JPH024334A - Magnetic resonance imaging method - Google Patents

Abstract

PURPOSE:To obtain a picture for diagnosis in a diseased part to depend on a brain surface by arranging a surface coil for the excitement and detection of proton with being closed to the head part of a patient and executing pulse sequence with a field echo method, for which an echo time is set to be longer. CONSTITUTION:A head part PH of a checked person P is set in the magnetic field center of a magnet assembly MA and a surface coil 13 is arranged in the side part of the head part PH. This surface coil 13 is driven by a transmitter 5 or a receiver 6 samely as an embedded probe 3 for whole body and transmission and reception can be executed. A 90 deg. pulse is transmitted by the embedded probe 3 for whole body and an inclining magnetic field Gs for slice is added from an inclining magnetic field generation coil 2. After that, an inverted inclining magnetic field Gr for read and an inclining magnetic field Ge for phase encode, whose intensity is variable, are added and an echo signal is collected from a slice part S by the surface coil 13 at an echo time TE. Since the above mentioned operation is repeated by a prescribed number, a data group is given to a computer system 11 and the picture is generated by this data group and displayed on a display device 12.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is directed to magnetic resonance (MR)
In particular, it relates to a magnetic resonance imaging method that utilizes the resonance phenomenon to obtain morphological information such as slice images of a subject (living body) and functional information such as spectroscopy.
For example, the present invention relates to a magnetic resonance imaging method suitable for imaging layer surface structures.

(Prior art) Magnetic resonance is a phenomenon in which an atomic nucleus with non-zero spin and magnetic moment placed in a static magnetic field resonantly absorbs and emits only electromagnetic waves of a specific frequency. The angular frequency ω0 (ωo−2πshi0.shi0
; Larmor frequency).

ω0−γHO Here, γ is the gyromagnetic ratio specific to the type of atomic nucleus,
Further, Ho is the static magnetic field strength.

An apparatus that performs biological diagnosis using the above-mentioned principle processes the electromagnetic waves of the same frequency as the above induced after the above-mentioned resonance absorption, and calculates the nuclear density, longitudinal relaxation time TI, transverse relaxation time T2. Diagnostic information that reflects information such as flow and chemical shift, such as slice images of a subject, can be obtained non-invasively.

Collecting diagnostic information by magnetic resonance can excite all parts of a subject placed in a static magnetic field and collect signals, but there are limitations in the equipment configuration and clinical requirements for imaging images. Therefore, in an actual device, a specific part is excited and its signal is collected.

In this case, the specific region to be imaged is generally a sliced region with a certain thickness;
Magnetic resonance signals (MR multiplied signals) of echo signals and FID signals from this slice site are collected by performing a data encoding process many times, and these data groups are subjected to image reconstruction processing using, for example, a two-dimensional Fourier transform method. By doing so, an image of the specific slice region is generated.

On the other hand, we will discuss clinical applications realized by using magnetic resonance imaging equipment. In other words, when performing surgical treatment for intracranial diseases, images depicting brain surface structures, including sensation, are an important guide for determining the location of localized lesions in the cortex and subcortex, and are important for determining the location of localized lesions in the cortex and subcortex. Accurate positioning is desired, and several attempts have been made to accomplish this using magnetic resonance imaging. An example will be explained below.

One method is to perform normal proton imaging using a head coil. In this method, the head coil is shaped like a cage so that it wraps around the head, so it collects signals from the entire head, so the image contains information from deep beneath the brain. As a result, the above-mentioned request for diagnosis cannot be fully met.

There is also a method of performing normal proton imaging using a surface coil. In this method, due to the sensitivity characteristics of the surface coil, that is, the areas close to the coil are highly sensitive, only signals from the surface layer, such as subcutaneous fat, are collected, and as a result, the above-mentioned diagnostic requirements are not met. It's not something that can be done.

In other words, neither of the above two methods can present an image that accurately represents the brain surface structure.

Furthermore, there is a method that attempts to express the brain surface structure using thin slice images, but this method does not allow you to see the front and rear parts of the head, the parietal area, and the base of the brain. It is not possible to diagnose the location of existing lesions.

(Problem to be solved by the invention) In this way, in the conventional technology, signals from cerebral effusion and fat are collected in the same way without distinction, so it is difficult to diagnose the location of a localized lesion in the cortex or subcortex. There was a problem in that it was not possible to obtain an image of the layer surface structure for the purpose of analysis.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic resonance imaging method capable of obtaining an image depicting the brain surface structure for diagnosing a lesion existing on the brain surface of the head.

