JPH0564057B2 - - Google Patents

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention is directed to magnetic resonance (MR).
The present invention relates to a magnetic resonance imaging device capable of imaging the morphological brain surface structure of a subject (living body) using the phenomenon of magnetic resonance.

(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. It resonates at the angular frequency ω ₀ (ω ₀ =2πν ₀ , ν ₀ ; Larmor frequency) shown in FIG.

ω ₀ =γH ₀ where γ is the gyromagnetic ratio specific to the type of atomic nucleus, and H ₀ is the static magnetic field strength.

The device that performs biological diagnosis using the above principles is
The electromagnetic waves of the same frequency as above that are induced after the above-mentioned resonance absorption are processed to generate diagnostic information that reflects information such as nuclear density, longitudinal relaxation time T1, transverse relaxation time T2, flow, chemical shift, etc. The aim is to obtain slice images, etc., 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. from,
The actual device excites a specific region and collects its signals.

In this case, the specific region to be imaged is generally a slice region with a certain thickness, and magnetic resonance signals (MR signals) such as echo signals and FID signals from this slice region are collected many times. The data is collected by performing a data encoding process, and an image of the specific slice region is generated by subjecting these data groups to image reconstruction processing using, for example, a two-dimensional Fourier transform method.

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 such as cerebral sulci are an important guide to knowing the location of lesions localized in the cortex and subcortex. Accurate positioning is often 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 images contain more information deep beneath the surface of the brain. As a result, it is not possible to meet the above-mentioned diagnostic requirements.

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

(Problem to be solved by the invention) In this way, in the conventional technology, signals from sulcal water and fat are collected in the same way without distinction, making it difficult to determine the location of lesions localized in the cortex or subcortex. There was a problem in that it was not possible to obtain brain surface structure images for diagnosis.

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

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems and achieve the objects, the present invention has the following structure. That is, the present invention according to claim 1 comprises: a static magnetic field generating means for generating a static magnetic field; a gradient magnetic field generating means for generating a gradient magnetic field; a pulse generating means; a receiving coil that detects a magnetic resonance signal related to protons and is disposed close to the head of the subject; and a receiving coil that detects a magnetic resonance signal related to protons; A magnetic field and a high-frequency pulse are applied under predetermined conditions to obtain a plurality of slice images of the head in which magnetic resonance signals related to water protons are emphasized and magnetic resonance signals related to fat protons are suppressed. a control means for executing a pulse sequence for depicting the brain surface structure using the multi-slice method; and a control means for executing the pulse sequence for depicting the brain surface structure using the multi-slice method obtained from the receiving coil by driving the control means. reconstructing means for reconstructing magnetic resonance signals related to execution of a pulse sequence to obtain a plurality of slice images of the head; and obtaining an image depicting a brain surface structure of the head based on the plurality of slice images. A magnetic resonance imaging apparatus comprising: means; and display means for displaying an image depicting a brain surface structure in the head obtained by the means.

The invention according to claim 2 provides: 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 generating means for generating a high frequency pulse for generating a magnetic resonance phenomenon related to protons. a receiving coil that detects a magnetic resonance signal related to protons and is placed close to the head of a subject; A multi-slice method is used to apply pulses under predetermined conditions, and to obtain a plurality of slice images of the head that emphasizes magnetic resonance signals related to water protons and suppresses magnetic resonance signals related to fat protons. a control means for executing a pulse sequence for depicting brain surface structure using the multi-slice method; and a control means for executing the pulse sequence for depicting brain surface structure using the multi-slice method obtained from the receiving coil by driving the control means. reconstructing means for reconstructing magnetic resonance signals related to execution to obtain a plurality of slice images of the head; assigning a predetermined weight to each of the plurality of slice images, and generating the weighted plurality of slice images; an addition means for adding up to obtain an image in which the brain surface structure in the head is depicted; and a display means for displaying an image in which the brain surface structure in the head obtained by the addition means is depicted. This is a magnetic resonance imaging apparatus characterized by:

