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Related Concept Videos

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
Thermal Sigmatropic Reactions: Overview01:16

Thermal Sigmatropic Reactions: Overview

Sigmatropic rearrangements are a class of pericyclic reactions in which a σ bond migrates from one part of a π system to another. These are intramolecular rearrangements where the total number of σ and π bonds remain unchanged.
Sigmatropic shifts are classified based on an order term [i, j ], where i and j indicate the number of atoms across which each end of the σ bond migrates. Below are examples of a [3,3] sigmatropic shift in 1,5-hexadiene, referred to as...
Hückel's Rule Diagram of π MOs: Frost Circle01:08

Hückel's Rule Diagram of π MOs: Frost Circle

The Frost circle or the inscribed polygon method is a graphical method for determining the relative energies of π molecular orbitals (MOs) for planar, fully conjugated, and monocyclic compounds. This method was first described by A. A. Frost and Boris Musulin in 1953.
A Frost circle is constructed by drawing a polygon whose number of edges is equal to the number of carbons of the given cyclic system, with one of the vertices pointing down. Then, a circle is drawn enclosing the polygon so that...
Fischer Projections02:18

Fischer Projections

Learning to draw Fischer projections of molecules and understanding their relevance plays a crucial role in the visual depiction of organic molecules. A Fischer projection is a two-dimensional projection on a planar surface to simplify the three-dimensional wedge–dash representation of molecules. This is especially helpful in the case of molecules with multiple chiral centers that can be difficult to draw. Here, all the bonds of interest are represented as horizontal or vertical lines. While...
¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Signal Flow Graphs01:18

Signal Flow Graphs

Signal-flow graphs offer a streamlined and intuitive approach to representing control systems, providing an alternative to traditional block diagrams. These graphs use branches to symbolize systems and nodes to represent signals, effectively illustrating the relationships and interactions within the system.
In a signal-flow graph, branches denote the system's transfer functions, while nodes represent the signals. The direction of signal flow is indicated by arrows, with the corresponding...

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Related Experiment Video

Updated: May 31, 2026

In Vitro Chemical Mapping of G-Quadruplex DNA Structures by Bis-3-Chloropiperidines
05:32

In Vitro Chemical Mapping of G-Quadruplex DNA Structures by Bis-3-Chloropiperidines

Published on: May 12, 2023

Fast CPMG-based Bloch-Siegert B(1)+ mapping.

T C Basse-Lüsebrink1, V J F Sturm, T Kampf

  • 1Department of Experimental Physics 5, University of Würzburg, Würzburg, Germany. thomas.basse-luesebrink@physik.uni-wuerzburg.de

Magnetic Resonance in Medicine
|June 21, 2011
PubMed
Summary
This summary is machine-generated.

Bloch-Siegert (BS) shift methods improve B(1)+ mapping accuracy and speed. This study extends BS mapping to multi-spin-echo imaging, offering faster acquisition and reduced signal loss, while assessing specific absorption rates.

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15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the &#181;s-ms Timescale
08:09

15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale

Published on: April 19, 2021

Area of Science:

  • Magnetic Resonance Imaging
  • Quantitative MRI
  • Pulse Sequence Design

Background:

  • B(1)+ mapping is crucial for quantitative MRI accuracy.
  • Magnitude-based methods suffer from inaccuracies and long scan times.
  • Bloch-Siegert (BS) shift-based methods offer improved accuracy and speed.

Purpose of the Study:

  • To extend Bloch-Siegert (BS) B(1)+ mapping to Carr, Purcell, Meiboom, Gill (CPMG)-based multi-spin-echo (MSE) and turbo-spin-echo (TSE) imaging.
  • To evaluate the performance of BS-CPMG-TSE sequences regarding acquisition speed and signal loss.
  • To assess the specific absorption rate (SAR) of BS-CPMG-TSE sequences compared to BS spin echo (BS-SE).

Main Methods:

  • Implementation of BS B(1)+ mapping within CPMG-based MSE and TSE sequences.
  • Comparison of acquisition time between BS-CPMG-TSE and BS-SE sequences.
  • Estimation and comparison of relative specific absorption rates (SAR) for BS-CPMG-TSE and BS-SE sequences.

Main Results:

  • BS-CPMG-TSE enables faster acquisition of B(1)+ information compared to BS-SE.
  • Spin echo-based techniques minimize signal loss due to T(2)* effects, crucial at high field strengths.
  • Relative SAR of BS-CPMG-TSE sequences was estimated and compared to BS-SE.

Conclusions:

  • BS-CPMG-MSE and BS-CPMG-TSE are viable extensions for accurate and efficient B(1)+ mapping.
  • These methods mitigate T(2)* related signal loss, enhancing robustness at high fields.
  • SAR assessment is essential for clinical translation of these advanced BS B(1)+ mapping techniques.