are described for obtaining 3-D vector flow in a volume. A modified version of the Transverse Oscillation (TO) velocity estimator is used, which exploits the focal lines generated with the tall elements of a RCA array. Validation of the method is made in a flow-rig system where circulating blood mimicking fluid produced a steady parabolic flow profile with a flow rate of 13.7 mL/s, translating to a peak velocity of 24.1 cm/s. A volume rate of 16.4 volumes per second is obtained, and estimated flow rates based on nine steered planes within the volume are investigated. A positive bias is found for all investigated planes lying in the range from 6.5% to 21.2% with the standard deviation being less than 4% for all cases. It is concluded that volumetric 3-D vector flow estimation is feasible with an RCA array with only 124 elements.
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fast plane wave 2 d vector flow imaging using Transverse Oscillation and directional beamforming
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2017Co-Authors: Jonas Kjaer Jensen, Matthias Bo Stuart, Michael Bachmann Nielsen, Carlos Armando Villagomez Hoyos, Caroline Ewertsen, Jørgen Arendt JensenAbstract:Several techniques can estimate the 2-D velocity vector in ultrasound. Directional beamforming (DB) estimates blood flow velocities with a higher precision and accuracy than Transverse Oscillation (TO), but at the cost of a high beamforming load when estimating the flow angle. In this paper, it is proposed to use TO to estimate an initial flow angle, which is then refined in a DB step. Velocity magnitude is estimated along the flow direction using cross correlation. It is shown that the suggested TO-DB method can improve the performance of velocity estimates compared with TO, and with a beamforming load, which is 4.6 times larger than for TO and seven times smaller than for conventional DB. Steered plane wave transmissions are employed for high frame rate imaging, and parabolic flow with a peak velocity of 0.5 m/s is simulated in straight vessels at beam-to-flow angles from 45° to 90°. The TO-DB method estimates the angle with a bias and standard deviation (SD) less than 2°, and the SD of the velocity magnitude is less than 2%. When using only TO, the SD of the angle ranges from 2° to 17° and for the velocity magnitude up to 7%. Bias of the velocity magnitude is within 2% for TO and slightly larger but within 4% for TO-DB. The same trends are observed in measurements although with a slightly larger bias. Simulations of realistic flow in a carotid bifurcation model provide visualization of complex flow, and the spread of velocity magnitude estimates is 7.1 cm/s for TO-DB, while it is 11.8 cm/s using only TO. However, velocities for TO-DB are underestimated at peak systole as indicated by a regression value of 0.97 for TO and 0.85 for TO-DB. An in vivo scanning of the carotid bifurcation is used for vector velocity estimations using TO and TO-DB. The SD of the velocity profile over a cardiac cycle is 4.2% for TO and 3.2% for TO-DB.
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Directional Transverse Oscillation Vector Flow Estimation
IEEE transactions on ultrasonics ferroelectrics and frequency control, 2017Co-Authors: Jørgen Arendt JensenAbstract:A method for estimating vector velocities using Transverse Oscillation (TO) combined with directional beamforming is presented. In directional TO (DTO), a normal focused field is emitted and the received signals are beamformed in the lateral direction Transverse to the ultrasound beam to increase the amount of data for vector velocity estimation. The approach is self-calibrating as the lateral Oscillation period is estimated from the directional signal through a Fourier transform to yield quantitative velocity results over a large range of depths. The approach was extensively simulated using Field IIpro and implemented on the experimental Synthetic Aperture Real-time Ultrasound System (SARUS) scanner in connection with a BK Medical 8820e convex array transducer. Velocity estimates for DTO are found for beam-to-flow angles of 60°, 75°, and 90°, and vessel depths from 24 to 156 mm. Using 16 emissions, the standard deviation (SD) for angle estimation at depths ranging from 24 to 104 mm is between 6.01° and 0.93° with a mean SD of 2.8°. The mean relative SD for the lateral velocity component is 9.2% and the mean relative bias −3.4% or four times lower than for traditional TO. The approach also works for deeper lying vessels with a slight increase in SD to 15.7%, but a maintained bias of −3.5% from 126 to 156 mm. Data for a pulsating flow have also been acquired for 15 cardiac cycles using a CompuFlow 1000 pump. The relative SD was here 7.4% for a femoral artery waveform.