[Structure of the Invention] (Means for Solving the Problems) The present invention has the following structure in order to solve the above problems and achieve the objects. That is, the present invention provides a magnetic resonance imaging method that detects magnetic resonance signals induced from a subject placed in a static magnetic field and generates morphological information or functional information of the induced region. A surface coil that performs at least one of proton excitation and detection is placed in the vicinity of the proton, and the echo time is set longer, or the chemical shift of water and fat is used to differentiate the respective magnetizations of water and fat. It is characterized by executing a pulse sequence using the field echo method,
As a means for achieving the same purpose, a special feature ( Effect) According to the above, the magnetic resonance signal from the water in the area with a certain thickness close to the surface coil is emphasized and the magnetic resonance signal from the fat is suppressed and detected, so that the magnetic resonance signal of the head is detected. It is possible to visualize the sensual image due to the water in the sensual area, and because it suppresses the magnetic resonance signals from the fat, the image created by the fat does not overlap with the sensual image due to the water, and it is possible to visualize the lesion on the brain surface. It is capable of presenting images suitable for diagnosis.

(Example) An example of the magnetic resonance imaging method according to 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 to which the magnetic resonance imaging method of the present invention is applied.

As shown in FIG. 1, the magnet assembly MA capable of accommodating the subject P therein may have a configuration using a static magnetic field coil (permanent magnet) using a normal conduction or superconductivity method. ) 1, and X for generating a gradient magnetic field for providing positional information of the magnetic resonance signal induction site.

Y- and Z-axis gradient magnetic field generating coils 2, and a transmitting and receiving system for transmitting a rotating high-frequency magnetic field and detecting an induced magnetic resonance signal (MR multiplied signal echo signal or FID signal), such as a transmitting coil and a receiving coil. It has an implantable whole body probe 3 consisting of.

If it is a superconducting system, it includes a refrigerant supply control system and mainly controls the energization of the static magnetic field power source, the transmitter 5, which controls the transmission of RF pulses, and the induced MR multiplied signal reception control. a receiver 6 that performs excitation control for each of the gradient magnetic field generating coils 2 on the
Y-axis and Z-axis gradient magnetic field power supplies 7, 8, and 9, a sequencer 10 capable of implementing a pulse sequence for data collection, a computer system 11 that controls these and performs signal processing of detection signals and display thereof, and a display. Device 1
2.

Furthermore, in this embodiment, the head PH of the subject P is placed at the center of the magnetic field of the magnet assembly MA, and the surface coil 13 is placed on the side of the head PH, as shown in FIG.

This surface coil 13 is driven by a transmitter 5 or a receiver 6 to be capable of transmitting and receiving, similarly to the implantable whole body probe 3.

Here, the pulse sequence for data collection is as follows:
The transmitter 5 is driven to apply an RF pulse of a rotating magnetic field from the transmitting coil of the implantable whole-body probe 3, and the gradient magnetic field power supplies 7, 8.9 are driven to generate a gradient magnetic field GX from the gradient magnetic field generating coil 2.

Gy and Gz are added for 1-phase encoding for slicing and for reading, and the surface coil 13 collects signals from a specific region. 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 FIG. Figure 3 shows
Magnetic resonance signals (spin echo signals) are collected using a 180° pulse of the spin echo method, which is a sequence of 90°-180° pulses, that is, a field echo method in which a gradient magnetic field is reversed instead of the magnetic field for converging magnetization. It is something. The slice thickness is relatively thick, for example, about 8 cm, and the echo time TE is longer than usual, for example, 22 m5ec (usually 14 rxsec).
It is as follows. ), and the pulse repetition interval TR is 100
m5ec (usually 501!1 seconds or less).

RF is an excitation pulse, Gs is a slicing gradient magnetic field in the Z-axis direction, G is a read gradient magnetic field in the X-axis direction, and Ge is an encoding gradient magnetic field. In this case, MR is a gradient magnetic field in the X-axis direction, and MR is an induced magnetic resonance signal, which in this case is an echo signal.

Under these condition settings, a 90° pulse was transmitted by the implantable whole body probe 3 and a slicing gradient magnetic field Gs was applied from the gradient magnetic field generating coil 2, and then the inverted read gradient magnetic field Gr and the intensity variable gradient magnetic field Gs were applied. A gradient magnetic field Ge for phase encoding is applied, and echo signals are collected from the slice site S by the surface coil 13 at an echo time TE.

By repeating this a predetermined number of times, a data group is provided to the computer system 11, an image is generated from this data group, and a display as shown in FIG. 4, for example, appears on the display device 12.

According to the magnetic resonance imaging method of this embodiment using the above-described image sequence, for a slice site S having a relatively thick slice thickness of about 8 CIIl, the echo signal obtained from this site is generated at a pulse repetition interval set to 100IIl sec. Due to the TR, the water recovers considerably between the TRs, so the resulting signal strength is large. Further, by setting the echo time TE to be longer than usual, for example, 22 n+sec, signals from fat are suppressed.

According to the above, signals can be obtained from the sensational water, but by using a surface coil with high sensitivity directly below the coil installation, signals from deep parts such as the ventricles and basal ganglia can be suppressed.
In addition, by setting the echo time TE longer than usual, signals mainly from fat components from the surface layer structure that are largely attenuated by the transverse relaxation time T2 are suppressed. Therefore, as shown in FIG. 3, sensational images are displayed on the display device 12 without overlap with other images, the positional relationship between the brain surface and the lesion is clear, and clinically extremely useful diagnostic information can be presented. can.

