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Matenchuk BA, Fujii KD, Skow RJ, Sobierajski FM, MacKay C, Steinback CD, Davenport MH. The Effects of Physical Activity on Arterial Stiffness during Pregnancy: An Observational Study. Appl Physiol Nutr Metab 2021; 47:234-242. [PMID: 34735778 DOI: 10.1139/apnm-2021-0121] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The objective of the present study was to investigate the relationship between moderate-to-vigorous physical activity (MVPA) and arterial stiffness in pregnancy. Thirty-nine women participated in this study resulting in 68 measurements in non-pregnant (NP; n=21), first (TM1; n=8), second (TM2; n=20), and third trimesters (TM3; n=19). Compliance, distensibility, elasticity, β-stiffness, and carotid to femoral (central) and carotid to finger (peripheral) pulse wave velocity (PWV) were assessed. MVPA was measured using accelerometry. Multilevel linear regressions adjusted for multiple tests per participant using random effects to generate β coefficients and 95% confidence intervals (CI) were performed. Distensibility, elasticity, β-stiffness, central- and peripheral-PWV did not differ between pregnant and non-pregnant assessments. Carotid artery compliance was higher in TM2 compared to NP. Central PWV (β Coef: -0.14, 95% CI: -0.27, -0.02) decreased from early to mid-pregnancy and increased in late pregnancy. Meeting the MVPA guidelines was significantly associated with central-PWV (Adj. β Coef: -0.34, 95% CI: -0.62, -0.06, p=0.016), peripheral-PWV (Adj. β Coef: -0.54, 95% CI: -0.91, -0.16, p=0.005), and distensibility (Adj. β Coef: -0.001, 95% CI: -0.002, -0.0001, p=0.018), in pregnancy. These results suggest that MVPA may be associated with improved (i.e. reduced) arterial stiffness in pregnancy. Novelty Bullets • Central PWV, distensibility, compliance, elasticity, and ß-stiffness, but not peripheral PWV, exhibited curvilinear relationships with gestational age • Central and peripheral PWV were lower in pregnant women who met the physical activity guidelines of 150 minutes of moderate-to-vigorous physical activity per week.
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Affiliation(s)
| | | | - Rachel J Skow
- University of Alberta, 3158, Edmonton, Alberta, Canada;
| | | | | | - Craig D Steinback
- University of Alberta, 3158, Faculty of Kinesiology, Sport & Recreation, Edmonton, Alberta, Canada;
| | - Margie H Davenport
- University of Alberta, 3158, Faculty of Kinesiology, Sport, & Recreation, Edmonton, Alberta, Canada.,University of Alberta, 3158, Program for Pregnancy and Postpartum Health, Edmonton, Alberta, Canada;
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2
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van der Bruggen MM, Reesink KD, Spronck PJM, Bitsch N, Hameleers J, Megens RTA, Schalkwijk CG, Delhaas T, Spronck B. An integrated set-up for ex vivo characterisation of biaxial murine artery biomechanics under pulsatile conditions. Sci Rep 2021; 11:2671. [PMID: 33514757 PMCID: PMC7846753 DOI: 10.1038/s41598-021-81151-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Accepted: 12/07/2020] [Indexed: 01/19/2023] Open
Abstract
Ex vivo characterisation of arterial biomechanics enables detailed discrimination of the various cellular and extracellular contributions to arterial stiffness. However, ex vivo biomechanical studies are commonly performed under quasi-static conditions, whereas dynamic biomechanical behaviour (as relevant in vivo) may differ substantially. Hence, we aim to (1) develop an integrated set-up for quasi-static and dynamic biaxial biomechanical testing, (2) quantify set-up reproducibility, and (3) illustrate the differences in measured arterial stiffness between quasi-static and dynamic conditions. Twenty-two mouse carotid arteries were mounted between glass micropipettes and kept fully vasodilated. While recording pressure, axial force (F), and inner diameter, arteries were exposed to (1) quasi-static pressure inflation from 0 to 200 mmHg; (2) 300 bpm dynamic pressure inflation (peaking at 80/120/160 mmHg); and (3) axial stretch (λz) variation at constant pressures of 10/60/100/140/200 mmHg. Measurements were performed in duplicate. Single-point pulse wave velocities (PWV; Bramwell-Hill) and axial stiffness coefficients (cax = dF/dλz) were calculated at the in vivo value of λz. Within-subject coefficients of variation were ~ 20%. Dynamic PWVs were consistently higher than quasi-static PWVs (p < 0.001); cax increased with increasing pressure. We demonstrated the feasibility of ex vivo biomechanical characterisation of biaxially-loaded murine carotid arteries under pulsatile conditions, and quantified reproducibility allowing for well-powered future study design.
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Affiliation(s)
- Myrthe M van der Bruggen
- Department of Biomedical Engineering, CARIM School for Cardiovascular Diseases, Maastricht University, Universiteitssingel 50, Room 3.359, 6229ER, Maastricht, The Netherlands
| | - Koen D Reesink
- Department of Biomedical Engineering, CARIM School for Cardiovascular Diseases, Maastricht University, Universiteitssingel 50, Room 3.359, 6229ER, Maastricht, The Netherlands
| | | | - Nicole Bitsch
- Muroidean Facility, CARIM School for Cardiovascular Diseases, Maastricht University, Maastricht, The Netherlands
| | - Jeroen Hameleers
- Department of Biomedical Engineering, CARIM School for Cardiovascular Diseases, Maastricht University, Universiteitssingel 50, Room 3.359, 6229ER, Maastricht, The Netherlands
| | - Remco T A Megens
- Department of Biomedical Engineering, CARIM School for Cardiovascular Diseases, Maastricht University, Universiteitssingel 50, Room 3.359, 6229ER, Maastricht, The Netherlands.,Institute for Cardiovascular Prevention, Ludwig-Maximilians-Universität, Munich, Germany
| | - Casper G Schalkwijk
- Department of Internal Medicine, CARIM School for Cardiovascular Diseases, Maastricht University Medical Centre+, Maastricht, The Netherlands
| | - Tammo Delhaas
- Department of Biomedical Engineering, CARIM School for Cardiovascular Diseases, Maastricht University, Universiteitssingel 50, Room 3.359, 6229ER, Maastricht, The Netherlands
| | - Bart Spronck
- Department of Biomedical Engineering, CARIM School for Cardiovascular Diseases, Maastricht University, Universiteitssingel 50, Room 3.359, 6229ER, Maastricht, The Netherlands. .,Department of Biomedical Engineering, School of Engineering & Applied Science, Yale University, New Haven, CT, USA.
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3
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Romanò F, Suresh V, Galie PA, Grotberg JB. Peristaltic flow in the glymphatic system. Sci Rep 2020; 10:21065. [PMID: 33273489 PMCID: PMC7713425 DOI: 10.1038/s41598-020-77787-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Accepted: 11/12/2020] [Indexed: 01/01/2023] Open
Abstract
The flow inside the perivascular space (PVS) is modeled using a first-principles approach in order to investigate how the cerebrospinal fluid (CSF) enters the brain through a permeable layer of glial cells. Lubrication theory is employed to deal with the flow in the thin annular gap of the perivascular space between an impermeable artery and the brain tissue. The artery has an imposed peristaltic deformation and the deformable brain tissue is modeled by means of an elastic Hooke's law. The perivascular flow model is solved numerically, discovering that the peristaltic wave induces a steady streaming to/from the brain which strongly depends on the rigidity and the permeability of the brain tissue. A detailed quantification of the through flow across the glial boundary is obtained for a large parameter space of physiologically relevant conditions. The parameters include the elasticity and permeability of the brain, the curvature of the artery, its length and the amplitude of the peristaltic wave. A steady streaming component of the through flow due to the peristaltic wave is characterized by an in-depth physical analysis and the velocity across the glial layer is found to flow from and to the PVS, depending on the elasticity and permeability of the brain. The through CSF flow velocity is quantified to be of the order of micrometers per seconds.
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Affiliation(s)
- Francesco Romanò
- Univ. Lille, CNRS, ONERA, Arts et Métiers Institute of Technology, Centrale Lille, UMR 9014 - LMFL - Laboratoire de Mécanique des Fluides de Lille - Kampé de Fériet, 59000, Lille, France.
| | - Vinod Suresh
- Auckland Bioeng. Inst. and Dept. Eng. Sci., University of Auckland, 70 Symonds Street, Bldg 439, Auckland, 1010, New Zealand
| | - Peter A Galie
- Dept. Biomed. Eng., Rowan University, 201 Mullica Hill Rd, Glassboro, NJ, 08028, USA
| | - James B Grotberg
- Dept. Biomed. Eng., University of Michigan, 2123 Carl A. Gerstacker Building, 2200 Bonisteel Boulevard, Ann Arbor, MI, 48109-2099, USA
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Madhloum N, Luyten LJ, Provost EB, De Boever P, Dockx Y, Sleurs H, Plusquin M, Roodt JO, Vrijens K, Nawrot TS. Establishing reference values for macro- and microvascular measurements in 4-to-5 year-old children of the ENVIRONAGE prospective birth cohort. Sci Rep 2020; 10:5107. [PMID: 32198402 PMCID: PMC7083909 DOI: 10.1038/s41598-020-61987-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Accepted: 12/30/2019] [Indexed: 01/01/2023] Open
Abstract
Cardiovascular risk factors are usually better tolerated, and can therefore be perceived as less harmful, at a young age. However, over time the effects of these adverse factors may persist or accumulate and lead to excess morbidity and mortality from cardiovascular diseases later in life. Until now, reference values for the basic cardiovascular health characteristics of 4-to-6 year-old children are lacking. Within a follow-up study of the ENVIRONAGE (ENVIRonmental influence ON early AGE) birth cohort we assessed various cardiovascular measurements in 288 children aged 4–5 years. For the macrovasculature, we measured their blood pressure and examined the intima-media thickness of the carotid artery (CIMT), the arterial elasticity (including the pulse-wave velocity (PWV), carotid distensibility (DC) and compliance (CC) coefficients), the carotid β stiffness index (SIβ) and Young’s Elastic Modulus (YEM). Retinal microvascular traits included the Central Retinal Arteriolar Equivalent (CRAE) and Central Retinal Venular Equivalent (CRVE). Age of the study population averaged (±SD) 4.2 (±0.4 years. Mean systolic and diastolic blood pressure were 97.9 (±8.1) mmHg and 54.7(±7.6) mmHg, respectively. CIMT for the total population averaged 487.1 (±68.1) µm. The average stiffness values for DC, CC, SIβ, and PWV were 78.7 (±34.2) 10−³/kPa, 1.61 (±0.59) mm2/kPa and 4.4 (±2.4), and 3.7 m/s (±0.9) respectively. The mean determined for YEM was 163.2 kPa (±79.9). Concerning the microvasculature, the average CRAE was 180.9 (±14.2) µm and the corresponding value for CRVE was 251.0 (±19.7) µm. In contrast to the macrovasculature, a significant gender-related difference existed for the microvasculature: in boys, both the CRAE (178.8 µm vs 182.6 µm; p = 0.03) and CRVE (247.9 µm vs 254.0 µm; p = 0.01) were narrower than in girls. We have provided reference values for young children to understand changes in the early cardiovascular health trajectory. Establishing these reference values of cardiovascular phenotypes at this young age is necessary to develop targeted health promotion strategies as well as for better understanding of the life course changes of both small and large blood vessels.
