JPS6266846A - Nmr examination apparatus using chemical shift value - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an NM imaging apparatus 11, and more particularly to an NMR examination apparatus that can reflect diagnostic information on a tomographic image of a subject using a chemical shift difference. .

[Background of the invention]

Conventional NMRM imaging equipment uses 1H nuclei.

It images the density or relaxation time. Recently, an attempt to image the It (nucleus density) of water and fat separately was announced at the NMR Medical Society and has attracted attention.This method involves taking tomographic images using the same method as before.Next Taking advantage of the difference in resonance frequency caused by the chemical shift of water and fat, the signal acquisition sequence (called a pulse sequence) is completely changed so that the water and fat signals have a phase difference of 180°, and a tomographic image is taken. A water distribution map or a fat distribution map is obtained from these two images by inter-image calculations.With this method, imaging must be performed twice, which increases the examination time required for imaging.

Furthermore, there are drawbacks such as a lack of accuracy due to errors caused by the two images not matching each other due to movement of the subject during the two images.

[Purpose of the invention]

Kikomei's objective is to provide an NMR inspection device using chemical shift values that can accurately capture water and fat distribution images in a short time using chemical shift differences.

[Summary of the invention]

In the present invention, a subject is placed in a magnetic field obtained by combining a magnetic field device that generates a static magnetic field and a gradient magnetic field device that generates gradients in magnetic fields in three mutually orthogonal directions, and the NMR signal of the subject is excited and detected. and a computer for processing the NMR signal and a display device for displaying the processed NMR signal, in which the NMR signal of the subject is 90
A combination of ° pulses and 180 ° pulses, and at least one
The 90° pulse and the 180° pulse are separated by at least 2
It is characterized by being able to take two values alternately.

[Embodiments of the invention]

Examples of the present invention will be described below.

FIG. 1 shows a block diagram of an NMR testing device according to the invention. A subject (not shown) is placed on a patient table 1 and introduced into a magnetic field 2 . A coil for applying a gradient magnetic field having a gradient in three directions of FiX-Y-Z and a high-frequency coil for exciting and observing the NMRM phenomenon (both not visible in the figure) are inserted inside the magnet. Gradient magnetic field 1 for the gradient magnetic field coil! Source 3 is connected and computer 4
It is driven by the control signal of NMIL signal
The signal is detected by a high-frequency coil, amplified to an appropriate level by a high-frequency circuit 5, and input to the meter a. In total, N M
The R signal is processed and displayed on the display monitor 6.

The pulse sequences used in the NM box inspection apparatus shown in FIGS. 1 & C are shown in FIGS. 2 and 3.

Pulse sequence shown in Figure 2 In humans, if a linear gradient magnetic field Gz is applied and a selected high-frequency magnetic field is applied to the subject, nuclear spins Q90 in the slice plane can be selectively reduced.
It is possible to tilt 0 (this is said to be
74). After the slice plane is determined, a gradient magnetic field Gy is applied in the Y direction to give in-plane position information to the nuclear spins. Resonance frequency of nuclear spin FiG
The height increases in proportion to the thicker the awn of y. Since this is observed as a phase difference, it is usually called the Y direction IJ phase encoding direction. After phase encoding in the Y direction,
A gradient magnetic field Qx is applied in the direction and the signal is 25656
Point sampling. By repeating signal sampling while changing the magnitude of Gy in 256 steps, data is obtained in a 256×256 matrix. 7 By subjecting these data to two-dimensional Fourier exchange, an NMR tomogram can be obtained. For the 90°-r-180' pulse sequence, the NMR signal is obtained as an echo signal after one hour.

When applying Qx, adjustment is made so that the area of the hatched area A and the area of the hatched area in FIG. 2 are equal.

That is, there is no phase rotation due to the gradient magnetic field Qx between the 90° and 180° pulses and between the 180° and echo signals. Sampling of the echo signal.

Effectively, this is carried out in proportion to the applied amount of Gx from when Gx is 0, so phase information in the X direction can be captured accurately.

Pulse sequence B in FIG. 3 is constructed so that the interval between 180°-echo signals is extended by τ.

With this configuration, when two or more components are present in the subject, a 72-hour phase difference appears in the echo signal. This is the phase matching Hr due to 1800 pulses.
, and from this point on, each component exhibits a precession motion at its own unique resonant frequency. This resonance frequency difference is called a chemical shift.

This pulse sequence Bk will be described when applied to water and fat. The chemical shift difference between water and fat is about 3.5 ppm. A magnetic field of 0.15 Tesla results in a frequency difference of 20 hertz. Therefore, if τ2 is set to 25m5eC, the phase difference between the water and fat signals becomes 180°. Figure 4 shows the water and fat signals and reconstructed images obtained by pulse sequence A and pulse sequence B. vinegar. If the signal obtained from a pulse sequence human is reconstructed, an image containing both water and fat can be obtained.

By adding the signals obtained from the pulse sequence human and the signals obtained from the pulse sequence B and reconstructing the image, an image of only fat can be obtained. Conversely, if the image is reconstructed after subtraction, an image of only water will be obtained.

FIG. 5 shows a combination of pulse sequence A and pulse sequence B. Here, Yo, Yr, Yz...Yz,
6 indicates the magnitude of the phase encode gradient magnetic field GY. The pulse train No. 1 is one that has been conventionally employed. The reason why the value of Gy is repeated twice is because the signal is averaged to improve the S/N ratio of the image. This pulse train is according to the invention. According to the example, images of water and fat,
water image.

Images of fat can be obtained at the same time. Furthermore, by adding these three types of images on the image, an image with an S/N equivalent to one pulse sequence can be obtained.

The above explanation assumes that the magnetic field generated by the magnet is uniform, but if the uniformity of the magnetic field is not negligible compared to the chemical shift value, it is possible to distinguish between phase rotation due to non-uniformity of the magnetic field and phase rotation due to chemical shift values. Can not. To counter this, it is possible to use a phantom filled with a homogeneous material to determine in advance the phase recursion caused by the inhomogeneity of the magnetic field, and then correct the obtained image.

〔Effect of the invention〕

According to the present invention, an NMR image of each component of a specimen having components with different chemical shifts and an independent NMR image in which each component is separated can be obtained within the same imaging time. This has the effect of increasing the possibility of diagnosis and expanding the scope of diagnosis.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the NM box inspection device according to the present invention, Fig. 2 is a time chart showing the pulse sequence of the conventional method, Fig. 3 is a time chart showing the pulse sequence according to the present invention, and Fig. 4 is the signal processing The explanatory diagram, FIG. 5, is a time chart showing a series of pulse sequences.

Claims (1)

[Claims] 1. A subject is placed in a magnetic field obtained by combining a magnetic field device that generates a static magnetic field and a gradient magnetic field device that creates gradients in the magnetic fields in three mutually orthogonal directions, and the NMR signal of the subject is The NMR signal of the subject is a combination of a 90° pulse and a 180° pulse. , and is configured to be detected as an echo signal due to at least one gradient magnetic field, and the interval between the 90° and 180° pulses is at least 2
An NMR inspection device using chemical shift values, characterized in that two values can be taken alternately. 2. In the invention described in claim 1, the above-mentioned 9
An NMR inspection device using a chemical shift value, characterized in that the interval between the 0° and 180° pulses is constant, and the time between the 180° pulse and the echo signal is set so that at least two values can be taken alternately.