JPH064065B2 - Magnetic resonance imaging equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention identifies a subject by applying a gradient magnetic field pulse and a high-frequency pulse to the subject placed in a static magnetic field. The present invention relates to a magnetic resonance imaging apparatus that excites a site and collects magnetic resonance signals induced after the excitation to generate diagnostic information of the specific site, and in particular, a waveform generator that generates a gradient magnetic field pulse or a high frequency pulse. An improved magnetic resonance imaging apparatus.

(Prior Art) A magnetic resonance (MR) phenomenon is a phenomenon in which an atomic nucleus having a nonzero spin and a magnetic moment placed in a static magnetic field resonantly absorbs and emits only an electromagnetic wave of a specific frequency. , This nucleus resonates at an angular frequency ω ₀ (ω ₀ = 2πν ₀ ; Larmor frequency) shown in the following formula.

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

A device for performing a biomedical diagnosis using the above principle performs signal processing of electromagnetic waves (magnetic resonance signals: echo signals and FID signals) of the same frequency as that induced after the above-mentioned resonance absorption, to obtain nuclear density, longitudinal The relaxation time T1, the lateral relaxation time T2, the flow, the diagnostic information in which the information such as the chemical shift is reflected, for example, the slice image of the subject is non-invasively obtained.

Further, the collection of diagnostic information by magnetic resonance is capable of exciting all the parts of the subject placed in a static magnetic field and collecting signals, but there are restrictions on the device configuration and clinical demands for imaging images. Therefore, in an actual device, excitation and signal acquisition of a specific part are performed.

Generally, an imaging method called a selective excitation method is used as a method for performing the excitation and signal acquisition of the above-described specific region. This selective excitation method will be briefly described. That is, a gradient magnetic field pulse that linearly changes the magnetic field in the direction perpendicular to the slice surface to be imaged is applied to the subject arranged in the static magnetic field. Then, the resonance frequency changes linearly in the direction perpendicular to the slice plane. Therefore, when a high-frequency pulse (RF pulse) having a bandwidth corresponding to the slice thickness is applied, it is possible to excite only the slice cross section and collect the magnetic resonance signal induced thereafter.

Here, the rising characteristics of the gradient magnetic field pulse waveform and the amplitude characteristics of the RF pulse waveform, which greatly affect the slice characteristics and the image quality, will be described.

That is, FIG. 4 is a block diagram showing the configuration of the gradient magnetic field system. The trapezoidal waveform shown in FIG. 5 (a), the rectangular waveform shown in FIG. 5 (b), and the ultrahigh speed shown in FIG. 5 (c). Waveform memory 20a in which voltage data for generating any of the sinusoidal waveforms applied to imaging is stored in the form of digital data, and is read from the waveform memory 20a by a control signal and a read control signal provided from a sequencer. D / A converter 20 for converting the converted waveform data into an analog signal
It is composed of a gradient magnetic field pulse waveform generator 20 composed of b, a gradient magnetic field power supply 21 composed of an amplifier for amplifying the gradient magnetic field pulse waveform from the waveform generator 20 to a predetermined size, and a gradient magnetic field coil 2. . Here, X, Y, Z
One of the axes is shown.

With the above configuration, the generation of the gradient magnetic field waveform is performed as follows. That is, in the waveform memory 20a, 0 is sequentially
The voltage data of V, 2.5V, 5V ... Is stored,
Amplitude 5 with a rise time of 1 msec in the excitation collection sequence
When a trapezoidal waveform of V is required, the waveform memory 20a
This is performed by reading out the voltage data 0V, 2.5V, 5V with time from the inside. That is, as shown in FIG. 4A, 0V is read at t1 in synchronization with the read control signal,
2.5V is read at t2, which is 50 μsec after t1,
5V is read at t3 after 50 μsec from
At t4 after a lapse of μsec, 5V is read out, and, after each of the data readings, the data is read from the D / A converter 20.
In b, an analog signal is formed to obtain a desired trapezoidal waveform. That is, by reading out the voltage data 0V, 2.5V, 5V corresponding to the amplitude at the times t1 to t3,
By setting the rise time to 1 msec and reading the voltage data 5V corresponding to the amplitude from time t4, a trapezoidal waveform having a rise time of 1 msec and an amplitude of 5V can be obtained.