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Affiliation(s)
- Narjes Madhloum
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium
| | - Leen J Luyten
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium.,Unité de Recherche en Biologie Cellulaire (URBC) - Namur Research Institute for Life Sciences (Narilis), Namur University, Namur, Belgium
| | - Eline B Provost
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium.,Health Unit, Flemish Institute for Technological Research (VITO), Mol, Belgium
| | - Patrick De Boever
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium.,Health Unit, Flemish Institute for Technological Research (VITO), Mol, Belgium
| | - Yinthe Dockx
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium
| | - Hanne Sleurs
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium
| | - Michelle Plusquin
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium
| | - Jos Op't Roodt
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium.,Department of Internal Medicine, Maastricht University Medical Centre (MUMC+), Maastricht, The Netherlands
| | - Karen Vrijens
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium
| | - Tim S Nawrot
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium. .,Department of Public Health & Primary Care, Occupational and Environmental Medicine, Leuven University, Leuven, Belgium.
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5
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Vera L, De Clercq D, Van Steenkiste G, Decloedt A, Chiers K, van Loon G. Differences in ultrasound-derived arterial wall stiffness parameters and noninvasive blood pressure between Friesian horses and Warmblood horses. J Vet Intern Med 2020; 34:893-901. [PMID: 32032455 PMCID: PMC7096643 DOI: 10.1111/jvim.15705] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Accepted: 01/10/2020] [Indexed: 12/26/2022] Open
Abstract
Background Aortic rupture is more common in Friesians compared to Warmbloods, which might be related to differences in arterial wall composition and, as such, arterial wall stiffness (AWS). Currently, nothing is known about differences in AWS between these breeds. Objectives Comparison of AWS parameters and noninvasive blood pressure between Friesians and Warmbloods. Animals One hundred one healthy Friesians and 101 age‐matched healthy Warmbloods. Methods Two‐dimensional and pulsed‐wave Doppler ultrasound examination was performed of the aorta, common carotid artery, and external iliac artery to define local and regional AWS parameters. Regional aortic AWS was estimated using aortic‐to‐external iliac artery pulse wave velocity (PWVa‐e) and carotid‐to‐external iliac artery pulse wave velocity (PWVc‐e). Noninvasive blood pressure and heart rate were recorded simultaneously. Results Systolic, diastolic, and mean arterial blood pressure and pulse pressure were significantly higher in Friesians compared to Warmbloods. No significant difference in heart rate was found. Most local AWS parameters (diameter change, compliance coefficient, distensibility coefficient) were significantly lower in Friesians compared to Warmbloods, indicating a stiffer aorta in Friesians. This difference could be confirmed by the regional stiffness parameters. A higher PWVa‐e and PWVc‐e was found in Friesians. For the cranial and caudal common carotid artery and external iliac artery, most local AWS parameters were not significantly different. Conclusions and clinical importance Results indicate that aortic AWS differs between Friesian and Warmblood horses. Friesians seem to have a stiffer aorta, which might be related to the higher incidence of aortic rupture in Friesians.
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Affiliation(s)
- Lisse Vera
- Department of Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Equine cardioteam, Ghent University, Merelbeke, Belgium
| | - Dominique De Clercq
- Department of Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Equine cardioteam, Ghent University, Merelbeke, Belgium
| | - Glenn Van Steenkiste
- Department of Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Equine cardioteam, Ghent University, Merelbeke, Belgium
| | - Annelies Decloedt
- Department of Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Equine cardioteam, Ghent University, Merelbeke, Belgium
| | - Koen Chiers
- Department of Pathology, Bacteriology and Poultry Diseases, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
| | - Gunther van Loon
- Department of Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Equine cardioteam, Ghent University, Merelbeke, Belgium
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6
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A Preprocess Method of External Disturbance Suppression for Carotid Wall Motion Estimation Using Local Phase and Orientation of B-Mode Ultrasound Sequences. BIOMED RESEARCH INTERNATIONAL 2019; 2019:6547982. [PMID: 31886237 PMCID: PMC6925731 DOI: 10.1155/2019/6547982] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Revised: 06/11/2019] [Accepted: 08/27/2019] [Indexed: 11/17/2022]
Abstract
Estimating the motions of the common carotid artery wall plays a very important role in early diagnosis of the carotid atherosclerotic disease. However, the disturbances caused by either the instability of the probe operator or the breathing of subjects degrade the estimation accuracy of arterial wall motion when performing speckle tracking on the B-mode ultrasound images. In this paper, we propose a global registration method to suppress external disturbances before motion estimation. The local vector images, transformed from B-mode images, were used for registration. To take advantage of both the structural information from the local phase and the geometric information from the local orientation, we proposed a confidence coefficient to combine them two. Furthermore, we altered the speckle reducing anisotropic diffusion filter to improve the performance of disturbance suppression. We compared this method with schemes of extracting wall displacement directly from B-mode or phase images. The results show that this scheme can effectively suppress the disturbances and significantly improve the estimation accuracy.
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7
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Arathy R, Nabeel PM, Joseph J, Sivaprakasam M. Accelerometric patch probe for cuffless blood pressure evaluation from carotid local pulse wave velocity: design, development, and
in vivo
experimental study. Biomed Phys Eng Express 2019. [DOI: 10.1088/2057-1976/ab1a82] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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8
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Sled JG, Stortz G, Cahill LS, Milligan N, Ayyathurai V, Serghides L, Morgen E, Seravalli V, Delp C, McShane C, Baschat A, Kingdom J, Macgowan CK. Reflected hemodynamic waves influence the pattern of Doppler ultrasound waveforms along the umbilical arteries. Am J Physiol Heart Circ Physiol 2019; 316:H1105-H1112. [PMID: 30794433 DOI: 10.1152/ajpheart.00704.2018] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The pulsatile pattern of blood motion measured by Doppler ultrasound within the umbilical artery is known to contain useful diagnostic information and is widely used to monitor pregnancies at risk of fetal growth restriction or stillbirth. Animal studies have identified reflected pressure waves traveling counter to the direction of blood flow as an important factor in the shape of these waveforms. In the present study, we establish a method to measure reflected waves in the human umbilical artery and assess their influence on blood velocity pulsation. Ninety-five pregnant women were recruited from a general obstetrics clinic between 26 and 37 wk of gestation and examined by Doppler ultrasound. Blood velocity waveforms were recorded for each umbilical artery at three locations along the umbilical cord. With the use of a computational procedure, a pair of forward and reverse propagating waves was identified to explain the variation in observed Doppler ultrasound waveforms along the cord. Among the data sets that met data quality requirements, waveforms in 93 of the 130 arteries examined agreed with the wave reflection model to within 1.5% and showed reflections ranging in magnitude from 3 to 52% of the forward wave amplitude. Strong reflections were associated with large differences in pulsatility between the fetal and placental ends of the cord. As reflections arise from transitions in the biomechanical properties of blood vessels, these observations provide a plausible mechanism for the link between abnormal waveforms and clinically significant placental pathology and could lead to more precise screening methods for detecting pregnancies complicated by placental disease. NEW & NOTEWORTHY The pulsatile pattern of blood motion measured by Doppler ultrasound within the umbilical artery is known to contain useful diagnostic information and is widely used to monitor pregnancies at risk of fetal growth restriction. We demonstrate based on a study of 95 pregnant women that the shape of these umbilical artery waveforms is explained by the presence of a reflected pressure wave traveling counter to the direction of blood flow.
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Affiliation(s)
- John G Sled
- Hospital for Sick Children , Toronto, Ontario , Canada.,Department of Medical Biophysics, University of Toronto , Toronto, Ontario , Canada.,Department of Obstetrics and Gynecology, University of Toronto , Toronto, Ontario , Canada
| | - Greg Stortz
- Hospital for Sick Children , Toronto, Ontario , Canada
| | | | | | | | - Lena Serghides
- Toronto General Hospital Research Institute, University Health Network , Toronto, Ontario , Canada.,Department of Immunology, University of Toronto , Toronto, Ontario , Canada
| | - Eric Morgen
- Mount Sinai Hospital , Toronto, Ontario , Canada.,Department of Laboratory Medicine and Pathobiology, University of Toronto , Toronto, Ontario , Canada
| | - Viola Seravalli
- Center for Fetal Therapy, Johns Hopkins Medicine, Baltimore, Maryland.,Department of Health Sciences, University of Florence , Florence , Italy
| | - Cassandra Delp
- Center for Fetal Therapy, Johns Hopkins Medicine, Baltimore, Maryland
| | - Cyrethia McShane
- Center for Fetal Therapy, Johns Hopkins Medicine, Baltimore, Maryland
| | - Ahmet Baschat
- Center for Fetal Therapy, Johns Hopkins Medicine, Baltimore, Maryland
| | - John Kingdom
- Department of Obstetrics and Gynecology, University of Toronto , Toronto, Ontario , Canada.,Mount Sinai Hospital , Toronto, Ontario , Canada
| | - Christopher K Macgowan
- Hospital for Sick Children , Toronto, Ontario , Canada.,Department of Medical Biophysics, University of Toronto , Toronto, Ontario , Canada
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Biswas M, Kuppili V, Saba L, Edla DR, Suri HS, Sharma A, Cuadrado-Godia E, Laird JR, Nicolaides A, Suri JS. Deep learning fully convolution network for lumen characterization in diabetic patients using carotid ultrasound: a tool for stroke risk. Med Biol Eng Comput 2018; 57:543-564. [PMID: 30255236 DOI: 10.1007/s11517-018-1897-x] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2018] [Accepted: 09/06/2018] [Indexed: 10/28/2022]
Abstract
Manual ultrasound (US)-based methods are adapted for lumen diameter (LD) measurement to estimate the risk of stroke but they are tedious, error prone, and subjective causing variability. We propose an automated deep learning (DL)-based system for lumen detection. The system consists of a combination of two DL systems: encoder and decoder for lumen segmentation. The encoder employs a 13-layer convolution neural network model (CNN) for rich feature extraction. The decoder employs three up-sample layers of fully convolution network (FCN) for lumen segmentation. Three sets of manual tracings were used during the training paradigm leading to the design of three DL systems. Cross-validation protocol was implemented for all three DL systems. Using the polyline distance metric, the precision of merit for three DL systems over 407 US scans was 99.61%, 97.75%, and 99.89%, respectively. The Jaccard index and Dice similarity of DL lumen segmented region against three ground truth (GT) regions were 0.94, 0.94, and 0.93 and 0.97, 0.97, and 0.97, respectively. The corresponding AUC for three DL systems was 0.95, 0.91, and 0.93. The experimental results demonstrated superior performance of proposed deep learning system over conventional methods in literature. Graphical abstract ᅟ.
