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Method for correcting echo wave plane imaging sequence

An imaging sequence and echo plane technology, which is applied in the direction of using nuclear magnetic resonance imaging system for measurement, magnetic variable measurement, scientific instruments, etc., can solve the problems of wasting scanning time, longer echo interval time, and unable to correct image deformation, etc. , to increase accuracy and save scanning time

Active Publication Date: 2008-01-23
SIEMENS HEALTHINEERS LTD
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Problems solved by technology

[0007] The unilateral readout gradient method only collects data at one polarity readout gradient. This method can completely avoid the N / 2 artifact problem, but it cannot correct the image deformation and waste scanning time
Moreover, due to the longer echo interval time, the displacement of the image in the phase encoding direction, and the image deformation caused by the uneven magnetic field is more serious

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  • Method for correcting echo wave plane imaging sequence

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Embodiment Construction

[0015] The method of the invention adopts a new phase correction method, and uses the image itself to obtain a phase map reflecting the inhomogeneity of the magnetic field to correct the deformation of the image.

[0016] As shown in Figure 2, the readout gradient of the pulse sequence adopted by the present invention adopts the bipolar readout mode as shown in label 8, that is, the double-echo EPI sequence, which has collected two images of the same level, and the collected images are not Simply add, but use the phase difference information to correct the distortion of the image. The readout gradient used for phase correction is shown in label 7. A total of 4 echo signals without phase encoding are collected, and the echo signals for phase correction collected with the same gradient polarity are used to correct odd-numbered and even-numbered echoes respectively. Wave image data.

[0017] The echo signal model for phase correction assuming homopolar readout gradient acquisiti...

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Abstract

The invention provides a way for correcting the imaging sequence of an echo plane. A plurality of echo signals are collected, the phase difference of the echo signals is calculated to correct the image data. Wherein, the phase difference goes through multi-order fitting, a fitting coefficient reflecting the cross-infection volume and frequency drift is worked out to carry out phase correction for the image data. The invention collects the EPI signals of two echoes to form two images, the info on time difference for collecting the two images is used to calculate the phase diagram reflecting the unevenness in the magnetic field, and the phase diagram is used to carry out deformation correction for the image. The invention takes full consideration of the influence from the uneven field during the calculation, basically corrects the displacement of the image, improves the accuracy for deformation correction in subsequent images without using additional sequence to get phase diagram, and saves scanning time.

Description

technical field [0001] The invention relates to a magnetic resonance imaging sequence, in particular to a correction method for an echo planar imaging (Echo Planar Imaging, EPI) sequence. Background technique [0002] The EPI sequence is a fast MRI sequence that requires only a single excitation pulse to obtain a complete image. The magnetic field gradient is periodically shifted, producing a series of gradient echoes; images of the excited plane are obtained by Fourier transforming the resulting echo series. [0003] In traditional EPI imaging, the phase encoding gradient and frequency encoding gradient of the sequence are shown as 3 and 5 in Figure 1, respectively. Due to the imperfection of the hardware system, such as eddy current, data acquisition delay, magnetic field drift, etc., in the The data read out under positive and negative frequency encoding gradients are not completely consistent, such as inconsistent echo centers, and the intervals between each line in k-s...

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01R33/56G01R33/20
Inventor 翁得河
Owner SIEMENS HEALTHINEERS LTD
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