As described above, since the rise time of the generated waveform depends on the amplitude, a large number of data groups based on the combination of the rise time and the amplitude must be prepared in the waveform memory 20a in order to obtain the required waveform. I have to. But,
When excitation collection sequences for various types are proposed and put to practical use in recent years, problems such as an enormous amount of data to be prepared and complicated read control are presented. It will be.

FIG. 6 is a block diagram showing the configuration of the RF system,
FIG. 7 shows an SEP generator 30 for generating a sink function waveform.
a and an RF pulse waveform generator 30 including an RF attenuator 30b that attenuates the waveform given from the SEP generator 30a by the amplitude control signal, and the RF pulse waveform from this waveform generator 30 is amplified to a predetermined magnitude. It is composed of an RF amplifier 31 and a transmission coil 3A. Here, the SEP generator 30a has a voltage data group corresponding to the amplitude similarly to the waveform generator 20 of the gradient magnetic field system shown in FIGS. 4 and 5, and a predetermined sink function waveform is obtained by reading control of the voltage data group. It is configured as follows.

With the above configuration, the generation of the RF pulse waveform is performed as follows. That is, when a 180 ° pulse is generated subsequently to a 90 ° pulse, first, the SEP generator 30a is activated by the waveform control signal given from the sequencer to generate a sync function waveform, and the amplitude of this waveform is adjusted by the RF attenuator 30b. Then, a 90 ° pulse is formed. And
The signal is amplified by the RF amplifier 3 and then given to the transmission coil 3A. Next, regarding the generation of a 180 ° pulse, similarly to the above, the amplitude of the sync function waveform is adjusted by the RF attenuator 30b to form a 180 ° pulse, which is amplified by the RF amplifier 3 and then given to the transmission coil 3A. .

In this case, the RF pulse changes its intensity according to the size of the subject and the morphology of the excitation site, and 90 °
Since the amplitude ratio condition between the pulse and the 180 ° pulse is 1: 2, it is necessary to adjust the RF attenuator 30b so as to match the size of the subject and the form of the excitation site. However, in recent years, when various kinds of excitation collection sequences according to the combination of 90 ° pulse and 180 ° pulse have been proposed and put into practical use, and the range of clinical application is expanded, RF Problems such as extremely complicated control of the attenuator 30b are presented.

(Problems to be Solved by the Invention) As described above, in the conventional technique, the rising characteristics and the strength (amplitude) characteristics have to be set in various forms, and the strength ( amplitude)
Waveform control of high-frequency pulses, whose characteristics must be set to various types, is used for reading control of voltage data groups and R
Since the sequential control of the F attenuator is performed, when various kinds of excitation and collection sequences are proposed and put into practical use and the range of clinical application is expanded, the control becomes extremely complicated. There was a problem that

Therefore, an object of the present invention is to improve the rising characteristics and the strength (amplitude).
High-precision and easy waveform control of gradient magnetic field pulses whose characteristics must be set to various forms and high-frequency pulses whose intensity (amplitude) characteristics must be set to various forms under a constant amplitude ratio Another object of the present invention is to provide a magnetic resonance imaging apparatus capable of performing the above.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a structure in which the following means are provided in order to solve the above problems and achieve the object. That is, the present invention provides a gradient magnetic field pulse based on a gradient magnetic field pulse waveform generated from a gradient magnetic field pulse waveform generator and a high frequency pulse waveform generated from a high frequency pulse waveform generator with respect to a subject arranged in a static magnetic field. A magnetic resonance imaging apparatus configured to generate a magnetic resonance phenomenon in a specific region of the subject by applying a high-frequency pulse based on the magnetic resonance imaging device to obtain diagnostic information by collecting a magnetic resonance signal from the specific region. At least one of the magnetic field pulse waveform generation unit and the high-frequency pulse waveform generation unit, shape data holding means for holding a plurality of shape data for defining at least one of the gradient magnetic field pulse waveform and the high-frequency pulse waveform, To define at least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform At least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform by multiplying the amplitude data holding means for holding a plurality of amplitude data and one of the plurality of shape data and one of the plurality of amplitude data Each of the plurality of shape data held in the shape data holding means is composed of at least a first side formed by a line segment connecting a plurality of points and a line segment connecting a plurality of points. It is characterized in that a plurality of polygons including the second side are defined.

