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Development of pulse sequences for hyperpolarized 13C magnetic resonance spectroscopic imaging of tumour metabolism
Metabolic imaging with hyperpolarized 13C-labeled cell substrates is a promising technique for imaging tissue metabolism in vivo. However, the transient nature of the hyperpolarization - and its depletion following excitation - limits the imaging time and the number of excitation pulses that can be used. A single-shot 3D imaging sequence has been developed and it is shown in this thesis to generate 13C MR images in tumour-bearing mice injected with hyperpolarized [1-13C]pyruvate. The pulse sequence acquires a stack-of-spirals at two spin echoes after a single excitation pulse and encodes the kz-dimension in an interleaved manner to enhance robustness to B0 inhomogeneity. Spectral-spatial pulses are used to acquire dynamic 3D images from selected hyperpolarized 13C-labeled metabolites. A nominal spatial/temporal resolution of 1.25 x 1.25 x 2.5 x 2 s was achieved in tumour images of hyperpolarized [1-13C]pyruvate and [1-13C]lactate acquired in vivo. An advanced sequence is also described in this thesis in a later study to acquire higher resolution images with isotropic voxels (1.25 x 1.25 x 1.25 ) at no cost of temporal resolution.
EPI is a sequence widely used in hyperpolarized 13C MRI because images can be acquired rapidly with limited RF exposure. However, EPI suffers from Nyquist ghosting, which is normally corrected for by acquiring a reference scan. In this thesis a workflow for hyperpolarized 13C EPI is proposed that requires no reference scan and, therefore, that does not sacrifice a time point in the dynamic monitoring of tissue metabolism.
To date, most of the hyperpolarized MRI on metabolism are based on 13C imaging, while 1H is a better imaging target for its 4 times higher gyromagnetic ratio and hence 16 times signal. In this thesis the world’s first dynamic 1H imaging in vivo of hyperpolarized [1-13C]lactate is presented, via a novel double-dual-spin-echo INEPT sequence that transfers the hyperpolarization from 13C to 1H, achieving a spatial resolution of 1.25 x 1.25
Single shot three-dimensional pulse sequence for hyperpolarized 13 C MRI.
PURPOSE: Metabolic imaging with hyperpolarized 13 C-labeled cell substrates is a promising technique for imaging tissue metabolism in vivo. However, the transient nature of the hyperpolarization, and its depletion following excitation, limits the imaging time and the number of excitation pulses that can be used. We describe here a single-shot three-dimensional (3D) imaging sequence and demonstrate its capability to generate 13 C MR images in tumor-bearing mice injected with hyperpolarized [1-13 C]pyruvate. METHODS: The pulse sequence acquires a stack-of-spirals at two spin echoes after a single excitation pulse and encodes the kz-dimension in an interleaved manner to enhance robustness to B0 inhomogeneity. Spectral-spatial pulses are used to acquire dynamic 3D images from selected hyperpolarized 13 C-labeled metabolites. RESULTS: A nominal spatial/temporal resolution of 1.25 × 1.25 × 2.5 mm3  × 2 s was achieved in tumor images of hyperpolarized [1-13 C]pyruvate and [1-13 C]lactate acquired in vivo. Higher resolution in the z-direction, with a different k-space trajectory, was demonstrated in measurements on a thermally polarized [1-13 C]lactate phantom. CONCLUSION: The pulse sequence is capable of imaging hyperpolarized 13 C-labeled substrates at relatively high spatial and temporal resolutions and is robust to moderate system imperfections. Magn Reson Med 77:740-752, 2017. © 2016 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.The work was supported by a Cancer Research UK Programme grant (17242) to KMB and by the CRUK-EPSRC Imaging Centre in Cambridge and Manchester (16465). JW was also supported, in part, by a grant from the Danish Strategic Research Council (LIFE-DNP: Hyperpolarized magnetic resonance for in vivo quantification of lipid, sugar and amino acid metabolism in lifestyle related diseases).This is the final version of the article. It first appeared from Wiley via https://doi.org/10.1002/mrm.2616
Wearable Coaxially-shielded Metamaterial for Magnetic Resonance Imaging
Recent advancements in metamaterials have yielded the possibility of a
wireless solution to improve signal-to-noise ratio (SNR) in magnetic resonance
imaging (MRI). Unlike traditional closely packed local coil arrays with rigid
designs and numerous components, these lightweight, cost-effective
metamaterials eliminate the need for radio frequency (RF) cabling, baluns,
adapters, and interfaces. However, their clinical adoption has been limited by
their low sensitivity, bulky physical footprint, and limited, specific use
cases. Herein, we introduce a wearable metamaterial developed using
commercially available coaxial cable, designed for a 3.0 T MRI system. This
metamaterial inherits the coaxially-shielded structure of its constituent
coaxial cable, effectively containing the electric field within the cable,
thereby mitigating the electric coupling to its loading while ensuring safer
clinical adoption, lower signal loss, and resistance to frequency shifts.
Weighing only 50g, the metamaterial maximizes its sensitivity by conforming to
the anatomical region of interest. MRI images acquired using this metamaterial
with various pulse sequences demonstrate an up to 2-fold SNR enhancement when
compared to a state-of-the-art 16-channel knee coil. This work introduces a
novel paradigm for constructing metamaterials in the MRI environment, paving
the way for the development of next-generation wireless MRI technology
History and physical principles of MRI
International audienceThe first chapter of the three-volume Magnetic Resonance Imaging Handbook describes the historical and physical background of modern nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) methods and techniques
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