Highly selective and π pulse generation

Silver, Michael S.; Joseph, R. I.; Hoult, D. I.

doi:10.1016/0022-2364(84)90181-1

Cited by 409 publications

(361 citation statements)

References 8 publications

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“…The repetition time TR was 3.375 msec, and TE was TR/2. For the inversion pulse a hyperbolic secant pulse with parameters ϭ 10, ␤ ϭ 400 sec Ϫ1 , and duration pw ϭ 5.12 msec was used (14). The saturation pulse consisted of a truncated adiabatic pulse with parameters ϭ 4, ␤ ϭ 1200 sec Ϫ1 , and pw ϭ 5.12 msec (adiabatic rapid half passage pulse (15)).…”

Section: Methodsmentioning

confidence: 99%

T₁ quantification with inversion recovery TrueFISP

Scheffler

Hennig

2001

Magnetic Resonance in Med

177

186

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A snapshot FLASH sequence can be used to acquire the time course of longitudinal magnetization during its recovery after a single inversion pulse. However, excitation pulses disturb the exponential recovery of longitudinal magnetization and may produce systematic errors in T 1 estimations. In this context the possibility of using the TrueFISP sequence to detect the recovery of longitudinal magnetization for quantitative T 1 measurements was examined. Experiments were performed on different Gd-doped water phantoms and on humans. Most T 1 quantification techniques are based on measuring the longitudinal magnetization at different time intervals TI after an inversion or saturation pulse (1-5). The magnitude of the longitudinal magnetization as a function of TI is then fitted to a monoexponential recovery function [M 0 (1 Ϫ e TI/T1 ) for saturation, and M 0 (1 Ϫ 2e TI/T1 ) for inversion recovery] to give T 1 and proton density M 0 values. Conventionally, one data set with a given TI is acquired after each inversion pulse and the experiment is repeated after a sufficient long recovery period (Ͼ 5T 1 ) with different TIs (single-point method (1)). As an alternative to this time-consuming technique, inversion recovery snapshot fast low-angle shot (FLASH) can be used (5). Here, the magnitude of the longitudinal magnetization is acquired continuously during its recovery using a FLASH sequence with low excitation flip angles of 5°to 10°. An intrinsic drawback of this method is the influence of the excitation pulses on the recovery of longitudinal magnetization even for small flip angles.Inversion recovery-prepared true Fast Imaging with Steady Precession (TrueFISP) was first proposed by Deimling and Heid (6) to modify the mainly T 2 -weighted image contrast of TrueFISP. In this work, we examined the possibility of replacing the intrinsically T 1 -weighted FLASH readout module by a TrueFISP readout module to continuously acquire the recovery of longitudinal magnetization. Quantitative T 1 measurements on phantoms and humans based on FLASH and TrueFISP were compared to the gold standard of separately acquired TI measurements. THEORYThe FISP sequence as proposed by Oppelt et al. (7) (now called TrueFISP (Siemens) or fully refocused SSFP (8)) consists of consecutive ␣ excitation pulses with alternating polarity. The gradient areas between these Ϯ␣ pulses are zero for all three gradient axes. Figure 1 shows one repetition cycle of TrueFISP, starting at the center of the ϩ␣ pulse and ending at the center of the Ϫ␣ pulse. At the beginning of one TR cycle the steady-state magnetization is aligned in the z direction and is then flipped into transverse magnetization by the ϩ␣/2 pulse. The echo is Fourier encoded by a symmetric readout gradient GR consisting of a dephasing period, a readout period, and a final rephasing step to refocus transverse magnetization. This pure transverse magnetization is finally flipped back to the z axis by the Ϫ␣/2 pulse. Except for T 2 and T* 2 effects, no transverse magnetization is lost between ␣ pu...

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Section: Methodsmentioning

confidence: 99%

T₁ quantification with inversion recovery TrueFISP

Scheffler

Hennig

2001

Magnetic Resonance in Med

177

186

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“…The distance restraints for SeR13 were derived from 15 N-edited NOESY-HSQC and 13 C-edited NOESY-HSQC spectra using a 1 mM uniformly 13 C, 15 N-enriched SeR13 sample. [25][26][27][28] The locations of the interfacial residues were identified by concentration-dependent chemical shifts and paramagnetic perturbation studies. NOE distances restraints for these residues were carefully assigned to exclude possible intermolecular NOEs.…”