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Affiliation(s)
- Mainak Biswas
- Department of Computer Science and Engineering, NIT Goa, Ponda, India
| | | | - Luca Saba
- Department of Radiology, A.O.U. Cagliari, Cagliari, Italy
| | | | - Harman S Suri
- Brown University, Providence, RI, USA.,Monitoring and Diagnostic Division, AtheroPoint™, Roseville, CA, USA
| | - Aditya Sharma
- Cardiovascular Division, University of Virginia, Charlottesville, VA, USA
| | - Elisa Cuadrado-Godia
- Dept. of Neurology, IMIM - Hospital del Mar, Passeig Marítim 25-29, Barcelona, Spain
| | | | - Andrew Nicolaides
- Vascular Screening and Diagnostic Centre, London, UK.,Department of Biological Sciences, University of Cyprus, Nicosia, Cyprus
| | - Jasjit S Suri
- Monitoring and Diagnostic Division, AtheroPoint™, Roseville, CA, USA.
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10
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Rey J, Sarntinoranont M. Pulsatile flow drivers in brain parenchyma and perivascular spaces: a resistance network model study. Fluids Barriers CNS 2018; 15:20. [PMID: 30012159 PMCID: PMC6048913 DOI: 10.1186/s12987-018-0105-6] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2018] [Accepted: 07/03/2018] [Indexed: 11/10/2022] Open
Abstract
Background In animal models, dissolved compounds in the subarachnoid space and parenchyma have been found to preferentially transport through the cortex perivascular spaces (PVS) but the transport phenomena involved are unclear. Methods In this study two hydraulic network models were used to predict fluid motion produced by blood vessel pulsations and estimate the contribution made to solute transport in PVS and parenchyma. The effect of varying pulse amplitude and timing, PVS dimensions, and tissue hydraulic conductivity on fluid motion was investigated. Results Periodic vessel pulses resulted in oscillatory fluid motion in PVS and parenchyma but no net flow over time. For baseline parameters, PVS and parenchyma peak fluid velocity was on the order of 10 μm/s and 1 nm/s, with corresponding Peclet numbers below 103 and 10−1 respectively. Peak fluid velocity in the PVS and parenchyma tended to increase with increasing pulse amplitude and vessel size, and exhibited asymptotic relationships with hydraulic conductivity. Conclusions Solute transport in parenchyma was predicted to be diffusion dominated, with a negligible contribution from convection. In the PVS, dispersion due to oscillating flow likely plays a significant role in PVS rapid transport observed in previous in vivo experiments. This dispersive effect could be more significant than convective solute transport from net flow that may exist in PVS and should be studied further.
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Affiliation(s)
- Julian Rey
- Department of Mechanical and Aerospace Engineering, University of Florida, PO Box 116250, Gainesville, FL, 32611, USA
| | - Malisa Sarntinoranont
- Department of Mechanical and Aerospace Engineering, University of Florida, PO Box 116250, Gainesville, FL, 32611, USA.
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11
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Uncertainty quantification and sensitivity analysis of an arterial wall mechanics model for evaluation of vascular drug therapies. Biomech Model Mechanobiol 2017; 17:55-69. [PMID: 28755237 PMCID: PMC5807551 DOI: 10.1007/s10237-017-0944-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2017] [Accepted: 07/17/2017] [Indexed: 02/07/2023]
Abstract
Quantification of the uncertainty in constitutive model predictions describing arterial wall mechanics is vital towards non-invasive assessment of vascular drug therapies. Therefore, we perform uncertainty quantification to determine uncertainty in mechanical characteristics describing the vessel wall response upon loading. Furthermore, a global variance-based sensitivity analysis is performed to pinpoint measurements that are most rewarding to be measured more precisely. We used previously published carotid diameter–pressure and intima–media thickness (IMT) data (measured in triplicate), and Holzapfel–Gasser–Ogden models. A virtual data set containing 5000 diastolic and systolic diameter–pressure points, and IMT values was generated by adding measurement error to the average of the measured data. The model was fitted to single-exponential curves calculated from the data, obtaining distributions of constitutive parameters and constituent load bearing parameters. Additionally, we (1) simulated vascular drug treatment to assess the relevance of model uncertainty and (2) evaluated how increasing the number of measurement repetitions influences model uncertainty. We found substantial uncertainty in constitutive parameters. Simulating vascular drug treatment predicted a 6% point reduction in collagen load bearing (\documentclass[12pt]{minimal}
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\begin{document}$$L_\mathrm {coll}$$\end{document}Lcoll), approximately 50% of its uncertainty. Sensitivity analysis indicated that the uncertainty in \documentclass[12pt]{minimal}
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\begin{document}$$L_{\mathrm {coll}}$$\end{document}Lcoll was primarily caused by noise in distension and IMT measurements. Spread in \documentclass[12pt]{minimal}
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\begin{document}$$L_{\mathrm {coll}}$$\end{document}Lcoll could be decreased by 50% when increasing the number of measurement repetitions from 3 to 10. Model uncertainty, notably that in \documentclass[12pt]{minimal}
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\begin{document}$$L_{\mathrm {coll}}$$\end{document}Lcoll, could conceal effects of vascular drug therapy. However, this uncertainty could be reduced by increasing the number of measurement repetitions of distension and wall thickness measurements used for model parameterisation.
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12
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Rahman A, Zhou YQ, Yee Y, Dazai J, Cahill LS, Kingdom J, Macgowan CK, Sled JG. Ultrasound detection of altered placental vascular morphology based on hemodynamic pulse wave reflection. Am J Physiol Heart Circ Physiol 2017; 312:H1021-H1029. [PMID: 28364018 DOI: 10.1152/ajpheart.00791.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Revised: 03/16/2017] [Accepted: 03/28/2017] [Indexed: 11/22/2022]
Abstract
Abnormally pulsatile umbilical artery (UA) Doppler ultrasound velocity waveforms are a hallmark of severe or early onset placental-mediated intrauterine growth restriction (IUGR), whereas milder late onset IUGR pregnancies typically have normal UA pulsatility. The diagnostic utility of these waveforms to detect placental pathology is thus limited and hampered by factors outside of the placental circulation, including fetal cardiac output. In view of these limitations, we hypothesized that these Doppler waveforms could be more clearly understood as a reflection phenomenon and that a reflected pulse pressure wave is present in the UA that originates from the placenta and propagates backward along the UA. To investigate this, we developed a new ultrasound approach to isolate that portion of the UA Doppler waveform that arises from a pulse pressure wave propagating backward along the UA. Ultrasound measurements of UA lumen diameter and flow waveforms were used to decompose the observed flow waveform into its forward and reflected components. Evaluation of CD1 and C57BL/6 mice at embryonic day (E)15.5 and E17.5 demonstrated that the reflected waveforms diverged between the strains at E17.5, mirroring known changes in the fractal geometry of fetoplacental arteries at these ages. These experiments demonstrate the feasibility of noninvasively measuring wave reflections that originate from the fetoplacental circulation. The observed reflections were consistent with theoretical predictions based on the area ratio of parent to daughters at bifurcations in fetoplacental arteries suggesting that this approach could be used in the diagnosis of fetoplacental vascular pathology that is prevalent in human IUGR. Given that the proposed measurements represent a subset of those currently used in human fetal surveillance, the adaptation of this technology could extend the diagnostic utility of Doppler ultrasound in the detection of placental vascular pathologies that cause IUGR.NEW & NOTEWORTHY Here, we describe a novel approach to noninvasively detect microvascular changes in the fetoplacental circulation using ultrasound. The technique is based on detecting reflection pulse pressure waves that travel along the umbilical artery. Using a proof-of-principle study, we demonstrate the feasibility of the technique in two strains of experimental mice.
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Affiliation(s)
- Anum Rahman
- Mouse Imaging Centre, Hospital for Sick Children, Toronto, Ontario, Canada.,Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
| | - Yu-Qing Zhou
- Mouse Imaging Centre, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Yohan Yee
- Mouse Imaging Centre, Hospital for Sick Children, Toronto, Ontario, Canada.,Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
| | - Jun Dazai
- Mouse Imaging Centre, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Lindsay S Cahill
- Mouse Imaging Centre, Hospital for Sick Children, Toronto, Ontario, Canada
| | - John Kingdom
- Department of Obstetrics and Gynecology, University of Toronto, Toronto, Ontario, Canada.,Mount Sinai Hospital, Toronto, Ontario, Canada; and
| | - Christopher K Macgowan
- Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada.,Physiology and Experimental Medicine, Hospital for Sick Children, Toronto, Ontario, Canada
| | - John G Sled
- Mouse Imaging Centre, Hospital for Sick Children, Toronto, Ontario, Canada; .,Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada.,Department of Obstetrics and Gynecology, University of Toronto, Toronto, Ontario, Canada.,Physiology and Experimental Medicine, Hospital for Sick Children, Toronto, Ontario, Canada
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13
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Head orientation should be considered in ultrasound studies on carotid artery distensibility. J Hypertens 2016; 34:1551-5. [DOI: 10.1097/hjh.0000000000000985] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Huang C, Su Y, Zhang H, Qian LX, Luo J. Comparison of Different Pulse Waveforms for Local Pulse Wave Velocity Measurement in Healthy and Hypertensive Common Carotid Arteries in Vivo. ULTRASOUND IN MEDICINE & BIOLOGY 2016; 42:1111-1123. [PMID: 26924694 DOI: 10.1016/j.ultrasmedbio.2015.12.021] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Revised: 12/12/2015] [Accepted: 12/28/2015] [Indexed: 06/05/2023]
Abstract
Pulse wave velocity (PWV), a measurement of arterial stiffness, can be estimated locally by determining the time delay of the pulse waveforms for a known distance as measured in an ultrasound image. Our aim was to compare three ultrasound-based methods for estimation of local PWV based on the measurement of diameter distension waveforms, displacement waveforms of the anterior wall and displacement waveforms of the posterior wall, respectively, in human common carotid arteries in vivo. The local PWVs at both systolic foot (PWVsf) and dicrotic notch (PWVdn) were estimated from ultrasound radiofrequency data of 25 healthy and 24 hypertensive patients for each method. PWV estimation using the distension waveform method was found to have the highest precision in both groups. Both PWVsf and PWVdn were significantly higher in the hypertensive group compared with the healthy group using the distension waveform method (PWVsf: 6.08 ± 1.70 m/s vs. 4.75 ± 0.92 m/s, p = 0.000014; PWVdn: 7.83 ± 2.26 m/s vs. 5.21 ± 0.95 m/s, p < 0.000001), whereas there was no significant difference at a significance level of 0.01 between the two groups when the anterior or posterior wall waveform method was used. Thus, the difference in arterial stiffness between the two groups could be discriminated well by the distension waveform method. The local PWV estimated using distension waveforms might be a promising index for arterial stiffness characterization and hypertension management.