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experimental 3 d vector velocity estimation with row column addressed arrays
Internaltional Ultrasonics Symposium, 2016Co-Authors: Simon Holbek, Matthias Bo Stuart, Jørgen Arendt JensenAbstract:Experimental 3-D vector flow estimates obtained with a 62+62 2-D row-column (RC) array with integrated apodization are presented. A Transverse Oscillation (TO) velocity estimator is implemented on a 3.0 MHz RC array, to yield real-time 3-D vector flow in a cross-sectional scan plane at 750 frames per second. The method is validated in a straight-vessel phantom (O = 8 mm) connected to a flow pump capable of generating time-varying carotid waveforms. The out-of-plane velocity component perpendicular to the cross section of the vessel and the cross-sectional area is used to estimate volumetric flow rates. The flow rate measured from five cycles is 2.3 mL/stroke ± 0.1 mL/stroke giving a negative 9.7% bias compared to the pump settings. It is concluded that 124 elements are sufficient to estimate 3-D vector flow, if they are positioned in a row-column wise manner.
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blood flow velocity in the popliteal vein using Transverse Oscillation ultrasound
Proceedings of SPIE, 2016Co-Authors: Thor Bechsgaard, Andreas Hjelm Brandt, Michael Bachmann Nielsen, Kristoffer Lindskov Hansen, Simon Holbek, Lars Lonn, Charlotte Strandberg, Niels Baekgaard, Jørgen Arendt JensenAbstract:Chronic venous disease is a common condition leading to varicose veins, leg edema, post-thrombotic syndrome and venous ulcerations. Ultrasound (US) is the main modality for examination of venous disease. Color Doppler and occasionally spectral Doppler US (SDUS) are used for evaluation of the venous flow. Peak velocities measured by SDUS are rarely used in a clinical setting for evaluating chronic venous disease due to inadequate reproducibility mainly caused by the angle dependency of the estimate. However, estimations of blood velocities are of importance in characterizing venous disease. Transverse Oscillation US (TOUS), a non-invasive angle independent method, has been implemented on a commercial scanner. TOUS's advantage compared to SDUS is a more elaborate visualization of complex flow. The aim of this study was to evaluate, whether TOUS perform equal to SDUS for recording velocities in the veins of the lower limbs. Four volunteers were recruited for the study. A standardized flow was provoked with a cuff compression-decompression system placed around the lower leg. The average peak velocity in the popliteal vein of the four volunteers was 151.5 cm/s for SDUS and 105.9 cm/s for TOUS (p <0.001). The average of the peak velocity standard deviations (SD) were 17.0 cm/s for SDUS and 13.1 cm/s for TOUS (p <0.005). The study indicates that TOUS estimates lower peak velocity with improved SD when compared to SDUS. TOUS may be a tool for evaluation of venous disease providing quantitative measures for the evaluation of venous blood flow.
Michael Bachmann Nielsen - One of the best experts on this subject based on the ideXlab platform.
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fast plane wave 2 d vector flow imaging using Transverse Oscillation and directional beamforming
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2017Co-Authors: Jonas Kjaer Jensen, Matthias Bo Stuart, Michael Bachmann Nielsen, Carlos Armando Villagomez Hoyos, Caroline Ewertsen, Jørgen Arendt JensenAbstract:Several techniques can estimate the 2-D velocity vector in ultrasound. Directional beamforming (DB) estimates blood flow velocities with a higher precision and accuracy than Transverse Oscillation (TO), but at the cost of a high beamforming load when estimating the flow angle. In this paper, it is proposed to use TO to estimate an initial flow angle, which is then refined in a DB step. Velocity magnitude is estimated along the flow direction using cross correlation. It is shown that the suggested TO-DB method can improve the performance of velocity estimates compared with TO, and with a beamforming load, which is 4.6 times larger than for TO and seven times smaller than for conventional DB. Steered plane wave transmissions are employed for high frame rate imaging, and parabolic flow with a peak velocity of 0.5 m/s is simulated in straight vessels at beam-to-flow angles from 45° to 90°. The TO-DB method estimates the angle with a bias and standard deviation (SD) less than 2°, and the SD of the velocity magnitude is less than 2%. When using only TO, the SD of the angle ranges from 2° to 17° and for the velocity magnitude up to 7%. Bias of the velocity magnitude is within 2% for TO and slightly larger but within 4% for TO-DB. The same trends are observed in measurements although with a slightly larger bias. Simulations of realistic flow in a carotid bifurcation model provide visualization of complex flow, and the spread of velocity magnitude estimates is 7.1 cm/s for TO-DB, while it is 11.8 cm/s using only TO. However, velocities for TO-DB are underestimated at peak systole as indicated by a regression value of 0.97 for TO and 0.85 for TO-DB. An in vivo scanning of the carotid bifurcation is used for vector velocity estimations using TO and TO-DB. The SD of the velocity profile over a cardiac cycle is 4.2% for TO and 3.2% for TO-DB.
