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Chemical shift imaging method and system

A technology of chemical shift and imaging method, applied in the direction of using nuclear magnetic resonance imaging system for measurement, magnetic resonance measurement, measurement device, etc., can solve the problem of long imaging time, etc., and achieve the effect of shortening the acquisition time

Active Publication Date: 2014-12-03
SHANGHAI UNITED IMAGING HEALTHCARE
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0006] Although the existing echo-planar spectroscopy imaging EPSI collects multiple echo signals at one time on the basis of chemical shift imaging CSI, which shortens the imaging time, the imaging time is still long, and the imaging speed needs to be further improved to meet the requirements of clinical applications. need

Method used

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Embodiment 1

[0041] First, step S101 is executed to apply a magnetic field to the region of interest according to the imaging sequence. Figure 4 It is a schematic diagram of the EPCSI sequence of the echo-planar chemical shift imaging of the present invention. Among them, Gs and Gr respectively represent the gradient of the layer selection direction and the gradient of the readout direction, RF represents the radio frequency pulse, and signal represents the generated echo signal data. Its phase encoding PE direction does not apply any encoding gradient, and the echo signal data (signal) is collected during the echo interval and the plateau period of the readout gradient. The acquisition method is the same as that of the EPI data readout method. The readout gradient pulse acquisition is used to obtain echo data, and the resolution in the PE direction can be obtained by saturation bands or selective pulses.

[0042]Different from EPSI, the technical scheme of the present invention excites ...

Embodiment 2

[0051] In the first embodiment, three radio frequency pulses are applied in step S101, after which, the echo chain of the EPI is used for data collection, and the echo signal will be superimposed in the middle of the plateau period of the readout gradient. In order to separate the echo signals, preferably, after each layer-selection gradient pulse applied in step S101, a dephasing gradient pulse with a fixed size and duration is applied immediately in the readout direction, so that finally in Three separate echo signal data will be obtained for each plateau of the readout gradient. Such as Figure 5 shown, which is Figure 4 An enlarged view of the echo signal signal, where radio frequency pulses RF1, RF2, and RF3 correspond to echo signals 1, 2, and 3, respectively. Controlling the size of the readout gradient Gr or the bandwidth of the readout gradient can allow better separation of the three echoes.

[0052] After the dephasing gradient pulse is applied, the three echo s...

Embodiment 3

[0056] Also for the problem in the first embodiment that it is not easy to read the independent data due to the overlap of the echo signal data, if the phase of each radio frequency pulse is encoded, and then the overlapping echo signals are decoded, the individual data can be completely separated and obtained. Corresponding echo signal data.

[0057] When the spectrum data is collected without encoding the phase of the RF pulse, the phase of the RF pulse and the phase of the ADC receiver are often cycled and averaged due to some reasons in the system and the NMR signal itself. Such as Figure 7 As shown, taking 4 cycles as an example, when performing RF pulse excitation, the RF pulses with phases of 0°, 90°, 180° and 270° are used for cyclic excitation, and then the four samples collected in one cycle The echo signal data is averaged, so the number of echo signal acquisitions is a multiple of 4. For the convenience of description later, the aforementioned phase values ​​of ...

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Abstract

The invention discloses a chemical shift imaging method and system. The method comprises the following steps: a) applying a magnetic field to a region of interest according to an imaging sequence, the imaging sequence comprising a plurality of radio-frequency pulses and a plurality of gradient pulses, wherein the radio-frequency pulses are excited continuously in sequence, and the gradient pulses comprise layer-selection gradient pulses and convergence gradient pulses, the last layer-selection gradient pulse being applied with one phase convergence gradient pulse, and the polarities of adjacent gradient pulses being opposite; b) collecting echo data through a series of gradient pulses with alternatively-opposite polarities by adopting a data reading mode of EPI; and c)carrying out data reconstruction to obtain a chemical shift image based on the echo data. Compared with a conventional chemical shift imaging CSI, according to the chemical shift imaging method and system in the technical scheme of the invention, the collection time is reduced to one order of magnitude, thereby helping to finish spectrum collection is a short time; and compared with echo planar spectrum imaging EPSI, 3-4 times of volume elements are collected under the same time and conditions.

Description

technical field [0001] The invention relates to the field of magnetic resonance imaging, in particular to a chemical shift imaging method and system thereof. Background technique [0002] In magnetic resonance imaging, the magnetic resonance signal used to form an image mainly comes from hydrogen protons in water, and other hydrogen nuclei have little influence on the image. For other chemical components such as fat, choline, amino acid, n-acetylaspartic acid (NAA), lactic acid, etc., the precession frequency of hydrogen protons changes due to the different distribution of electron clouds around the hydrogen atoms. For water and fat, the chemical bond of hydrogen protons in water molecules is 0-H bond, and the chemical bond of hydrogen protons in fat molecules is C-H bond. The precession frequency of hydrogen protons in water molecules is higher than that of hydrogen protons in fat molecules The frequency is slightly faster, and the difference is 3.5ppm (ppm is a few parts ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01R33/485G01R33/48
Inventor 蒋先旺
Owner SHANGHAI UNITED IMAGING HEALTHCARE
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