JPH0663027A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To obviate a discomfort sense and a restrained sense of a patient by shortening an image pickup time as much as possible even in the case plural image pickup parts are present thereon by constituting a device so that an NMR signal is received by switching and using a designated high frequency receiving coil in accordance with each image pickup period by a switching pattern table. CONSTITUTION:By using a positioning image picked up in advance, a position image-picked up actually is determined with regard to each part. Subsequently, a pulse sequence for photographing all image pickup position is formed by a CPU 19. Then, a switching pattern table is formed. Thereafter, the pulse sequence and the switching pattern table are set to a pulse sequencer 18 and execution of the pulse sequence is requested repeatedly to the pulse sequencer 18 at the interval of a prescribed repeating time TR. In such a manner, the images of two image pickup parts can be picked up simultaneously by using each separate surface high frequency receiving coil 5, 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance (NMR) imaging apparatus for obtaining a tomographic image of a subject such as a living body.

[0002]

2. Description of the Related Art In a magnetic resonance imaging apparatus, when an atomic nucleus is placed in a uniform static magnetic field, the spin of the atomic nucleus precesses around the static magnetic field. High frequency pulse (RF pulse) with the same frequency
Is used to obtain a tomographic image of an object to be diagnosed, such as a living body, by utilizing the property of causing a magnetic resonance phenomenon.

A block diagram of a general magnetic resonance imaging apparatus is shown in FIG. 3, and its operation will be described below. The subject 1 is placed inside a static magnetic field (main magnetic field) coil 2 that generates a uniform static magnetic field. The computer system 16 includes a pulse sequencer 18, a CPU 19, a hard disk 2
0, digital input interface 21, console 2
2. The processor 23 is included and is connected by the system bus 17.

When an image pickup command is input from the console 22, the CPU 19 activates the pulse sequencer 18. The pulse sequencer 18 sets the X-axis, Y-axis, and
Gradient magnetic field power supply (Gx) 8 corresponding to the Z-axis (Gy)
The gradient magnetic field coil 3 and the high frequency transmitting coil 4 generate a predetermined gradient magnetic field and a high frequency rotating magnetic field by controlling 9, 9, the same (Gz) 10, the high frequency oscillator 11, and the high frequency transmitter 12. Here, the pulse sequencer 18, the gradient magnetic field power supplies 8, 9, 10, the gradient magnetic field coil 3, etc. constitute a gradient magnetic field generator.

N generated from the subject 1 in such a state
The MR signal is received by the surface high-frequency receiving coil 5 or 6, detected and amplified by the high-frequency receiver 13 and the phase detector 14, and then converted into a digital signal by the A / D converter 15, and the digital input interface 21 is used. Read into computer system 16 via. The read data is temporarily stored in the hard disk 20 or the arithmetic processing unit 23, and when all the data collection is completed, the arithmetic processing unit 23 performs image reconstruction calculation, and then the console 22 is used as a tomographic image. Is displayed in.

Next, an example of a typical pulse sequence in the above operation is shown in FIG. In the figure, (a) is RF
Pulses (high-frequency magnetic field), (b), (c), and (d) indicate outputs of gradient magnetic fields Gx, Gy, and Gz. In these signals, 201 is a 90 ° pulse, 202 is a gradient magnetic field for performing slice selection to specify a tomographic plane, 203 is a gradient magnetic field for performing frequency encoding, and 204 is a gradient magnetic field for performing phase encoding. Here, when obtaining an L × M matrix image on the console 22, the NMR signal 2 shown in (e) is used.
05 is sampled by the A / D converter 15 only at L points. This collected data is shown as 206 in FIG.

The signals 201 to 206 change the gradient magnetic field 204 for phase encoding as shown in FIG.
Imaging is repeated M times at regular intervals TR. The L × M point data thus obtained is subjected to an image reconstruction operation including a two-dimensional Fourier transform by the arithmetic processing unit 23 to obtain the two-dimensional image data of the tomographic plane of the subject 1. Is getting Note that there are various patterns in the sequence of the above-described application of the high-frequency magnetic field, the gradient magnetic field, the collection of NMR signals, and the like.
Shows only one example.

In such a magnetic resonance imaging apparatus, the surface high-frequency receiving coil is brought close to the imaging region of the subject 1 to improve the quality of the obtained image. Further, as shown in FIG. 3, there are cases where a plurality of high frequency receiving coils for the surface are used to image a plurality of parts. For example, when performing both left and right imaging in order to compare the images of the left and right joints, such as an examination of the temporomandibular joint, set the surface high-frequency receiving coil for the temporomandibular joint close to each of the left and right imaging parts, First, use the high frequency receiving coil for the surface on the right side (or left side) to perform imaging,
Next, imaging is performed using the left (or right) surface high frequency receiving coil.

