Two-dimensional frequency-swept pulse with resilience to both B1 and B0 inhomogeneity

Abstract

Applications of multidimensional spatially-selective pulses are sometimes limited by their long pulse durations resulting from the need to execute a modulated gradient waveform in concert with RF transmission. Here, we introduce a method to design two-dimensional selective adiabatic pulses using a Cartesian k-space trajectory. The full pulse can be sampled using various undersampled segments to create a multidimensional pulse resilient to large off-resonances. Moreover, the pulse can be designed to be resilient to B 1 + inhomogeneity. Experimental demonstrations of fully segmented and single-shot k-space sampling patterns are presented.

Contemporary approaches to high-field magnetic resonance imaging with large field inhomogeneity

“…Alternatively, if a modest amount of image distortion is acceptable, a short echo time gradient echo sequence can be used with frequency encoding in one dimension with a high receiver bandwidth [36,52]. While the high receiver bandwidth in general decreases the SNR, the increased SNR at high-field and/or with receiver arrays [53] aids in offsetting losses due to the increased receiver bandwidth.…”

Parallel transmission 2D RARE imaging at 7T with transmit field inhomogeneity mitigation and local SAR control

“…Several solutions have been developed to address the transmit field inhomogeneity and increased SAR at 7T. Slice-selective adiabatic RF pulses provide great immunity to transmit field inhomogeneity [12][13][14]; however, they usually require a longer pulse duration or more RF power than conventional RF pulses [13][14][15][16]. Variable-rate selective excitation (VERSE) method [17] as well as low-and variable-flip-angle echo trains designed by the extended phase algorithm [18,19] have been proposed as effective ways of reducing SAR.…”

Parallel transmit optimized 3D composite adiabatic spectral‐spatial pulse for spectroscopy

“…11 In general, SPSP pulses were usually constrained to be 2D-selective with applications demonstrated in brain, prostate, and other targets. [11][12][13][14][15][16][17] As opposed to one-dimensional pulses, a unique advantage of 2D and 3D spatially selective pulses is the ability to compensate for B 0 and B 1 field inhomogeneities, 8,10,18 while 2D-SPSP pulses are affected by off-resonance effects the same way as one-dimensional pulses. 18 Although 2D spatially selective pulses have potential advantages for use as subpulses in 3D-SPSP pulse, such use has been limited to date due to their increased duration and limited bandwidths, although introduced shortly after 2D pulses.…”

“…An alternative to using RF pulses, which are solely spatially selective, spatial‐spectral (SPSP) pulses have been introduced to provide both spatial and spectral selectivity, in which a series of subpulses define the spatial selectivity, and an “envelope” (or “parent pulse”) defines the spectral selectivity by modulating the amplitude and phase of the subpulses. Despite its early introduction and later extended work, 5‐10 one limiting drawback of such pulses is their long duration due to the limitations in peak RF amplitude and gradient slew rate, especially at UHF, although a recent study presented an optimized SPSP pulse that mitigated these issues 11 . In general, SPSP pulses were usually constrained to be 2D‐selective with applications demonstrated in brain, prostate, and other targets 11‐17 …”