av P Dyverfeldt · 2010 · Citerat av 6 — Quantification of Intravoxel Velocity Standard Deviation and Turbulence Intensity by necessary to obtain a dephasing that results in a detectable signal loss.

meta-DENSE complex acquisition for reduced intravoxel dephasing. Anthony Aletras & A E Arai, 2004, In: Journal of Magnetic Resonance. 169, 2, p. 246-249.

In gradient-echo images, not in spin-echo images, these local fields cause intravoxel dephasing of the water signal of the surrounding tissue. This description of the contrast enhancement has been confirmed by a series of in vitro blood sample experiments and image simulations. Errors arise from intravoxel dephasing and the intravoxel asymmetry. The spectral leakage due to intravoxel dephasing is roughly 6-8% from one voxel to one of its nearest neighbors.

Intravoxel dephasing

Because of the rephasing Gradient moment nulling is a technique used to reduce flow artifacts in our image and intravoxel dephasing. It is also a technique used in bright blood imaging. 18: Intravoxel dephasing helps in distinguishing arachnoid cysts from webs. Findings and procedure details. Commonly encountered artifacts on MRI due to CSF Fig. 18: Intravoxel dephasing helps in distinguishing arachnoid cysts from webs. Correction of the artifact can be achieved with the help of imaging using smaller TY - JOUR. T1 - meta-DENSE complex acquisition for reduced intravoxel dephasing.

The refocusing mechanism fails if intravoxel dephasing exceeds over ±180º manifest by band-like artifacts. During the last decade modern scanners have overcome these limitations making bSSFP a viable and useful sequence on most mid- and high-field systems.

intra-voxel dephasing, at least three methods have been presented previously: Method 1 (Isochromat Summation, IS) numerical methods populating the input model voxel with numerous isochromats (magnetization vectors) and thus effectively increasing the model resolution [3], Experiments were performed with a 0.2 T magnet on a network of small interacting air-filled cylinders along with Magnetic resonance imaging (MRI) simulations integrating intravoxel dephasing. Signal decay over echo time was assessed at different pixel sizes on real and simulated images.

MR vessel wall imaging refers to MRI techniques used to evaluate for disease within the walls of arteries, beyond the luminal abnormalities depicted on angiographic imaging.This can be used anywhere in the body but is particularly important intracranially in distinguishing between various causes of luminal stenosis such as intracranial atherosclerotic disease versus vasculitis.

All spins are completely in phase at the instant of the spin echo, but immediately begin to dephase at a rate proportional to the amount of magnetic field inhomogeneity within the voxel. For voxels near metal or air/tissue boundaries, this can be considerable. Another cause of dephasing is intravoxel dephasing. Because of laminar flow, different velocities may exist within a voxel, thus leading to phase dispersion (incoherence) and signal loss. How to decrease intravoxel dephasing and increase SNR: Experiments were performed with a 0.2 T magnet on a network of small interacting air-filled cylinders along with Magnetic resonance imaging (MRI) simulations integrating intravoxel dephasing.

Fourier transformation results voxel dephasing originates from an increase in broadness of Efficient and Accurate Bloch-based Simulation of Intra-voxel Dephasing using Multiple Isochomats and Magnetization Spatial Gradients Zhipeng Cao 1, Christopher T. Sica, Giuseppe Carluccio 2, and Christopher M. Collins Displacement encoding with stimulated echoes (DENSE) with a meta-DENSE readout and RF phase cycling to suppress the STEAM anti-echo is described for reducing intravoxel dephasing signal loss. Signal loss due to flow is induced via intravoxel dephasing which, according to Eq. 1, is dependent on velocity profile and m1. For a certain velocity profile, the flow suppression capability of FSD-preparation is determined by m1. The varied flow velocities and directions result in more rapid dephasing and signal loss termed “intravoxel dephasing.” A commonly encountered CSF flow artifact is the signal void in the dorsal subarachnoid space on sagittal T2-weighted images of the thoracic spine ( Fig. 13 ). The refocusing mechanism fails if intravoxel dephasing exceeds over ±180º manifest by band-like artifacts. During the last decade modern scanners have overcome these limitations making bSSFP a viable and useful sequence on most mid- and high-field systems. MATERIALS AND METHODS: Experiments were performed with a 0.2 T magnet on a network of small interacting air-filled cylinders along with Magnetic resonance imaging (MRI) simulations integrating intravoxel dephasing.
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phase difference between stationary nuclei and flowing nuclei in voxel, nuclei insame voxel are out of phase with each other, results inredirection of signal amplitude. flow phenomena compensation.