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blood flow velocity in the popliteal vein using Transverse Oscillation ultrasound
Proceedings of SPIE, 2016Co-Authors: Thor Bechsgaard, Andreas Hjelm Brandt, Michael Bachmann Nielsen, Kristoffer Lindskov Hansen, Simon Holbek, Lars Lonn, Charlotte Strandberg, Niels Baekgaard, Jørgen Arendt JensenAbstract:Chronic venous disease is a common condition leading to varicose veins, leg edema, post-thrombotic syndrome and venous ulcerations. Ultrasound (US) is the main modality for examination of venous disease. Color Doppler and occasionally spectral Doppler US (SDUS) are used for evaluation of the venous flow. Peak velocities measured by SDUS are rarely used in a clinical setting for evaluating chronic venous disease due to inadequate reproducibility mainly caused by the angle dependency of the estimate. However, estimations of blood velocities are of importance in characterizing venous disease. Transverse Oscillation US (TOUS), a non-invasive angle independent method, has been implemented on a commercial scanner. TOUS's advantage compared to SDUS is a more elaborate visualization of complex flow. The aim of this study was to evaluate, whether TOUS perform equal to SDUS for recording velocities in the veins of the lower limbs. Four volunteers were recruited for the study. A standardized flow was provoked with a cuff compression-decompression system placed around the lower leg. The average peak velocity in the popliteal vein of the four volunteers was 151.5 cm/s for SDUS and 105.9 cm/s for TOUS (p <0.001). The average of the peak velocity standard deviations (SD) were 17.0 cm/s for SDUS and 13.1 cm/s for TOUS (p <0.005). The study indicates that TOUS estimates lower peak velocity with improved SD when compared to SDUS. TOUS may be a tool for evaluation of venous disease providing quantitative measures for the evaluation of venous blood flow.
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convex array vector velocity imaging using Transverse Oscillation and its optimization
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2015Co-Authors: Jørgen Arendt Jensen, Andreas Hjelm Brandt, Michael Bachmann NielsenAbstract:A method for obtaining vector flow images using the Transverse Oscillation (TO) approach on a convex array is presented. The paper presents optimization schemes for TO fields and evaluates their performance using simulations and measurements with an experimental scanner. A 3-MHz 192-element convex array probe (pitch 0.33 mm) is used in both simulations and measurements. A parabolic velocity profile is simulated at a beam-to-flow angle of 90°. The optimization routine changes the lateral Oscillation period λ as a function of depth to yield the best possible estimates based on the energy ratio between positive and negative spatial frequencies in the ultrasound field. The energy ratio is reduced from −17.1 dB to −22.1 dB. Parabolic profiles are estimated on simulated data using 16 emissions. The optimization gives a reduction in standard deviation from 8.81% to 7.4% for 16 emissions, with a reduction in lateral velocity bias from −15.93% to 0.78% at 90° (Transverse flow) at a depth of 40 mm. Measurements have been performed using the experimental ultrasound scanner and a convex array transducer. A bias of −0.93% was obtained at 87° for a parabolic velocity profile along with a standard deviation of 6.37%. The livers of two healthy volunteers were scanned using the experimental setup. The in vivo images demonstrate that the method yields realistic estimates with a consistent angle and mean velocity across three heart cycles.
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velocity estimation of the main portal vein with Transverse Oscillation
Internaltional Ultrasonics Symposium, 2015Co-Authors: Andreas Hjelm Brandt, Michael Bachmann Nielsen, Kristoffer Lindskov Hansen, Jørgen Arendt JensenAbstract:This study evaluates if Transverse Oscillation (TO) can provide reliable and accurate peak velocity estimates of blood flow the main portal vein. TO was evaluated against the recommended and most widely used technique for portal flow estimation, Spectral Doppler Ultrasound (SDU). The main portal vein delivers blood from the bowls to the liver, and patients with certain liver diseases have decreased flow in the portal vein. Errors in velocity estimation with SDU are well described, when the beam-to-flow angle is >70 degrees. TO estimates the flow angle independently and is not limited by the beam-to-flow angle. It is less operators depended, as no angle correction is necessary. TO measurements were performed with a 3 MHz convex probe (BK medical 8820e, Herlev, Denmark) connected to the experimental ultrasound scanner SARUS (Synthetic Aperture Real-time Ultrasound Scanner). SDU velocity measurements were performed with a commercial ultrasound scanner (BK 3000, BK Ultrasound, Herlev Denmark) and a convex probe (BK ultrasound 6C2, Herlev, Denmark). Ten healthy volunteers were scanned, and recordings of the portal flow during 3–5 heartbeats were conducted with an intercostal and subcostal view. Intercostal TO peak velocities were not significantly different from SDU peak velocities (TO=0.203m/s, SDU=0.202m/s, p=0.94). Subcostal and Intercostal obtained TO values were not significantly different (intercostal mean TO=0.203m/s, subcostal mean TO=0.180m/s, p=0.26). SDU values obtained intercostal and subcostal were significantly different (intercostal mean SDU=0.202m/s, subcostal mean SDU=0.320m/s, p<0.001). Standard deviation for TO beam-to-flow angle was 10.3°–91.5°, indicating a large beam-to-flow angle variability in the portal vein. This can affect the peak velocity estimation, and is not addressed in SDU. The TO convex array implementation provides the first vector velocity measurements below 60mm (mean 89mm), and is a useful alternative for flow estimation in abdominal ultrasound. It may provide new information of abdominal fluid dynamics and yield both velocity and angle estimates for a more realistic flow characterization.
