Phase‐encoded xSPEN: A novel high‐resolution volumetric alternative to RARE MRI

Zhang, Zhiyong; Lustig, Michael; Frydman, Lucio

doi:10.1002/mrm.27143

Cited by 10 publications

(7 citation statements)

References 37 publications

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“…By virtue of its hyperbolic phase profile, this pulse has potential applications in xSPEN MRI [19], [20]. In that method, a hyperbolic phase profile permits an acceleration of data acquisition by utilizing the correlation between k-space and image space when a hyperbolic or parabolic phase profile is present.…”

Section: Discussionmentioning

confidence: 99%

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

Mullen

Kobayashi

2019

Journal of Magnetic Resonance

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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.

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Section: Discussionmentioning

confidence: 99%

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

Mullen

Kobayashi

2019

Journal of Magnetic Resonance

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“…The SPENbased DTI acquisition sequences here produced could also serve as "templates" for additional biologically-relevant experiments, including measurements of cell body density (Palombo et al, 2020), axon diameter (Veraart et al, 2020), kurtosis, or other measures of local microstructure (Yon et al, 2020). Such tests, as well as comparisons with other approaches such as xSPEN (Solomon et al, 2017b;Zhang et al, 2018), are in progress. Also under investigation is how can these sequences target challenging brain regions while dealing with B 1 inhomogeneities, when performing high-resolution DTI studies on humans at ultrahigh fields like 7T.…”

Section: Discussionmentioning

confidence: 99%

High-Resolution 3D in vivo Brain Diffusion Tensor Imaging at Ultrahigh Fields: Following Maturation on Juvenile and Adult Mice

et al. 2020

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Diffusion tensor imaging (DTI) is a well-established technique for mapping brain microstructure and white matter tracts in vivo. High resolution DTI, however, is usually associated with low intrinsic sensitivity and therefore long acquisition times. By increasing sensitivity, high magnetic fields can alleviate these demands, yet high fields are also typically associated with significant susceptibility-induced image distortions. This study explores the potential arising from employing new pulse sequences and emerging hardware at ultrahigh fields, to overcome these limitations. To this end, a 15.2 T MRI instrument equipped with a cryocooled surface transceiver coil was employed, and DTI experiments were compared between SPatiotemporal ENcoding (SPEN), a technique that tolerates well susceptibility-induced image distortions, and double-sampled Spin-Echo Echo-Planar Imaging (SE-EPI) methods. Following optimization, SE-EPI afforded whole brain DTI maps at 135 μm isotropic resolution that possessed higher signal-to-noise ratios (SNRs) than SPEN counterparts. SPEN, however, was a better alternative to SE-EPI when focusing on challenging regions of the mouse brain –including the olfactory bulb and the cerebellum. In these instances, the higher robustness of fully refocused SPEN acquisitions coupled to its built-in zooming abilities, provided in vivo DTI maps with 75 μm nominal isotropic spatial resolution. These DTI maps, and in particular the mean diffusion direction (MDD) details, exhibited variations that matched very well the anatomical features known from histological brain Atlases. Using these capabilities, the development of the olfactory bulb (OB) in live mice was followed from week 1 post-partum, until adulthood. The diffusivity of this organ showed a systematic decrease in its overall isotropic value and increase in its fractional anisotropy with age; this maturation was observed for all regions used in the OB's segmentation but was most evident for the lobules' centers, in particular for the granular cell layer. The complexity of the OB neuronal connections also increased during maturation, as evidenced by the growth in directionalities arising in the mean diffusivity direction maps.

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“…Figure 1a introduces the FOCUSED-xSPEN pulse sequence. The sequence was designed based on xSPEN's use of two 180˚ frequency swept pulses in the presence of a constant gradient and of a bipolar one (10,26,27); when considering that in the present instance spins will be subject to the constant effect of a sizable field inhomogeneity Bo = f/, the need for applying a constant external gradient disappears: Bo will take this role, and the encoding part of the sequence becomes the segment encased by the dashed rectangle in Figure 1a. 𝐺 𝑧 𝑧.…”

Section: Methodsmentioning

confidence: 99%

Improving MRI's slice selectivity in the presence of strong, metal-derived inhomogeneities

Farkash

Liberman

Martinho

et al. 2020

Magnetic Resonance Imaging

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Purpose: To develop schemes that deliver faithful 2D slices near field heterogeneities of the kind arising from non-ferromagnetic metal implants, with reduced artifacts and shorter scan times.Methods: An excitation scheme relying on cross-term spatio-temporal encoding (xSPEN) was used as basis for developing the new inhomogeneity-insensitive, slice-selective pulse scheme. The resulting Fully refOCUSED cross-term SPatiotemporal ENcoding (FOCUSED-xSPEN)approach involved four adiabatic sweeps. The method was evaluated in silico, in vitro and in vivo using mice models, and compared against a number of existing and of novel alternatives based on both conventional and swept RF pulses, including an analogous method based on LASER's selectivity spatial selectivity. Results:Calculations and experiments confirmed that multi-sweep derivatives of xSPEN and LASER can deliver localized excitation profiles, centered at the intended positions and endowed with enhanced immunity to B0 and B1 distortions. This, however, is achieved at the expense of higher SAR than non-swept counterparts. Furthermore, single-shot FOCUSED-xSPEN and LASER profiles covered limited off-resonance ranges. This could be extended to bands covering arbitrary off-resonance values with uniform slice widths, by looping the experiments over a number of scans possessing suitable transmission and reception offsets. Conclusions:A series of novel approaches were introduced to select slices near metals, delivering robustness against Bo and B1 + field inhomogeneities.

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Phase‐encoded xSPEN: A novel high‐resolution volumetric alternative to RARE MRI

Abstract: A new MRI strategy is introduced delivering high in- and through-plane resolutions while enjoying full Fourier multiplexing, leading to fast acquisitions with high SNR.

Cited by 10 publications

References 37 publications

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

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

High-Resolution 3D in vivo Brain Diffusion Tensor Imaging at Ultrahigh Fields: Following Maturation on Juvenile and Adult Mice

Improving MRI's slice selectivity in the presence of strong, metal-derived inhomogeneities

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