Volume imaging with MR phased arrays

Hayes, Cecil E.; Hattes, Neil; Roemer, Peter B.

doi:10.1002/mrm.1910180206

Cited by 171 publications

(110 citation statements)

References 5 publications

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“…Note that the net SNR is always highest for the largest number of elements, despite the fact that the smaller individual coils of the multielement arrays have markedly reduced individual SNR at the selected depth. This result is consistent with the predictions of superposition principles, which suggest that the loss of depth sensitivity by small individual elements will be compensated by an associated increase in the number of elements, provided that noise from individual coil circuits is kept under control (15)(16)(17)(18). As an illustration of the superposition argument, imagine that a single rectangular coil is divided into two coils each with half the total area.…”

supporting

confidence: 88%

Rapid Volumetric MRI Using Parallel Imaging With Order-of-Magnitude Accelerations and a 32-Element RF Coil Array

et al. 2005

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Rationale and Objectives-Many clinical applications of Magnetic Resonance Imaging are constrained by basic limits on imaging speed. Parallel MRI relaxes these limits by using the sensitivity patterns of arrays of radiofrequency receiver coils to encode spatial information in a manner complementary to traditional encoding with magnetic field gradients. Until now, parallel MRI has been used to achieve modest improvements in imaging speed; order-of-magnitude improvements have been elusive given fundamental losses in signal-to-noise ratio. The goal of this work was to demonstrate that, with appropriate hardware and careful SNR management, rapid volumetric imaging at high accelerations is in fact feasible.Materials and Methods-Contrast-enhanced MRI with an axial 3D spoiled gradient echo imaging sequence was performed in healthy adult subjects using a 32-element RF coil array and a prototype 32-channel MR imaging system. Large imaging volumes were prescribed, in place of traditional limited slabs targeted only to suspect regions.Results-As much as 16-fold net accelerations of imaging were achieved repeatably using this approach. The use of large 3D volumes allowed comprehensive anatomical coverage at clinically useful spatial and/or temporal resolution. The need for careful, time-consuming, and subject-specific scan prescription was also eliminated. Conclusion-The highly parallel imaging approach presented here allows previously inaccessible volumetric coverage for time-sensitive MRI examinations such as contrast-enhanced MRA, and simultaneously provides a substantially simplified imaging paradigm. The resulting capability for rapid volumetric imaging promises to combine the strengths of MRI with some of the advantages of alternative imaging modalities such as multidetector CT.

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supporting

confidence: 88%

Rapid Volumetric MRI Using Parallel Imaging With Order-of-Magnitude Accelerations and a 32-Element RF Coil Array

et al. 2005

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“…Two coils with different coil geometry were used: a commercially available four-coil spine array consisting of linearly arranged 100 mm square coils and a locally developed four-coil receive only head coil consisting of 300 mm square coils wrapped around a cylindrical former (13,14). In both cases the individual coils were geometrically isolated from nearest neighbors by overlapping and any coupling minimized further by low-impedance preamplifier circuitry.…”

Section: Methodsmentioning

confidence: 99%

Generalized SMASH imaging

Bydder

Larkman

Hajnal

2001

Magnetic Resonance in Med

107

123

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A generalized parallel imaging method has been developed that uses coil profiles to generate missing k-space lines. The proposed method is an extension of SMASH, which uses linear combinations of coil sensitivity profiles to synthesize spatial harmonics. In the generalized SMASH approach described here, coil sensitivity profiles are represented directly in the Fourier domain to provide a general description of the spatial properties of the coils. This removes restrictions imposed by conventional SMASH, so that the choice and position of the receiver coils can be made on the basis of sensitivity to the volume of interest rather than suitability for constructing spatial harmonics. Generalized SMASH also intrinsically allows the freedom to accommodate acquisitions with uniform or nonuniform k-space sampling. Parallel imaging makes use of spatial sensitivity differences between individual coils in an array to partially replace gradient encoding during image acquisition. This reduces acquisition times by decreasing the number of phase encoded lines of k-space that must be acquired. There are three implementations of parallel imaging reported in the literature, known as SENSE (1-4), SMASH (5-7), and SPACE-RIP (8). All these methods require information about the coil sensitivity profiles (reference data), which is used to regenerate a full image dataset from a subsampled k-space acquisition (target data). The reference data is usually obtained as a separate acquisition, often with the subject in situ, although some implementations integrate the reference data acquisition with the target data acquisition (7,9). SENSE (1-4) operates in the image domain for both the target image data and the coil reference data. We use the name SENSE to refer to the Cartesian sampled form. The method used with other k-space trajectories will be referred to explicitly as non-Cartesian SENSE. In SENSE, the target data is acquired with a reduced field of view (FOV), which results in aliasing, and is then unfolded to the full FOV on a pixel-by-pixel basis using the reference data. Reduced FOV imaging imposes a requirement of uniformly spaced samples in the phase encode direction in k-space. Since all processing is done in the image domain, individual pixels in the reduced FOV data get unfolded by integer numbers of final pixels (i.e., 131, 132, 133, etc). This requires the solution of a set of linear simultaneous equations in which pixel intensities are weighted by the coil sensitivity at the final pixel locations. The numerical condition of these equations determines the local noise properties of the unfolded image (3,10), so that the signal-to-noise ratio (SNR) varies from pixel to pixel (3). The resulting patterns of noise variation generally reflect the coil geometry and can have a strong perceptual effect. The SENSE method is very flexible and can be used with any coil geometry, provided satisfactory numerical conditioning is achieved at the pixel locations of interest.SMASH (5,6) operates in k-space for the target image data but uses a...

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“…Present-day MRI relies strongly on signal detection with receiver arrays, which were first described in the late 1980s (1)(2)(3)(4) and analyzed in detail by Roemer et al (4). Initially, receiver arrays were devised and used to enhance the net signal-to-noise ratio (SNR) compared with single-coil acquisitions.…”

mentioning

confidence: 99%

Stretchable coil arrays: Application to knee imaging under varying flexion angles

Nordmeyer-Massner

Zanche

Pruessmann

2011

Magnetic Resonance in Med

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To fit high-density receiver arrays for MRI closely around individual target anatomies, there is a need to provide a high degree of geometric adjustability with ease of handling and patient comfort. In this work, this is accomplished by the construction of a coil array that is stretchable such that it automatically conforms to a given anatomy's shape and size. Stretchability is implemented by creating the coil conductors from braided wire mounted on an elastic textile substrate. The signal-to-noise ratio yield of such coils is measured by MRI experiments at 3 T, and the signal-to-noise ratio effect of coil stretching is investigated with and without adjustment of the matching between each coil and the respective preamplifier. Four-channel and eight-channel arrays of stretchable receiver coils are evaluated in phantoms as well as for in vivo imaging of the human knee. Exploiting stretchability, it is demonstrated that the knee can be imaged under varying flexion angles up to 60°while maintaining closely coupled array detection, high signal-to-noise ratio, and uniform coverage of the entire joint. Magn Reson Med 67:872-879, 2012. V C 2011 Wiley Periodicals, Inc.

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Volume imaging with MR phased arrays

Cited by 171 publications

References 5 publications

Rapid Volumetric MRI Using Parallel Imaging With Order-of-Magnitude Accelerations and a 32-Element RF Coil Array

Rapid Volumetric MRI Using Parallel Imaging With Order-of-Magnitude Accelerations and a 32-Element RF Coil Array

Generalized SMASH imaging

Stretchable coil arrays: Application to knee imaging under varying flexion angles

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