Nuclear magnetic resonance imaging: Contrast-to-noise ratio as a function of strength of magnetic field

Hart, H. R.; Bottomley, Paul A.; Edelstein, William A.; Karr, S. G.; Leue, William M.; Mueller, O.; Redington, R. W.; Schenck, John F.; Smith, L.S.; Vatis, Dimitrios

doi:10.1016/0730-725x(84)90077-8

Cited by 7 publications

(6 citation statements)

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“…Relative SNR values of the antenna arrays were numerically calculated by combining the normalized receive B 1 (

{normalB}_{1}^{-}

) distributions of individual antenna elements in a root sum‐of‐squares (RSOS) fashion and scaling with the square of B 0 to account for the field‐strength related increase in signal power :

{SNR}_{relative} \sim {(\frac{{normalB}_{0}}{7.0})}^{2} . \sqrt{{true \sum}_{n = 1}^{10} {(\frac{| {normalB}_{1, n}^{-} |}{\sqrt{{normalP}_{normaln}}})}^{2}}

where B 0 is the field strength,

\frac{| {normalB}_{1, n}^{-} |}{\sqrt{{normalP}_{normaln}}}

is the magnitude of the receive B 1 field normalized to 1 W of accepted power for the n th antenna element.…”

Section: Methodsmentioning

confidence: 99%

Toward imaging the body at 10.5 tesla

Ertürk

Eryaman

et al. 2016

Magnetic Resonance in Med

106

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Purpose To explore the potential of performing body imaging at 10.5T compared to 7.0T through evaluating the transmit/receive performance of similarly configured dipole antenna arrays. Methods Fractionated dipole antenna elements for 10.5T body imaging were designed and evaluated using numerical simulations. Transmit performance of antenna arrays inside the prostate, kidneys and heart were investigated and compared to those at 7.0T using both phase-only RF shimming and multi-spoke pulses. Signal-to-noise ratio (SNR) comparisons were also performed. A 10-channel antenna array was constructed to image the abdomen of a swine at 10.5T. Numerical methods were validated with phantom studies at both field strengths. Results Similar power efficiencies were observed inside target organs with phase-only shimming, but RF non-uniformity was significantly higher at 10.5T. Spokes RF pulses allowed similar transmit performance with accompanying local SAR increases of 25–90% compared to 7.0T. Relative SNR gains inside the target anatomies were calculated to be >2-fold higher at 10.5T, and 2.2-fold SNR gain was measured in a phantom. Gradient echo and fast spin echo imaging demonstrated the feasibility of body imaging at 10.5T with the designed array. Conclusion While comparable power efficiencies can be achieved using dipole antenna arrays with static shimming at 10.5T; increasing RF non-uniformities underscore the need for efficient, robust and safe parallel transmission methods.

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“…Relative SNR values of the antenna arrays were numerically calculated by combining the normalized receive B 1 (

{normalB}_{1}^{-}

) distributions of individual antenna elements in a root sum‐of‐squares (RSOS) fashion and scaling with the square of B 0 to account for the field‐strength related increase in signal power :

{SNR}_{relative} \sim {(\frac{{normalB}_{0}}{7.0})}^{2} . \sqrt{{true \sum}_{n = 1}^{10} {(\frac{| {normalB}_{1, n}^{-} |}{\sqrt{{normalP}_{normaln}}})}^{2}}

where B 0 is the field strength,

\frac{| {normalB}_{1, n}^{-} |}{\sqrt{{normalP}_{normaln}}}

is the magnitude of the receive B 1 field normalized to 1 W of accepted power for the n th antenna element.…”

Section: Methodsmentioning

confidence: 99%

Toward imaging the body at 10.5 tesla

Ertürk

Eryaman

et al. 2016

Magnetic Resonance in Med

106

View full text Add to dashboard Cite

show abstract

“…When a paramagnetic contrast agent is introduced and accumulates in the tissue of interest, it produces changes in the spin-lattice relaxation (T 1 contrast) and/or the spin-spin relaxation (T 2 contrast) dynamics of protons in nearby water molecules. 147,148 This change allows one to differentiate the tissue of interest from others. Contrast agents are called either T 1 or T 2 agents, depending on whether the relative change in relaxation times is greater for T 1 or T 2 .…”

