The Return of the Frequency Sweep: Designing Adiabatic Pulses for Contemporary NMR

Garwood, Michael; DelaBarre, Lance

doi:10.1006/jmre.2001.2340

Cited by 853 publications

(947 citation statements)

References 76 publications

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“…Further correlations were obtained when taking into consideration the adiabaticity factor of the pump pulse on the central transition, Q CT . This factor quantifies the adiabaticity of the pump pulse and unifies all essential pulse parameters in one single parameter [31,38,39]. As is seen in Fig.…”

Section: Deer With a Single Chirp Pump Pulsementioning

confidence: 99%

Gd(III)–Gd(III) distance measurements with chirp pump pulses

Doll

Wili

et al. 2015

Journal of Magnetic Resonance

110

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The broad EPR spectrum of Gd(III) spin labels restricts the dipolar modulation depth in distance measurements between Gd(III) pairs to a few percent. To overcome this limitation, frequency-swept chirp pulses are utilized as pump pulses in the DEER experiment. Using a model system with 3.4 nm Gd-Gd distance, application of one single chirp pump pulse at Q-band frequencies leads to modulation depths beyond 10%. However, the larger modulation depth is counteracted by a reduction of the absolute echo intensity due to the pump pulse. As supported by spin dynamics simulations, this effect is primarily driven by signal loss to double-quantum coherence and specific to the Gd(III) high spin state of S = 7/2. In order to balance modulation depth and echo intensity for optimum sensitivity, a simple experimental procedure is proposed. An additional improvement by 25% in DEER sensitivity is achieved with two consecutive chirp pump pulses. These pulses pump the Gd(III) spectrum symmetrically around the observation position, therefore mutually compensating for dynamical Bloch-Siegert phase shifts at the observer spins. The improved sensitivity of the DEER data with modulation depths on the order of 20% is due to mitigation of the echo reduction effects by the consecutive pump pulses. In particular, the second pump pulse does not lead to additional signal loss if perfect inversion is assumed. Moreover, the compensation of the dynamical Bloch-Siegert phase prevents signal loss due to spatial dependence of the dynamical phase, which is caused by inhomogeneities in the driving field. The new methodology is combined with pre-polarization techniques to measure long distances up to 8.6 nm, where signal intensity and modulation depth become attenuated by long dipolar evolution windows. In addition, the influence of the zero-field splitting parameters on the echo intensity is studied with simulations. Herein, larger sensitivity is anticipated for Gd(III) complexes with zero-field splitting that is smaller than for the employed Gd-PyMTA complex.

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Section: Deer With a Single Chirp Pump Pulsementioning

confidence: 99%

Gd(III)–Gd(III) distance measurements with chirp pump pulses

Doll

Wili

et al. 2015

Journal of Magnetic Resonance

110

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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%

“…First to simplify the calculations, the effective magnetic field in the slice selective direction was expressed as the linear combination of the static magnetic field and the local gradient field [12,13]. Second, to model the effect of an AFP pulse on the timedependent magnetization, the nonlinear phase dispersion across a slice generated by the HS (HS1, R10) pulse [3] was expressed as a quadratic phase offset [6,7] to the linear phase dispersion. The derived total b-value contained a cross-term from the interaction between the pulsed diffusion gradients applied in the phase encoding direction and the phase encoding gradients.…”

Section: B-value Calculation Using the Bloch-torrey Equationmentioning

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%

“…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]. However, following excitation, and in the presence of spatial encoding gradients, selective hyperbolic secant (HS) adiabatic full passage (AFP) pulses generate spin phase that is approximately quadratically related to the pulse frequency [6,7] and therefore approximately quadratically proportional to the spatial coordinate of the spins [8].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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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Garwood, Michael: Frequency-Modulated Pulses in the Early Days of Biomedical NMR

Garwood

2011

Encyclopedia of Magnetic Resonance

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The Return of the Frequency Sweep: Designing Adiabatic Pulses for Contemporary NMR

Cited by 853 publications

References 76 publications

Gd(III)–Gd(III) distance measurements with chirp pump pulses

Gd(III)–Gd(III) distance measurements with chirp pump pulses

Enhanced diffusion weighting generated by selective adiabatic pulse trains

Garwood, Michael: Frequency-Modulated Pulses in the Early Days of Biomedical NMR

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