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Affiliation(s)
- Chengwu Huang
- Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China; Center for Biomedical Imaging Research, Tsinghua University, Beijing, China
| | - Yuan Su
- Department of Ultrasound, Beijing Friendship Hospital, Capital Medical University, Beijing, China
| | - Hong Zhang
- Department of Ultrasound, Beijing Friendship Hospital, Capital Medical University, Beijing, China
| | - Lin-Xue Qian
- Department of Ultrasound, Beijing Friendship Hospital, Capital Medical University, Beijing, China
| | - Jianwen Luo
- Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China; Center for Biomedical Imaging Research, Tsinghua University, Beijing, China.
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15
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Li F, He Q, Huang C, Liu K, Shao J, Luo J. High frame rate and high line density ultrasound imaging for local pulse wave velocity estimation using motion matching: A feasibility study on vessel phantoms. ULTRASONICS 2016; 67:41-54. [PMID: 26773791 DOI: 10.1016/j.ultras.2015.12.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 11/20/2015] [Accepted: 12/28/2015] [Indexed: 06/05/2023]
Abstract
Pulse wave imaging (PWI) is an ultrasound-based method to visualize the propagation of pulse wave and to quantitatively estimate regional pulse wave velocity (PWV) of the arteries within the imaging field of view (FOV). To guarantee the reliability of PWV measurement, high frame rate imaging is required, which can be achieved by reducing the line density of ultrasound imaging or transmitting plane wave at the expense of spatial resolution and/or signal-to-noise ratio (SNR). In this study, a composite, full-view imaging method using motion matching was proposed with both high temporal and spatial resolution. Ultrasound radiofrequency (RF) data of 4 sub-sectors, each with 34 beams, including a common beam, were acquired successively to achieve a frame rate of ∼507 Hz at an imaging depth of 35 mm. The acceleration profiles of the vessel wall estimated from the common beam were used to reconstruct the full-view (38-mm width, 128-beam) image sequence. The feasibility of mapping local PWV variation along the artery using PWI technique was preliminarily validated on both homogeneous and inhomogeneous polyvinyl alcohol (PVA) cryogel vessel phantoms. Regional PWVs for the three homogeneous phantoms measured by the proposed method were in accordance with the sparse imaging method (38-mm width, 32-beam) and plane wave imaging method. Local PWV was estimated using the above-mentioned three methods on 3 inhomogeneous phantoms, and good agreement was obtained in both the softer (1.91±0.24 m/s, 1.97±0.27 m/s and 1.78±0.28 m/s) and the stiffer region (4.17±0.46 m/s, 3.99±0.53 m/s and 4.27±0.49 m/s) of the phantoms. In addition to the improved spatial resolution, higher precision of local PWV estimation in low SNR circumstances was also obtained by the proposed method as compared with the sparse imaging method. The proposed method might be helpful in disease detections through mapping the local PWV of the vascular wall.
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Affiliation(s)
- Fubing Li
- Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China; Center for Biomedical Imaging Research, Tsinghua University, Beijing 100084, China
| | - Qiong He
- Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China; Center for Biomedical Imaging Research, Tsinghua University, Beijing 100084, China
| | - Chengwu Huang
- Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China; Center for Biomedical Imaging Research, Tsinghua University, Beijing 100084, China
| | - Ke Liu
- Division of Electronics and Information Technology, National Institute of Metrology, Beijing 100013, China
| | - Jinhua Shao
- Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China
| | - Jianwen Luo
- Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China; Center for Biomedical Imaging Research, Tsinghua University, Beijing 100084, China.
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Deng CX, Hong X, Stegemann JP. Ultrasound Imaging Techniques for Spatiotemporal Characterization of Composition, Microstructure, and Mechanical Properties in Tissue Engineering. TISSUE ENGINEERING PART B-REVIEWS 2016; 22:311-21. [PMID: 26771992 DOI: 10.1089/ten.teb.2015.0453] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Ultrasound techniques are increasingly being used to quantitatively characterize both native and engineered tissues. This review provides an overview and selected examples of the main techniques used in these applications. Grayscale imaging has been used to characterize extracellular matrix deposition, and quantitative ultrasound imaging based on the integrated backscatter coefficient has been applied to estimating cell concentrations and matrix morphology in tissue engineering. Spectral analysis has been employed to characterize the concentration and spatial distribution of mineral particles in a construct, as well as to monitor mineral deposition by cells over time. Ultrasound techniques have also been used to measure the mechanical properties of native and engineered tissues. Conventional ultrasound elasticity imaging and acoustic radiation force imaging have been applied to detect regions of altered stiffness within tissues. Sonorheometry and monitoring of steady-state excitation and recovery have been used to characterize viscoelastic properties of tissue using a single transducer to both deform and image the sample. Dual-mode ultrasound elastography uses separate ultrasound transducers to produce a more potent deformation force to microscale characterization of viscoelasticity of hydrogel constructs. These ultrasound-based techniques have high potential to impact the field of tissue engineering as they are further developed and their range of applications expands.
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Affiliation(s)
- Cheri X Deng
- Department of Biomedical Engineering, University of Michigan , Ann Arbor, Michigan
| | - Xiaowei Hong
- Department of Biomedical Engineering, University of Michigan , Ann Arbor, Michigan
| | - Jan P Stegemann
- Department of Biomedical Engineering, University of Michigan , Ann Arbor, Michigan
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Microscale characterization of the viscoelastic properties of hydrogel biomaterials using dual-mode ultrasound elastography. Biomaterials 2016; 88:12-24. [PMID: 26928595 DOI: 10.1016/j.biomaterials.2016.02.019] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Revised: 02/11/2016] [Accepted: 02/16/2016] [Indexed: 01/21/2023]
Abstract
Characterization of the microscale mechanical properties of biomaterials is a key challenge in the field of mechanobiology. Dual-mode ultrasound elastography (DUE) uses high frequency focused ultrasound to induce compression in a sample, combined with interleaved ultrasound imaging to measure the resulting deformation. This technique can be used to non-invasively perform creep testing on hydrogel biomaterials to characterize their viscoelastic properties. DUE was applied to a range of hydrogel constructs consisting of either hydroxyapatite (HA)-doped agarose, HA-collagen, HA-fibrin, or preosteoblast-seeded collagen constructs. DUE provided spatial and temporal mapping of local and bulk displacements and strains at high resolution. Hydrogel materials exhibited characteristic creep behavior, and the maximum strain and residual strain were both material- and concentration-dependent. Burger's viscoelastic model was used to extract characteristic parameters describing material behavior. Increased protein concentration resulted in greater stiffness and viscosity, but did not affect the viscoelastic time constant of acellular constructs. Collagen constructs exhibited significantly higher modulus and viscosity than fibrin constructs. Cell-seeded collagen constructs became stiffer with altered mechanical behavior as they developed over time. Importantly, DUE also provides insight into the spatial variation of viscoelastic properties at sub-millimeter resolution, allowing interrogation of the interior of constructs. DUE presents a novel technique for non-invasively characterizing hydrogel materials at the microscale, and therefore may have unique utility in the study of mechanobiology and the characterization of hydrogel biomaterials.
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Sahani AK, Joseph J, Radhakrishnan R, Sivaprakasam M, Seshadri S. Comparison of measurement of the augmentation index from ARTSENS and eTRACKING. Biomed Phys Eng Express 2016. [DOI: 10.1088/2057-1976/2/1/015007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Witzenburg CM, Dhume RY, Lake SP, Barocas VH. Automatic Segmentation of Mechanically Inhomogeneous Tissues Based on Deformation Gradient Jump. IEEE TRANSACTIONS ON MEDICAL IMAGING 2016; 35:29-41. [PMID: 26168433 PMCID: PMC4739827 DOI: 10.1109/tmi.2015.2453316] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Variations in properties, active behavior, injury, scarring, and/or disease can all cause a tissue's mechanical behavior to be heterogeneous. Advances in imaging technology allow for accurate full-field displacement tracking of both in vitro and in vivo deformation from an applied load. While detailed strain fields provide some insight into tissue behavior, material properties are usually determined by fitting stress-strain behavior with a constitutive equation. However, the determination of the mechanical behavior of heterogeneous soft tissue requires a spatially varying constitutive equation (i.e., one in which the material parameters vary with position). We present an approach that computationally dissects the sample domain into many homogeneous subdomains, wherein subdomain boundaries are formed by applying a betweenness based graphical analysis to the deformation gradient field to identify locations with large discontinuities. This novel partitioning technique successfully determined the shape, size and location of regions with locally similar material properties for: (1) a series of simulated soft tissue samples prescribed with both abrupt and gradual changes in anisotropy strength, prescribed fiber alignment, stiffness, and nonlinearity, (2) tissue analogs (PDMS and collagen gels) which were tested biaxially and speckle tracked (3) and soft tissues which exhibited a natural variation in properties (cadaveric supraspinatus tendon), a pathologic variation in properties (thoracic aorta containing transmural plaque), and active behavior (contracting cardiac sheet). The routine enables the dissection of samples computationally rather than physically, allowing for the study of small tissues specimens with unknown and irregular inhomogeneity.
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Affiliation(s)
- Colleen M. Witzenburg
- University of Minnesota, Minneapolis, MN 55455 USA and is now with the University of Virginia, Charlottesville, VA 22908 USA
| | | | - Spencer P. Lake
- University of Minnesota, Minneapolis, MN 55455 USA as is now with Washington University, St. Louis, MO 63130 USA
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Sahani AK, Joseph J, Radhakrishnan R, Sivaprakasam M. Automatic Measurement of End-Diastolic Arterial Lumen Diameter in ARTSENS. J Med Device 2015. [DOI: 10.1115/1.4030873] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Over past few years, we are developing a system for facilitating large scale screening of patients for cardiovascular risk—arterial stiffness evaluation for noninvasive screening (ARTSENS). ARTSENS is an image-free device that uses a single element ultrasound transducer to obtain noninvasive measurements of arterial stiffness (AS) in a fully automated manner. AS is directly proportional to end-diastolic lumen diameter (Dd). Multilayered structure of the arterial walls and indistinct characteristics of intima-lumen interface (ILI) makes it quite difficult to accurately estimate Dd in A-mode radio-frequency (RF) frames obtained from ARTSENS. In this paper, we propose a few methods based on fitting simple mathematical models to the echoes from arterial walls, followed by a novel method to fuse the information from curve fitting error and distension curve to arrive at an accurate measure of Dd. To bring down the curve fitting time and facilitate processing on low-end processors, a novel approach using the autocorrelation of echoes from opposite walls of the artery has been discussed. The methods were analyzed for their comparative accuracy against reference Dd obtained from 85 human volunteers using Hitachi-Aloka eTRACKING system. Dd from all reported methods show strong and statistically significant positive correlation with eTRACKING and mean error of less than 7% could be achieved. As expected, Dd from all methods show significant positive correlation with age.
