JPH0564056B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic resonance imaging apparatus capable of obtaining images depicting nerve roots.

(Conventional technology) Myelography and other diagnostic methods for radiculopathy
It is known that diagnostic imaging methods such as CT myelography are useful, but in recent years, attempts have been made to diagnose radiculopathy using MRI (magnetic resonance imaging) equipment, which has been attracting attention as an imaging diagnostic device. being done. This is done by thinly slicing the area where the nerve root exists to create a partial volume with the surrounding tissue (mainly fat).
This is to visualize nerve roots while reducing the influence of effects.

(Problems to be Solved by the Invention) The conventional method described above has the following problems. In other words, because the nerve root has a complicated path, one nerve root is depicted spread over multiple slice planes, and only a portion of the nerve root is depicted within one thin slice plane. ing. For this reason, there was a problem in that the running state of the nerve roots could not be well understood.

Furthermore, regarding the fat surrounding the nerve root and the nerve root, the fat usually appears as a higher signal, making it difficult to observe the nerve root.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic resonance imaging apparatus that makes it possible to easily distinguish between nerve roots and other tissues, and to obtain images that allow a good understanding of the running state of the nerve roots.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a structure in which the following measures are taken to solve the above problems and achieve the objects. That is, the magnetic resonance imaging apparatus according to the present invention includes a static magnetic field generating means for generating a static magnetic field, a gradient magnetic field generating means for generating a gradient magnetic field, and a high frequency pulse for generating a high frequency pulse for generating a magnetic resonance phenomenon related to protons. a pulse generating means; a receiving coil for detecting a magnetic resonance signal related to protons and disposed near a portion of the subject where a nerve root to be imaged is present; and a receiving coil disposed in the subject in the static magnetic field. The gradient magnetic field and the high frequency pulse are applied to the specimen under predetermined conditions, and the magnetic resonance signal associated with water protons is emphasized and the magnetic resonance signal associated with fat protons is suppressed. a control means for executing a pulse sequence for thickly exciting magnetic resonance in a region where a nerve root is present; A means for obtaining an image in which a nerve root is depicted at a location where the nerve root exists;

(Function) According to this configuration, by making the slice thick, the entire nerve root, which has a complicated course, can be visualized in one slice image, and a sequence that suppresses signals from fat can be visualized. By executing this, signals mainly from water will be collected, so the image of the fat surrounding the nerve root will be suppressed, making it easier to observe the nerve root.

(Example) An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the overall configuration of a magnetic resonance imaging apparatus according to the present invention.

As shown in Fig. 1, the magnet assembly MA, which is capable of housing the subject P, is equipped with a static magnetic field coil (configured using permanent magnets) based on normal conductivity or superconductivity. ) 1, and
Y- and Z-axis gradient magnetic field generating coils 2, and a transmitting/receiving system for transmitting a rotating high-frequency magnetic field and detecting the induced magnetic resonance signals (MR signals: echo signals and FID signals), such as transmitting coils and receiving coils. It has an implantable whole body probe 3A consisting of.

Then, the gradient magnetic field generating coil 2 for the X, Y, and Z axes
an X-axis, Y-axis, and Z-axis gradient magnetic field power supply 4 that performs excitation control of each of the above, a transmitter 5 that performs transmission control of RF pulses, a receiver 6 that performs reception control of induced MR signals,
It is comprised of a sequencer 7 that can execute a pulse sequence for data collection, a computer system 8 that controls these, processes detected signals, and displays them, and a display 9.

In addition, in this example, the magnetic assembly
The waist PW of the subject P is placed at the center of the magnetic field of MA, and the surface coil 3B is placed directly below the waist PW.
This surface coil 3B is driven by a transmitter 5 or a receiver 6 to be capable of transmitting and receiving, similarly to the implantable whole body probe 3A.

Here, in the pulse sequence for data collection, the transmitter 5 is driven, an RF pulse of a rotating magnetic field is applied from the transmitting coil of the implantable whole body probe 3A, and the gradient magnetic field power supply 4 is driven to generate a gradient magnetic field. Gradient magnetic fields Gx, Gy, and Gz are applied from the coil 2 for slicing, phase encoding, and reading, and signals from a specific region are collected by the surface coil 3B. This sequence is repeated a predetermined number of times to obtain a data group, and an image is generated from this data group.

Next, the pulse sequence for acquiring the above-mentioned image will be specifically explained with reference to FIGS. 2 and 3. In other words, as schematically shown in Figure 2, the sequence of this example is such that the echo time is adjusted so that the proton spins of water are 180 degrees to the proton spins of fat, that is, both spins are oriented in opposite directions.
T _E was set (for example, when the static magnetic field H ₀ = 0.5 T, the resonance frequency of protons is 21.3 MHz, and the echo time T _E is 20.1 msec, the magnetization of water and the oxidation of fat are 180° However, the echo time T _E
=20.1±1.0msec is the allowable range. ) sequence, as shown in Figure 3, 90°−
Magnetic resonance signals (spin echo signals) are collected using the 180° pulse of the spin echo method, which is a sequence of 180° pulses, that is, the field echo method in which the gradient magnetic field is reversed instead of the magnetic field used to converge magnetization. .