Regarding the above-mentioned image pickup method, a method of picking up the left and right temporomandibular joints as shown in FIG. 5 will be described as a concrete example. First, the changeover switch 7 in FIG. 3 is operated so that the front surface high-frequency receiving coil 5 (hereinafter referred to as “the side”) is turned on, and a pulse sequence for imaging four images as shown in FIG. 6 is created. At this time, the period (1) to the period (4) in FIG. 6 correspond to the imaging position (1) to the imaging position (4) in FIG. 5, respectively. Also, the high frequency magnetic field and the gradient magnetic field G in each period
The operation patterns of x, Gy, Gz and A / D conversion are shown in FIG.
(A), (b), (c), (d), (f).

By setting the above pulse sequence in the pulse sequencer 18 and operating according to this pulse sequence, four images on the side in FIG. 5 can be obtained. It should be noted that a fixed pause period is provided after the lapse of the period (1) to the period (4) in each of the M times of imaging. Then, after the side imaging is completed, the changeover switch 7
Is switched so that the surface high-frequency receiving coil 6 (below) side is turned on. Next, a pulse sequence is created so that the period (1) to the period (4) in FIG. 6 correspond to the imaging position (5) to the imaging position (8) in FIG. 5, respectively.
By setting the above pulse sequence in the pulse sequencer 18 and operating according to this pulse sequence,
It is possible to obtain four images on the side of.

[0011]

[Problems to be Solved by the Invention] In actual clinical practice,
The normal imaging time of the magnetic resonance imaging apparatus is relatively long, from several minutes to several tens of minutes, and when two surface high-frequency receiving coils are switched to image two sites as in the above-mentioned examination of the temporomandibular joint. However, there is a drawback that the imaging time is doubled and the patient feels uncomfortable and restrained. The present invention has been made to solve the above problems, and an object of the present invention is to reduce the imaging time as much as possible even when there are a plurality of imaging sites to eliminate the discomfort and the feeling of being restrained by the patient. Another object of the present invention is to provide a magnetic resonance imaging apparatus.

[0012]

In order to achieve the above object, the present invention provides an imaging region with an NMR signal generated from a subject placed in a uniform static magnetic field and to which a high frequency pulse is applied. A magnetic resonance imaging apparatus that receives a plurality of high-frequency receiving coils that can be switched in accordance with the received signals, converts the received signals into digital signals, and performs an image reconstruction operation by a computer system to generate a tomographic image of the imaged region, An NMR signal is obtained by switching the high-frequency receiving coil specified by the switching pattern table according to each imaging period with a switch according to the imaging pulse sequence in which the imaging period set for each imaging region does not have a pause period and continues. Is to receive.

[0013]

In the present invention, the imaging period by the plurality of high-frequency receiving coils corresponding to each imaging region is made continuous to create a pulse sequence without a pause period, and based on the switching pattern table, the imaging sequence is performed in advance for each imaging period. Toggle the switch to use the designated high frequency receiver coil. As a result, the period corresponding to the conventional idle period can be used as an image capturing (reception) period by another high frequency receiving coil, and the image capturing time of the two parts is halved as compared with the conventional one.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An imaging method using a plurality of surface high-frequency receiving coils according to the present invention will be described below by taking the above-mentioned imaging of the temporomandibular joint as an example. First, using the preliminarily imaged positioning image 24 as shown in FIG. 5, the actual imaging position for each part is determined as shown in FIG.
Next, the CPU 19 creates a pulse sequence for imaging the imaging positions on the above side and all sides. At this time, various combinations of the correspondence between the period (1) to the period (8) shown in FIG. 1 and the image capturing position (1) to the image capturing position (8) shown in FIG. 5 are conceivable. Period 1 (1)
It is assumed that the pulse sequence is created so that the period from (1) to (8) corresponds to the imaging position (1) to the imaging position (8) in FIG. 5, respectively.

Next, the CPU 19 creates a table (hereinafter referred to as a switching pattern table) 25 as shown in FIG. 2, which shows the state of the changeover switch 7 in each image pickup period from the period (1) to the period (8) in FIG. In the switching pattern table 25, SW1 of the changeover switch 7 is described if the imaging position corresponding to each period is on the side, and SW2 is described on the side, but binary data such as 0, 1 is actually set. To be done. The switching pattern table 25 of FIG. 2 describes the case where the period (1) to the period (8) of FIG. 1 correspond to the imaging position (1) to the imaging position (8) of FIG. 5, respectively. By changing the program that creates the switching pattern table 25. Various combinations of the period of FIG. 1 and the imaging position of FIG. 5 can be supported.

As is apparent from the pulse sequence of FIG. 1 and the switching pattern table 25 of FIG. 2, in the present embodiment, there is no pause period for each imaging number in FIG. Is divided into two and the state of the changeover switch 7 is set to each of them (SW1 side or SW2
Side), that is, the image data is collected by receiving signals from both the side and the side of the front surface high-frequency receiving coil by one image pickup.