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Affiliation(s)
- Ashish Kumar Sahani
- Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India e-mail:
| | - Jayaraj Joseph
- Healthcare Technology Innovation Centre, Indian Institute of Technology Madras, Chennai 600 036, India e-mail:
| | | | - Mohanasankar Sivaprakasam
- Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India
- Healthcare Technology Innovation Centre, Indian Institute of Technology Madras, Chennai 600 036, India e-mail:
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Hoskins PR, Kenwright DA. Recent developments in vascular ultrasound technology. ULTRASOUND : JOURNAL OF THE BRITISH MEDICAL ULTRASOUND SOCIETY 2015; 23:158-65. [PMID: 27433252 DOI: 10.1177/1742271x15578778] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
This article describes four technologies relevant to vascular ultrasound which are available commercially in 2015, and traces their origin back through the research literature. The technologies are 3D ultrasound and its use in plaque volume estimation (first described in 1994), colour vector Doppler for flow visualisation (1994), wall motion for estimation of arterial stiffness (1968), and shear wave elastography imaging of the arterial wall (2010). Overall these technologies have contributed to the understanding of vascular disease but have had little impact on clinical practice. The basic toolkit for vascular ultrasound has for the last 25 years been real-time B-mode, colour flow and spectral Doppler. What has changed over this time is improvement in image quality. Looking ahead it is noted that 2D array transducers and high frame rate imaging continue to spread through the commercial vascular ultrasound sector and both have the potential to impact on clinical practice.
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Affiliation(s)
- P R Hoskins
- Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, EH16 4TJ
| | - D A Kenwright
- Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, EH16 4TJ
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Huang C, Ren TL, Luo J. Effects of parameters on the accuracy and precision of ultrasound-based local pulse wave velocity measurement: a simulation study. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2014; 61:2001-2018. [PMID: 25474776 DOI: 10.1109/tuffc.2014.006597] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Quantification of arterial stiffness, such as pulse wave velocity (PWV), is increasingly used in the risk assessment of cardiovascular disease. Pulse wave imaging (PWI) is an emerging ultrasound-based technique to noninvasively measure the local PWV instead of the global PWV, as in conventional methods. In PWI, several key parameters, including the frame rate of ultrasound imaging, motion estimation rate (MER), number of scan lines, image width, PWV value, and sonographic signal-to-noise ratio (SNRs), play an important but still unclear role in the accuracy and precision of PWV measurement. In this study, computer simulations were performed to investigate the fundamental effects of these parameters on the PWV measurement. The pulse waveform was estimated by speckle tracking on ultrasound RF signals acquired at a frame rate of 2083 Hz from a location on the common carotid artery of a healthy subject. By applying different time delays on the estimated waveform based on specific PWI parameters, the pulse waveforms at others locations were simulated. Ultrasound RF signals of the artery during the pulse wave propagation were generated from a 2-D convolutional image formation model. The PWI technique was applied to estimate the PWV at different values of frame rate, MER, number of scan lines, image width, PWV, and SNRs. The performance of the PWV estimation was evaluated by measuring the relative error, coefficient of variation (CV) and coefficient of determination (R(2)). The results showed that PWVs could be correctly measured when the frame rate was higher than a certain value (i.e., minimum frame rate), below which the estimated error increased rapidly. The minimum frame rate required for PWV estimation was found to increase with the value of PWV. An optimal MER was found (i.e., about 200 Hz) and allowed better performance of PWV measurement. The CV of PWV estimation decreased and R(2) increased with number of scan lines and image width, indicating that the performance of the PWV estimation could be improved with a larger number of scan lines and image width. For a given sufficiently high frame rate, a higher PWV value was found to deteriorate the PWV estimation, as indicated by an increasing CV and decreasing R(2). The simulation results were in good agreement with the theoretical analysis. Finally, high-quality PWV estimation could be obtained as long as the SNRs was higher than about 30 dB. The quantitative effects of the key parameters obtained from this study might provide important guidelines for parameter optimization in ultrasound-based local PWV measurement in vivo.
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Messas E, Pernot M, Couade M. Arterial wall elasticity: State of the art and future prospects. Diagn Interv Imaging 2013; 94:561-9. [PMID: 23619291 DOI: 10.1016/j.diii.2013.01.025] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Sahani AK, Joseph J, Sivaprakasam M. Automatic measurement of lumen diameter of carotid artery in A-Mode ultrasound. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2013; 2013:3873-3876. [PMID: 24110577 DOI: 10.1109/embc.2013.6610390] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Accurate measurement of lumen diameter is essential for correct estimation of arterial compliance. We have been developing a new non-invasive arterial compliance measurement tool using a single element ultrasound transceiver. In this paper we propose a new method for measurement of lumen diameter from single line of Radio-Frequency Signal (RF) obtained from the common carotid artery (CCA). The method is free from fixed thresholds and uses shape fitting to get objective measurement. The accuracy of the algorithm was found to be better than 5 % for software simulated and phantom arteries and better than 10 % in case of data obtained from CCA of human volunteers.
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Rouleau L, Tremblay D, Cartier R, Mongrain R, Leask RL. Regional variations in canine descending aortic tissue mechanical properties change with formalin fixation. Cardiovasc Pathol 2012; 21:390-7. [DOI: 10.1016/j.carpath.2011.12.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2010] [Revised: 10/17/2011] [Accepted: 12/15/2011] [Indexed: 11/16/2022] Open
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Hartley CJ, Reddy AK, Madala S, Entman ML, Michael LH, Taffet GE. Doppler velocity measurements from large and small arteries of mice. Am J Physiol Heart Circ Physiol 2011; 301:H269-78. [PMID: 21572013 DOI: 10.1152/ajpheart.00320.2011] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
With the growth of genetic engineering, mice have become increasingly common as models of human diseases, and this has stimulated the development of techniques to assess the murine cardiovascular system. Our group has developed nonimaging and dedicated Doppler techniques for measuring blood velocity in the large and small peripheral arteries of anesthetized mice. We translated technology originally designed for human vessels for use in smaller mouse vessels at higher heart rates by using higher ultrasonic frequencies, smaller transducers, and higher-speed signal processing. With these methods one can measure cardiac filling and ejection velocities, velocity pulse arrival times for determining pulse wave velocity, peripheral blood velocity and vessel wall motion waveforms, jet velocities for the calculation of the pressure drop across stenoses, and left main coronary velocity for the estimation of coronary flow reserve. These noninvasive methods are convenient and easy to apply, but care must be taken in interpreting measurements due to Doppler sample volume size and angle of incidence. Doppler methods have been used to characterize and evaluate numerous cardiovascular phenotypes in mice and have been particularly useful in evaluating the cardiac and vascular remodeling that occur following transverse aortic constriction. Although duplex ultrasonic echo-Doppler instruments are being applied to mice, dedicated Doppler systems are more suitable for some applications. The magnitudes and waveforms of blood velocities from both cardiac and peripheral sites are similar in mice and humans, such that much of what is learned using Doppler technology in mice may be translated back to humans.
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Affiliation(s)
- Craig J Hartley
- Section of Cardiovascular Research, Department of Medicine, Baylor College of Medicine, and Methodist DeBakey Heart and Vascular Center, Houston TX, 77030, USA.
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Wang P, Olbricht WL. Fluid mechanics in the perivascular space. J Theor Biol 2011; 274:52-7. [DOI: 10.1016/j.jtbi.2011.01.014] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2009] [Revised: 01/10/2011] [Accepted: 01/10/2011] [Indexed: 10/18/2022]
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Beijers HJBH, Henry RMA, Bravenboer B, Ferreira I, Dekker JM, Nijpels G, Stehouwer CDA. Metabolic syndrome in nondiabetic individuals associated with maladaptive carotid remodeling: the Hoorn Study. Am J Hypertens 2011; 24:429-36. [PMID: 21212746 DOI: 10.1038/ajh.2010.256] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
BACKGROUND The metabolic syndrome (MetS) is associated with an increased risk of stroke. Arterial remodeling could play an important role herein as maladaptive remodeling is a risk factor for stroke. The purpose of this study was to investigate whether MetS was associated with maladaptive remodeling of the carotid artery and if any such association was independent of hemodynamic variables. METHODS We studied 385 (n = 195 women) nondiabetic, elderly subjects. A MetS z-score (average of sex-specific z-scores of the five MetS traits) was constructed. Intima-media thickness (IMT) and interadventitial diameter (IAD) were assessed by ultrasonography, and lumen diameter (LD), and circumferential wall stress (CWS) were calculated. Multiple linear regression analysis was used to investigate the association between MetS and carotid remodeling. RESULTS After adjustment for age, sex, height, prior cardiovascular disease (CVD), dyslipidemia, and smoking, MetS was independently associated with a greater IAD (regression coefficient (β) per s.d. increase in MetS z-score (95% confidence interval), 0.45 mm (0.28; 0.63)), LD (0.41 mm (0.25; 0.58)) and CWS (5.56 kPa (3.71; 7.42)). These associations were attenuated after additional adjustment for inflammatory, metabolic and particularly hemodynamic variables, but remained statistically significant. No significant association was found between MetS and IMT (0.020 mm (-0.006; 0.046)). CONCLUSIONS MetS is associated with maladaptive remodeling of the carotid artery, which is the result of changes in LD, IAD, and, to a lesser extent, IMT. This process is independent of hemodynamic variables. Whether this association and process will be observed in a broader population and explains the increased risk of stroke in MetS deserves further study.