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Transverse Oscillation vector flow imaging for transthoracic echocardiography
Medical Imaging 2015: Ultrasonic Imaging and Tomography, 2015Co-Authors: David Bradway, Michael Bachmann Nielsen, Kristoffer Lindskov Hansen, Jørgen Arendt JensenAbstract:This work presents the development and first results of in vivo transthoracic cardiac imaging using an implementation of Vector Flow Imaging (VFI) via the Transverse Oscillation (TO) method on a phased-array transducer. Optimal selection of the lateral wavelength of the Transversely-oscillating receive field is described, and results from Field II simulations are presented. Measurements are made using the SARUS experimental ultrasound scanner driving an intercostal phased-array probe. The acquisition sequence was composed of interleaved frames of 68-line B-mode and 17-direction, 32-shot vector velocity flow images. A flow pump was programmed for constant flow for in vitro acquisitions at varying depths in a tissue-mimicking fluid. Additionally, mitral, aortic, and tricuspid valves of two healthy volunteers were scanned from intercostal acoustic windows. The acquired RF data were beam-formed via the TO method, and fourth-order estimators were employed for the velocity estimation. The resulting images were compared with those from conventional spectral Doppler and color flow mapping sequences. VFI is shown to be a clinically-feasible tool, which enables new flexibility for choosing acoustic windows, visualizing turbulent flow patterns, and measuring velocities.
Kristoffer Lindskov Hansen - One of the best experts on this subject based on the ideXlab platform.
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blood flow velocity in the popliteal vein using Transverse Oscillation ultrasound
Proceedings of SPIE, 2016Co-Authors: Thor Bechsgaard, Andreas Hjelm Brandt, Michael Bachmann Nielsen, Kristoffer Lindskov Hansen, Simon Holbek, Lars Lonn, Charlotte Strandberg, Niels Baekgaard, Jørgen Arendt JensenAbstract:Chronic venous disease is a common condition leading to varicose veins, leg edema, post-thrombotic syndrome and venous ulcerations. Ultrasound (US) is the main modality for examination of venous disease. Color Doppler and occasionally spectral Doppler US (SDUS) are used for evaluation of the venous flow. Peak velocities measured by SDUS are rarely used in a clinical setting for evaluating chronic venous disease due to inadequate reproducibility mainly caused by the angle dependency of the estimate. However, estimations of blood velocities are of importance in characterizing venous disease. Transverse Oscillation US (TOUS), a non-invasive angle independent method, has been implemented on a commercial scanner. TOUS's advantage compared to SDUS is a more elaborate visualization of complex flow. The aim of this study was to evaluate, whether TOUS perform equal to SDUS for recording velocities in the veins of the lower limbs. Four volunteers were recruited for the study. A standardized flow was provoked with a cuff compression-decompression system placed around the lower leg. The average peak velocity in the popliteal vein of the four volunteers was 151.5 cm/s for SDUS and 105.9 cm/s for TOUS (p <0.001). The average of the peak velocity standard deviations (SD) were 17.0 cm/s for SDUS and 13.1 cm/s for TOUS (p <0.005). The study indicates that TOUS estimates lower peak velocity with improved SD when compared to SDUS. TOUS may be a tool for evaluation of venous disease providing quantitative measures for the evaluation of venous blood flow.
