NMR/MRI Articles

NMR Sequence—CPMG Sequence

NMR Sequence—CPMG Sequence

Although FID experiment is useful for setting upNMR instrumentation, it has some disadvantages. The main disadvantage is that the decay constant (or shape) of data acquired with FID is affected not only by the sample properties, but also the homogeneity (or uniformity) of the magnetic field over the sample. Most scientists are only interested in the influence of sample properties on the NMR data, so removing the effect of the magnetic field on the decay of the NMR data would be extremely useful. Fortunately, the effects of the magnet on the signal can be removed by using a special pulse sequence called CPMG sequence.   Fig 1: CPMG sequence CPMG sequence is one of the important means to measure transverse relaxation time of the sample. The CPMG sequence involves ……

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NMR Relaxations

NMR Relaxations

In benchtop nmr experiments, there are two main relaxations, spin-lattice relaxation and spin-spin relaxation. The following figure is the recovery curve of T1 and T2. Fig 1: T1 recovery curve and T2 recovery curve Spin-lattice relaxation is also called longitudinal (or T1) relaxation. T1 is a time that suggests the speed of spin-lattice relaxation. Each material has an instinct resonance frequency. In NMR experiments, if the resonance frequency of material is close to the magnetic frequency, the energy exchange between them will be easy and T1 will be short. If the resonance frequency of material is far from the magnetic frequency, the energy exchange between them will be hard and T1 will be long. In benchtop NMR experiments, the frequency of magnetic field is often……

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Basis of magnetic resonance imaging (MRI)  Imaging Directions

Basis of magnetic resonance imaging (MRI) Imaging Directions

Samples during magnetic resonance imaging (MRI) experiments, the first question to consider is to determine the direction of three related imaging: selected layer direction (G Slice I), phase encoding direction (G Phase I) and the frequency-encoding direction (G Read I) In Fig 1, we can see relationship between orthogonal coordinates and the direction of the magnetic field. In the coordinates, Z direction is defined as up and down according to the NMR instrumentation. Y direction is defined as front and back. X direction is defined as left and right. Usually, we make the NMR imaging directions coincide the orthogonal coordinates, i.e. we use X/Y/Z to be slice/phase/read direction. However, we can also make the imaging direction not coincide the orthogonal coordinates……

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How to Uniform the Homogeneity of the Magnetic Field

How to Uniform the Homogeneity of the Magnetic Field

How to Uniform the Homogeneity of the Magnetic Field   The homogeneity of the magnetic field which generates only by the magnet sometimes is not very perfect. However, if we want to get a perfect image, we will need a uniform magnetic field. In our NMR instrument, we can use the gradient amplifier unit to improve the homogeneity of the magnetic field. (1)Find the correct central frequency. (2)Switch on the power supply of the Gradient Amplifier Unit. Fig 1 switch on the power supply of GAU   After the gradient unit start, a gradient field will be obtained by the gradient unit through the gradient coil, so the uniformity of the original magnetic field in the magnet is being destroyed. Therefore the first thing we need to do is electronic shimming after w……

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The Framework of Benchtop NMR

The Framework of Benchtop NMR

“MicroMR” is a new type of nuclear magnetic resonance imaging NMR analyzer that has both analyzing and imaging functions. It is more accurate and more stable than the old types. Comparing to the old types, it has following advantages. Firstly, it has an independent Pulse Sequence Generator (PSG) that can control pulse sequence precisely and stably. Secondly, it has both Radio Frequency (RF) transmitting circuit and RF receiving circuit, which can enhance the signal-to-noise ratio of Nuclear Magnetic Resonance (NMR) signals. Lastly, it has a temperature control system with high accuracy, which guarantees the repeatability of measurement. The following is the framework of benchtop NMR Fig 1:The framework of NIUMAG benchtop NMR According to the function, bench top NMR ……

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