JPH01155835A - Magnetic resonance imaging method - Google Patents

Abstract

PURPOSE:To increase the taking number of images per a unit time while shortening a time, by together using an RF magnetic field and an inclined magnetic field with respect to the first-n-th regions. CONSTITUTION:X-, Y- and Z-axis inclined magnetic field coils 2 are excited and supplies 5, 6, 7. At this time of transmission, a transmitting-receiving coil 3 is driven by a transmitter 8 and, at the time of reception, said coil 3 is driven by a receiver 9. A 90 deg.-pulse and a slicing inclined magnetic field are successively allowed to act in order to excite the first-n-th regions and, next, an inclined magnetic field for phase encoding and 180 deg.-phase are together used to be allowed to act on the first-n-th regions and an inclined magnetic field for frequency encoding is allowed to act on the first-n-th regions in a state divided between the 90 deg.-phase and the 180 deg.-pulse and the magnetic resonance signals from the first-n-th regions are respectively detected by the receiver 9.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to magnetic resonance (MR: w+aonetic
res.

The present invention relates to a magnetic resonance imaging method for obtaining diagnostic information on different parts of a subject by utilizing the phenomenon (nance), and particularly relates to a magnetic resonance imaging method that can shorten data collection time in multi-slice imaging.

(Prior art) Magnetic resonance is a phenomenon in which atomic nuclei with non-zero spin and magnetic moment placed in a static magnetic field resonantly absorb and emit only electromagnetic waves of a specific frequency. If HO is the gyromagnetic ratio specific to , and HO is the static magnetic field strength, then this atomic nucleus resonates at an angular frequency of 0 as shown in the following equation.

ω03γHa In a method of performing biological diagnosis using the above principle, electromagnetic waves of the same frequency as above, which are induced after the above-mentioned resonance absorption, are subjected to signal processing to obtain, for example, a cross section of the subject.

In this case, collecting diagnostic information by magnetic resonance can excite all parts of the subject placed in a static magnetic field and collect signals, but there are limitations in the equipment configuration and clinical aspects of the imaging image. Due to the request, we actually excite a specific slice plane and collect its signals.

FIG. 2 is a diagram showing a general configuration of a magnetic resonance diagnostic apparatus using the above-described principle.

As shown in FIG. 2, the magnet assembly MA that accommodates the subject P therein includes, for example, a superconducting or normal conducting static magnetic field coil that generates a high-intensity static magnetic field that acts on the subject P. 1, three gradient magnetic field coils 2 that generate gradient magnetic fields along the X-, Y-, and Z-axis directions, and a transmitting/receiving coil 3 for excitation and signal collection, which serves for example as both transmitting and receiving functions.

It also has a static magnetic field control system 4 that performs excitation control of the static magnetic field coil 1 and coolant supply control. X, Y.

The two-axis gradient magnetic field coil 2 has an X-, Y-, and Z-axis gradient magnetic field power source 5.
Excitation is controlled by 6.7. The transmitter/receiver coil 3 is driven by a transmitter 8 during transmission (excitation) and by a receiver 9 during reception (signal collection).

In addition, the X, Y, Z axis gradient magnetic field power supplies 5, 6.7 and the transmitter 8
, a sequencer 10 that executes the gradient magnetic field and transmission/reception signal generation sequence by the receiver 9, for example, the multi-slice image capturing sequence shown in FIG. The computer system 11 includes a computer system 11 for displaying a generated image, and a display system 12 for displaying a generated image.

FIG. 3 is a diagram showing an example of a multi-slice image capturing sequence executed by the sequencer 10. Below, the third
A multi-slice image capturing sequence of a conventional magnetic resonance imaging method shown in the figure will be explained. That is,
This multi-slice image capturing sequence is capable of collecting data (11 air resonance signals) for generating two slice plane images, and the first encoding for the first plane is performed as shown in FIG. 3(a). as 906 pulses and 180°
A pulse is generated, and respective gradient magnetic fields for 9-phase encoding for slices (not shown) and WA wave number encoding are generated, and an echo signal (SE) by the first encoding is obtained at echo time TE.

Next, the second encoding is performed on the same first side. During the second encoding period, that is, within the repetition time TR, a 90° pulse and a 1806 pulse are generated as the first encoding for the second surface as shown in FIG.
Generate a respective gradient magnetic field for frequency encoding and when echoing! ! An echo signal (SE) is obtained by the first encoding using flTE. After that, second encoding is performed on the first side.

The procedure shown in FIG. 3(a) for the first surface is repeated a predetermined number of times corresponding to the number of matrices, and at this time, the procedure shown in FIG. 3(b) is repeated for the number of matrices within the repetition time for the first surface. Repeat the specified number of times. As a result, the data collection for the second side will also end when the data collection for the first side is completed, making it possible to complete the data collection for two images within the data collection time normally required to generate one image. become.

As described above, according to the conventional method, by performing a sequence for another surface (3 to 20 surfaces) within the repetition time of a sequence for one surface, it is possible to increase the number of images taken per unit time. , diagnostic efficiency can be improved.

(Problem to be solved by the invention) However, in the above-mentioned method, each set of RF magnetic field and gradient magnetic field is executed many times using Flfl (repetition time) when idle. of! The number of images obtained with one shooting operation was approximately 3 to 20, which was unsatisfactory in terms of photographic efficiency.