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velocity estimation of the main portal vein with Transverse Oscillation
Internaltional Ultrasonics Symposium, 2015Co-Authors: Andreas Hjelm Brandt, Michael Bachmann Nielsen, Kristoffer Lindskov Hansen, Jørgen Arendt JensenAbstract:This study evaluates if Transverse Oscillation (TO) can provide reliable and accurate peak velocity estimates of blood flow the main portal vein. TO was evaluated against the recommended and most widely used technique for portal flow estimation, Spectral Doppler Ultrasound (SDU). The main portal vein delivers blood from the bowls to the liver, and patients with certain liver diseases have decreased flow in the portal vein. Errors in velocity estimation with SDU are well described, when the beam-to-flow angle is >70 degrees. TO estimates the flow angle independently and is not limited by the beam-to-flow angle. It is less operators depended, as no angle correction is necessary. TO measurements were performed with a 3 MHz convex probe (BK medical 8820e, Herlev, Denmark) connected to the experimental ultrasound scanner SARUS (Synthetic Aperture Real-time Ultrasound Scanner). SDU velocity measurements were performed with a commercial ultrasound scanner (BK 3000, BK Ultrasound, Herlev Denmark) and a convex probe (BK ultrasound 6C2, Herlev, Denmark). Ten healthy volunteers were scanned, and recordings of the portal flow during 3–5 heartbeats were conducted with an intercostal and subcostal view. Intercostal TO peak velocities were not significantly different from SDU peak velocities (TO=0.203m/s, SDU=0.202m/s, p=0.94). Subcostal and Intercostal obtained TO values were not significantly different (intercostal mean TO=0.203m/s, subcostal mean TO=0.180m/s, p=0.26). SDU values obtained intercostal and subcostal were significantly different (intercostal mean SDU=0.202m/s, subcostal mean SDU=0.320m/s, p<0.001). Standard deviation for TO beam-to-flow angle was 10.3°–91.5°, indicating a large beam-to-flow angle variability in the portal vein. This can affect the peak velocity estimation, and is not addressed in SDU. The TO convex array implementation provides the first vector velocity measurements below 60mm (mean 89mm), and is a useful alternative for flow estimation in abdominal ultrasound. It may provide new information of abdominal fluid dynamics and yield both velocity and angle estimates for a more realistic flow characterization.
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Transverse Oscillation vector flow imaging for transthoracic echocardiography
Medical Imaging 2015: Ultrasonic Imaging and Tomography, 2015Co-Authors: David Bradway, Michael Bachmann Nielsen, Kristoffer Lindskov Hansen, Jørgen Arendt JensenAbstract:This work presents the development and first results of in vivo transthoracic cardiac imaging using an implementation of Vector Flow Imaging (VFI) via the Transverse Oscillation (TO) method on a phased-array transducer. Optimal selection of the lateral wavelength of the Transversely-oscillating receive field is described, and results from Field II simulations are presented. Measurements are made using the SARUS experimental ultrasound scanner driving an intercostal phased-array probe. The acquisition sequence was composed of interleaved frames of 68-line B-mode and 17-direction, 32-shot vector velocity flow images. A flow pump was programmed for constant flow for in vitro acquisitions at varying depths in a tissue-mimicking fluid. Additionally, mitral, aortic, and tricuspid valves of two healthy volunteers were scanned from intercostal acoustic windows. The acquired RF data were beam-formed via the TO method, and fourth-order estimators were employed for the velocity estimation. The resulting images were compared with those from conventional spectral Doppler and color flow mapping sequences. VFI is shown to be a clinically-feasible tool, which enables new flexibility for choosing acoustic windows, visualizing turbulent flow patterns, and measuring velocities.
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novel flow quantification of the carotid bulb and the common carotid artery with vector flow ultrasound
Ultrasound in Medicine and Biology, 2014Co-Authors: Mads Møller Pedersen, Michael Johannes Pihl, Per Haugaard, Michael Bachmann Nielsen, Kristoffer Lindskov Hansen, Lars Lonn, Theis Lange, Jørgen Arendt JensenAbstract:Abstract Abnormal blood flow is usually assessed using spectral Doppler estimation of the peak systolic velocity. The technique, however, only estimates the axial velocity component, and therefore the complexity of blood flow remains hidden in conventional ultrasound examinations. With the vector ultrasound technique Transverse Oscillation the blood velocities of both the axial and the Transverse directions are obtained and the complexity of blood flow can be visualized. The aim of the study was to determine the technical performance and interpretation of vector concentration as a tool for estimation of flow complexity. A secondary aim was to establish accuracy parameters to detect flow changes/patterns in the common carotid artery (CCA) and the carotid bulb (CB). The right carotid bifurcation including the CCA and CB of eight healthy volunteers were scanned in a longitudinal plane with vector flow ultrasound (US) using a commercial vector flow ultrasound scanner (ProFocus, BK Medical, Denmark) with a linear 5 MHz transducer Transverse Oscillation vector flow software. CCA and CB areas were marked in one cardiac cycle from each volunteer. The complex flow was assessed by medical expert evaluation and by vector concentration calculation. A vortex with complex flow was found in all carotid bulbs, whereas the CCA had mainly laminar flow. The medical experts evaluated the flow to be mainly laminar in the CCA (0.82 ± 0.14) and mainly complex (0.23 ± 0.22) in the CB. Likewise, the estimated vector concentrations in CCA (0.96 ± 0.16) indicated mainly laminar flow and in CB (0.83 ± 0.07) indicated mainly turbulence. Both methods were thus able to clearly distinguish the flow patterns of CCA and CB in systole. Vector concentration from angle-independent vector velocity estimates is a quantitative index, which is simple to calculate and can differentiate between laminar and complex flow.
