NMR imaging method

Details NMR imaging method NMR imaging method

1988-09-15

1993-09-14

Tokar, Michael J.

Electricity: measuring and testing

Particle precession resonance

Using a nuclear resonance spectrometer system

G01R 3320

Patent

active

052452816

DESCRIPTION:

BRIEF SUMMARY
FIELD OF INVENTION

This invention generally relates to an improved NMR imaging method used to develop a sectional image of a subject using scan data collected from the subject based on a nuclear magnetic resonance phenomenon. More specifically, this NMR imaging method enables imaging by using a non-square scan matrix with different vertical and horizontal dimensions, while maintaining isotropic pixel resolution.


BACKGROUND OF INVENTION

An NMR imaging device consists of a magnet section that includes a static magnetic field coil that provides a homogeneous static magnetic field, and a gradient magnetic field coil that provides a magnetic field having a linear gradient in each direction (x, y, and z) in a magnetic field with the same direction as the static magnetic field. Also included are transmission and reception sections that apply a high-frequency pulse (high frequency electromagnetic wave) to a subject placed in a magnetic field formed by the magnet section to detect NMR signals from the subject, and control and image processing sections that control the operation of the transmission, reception, and the above magnet sections to process the detected data and display images.
An NMR imaging device with the above mentioned configuration is driven in the pulse sequence of a two-dimensional Fourier method as shown in FIG. 4. This device collects data from the desired section of a subject. In other words, the imaging device applies slice gradient magnetic field G.sub.z and a 90.degree. pulse (excitation RF signal) simultaneously to selectively excite the nuclear spin within a specific slice area of the subject. Then the device applies rephase gradient magnetic field G.sub.z to recover the spin phase deviation generated during slicing, while simultaneously applying dephase gradient magnetic field G.sub.z to provide spin with a phase difference to generate a spin echo signal. The device then applies warp gradient G.sub.y. Then, all gradients are nullified and a 180.degree. pulse is applied to invert the spin phase. Then, if read gradient G.sub.x is applied, a spin whose phase was dispersed due to the dephase gradient magnetic field has the phase matched again to enable an NMR signal to be observed as a so-called "spin echo signal." This NMR signal is equivalent to one line (one view) of the spin distribution of a subject after two-dimensional Fourier transformation.
Because line selection is determined by the product of the size of warp gradient magnetic field G.sub.y and the application time, the data required for image configuration can be collected by repeating the sequence shown in FIG. 4, while varying the size of the gradient magnetic field.
A scan matrix used for scanning a desired field of view (FOV) in a pulse sequence of the above mentioned two-dimensional Fourier method is generally a square matrix (matrix having four equal sides) of 64 Ch.times.64 views, 128 Ch.times.128 views, 256 Ch.times.256 views, or 512 Ch.times.512 views. Moreover, an image matrix used for reconfiguring images using such data is either a square matrix of 512.times.512, 256.times.256, etc., or their cutouts in a circular shape. For such a matrix, the vertical and horizontal resolution of an image becomes isotropic so that a natural image can be obtained. However, if the field of view is oval, the device may scan a wide area of air where no subject exists, and the data of sections not related to the image is collected, while taking a longer scan time than actually needed. Conversely, the scanning time in Fourier transformation is known to be roughly proportionate to the number of samples (number of views) in the warp direction. Therefore, it is understood that to reduce the scanning time, the number of samples in the warp direction should be reduced, that is, scanning should be done using a non-square matrix. Actually, certain data is collected according to the scanning method of 512.times.256 or 256.times.128 (sample number.times.view number) for example. In such cases, when the scan time is reduced, no isotropy can be obt

REFERENCES:
patent: 4593247 (1986-06-01), Glover
patent: 4748411 (1988-05-01), Holland

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