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Journal of Magnetic Resonance - Research Outputs - Lund

The effects of intravoxel dephasing and incomplete slice refocusing on susceptibility contrast in gradient-echo MRI. Spin dephasing arising from intravoxel internal gradient lowers the signal-to-noise ratio (SNR) and therefore de-gradesthequalityofgradient-echoimages,especiallythose acquired at long TE. This dephasing effect can be lessened with increased in-plane spatial resolution and reduced 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. 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.

Accordingly, the inverse T2*MRI model consists of two inverse computation steps. 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& The large blood signal is minimally affected by intravoxel dephasing, which is typically caused by complex flow and susceptibility variations. Because the contrast-.

Real-time fMRI Biofeedback Targeting the Orbitofrontal Cortex

For simplicity, assume a two-dimensional problem. On the other hand, intravascular-dephasing effects scale with dHb concentration and are therefore most prominent in the draining veins.

Real-time fMRI Biofeedback Targeting the Orbitofrontal Cortex

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.

‘‘intravoxel dephasing,’’ but also from incomplete refocus-phase-encoding direction shift the gradient echo along corre-ing of the slice-selection gradient. Moreover, while intra-sponding directions in k space.
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– small to medium flip angles. 9 Oct 22, 2018 large gradient encoding magnitudes as well as dephasing artefacts caused by subject motion, which is particularly challenging in fetal MRI. Removal of intravoxel dephasing artifact in gradient-echo images using a field- map based RF refocusing technique. Magn Reson Med. 1999 Oct;42(4):807-12. 3D TOF CE-MRA has improved spatial resolution, less saturation effects and intravoxel dephasing, and better evaluation of aneurysm lumen. With this technique, Jan 30, 2016 complex T2* image via an intravoxel dephasing average. Accordingly, the inverse T2*MRI model consists of two inverse computation steps.

meta-DENSE complex acquisition for reduced intravoxel dephasing. / Aletras, Anthony; Arai, A E. In: Journal of Magnetic Resonance, Vol. 169, No. 2, 2004, p. 246-249. meta-DENSE complex acquisition for reduced intravoxel dephasing. Aletras, Anthony LU and Arai, A E In Journal of Magnetic Resonance 169 (2). p.246-249.
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Dephasing is proportional to the square of the time (diffusion time) during which the gradients are … (1999) Chen, Wyrwicz. Magnetic Resonance in Medicine. 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-sel The most effective method for reducing intravoxel dephasing is to shorten the echo time (TE); however, the amount that TE can be shortened in conventional sequences is limited. A new sequence incorporating velocity-dependent slice excitation and ultrashort TE (UTE) centric radial readout trajectories is proposed that reduces TE from 2.85 to 0.65 ms. How to decrease intravoxel dephasing and increase SNR: Decrease the voxel size (increase spatial resolution), either by increasing the matrix (trade-off: will reduce signal-to-noise ratio ) or by reducing the FOV (trade-off: may cause wraparound). Only gold members can continue reading.

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 At very low diffusion weighting the diffusion MRI signal is affected by intravoxel incoherent motion (IVIM) caused by dephasing of magnetization due to incoherent blood flow in capillaries or other sources of microcirculation. 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.
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Real-time fMRI Biofeedback Targeting the Orbitofrontal Cortex

Aletras, Anthony LU and Arai, A E In Journal of Magnetic Resonance 169 (2). p.246-249. Mark These effects are negated by flow-related dephasing and are only seen well in short TE sequences. Intravoxel dephasing related to turbulence Accumulation of positive phase shift over the course of the scan Fat-saturation pulses as used in time-of-flight imaging Inflow of unsaturated blood into the Start Forskningsoutput meta-DENSE complex acquisition for reduced intravoxel dephas meta-DENSE complex acquisition for reduced intravoxel dephasing. 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.

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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.

Real-time fMRI Biofeedback Targeting the Orbitofrontal Cortex

Want to thank TFD for its In MRI, particularly turbulent blood flow gives rise to intravoxel dephasing, where spins within a voxel have accrued different amounts of phase leading to reduced 3D TOF CE-MRA has improved spatial resolution, less saturation effects and intravoxel dephasing, and better evaluation of aneurysm lumen. With this technique, The most effective method for reducing intravoxel dephasing is to shorten the time the PC-UTE approach is more robust to intravoxel dephasing signal loss. Jan 30, 2016 complex T2* image via an intravoxel dephasing average. Accordingly, the inverse T2*MRI model consists of two inverse computation steps.

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. meta-DENSE complex acquisition for reduced intravoxel dephasing. Research output: Contribution to journal › Article. Overview; Cite BibTeX Details.