| 1. |
- Erlöv, Tobias, et al.
(author)
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A robust and fast method for arterial lumen diameter and intima-media thickness measurements
- 2012
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In: 2012 IEEE International Ultrasonics Symposium (IUS). - 9781467345613 - 9781467345620 ; , s. 1678-1681
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Conference paper (peer-reviewed)abstract
- Lumen diameter, distension and intima-media thickness (IMT) in human arteries are important parameters in cardiovascular research. The signal reflected from the arterial wall strongly depends on the ultrasound scanner and settings. The signal also varies with age and health of the subject. A general method insensitive with respect to the subject and the scanner would be of great help. We have developed a novel and robust method for ARTerIal Characterization (ARTIC), suitable for real-time in vivo measurements of diameter, distension and IMT using B-Mode images. The aim of this study was to evaluate ARTIC on different subjects and scanners. ARTIC was evaluated in vivo in different groups of subjects using two scanners, HDI5000 (Philips Medical Systems, Bothell, WA, USA) and ULA-OP (University of Florence, Italy). First, a comparison was made against a previous method validated on phantoms. Then measurements of young (healthy) and old (healthy and unhealthy) subjects were evaluated for both scanners. Finally, a comparison between scanners was made. The evaluation of different subjects shows a coefficient of variation (CV) ranging from 1.4-2.0% for diameter, 4.3-8.8% for distension and 3.6-6.6% for IMT.
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| 2. |
- Evertsson, Maria, et al.
(author)
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Towards real-time magnetomotive ultrasound imaging
- 2017
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In: 2017 IEEE International Ultrasonics Symposium, IUS 2017. - 9781538633830
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Conference paper (peer-reviewed)abstract
- Magnetomotive ultrasound (MMUS) imaging indirectly enables visualization of magnetic nanoparticles (MNPs) with ultrasound. An external time varying magnetic field displaces MNPs and thus their closest surrounding, the induced displacement is tracked in the US data and color-coded on B-mode images. However, images are currently processed offline, which is time consuming and precludes clinical use of MMUS. In this work, the previously proposed MMUS algorithm (DOI: TUFFC.2013.2591) is automated and implemented online on the ULA-OP scanner.
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| 3. |
- Evertsson, Maria, et al.
(author)
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Towards real-time magnetomotive ultrasound imaging
- 2017
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In: 2017 IEEE International Ultrasonics Symposium, IUS 2017. - 9781538633830
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Conference paper (peer-reviewed)abstract
- Enabling detection of nanoparticles with ultrasound can open new application avenues for the ultrasound technique. Magnetomotive ultrasound (MMUS) is a technique under development which indirectly visualizes magnetic nanoparticles. In MMUS, an external time-varying magnetic field acts to displace the nanoparticles, and thus their closest surrounding. This induced displacement is subsequently detected and the nanoparticle location may then be revealed. The MMUS technique has shown to be promising in both phantom and animal studies but limited efforts have been made on optimizing the technique for clinical applications in the sense of providing real-time bedside imaging. In this work, the previously proposed MMUS algorithm is automated and implemented online on the ULA-OP scanner. To evaluate the online implementation, a phantom made of styrene-ethylene/butylene-styrene and mineral oil with a 2 % magnetic ferrite particle inclusion was used. MMUS displacement was calculated in the entire image area, 192×230 pixels, and in a sub-region of 130×90 pixels, covering the inclusion. It was found that the automated online implementation computes one full MMUS image in 2.8 seconds and the sub-region in 1.17 seconds, which should be compared to 1-2 minutes in post processing mode. An immediate on-screen change in the magnetomotive displacement could be observed as the applied magnetic field was altered.
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| 4. |
- Ricci, Stefano, et al.
(author)
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Accuracy and reproducibility of a novel dynamic volume flow measurement method.