(Operation) According to such a configuration, by combining the shape data of the object to be multiplied and the amplitude data, the gradient magnetic field pulse waveform easily has various rising characteristics and intensity (amplitude) characteristics. Further, as the high-frequency pulse waveform, it is possible to easily obtain various intensity (amplitude) characteristics with a constant amplitude ratio.

Further, at least one of the gradient magnetic field pulse waveform shape data and the high frequency pulse waveform shape data is a polygon including a first side formed by a line segment connecting a plurality of points and a second side formed by a line segment connecting a plurality of points. The intermediate portion of each side of at least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform can be defined in detail, and at least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform can be controlled with high accuracy. it can. You will be able to get it. Moreover, at least one of the gradient magnetic field pulse waveform shape data and the high-frequency pulse waveform shape data is a polygon including a first side including a line segment connecting a plurality of points and a second side including a line segment connecting a plurality of points. The intermediate portion of each side of at least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform can be defined in detail, and at least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform can be controlled with high accuracy. It is possible.

(Embodiment) An embodiment of the magnetic resonance imaging apparatus according to the present invention will be described below with reference to FIG.

As shown in FIG. 1, a magnet assembly MA capable of accommodating a subject P therein.
Is a static magnetic field magnet (sometimes a shim coil for static magnetic field correction is added) 1 of a permanent magnet, a normal conducting magnet, a superconducting magnet, or a combination thereof, and position information of a magnetic resonance signal inducing portion. From a gradient magnetic field generating coil 2 that generates a gradient magnetic field for application and a coil that is a transmission / reception system (transmission coil 3A, reception coil 3B) for transmitting a high-frequency pulse for excitation and detecting an induced magnetic resonance signal The probe 3 is

A gradient magnetic field power supply 5 forming a gradient magnetic field system for giving a desired gradient magnetic field pulse to the gradient magnetic field coil 2 is supplied with gradient magnetic field waveform data from a gradient magnetic field pulse waveform generator 5.

Further, the RF amplifier 6 forming a transmission system for supplying the probe 3 with the power for generating the high frequency pulse for excitation receives the RF pulse waveform data from the RF pulse waveform generator 7.

Further, the signal from the receiving coil 3B of the probe 3 is amplified to such an extent that it can be applied to the subsequent processing, and its output is phase-detected by the real number part and the imaginary number part, and this phase detection output is converted into a digital signal, and this A / A receiver 8 for introducing a D conversion output into a computer system 10 described later is provided.

Further, it has a controller 9 for executing the excitation and collection pulse sequence, a computer 10 for controlling these and performing signal processing of a detection signal, and a monitor 11 for displaying an image generated by the computer system 10.

In the above, the gradient magnetic field pulse waveform generator 5 includes a shape data memory 5a that stores in advance waveform shape data that serves as a reference for any or all of a trapezoidal waveform, a rectangular waveform, and a sine wave waveform, and a required gradient magnetic field. Amplitude data memory 5 for storing amplitude data for setting the maximum amplitude value of the pulse
b, a multiplier 5c for multiplying the shape data from the shape data memory 5a and the amplitude data from the amplitude data memory 5b, and a D / A converter 5d for converting the multiplication result by the multiplier 5c into an analog signal. ing. The shape data memory 5a stores a plurality of gradient magnetic field pulse waveform shape data, and each of the plurality of gradient magnetic field pulse waveform shape data includes a first gradient side (first side) formed by a line segment connecting a plurality of points, Upper and lower sides consisting of line segments connecting multiple points,
A second inclined side (second side) formed by a line segment connecting a plurality of points,
It defines a plurality of trapezoids that have a lower base and. That is, specifically, as an example, specifically, voltage data (0V, 0.5V, 1V, 1V, 1V, 1V, 1V, 1V, 1V,
0.5V, 0V) is stored. FIG. 2A shows one trapezoid which is one gradient magnetic field pulse waveform shape data. This trapezoid, as shown in FIG.
Time t1 (0V) -Time t2 (0.5V) -Time t3
A first inclined side formed by a line segment connecting (1V) and time t3
(1V) to time t4 (1V) to time t5 (1V) to time t6 (1V) to time t7 (1V) and the upper base of the line segment, and time t7 (1V) to time t8 (0.5V) to It has a second inclined side formed by a line segment connecting time t9 (0V) and a lower base side. Further, the voltage data (1V, 5V, 10V for setting the maximum amplitude value is stored in the amplitude data memory 5b.
V) is memorized. Here, a control signal for data selection for the shape data memory 5a and the amplitude data memory 5b is given from the controller 9.