Section: Capabilitymentioning

confidence: 99%

New Generation Cadmium-Free Quantum Dots for Biophotonics and Nanomedicine

et al. 2016

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This review summarizes recent progress in the design and applications of cadmium-free quantum dots (Cd-free QDs), with an emphasis on their role in biophotonics and nanomedicine. We first present the features of Cd-free QDs and describe the physics and emergent optical properties of various types of Cd-free QDs whose applications are discussed in subsequent sections. Selected specific QD systems are introduced, followed by the preparation of these Cd-free QDs in a form useful for biological applications, including recent advances in achieving high photoluminescence quantum yield (PL QY) and tunability of emission color. Next, we summarize biophotonic applications of Cd-free QDs in optical imaging, photoacoustic imaging, sensing, optical tracking, and photothermal therapy. Research advances in the use of Cd-free QDs for nanomedicine applications are discussed, including drug/gene delivery, protein/peptide delivery, image-guided surgery, diagnostics, and medical devices. The review then considers the pharmacokinetics and biodistribution of Cd-free QDs and summarizes current studies on the in vitro and in vivo toxicity of Cd-free QDs. Finally, we provide perspectives on the overall current status, challenges, and future directions in this field.

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“…For microscopy in a well‐designed spectrometer, the principal source of noise is the RF coil rather than the sample, as contrasted with conventional imaging. As a result, SNR is expected to scale more nearly as ω 7/4 (where ω is the Larmor frequency) for microscopy studies as compared with scaling as ω for conventional imaging studies (17). Thus, an increase in magnetic field strength from 4.7T as used here to 18.8T—readily achievable with commercially available NMR magnets—would allow voxel size to be decreased from (60 μm) 3 to (38 μm) 3 with no penalty in image acquisition time.…”

Section: Discussionmentioning

confidence: 99%

Water and lipid MRI of the Xenopus oocyte

Sehy¹,

Ackerman

2001

Magnetic Resonance in Med

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Oocytes of Xenopus laevis are large, single cells that provide a promising model system for the exploration of the MR biophysics fundamental to more complex living systems. Previous studies have generally employed 2D spin-echo sequences with an image slice thickness greater than the thickness of the cellular volumes of interest. Also, the large cytoplasmic lipid signal has typically been ignored. This study describes separate, highresolution 3D measurements of the water and lipid spin densities, T 1 and T 2 relaxation time constants, and the water apparent diffusion rate constant (ADC) in the Xenopus oocyte without significant partial volume artifacts. The lipid spin-density and values for water MR properties varied monotonically from the vegetal to animal poles, indicating that the border between the poles is not sharply demarcated. The Xenopus laevis oocyte is a well-established cell model used in many branches of modern experimental biology. This versatile cell provides a promising model platform upon which to explore fundamental aspects of the MR biophysics underlying more complex living systems. In particular, the ability to spatially resolve the intracellular compartment allows the direct testing of hypotheses regarding various MR properties of the cytoplasm and nucleus. Recent efforts to integrate confocal microscopy and MR imaging will likely augment the capability of such experiments (1).Aguayo et al. (2) reported the first MR images of the Xenopus oocyte in 1986. Along with intriguing contrast between intracellular regions, the authors described a strong chemical shift artifact from cytoplasmic lipid. Posse and Aue (3) further characterized this lipid signal using a 4D spectroscopic imaging technique. Both studies localized the lipid signal to the cytoplasm, with little or no lipid signal arising from the nucleus. Since these initial studies, several investigators have calculated spin densities and T 2 and/or T 1 relaxation time constants for the oocyte nucleus, animal pole, and vegetal pole in control or altered cells (4 -6). The effect of the unknown, spatially varying lipid spin-density on these calculations, if any, has been largely ignored. Further, these studies have routinely employed 2D spin-echo sequences with slice profiles thicker than the cellular volumes of interest (VOIs), raising concerns regarding partial volume effects. This shortcoming is especially detrimental to studies of the nucleus, which has a diameter of only 300 m.Herein we present separate, high-resolution 3D measurements of the water and lipid spin densities, T 1 and T 2 relaxation time constants, and the water apparent diffusion coefficient (ADC) in the Xenopus oocyte without significant partial volume artifacts. We challenge the conventional binary segmentation of the oocyte cytoplasm into vegetal and animal poles and recognize cylindrical symmetry about the vegetal-animal (V-A) axis. Lipid-specific imaging is demonstrated for which water suppression is achieved via high diffusion weighting in the imaging sequence. We corr...

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Nuclear magnetic resonance imaging: Contrast-to-noise ratio as a function of strength of magnetic field

Cited by 7 publications

References 0 publications

Toward imaging the body at 10.5 tesla

Toward imaging the body at 10.5 tesla

New Generation Cadmium-Free Quantum Dots for Biophotonics and Nanomedicine

Water and lipid MRI of the Xenopus oocyte

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