- 2013
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In: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 39:10, s. 1903-1914
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Journal article (peer-reviewed)abstract
- In clinical practice, blood volume flow (BVF) is typically calculated assuming a perfect parabolic and axisymmetric velocity distribution. This simple approach cannot account for the complex flow configurations that are produced by vessel curvatures, pulsatility and diameter changes and, therefore, results in a poor estimation. Application of the Womersley model allows compensation for the flow distortion caused by pulsatility and, with some adjustment, the effects of slight curvatures, but several problems remain unanswered. Two-and three-dimensional approaches can acquire the actual velocity field over the whole vessel section, but are typically affected by a limited temporal resolution. The multigate technique allows acquisition of the actual velocity profile over a line intersecting the vessel lumen and, when coupled with a suitable wall-tracking method, can offer the ideal trade-off among attainable accuracy, temporal resolution and required calculation power. In this article, we describe a BVF measurement method based on the multigate spectral Doppler and a B-mode edge detector algorithm for wall-position tracking. The method has been extensively tested on the research platform ULA-OP, with more than 1700 phantom measurements at flow rates between 60 and 750 mL/min, steering angles between 10 degrees and 22 degrees and constant, sinusoidal or pulsed flow trends. In the averaged BVF measurement, we found an underestimation of about-5% and a coefficient of variability (CV) less than 6%. In instantaneous measurements (e.g., systolic peak) the CV was in the range 2%-8.5%. These results were confirmed by a preliminary test on the common carotid artery of 10 volunteers (CV = 2%-11%). (E-mail: stefano.ricci@unifi.it) (C) 2013 World Federation for Ultrasound in Medicine & Biology.
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| 5. |
- Ricci, S., et al.
(author)
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Volume flow assessment through simultaneous B-mode and Multigate Doppler
- 2012
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In: 2012 IEEE International Ultrasonics Symposium, IUS 2012. - 9781467345613 - 9781467345620 ; , s. 1588-1591
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Conference paper (other academic/artistic)abstract
- The typical approach for volumetric blood flow assessment consists of a velocity measurement performed in a single sample volume placed in the vessel centre, combined to an estimate of the average diameter. This simple approach produces large inaccuracies since it does not account for the complex flow configurations produced by complicated artery geometries and/or pulsatile conditions. Moreover, diameter changes, which in important regions like the common carotid artery can be larger than 10%, are totally neglected. In this work we propose an alternative volume flow method which overcomes some of the aforementioned limitations through the simultaneous measurement of the wall positions and of the velocity distribution in the artery. The wall positions are tracked by a detector based on the First Order Absolute Moment working on B-mode data, while the velocity profile is obtained by a Multigate Spectral Doppler analysis applied to PW-mode data. The method was implemented on the ULA-OP research system and validated on a flow phantom with more than 1700 experiments performed in rigid and flexible pipes. We found a systematic underestimation of 3.7% with 5.0% standard deviation. The mean coefficient of variation (CV) was 1.7%.
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| 6. |
- Ricci, Stefano, et al.
(author)
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Volumetric Blood Flow Assessment through Multigate Spectral Doppler
- 2009
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In: 2009 IEEE International Ultrasonics Symposium. - 9781424443895 ; , s. 570-573
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Conference paper (other academic/artistic)abstract
- Volumetric blood flow measurements require the assessment of both the velocity distribution and the cross-sectional area of the vessel. Unfortunately several difficulties hamper such a measurement in standard approaches. A new dual beam method has been recently introduced in which the Doppler spectral symmetry is exploited to finely orientating the first beam at 90° with respect to the flow, so that the remaining beam can perform a velocity measurement with known Doppler angle. In this paper it is shown how this special beam configuration proves particularly suitable for volume flow measurements. While the transverse beam performs a diameter measurement with optimal orientation, the velocity distribution along the second beam is measured through multigate spectral analysis. The method has been coded on a research system. In-vitro experiments produced a bias less then 7% with a coefficient of variability (CV) less then 5%. In preliminary tests on 3 volunteers CVs within 10% were obtained.
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| 7. |
- Rydén Ahlgren, Åsa, et al.
(author)
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Profound Increase in Longitudinal Displacements of the Porcine Carotid Artery Wall Can Take Place Independently of Wall Shear Stress: A Continuation Report.
- 2015
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In: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 41:5, s. 1342-1353
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Journal article (peer-reviewed)abstract
- The mechanisms underlying longitudinal displacements of the arterial wall, that is, displacements of the wall layers along the artery, and the resulting intramural shear strain remain largely unknown. We have already found that these displacements undergo profound changes in response to catecholamines. Wall shear stress, closely related to wall shear rate, represents the viscous drag exerted on the vessel wall by flowing blood. The aim of the work described here was to study possible relations between the wall shear rate and the longitudinal displacements. We investigated the carotid arteries of five anesthetized pigs in different hemodynamic situations using in-house developed non-invasive ultrasound techniques. The study protocol included administration of epinephrine, norepinephrine and β-blockade (metoprolol). No significant correlation between longitudinal displacement of the intima-media complex and wall shear rate was found. This result suggests that one or multiple pulsatile forces other than wall shear stress are also working along arteries, strongly influencing arterial wall behavior.
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