Moment and direction of the spoiler gradient for effective artifact suppression in RF‐spoiled gradient echo imaging

Leupold, Jochen; Hennig, Jürgen; Scheffler, Klaus

doi:10.1002/mrm.21614

Cited by 18 publications

(31 citation statements)

References 9 publications

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“…This is also supported by experiments, namely an observed monotonic decay of artifacts with increasing spoiler gradient moment (14). Equation [18] is also consistent with the observation that artifacts show mainly ghosts of objects edges (13), since for m = n the magnitude of k − (n − m) · p will be minimal for certain off-center k-values (14).…”

Section: Connection With Measurementsupporting

confidence: 83%

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Analytical solution to the transient phase of steady‐state free precession sequences

Ganter

2009

Magnetic Resonance in Med

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The transient phase of short-TR steady-state free precession (SSFP) sequences exhibits an often striking complexity and is not only important for nonequilibrium applications (e.g., rapid T 1 -measurements), but can also cause severe artifacts in conventional imaging. In both cases, balanced SSFP sequences are practically (with regard to preparation efficiency) and conceptually (concerning the theoretical understanding of the decay) easier to handle their unbalanced counterparts, for which currently no theory is available. Based on a decomposition of coherence pathways into irreducible subpaths, an exact mathematical solution to the transient phase of unbalanced SSFP sequences is presented in this article, which also includes the known results for balanced SSFP and the steady state of arbitrary SSFP sequences as special cases. As an application, it is shown that the familiar Look-Locker expression for the accelerated magnetization recovery in RFspoiled sequences is only valid for T 2 → 0. In addition to oscillatory perturbations, systematic deviations from the monoexponential decay are observed for T 2 > 0 as a consequence of memory effects. Magn Reson Med 62:149-164, 2009.

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Section: Connection With Measurementsupporting

confidence: 83%

“…[14], thus follows immediately from the quotient criterion for absolute convergent series after setting a…”

Section: Acknowledgmentsmentioning

confidence: 99%

Analytical solution to the transient phase of steady‐state free precession sequences

Ganter

2009

Magnetic Resonance in Med

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“…The spoiling moments of these gradients in all three directions after each RF pulse were set to generate a phase distribution of at least 36π within one voxel. Second, a phase-cycled RF spoiling scheme was applied consecutively to each catalyzation chain pulse (19). In order to use a very short TR which is less than 5 times T 2 , variant gradient spoiling strategies were set in different TRs to avoid generating stimulated echos.…”

Section: Methodsmentioning

confidence: 99%

Rapid 3D radiofrequency field mapping using catalyzed double‐angle method

Wang

Zuehlsdorff²,

Larson

2009

NMR in Biomedicine

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A new method is presented for rapid and accurate large volumetric radiofrequency (RF) field (B 1 + ) mapping. This method is a modification of the double-angle method (DAM) which accelerates imaging speed and applies 3D acquisition to improve B 1 + measurement accuracy. It reduces repetition time and scan time by introducing a catalyzation RF pulse chain at the end of each DAM repetition cycle. The catalyzation pulse chain ensures that, after each TR period, the longitudinal magnetizations reach the same state for both measurements at two flip angles for the DAM so that the long TR requirement (TR ≥ 5T 1 ) for complete relaxation of longitudinal magnetization of DAM becomes unnecessary. A multi-echo imaging sequence is additionally incorporated to further improve the efficiency of data acquisition. Simulations demonstrate an excellent flip angle measurement accuracy for catalyzed DAM even with TR ≪ T 1 . Phantom and in vivo volunteer studies are presented to demonstrate the catalyzation effect upon B 1 + mapping and the application of 3D catalyzed DAM for rapid and accurate large volume RF field mapping. KeywordsRadiofrequency (RF) field mapping; double-angle method (DAM); multi-echo imaging; quantitative MRI

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“…For shorter TRs, it is possible to cause deliberate dephasing by applying a large gradient, called a 'dephasing' or 'crusher' gradient, after the readout. The dephasing gradient causes the spins across the slice or slab to precess at vastly different frequencies, quickly decohering or 'spoiling' the signal (Leupold, Hennig, & Scheffler, 2008). This technique is called 'gradient spoiling.'…”

Section: Flash or Spoiled Grementioning

confidence: 99%