Intravoxel dephasing, leading to signal phase cancellation in the voxel, can be quantified by T2* relaxation measurements. Intervoxel dephasing can be characterized by the standard deviation of the phase image histogram. Materials and methods Experiments were performed with Keywords Magnetic susceptibility · Intravoxel dephasing · a 0.2 T magnet on a network of small interacting air-ﬁlled Signal loss · Artefacts · MRI simulation · cylinders along with Magnetic resonance imaging (MRI) Field inhomogeneity simulations integrating intravoxel dephasing.
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Since magnetic properties of changing blood oxygenation (Y) affect the tissue water MRI signal through intravoxel spin dephasing (Kennan et al., 1994), changes in Y can be differentially captured with the transverse relaxation rates as measured by gradient-echo R 2 * and spin-echo (R2).

Moreover, while intra-sponding directions in k space. Fourier transformation results voxel dephasing originates from an increase in broadness of Efficient and Accurate Bloch-based Simulation of Intra-voxel Dephasing using Multiple Isochomats and Magnetization Spatial Gradients Zhipeng Cao 1, Christopher T. Sica, Giuseppe Carluccio 2, and Christopher M. Collins 1Radiology, The Pennsylvania State University, Hershey, PA, United States, 2Radiology, New York University, New York City, NY, United States Many different mechanisms have been found to influence intravoxel dephasing signal loss in stenotic jets including higher‐order motion, e.g., acceleration (11-14), alignment of the image plane with the jet (15, 16), voxel size and partial volume effects in voxels with large velocity distributions (10, 17-20) the user‐defined velocity encoding (Venc) , and turbulence imposing small velocity Materials and methods Experiments were performed with a 0.2T magnet on a network of small interacting air-filled cylinders along with Magnetic resonance imaging (MRI) simulations integrating intravoxel dephasing. Signal decay over echo time was assessed at different pixel sizes on real and simulated images.

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Signal loss due to flow is induced via intravoxel dephasing which, according to Eq. 1, is dependent on velocity profile and m1. For a certain velocity profile, the flow suppression capability of FSD-preparation is determined by m1. Haacke et al. (25) presented a mathematical description of …

Signal loss due to flow is induced via intravoxel dephasing which, according to Eq. 1, is dependent on velocity profile and m1. For a certain velocity profile, the flow suppression capability of FSD-preparation is determined by m1. Haacke et al. (25) presented a mathematical description of the signal loss induced by FSD Intravoxel dephasing causes signal loss and thus intensity attenuation in the images. The new rephasing factor we introduce, which changes the intensity of a voxel in images during the registration, is used to improve the accuracy of the intensity-based nonrigid registration method and mitigate the intensity attenuation effect. intravoxel dephasing effect is mainly along the slice selec-tion direction and is termed the slice dephasing artifact. Shimmingcangenerallyreducethemagneticfieldinhomo-geneity.

intravoxel dephasing and amplitude of the section-selecting gradient. The contrast-to-noiseratio (CNR) between CSF and the cerebellar peduncle, and the visibility of the cranial nerves and vertebrobasilar artery were signiﬁcantly improved on 3D images in 17 subjects.

Errors arise from intravoxel dephasing and the intravoxel asymmetry. The spectral leakage due to intravoxel dephasing is roughly 6-8% from one voxel to one of its nearest neighbors.

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