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New developments in vector velocity imaging using the Transverse Oscillation approach
Medical Imaging 2013: Ultrasonic Imaging Tomography and Therapy, 2013Co-Authors: Jørgen Arendt Jensen, Michael Johannes Pihl, Jacob Bjerring Olesen, Peter Møller Hansen, Kristoffer Lindskov Hansen, Michael Bachmann NielsenAbstract:Vector velocity imaging using the Transverse Oscillation (TO) approach has recently been FDA approved for linear array transducers on a commercial platform. It can now be used clinically for studying the complex ow at e.g. bifurcations, valves, and the heart in real time. Several clinical examples from venous ow to rotational ow in the heart will be shown. The technique is also being further developed and adapted for convex and phased array probes, for spectral velocity estimation, pressure estimation, and for three dimensional velocity tensor imaging. It is shown how the methods are optimized using Field II simulations along with several examples of their performance.
Michael Johannes Pihl - One of the best experts on this subject based on the ideXlab platform.
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novel flow quantification of the carotid bulb and the common carotid artery with vector flow ultrasound
Ultrasound in Medicine and Biology, 2014Co-Authors: Mads Møller Pedersen, Michael Johannes Pihl, Per Haugaard, Michael Bachmann Nielsen, Kristoffer Lindskov Hansen, Lars Lonn, Theis Lange, Jørgen Arendt JensenAbstract:Abstract Abnormal blood flow is usually assessed using spectral Doppler estimation of the peak systolic velocity. The technique, however, only estimates the axial velocity component, and therefore the complexity of blood flow remains hidden in conventional ultrasound examinations. With the vector ultrasound technique Transverse Oscillation the blood velocities of both the axial and the Transverse directions are obtained and the complexity of blood flow can be visualized. The aim of the study was to determine the technical performance and interpretation of vector concentration as a tool for estimation of flow complexity. A secondary aim was to establish accuracy parameters to detect flow changes/patterns in the common carotid artery (CCA) and the carotid bulb (CB). The right carotid bifurcation including the CCA and CB of eight healthy volunteers were scanned in a longitudinal plane with vector flow ultrasound (US) using a commercial vector flow ultrasound scanner (ProFocus, BK Medical, Denmark) with a linear 5 MHz transducer Transverse Oscillation vector flow software. CCA and CB areas were marked in one cardiac cycle from each volunteer. The complex flow was assessed by medical expert evaluation and by vector concentration calculation. A vortex with complex flow was found in all carotid bulbs, whereas the CCA had mainly laminar flow. The medical experts evaluated the flow to be mainly laminar in the CCA (0.82 ± 0.14) and mainly complex (0.23 ± 0.22) in the CB. Likewise, the estimated vector concentrations in CCA (0.96 ± 0.16) indicated mainly laminar flow and in CB (0.83 ± 0.07) indicated mainly turbulence. Both methods were thus able to clearly distinguish the flow patterns of CCA and CB in systole. Vector concentration from angle-independent vector velocity estimates is a quantitative index, which is simple to calculate and can differentiate between laminar and complex flow.
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a Transverse Oscillation approach for estimation of three dimensional velocity vectors part ii experimental validation
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2014Co-Authors: Michael Johannes Pihl, Matthias Bo Stuart, Borislav Gueorguiev Tomov, Morten Fischer Rasmussen, Jørgen Arendt JensenAbstract:The 3-D Transverse Oscillation method is investi- gated by estimating 3-D velocities in an experimental flow-rig system. Measurements of the synthesized Transverse oscillating fields are presented as well. The method employs a 2-D trans- ducer; decouples the velocity estimation; and estimates the axi- al, Transverse, and elevation velocity components simultaneous- ly. Data are acquired using a research ultrasound scanner. The velocity measurements are conducted with steady flow in six- teen different directions. For a specific flow direction with (α, β) = (45, 15)°, the mean estimated velocity vector at the center of the vessel is (vx, vy, vz) = (33.8, 34.5, 15.2) ± (4.6, 5.0, 0.6) cm/s where the expected velocity is (34.2, 34.2, 13.0) cm/s. The ve- locity magnitude is 50.6 ± 5.2 cm/s with a bias of 0.7 cm/s. The flow angles α and β are estimated as 45.6 ± 4.9° and 17.6 ± 1.0°. Subsequently, the precision and accuracy are calculated over the entire velocity profiles. On average for all direction, the relative mean bias of the velocity magnitude is −0.08%. For α and β, the mean bias is −0.2° and −1.5°. The relative standard deviations of the velocity magnitude ranges from 8 to 16%. For the flow angles, the ranges of the mean angular deviations are 5° to 16° and 0.7° and 8°.
