Local shape adaptation for curved slice selection

Weber, Hans; Haas, Martín; Kokorin, Denis; Gallichan, Daniel; Hennig, Jürgen; Zaitsev, Maxim

doi:10.1002/mrm.24906

Cited by 12 publications

(10 citation statements)

References 11 publications

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“…Recent developments in nonlinear encoding have considered combinations of traditional linear gradients together with curvilinear multipolar fields or quadratic rotation‐symmetric fields . The potential of the SEMs' nonlinearity is that they allow the design of inhomogeneous k‐space sampling patterns for more efficient acquisitions . If we neglect relaxation effects, the magnetic resonance signal

s_{q}

from the q ‐th RF channel in a multichannel array with

n_{c}

elements, should satisfy the following equation ,

s_{q} (t) = \int_{Ω} m (boldx) C_{q} (boldx) e^{i Φ (x, t)} d x

where

m (boldx)

is the magnetization at location

boldx

= [x,y,z] T ,

C_{q} (boldx)

is the sensitivity of q th coil, and the integral is over Ω, the region of interest.…”

Section: Theorymentioning

confidence: 99%

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Fast rotary nonlinear spatial acquisition (FRONSAC) imaging

Wang

Tam

Constable

et al. 2015

Magnetic Resonance in Med

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Purpose Nonlinear spatial encoding magnetic fields (SEMs) have been studied to reconstruct images from a minimum number of echoes. Previous work has also explored single shot trajectories in nonlinear SEMs. However, the search continues for optimal schemes that apply nonlinear SEMs to improve spatial encoding efficiency and image quality. Theory and Methods We enhance the encoding efficiency of standard linear gradient trajectories by adding a rapidly rotating nonlinear SEM of moderate amplitude, the so called FRONSAC (Fast ROtary Nonlinear Spatial ACquisition) imaging. This additional gradient greatly improves the image quality of highly undersampled single-shot trajectories, including EPI, Spiral, and Rosette trajectories. Results Our simulations, including noise and dephasing effects, test the effect of adding FRONSAC gradients, demonstrating the applicability of this approach. Performance is explained by demonstrating the additional k-space sampling the nonlinear gradient provides. Studies of the optimal amplitude and frequency of the additional FRONSAC field are presented, and the role of enhanced sampling during the readout demonstrated. Dynamic field mapping in a second-order gradient system shows the proposed gradient waveforms are feasible. Conclusions Images resulting from highly undersampled existing k-space trajectories, such as EPI, Spiral and Rosette, are greatly enhanced simply by adding a rotating nonlinear SEM field.

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s_{q}

from the q ‐th RF channel in a multichannel array with

n_{c}

elements, should satisfy the following equation ,

s_{q} (t) = \int_{Ω} m (boldx) C_{q} (boldx) e^{i Φ (x, t)} d x

where

m (boldx)

is the magnetization at location

boldx

= [x,y,z] T ,

C_{q} (boldx)

is the sensitivity of q th coil, and the integral is over Ω, the region of interest.…”

Section: Theorymentioning

confidence: 99%

“…Other researchers have taken more empirical approaches to designing nonlinear encoding trajectories, such as the MDE work by Lin (20) and optimization schemes being pursued by Layton et al (21). Much effort has also gone into improving the reconstruction algorithms for data obtained with nonlinear SEMs (22)(23)(24)(25)(26)(27)(28).…”

Section: Introductionmentioning

confidence: 99%

Fast rotary nonlinear spatial acquisition (FRONSAC) imaging

Wang

Tam

Constable

et al. 2015

Magnetic Resonance in Med

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“…Although the proposed methods create locally linear gradient fields, these fields can also be regarded as N‐SEMs in general. N‐SEMs have proven to be useful in many aspects of both the reception and excitation phases of an imaging sequence. Therefore, increased hardware complexity is useful for many other purposes in addition to multi‐slice excitation with a single‐band RF pulse.…”

Section: Discussionmentioning

confidence: 99%

A z‐gradient array for simultaneous multi‐slice excitation with a single‐band RF pulse

Ertan

Taraghinia

Sadeghi

et al. 2017

Magnetic Resonance in Med

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“…In the reception phase of a pulse sequence, the N‐SEMs are utilized in accelerating the scan, reducing the FOV, reducing the peripheral nerve stimulation (PNS), and increasing the resolution at the periphery of the object . For the excitation part of a pulse sequence, it has been shown that the N‐SEMs can be used to excite curved slices, reduce the FOV with localized excitation, and reduce the SAR, in addition to the B 1 + inhomogeneity correction. Additionally, the dynamic shimming methods using time‐varying higher‐order spatial field terms can be considered as an application for the N‐SEMs.…”

Section: Discussionmentioning

confidence: 99%

Simultaneous use of linear and nonlinear gradients for B₁⁺ inhomogeneity correction

Ertan

Atalar

2017

NMR in Biomedicine

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The simultaneous use of linear spatial encoding magnetic fields (L-SEMs) and nonlinear spatial encoding magnetic fields (N-SEMs) in B inhomogeneity problems is formulated and demonstrated with both simulations and experiments. Independent excitation k-space variables for N-SEMs are formulated for the simultaneous use of L-SEMs and N-SEMs by assuming a small tip angle. The formulation shows that, when N-SEMs are considered as an independent excitation k-space variable, numerous different k-space trajectories and frequency weightings differing in dimension, length, and energy can be designed for a given target transverse magnetization distribution. The advantage of simultaneous use of L-SEMs and N-SEMs is demonstrated by B inhomogeneity correction with spoke excitation. To fully utilize the independent k-space formulations, global optimizations are performed for 1D, 2D RF power limited, and 2D RF power unlimited simulations and experiments. Three different cases are compared: L-SEMs alone, N-SEMs alone, and both used simultaneously. In all cases, the simultaneous use of L-SEMs and N-SEMs leads to a decreased standard deviation in the ROI compared with using only L-SEMs or N-SEMs. The simultaneous use of L-SEMs and N-SEMs results in better B inhomogeneity correction than using only L-SEMs or N-SEMs due to the increased number of degrees of freedom.

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Local shape adaptation for curved slice selection

Abstract: Multidimensional excitation allows imaging of curved slices with constant thickness. It also has the potential for further modification of the slice shape for increased ability to adapt to the anatomy.

Cited by 12 publications

References 11 publications

Fast rotary nonlinear spatial acquisition (FRONSAC) imaging

Fast rotary nonlinear spatial acquisition (FRONSAC) imaging

A z‐gradient array for simultaneous multi‐slice excitation with a single‐band RF pulse

Simultaneous use of linear and nonlinear gradients for B₁⁺ inhomogeneity correction

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Local shape adaptation for curved slice selection

Abstract: Multidimensional excitation allows imaging of curved slices with constant thickness. It also has the potential for further modification of the slice shape for increased ability to adapt to the anatomy.

Cited by 12 publications

References 11 publications

Fast rotary nonlinear spatial acquisition (FRONSAC) imaging

Fast rotary nonlinear spatial acquisition (FRONSAC) imaging

A z‐gradient array for simultaneous multi‐slice excitation with a single‐band RF pulse

Simultaneous use of linear and nonlinear gradients for B1+ inhomogeneity correction

Contact Info

Product

Resources

About

Simultaneous use of linear and nonlinear gradients for B₁⁺ inhomogeneity correction