In this case, since a field echo method is used in which the pulse repetition interval TR 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. here,
Using chemical shift between water and fat, the magnetization of each is oriented 90 degrees (the magnetization of water and the magnetization of fat are perpendicular to each other).

) or 180° (the magnetization of water and the magnetization of fat are directed in opposite directions) using a field echo method in which differentiation is performed. As a result, signals from fat are suppressed, and the same effect as described above can be obtained.

Here, a specific example will be explained. For example, if the static magnetic field H, is 0.
At 5 Tesla, the resonant frequency of protons is 21.3MHz
At that time, the chemical shift between water and fat is 3.
It is 5ppn. Here, the echo time TE is 16.8i
sec, the magnetization of water and the magnetization of fat are oriented at 90°, and when the echo time TE is 20.1 115 ec, the magnetization of water and the magnetization of fat are oriented 180°.

Next, still another embodiment of the present invention will be described.

Here, first RF pulse: α (α 90°) second RF pulse
Pulse: 180'' - third RF pulse = 180° sequence, which uses a pulse sequence of the spin echo method to collect the second echo signal.

That is, as shown in Fig. 5, unlike the normal spin echo method, the first RF pulse is set at an angle smaller than 90°, and the echo signal is collected after the third RF pulse, so that the longitudinal magnetization is large and the longitudinal relaxation time is The influence of Tl is reduced, and signals from fat are suppressed as in each of the above-mentioned embodiments. In this case, since no time is required for the magnetization to return to the thermally parallel state, the pulse repetition interval TR may be 500 to 600 m5ec.

The present applicant has previously filed a patent application similar to this embodiment. In the invention described in the specification and drawings of the earlier application (Japanese Patent Application No. 1982-232949 filed on September 17, 1988, title of the invention is "Magnetic Resonance Imaging Method"), one surface coil is used. A similar effect is obtained with a spin echo sequence in which the echo time is set longer than usual (250 msec) and the pulse repetition interval TR is set longer than usual (200 On+5 ec).

The above embodiment has the following advantages compared to the invention of the earlier application. That is, in the invention according to the earlier application, for example, if the pulse repetition interval TR is 2 seconds and encoding is performed 256 times, the data collection time is 2X.
It takes 256-512 seconds, but in this example, the pulse repetition interval TR may be 500-600 m5ec.
．． It takes 5 (0,6) x 256-128 (153,6) seconds, and data collection can be completed in a few minutes.
It's advantageous.

The invention can be modified in various ways without departing from the gist of the invention.

[Effects of the Invention] As described above, in the present invention, a surface coil that performs only one of proton excitation and proton detection is placed close to the subject's head, the echo time is set to be long, and the water It is characterized by executing a pulse sequence using a field echo method that differentiates the respective magnetization of water and fat by utilizing the chemical shift of fat and water. -180”180
It is characterized by executing a pulse sequence for collecting a second echo signal.

According to the above, since the magnetic resonance signal from water in a region with a certain thickness close to the surface coil is detected while being emphasized and the magnetic resonance signal from fat is suppressed, It is possible to visualize a sensational image due to water, and furthermore, it suppresses magnetic resonance signals from fat, so that the image expressed by fat does not overlap with the sensational image caused by water, and it is possible to diagnose a lesion located on the brain surface. It is possible to present an image suitable for this purpose.

Therefore, according to the present invention, it is possible to provide a magnetic resonance imaging method that can obtain an image depicting the brain surface structure for diagnosing a lesion existing on the brain surface of the head.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a magnetic resonance imaging apparatus to which an embodiment of the magnetic resonance imaging method according to the present invention is applied, FIG. 2 is a diagram showing the arrangement of surface coils in the same embodiment, and FIG. FIG. 4 is a diagram showing an example of a generated image, and FIG. 5 is a diagram showing an example of a pulse sequence according to another embodiment of the present invention. MA... Magnet assembly, 1... Static magnetic field coil, 2... Gradient magnetic field generation coil for x, y, and z axes, 3
... Implantable whole body probe, 4... Static magnetic field control system, 5... Transmitter, 6... Receiver, 7... X-axis gradient magnetic field power supply, 8... Y-axis gradient magnetic field Power supply, 9... Z-axis gradient magnetic field power supply, 10... Sequencer, 11... Computer system, 12... Display device, 13... Surface coil. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure Figure Figure

Claims (2)

[Claims] (1) In a magnetic resonance imaging method that detects magnetic resonance signals induced from a subject placed in a static magnetic field and generates morphological information or functional information of the induced region, Place a surface coil that performs at least one of proton excitation and detection, and set a longer echo time, or use chemical shift of water and fat to differentiate the respective magnetizations of water and fat. A magnetic resonance imaging method characterized by executing a pulse sequence using a field echo method. (2) In a magnetic resonance imaging method that detects magnetic resonance signals induced from a subject placed in a static magnetic field and generates morphological information or functional information of the induced region, A surface coil that performs at least one of excitation and detection of protons is arranged, and α (α<90°
)-180°-180° series of pulse sequences for collecting second echo signals.