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a Transverse Oscillation approach for estimation of three dimensional velocity vectors part i concept and simulation study
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2014Co-Authors: Michael Johannes Pihl, Jørgen Arendt JensenAbstract:A method for 3-D velocity vector estimation us- ing Transverse Oscillations is presented. The method employs a 2-D transducer and decouples the velocity estimation into three orthogonal components, which are estimated simultane- ously and from the same data. The validity of the method is investigated by conducting simulations emulating a 32 × 32 matrix transducer. The results are evaluated using two per- formance metrics related to precision and accuracy. The study includes several parameters including 49 flow directions, the SNR, steering angle, and apodization types. The 49 flow direc- tions cover the positive octant of the unit sphere. In terms of accuracy, the median bias is −2%. The precision of vx and vy depends on the flow angle β and ranges from 5% to 31% rela- tive to the peak velocity magnitude of 1 m/s. For comparison, the range is 0.4 to 2% for vz. The parameter study also reveals, that the velocity estimation breaks down with an SNR between −6 and −3 dB. In terms of computational load, the estimation of the three velocity components requires 0.75 billion floating point operations per second (0.75 Gflops) for a realistic setup. This is well within the capability of modern scanners.
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Real-time GPU implementation of Transverse Oscillation vector velocity flow imaging
Medical Imaging 2014: Ultrasonic Imaging and Tomography, 2014Co-Authors: David Bradway, Michael Johannes Pihl, Svetoslav Ivanov Nikolov, Andreas Krebs, Borislav Gueorguiev Tomov, Carsten Kjaer, Jørgen Arendt JensenAbstract:Rapid estimation of blood velocity and visualization of complex flow patterns are important for clinical use of diagnostic ultrasound. This paper presents real-time processing for two-dimensional (2-D) vector flow imaging which utilizes an off-the-shelf graphics processing unit (GPU). In this work, Open Computing Language (OpenCL) is used to estimate 2-D vector velocity flow in vivo in the carotid artery. Data are streamed live from a BK Medical 2202 Pro Focus UltraView Scanner to a workstation running a research interface software platform. Processing data from a 50 millisecond frame of a duplex vector flow acquisition takes 2.3 milliseconds seconds on an Advanced Micro Devices Radeon HD 7850 GPU card. The detected velocities are accurate to within the precision limit of the output format of the display routine. Because this tool was developed as a module external to the scanner's built-in processing, it enables new opportunities for prototyping novel algorithms, optimizing processing parameters, and accelerating the path from development lab to clinic.
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New developments in vector velocity imaging using the Transverse Oscillation approach
Medical Imaging 2013: Ultrasonic Imaging Tomography and Therapy, 2013Co-Authors: Jørgen Arendt Jensen, Michael Johannes Pihl, Jacob Bjerring Olesen, Peter Møller Hansen, Kristoffer Lindskov Hansen, Michael Bachmann NielsenAbstract:Vector velocity imaging using the Transverse Oscillation (TO) approach has recently been FDA approved for linear array transducers on a commercial platform. It can now be used clinically for studying the complex ow at e.g. bifurcations, valves, and the heart in real time. Several clinical examples from venous ow to rotational ow in the heart will be shown. The technique is also being further developed and adapted for convex and phased array probes, for spectral velocity estimation, pressure estimation, and for three dimensional velocity tensor imaging. It is shown how the methods are optimized using Field II simulations along with several examples of their performance.
Hervé Liebgott - One of the best experts on this subject based on the ideXlab platform.
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Simultaneous Tissue and Flow Estimation at High Frame Rate Using Plane Wave and Transverse Oscillation on in Vivo Carotid
2018Co-Authors: Vincent Perrot, Hervé Liebgott, Anne Long, Didier VrayAbstract:In this study, a method to estimate tissue motion and vector flow fields, from a unique ultrasound plane wave sequence, was applied to several in vivo carotid data sets. Moreover, pulse wave velocity was also extracted thanks to the wall velocity estimates. Acquisitions were performed at high frame rate using horizontal plane waves without compounding (5 000 Hz). Results showed that the method could simultaneously yield wall velocity and flow in case of low or high flow rates and even when complex patterns occur. Moreover, pulse wave velocities were estimated from two distinct waves; one is measured from the foot of displacement (forward wave) while the second one is extracted at the dicrotic notch. The forward wave has been estimated with a value of 3.25 ± 0.81 m/s while the second one has been measured at 5.43 ± 1.30 m/s; the difference can be explained with the two different pre-loads on the artery wall. Overall, the method can simultaneously extract fast and complex phenomena that can occur in both tissue and flow. Thanks to the simultaneous assessment of those characteristics, new pathological indicators could be discovered by studying the relationship and synchronization between flow and wall motion.
