Interaction between secondary velocities, flow pulsation and vessel morphology in the common carotid artery

Tortoli, Piero; Michelassi, Vittorio; Bambi, G.; Guidi, Francesco; Righi, D.

doi:10.1016/s0301-5629(02)00705-6

Cited by 62 publications

(45 citation statements)

References 14 publications

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“…This is attributed, in part, to the limited range-velocity product of pulsed Doppler velocimeters (aliasing), to the difficulty in correcting for angle in the presence of disturbed and non-axial flow (Tortoli et al, 2003), and to alterations in the velocity profile (Nichols and O'Rourke, 1998). However, as shown in Figure 4, the alias limit of 4.5 m/s was never exceeded in our experiments with mice, and the use of a Doppler angle close to zero would have minimized any potential errors due to disturbed flow and non-axial velocities (Li et al, 2003).…”

Section: Factors Affecting Baseline and Hyperemic Velocitiesmentioning

confidence: 99%

Effects of Isoflurane on Coronary Blood Flow Velocity in Young, Old and ApoE−/− Mice Measured by Doppler Ultrasound

Hartley

Reddy

Madala

et al. 2007

Ultrasound in Medicine & Biology

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The commonly used anesthetic agent, isoflurane (ISO), is a potent coronary vasodilator which could potentially be used in the assessment of coronary reserve, but its effects on coronary blood flow in mice are unknown. Coronary reserve is reduced by age, coronary artery disease, and other cardiac pathologies in man, and some of these conditions can now be modeled in mice. Accordingly, we used Doppler ultrasound to measure coronary flow velocity in mice anesthetized at low (1%) and at high (2.5%) levels of ISO to generate baseline (B) and elevated hyperemic (H) and Y and between A and O were significant (P < 0.01), while the differences in hyperemic velocities were not (P > 0.05). H/B was higher in old mice due to decreased baseline flow rather than increased hyperemic flow velocity. In contrast ApoE −/− mice have increased baseline and hyperemic velocities perhaps due to coronary lesions. The differences in baseline velocities between young and old mice could be due to age-related changes in basal metabolism or to differential sensitivity to isoflurane. We conclude that Doppler ultrasound combined with coronary vasodilation via isoflurane could provide a convenient and noninvasive method to estimate coronary reserve in mice, but also that care must be taken when assessing coronary flow in mice under isoflurane anesthesia because of its potent coronary vasodilator properties.

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Section: Factors Affecting Baseline and Hyperemic Velocitiesmentioning

confidence: 99%

Effects of Isoflurane on Coronary Blood Flow Velocity in Young, Old and ApoE−/− Mice Measured by Doppler Ultrasound

Hartley

Reddy

Madala

et al. 2007

Ultrasound in Medicine & Biology

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“…A common choice of tag delivery function model is 'plug-flow' (i.e., constant and without dispersion). However, it is known that blood flow in the major arteries is likely to be poorly approximated by simple plug-flow, as it is both highly pulsatile and has a time-varying nonuniform cross-sectional flowprofile (5). Indeed, Wu et al (6) recently demonstrated experimentally that both flow dispersion and flow pulsatility have a significant effect on the ASL signal.…”

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confidence: 99%

Modeling the effects of dispersion and pulsatility of blood flow in pulsed arterial spin labeling

Gallichan

Jezzard

2008

Magnetic Resonance in Med

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Arterial spin labeling (ASL) is a method of using MRI to image cerebral perfusion. For the measurement to be calibrated, a model is required describing the kinetics of the flow of the inverted blood from the labeling region to the imaging region. It is common to assume plug-flow, but alternatives such as a Gaussian distribution of arrival times have also been suggested. In this study a physiologically based model for dispersion is developed and compared to existing models when fit to experimental data. The model is based on the assumption of parabolic flow in the major arteries, and also allows inclusion of cardiac pulsatility. It was found that fitting using the proposed model leads to higher perfusion estimates, with the difference becoming more pronounced in regions where the dispersion is greater. This suggests that current models may underestimate perfusion in these areas. However, fitting using the proposed model also leads to high uncertainties in parameter estimates due to non-orthogonality of the parameters. Effects due to pulsatility are expected to be observable, but when no cardiacgating is used the mean curve over several cardiac cycles is predicted to closely match the curve which assumes constant flow. Key words: pulsed arterial spin labeling; ASL; pulsatility; dispersionArterial spin labeling (ASL) involves acquiring images with and without inversion of water proton spins proximal to the area of interest, thereby allowing the measurement of cerebral blood flow (CBF) without requiring administration of an exogenous tracer (1-3). In order for the measurement to be quantitative, a kinetic model of the tag delivery process needs to be assumed and fit to the data to obtain the flow parameters. Buxton et al. (4) presented a general modeling framework for ASL which includes a tag delivery function that can be modeled to incorporate the dispersion of the tag between the tagging region and the imaging voxel. A common choice of tag delivery function model is 'plug-flow' (i.e., constant and without dispersion). However, it is known that blood flow in the major arteries is likely to be poorly approximated by simple plug-flow, as it is both highly pulsatile and has a time-varying nonuniform cross-sectional flowprofile (5). Indeed, Wu et al. (6) recently demonstrated experimentally that both flow dispersion and flow pulsatility have a significant effect on the ASL signal. They also presented a model to estimate the effect of the cardiac cycle on the ASL signal, but that model appears to implicitly assume plug-flow when calculating the variation in tag-volume. The dispersion is accounted for by assuming a Gaussian distribution of transit delays.Hrabe and Lewis (7) presented analytical forms of the kinetic model by assuming various tag delivery functions that included dispersion and concluded by advocating the assumption of a Gaussian distribution of tag arrival times at the imaging voxel. They justified this choice physiologically by assuming that the primary source of dispersion would be in vessels close to ...