Therefore, an object of the present invention is to provide a magnetic resonance imaging method that can further improve imaging efficiency.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a structure in which the following means are taken to solve the above problems and achieve the object. That is, the present invention provides a magnetic resonance imaging method in which a specific region of a subject placed in a static magnetic field is excited, and a magnetic resonance signal induced from the excited region is detected to generate morphological information or functional information of the region. , a 90' pulse and a slicing gradient magnetic field are sequentially applied to excite the first to nth parts, and then a phase encoding gradient magnetic field and 1800 pulses are jointly applied to the first to nth parts. At the same time, the frequency encoding gradient magnetic field for the first to nth parts is divided between the 90' pulse and the 180'' pulse at the first to nth parts, and the frequency encoding gradient magnetic field is applied to the first to nth parts. It is characterized by detecting magnetic resonance signals respectively.

(Function) According to such a configuration, it becomes possible to obtain data from the first to nth parts at different echo times, and in this case, the RF magnetic field and the gradient magnetic field are applied to the first to nth parts. Since it is used in combination, time can be shortened and the number of images taken per unit time can be increased.

<Example> An example of the magnetic resonance imaging method according to the present invention will be described below with reference to FIG.

The example shown in FIG. 1 is a multi-slice image photographing sequence in which the first surface and the second surface are obtained in one photographing procedure. As shown in FIG. 1, a 90' pulse and a slicing gradient magnetic field GS1 corresponding to the first surface are applied to excite the first surface. Next, a 90' pulse and a slicing gradient magnetic field GS2 corresponding to the second surface are applied to excite the second surface.

Then, a phase encoding gradient magnetic field GE with variable intensity of 1800 pulses is applied to the first surface and the second surface, and the strength is enough to excite both the first surface and the second surface at the same time when applying these 1806 pulses. A slicing gradient magnetic field G having
Apply S3.

The frequency encoding gradient magnetic field GR is divided into two parts (GRl
, GR2)L, is applied.

To read the echo signal, an echo frequency encoding gradient magnetic field GR3 is applied, and by applying this GR3, an echo signal SE2 is induced from the second surface at an echo time TE2. This is received by a receiving coil (not shown). next,
When the GS2 previously added to the first surface is canceled by applying the slicing gradient magnetic field GS4, an echo signal SE is generated from the first surface at an echo time TE1 while applying GR3.
1 induces. This is received by a receiving coil (not shown).

The above is one encoding procedure, and by repeating this a number of times corresponding to the number of image matrices, it becomes possible to generate two images in one photographing procedure.

Therefore, compared to the conventional method, the number of images (data sets) that can be collected within the same amount of time is approximately twice as large.

As described above, according to this embodiment, the RF magnetic field and the gradient magnetic field are partially shared when exciting and signal collecting two slice planes, so that the time required for signal collection can be shortened. , which increases the number of images taken per unit time.

Furthermore, since two slice images with different echo times can be obtained in one imaging procedure, two medically useful images are obtained. For example, the first plane with a long echo time has high contrast and allows you to easily understand the spread of the lesion, and the second plane with a short echo time has a high S/S/
N, which is suitable for anatomical recognition.

Although the above example describes excitation and signal collection for two surfaces, it is also possible to simultaneously excite and collect signals for three or more surfaces. In this case as well, although the 90' pulse and the gradient magnetic field for slicing are applied to the festival, the 1800 pulse and the gradient magnetic field for phase encoding are shared, and the gradient for frequency encoding! The tl field is divided between a 90° pulse and a 180° pulse for each song, and
The gradient magnetic field for slicing that is applied excessively is canceled later.

Various modifications can be made without departing from the gist of the invention.

[Effects of the Invention] As described above, in the present invention, in order to excite the first to nth parts, a 90'' pulse and a slicing gradient magnetic field are sequentially applied, and then a phase adjustment is applied to the first to nth parts. The encoding gradient magnetic field and the 180° pulse are used in common, and the frequency encoding gradient magnetic field for the first to nth parts is applied to the frequency encoding gradient magnetic field for the first to nth parts.
The action is divided between the ° pulse and the 180 ° pulse,
By detecting the magnetic resonance signals from the first to nth parts, respectively, the first to nth parts at different echo times are detected.
It is now possible to obtain data from the nth site,
In this case, since the RF magnetic field and the gradient magnetic field are used together for the first to nth parts, time can be shortened, which increases the number of images taken per unit time. Therefore, according to the present invention, a magnetic resonance imaging method that can further improve imaging efficiency can be provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the magnetic resonance imaging method according to the present invention, FIG. 2 is a diagram showing a general configuration of a magnetic resonance diagnostic apparatus, and FIG. 3 is a diagram explaining a conventional example. MA... Magnet assembly, 1... Static magnetic field coil, 2... Gradient magnetic field coil, 3... Transmission/reception coil,
4... Static magnetic field control system, 5, 6.7... Gradient magnetic field power supply, 8... Transmitter, 9... Receiver, 10... Sequencer, 11... Computer system, 12. ...Display system. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] In a magnetic resonance imaging method, in which a specific part of a subject placed in a static magnetic field is excited, and a magnetic resonance signal induced from the excited part is detected to generate morphological information or functional information of the part, first to nth 9 each to excite the site.
A 0° pulse and a slicing gradient magnetic field are sequentially applied, and then a phase encoding gradient magnetic field and a 180° pulse are applied in common to the first to nth parts, and frequency encoding is applied to the first to nth parts. The gradient magnetic field is applied to the 90° pulse and the 18
0° pulse and act on the first to nth pulses.
A magnetic resonance imaging method characterized by detecting magnetic resonance signals from each region.