Broadband excitation pulses with variable RF amplitude‐dependent flip angle (RADFA)

Koos, Martin R. M.; Feyrer, Hannes

doi:10.1002/mrc.4297

Cited by 17 publications

(17 citation statements)

References 56 publications

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“…A systematic search of physical limits by pulse optimizations was conducted in a similar way to the original RADFA study . For the fractional effective pulse length

τ_{normalp}^{eff} = (1 - R) τ_{normalp}

, values from R =0 to 1 in steps of 0.1 were examined.…”

Section: Resultsmentioning

confidence: 99%

“…A novel class of RF‐amplitude‐limited broadband pulses has been introduced that combines the flexibility and applicability of RADFA pulses, which allow the setting of arbitrary effective flip angles within the range of 0° to 180°, with the linear phase introduced originally in the ICEBERG pulses . Compared with conventional RF‐amplitude‐limited RADFA pulses, the new class of pulses has the advantage that the accessible bandwidths can be roughly doubled while the excitation quality is at least as good as for the R =0 RADFA pulse.…”

Section: Discussionmentioning

confidence: 99%

“…Assuming a shaped pulse consisting of N individual pulses of constant amplitude and phase, indexed by i and each of duration Δ t , the resulting Hamiltonian during a pulse can be written as

scriptH ((), i, {normal Ω}_{j}, α_{k}) = \frac{2 α_{k}}{π} ((), ω_{i}^{normalx} \cdot I_{normalx} + ω_{i}^{normaly} \cdot I_{normaly}) + {normal Ω}_{j} \cdot I_{normalz}

with the controls of the i th pulse increment

ω_{i}^{normalx}

and

ω_{i}^{normaly}

, the effective flip angle α k and the offset Ω j . As previously defined for RADFA pulses, the scaling of the RF‐amplitude is directly correlated to the overall effective flip angle α k and

ω_{i}^{normalx}

and

ω_{i}^{normaly}

are the RF‐amplitudes of an effective π /2 or 90° pulse. With the propagators

U_{N} ((), {normal Ω}_{j}, α_{k}) = {falsefalse}_{\prod}^{i = 1} {normale}^{normali scriptH ((), i, {normal Ω}_{j}, α_{k}) normal Δ t},

the final spin density operator ρ N is calculated

ρ_{N} ((), {normal Ω}_{j}, α_{k}) = U_{N} ((), {normal Ω}_{j}, α_{k} ...)

…”

Section: Theorymentioning

confidence: 99%

“…Recently, a new class of broadband excitation pulses with adjustable, RF‐amplitude‐dependent effective flip angles, so‐called RADFA pulses, has been introduced and studied with respect to their physical limits . Such pulses can be used in Ernst angle‐type and other applications as they allow the arbitrary adjustment of effective flip angles between 0° and 180° and therefore provide a general flexibility not known from other broadband pulses with specific flip angles.…”

Section: Introductionmentioning

confidence: 99%

“…[37][38][39][40][41] Recently, a new class of broadband excitation pulses with adjustable, RF-amplitude-dependent effective flip angles, so-called RADFA pulses, has been introduced and studied with respect to their physical limits. [42] Such pulses can be used in Ernst angle-type and other applications as they allow the arbitrary adjustment of effective flip angles between 0 ı and 180 ı and therefore provide a general flexibility not known from other broadband pulses with specific flip angles. While wide bandwidths with convenient pulse lengths can be achieved with RF-power-limited RADFA pulses, [42] the more applicable RF-amplitude restricted RADFA pulses show a significant performance breakdown at a bandwidth of 2-3 times the maximum RF-amplitude of the effective 90 ı flip angle excitation.…”

Section: Introductionmentioning

confidence: 99%

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Broadband RF‐amplitude‐dependent flip angle pulses with linear phase slope