On the other hand, the RF pulse waveform generator 7 stores a shape data memory 7a in which waveform shape data serving as a reference of a sync function waveform is stored in advance, and amplitude data for setting a required maximum amplitude value of the RF pulse. The amplitude data memory 7b, the multiplier 7c for multiplying the shape data from the shape data memory 7a and the amplitude data from the amplitude data memory 7b, and the D / A conversion for converting the multiplication result by the multiplier 7c into an analog signal. 7d. The shape data memory 7a stores a plurality of RF pulse waveform shape data, and each of the plurality of RF pulse waveform shape data has a first inclined side (first side) composed of a line segment connecting a plurality of points, and a vertex. , A plurality of triangles having a second inclined side (second side) formed by a line segment connecting a plurality of points and a bottom side. That is, specifically, as an example, specifically, voltage data (0 V, 0.5 V, 1 V, 0.5) for the sink function waveform normalized with the maximum amplitude value is stored in the shape data memory 7a.
V, 0V) is stored. Figure 3 (a) shows one R
One triangle which is F pulse waveform shape data is shown. As shown in FIG. 3 (a), this triangle has a time t
1 (0V) to time t2 (0.5V) to time t3 (1V)
A first inclined side formed by a line segment connecting the lines, a vertex at time t3 (1V), time t3 (1V) to time t4 (0.5V)
A second inclined side formed by a line segment connecting time t5 (0 V),
Has a base and. Further, the voltage data (1V, 5V, 10V for setting the maximum amplitude value is stored in the amplitude data memory 7b.
V) is memorized. Here, a control signal for selecting data for the shape data memory 7a and the amplitude data memory 7b is given from the controller 9.

The operation of the present embodiment configured as above will be described.

For example, as a gradient magnetic field pulse waveform, the rise time is 1 ms
ec and trapezoidal waveform with maximum amplitude 5V and rise time 1ms
ec and a trapezoidal waveform with a maximum amplitude of 10V are required, and
An attempt is made to implement an excitation acquisition sequence that requires a sink function waveform with a maximum amplitude of 5V and a sink function waveform with a maximum amplitude of 10V as RF pulse waveforms. In this case, the controller 9 gives a control signal for selecting data to the gradient magnetic field pulse waveform generator 5 and the RF pulse waveform generator 7.

That is, the voltage data (0V, 0.5V, 1V, 1V, 1V, for the trapezoidal waveform, which is stored in the shape data memory 5a and is normalized by the maximum amplitude value shown in FIG.
1V, 1V, 0.5V, 0V), and voltage data 5V of the voltage data (1V, 5V, 10V) for setting the maximum amplitude value stored in the amplitude data memory 5b.
Is read out and each data is multiplied by the multiplier 5c.
When sequentially converted to an analog signal by the D / A converter 5d, a trapezoidal waveform having a rise time of 1 msec and a maximum amplitude of 5 V shown in FIG. 2B is obtained as a gradient magnetic field pulse waveform.

Voltage data (0V, 0.5V, 1V, 1V, 1V, 1 for the trapezoidal waveform stored in the shape data memory 5a and normalized by the maximum amplitude value shown in FIG.
V, 1V, 0.5V, 0V), and voltage data 10V of the voltage data (1V, 5V, 10V) for setting the maximum amplitude value stored in the amplitude data memory 5b.
Is read out and each data is multiplied by the multiplier 5c.
When sequentially converted into an analog signal by the D / A converter 5d, a trapezoidal waveform having a rise time of 1 msec and a maximum amplitude of 10 V shown in FIG. 2C is obtained as a gradient magnetic field pulse waveform.

