FLASH imaging: Rapid NMR imaging using low flip-angle pulses

Haase, Axel; Frahm, Jens; Matthaei, D.; Hänicke, W.; Merboldt, Klaus‐Dietmar

doi:10.1016/j.jmr.2011.09.021

Cited by 371 publications

(164 citation statements)

References 12 publications

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“…In this study, a T1-weighted 3D FLASH (fast low-angle shot) sequence was chosen due to its fast imaging time and suitability for in vivo application [28]. In the FLASH sequence, transverse magnetization is spoiled and the steady-state longitudinal magnetization depends on T1 and the flip angle.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of intervertebral disc cartilaginous endplate structure using magnetic resonance imaging

et al. 2013

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Purpose The cartilaginous endplate (CEP) is a thin layer of hyaline cartilage positioned between the vertebral endplate and nucleus pulposus (NP) that functions both as a mechanical barrier and as a gateway for nutrient transport into the disc. Despite its critical role in disc nutrition and degeneration, the morphology of the CEP has not been well characterized. The objective of this study was to visualize and report observations of the CEP three-dimensional morphology, and quantify CEP thickness using an MRI FLASH (fast low-angle shot) pulse sequence. Methods MR imaging of ex vivo human cadaveric lumbar spine segments (N = 17) was performed in a 7T MRI scanner with sequence parameters that were selected by utilizing highresolution T1 mapping, and an analytical MRI signal model to optimize image contrast between CEP and NP. The CEP thickness at five locations along the mid-sagittal AP direction (center, 5 mm, 10 mm off-center towards anterior and posterior) was measured, and analyzed using two-way ANOVA and a post hoc Bonferonni test. For further investigation, six in vivo volunteers were imaged with a similar sequence in a 3T MRI scanner. In addition, decalcified and undecalcified histology was performed, which confirmed that the FLASH sequence successfully detected the CEP. Results CEP thickness determined by MRI in the midsagittal plane across all lumbar disc levels and locations was 0.77 ± 0.24 mm ex vivo. The CEP thickness was not different across disc levels, but was thinner toward the center of the disc. Conclusions This study demonstrates the potential of MRI FLASH imaging for structural quantification of the CEP geometry, which may be developed as a technique to evaluate changes in the CEP with disc degeneration in future applications.

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Section: Introductionmentioning

confidence: 99%

Evaluation of intervertebral disc cartilaginous endplate structure using magnetic resonance imaging

et al. 2013

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“…dM + (r, t) dt = i ω(r, t)M + (r, t) − D M + (r, t), (1) where D is the gas diffusion coefficient. 1 As usual, Eq.…”

Section: Theoretical Considerationsmentioning

confidence: 99%

“…1 As usual, Eq. 1 is written for convenience in the rotating Larmor frame and ω(r, t) is the local value of the Larmor angular frequency shift resulting from the time-dependent applied field gradients.…”

Section: Theoretical Considerationsmentioning

confidence: 99%

“…Firstly, the initially available magnetisation is non renewable and thus has to be used up efficiently. Small tip angle excitation, based on the FLASH (Fast Low Angle SHot) sequence [1] is most often used for radial or Cartesian k-space sampling, sometimes with a variable flip angle approach [2]. Secondly, high gas diffusivity leads to rapid signal loss and to image blurring, which sets joint constraints on the acquisition time and on the readout gradient.…”

Section: Introductionmentioning

confidence: 99%

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Achieving high spatial resolution and high SNR in low-field MRI of hyperpolarised gases with Slow Low Angle SHot

Safiullin¹,

Talbot²,

Nacher³

2013

Journal of Magnetic Resonance

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MRI of hyperpolarised gases is usually performed with fast data acquisition to achieve high spatial resolutions despite rapid diffusion-induced signal attenuation. We describe a double-cross k-space sampling scheme suitable for slow low angle shot (SLASH) acquisition and yielding an increased SNR. It consists of a series of anisotropic partial acquisitions with a reduced resolution in the read direction, which alleviates signal attenuation and still provides a high isotropic resolution. The advantages of SLASH imaging over conventional FLASH imaging are evaluated analytically, using numerical lattice calculations, and experimentally in phantom cells filled with hyperpolarised 3 He-N2 gas mixtures. Low-field MRI is performed (here 2.7 mT), a necessary condition to obtain long T * 2 values in lungs for slow acquisition. Two additional benefits of the SLASH scheme over FLASH imaging have been demonstrated: it is less sensitive to the artefacts due to concomitant gradients and it allows measuring apparent diffusion coefficients for an extended range of times.

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“…The potentialities of MRI are, however, conditioned by imaging speed. To meet the growing need for functional imaging and moving organ imaging, fast acquisition techniques such as fast low-angle shot (FLASH) (1,2), echo planar imaging (EPI) (3), and rapid acquisition with relaxation enhancement (RARE) (4) have been developed and are used in clinics. However, the speed at which data can be measured in MRI is fundamentally limited by physical and physiological constraints.…”

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confidence: 99%

MRI reconstruction from 2D truncated k‐space

Luo¹,

Zhu²,

Li³

et al. 2011

Magnetic Resonance Imaging

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Purpose: To shorten acquisition time by means of both partial scanning and partial echo acquisition and to reconstruct images from such 2D partial k-space acquisitions. Materials and Methods:We propose an approach to reconstructing magnetic resonance images from 2D truncated k-space in which the k-space is truncated in both phase-and frequency-encoding directions. Unlike conventional reconstruction techniques, the proposed approach is based on a newly developed 2D singularity function analysis (SFA) model and a sparse representation of an image whose parameters can be estimated from the 2D partial k-space data. Such a sparse representation leads to an accurate recovery of the missing k-space data and, hence, an accurate reconstruction of the image.Results: The proposed approach can reconstruct an image from as little as 20%-30% of the k-space data and the quality of the reconstructed image is comparable to the reference image that is reconstructed from the complete k-space data. Conclusion:Despite the high asymmetry of a 2D truncated k-space, the proposed approach allows for accurate reconstruction without the need of phase correction and, thus, overcomes the assumption of slow phase variations that is usually required by the existing reconstruction methods. It provides a new way of fast imaging for applications that require a significant reduction of the acquisition time.

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FLASH imaging: Rapid NMR imaging using low flip-angle pulses

Cited by 371 publications

References 12 publications

Evaluation of intervertebral disc cartilaginous endplate structure using magnetic resonance imaging

Evaluation of intervertebral disc cartilaginous endplate structure using magnetic resonance imaging

Achieving high spatial resolution and high SNR in low-field MRI of hyperpolarised gases with Slow Low Angle SHot

MRI reconstruction from 2D truncated k‐space

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