Koos

Feyrer

2017

Magnetic Reson in Chemistry

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Pulse sequences in NMR spectroscopy sometimes require the application of pulses with effective flip angles different from 90° and 180°. Previously (Magn. Reson. Chem. 2015, 53, 886-893), offset-compensated broadband excitation pulses with RF-amplitude-dependent effective flip angles (RADFA) were introduced that are applicable in such cases. However, especially RF-amplitude-restricted RADFA pulses turned out to perform not as good as desired in terms of achievable bandwidths. Here, a class of RF-amplitude-restricted RADFA pulses with linear phase slope is introduced that allows excitation over much larger bandwidths with better performance. In this theoretical work, the basic principle of the pulse class is explained, their physical limits explored, and their properties, also compared with other pulse classes, discussed in detail. Copyright © 2017 John Wiley & Sons, Ltd.

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“…A systematic search of physical limits by pulse optimizations was conducted in a similar way to the original RADFA study . For the fractional effective pulse length

τ_{normalp}^{eff} = (1 - R) τ_{normalp}

, values from R =0 to 1 in steps of 0.1 were examined.…”

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…Assuming a shaped pulse consisting of N individual pulses of constant amplitude and phase, indexed by i and each of duration Δ t , the resulting Hamiltonian during a pulse can be written as

scriptH ((), i, {normal Ω}_{j}, α_{k}) = \frac{2 α_{k}}{π} ((), ω_{i}^{normalx} \cdot I_{normalx} + ω_{i}^{normaly} \cdot I_{normaly}) + {normal Ω}_{j} \cdot I_{normalz}

with the controls of the i th pulse increment

ω_{i}^{normalx}

and

ω_{i}^{normaly}

, the effective flip angle α k and the offset Ω j . As previously defined for RADFA pulses, the scaling of the RF‐amplitude is directly correlated to the overall effective flip angle α k and

ω_{i}^{normalx}

and

ω_{i}^{normaly}

are the RF‐amplitudes of an effective π /2 or 90° pulse. With the propagators

U_{N} ((), {normal Ω}_{j}, α_{k}) = {falsefalse}_{\prod}^{i = 1} {normale}^{normali scriptH ((), i, {normal Ω}_{j}, α_{k}) normal Δ t},

the final spin density operator ρ N is calculated

ρ_{N} ((), {normal Ω}_{j}, α_{k}) = U_{N} ((), {normal Ω}_{j}, α_{k} ...)

…”

Section: Theorymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Broadband RF‐amplitude‐dependent flip angle pulses with linear phase slope

Koos

Feyrer

2017

Magnetic Reson in Chemistry

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Broadband Excitation by Method of Double Sweep

Khaneja

Kumar

2017

Appl Magn Reson

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The paper describes the design of broadband excitation pulses in high resolution NMR by method of double sweep. We first show the design of a pulse sequence that produces broadband excitation to the equator of Bloch sphere with phase linearly dispersed as frequency. We show how this linear dispersion can then be refocused by nesting free evolution between two adiabatic inversions (sweeps). We then show how this construction can be generalized to exciting arbitrary large bandwidths without increasing the peak rf-amplitude and by incorporating more adiabatic sweeps. Finally, we show how the basic design can then be modified to give a broadband x rotation over arbitrary large bandwidth and with limited rf-amplitude. Experimental excitation profiles for the residual HDO signal in a sample of 99.5% D 2 0 are displayed as a function of resonance offset. Application of the excitation is shown for 13 C excitation in a labelled sample of Alanine.

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Design of NMR Pulses by Iterative Optimization of Phases

Shetty

Khaneja

2023

Appl Magn Reson

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Broadband excitation pulses with variable RF amplitude‐dependent flip angle (RADFA)

Cited by 17 publications

References 56 publications

Broadband RF‐amplitude‐dependent flip angle pulses with linear phase slope

Broadband RF‐amplitude‐dependent flip angle pulses with linear phase slope

Broadband Excitation by Method of Double Sweep

Design of NMR Pulses by Iterative Optimization of Phases

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