Next, the pulse sequence of FIG. 1 and FIG.
And the switching pattern table 25 are set in the pulse sequencer 18 to repeatedly request the pulse sequencer 18 to execute the pulse sequence at a constant repetition time TR. 1G shows the status signal 207 of the changeover switch 7. The pulse sequencer 18 requested to execute the pulse sequence first switches the changeover switch 7 according to the value set in the period (1) of the changeover pattern table 25. Then, the pulse sequencer 18 operates the high-frequency oscillator 11, the high-frequency transmitter 12, the gradient magnetic field power supplies (Gx) 8, the same (Gy) 9, and the same (Gz) 10 in accordance with the above-mentioned pulse sequence to cause magnetic resonance at a predetermined imaging position. Cause a phenomenon.

The NMR signal (echo signal) generated by the magnetic resonance phenomenon is received by the surface high-frequency receiving coil 5 or 6 which is in a state receivable by the changeover switch 7, and is received by the high-frequency receiver 13 and the phase detector 14. After detection / amplification, it is stored in the arithmetic processing unit 23 or the hard disk 20 in the computer system 16 through the A / D converter 15. The pulse sequencer 18 reads the state of the changeover switch 7 for the next period from the changeover pattern table 25 at the time when the A / D conversion of the echo signal is completed, and if necessary, the changeover switch 7,
That is, the high frequency receiving coil to be used is switched.

By repeating the above operation for the imaging period created by the pulse sequence, the echo signals at all the specified imaging positions are collected. However, A of the last period of the pulse sequence (period (8) in the case of FIG. 1)
When the D / D conversion is completed, the switching pattern table 2
It is assumed that the changeover switch 7 is changed over by reading the state of the changeover switch 7 at the beginning of 5, ie, the period (1).

As described above, according to this embodiment, the switching pattern table 25 showing the setting state of the changeover switch 7 is created in advance according to the predetermined pulse sequence,
Data is read from the switching pattern table 25, and the changeover switch 7 is operated in conjunction with the pulse sequence, so that images of two imaged parts are imaged at once using separate high-frequency surface receiving coils 5 and 6. You can In this embodiment, the case where the two surface high-frequency receiving coils 5 and 6 are used is illustrated. However, the changeover switch 7 has a large number of changeover points, and the program for creating the changeover pattern table 25 is changed. Therefore, it can be easily applied to the case where three or more surface high-frequency receiving coils are used.

[0021]

As described above, according to the present invention, a plurality of high-frequency receiving coils corresponding to respective imaging regions are made to be continuous in the imaging period to create a pulse sequence having no rest period, and each imaging is performed based on the switching pattern table. The high frequency receiving coil designated in advance according to the period is switched and used. As a result, the period corresponding to the conventional pause period can be used as an imaging period by another high-frequency receiving coil, the number of times of imaging is reduced, and the imaging time of the two parts is halved as compared with the conventional one. It is possible to reduce the discomfort and restraint feeling of the patient due to the medical examination, and to significantly improve the diagnosis efficiency.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a pulse sequence used in imaging using two surface high-frequency receiving coils according to an embodiment of the present invention.

FIG. 2 is a diagram showing a switching pattern table in the embodiment.

FIG. 3 is a block diagram of a conventional general magnetic resonance imaging apparatus.

FIG. 4 is a diagram showing an example of a pulse sequence using a two-dimensional Fourier transform method.

FIG. 5 is a diagram showing an example of an image pickup position conventionally performed by using two surface high-frequency receiving coils.

6 is a diagram showing an example of a pulse sequence used in the imaging of FIG.

[Explanation of symbols]

 1 subject 2 static magnetic field coil 3 gradient magnetic field coil 4 high frequency transmitting coil 5, 6 surface high frequency receiving coil 7 changeover switch 8 gradient magnetic field power supply (Gx) 9 gradient magnetic field power supply (Gy) 10 gradient magnetic field power supply (Gz) 11 high frequency oscillator 12 high-frequency transmitter 13 high-frequency receiver 14 phase detector 15 A / D converter 16 computer system 17 system bus 18 pulse sequencer 19 CPU 20 hard disk 21 digital input interface 22 console 23 arithmetic processor 24 positioning image 25 switching pattern table

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Sada Hiura 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (1)

[Claims] 1. An NMR signal generated from a subject, which is placed in a uniform static magnetic field and to which a high frequency pulse is applied, is received by a plurality of high frequency receiving coils that can be switched according to an imaging region, and this reception is performed. In a magnetic resonance imaging apparatus for converting a signal into a digital signal and performing an image reconstruction operation by a computer system to generate a tomographic image of the imaging region, the imaging period set for each imaging region does not have a pause period. A magnetic resonance imaging apparatus characterized by receiving a NMR signal by switching and using a high-frequency receiving coil designated by a switching pattern table according to each imaging period according to a continuous pulse sequence.