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Related Concept Videos

Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

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In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
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NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

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The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
3.0K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

1.4K
Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
1.4K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

1.6K
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
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Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

1.5K
Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
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Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

5.0K
All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not contribute to...
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Related Experiment Video

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Magnetic Resonance Imaging Quantification of Pulmonary Perfusion using Calibrated Arterial Spin Labeling
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Arterial Spin-Labeling MRI Identifies Hypervascular Meningiomas.

Vera Mayercik1, Mingming Ma1, Samantha Holdsworth1

  • 1Department of Radiology, Division of Neuroimaging and Neurointervention, Stanford University, Stanford University Medical Center, 300 Pasteur Dr, Grant Bldg, Rm S031E, Stanford, CA 94305.

AJR. American Journal of Roentgenology
|July 31, 2019
PubMed
Summary

Arterial spin-labeling (ASL) MRI can identify hypervascular meningiomas by measuring tumor blood flow. This noninvasive technique correlates with digital subtraction angiography (DSA) findings, aiding in presurgical planning.

Keywords:
ASLcerebral angiogramhypervascularmeningioma

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Area of Science:

  • Neuroradiology
  • Medical Imaging
  • Oncology

Background:

  • Hypervascular meningiomas require preoperative identification for potential embolization.
  • Minimizing intraoperative blood loss is crucial in meningioma surgery.
  • Digital subtraction angiography (DSA) is an established method for assessing tumor vascularity.

Purpose of the Study:

  • To investigate the correlation between arterial spin-labeling (ASL) MRI blood flow and tumor vascularity on DSA in meningiomas.
  • To evaluate ASL MRI as a noninvasive tool for detecting hypervascular meningiomas.

Main Methods:

  • Retrospective analysis of 39 meningiomas in 34 patients who underwent both ASL MRI and DSA.
  • Independent calculation of normalized tumor blood flow (TBF) from ASL images by two raters.
  • Assessment of tumor blush presence on DSA and correlation with normalized TBF.

Main Results:

  • Mean normalized TBF was significantly higher in meningiomas with tumor blush on DSA (p < 0.001).
  • Excellent interrater agreement (ICC = 0.91) for TBF measurements.
  • ASL MRI demonstrated an AUC of 0.82 for identifying tumor vascularity, with a TBF cut point of 2.7 offering 88% sensitivity and 67% specificity.

Conclusions:

  • ASL MRI shows significant potential as a noninvasive screening tool for hypervascular meningiomas.
  • Normalized TBF measured by ASL MRI correlates well with DSA-assessed tumor vascularity.
  • This technique may help identify meningiomas suitable for presurgical embolization.