A complication in prescan strategy when using surface coils

Jeśmanowicz, A; Froncisz, Wojciech; Hyde, James S.

doi:10.1002/mrm.1910050403

Cited by 5 publications

(1 citation statement)

References 3 publications

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“…This can be understood as an offset in the center of k-space due to the RF coil phase gradient (25). In SEA, a "phase compensation" gradient pulse is used to impart a linear phase gradient across the voxels to counter the effect of the B 1 phase gradient (15).…”

Section: Insertable Phase Compensation Gradient Coilmentioning

confidence: 99%

Exploration of highly accelerated magnetic resonance elastography using high-density array coils

Bosshard

Yallapragada

McDougall

et al. 2017

Quant. Imaging Med. Surg.

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Background: Magnetic resonance elastography (MRE) measures tissue mechanical properties by applying a shear wave and capturing its propagation using magnetic resonance imaging (MRI). By using high density array coils, MRE images are acquired using single echo acquisition (SEA) and at high resolutions with significantly reduced scan times.Methods: Sixty-four channel uniplanar and 32×32 channel biplanar receive arrays are used to acquire MRE wave image sets from agar samples containing regions of varying stiffness. A mechanical actuator triggered by a stepped delay time introduces vibrations into the sample while a motion sensitizing gradient encodes micrometer displacements into the phase. SEA imaging is used to acquire each temporal offset in a single echo, while multiple echoes from the same array are employed for highly accelerated imaging at high resolutions. Additionally, stiffness variations as a function of temperature are studied by using a localized heat source above the sample. A custom insertable gradient coil is employed for phase compensation of SEA imaging with the biplanar array to allow imaging of multiple slices.Results: SEA MRE images show a mechanical shear wave propagating into and across agar samples. A set of 720 images was obtained in 720 echoes, plus a single reference scan for both harmonic and transient MRE.A set of 2,950 wave image frames was acquired from pairs of SEA images captured during heating, showing the change in mechanical wavelength with the change in agar properties. A set of 240 frames was acquired from two slices simultaneously using the biplanar array, with phase images processed into displacement maps. Combining the narrow sensitivity patterns and SNR advantage of the SEA array coil geometry allowed acquisition of a data set with a resolution of 156 µm × 125 µm × 1,000 µm in only 64 echoes, demonstrating high resolution and high acceleration factors.Conclusions: MRE using high-density arrays offers the unique ability to acquire a single frame of a propagating mechanical vibration with each echo, which may be helpful in non-repeatable or destructive testing. Highly accelerated, high resolution MRE may be enabled by the use of large arrays of coils such as used for SEA, but at lower acceleration rates supporting the higher resolution than provided by SEA imaging.

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Section: Insertable Phase Compensation Gradient Coilmentioning

confidence: 99%

Exploration of highly accelerated magnetic resonance elastography using high-density array coils

Bosshard

Yallapragada

McDougall

et al. 2017

Quant. Imaging Med. Surg.

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Single echo acquisition MRI using RF encoding

Wright

McDougall

2009

NMR in Biomedicine

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Encoding of spatial information in magnetic resonance imaging is conventionally accomplished by using magnetic field gradients. During gradient encoding, the position in k-space is determined by a time-integral of the gradient field, resulting in a limitation in imaging speed due to either gradient power or secondary effects such as peripheral nerve stimulation. Partial encoding of spatial information through the sensitivity patterns of an array of coils, known as parallel imaging, is widely used to accelerate the imaging, and is complementary to gradient encoding. This paper describes the one-dimensional limit of parallel imaging in which all spatial localization in one dimension is performed through encoding by the radiofrequency (RF) coil. Using a one-dimensional array of long and narrow parallel elements to localize the image information in one direction, an entire image is obtained from a single line of k-space, avoiding rapid or repeated manipulation of gradients. The technique, called single echo acquisition (SEA) imaging, is described, along with the need for a phase compensation gradient pulse to counteract the phase variation contained in the RF coil pattern which would otherwise cause signal cancellation in each imaging voxel. Image reconstruction and resolution enhancement methods compatible with the speed of the technique are discussed. MR movies at frame rates of 125 frames per second are demonstrated, illustrating the ability to monitor the evolution of transverse magnetization to steady state during an MR experiment as well as demonstrating the ability to image rapid motion. Because this technique, like all RF encoding approaches, relies on the inherent spatially varying pattern of the coil and is not a time-integral, it should enable new applications for MRI that were previously inaccessible due to speed constraints, and should be of interest as an approach to extending the limits of detection in MR imaging.

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Basic Reconstruction Algorithms for Parallel Imaging

Griswold

Parallel Imaging in Clinical MR Applications

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A complication in prescan strategy when using surface coils

Cited by 5 publications

References 3 publications

Exploration of highly accelerated magnetic resonance elastography using high-density array coils

Exploration of highly accelerated magnetic resonance elastography using high-density array coils

Single echo acquisition MRI using RF encoding

Basic Reconstruction Algorithms for Parallel Imaging

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