Selection of a convolution function for Fourier inversion using gridding (computerised tomography application)

Jackson, John I.; Meyer, Craig H.; Nishimura, Dwight G.; Macovski, Albert

doi:10.1109/42.97598

Cited by 981 publications

(945 citation statements)

References 16 publications

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“…This is necessary to avoid spatial blurring for off‐resonant signals. Gridding 39 using a Kaiser‐Bessel kernel (kernel width of 3) was performed with an overgridding factor of 2. After gridding, the data were spatially Fourier transformed and cropped to the intended FOV.…”

Section: Methodsmentioning

confidence: 99%

Density‐weighted concentric circle trajectories for high resolution brain magnetic resonance spectroscopic imaging at 7T

Hingerl

Bogner

Moser

et al. 2017

Magnetic Resonance in Med

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PurposeFull‐slice magnetic resonance spectroscopic imaging at ≥7 T is especially vulnerable to lipid contaminations arising from regions close to the skull. This contamination can be mitigated by improving the point spread function via higher spatial resolution sampling and k‐space filtering, but this prolongs scan times and reduces the signal‐to‐noise ratio (SNR) efficiency. Currently applied parallel imaging methods accelerate magnetic resonance spectroscopic imaging scans at 7T, but increase lipid artifacts and lower SNR‐efficiency further. In this study, we propose an SNR‐efficient spatial‐spectral sampling scheme using concentric circle echo planar trajectories (CONCEPT), which was adapted to intrinsically acquire a Hamming‐weighted k‐space, thus termed density‐weighted‐CONCEPT. This minimizes voxel bleeding, while preserving an optimal SNR.Theory and MethodsTrajectories were theoretically derived and verified in phantoms as well as in the human brain via measurements of five volunteers (single‐slice, field‐of‐view 220 × 220 mm2, matrix 64 × 64, scan time 6 min) with free induction decay magnetic resonance spectroscopic imaging. Density‐weighted‐CONCEPT was compared to (a) the originally proposed CONCEPT with equidistant circles (here termed e‐CONCEPT), (b) elliptical phase‐encoding, and (c) 5‐fold Controlled Aliasing In Parallel Imaging Results IN Higher Acceleration accelerated elliptical phase‐encoding.ResultsBy intrinsically sampling a Hamming‐weighted k‐space, density‐weighted‐CONCEPT removed Gibbs‐ringing artifacts and had in vivo +9.5%, +24.4%, and +39.7% higher SNR than e‐CONCEPT, elliptical phase‐encoding, and the Controlled Aliasing In Parallel Imaging Results IN Higher Acceleration accelerated elliptical phase‐encoding (all P < 0.05), respectively, which lead to improved metabolic maps.ConclusionDensity‐weighted‐CONCEPT provides clinically attractive full‐slice high‐resolution magnetic resonance spectroscopic imaging with optimal SNR at 7T. Magn Reson Med 79:2874–2885, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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Section: Methodsmentioning

confidence: 99%

Density‐weighted concentric circle trajectories for high resolution brain magnetic resonance spectroscopic imaging at 7T

Hingerl

Bogner

Moser

et al. 2017

Magnetic Resonance in Med

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“…Images were acquired using a double-resonant (32.59 MHz/123.2 MHz) birdcage coil (Rapid Biomed GmbH, Wü rzburg, Germany) and were reconstructed offline with Matlab (Mathworks, Natick, MA). The k-space data were regridded with an oversampling ratio of 2 using a Kaiser-Bessel kernel (25) and Fourier transformed by a conventional fast Fourier transform (FFT) without filtering.…”