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Simultaneous pulse wave and flow estimation at high-framerate using plane wave and Transverse Oscillation on carotid phantom
2017Co-Authors: Vincent Perrot, Didier Vray, Lorena Petrusca, Adeline Bernard, Hervé LiebgottAbstract:In this paper a global estimation method based on Transverse Oscillation to simultaneously extract wall and flow velocities at high-framerate is presented. Several carotid phantoms with various parameters were made to validate the method. All acquisitions were performed at high-framerate (7 500 images per second) using horizontal plane wave with a 3 cycles sinusoidal transmit pulse. Transverse Oscillation was introduced in post-acquisition. Finally, velocity vectors were extracted thanks to a phase based estimator with a region of interest of 2 mm (8 axial wavelengths) per 2.96 mm (2 lateral wavelengths) for each pixel. Results are promising, all standard deviations are lower than 10 % and the method is now validated for a deeper study. Indeed, flow and pulse wave velocities computed by the algorithm are in accordance with pressure columns and number of freezethaw cycles.
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Cardiac Motion estimation based on Transverse Oscillation and ultrafast diverging wave imaging
2015 IEEE International Ultrasonics Symposium (IUS), 2015Co-Authors: Philippe Joos, Sébastien Salles, Didier Vray, Barbara Nicolas, Hervé LiebgottAbstract:Ultrafast ultrasound imaging using plane waves (PW) has demonstrated its potential in assessing complicated motion patterns in the blood or in the tissue. On the other hand, the introduction of Transverse Oscillations (TO) combined with Phase Based vector Motion estimation algorithms (PBM) has shown to be a very promising technique to improve Transverse motion estimation. Cardiac imaging could greatly benefit of a combination of ultrafast TO and PBM. Unfortunately, due to the presence of the ribs, cardiac imaging has to be done with a phased array. Consequently ultrafast imaging of the heart is usually performed with diverging waves (DW) instead of PW. In this paper, the objective is to extend our previously developed ultrafast PW TO technique to ultrafast imaging of the heart using DW. A validation of the method is proposed using CREANUIS simulations with a realistic cardiac sequence.
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Plane-Wave Transverse Oscillation for High-Frame-Rate 2-D Vector Flow Imaging
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2015Co-Authors: Matteo Lenge, Alessandro Ramalli, Piero Tortoli, Christian Cachard, Hervé LiebgottAbstract:Transverse Oscillation (TO) methods introduce Oscillations in the pulse–echo field (PEF) along the direction Transverse to the ultrasound propagation direction. This may be exploited to extend flow investigations toward multidimensional estimates. In this paper, the TOs are coupled with the transmission of plane waves (PWs) to reconstruct high-framerate RF images with bidirectional Oscillations in the pulse–echo field. Such RF images are then processed by a 2-D phase-based displacement estimator to produce 2-D vector flow maps at thousands of frames per second. First, the capability of generating TOs after PW transmissions was thoroughly investigated by varying the lateral wavelength, the burst length, and thetransmission frequency. Over the entire region of interest, the generated lateral wavelengths, compared with the designed ones, presented bias and standard deviation of −3.3 ± 5.7% and 10.6 ± 7.4% in simulations and experiments, respectively. The performance of the ultrafast vector flow mapping method was also assessed by evaluating the differences between the estimated velocities and the expected ones. Both simulationsand experiments show overall biases lower than 20% when varying the beam-to-flow angle, the peak velocity, and the depth of interest. In vivo applications of the method on the common carotid and the brachial arteries are also presented.
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Estimation of arterial wall motion using ultrafast imaging with Transverse Oscillations: Phantom study
2014 IEEE International Ultrasonics Symposium, 2014Co-Authors: Sébastien Salles, Hervé Liebgott, Didier Vray, Simon Lai, Damien GarciaAbstract:This paper presents an experimental study of two dimensional (2D) tissue motion estimation in ultrafast imaging using Transverse Oscillation and a phase based motion estimation. In this study, the motion is measured all along the wall of an artery phantom. The method employs ultrafast imaging which has become a world-wide used modality, with several promising clinical application, Transverse Oscillations technics which allow improving the motion estimation in Transverse direction i.e. perpendicular to the beam axis, and a phase-based motion estimation. The experiment in vitro results show that the motion estimation is very reproducible all along the phantom wall, and even if the wall displacement estimable are very small (0.001 pixel), our method is able to estimate the 2D motion.