The invention according to claim 3 provides the following: static magnetic field generating means for generating a static magnetic field; gradient magnetic field generating means for generating a gradient magnetic field; and high-frequency pulse generating means for generating a high-frequency pulse for generating a magnetic resonance phenomenon related to protons. a receiving coil that detects a magnetic resonance signal related to protons and is placed close to the head of a subject; A multi-slice method is used to apply pulses under predetermined conditions, and to obtain a plurality of slice images of the head that emphasizes magnetic resonance signals related to water protons and suppresses magnetic resonance signals related to fat protons. a control means for executing a pulse sequence for depicting brain surface structure using the multi-slice method; and a control means for executing the pulse sequence for depicting brain surface structure using the multi-slice method obtained from the receiving coil by driving the control means. reconstructing means for reconstructing the magnetic resonance signals involved in the execution to obtain a plurality of slice images of the head; and assigning a predetermined weight to each matrix component of each of the plurality of slice images, and adding a predetermined weight to each matrix component of the plurality of slice images. an adding means for obtaining an image in which a brain surface structure in the head is depicted by adding the plurality of slice images having the same shape, and displaying an image in which the brain surface structure in the head obtained by the addition means is depicted. A magnetic resonance imaging apparatus comprising: a display means for displaying a magnetic resonance image;

The invention according to claim 4 is characterized in that the adding means in the invention according to claim 2 or 3 is configured to add the plurality of slice images while shifting the position of each slice image.

The invention according to claim 5 is characterized in that the receiving coil according to any one of claims 1 to 3 has a cylindrical shape that can wrap around the head.

(Operation) According to the invention according to claim 1, by executing the pulse sequence for depicting the brain surface structure using the multi-slice method, water in each slice region close to the receiving coil is reduced. Since the magnetic resonance signals from the fat are enhanced and the magnetic resonance signals from the fat are suppressed, it is possible to visualize the cerebral sulcus image of the water in the cerebral sulci of the head, while suppressing the magnetic resonance signals from the fat. Therefore, the image depicted by fat is not superimposed on the image depicted by the water in the cerebral sulcus,
Brain surface structure images corresponding to each slice site suitable for diagnosing a lesion existing on the brain surface can be presented. Further, by referring to each slice image, the positional relationship in the depth direction can be easily known. In this case, the brain surface structure image and the normal slice image can be obtained in one imaging procedure, so the brain surface structure image and the normal slice image can be observed simultaneously, improving diagnostic efficiency. .

According to the invention according to claim 2 or 3, claim 1
In addition to being able to obtain the same effect as the invention related to,
Since the brain surface structure image is obtained by assigning a predetermined weight to each of a plurality of slice images and adding the weighted plurality of slice images, phase disturbance is suppressed as much as possible.

According to the invention according to claim 4, two images with different viewing directions can be obtained, and stereo viewing can be performed using these two images.

According to the invention according to claim 5, since the cylindrical receiving coil that can wrap around the head is used, the head to be photographed and the receiving coil can be easily set in any positional relationship, so that the receiving coil can be set easily and in any desired position. It is possible to obtain an image of the brain surface structure viewed from the direction.

(Example) An example of a magnetic resonance imaging apparatus 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 method of the present invention is applied.

As shown in Fig. 1, a magnet assembly MA capable of accommodating a subject P therein is equipped with a static magnetic field coil using a normal conducting or superconducting method (even if it is configured using a permanent magnet). ) 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 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 3 consisting of.

If it is a superconducting method, it includes a refrigerant supply control system and mainly controls the energization of the static magnetic field power supply, a static magnetic field control system 4, a transmitter 5 that controls the transmission of RF pulses, and controls the induced MR signal. Receiver 6, X-axis, Y-axis, and Z-axis gradient magnetic field power supplies 7, 8, and 9 that control the excitation of the X-, Y-, and Z-axis gradient magnetic field generating coils 2, and implement a pulse sequence for data collection. A sequencer 10 capable of
It is comprised of a computer system 11 and a display device 12 that control these and perform signal processing and display of detection signals.