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Hartley CJ, Reddy AK, Madala S, Entman ML, Taffet GE. Feasibility of dual Doppler velocity measurements to estimate volume pulsations of an arterial segment. ULTRASOUND IN MEDICINE & BIOLOGY 2010; 36:1169-1175. [PMID: 20620703 PMCID: PMC2904320 DOI: 10.1016/j.ultrasmedbio.2010.04.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Revised: 04/06/2010] [Accepted: 04/08/2010] [Indexed: 05/29/2023]
Abstract
If volume flow was measured at each end of an arterial segment with no branches, any instantaneous differences would indicate that volume was increasing or decreasing transiently within the segment. This concept could provide an alternative method to assess the mechanical properties or distensibility of an artery noninvasively using ultrasound. The goal of this study was to determine the feasibility of using Doppler measurements of pulsatile velocity (opposed to flow) at two sites to estimate the volume pulsations of the intervening arterial segment. To test the concept over a wide range of dimensions, we made simultaneous measurements of velocity in a short 5 mm segment of a mouse common carotid artery and in a longer 20 cm segment of a human brachial-radial artery using a two-channel 20 MHz pulsed Doppler and calculated the waveforms and magnitudes of the volume pulsations during the cardiac cycle. We also estimated pulse wave velocity from the velocity upstroke arrival times and measured artery wall motion using tissue Doppler methods for comparison of magnitudes and waveforms. Volume pulsations estimated from Doppler velocity measurements were 16% for the mouse carotid artery and 4% for the human brachial artery. These values are consistent with the measured pulse wave velocities of 4.2 m/s and 10 m/s, respectively, and with the mouse carotid diameter pulsation. In addition, the segmental volume waveforms resemble diameter and pressure waveforms as expected. We conclude that with proper application and further validation, dual Doppler velocity measurements can be used to estimate the magnitude and waveform of volume pulsations of an arterial segment and to provide an alternative noninvasive index of arterial mechanical properties.
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Affiliation(s)
- Craig J Hartley
- Department of Medicine, Baylor College of Medicine and The Methodist DeBakey Heart and Vascular Center, Houston, TX 77030, USA.
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Balocco S, Basset O, Courbebaisse G, Boni E, Frangi AF, Tortoli P, Cachard C. Estimation of the viscoelastic properties of vessel walls using a computational model and Doppler ultrasound. Phys Med Biol 2010; 55:3557-75. [PMID: 20508319 DOI: 10.1088/0031-9155/55/12/019] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Human arteries affected by atherosclerosis are characterized by altered wall viscoelastic properties. The possibility of noninvasively assessing arterial viscoelasticity in vivo would significantly contribute to the early diagnosis and prevention of this disease. This paper presents a noniterative technique to estimate the viscoelastic parameters of a vascular wall Zener model. The approach requires the simultaneous measurement of flow variations and wall displacements, which can be provided by suitable ultrasound Doppler instruments. Viscoelastic parameters are estimated by fitting the theoretical constitutive equations to the experimental measurements using an ARMA parameter approach. The accuracy and sensitivity of the proposed method are tested using reference data generated by numerical simulations of arterial pulsation in which the physiological conditions and the viscoelastic parameters of the model can be suitably varied. The estimated values quantitatively agree with the reference values, showing that the only parameter affected by changing the physiological conditions is viscosity, whose relative error was about 27% even when a poor signal-to-noise ratio is simulated. Finally, the feasibility of the method is illustrated through three measurements made at different flow regimes on a cylindrical vessel phantom, yielding a parameter mean estimation error of 25%.
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Zhang Y, Su N, Li Z, Gou Z, Chen Q, Zhang Y. Assessment of arterial distension based on continuous wave Doppler ultrasound with an improved Hilbert-Huang processing. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2010; 57:203-213. [PMID: 20040447 DOI: 10.1109/tuffc.2010.1399] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A novel approach based on continuous wave (CW) Doppler ultrasound and the Hilbert-Huang transform with end-effect restraint by mirror extending is proposed to assess arterial distension. In the approach, bidirectional Doppler signals were first separated using the phasing-filter technique from the mixed quadrature Doppler signals, which were produced by bidirectional blood and vessel wall movements. Each separated unidirectional signal was decomposed into intrinsic mode functions (IMFs) using the empirical mode decomposition with end effect restraint by mirror extending algorithm, and then the relevant IMFs that contribute to the vessel wall components were identified. Finally, the displacement waveforms of the vessel wall were calculated by integrating its moving velocity waveforms, which were extracted from the bidirectional Hilbert spectrum estimated from the identified wall IMFs. This approach was applied to simulated and clinical Doppler signals from normal common carotid arteries (CCAs). In the simulation study, the estimated wall moving velocity and displacement waveforms were compared with the theoretical ones, respectively. The mean and standard deviation of the root-mean-square errors between the estimated and theoretical wall distension of the 30 realizations was 4.2 +/- 0.4 microm. In the clinical study, peak-to-peak distension was extracted in a subject and then averaged over 15 cardiac cycles, resulting in 603 +/- 22 microm. The mean and standard deviation of the CCA distension averaged over the experimental measurements of 12 healthy subjects gave the result of 620 +/- 154 microm. The clinical results were in agreement with those measured by using the multigate Doppler ultrasound and echo tracking systems. The results show that based on the CW Doppler ultrasound, the proposed approach is practical for extracting arterial wall peak-to-peak distension correctly and could be an alternative method for the vessel wall distension estimation.
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Affiliation(s)
- Yufeng Zhang
- Department of Electronic Engineering, Information School, Yunnan University, Kunming, Yunnan, China
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Confluence of incident and reflected waves interferes with systolic foot detection of the carotid artery distension waveform. J Hypertens 2008; 26:2374-80. [DOI: 10.1097/hjh.0b013e328311cdd5] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Teng XF, Zhang YT. Theoretical study on the effect of sensor contact force on pulse transit time. IEEE Trans Biomed Eng 2007; 54:1490-8. [PMID: 17694870 DOI: 10.1109/tbme.2007.900815] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Pulse transit time (PTT) has been widely used for noninvasive examination of the arterial viscoelastic properties, such as elasticity, compliance, and stiffness of the vessel walls. PTT is usually determined as the time interval between the peak of the electrocardiogram R wave and the foot of the photoplethysmogram (PPG). However, it was observed that the PPG is affected by the applied contact force between the photoplethysmographic sensor and the measurement site, e.g., finger. In this study, the nonlinear biomechanical properties of the finger arterial wall were considered when investigating the changes in PTT with varying contact force. Emphasis was placed on the changes in the shape of the arterial wall pressure-volume curve. The simulation results indicated that at positive transmural pressure, PTT increased with the applied contact force, reaching the maximum at zero transmural pressure and remaining at a constant level at negative transmural pressure. The theoretical analysis was further verified by the experiments carried out on thirty young subjects and six elderly subjects using twelve discrete levels of contact force.
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Affiliation(s)
- Xiao-Fei Teng
- Joint Research Center for Biomedical Engineering, Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China.
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35
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Hartley CJ, Reddy AK, Madala S, Entman ML, Michael LH, Taffet GE. Noninvasive ultrasonic measurement of arterial wall motion in mice. CONFERENCE PROCEEDINGS : ... ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL CONFERENCE 2007; 2004:3688-91. [PMID: 17271094 DOI: 10.1109/iembs.2004.1404036] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
To facilitate assessment of arterial function, we developed a noninvasive Doppler method for measuring vessel motion in genetically altered mice. A 20 MHz probe was held by an alligator clip and positioned over the carotid arteries of 16 mice including six 3 to 5-month old wild-type (WT), four 30-month old senescent (Old), two apolipoprotein-E (ApoE), and four alpha smooth muscle actin (alphaSMA) mice. Doppler signals were obtained simultaneously from both vessel walls and from blood flow using one or two probes. The displacement signals from the near and far walls were subtracted to generate a diameter signal from which the excursion and an augmentation index were calculated. The excursion ranged between 13 microm (in ApoE) and 95 microm (in alphaSMA). The augmentation index was lowest in the WT mice (0.06) and highest in the Old mice (0.29). This noninvasive method is able to identify and confirm characteristic changes in arterial properties associated with age, atherosclerosis, and the absence of vascular tone.
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Affiliation(s)
- Craig J Hartley
- Sections of Cardiovascular Sciences and Geriatrics, Dept. of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
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36
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Hermeling E, Reesink KD, Reneman RS, Hoeks APG. Measurement of local pulse wave velocity: effects of signal processing on precision. ULTRASOUND IN MEDICINE & BIOLOGY 2007; 33:774-81. [PMID: 17383803 DOI: 10.1016/j.ultrasmedbio.2006.11.018] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2006] [Revised: 11/03/2006] [Accepted: 11/03/2006] [Indexed: 05/14/2023]
Abstract
Pulse wave velocity (PWV) provides information about the mechanical properties of the vessel: the stiffer the artery is, the higher the PWV will be. PWV measured over a short arterial segment facilitates direct characterization of local wall properties corrected for prevailing pressure without the necessity of measuring pulse pressure locally. Current methods for local PWV assessment have a poor precision, but it can be improved by applying linear regression to a characteristic time-point in distension waveforms as recorded simultaneously by multiple M-line ultrasounds. We investigated the precision of this method in a phantom scaled according to realistic in vivo conditions. Special attention was paid to the identification of the foot of the wave, using the maximum of the second derivative, the intersecting tangent and the 20% threshold method. Before foot detection, the distension waveforms were subjected to preprocessing with various filters. The precision of the maximum of the second derivative had a coefficient of variation (CV) of 0.45% and 10.45% for an eighth and second order low pass filter, respectively. The intersecting tangent and the threshold method were less sensitive to filtering; the CVs were 0.66% and 0.68% for the high order filter and 2.36% and 1.43% for the low order filter, respectively. We conclude that foot detection by a threshold of 20% or by the tangent method are more suitable to identify the foot of the wave to measure local PWV. Both methods are less sensitive to (phase) noise than the maximum of the second derivative method and exhibit good precision with a CV of less than 1%.
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Affiliation(s)
- Evelien Hermeling
- Department of Biophysics, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands
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37
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Lu MH, Zheng YP, Huang QH. A novel method to obtain modulus image of soft tissues using ultrasound water jet indentation: a phantom study. IEEE Trans Biomed Eng 2007; 54:114-21. [PMID: 17260862 DOI: 10.1109/tbme.2006.884646] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The alteration of tissue stiffness is generally known to be associated with pathological changes. Ultrasound indentation is one of the methods that can be used to assess the mechanical properties of the soft tissues. It uses a flat-ended ultrasound transducer to directly contact the tissue to sense tissue deformation under an applied load. This paper introduced a novel noncontact ultrasound indentation system using water jet compression. The key idea was to utilize a water jet as the indenter as well as the coupling medium for propagation of the ultrasound beam. High frequency focused ultrasound (20 MHz) was used to measure the indentation deformation at a microscopic level. It has been demonstrated that the system could effectively assess the tissue-mimic phantoms with different stiffness. Water jet coupling allows the system to conduct C-scan on soft tissues rapidly and conveniently. By applying different pressures while taking C-scan sequences, the modulus images of the phantoms could be obtained based on the applied pressure and the phantom deformation and thickness. This paper presented the preliminary results on gel phantoms. The spatial resolution, the contrast resolution of the measurements and the reproducibility of the results were also discussed.