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“…The voxel should also be small enough that the assumption of a monotonically increasing or decreasing intravoxel velocity profile is not violated. These assumptions must be reevaluated when studying subjects with highly stenotic arteries (34)(35)(36)(37)(38). It is straightforward to determine if one of these conditions has been violated by analyzing the velocity distributions.…”

Section: Discussionmentioning

confidence: 99%

Feasibility of in vivo measurement of carotid wall shear rate using spiral fourier velocity encoded MRI

Carvalho

Nielsen

Nayak

2010

Magnetic Resonance in Med

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Arterial wall shear stress is widely believed to influence the formation and growth of atherosclerotic plaque; however, there is currently no gold standard for its in vivo measurement. The use of phase contrast MRI has proved to be challenging due to partial-volume effects and inadequate signal-to-noise ratio at the high spatial resolutions that are required. This work evaluates the use of spiral Fourier velocity encoded MRI as a rapid method for assessing wall shear rate in the carotid arteries. Wall shear rate is calculated from velocity histograms in voxels spanning the blood/vessel wall interface, using a method Atherosclerosis affects over 18 million Americans. The associated formation, growth, and rupture of intraarterial plaque represent the fundamental process leading to myocardial infarction and thrombotic stroke. Arterial wall shear stress (WSS)-the drag force acting on the endothelium as a result of blood flow-is widely believed to influence the formation and growth of atherosclerotic plaque and may have prognostic value. WSS can be estimated as the product of wall shear rate (WSR) and blood viscosity (µ), where WSR is the radial gradient of blood flow velocity (dv /dr) at the vessel wall. Low WSS (1,2) and highly oscillatory WSS (3) have been linked to the formation and growth of atherosclerotic plaques, and this link has been validated in vitro (4). High WSS has also been hypothesized as a factor responsible for the topography of atherosclerotic lesions (5). Serial and noninvasive WSS measurement would be of value to the in vivo testing of these hypotheses and to better our understanding of the causal relationships between hemodynamics and the process of atherosclerotic plaque formation, growth, and rupture.Direct methods for measuring WSS are highly invasive and/or can only be used in conjunction with in vitro models (6-8). Indirect methods for measuring WSS are based on extrapolation of the measured axial velocity profile near the vessel wall (9), which can be measured by either ultrasound (10,11) or MRI (11-16). The accuracy of such methods is limited by data quality and the spatial resolution of the velocity estimates. Particularly, phase contrast (PC) MRI suffers from partial-volume effects (17) and inadequate signal-to-noise ratio (SNR) at high spatial resolutions (Fig. 1). PC is not currently capable of providing accurate absolute measurements of WSS (18) and has been shown to underestimate blood flow velocities in the carotid bifurcation by 31-39% (19). An alternative approach for estimating WSS is to reconstruct a complex flow field via computational fluid dynamics (CFD) simulation, using vascular geometries and input/output functions derived from noninvasive imaging data (20)(21)(22). This approach is computationally intense and may be sensitive to many assumptions and simplifications that are frequently made about the properties of blood and endothelium. CFD is also limited in modeling wall compliance and is sensitive to boundary conditions (11).In 1995, Frayne and Rutt (23) proposed a no...

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Interaction between secondary velocities, flow pulsation and vessel morphology in the common carotid artery

Cited by 62 publications

References 14 publications

Effects of Isoflurane on Coronary Blood Flow Velocity in Young, Old and ApoE−/− Mice Measured by Doppler Ultrasound

Effects of Isoflurane on Coronary Blood Flow Velocity in Young, Old and ApoE−/− Mice Measured by Doppler Ultrasound

Modeling the effects of dispersion and pulsatility of blood flow in pulsed arterial spin labeling

Feasibility of in vivo measurement of carotid wall shear rate using spiral fourier velocity encoded MRI

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