NMR/MRI Articles

How to Find the Central Frequency of NMR Analyzer?

How to Find the Central Frequency of NMR Analyzer?

How to Find the Central Frequency of NMR Analyzer?   Basic principle of NMR analyzer : The spin frequency of hydrogen atoms in a certain magnetic field obeys the following rule. γ*B0=ω , where B0 is the magnetic field strength of the NMR analyzer, γ is the magnetogyric ratio of hydrogen and ω is called larmor frequency (also called central frequency) which is the resonance frequency of hydrogen atoms in a certain magnetic field. If the RF frequency is equal to larmor frequency, the resonance phenomenon of hydrogen atoms can occur. However the material of our magnet is very sensitive to temperature. Even a little variation of temperature can cause the variation B0 which also causes the variation of central frequency. Therefore, at the very beginning of the NMR exp……

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Principle of Oil &Moisture Content Testing

Principle of Oil &Moisture Content Testing

Principle of Oil &Moisture Content Testing   The hard pulse echo sequence originating from CPMG sequence with only one echo count, namely only one 180° pulse after the 90° pulse, shown in Figure 1, is applied to measure the Oil &Moisture content in seed by means of NMR technology. After 90° pulse, FID signal appears and after 180° pulse, echo signal appears.     Figure 1 Testing Oil &Moisture content of seed by applying CPMG sequence In CPMG sequence, the line composed of all echo peak points, whose decaying speed is proportionate to exp(-t/T2), embodies the decaying process of spin-spin(T2) relaxation. T2 is the transverse relaxation time of the hydrogenous substances in samples. Supposing there exist different kinds of hydrogen in a sample, ……

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NMR Sequence—Hard Pulse FID Sequence

NMR Sequence—Hard Pulse FID Sequence

In NMR system, RF pulse is one type of pulse which is used to generate RF magnetic field. And the RF magnetic field is the power that stimulates the sample and generates NMR signals. Therefore, different RF pulse sequences can cause different results. Hard pulse is a narrow and strong rectangle RF pulse. The frequency width of this type of pulse is wide and its main petal is large enough to cover the width of absorption frequency of the sample. So the hard pulse can excite the whole sample encircled by the RF coil. And the hard pulse sequence is usually used in relaxation analysis. The time domain graph of the NMR FID (Free Induction Decay) sequence is displayed as Figure 1. Its parameters are listed and interpreted as follows. NMR Hrad Pulse FID Sequence:   Fig……

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Formation of NMR Signal

Formation of NMR Signal

It is known to us that all matter consists of atoms, which is the main particle in the nucleus and from which the NMR signal generates. For example, due to the positive electricity and rapid spinning itself, the hydrogen proton can be considered as a ring current. The electromagnetic theory states a truth that electricity generates magnetism. Thus, proton can be looked as a magnetic needle for the magnetic moment it produces. Difference of direction of the countless magnetic needles in each sample keeps the total magnetic moment to be zero by cancelling each other out. Once a sample is placed in a static magnetic field, its original balance will be stricken. According to the principles of quantum mechanics, we know that the space orientations of nuclear magnetic mome……

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Bimodal MRI & NIR Liposome Nanoprobe for Tumor Targeted Molecular Imaging

Bimodal MRI & NIR Liposome Nanoprobe for Tumor Targeted Molecular Imaging

NIUMAG A Bimodal MRI and NIR Liposome Nanoprobe for Tumor Targeted Molecular Imaging Abstract  The combination of complementary MRI and NIR imaging methods evolved to provide an even more powerful bioimaging tool. Herein, a novel bimodal MRI/NIR nanoprobe GCF-HDA was prepared via a facile self-assembly approach of three types of amphiphilic structures in aqueous solution. The Stokes shift of the NIR moiety increased from 30 to 150 nm and fluorescence quantum yield increased from 1.5 to 8% after conjugation with electron-rich hexadecylamine (HDA) to organic dye Cy7. The photostability of the nanoprobe GCF-HDA was dramatically improved after involving the newly synthesized dye. Molecular dynamics simulation demonstrated that the GCF-HDA is composed of 2.0–3.5 nm clus……

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