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Affiliation(s)
- Min-Hua Lu
- Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hong Kong, China.
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38
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Dobson G, Flewitt J, Tyberg JV, Moore R, Karamanoglu M. Endografting of the Descending Thoracic Aorta Increases Ascending Aortic Input Impedance and Attenuates Pressure Transmission in Dogs. Eur J Vasc Endovasc Surg 2006; 32:129-35. [PMID: 16564712 DOI: 10.1016/j.ejvs.2006.01.020] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Accepted: 01/21/2006] [Indexed: 10/24/2022]
Abstract
OBJECTIVES Endografting is being used to manage aneurysms, dissections and acute traumatic disruptions of the thoracic aorta. The acute effects of such interventions on ventricular afterload and on pressure wave transmission characteristics are not well known. METHODS In five dogs, a 55 mm endograft was introduced into the descending aorta, just distal to the left subclavian artery, with oversizing of 20%. Following formaldehyde induced complete heart block, the hearts were paced (30-120bpm). The ascending aortic pressures and flows were recorded using Millar micro-tip manometers and ultrasonic flowmeters, respectively. Arterial pressures proximal and distal to the stent site were also recorded. For each heart rate, parameters of a modified Windkessel (SVR: systemic vascular resistance, Z0: characteristic impedance, C: total arterial compliance) were estimated. The pulse wave velocity (PWV) and reflection coefficient (Gamma) were calculated from the pressure wave transfer functions. RESULTS The Z0 (0.25+/-0.05 vs 0.41+/-0.06 mmHg/ml s(-1), P<.05) was increased and C was decreased (0.45+/-0.07 vs 0.28+/-0.04 ml/mmHg, P<0.001) following endograft placement. SVR tended to increase (P=.06) and ascending aortic Gamma was unchanged. The PWV increased (418+/-67 vs 755+/-135 cm/s, P<.05) and the distal Gamma decreased (0.09+/-0.10 vs -0.49+/-0.07, P<.05). CONCLUSIONS Endografting in the proximal descending aorta cause unfavorable changes in the ascending aortic input impedance and an increase in the PWV through the grafted segment, consistent with an increase in the modulus of elasticity. The grafts produce a negative Gamma at the distal end, an uncommon occurrence in the systemic circulation. Whether this change is of sufficient magnitude to result in post-graft dilation is unknown.
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Affiliation(s)
- G Dobson
- Department of Anesthesia and Surgery, University of Calgary, Calgary, Alta., Canada.
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Du H, Liu J, Pellot-Barakat C, Insana MF. Optimizing multicompression approaches to elasticity imaging. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2006; 53:90-9. [PMID: 16471435 PMCID: PMC2736134 DOI: 10.1109/tuffc.2006.1588394] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Breast lesion visibility in static strain imaging ultimately is noise limited. When correlation and related techniques are applied to estimate local displacements between two echo frames recorded before and after a small deformation, target contrast increases linearly with the amount of deformation applied. However, above some deformation threshold, decorrelation noise increases more than contrast such that lesion visibility is severely reduced. Multicompression methods avoid this problem by accumulating displacements from many small deformations to provide the same net increase in lesion contrast as one large deformation but with minimal decorrelation noise. Unfortunately, multicompression approaches accumulate echo noise (electronic and sampling) with each deformation step as contrast builds so that lesion visibility can be reduced again if the applied deformation increment is too small. This paper uses signal models and analysis techniques to develop multicompression strategies that minimize strain image noise. The analysis predicts that displacement variance is minimal in elastically homogeneous media when the applied strain increment is 0.0035. Predictions are verified experimentally with gelatin phantoms. For in vivo breast imaging, a strain increment as low as 0.0015 is recommended for minimum noise because of the greater elastic heterogeneity of breast tissue.
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Affiliation(s)
- Huini Du
- Department of Biomedical Engineering, University of California, Davis, CA 95616, USA.
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40
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Cinthio M, Ahlgren AR, Jansson T, Eriksson A, Persson HW, Lindström K. Evaluation of an ultrasonic echo-tracking method for measurements of arterial wall movements in two dimensions. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2005; 52:1300-11. [PMID: 16245599 DOI: 10.1109/tuffc.2005.1509788] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The longitudinal movement of blood vessel walls has so far gained little or no attention, as it has been presumed that these movements are of a negligible magnitude. However, modern high-resolution ultrasound scanners can demonstrate that the inner layers of the arterial wall exhibit considerable movements in the longitudinal direction. This paper evaluates a new, noninvasive, echo-tracking technique, which simultaneously can track both the radial and the longitudinal movements of the arterial wall with high resolution in vivo. Initially, the method is evaluated in vitro using a specially designed ultrasound phantom, which is attached to and moved by an X-Y system, the movement of which was compared with two high-resolution triangulation lasers. The results show an inaccuracy of 2.5% full scale deflection (fsd), reproducibility of 12 microm and a resolution of 5 microm, which should be more than sufficient for in vivo studies. The ability of the method is also demonstrated in a limited in vivo study in which a preselected part of the inner vessel wall of the right common carotid artery of a healthy volunteer is tracked in two dimensions over many cardiac cycles. The results show well reproducible x-y movement loops in which the recorded radial and longitudinal movements both are of the magnitude millimetre.
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Affiliation(s)
- Magnus Cinthio
- Department of Electrical Measurements, Lund University, 221 00 Lund, Sweden.
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41
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Reneman RS, Meinders JM, Hoeks APG. Non-invasive ultrasound in arterial wall dynamics in humans: what have we learned and what remains to be solved. Eur Heart J 2005; 26:960-6. [PMID: 15764612 DOI: 10.1093/eurheartj/ehi177] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In the past decades, non-invasive vascular ultrasound has substantially improved our insights into artery wall dynamics under normal circumstances and in disease. Although we have learned a lot, the methods in use are subject to improvement. In this review, we discuss the most important achievements in non-invasive assessment of dynamic artery wall properties in humans with emphasis on the clinical relevance of the observations. Special attention will be paid to the changes observed in aging, and in essential and borderline hypertension, because the loss of compliance (i.e. the ability to store volume thereby reducing pressure increases during ejection) of the elastic arteries in the elderly and in these patients possibly has consequences on their management. The changes in dynamic artery wall properties in diabetes and atherosclerosis are briefly discussed as well. A new approach to the determination of baroreceptor sensitivity, using artery stretch as input, is presented. The review starts with a description of the parameters most commonly used to describe dynamic artery wall properties and of the techniques employed to assess these parameters. The problems encountered in these assessments and the possible solutions to these problems are addressed as well.
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Affiliation(s)
- Robert S Reneman
- Department of Physiology, Cardiovascular Research Institute Maastricht, University of Maastricht, PO Box 616, 6200 MD Maastricht, The Netherlands.
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42
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Henry RMA, Ferreira I, Kostense PJ, Dekker JM, Nijpels G, Heine RJ, Kamp O, Bouter LM, Stehouwer CDA. Type 2 diabetes is associated with impaired endothelium-dependent, flow-mediated dilation, but impaired glucose metabolism is not; The Hoorn Study. Atherosclerosis 2004; 174:49-56. [PMID: 15135250 DOI: 10.1016/j.atherosclerosis.2004.01.002] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2003] [Revised: 12/09/2003] [Accepted: 01/05/2004] [Indexed: 11/26/2022]
Abstract
BACKGROUND Type 2 diabetes (DM2) and impaired glucose metabolism (IGM) are associated with an increased cardiovascular disease risk. Impaired endothelial synthesis of nitric oxide (NO) is an important feature of atherothrombosis and can be estimated from endothelium-dependent flow-mediated dilation (FMD). It is controversial whether or not FMD is impaired in DM2 and IGM. We investigated this issue in a population-based setting. METHODS AND RESULTS In the study population (n = 650; 246 with normal glucose metabolism (NGM), 135 with IGM and 269 with DM2; mean age: 67.6 years), FMD and endothelium-independent nitroglycerine-mediated dilation (NMD) were ultrasonically estimated from the brachial artery and expressed as the absolute change in diameter in mm. The increase in diameter (mean +/- standard deviation) in NGM, IGM and DM2 was 0.19 +/- 0.15, 0.19 +/- 0.18 and 0.13 +/- 0.17 MD and 0.45 +/- 0.21, 0.43 +/- 0.24 and 0.45 +/- 0.25 for NMD. After adjustment for age, sex, baseline diameter and percentage increase in peak systolic velocity, DM2, as compared to NGM, remained associated with impaired FMD (regression coefficient beta (95%CI)) as compared to NGM, -0.06 mm (-0.09 to -0.03). IGM was not associated with impaired FMD (beta, 0.01 mm (-0.02 to 0.04)). Additional adjustment for conventional cardiovascular risk factors did not alter these associations. Hyperglycemia or hyperinsulinemia explained 2% of the association between DM2 and FMD. NMD was not associated with glucose tolerance. CONCLUSIONS This study shows that DM2 is independently associated with impaired FMD. Hyperglycemia and hyperinsulinemia contribute minimally to this association. Impaired FMD may therefore, in part, explain the increased cardiovascular disease risk in DM2, whereas the normal FMD in IGM suggests that other forms of endothelial dysfunction are important in explaining the increased cardiovascular disease risk in IGM.
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Affiliation(s)
- Ronald M A Henry
- Institute for Research in Extramural Medicine, VU University Medical Center, Amsterdam, The Netherlands
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43
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Ruiz-Feria CA, Zhang D, Nishimura H. Age- and sex-dependent changes in pulse pressure in fowl aorta. Comp Biochem Physiol A Mol Integr Physiol 2004; 137:311-20. [PMID: 15123204 DOI: 10.1016/j.cbpb.2003.10.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2003] [Revised: 10/07/2003] [Accepted: 10/08/2003] [Indexed: 10/26/2022]
Abstract
Chickens (males more than females) have higher blood pressure (BP) than most mammals and spontaneously develop vascular neointimal plaques (NP) and diffuse subendothelial thickening in the lower segment of the abdominal aorta (AbA, referred to as 'NP-prone area') that partly resemble atherosclerotic lesions in mammals. NP areas, which are larger in males, have a causal relationship with incremental increases in BP during maturation. We hypothesize that decreased wall distensibility and altered hemodynamic forces at the NP-prone area may contribute to the NP formation. We measured pressure pulse wave (PW) and systolic and diastolic BP along the descending aorta in anesthetized chickens at different ages using an intravascular microtip transducer and calculated pulse pressure (PP) as an indicator for artery distensibility. At all ages examined and in both sexes, the PW showed a sharper peak at the more peripheral locations and the amplitude of the PW increased as it descended the aorta. PP, expressed as relative increases from the PP in the aortic arch (%), was 40.4+/-12.6 and 71.4+/-18.6 at the AbA and ischiadic artery, respectively, in young males (24-27 weeks); 23.5+/-8.6 and 43.8+/-16.2 in adults (72-75 weeks); and 5.4+/-3.4 and 9.1+/-4.9 in chicks (5-7 weeks). Location-dependent increases in PP were significantly higher in young males (P<0.05). The PP increases in females were not different among the three age groups. The contour of the PW in the proximal aorta changes in older birds, exhibiting steeper increases in the ascending and descending limbs, suggesting that faster wave reflection from the periphery augments peak systolic pressure. NP was most frequently seen in the lower segment of the abdominal aorta in older males. These results suggest that: (1) site-dependent increases in PP amplitude are marked in young males, possibly reflecting a reduction in arterial wall elasticity enhanced by incremental rises in BP, and (2) NP formation may contribute to the stiffness of aortic walls in the NP-prone area.