Then, the slice thickness is relatively thick, for example, about 15 to 40 mm, and the echo time T _E is set to, for example, 15 to 30 msec or 4 to 10 msec, according to the setting criteria mentioned above.
The pulse repetition interval T _R is 100 to 500 msec, which is the time for the proton spin of water to recover.
The flip angle α° of the oxidation vector is set to 10° to 40° in order to emphasize water protons, and a gradient magnetic field shown in the shaded area is added in order to eliminate the phase shift due to the flow.

Note that Gs is the gradient magnetic field for slicing, and in this case, Z
The axial gradient magnetic field, G _R is a read gradient magnetic field in the X-axis direction, and G _E is the encoding gradient magnetic field, in this case a Y-axis gradient magnetic field.

Under these condition settings, the implantable whole-body probe 3A transmits α° pulses, and the gradient magnetic field Gs for slicing is applied from the gradient magnetic field generating coil 2, and then the gradient magnetic field G for reversing _G and the intensity variable are applied. Add a gradient magnetic field _G for phase encoding of
Echo signals are collected from the slice site S by the surface coil 3B at the echo time _TE . By repeating this a predetermined number of times, the computer system 8
is given a data group, and an image is generated from this data group, so that an image as shown in FIG. 5, for example, appears on the display 9, that is, an image in which the running form of the nerve root is well depicted.

According to the method of this embodiment using the above image sequence, the slice thickness is 15 to 40 mm, which is relatively thick.
For a slice site S of about mm, the echo signal obtained from the site is determined by the pulse repetition interval _TR set to 100 to 500 msec, and the water recovers considerably during that _TR , so the signal intensity obtained is large. .
In addition, as mentioned above, water oxidation and fat oxidation are 180°
The echo time T _E set so that the signal from fat is suppressed. Furthermore, since the slice region S is placed at the center of the magnetic field and the surface coil 3B is placed directly below the region A, reception sensitivity is high.

According to the above, a signal is obtained from the water from the slice site S of the waist PW, but a signal from the fat is suppressed. Therefore, as shown in Fig. 5, the running form of the nerve root can be well depicted on one image.Also, in order to compensate for the shift in signal phase due to the flow, the shaded area shown in the figure is Since a gradient magnetic field is applied, artifacts due to the flow of cerebrospinal fluid (CSF) will not occur. Therefore, it becomes possible to clearly distinguish the nerve roots from other tissues and observe them.

In the above case, since the field echo method is used in which the repetition interval T _R can be made shorter than other pulse sequences, such as spin echo sequences, the time required for data collection is short.

Next, other embodiments of the present invention will be described. That is, since the sequences used in the present invention mainly suppress fat signals, in addition to the above-mentioned sequences, as shown in Fig. 4, STIR
In the (Short TI Inversion Recovery) sequence, a TI selected to reduce the signal from fat to zero can be applied. In addition, SE methods with extremely long echo times T _E , e.g. T _R = 1500 to 3000 m
sec, T _E = 150 to 400 msec can be applied. Of course, the arrangement of the slice parts, the arrangement of the transmitting and receiving coils, etc. can be selected as appropriate. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As described above, in the present invention, a slice is thickly excited with respect to protons at a site where a nerve root of a subject is visualized, and signals are collected and imaged using a sequence that suppresses signals from fat. As a result, by making the slices thicker, the entire complex nerve root can be visualized in a single slice image.Also, by executing a sequence that suppresses signals from fat, mainly Since signals from water are collected, images of the fat surrounding the nerve root are suppressed, making it easier to observe the nerve root.

Therefore, according to the present invention, it is possible to provide a magnetic resonance imaging apparatus that makes it possible to easily distinguish between nerve roots and other tissues and to obtain images that allow a good understanding of the running state of the nerve roots.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a magnetic resonance imaging apparatus according to the present invention, FIGS. 2 and 3 are diagrams showing an example of a pulse sequence in the same embodiment, and FIG. 4 is a diagram showing another embodiment of the present invention. FIG. 5 is a diagram showing an example of a generated image. MA... Magnet assembly, 1... Static magnetic field coil, 2... Gradient magnetic field generation coil for X, Y, and Z axes, 3A... Implantable whole body probe, 3B...
... surface coil, 4 ... gradient magnetic field power supply, 5 ... transmitter, 6 ... receiver, 7 ... sequencer, 8 ... computer system, 9 ... display.

Claims (1)

[Scope of Claims] 1. Static magnetic field generating means for generating a static magnetic field; Gradient magnetic field generating means for generating a gradient magnetic field; High-frequency pulse generating means for generating a high-frequency pulse for generating a magnetic resonance phenomenon related to protons. , a receiving coil for detecting a magnetic resonance signal related to protons, which is placed near a portion of the subject where a nerve root to be imaged exists; The method is for applying a gradient magnetic field and a high-frequency pulse under predetermined conditions, and the nerve root is present under conditions that emphasize magnetic resonance signals related to water protons and suppress magnetic resonance signals related to fat protons. a control means for executing a pulse sequence to thickly excite the nerve root in the region where the nerve root is present; A magnetic resonance imaging apparatus comprising: means for obtaining an image in which nerve roots are depicted;