Velocity‐selective RF pulses in MRI

Rochefort, Ludovic de; Maı̂tre, Xavier; Bittoun, J.; Durand, Emmanuel

doi:10.1002/mrm.20751

Cited by 29 publications

(33 citation statements)

References 20 publications

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“…If the transverse magnetization is spoiled following the tip-up RF pulse (by means of spoiler gradients), the resulting longitudinal magnetization will be modulated by cos(ϕ). Interestingly, while the velocity encoding effect has found extensive applications in phase contrast MRI of flow (18,20) and moving tissues (21), and in the design of flow-selective excitation (22-24) or magnetization preparation (16), its use in flow-suppressed MRI was demonstrated only recently for vascular imaging (8-11). …”

Section: Methodsmentioning

confidence: 99%

Effective motion‐sensitizing magnetization preparation for black blood magnetic resonance imaging of the heart

Nguyen

Rochefort

Spincemaille

et al. 2008

Magnetic Resonance Imaging

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Purpose:To investigate the effectiveness of flow signal suppression of a motion-sensitizing magnetization preparation (MSPREP) sequence and to optimize a 2D MSPREP steadystate free precession (SSFP) sequence for black blood imaging of the heart. Materials and Methods:Using a flow phantom, the effect of varying field of speed (FOS), b-value, voxel size, and flow pattern on the flow suppression was investigated. In seven healthy volunteers, black blood images of the heart were obtained at 1.5T with MSPREP-SSFP and double inversion recovery fast spin echo (DIR-FSE) techniques. Myocardium and blood signal-to-noise ratio (SNR) and myocardium-toblood contrast-to-noise ratio (CNR) were measured. The optimal FOS that maximized the CNR for MSPREP-SSFP was determined.Results: Phantom data demonstrated that the flow suppression was induced primarily by the velocity encoding effect. In humans, FOS ϭ 10 -20 cm/s was found to maximize the CNR for short-axis (SA) and four-chamber (4C) views. Compared to DIR-FSE, MSPREP-SSFP provided similar blood SNR efficiency in the SA basal and mid-views and significantly lower blood SNR efficiency in the SA apical (P ϭ 0.02) and 4C (P ϭ 0.01) views, indicating similar or better blood suppression. Conclusion:Velocity encoding is the primary flow suppression mechanism of the MSPREP sequence and 2D MSPREP-SSFP black blood imaging of the heart is feasible in healthy subjects. THE CLINICAL EVALUATION of cardiac and vascular structures using magnetic resonance imaging (MRI) often requires the suppression of intravascular signal (black blood [BB] imaging) to improve vessel wall and cardiac chamber visualization. BB imaging is commonly performed using double inversion recovery (DIR) (1-5) or spatial saturation of upstream blood (6,7). Both techniques rely on the inflow of blood with nulled signal into the imaging volume and consequently become less effective for thick imaging volumes and for in-plane flow. To overcome this problem, a BB magnetization preparation technique was developed by utilizing motion-sensitizing gradients to dephase all moving blood spins prior to imaging (8 -10). BB images of the aortic and carotid vessel walls were obtained successfully in humans using this approach (11-13). Because the preparation sequence-consisting of 90 -180 -90 nonselective RF pulses and a pair of identical unipolar gradients around the 180 pulse-was originally developed for diffusion sensitization, this technique is often referred to as "diffusion-prepared" or "diffusion-based" in the literature (10 -12). In the presence of weak diffusion-sensitizing gradients such as those used in BB imaging, this description is inadequate because the flow signal attenuation originates primarily from the velocity encoding effect on coherently moving spins and only slightly from the diffusion effect on incoherently moving spins, as briefly pointed out in recent works (13,14). A full experimental investigation of the underlying signal attenuation mechanisms is therefore important and, to the best of our knowledge, has ...

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Section: Methodsmentioning

confidence: 99%

Effective motion‐sensitizing magnetization preparation for black blood magnetic resonance imaging of the heart

Nguyen

Rochefort

Spincemaille

et al. 2008

Magnetic Resonance Imaging

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“…The earliest version of VS excitation pulse consists of multiple rectangular RF pulses of small flip angle interleaved with bipolar gradients . This baseline design is short and easy to implement but is prone to excitation profile shifting in proportion to off‐resonance.…”

Section: Introductionmentioning

confidence: 99%

Characterization and suppression of stripe artifact in velocity‐selective magnetization‐prepared unenhanced MR angiography

Shin

Qin

2018

Magnetic Resonance in Med

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“…Under the excitation k‐space formalism, the transverse component of excited magnetization

M_{xy} (r, v, f)

can be written as the Fourier transform of the RF B 1 field deposited on k r ‐ k v ‐ k f space, where k r , k v , and k f are reciprocal Fourier variables of spatial position r , velocity v , and off‐resonance f , respectively .

\begin{matrix} M_{xy} (r, v, f) = i γ M_{0} \int_{0}^{T} B_{1} (t) e^{i 2 π [k_{r} \cdot r + k_{v} \cdot v + k_{f} f]} d t k_{r} (t) = \frac{γ}{2 π} \int_{t}^{T} G (s) ds, k_{v} (t) = \frac{γ}{2 π} \int_{t}^{T} (t - s) G (s) ds, k_{f} (t) = T - t \end{matrix}

where γ,

M_{0}

, and T are the gyromagnetic ratio, magnetization at equilibrium, and pulse duration, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…The most systematic framework for designing VS excitation pulse sequences was provided by de Rochefort et al . The excitation k‐space initially introduced for spatially selective excitation by Pauly et al was extended to include the velocity Fourier variable.…”

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confidence: 99%

Off‐resonance‐robust velocity‐selective magnetization preparation for non‐contrast‐enhanced peripheral MR angiography

Shin

Nishimura

2012

Magnetic Resonance in Med

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Purpose To develop a new velocity-selective (VS) excitation pulse sequence which is robust to field inhomogeneity and demonstrate its application to non-contrast-enhanced (NCE) peripheral MR angiography (MRA). Methods The off-resonance-robust VS saturation pulse is designed by incorporating 180° refocusing pulses into the k-space-based reference design and tailoring sequence parameters in a velocity region of interest. The VS saturation pulse is used as magnetization preparation for NCE peripheral MRA to suppress background tissues but not arterial blood based on their velocities. NCE peripheral MRA using the proposed VS preparation was tested in healthy volunteers and a patient with arterial stenosis. Results Calf angiograms obtained using the new VS preparation show more uniform background suppression than the reference VS preparation, as demonstrated by larger mean values and smaller standard deviations of artery-to-vein and artery-to-muscle contrast-to-noise ratios (71.0 ± 11.4 and 75.3 ± 12.1 versus 61.7 ± 22.7 and 58.5 ± 27.8). Two-station peripheral MRA using the new VS preparation identifies stenosis of the femoral and popliteal arteries in the patient, as validated by digital subtraction angiography. Conclusion NCE MRA using the new VS magnetization preparation can reliably provide high angiographic contrast in the lower extremities with significantly improved immunity to field inhomogeneity.

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Velocity‐selective RF pulses in MRI

Cited by 29 publications

References 20 publications

Effective motion‐sensitizing magnetization preparation for black blood magnetic resonance imaging of the heart

Effective motion‐sensitizing magnetization preparation for black blood magnetic resonance imaging of the heart

Characterization and suppression of stripe artifact in velocity‐selective magnetization‐prepared unenhanced MR angiography

Off‐resonance‐robust velocity‐selective magnetization preparation for non‐contrast‐enhanced peripheral MR angiography

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