On the other hand, voltage data (0V, 0.5V, 1V, 0.5V, for the sync function waveform, which is stored in the shape data memory 7a and normalized by the maximum amplitude value shown in FIG.
0V) is read out and the voltage data (1V, 5V, for storing the maximum amplitude value stored in the amplitude data memory 7b) is read.
Voltage data 5V out of 10V) is read out, and each data is multiplied by the multiplier 7c. When sequentially converted into an analog signal by the D / A converter 7d, a third RF pulse waveform is obtained.
The sink function waveform with the maximum amplitude of 5 V shown in FIG.

On the other hand, voltage data (0V, 0.5V, 1V, 0.5V, for the sync function waveform, which is stored in the shape data memory 7a and normalized by the maximum amplitude value shown in FIG.
0V) is read out and the voltage data (1V, 5V, for storing the maximum amplitude value stored in the amplitude data memory 7b) is read.
10V), the voltage data 10V is read out, and the multiplier 7c
Each data is multiplied by. Sequential D / A converter 7d
When converted into an analog signal by, a sink function waveform with a maximum amplitude of 10 V shown in FIG. 3C is obtained as an RF pulse waveform.

In the example described above, the trapezoid related to the gradient magnetic field pulse waveform in FIG. 2A has the time t2 on the first inclined side.
It has an intermediate part of (0.5 V) and an intermediate part of time t8 (0.5 V) on the second inclined side. Further, the triangle related to the RF pulse waveform in FIG. 3 (a) has an intermediate portion at time t2 (0.5 V) on its first inclined side,
The inclined side has an intermediate portion at time t4 (0.5 V). Since these gradient magnetic field pulse waveforms and RF pulse waveforms are represented by polygons including the first inclined side and the second inclined side having the intermediate portion, the polygon can be defined with high accuracy. Become. For example, when the sink function relating to the RF pulse waveform shown in FIG. 3 having the first peak and the second peaks on both sides is defined, the second peaks on both sides can also be defined with high accuracy, so that the slice characteristic is improved. Can contribute to.

The example described above requires a trapezoidal waveform with a rise time of 1 msec and a maximum amplitude of 5 V as a gradient magnetic field pulse waveform and a trapezoidal waveform with a rise time of 1 msec and a maximum amplitude of 10 V, and the RF pulse waveform with a maximum amplitude of 5 V. This is an example of a case where an excitation collection sequence that requires a sinc function waveform and a sinc function waveform with a maximum amplitude of 10 V is to be performed.
By preparing shape data and amplitude data to be stored in each memory according to the type of F pulse waveform, desired gradient magnetic field pulse waveform and RF pulse waveform can be immediately obtained only by simple data selection control.

In the above embodiment, the gradient magnetic field pulse waveform generator 5 is used to generate the gradient magnetic field pulse waveform and the RF pulse waveform.
Although the RF pulse waveform generator 7 and the RF pulse waveform generator 7 are provided, either one may adopt the conventional configuration. Further, the gradient magnetic field pulse waveform generator 5 and the RF pulse waveform generator 7 may be configured by one waveform generator.

Besides, various modifications can be made without departing from the scope of the present invention.

As described above, according to the present invention, the gradient magnetic field pulse based on the gradient magnetic field pulse waveform generated from the gradient magnetic field pulse waveform generator and the high frequency pulse waveform generator are applied to the subject placed in the static magnetic field. By applying a high frequency pulse based on a high frequency pulse waveform generated from the magnetic field, a magnetic resonance phenomenon is caused in a specific region of the subject, and a magnetic resonance signal is collected from the specific region to obtain diagnostic information. In the resonance imaging apparatus, at least one of the gradient magnetic field pulse waveform generation unit and the high frequency pulse waveform generation unit holds a plurality of shape data for defining at least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform. Shape data holding means, and at least the gradient magnetic field pulse waveform and the high frequency pulse waveform Amplitude data holding means for holding a plurality of amplitude data for defining one, by multiplying one of the plurality of shape data and one of the plurality of amplitude data, the gradient magnetic field pulse waveform and the high frequency pulse And a plurality of shape data held by the shape data holding means, wherein each of the plurality of shape data held by the shape data holding means has at least a first side and a plurality of first sides each including a line segment connecting a plurality of points. By defining a plurality of polygons including the second side formed by the line segment connecting the points, the combination of the shape data to be multiplied and the amplitude data makes it possible to obtain the rising characteristics and the strength ( Various amplitude characteristics can be easily obtained, and the high frequency pulse waveform has a constant amplitude ratio (amplitude). Characteristics it is possible to easily obtain those which are various forms.