Section: Sequence Designmentioning

confidence: 99%

Sodium MRI using a density‐adapted 3D radial acquisition technique

Nagel

Laun

Weber

et al. 2009

Magnetic Resonance in Med

246

256

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A density-adapted three-dimensional radial projection reconstruction pulse sequence is presented which provides a more efficient k-space sampling than conventional three-dimensional projection reconstruction sequences. The gradients of the density-adapted three-dimensional radial projection reconstruction pulse sequence are designed such that the averaged sampling density in each spherical shell of k-space is constant. Due to hardware restrictions, an inner sphere of k-space is sampled without density adaption. This approach benefits from both the straightforward handling of conventional three-dimensional projection reconstruction sequence trajectories and an enhanced signal-to-noise ratio (SNR) efficiency akin to the commonly used three-dimensional twisted projection imaging trajectories. Benefits for low SNR applications, when compared to conventional three-dimensional projection reconstruction sequences, are demonstrated with the example of sodium imaging. In simulations of the point-spread function, the SNR of small objects is increased by a factor 1.66 for the densityadapted three-dimensional radial projection reconstruction pulse sequence sequence. Using analytical and experimental phantoms, it is shown that the density-adapted three-dimensional radial projection reconstruction pulse sequence allows higher resolutions and is more robust in the presence of field inhomogeneities. High-quality in vivo images of the healthy human leg muscle and the healthy human brain are acquired. For equivalent scan times, the SNR is up to a factor of 1.8 higher and anatomic details are better resolved using density-adapted three-dimensional radial projection reconstruction pulse sequence. Key words: sodium magnetic resonance imaging; densityadapted sampling; radial imaging; projection reconstruction; sampling density; field inhomogeneities Sodium ( 23 Na) ions play an important role in cellular homeostasis and cell viability. In healthy tissue, the extracellular sodium concentration ([Na ϩ ] ex ϭ 145 mM) is about 10 times higher than the intracellular concentration ([Na ϩ ] in ϭ 10-15 mM) (1). Using sodium MRI, volume-and relaxation-weighted signal of these compartments can be measured. Thus, sodium MRI is a promising diagnostic tool since pathologic processes can alter this ion gradient.Many studies investigating the usefulness of sodium MRI in human pathologies have been performed recently. Brain neoplasia and sustained cell depolarization, a precursor of cell division, lead to an increase of the intracellular sodium concentration and to a rise in the average tissue sodium concentration (2). Furthermore, the application of sodium MRI has been shown to be valuable for muscular channelopathies (3,4), brain tumors (5), the human kidney (6), myocardial infarction (7), and cerebral ischemia (8,9) diagnostics.However, sodium MRI remains a challenging technique for several reasons. The sodium nucleus exhibits a fast biexponential transversal relaxation in the extreme narrowing limit, i.e., if the correlation time is much shorter...

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“…All raw-data for the spiral sequence was re-gridded to a 512 Â 512 matrix and reconstructed off line using an in-house Matlab (Mathworks, Natick, MA) program based on Jackson et al (40) and Bernstein et al (41). A sliding data window (42) was applied taking the four most recent interleaved spiral readouts for reconstruction, which allowed the time between images to be reduced from the 318 ms of truly independent velocity images down to 79.56 ms. ''Swirl'' artifacts were expected to arise from flow variability between interleaves (31,43), especially from incomplete suppression of arterial blood.…”

Section: Non-gated Interleaved Spirals (Isp)mentioning

confidence: 99%

MR phase‐contrast velocity mapping methods for measuring venous blood velocity in the deep veins of the calf

Pierce

Gatehouse

et al. 2011

Magnetic Resonance Imaging

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Purpose: To evaluate the feasibility of using un-gated, real-time MRI for venous blood velocity mapping in the calf, comparing an interleaved spiral k-space sequence (ISP) against a standard segmented gradient echo sequence (GRE). Materials and Methods:A flow phantom with a variable flow-rate was scanned using both GRE and ISP sequences for an in vitro comparison. Seven subjects were scanned prone, performing metronome guided breathing, using the (externally triggered) segmented GRE and real-time ISP sequences. The segmented GRE acquisition duration was 2.5 mins (22 guided respiratory cycles) and the ISP sequence ran continuously for 35s, 4 full guided respiratory cycles. Mean velocity from each of the deep veins was measured and peak mean velocity, peak flow rate and cumulative volume flow over a respiratory cycle compared between sequences.Results: The two sequences compared well both in vitro and in vivo. The real-time ISP sequence showed shortterm variations in mean velocity superimposed on the respiratory induced flow, which were averaged out using the segmented GRE sequence. Conclusion:Real-time ISP provides comparable timeaveraged flow results to the standard sequence with additional information on real-time flow variations and so could be used for further investigation into venous blood flow in the lower leg.

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Selection of a convolution function for Fourier inversion using gridding (computerised tomography application)

Cited by 981 publications

References 16 publications

Density‐weighted concentric circle trajectories for high resolution brain magnetic resonance spectroscopic imaging at 7T

Density‐weighted concentric circle trajectories for high resolution brain magnetic resonance spectroscopic imaging at 7T

Sodium MRI using a density‐adapted 3D radial acquisition technique

MR phase‐contrast velocity mapping methods for measuring venous blood velocity in the deep veins of the calf

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