In addition, in this example, the magnetic assembly
The head PH of the subject P is placed at the center of the magnetic field of the MA, and the head coil 13 is arranged as a cylindrical coil so as to surround the head PH, as shown in FIG.
This head coil 13 is driven by a transmitter 5 or a receiver 6 to enable transmission and reception, similarly to the implantable whole body probe 3.

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 3 or the head coil 13, and the gradient magnetic field power supply 7, 8 and 9, gradient magnetic fields Gx, Gy, and Gz are applied from the gradient magnetic field generating coil 2 for slicing, phase encoding, and reading, and signals from a specific region are sent to the receiving coil of the implantable whole body probe 3 or The head coil 13 collects the data. This sequence is repeated a predetermined number of times to obtain a data group,
An image is generated from this data group.

In addition, in the pulse sequence for collecting images described above, the head PH of the subject P is targeted for imaging regarding protons, and fat signals are suppressed and water (cerebrospinal fluid: CSF) signals are emphasized. This sequence is based on the spin echo method or field echo method, and is executed in multi-slice mode. Note that the reason why the signal from water is emphasized and the signal from fat is suppressed is based on the fact that there is a difference in chemical shift between water and fat regarding protons. Here, in the spin echo method, the echo time T _E is set to be longer than usual, for example, about 250 msec (usually about 80 msec), and the pulse repetition interval T _R is set to 2000 msec.
(usually about 500 msec).
In addition, as a field echo method, the echo time
Set T _E to be longer than usual, for example, about 20 to 30 msec (usually about 14 msec), and set the pulse repetition interval T _R to about 80 to 1000 msec (usually about 50 msec).
It is about sec. ). Furthermore, the flip angle of the RF pulse is set at 10 to 20 degrees.

In addition, RF is the excitation pulse, Gs is the gradient magnetic field for slicing, in this case, the gradient magnetic field in the Z-axis direction, Gr is the gradient magnetic field for reading, which in this case is the gradient magnetic field in the X-axis direction, and Ge is the gradient magnetic field for encoding. In this case, it is a gradient magnetic field in the Y-axis direction, and MR is an induced magnetic co-component signal, which in this case is an echo signal.

Under such condition settings, an RF pulse is transmitted by the transmitting coil or head coil 13 of the implantable whole body probe 3, and a gradient magnetic field Gs for slicing is applied from the gradient magnetic field generating coil 2, and then the lead is reversed. Adding a gradient magnetic field Gr and a gradient magnetic field Ge for phase encoding with variable intensity, the echo time is
Echo signals are collected from the multi-slice region using the head coil 13 at T _E. By repeating this a predetermined number of times, a data group is provided to the computer system 11, and a multi-slice image is generated from this data group. Then, this multi-slice image is subjected to addition processing in the computer system 11 using a method described later, and an added image and a current multi-slice image are obtained (see FIG. 2).
It is displayed on the display device 12.

Here, the addition processing of multi-slice images will be explained.

Addition processing methods 1, 2, and 3 described below are methods to obtain sensitivity characteristics similar to those using surface coils and to obtain a signal suppression effect depending on the position (depth) of the lesion (region of interest). Yes, addition processing method 4
is a method for obtaining images for stereo viewing.

<Addition processing method 1> N multi-slice images (matrix)
Let Mk (i, j). k=1, 2,..., N, i,
j = 1 to 256 (matrix).

The image obtained by weighted addition of these images is S(i,
j).

S(i, j)= _N 〓 ^k=1 ak·Mk(i, j) Here, for ak, a value (coefficient) corresponding to, for example, the sensitivity of the surface coil is used. Figure 3 shows the characteristics of the relationship between the depth of the surface coil and the sensitivity.
For example, if a lesion exists at a position 5 cm away from the coil (head coil 13) and you want to clearly visualize the lesion with the same characteristics as when using a surface coil, then follow the method shown in Figure 3. If we determine ak, we get the following.

a1=1.0, a2=0.9, a3=0.75, a4=0.6, a5=
0.5,... In other words, by selecting the value of the coefficient ak attached to each slice image to an appropriately smaller value as the slice position becomes deeper, signals in deep parts such as the ventricles and basal ganglia are suppressed, and as a result, , signals from deep parts such as the ventricles and basal ganglia are suppressed, and the image depicted by fat no longer overlaps the image depicted by the cerebral sulci.