Further, at least one of the gradient magnetic field pulse waveform shape data and the high frequency pulse waveform shape data is a polygon including a first side formed by a line segment connecting a plurality of points and a second side formed by a line segment connecting a plurality of points. The intermediate portion of each side of at least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform can be defined in detail, and at least one of the gradient magnetic field pulse waveform and the high frequency pulse can be controlled with high accuracy. . You will be able to get it. Moreover, at least one of the gradient magnetic field pulse waveform shape data and the high-frequency pulse waveform shape data is a polygon including a first side including a line segment connecting a plurality of points and a second side including a line segment connecting a plurality of points. The intermediate portion of each side of at least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform can be defined in detail, and at least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform can be controlled with high accuracy. It is possible.

Therefore, according to the present invention, the rising characteristic and the intensity (amplitude) characteristic must be set to various forms, and the intensity (amplitude) characteristic can be set to various forms under a gradient magnetic field pulse or a constant amplitude ratio. It is possible to provide a magnetic resonance imaging apparatus capable of easily controlling the waveform of a high frequency pulse that must be set with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a magnetic resonance imaging apparatus according to the present invention, FIG. 2 is a diagram for explaining generation of a gradient magnetic field in the embodiment, and FIG. 3 is an RF in the embodiment.
FIGS. 4 and 5 are diagrams for explaining the generation of pulses, FIGS. 4 and 5 are diagrams showing a configuration for generating a conventional gradient magnetic field, and FIG.
FIG. 7 is a diagram showing a configuration of an F pulse system, and FIG. 7 is a diagram showing a sync function waveform. 1 ... Static magnetic field magnet, 2 ... Gradient magnetic field coil, 3 ... Probe,
3A ... Transmitting coil, 3B ... Receiving coil, 4 ... Gradient magnetic field power source, 5 ... Gradient magnetic field pulse waveform generator, 6 ... RF amplifier,
7 ... RF pulse waveform generator, 8 ... Receiver, 9 ... Controller, 10 ... Computer, 11 ... Monitor.

Front page continuation (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 9118-2J G01N 24/08 L 8203-2G G01R 33/22 Y

Claims (1)

[Claims] 1. A gradient magnetic field pulse based on a gradient magnetic field pulse waveform generated from a gradient magnetic field pulse waveform generator and a high frequency pulse waveform generated from a high frequency pulse waveform generator for a subject placed in a static magnetic field. By applying a high-frequency pulse, a magnetic resonance phenomenon is caused in a specific region of the subject, and a magnetic resonance imaging apparatus configured to collect a magnetic resonance signal from the specific region to obtain diagnostic information, wherein the gradient magnetic field At least one of the pulse waveform generation unit and the high-frequency pulse waveform generation unit, shape data holding means for holding a plurality of shape data for defining at least one of the gradient magnetic field pulse waveform and the high-frequency pulse waveform, A plurality of gradient magnetic field pulse waveforms and a plurality of for defining at least one of the high frequency pulse waveforms Amplitude data holding means for holding width data, by multiplying one of the plurality of shape data and one of the plurality of amplitude data, one of at least one of the gradient magnetic field pulse waveform and the high frequency pulse waveform Each of the plurality of shape data held in the shape data holding means includes at least a first side formed of a line segment connecting a plurality of points and a line segment formed of a line segment connecting a plurality of points. A magnetic resonance imaging apparatus characterized by defining a plurality of polygons including two sides.