A Velocity <i>k</i>‐Space Analysis of Flow Effects in Echo‐Planar and Spiral Imaging

Nishimura, Dwight G.; Irarrázabal, Pablo; Meyer, Craig H.

doi:10.1002/mrm.1910330414

Cited by 164 publications

(145 citation statements)

References 10 publications

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“…Further work should aim to improve acquisition speed, for example by using a shared reference image (45). The ''swirl'' artefact associated with changing signal during spiral acquisitions (31,43) was visible during the sharp increases in venous blood velocity but was concentrated at a radius of FoV/N (150/4) from the veins being measured and so away from the deep veins of interest. However, anatomical variations may cause these ''swirls'' to lie on vessels of interest where multiple veins are at this distance apart.…”

Section: Discussionmentioning

confidence: 99%

“…An un-gated sequence was developed, using spiral readout gradients due to their advantages for flow imaging (30,31) and greater coverage of k-space per excitation, and velocity-encode preparation, than acquired by a standard Cartesian acquisition. A (1, 1) binomial pulse series for spectral-spatial water excitation (32) was used to avoid exciting the fat signal because of its off-resonance blurring artefact in spiral imaging (33), followed by bipolar velocity encoding gradients (achieving a final through plane V enc ¼ 8.3 cm/s) and the spiral readout gradient (Fig.…”

Section: Non-gated Interleaved Spirals (Isp)mentioning

confidence: 99%

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MR phase‐contrast velocity mapping methods for measuring venous blood velocity in the deep veins of the calf

Pierce

Gatehouse

et al. 2011

Magnetic Resonance Imaging

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Purpose: To evaluate the feasibility of using un-gated, real-time MRI for venous blood velocity mapping in the calf, comparing an interleaved spiral k-space sequence (ISP) against a standard segmented gradient echo sequence (GRE). Materials and Methods:A flow phantom with a variable flow-rate was scanned using both GRE and ISP sequences for an in vitro comparison. Seven subjects were scanned prone, performing metronome guided breathing, using the (externally triggered) segmented GRE and real-time ISP sequences. The segmented GRE acquisition duration was 2.5 mins (22 guided respiratory cycles) and the ISP sequence ran continuously for 35s, 4 full guided respiratory cycles. Mean velocity from each of the deep veins was measured and peak mean velocity, peak flow rate and cumulative volume flow over a respiratory cycle compared between sequences.Results: The two sequences compared well both in vitro and in vivo. The real-time ISP sequence showed shortterm variations in mean velocity superimposed on the respiratory induced flow, which were averaged out using the segmented GRE sequence. Conclusion:Real-time ISP provides comparable timeaveraged flow results to the standard sequence with additional information on real-time flow variations and so could be used for further investigation into venous blood flow in the lower leg.

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Section: Discussionmentioning

confidence: 99%

Section: Non-gated Interleaved Spirals (Isp)mentioning

confidence: 99%

MR phase‐contrast velocity mapping methods for measuring venous blood velocity in the deep veins of the calf

Pierce

Gatehouse

et al. 2011

Magnetic Resonance Imaging

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“…Spatial blurring may occur if inplane velocities are present in the voxels of interest, which would be the case for oblique planes. However, spiral trajectories have been shown to provide excellent immunity to flow artifacts compared with other k-space trajectories (e.g., 2DFT, echo-planar imaging), and distortion should be minimal even in the presence of high velocity flow (e.g., stenosis) (32). Spatial blurring due to in-plane flow could potentially be incorporated into the model proposed in Eq.…”

Section: Discussionmentioning

confidence: 99%

“…Spatial blurring due to in-plane flow could potentially be incorporated into the model proposed in Eq. 2, using the formalism introduced by Nishimura et al (32).…”

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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“…The characteristics and appearances of these artifacts are determined by the shape of the trajectory. To have good flow/motion properties, the gradient first moment should be small near the k-space origin, and smoothly varying as a function of the distance to the origin (15,16). In the case of 3DFT, off-resonance manifests as a displacement of the object, since phase accrual is done in the same k-space direction for every readout.…”

Section: K-space Propertiesmentioning

confidence: 99%

Fast three‐dimensional k‐space trajectory design using missile guidance ideas

Mir¹,

Guesalaga²,

Spiniak³

et al. 2004

Magnetic Resonance in Med

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Three-dimensional (3D) k-space trajectories are needed to acquire volumetric images in MRI. While scan time is determined by the trajectory efficiency, image quality and distortions depend on the shape of the trajectories. There are several 3D trajectory strategies for sampling the k-space using rectilinear or curve schemes. Since there is no evidence about their optimality in terms of image quality and acquisition time, a new design method based on missile guidance ideas is explored. Since air-to-air missile guidance shares similar goals and constraints with the problem of k-space trajectory design, a control approach for missiles is used to design a 3D trajectory. The k-space is divided into small cubes, and each one is treated as a target to be sampled. The main goal is to cover the entire space as quickly and efficiently as possible, with good performance under different conditions. This novel design method is compared to other trajectories using simulated and real data.

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A Velocity k‐Space Analysis of Flow Effects in Echo‐Planar and Spiral Imaging

Cited by 164 publications

References 10 publications

MR phase‐contrast velocity mapping methods for measuring venous blood velocity in the deep veins of the calf

MR phase‐contrast velocity mapping methods for measuring venous blood velocity in the deep veins of the calf

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

Fast three‐dimensional k‐space trajectory design using missile guidance ideas

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