Therefore, in the image displayed on the display device 12, the cerebral sulci are depicted 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. .

<Additive processing method 2> Additive processing method 1 was simply to obtain the same characteristics as the surface coil, but additive processing method 2
This method obtains the same characteristics as the surface coil, and also selects the value of the weighting coefficient ak according to the position (depth) of the lesion.

That is, as shown in FIG. 4a, when the lesion exists at a shallow position, the deeper the slice is located, the smaller the value of the coefficient ak and the greater the degree of reduction. For example, as shown in FIG. 4b, a1=1.0, a2=0.9, a3=0.6, a4=0.2, etc. are selected. When selected in this way, during addition, water (CSF) signals from deep slices such as in the ventricle are suppressed, and signal overlap is also suppressed.As a result, the summed image is This clearly depicts the structure of the brain surface, including the lesions present in the brain.

Contrary to the above, as shown in FIG. 5a, if the lesion exists in a deep position, the degree of decrease in ak is reduced. For example, as shown in FIG. 5b, a1=1.0, a2=0.95, a3=0.8, a4=0.7, etc. are selected.

<Addition processing method 3> In addition processing methods 1 and 2, a weighting coefficient ak is attached to each slice image, but in addition processing method 3, a weighting coefficient ak is attached to matrices i and j, which are internal elements of each slice image. A weighting factor ak is assigned accordingly.

S (i, j) = _N 〓 ^{k = 1} ak (i, j)・Mk (i, j) For example, if you want to emphasize the brain surface in particular, by selecting ak as below, you can It becomes heavier in shape.

ak(i,j)=√(−) ^{2 2} +(
-128) ² 128+(-128) ² 128 k=1, 2, 3,..., N, i, j=1, 2,
3,...,256 <Addition processing method 4> Addition processing method 4 enables stereo viewing through addition processing. In other words, when performing weighted addition in addition processing methods 1, 2, and 3, the viewing direction can be changed by shifting the position of each slice image, and as a result, the viewing direction can be changed without scanning two images with different viewing directions. , enables stereo viewing with only one multi-slice image.

That is, given Δi and Δj, images S(i, j)′ with different viewing directions are obtained by S(i, j)= _N 〓 ^k=1 ak・Mk(i + k(Δi), j+k(Δj)) Create. In this case, when Δi and Δj are non-integers, interpolation such as linear interpolation is performed as appropriate to create an image.

For example, if the pixels of the image Mk (i, j) are 1
mm, and the slice thickness is 10 mm.

If Δi=1 (that is, 1 mm) and Δj=0, the sixth
As shown in the figure, the viewing direction is approximately 5.7° (= tan ^-1 1/
10), and it becomes possible to perform stereo viewing using images S and S'.

The present applicant has previously filed a patent application for an invention related to this embodiment. Future application (Showa 62
In the invention described in the specification and drawings of Japanese Patent Application No. 62-232949 filed on September 17, 2007 (title of the invention "Magnetic Resonance Imaging Method"), a surface coil is used, and the slice thickness is approximately 8 cm. Slice and
The same effect as in this example can be obtained using the spin echo method in which the echo time is set longer than usual (250 msec) and the pulse repetition interval T _R is set longer than usual (2000 msec), that is, brain surface structure images ( SAS images (Surface Anatomy Scan) can be obtained.

The above embodiment has the following advantages compared to the invention of the earlier application. That is, it is possible to capture a SAS image viewed from a desired direction without being specified by the installation position of the surface coil, unlike the invention of the previous application. Furthermore, since a head coil is used, setting is easy. By referring to the added image and the slice image, the positional relationship in the depth direction can be easily determined. By appropriately adjusting the weighting coefficients during addition according to the location of the lesion and the case, it becomes possible to obtain a SAS image that accurately represents the location of the lesion and the case. Stereo viewing can be performed without rescanning in a different viewing direction. Since the slice thickness is small, the voxels during imaging are small, so phase disturbances are small and signal degradation is small.

