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.

May 28, 2016 This was due to high velocity of CSF and subsequent turbulent flow resulting in intravoxel dephasing. Patient had normal pressure hydrocephalus

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. Read "Signal decay due to susceptibility-induced intravoxel dephasing on multiple air-filled cylinders: MRI simulations and experiments, Magnetic Resonance Materials in Physics, Biology and Medicine" on DeepDyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. Another cause of dephasing is intravoxel dephasing.

Intravoxel dephasing

swedish website; Menu. Home; International Admissions. Why study at Lund University 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. 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) (21), and turbulence imposing small velocity fluctuations superimposed on the principal velocity (22).

It was found that a theta of 2 pi/3 radians has optimal S/N but that a theta of pi radians is a good compromise and that phase encoding of (O, pi, 2 pi) radians offer an advantage over the previous method, which used (-pi, O, pi) increments, in that a T2' (intravoxel susceptibility dephasing) image may be obtained in addition to the usual water, fat, and Bo images.

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. This RF phase cycling scheme, when combined with existing meta-DENSE suppression of the T 1 recovering signal, yields higher quality DENSE myocardial strain maps. Signal loss due to flow is induced via intravoxel dephasing which, according to Eq. 1, is dependent on velocity profile and m1.

We show that intravoxel gradient dephasing, which is normally associated only with signal loss, can distort phase evolution and affect a voxel’s apparent frequency. In Section III, we demonstrate these distortions experimentally, comparing gradient maps taken at different slice thicknesses and offsets, which show good agreement with the analytical expression.

Overestimation trend of CEMRA is confirmed and the reduction of voxel size, decreasing the dephasing intravoxel effect, allows to have a better overlapping of stenosis morphology on CEMRA compared with DSA, but it does not yield diagnostic gain in the stenosis grading. PMID: 12594561 [Indexed for MEDLINE] Publication Types: Comparative Study; MeSH terms 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. 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. This RF phase cycling scheme, when combined with existing meta-DENSE suppression of the T 1 recovering signal, yields higher quality DENSE myocardial strain maps. The refocusing mechanism fails if intravoxel dephasing exceeds over ±180º manifest by band-like artifacts.

(25) presented a mathematical description of … rephasing gradient (red oval), leading to a small amount of intravoxel dephasing that eliminates the effects of rapidly fluctuating gradient fields. Figure 2 a) linear PE, b) meta-DENSE complex acquisition for reduced intravoxel dephasing. Aletras, Anthony LU and Arai, A E ( 2004 ) In Journal of Magnetic Resonance 169 (2) . p.246-249 Mark A technique is proposed to compensate for the slice dephasing artifact and improve the signal‐to‐noise ratio (SNR) of gradient‐echo images. This method is composed of two components: mapping of the internal gradient and design of the slice‐selective radiofrequency (RF) pulse. The RF pulse is designed with its phase response as the negative of the product of a chosen echo time and the Frahm, J., Merboldt, K. D., & Haenicke, W. (1995).
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Home; International Admissions. Why study at Lund University rephasing gradient (red oval), leading to a small amount of intravoxel dephasing that eliminates the effects of rapidly fluctuating gradient fields.

For a certain velocity profile, the flow suppression capability of FSD-preparation is determined by m1.
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The jet is larger than in the cine above because the gradient echo sequence has a longer TE (6 ms vs. 2 ms), which allows for more intravoxel dephasing. In MRI

En högre bandbredd används även för att minska The simulation is based on physical principles and is able to produce possible artifacts in MRI images like intra-voxel dephasing, chemical shift, and cross-talk. Indeed, some locations are particularly sensitive to eg coil sensitivity or intra-voxel dephasing, which can result in a reduced tSNR at specific functional brain Moreover, the difference in magnetic susceptibility ([chi]) of tumors and normal tissues accelerates intravoxel dephasing of transverse magnetization in tumor and creates off-resonance effects or [T.sup.*sub.2] contrast, a combination of spin-spin relaxation ([T.sub.2]) and [B.sub.0] magnetic field inhomogeneity. 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). 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.

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Steady-state free precession (SSFP) imaging is a magnetic resonance imaging ( MRI) The refocusing mechanism fails if intravoxel dephasing exceeds over ± 180º manifest by band-like artifacts. During the last decade modern scanners have&

meta-DENSE complex acquisition for reduced intravoxel dephasing. Forskningsoutput: Tidskriftsbidrag › Artikel i vetenskaplig tidskrift. Översikt; Cite Bibtex Detaljer. Författare: Anthony Aletras; A E Arai; Externa organisationer: National Heart Lung and Blood 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. Spin dephasing under nonlinear gradients: Implications for imaging and field mapping.