Section: Determining the Monomeric Structure Of Ser13mentioning

confidence: 99%

Three‐dimensional structure of the weakly associated protein homodimer SeR13 using RDCs and paramagnetic surface mapping

et al. 2010

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The traditional NMR-based method for determining oligomeric protein structure usually involves distinguishing and assigning intra-and intersubunit NOEs. This task becomes challenging when determining symmetric homo-dimer structures because NOE cross-peaks from a given pair of protons occur at the same position whether intra-or intersubunit in origin. While there are isotope-filtering strategies for distinguishing intra from intermolecular NOE interactions in these cases, they are laborious and often prove ineffectual in cases of weak dimers, where observation of intermolecular NOEs is rare. Here, we present an efficient procedure for weak dimer structure determination based on residual dipolar couplings (RDCs), chemical shift changes upon dilution, and paramagnetic surface perturbations. This procedure is applied to the Northeast Structural Genomics Consortium protein target, SeR13, a negatively charged Staphylococcus epidermidis dimeric protein (K d 3.4 6 1.4 mM) composed of 86 amino acids. A structure determination for the monomeric form using traditional NMR methods is presented, followed by a dimer structure determination using docking under orientation constraints from RDCs data, and scoring under residue pair potentials and shape-based predictions of RDCs. Validation using paramagnetic surface perturbation and chemical shift perturbation data acquired on sample dilution is also presented. The general utility of the dimer structure determination procedure and the possible relevance of SeR13 dimer formation are discussed.

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“…The LASER sequence used for diffusion weighted imaging measurements. G d y is the pulsed gradient applied in the y-direction, G r and G ro are frequency encoding and readout gradients, respectively, G p is phase encoding gradient, G s is the slice selection gradient, Δ is the diffusion time, δ is the width of G d y , Ω is the time delay between two phase encoding gradients, α is the half-width of an AFP pulse, β is the width of G p and G r , t [1][2][3][4] , are the time delays between pulsed gradients, τ is the time interval between the first AFP pulses of the two AFP-AFS pulse trains, n is the number of AFP pulses contained in a pulse train, and η is the half-width of the readout gradient (G ro ). Sample images acquired using the PGSE and nAFP-AFS-LASER sequences with n = 1, 3, 5, and 7 for (a) Ph-1, the bead phantom, and (b) Ph-4, the nickel(II) doped water phantom.…”

Section: Discussionmentioning

confidence: 99%

“…Frequency modulated adiabatic full passage pulses can generate a high degree of magnetic spin coherence that is immune to B 1 inhomogeneity [1][2][3][4]. The localization by adiabatic selective refocusing (LASER) pulse sequence developed by Garwood and DelaBarre [3] exploits this property to achieve sharply defined excitation profiles in single voxel magnetic resonance spectroscopy (MRS) and imaging pulse sequences [5].…”

Section: Introductionmentioning

confidence: 99%

Enhanced diffusion weighting generated by selective adiabatic pulse trains

Sun

Bartha

2007

Journal of Magnetic Resonance

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A theoretical description and experimental validation of the enhanced diffusion weighting generated by selective adiabatic full passage (AFP) pulse trains is provided. Six phantoms (Ph-1 to Ph-6) were studied on a 4T Varian/Siemens whole body MRI system. Phantoms consisted of 2.8 cm diameter plastic tubes containing a mixture of 10 μm ORGASOL polymer beads and 2 mM Gd-DTPA dissolved in 5% agar (Ph-1) or nickel(II) ammonium sulphate hexahydrate doped (56.3 mM -0.8 mM) water solutions (Ph-2 to Ph-6). A customized localization by adiabatic selective refocusing (LASER) sequence containing slice selective AFP pulse trains and pulsed diffusion gradients applied in the phase encoding direction was used to measure 1 H 2 O diffusion. The b-value associated with the LASER sequence was derived using the Bloch-Torrey equation. The apparent diffusion coefficients measured by LASER were comparable to those measured by a conventional pulsed gradient spin-echo (PGSE) sequence for all phantoms. Image signal intensity increased in Ph-1 and decreased in Ph-2 -Ph-6 as AFP pulse train length increased while maintaining a constant echotime. These experimental results suggest that such AFP pulse trains can enhance contrast between regions containing microscopic magnetic susceptibility variations and homogeneous regions in which dynamic dephasing relaxation mechanisms are dominant.

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Highly selective and π pulse generation

Cited by 409 publications

References 8 publications

T₁ quantification with inversion recovery TrueFISP

T₁ quantification with inversion recovery TrueFISP

Three‐dimensional structure of the weakly associated protein homodimer SeR13 using RDCs and paramagnetic surface mapping

Enhanced diffusion weighting generated by selective adiabatic pulse trains

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Highly selective and π pulse generation

Cited by 409 publications

References 8 publications

T1 quantification with inversion recovery TrueFISP

T1 quantification with inversion recovery TrueFISP

Three‐dimensional structure of the weakly associated protein homodimer SeR13 using RDCs and paramagnetic surface mapping

Enhanced diffusion weighting generated by selective adiabatic pulse trains

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T₁ quantification with inversion recovery TrueFISP

T₁ quantification with inversion recovery TrueFISP