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Affiliation(s)
- Ciro A Ruiz-Feria
- Department of Physiology, University of Tennessee Health Science Center, 894 Union Avenue, Memphis, TN 38163, USA
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Hartley CJ, Reddy AK, Madala S, Entman ML, Michael LH, Taffet GE. Noninvasive ultrasonic measurement of arterial wall motion in mice. Am J Physiol Heart Circ Physiol 2004; 287:H1426-32. [PMID: 15317682 DOI: 10.1152/ajpheart.01185.2003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Despite the extensive use of genetically altered mice to study cardiovascular physiology and pathology, it remains difficult to quantify arterial function noninvasively in vivo. We have developed a noninvasive Doppler method for quantifying vessel wall motion in anesthetized mice. A 20-MHz probe was held by an alligator clip and positioned over the carotid arteries of 16 mice, including six 3- to 5-mo-old wild-type (WT), four 30-mo-old senescent (old), two apolipoprotein E null (ApoE), and four α-smooth muscle actin null (α-SMA) mice. Doppler signals were obtained simultaneously from both vessel walls and from blood flow. The calculated displacement signals from the near and far walls were subtracted to generate a diameter signal from which the excursion and an augmentation index were calculated. The excursion ranged between 13 μm (in ApoE) and 95 μm (in α-SMA). The augmentation index was lowest in the WT mice (0.06) and highest in the old mice (0.29). We conclude that Doppler signal processing may be used to measure vessel wall motion in mice with high spatial and temporal resolution and that diameter signals can replace pressure signals for calculating the augmentation index. This noninvasive method is able to identify and confirm characteristic changes in arterial properties previously associated with age, atherosclerosis, and the absence of vascular tone.
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Affiliation(s)
- Craig J Hartley
- Department of Medicine, The Methodist DeBakey Heart Center, Baylor College of Medicine, Houston, Texas 77030, USA.
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45
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McCulloch AD, Harris AB, Sarraf CE, Eastwood M. New Multi-cue Bioreactor for Tissue Engineering of Tubular Cardiovascular Samples under Physiological Conditions. ACTA ACUST UNITED AC 2004; 10:565-73. [PMID: 15165473 DOI: 10.1089/107632704323061924] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
In the present study we have developed a multi-cue bioreactor (MCB) that is capable of delivering a range of stimuli to assist the development of a tissue-engineered construct. The MCB provides an accurate and utilizable computer-controlled pulsatile pump and strain induction mechanism and it has the capability of applying physiological conditions to samples. The device described here emulates the pressure and straining environment found at the aortic root. This function, along with an integral perfusion and sterile containment system, allows for long-term culture and whole-tissue testing capability. Aortic and pulmonary arteries were obtained from freshly isolated porcine hearts and subjected to various loading regimens (Deltapressure/flow/force). Through analyzing data acquired by the MCB transducer array it was possible to differentiate the dynamic mechanical properties of the tissue types tested. In addition, the MCB illustrates a novel concept in cardiovascular tissue engineering: being able to support long-term tissue culture of cell-seeded substrates while they are under the influence of mechanical cues. After 7 days of pulsation in the MCB cell alignment was observed. The MCB represents a versatile model that will enable the development of tissue engineering not only for cardiovascular tissue, but for all tubular tissues such as esophageal, tracheal, and bronchial systems.
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Affiliation(s)
- Andrew D McCulloch
- Centre for Tissue Engineering Research, Department of Biomedical Sciences, University of Westminster, London, United Kingdom.
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Meinders JM, Hoeks APG. Simultaneous assessment of diameter and pressure waveforms in the carotid artery. ULTRASOUND IN MEDICINE & BIOLOGY 2004; 30:147-54. [PMID: 14998666 DOI: 10.1016/j.ultrasmedbio.2003.10.014] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2003] [Revised: 09/22/2003] [Accepted: 10/14/2003] [Indexed: 05/10/2023]
Abstract
Simultaneous assessment of diameter and pressure waveforms allows the calculation of the incremental compliance, distensibility, pulse wave velocity and elastic modulus as function of the distending pressure. However, the waveforms must be obtained at the same position and acquired and processed with the same filter characteristics to circumvent possible temporal and spatial changes in amplitude and phase. In this paper, arterial diameter waveforms are assessed by means of ultrasound (US) and converted to pressure using an empirically derived exponential relationship between pressure and arterial cross-section. The derived pressure waveform is calibrated to brachial end diastolic and mean arterial pressure by iteratively changing the wall rigidity coefficient (i.e., the exponential power). Because pressure is derived directly from arterial cross-section, no phase delay is introduced due to spatial separation or different filter characteristics. The method was evaluated for the left common carotid artery of 51 healthy subjects ranging in age from 22 to 75 years old. In healthy subjects, the carotid pulse pressure is 29% lower than the brachial pulse pressure. Continuous assessment of arterial properties confirms that pulse-wave velocity and incremental elastic modulus increase, whereas distensibility and compliance decrease, as function of increasing distending blood pressure.
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Affiliation(s)
- Jan M Meinders
- Department of Biophysics, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands.
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47
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Abstract
For millennia, physicians have used palpation as a part of the physical examination to detect pathology. The ubiquitous presence of "stiffer" tissue associated with pathology often represents an early warning sign for disease, as in the cases of breast or prostate cancer. Very often tumors are found at surgery that were occult even with modern imaging instruments. This implies that methods for estimating "hardness" of tissues would add a weapon to the medical armamentarium. To this end, this review discusses several methods of estimating tissue hardness using internal or external means of applying stress (force per unit area) and several associated methods of detecting the resulting strain (fractional length change) in an effort to image a tissue mechanical property, such as Young's modulus (ratio of stress to strain). Some investigators have developed methods of estimating stiffness or modulus, but most methods result in qualitative images of stiffness. Nevertheless, such estimates may add a great deal of information not currently available to the current field of medical imaging.
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Affiliation(s)
- James F Greenleaf
- Basic Ultrasound Research Laboratory, Department of Physiology and Biophysics, Mayo Clinic Rochester, Rochester, Minnesota 55905, USA,
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Bilston LE, Fletcher DF, Brodbelt AR, Stoodley MA. Arterial pulsation-driven cerebrospinal fluid flow in the perivascular space: a computational model. Comput Methods Biomech Biomed Engin 2003; 6:235-41. [PMID: 12959757 DOI: 10.1080/10255840310001606116] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
This study was conducted to determine whether local arterial pulsations are sufficient to cause cerebrospinal fluid (CSF) flow along perivascular spaces (PVS) within the spinal cord. A theoretical model of the perivascular space surrounding a "typical" small artery was analysed using computational fluid dynamics. Systolic pulsations were modelled as travelling waves on the arterial wall. The effects of wave geometry and variable pressure conditions on fluid flow were investigated. Arterial pulsations induce fluid movement in the PVS in the direction of arterial wave travel. Perivascular flow continues even in the presence of adverse pressure gradients of a few kilopascals. Flow rates are greater with increasing pulse wave velocities and arterial deformation, as both an absolute amplitude and as a proportion of the PVS. The model suggests that arterial pulsations are sufficient to cause fluid flow in the perivascular space even against modest adverse pressure gradients. Local increases in flow in this perivascular pumping mechanism or reduction in outflow may be important in the etiology of syringomyelia.
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Affiliation(s)
- Lynne E Bilston
- Prince of Whales Medical Research Institute, University of New South Whales, Barker St, Randwick, NSW 2031, Australia.
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Mai JJ, Lupotti FA, Insana MF. Vascular elasticity from regional displacement estimates. ULTRASONIC IMAGING 2003; 25:171-192. [PMID: 14870802 DOI: 10.1177/016173460302500305] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A recently-developed ultrasonic technique for measuring elastic properties of vascular tissue is evaluated using computer simulations, phantom and in vivo human measurements. A time sequence of displacement images is measured over the cardiac cycle to describe the spatial and temporal patterns of deformation surrounding arteries. This information is combined with a mathematical model to estimate an elastic modulus. Computer simulations of ultrasonic echo data from deformed tissues are analyzed to define a signal processing approach. Measurements in flow phantoms, with and without vessel-simulating channel walls, provide an assessment of the accuracy and precision of this technique for vascular elasticity measurements. Finally, preliminary results for the stiffness index (beta) in a study group of healthy human volunteers are compared with previously reported data. We find that careful measurement technique is required to control measurement variability.
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Affiliation(s)
- Jerome J Mai
- Department of Biomedical Engineering, University of California, Davis, CA 95616, USA
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Kargel C, Höbenreich G, Trummer B, Insana MF. Adaptive clutter rejection filtering in ultrasonic strain-flow imaging. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2003; 50:824-835. [PMID: 12894916 PMCID: PMC2715560 DOI: 10.1109/tuffc.2003.1214502] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
This paper introduces strain-flow imaging as a potential new technique for investigating vascular dynamics and tumor biology. The deformation of tissues surrounding pulsatile vessels and the velocity of fluid in the vessel are estimated from the same data set. The success of the approach depends on the performance of a digital filter that must separate echo signal components caused by flow from tissue motion components that vary spatially and temporally. Eigenfilters, which are an important tool for naturally separating signal components adaptively throughout the image, perform very well for this task. The method is examined using two tissue-mimicking flow phantoms that provide stationary and moving clutter associated with pulsatile flow.
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Affiliation(s)
- Christian Kargel
- Department of Medical Information Technology at the Carinthia Tech. Institute, University of Applied Sciences, Austria (e-mail: )
| | - Gernot Höbenreich
- Department of Biomedical Engineering, University of California, Davis (e-mail: )
| | - Birgit Trummer
- Department of Biomedical Engineering, University of California, Davis
| | - Michael F. Insana
- Department of Biomedical Engineering, University of California, Davis (e-mail: )
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