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Approaching ultimate intrinsic signal-to-noise ratio with loop and dipole antennas.

ABSTRACT: PURPOSE:Previous work with body-size objects suggested that loops are optimal MR detectors at low fields, whereas electric dipoles are required to maximize signal-to-noise ratio (SNR) at ultrahigh fields (???7?T). Here we investigated how many loops and/or dipoles are needed to approach the ultimate intrinsic SNR (UISNR) at various field strengths. METHODS:We calculated the UISNR inside dielectric cylinders mimicking different anatomical regions. We assessed the performance of various arrays with respect to the UISNR. We validated our results by comparing simulated and experimental coil performance maps. RESULTS:Arrays with an increasing number of loops can rapidly approach the UISNR at fields up to 3 T, but are suboptimal at ultrahigh fields for body-size objects. The opposite is true for dipole arrays. At 7?T and above, 16 dipoles provide considerably larger central SNR than any possible loop array, and minimal g factor penalty for parallel imaging. CONCLUSIONS:Electric dipoles can be advantageous at ultrahigh fields because they can produce both curl-free and divergence-free currents, whereas loops are limited to divergence-free contributions only. Combining loops and dipoles may be optimal for body imaging at 3?T, whereas arrays of loops or dipoles alone may perform better at lower or higher field strengths, respectively. Magn Reson Med 79:1789-1803, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

SUBMITTER: Lattanzi R

PROVIDER: S-EPMC5754268 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature

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Approaching ultimate intrinsic signal-to-noise ratio with loop and dipole antennas.

Lattanzi Riccardo R Wiggins Graham C GC Zhang Bei B Duan Qi Q Brown Ryan R Sodickson Daniel K DK

Magnetic resonance in medicine 20170704 3

<h4>Purpose</h4>Previous work with body-size objects suggested that loops are optimal MR detectors at low fields, whereas electric dipoles are required to maximize signal-to-noise ratio (SNR) at ultrahigh fields ( ≥ 7 T). Here we investigated how many loops and/or dipoles are needed to approach the ultimate intrinsic SNR (UISNR) at various field strengths.<h4>Methods</h4>We calculated the UISNR inside dielectric cylinders mimicking different anatomical regions. We assessed the performance of var ...[more]

PMID: 28675512

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Project description:MotivationTarget-specific hybridization depends on oligo-probe characteristics that improve hybridization specificity and minimize genome-wide cross-hybridization. Interplay between specific hybridization and genome-wide cross-hybridization has been insufficiently studied, despite its crucial role in efficient probe design and in data analysis.ResultsIn this study, we defined hybridization specificity as a ratio between oligo target-specific hybridization and oligo genome-wide cross-hybridization. A microarray database, derived from the Genomic Comparison Hybridization (GCH) experiment and performed using the Affymetrix platform, contains two different types of probes. The first type of oligo-probes does not have a specific target on the genome and their hybridization signals are derived from genome-wide cross-hybridization alone. The second type includes oligonucleotides that have a specific target on the genomic DNA and their signals are derived from specific and cross-hybridization components combined together in a total signal. A comparative analysis of hybridization specificity of oligo-probes, as well as their nucleotide sequences and thermodynamic features was performed on the database. The comparison has revealed that hybridization specificity was negatively affected by low stability of the fully-paired oligo-target duplex, stable probe self-folding, G-rich content, including GGG motifs, low sequence complexity and nucleotide composition symmetry.ConclusionFiltering out the probes with defined 'negative' characteristics significantly increases specific hybridization and dramatically decreasing genome-wide cross-hybridization. Selected oligo-probes have two times higher hybridization specificity on average, compared to the probes that were filtered from the analysis by applying suggested cutoff thresholds to the described parameters. A new approach for efficient oligo-probe design is described in our study.Contactshabalin@ncbi.nlm.nih.gov or olga.matveeva@gmail.comSupplementary informationSupplementary data are available at Bioinformatics online.

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Approaching ultimate intrinsic signal-to-noise ratio with loop and dipole antennas.

Publications

Approaching ultimate intrinsic signal-to-noise ratio with loop and dipole antennas.

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