In addition, in the invention related to the previous related application, for example, if the pulse repetition interval T _R is 2 seconds and the encoding is 256 times, the data collection time is 2 × 256
= 512 seconds, but if the field echo method is used in this example, the pulse repetition interval T _R will be 80 to 1000 seconds.
Since msec is sufficient, 0.08 (1.0) x 256 = 20.48 (256)
This is advantageous because data collection can be completed in an extremely short time.

In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a magnetic resonance imaging apparatus capable of obtaining images depicting brain surface structures.

[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 method according to the present invention is applied, FIG. 2 is a diagram showing an example of a multi-slice in the same embodiment, and FIG. FIGS. 4 and 5 are diagrams showing sensitivity characteristics, FIGS. 4 and 5 are diagrams showing coefficients in addition processing, and FIG. 6 is a diagram showing stereo viewing. 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... Head coil.

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 that detects a magnetic resonance signal related to protons and is placed close to the head of a subject; and a receiver coil that is placed in the static magnetic field and applies the gradient magnetic field and high-frequency pulse to the subject. is applied under predetermined conditions, and the multi-slice method is used to obtain a plurality of slice images of the head in which magnetic resonance signals related to water protons are emphasized and magnetic resonance signals related to fat protons are suppressed. a control means for executing a pulse sequence for depicting a brain surface structure using the multi-slice method together with the multi-slice method obtained from the receiving coil by driving the control means; reconstructing means for reconstructing magnetic resonance signals according to the above to obtain a plurality of slice images of the head; means for obtaining an image depicting a brain surface structure of the head based on the plurality of slice images; A magnetic resonance imaging apparatus comprising: a display means for displaying an image depicting a brain surface structure in the head obtained by the means; 2. 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; Magnetic resonance related to protons. A receiving coil that detects a signal and is placed close to the head of the subject; and the gradient magnetic field and high-frequency pulse are applied under predetermined conditions to the subject placed in the static magnetic field. brain surface structure using a multi-slice method in order to obtain a plurality of slice images of the head in which magnetic resonance signals related to water protons are emphasized and magnetic resonance signals related to fat protons are suppressed. a control means for executing a pulse sequence for imaging; and when the control means is driven, a magnetic resonance signal related to the execution of the pulse sequence for imaging a brain surface structure using the multi-slice method obtained from the receiving coil is provided. reconstructing means for reconstructing a plurality of slice images of the head; assigning a predetermined weight to each of the plurality of slice images, and adding the weighted plurality of slice images to obtain a plurality of slice images of the head; Magnetic resonance comprising: an addition means for obtaining an image in which a brain surface structure is depicted; and a display means for displaying an image in which the brain surface structure in the head obtained by the addition means is depicted. Imaging equipment. 3. 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 producing a magnetic resonance phenomenon related to protons; Magnetic resonance related to protons. A receiving coil that detects a signal and is placed close to the head of the subject; and the gradient magnetic field and high-frequency pulse are applied under predetermined conditions to the subject placed in the static magnetic field. brain surface structure using a multi-slice method in order to obtain a plurality of slice images of the head in which magnetic resonance signals related to water protons are emphasized and magnetic resonance signals related to fat protons are suppressed. a control means for executing an imaging pulse sequence; and when the control means is driven, magnetic resonance signals related to execution of the brain surface structure imaging pulse sequence using the multi-slice method obtained from the receiving coil are provided. Reconstruction means for reconstructing a plurality of slice images of the head; and assigning a predetermined weight to each matrix component of each of the plurality of slice images, and obtaining the plurality of slice images having the weighted matrix components. an addition means for obtaining an image in which the brain surface structure in the head is depicted by adding the above, and a display means for displaying an image in which the brain surface structure in the head obtained by the addition means is depicted. A magnetic resonance imaging device characterized by: 4. The magnetic resonance imaging apparatus according to claim 2, wherein the adding means adds the plurality of slice images while shifting the position of each slice image. 5. The magnetic resonance imaging apparatus according to claim 1, wherein the receiving coil has a cylindrical shape that can wrap around the head.