JP3516420B2 - Magnetic resonance imaging system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), and more particularly to a display technique for showing the relationship between the characteristics of an image obtained by imaging with an MRI apparatus and the imaging parameters. Is.

[0002]

2. Description of the Related Art An MRI apparatus uses a nuclear magnetic resonance phenomenon to image the inside of a subject. For imaging with an MRI apparatus, the subject is placed in a static magnetic field and RF is applied to the subject.
An NM generated from the inside of a subject by applying a pulse and a gradient magnetic field in two or three directions according to a predetermined pulse sequence.
Detect the R signal and image it. The factors that determine the quality of the obtained image include spatial resolution, contrast, and SN ratio, and images with good spatial resolution, contrast, and SN ratio are indispensable in medical diagnosis.

By the way, in the MRI apparatus, it is necessary to set various parameters for imaging prior to imaging.
Here, the factors that determine the image quality are referred to as image quality parameters, and various parameters that are determined prior to imaging are referred to as shooting parameters, but there is a deep relationship between them. The shooting parameter is, for example, F that represents the size of the field of view for imaging.
OV (abbreviation of Field of View), repetition time (TR) of pulse sequence that is repeatedly performed, time from excitation of nuclear spins at the inspection site to generation of NMR echo signal,
That is, the echo time (TE), the thickness of the cross section of the object to be imaged, that is, the slice thickness (Thickness), the number of NMR signals (Projection) required for one image configuration, and the NM of the same encoding.
The number of additions of the R signal (NSA) and the like are available.

The operator inputs the above-mentioned photographing parameters prior to photographing, but at the time of inputting, the image quality of the photographed image is set while imagining based on the conventional photographing experience. .

[0005]

Therefore, there has been a problem that an operator who has little experience in imaging spends a considerable amount of time in setting imaging parameters, resulting in a decrease in diagnostic efficiency. Further, as described above, the image quality parameter largely depends on the shooting parameter. However, when an attempt is made to change the shooting parameter, how the image quality parameter changes due to the change should be immediately understood by an unskilled person. It is difficult to understand, and it is not uncommon for the operator to notice the mistaken setting of the photographing parameter only after seeing the photographed image, and improvement thereof has been desired.

Therefore, the present invention has been made in view of the above problems, and a first object of the present invention is to display the relationship between the image quality parameter of an obtained image and the imaging parameter on a display device in an MRI apparatus. The purpose is to facilitate setting of shooting parameters by referring to the display. A second object of the present invention is to determine how the image quality parameters change when the imaging parameters are changed in the MRI apparatus.
The purpose is to notify the operator prior to imaging.

[0007]

In order to achieve the first object, the present invention stores shooting parameters necessary for shooting MR images and image quality parameters indicating image quality characteristics of MR images in a predetermined format. Storage means, display means for displaying the contents read from the storage means, input means for selectively inputting and designating at least any one of the image quality parameter or the photographing parameter displayed on the display means, A parameter related to the parameter designated by the input means is obtained, and identification information adding means for adding identification information to the output of the storage means is added to the MRI apparatus so that only the related parameters can be identified. It has a feature.

In order to achieve the second object of the present invention, the photographing parameter input means for inputting the setting of the parameter value necessary for photographing the MR image and the change of the setting value, the photographing parameter value and the MR Storage means for storing image quality parameters indicating image quality characteristics of the image in a predetermined format, display means for displaying the contents read from the storage means, and calculation software for the relationship between the shooting parameters and the image quality parameters are provided. The image quality parameter for the set shooting parameter and the image quality parameter for the changed shooting parameter are obtained, and the change state obtained by comparing the image quality parameter for the changed shooting parameter with that at the time of setting is obtained, and the change is made to the format in the storage means. A calculation means for outputting a signal for writing the state is added to the MRI apparatus. It is intended.

[0009]

According to the first aspect of the invention, the image quality parameter and the photographing parameter stored in the storage means in the predetermined format are read out and displayed on the display means.
When at least one of the image quality parameter or the photographing parameter is selectively designated by the input means while referring to the display screen, the identification information giving means is associated with the designated parameter in response to the input signal. Parameters are obtained, and identification information, for example, a luminance difference or a hue difference is added to the stored contents in the storage means so that only related parameters can be discriminated from other parameters. The contents of the storage means to which the identification information is added are read out and displayed on the display means. This allows the operator to easily understand the relationship between the parameters.

According to the second aspect of the present invention, the image quality parameter and the photographing parameter are stored in the storage means in a predetermined format, and when the photographing parameter is input and set from the photographing parameter input means, the format has the set value. The contents included are displayed on the display means. Here, when the photographing parameter is changed and inputted by the photographing parameter inputting means, the calculating means obtains the image quality parameter for the photographing parameter before the change and the image quality parameter for the changed photographing parameter by the calculation software, obtains the change state, and stores A signal for writing the changed state is output to the means. Therefore, the storage unit outputs the display signal in the format in which the changed state is written, and the display signal is displayed on the display unit. This allows the operator to know the change in the image quality due to the change in the shooting parameter before viewing the shot image.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 6 is a block diagram showing a schematic configuration of the entire MRI apparatus embodying the present invention. The RMI device shown in FIG. 6 is roughly classified into a central processing unit (CPU) 1, a sequencer 2, a transmission system 3, a static magnetic field generation magnet 4, a gradient magnetic field generation system 5, a reception system 6, and a signal. It comprises a processing / display system 7 and a console 8.

The CPU 1 is a keyboard 8 of the console 8.
The sequencer 2, the transmission system 3, the gradient magnetic field generation system 5, the reception system 6, and the signal processing / display system 7 are controlled in accordance with a measurement pulse sequence and an imaging parameter input from an input device such as 1. , A transmission system 3, a gradient magnetic field generation system 5, and a reception system, based on a control command from the CPU 1, various commands necessary for collecting measurement data for obtaining a tomographic image of the subject 100 in accordance with the pulse sequence and imaging parameters. 6 is output.

The transmission system 3 includes a synthesizer 31, a modulator 32, a high frequency amplifier 33, and an electromagnetic wave (R
The irradiation coil 34 for irradiating the F pulse) is provided, and the high frequency pulse output from the synthesizer 31 is amplitude-modulated by the modulator 32 according to a command from the sequencer 2, and the high-frequency amplifier 33 amplifies the amplitude-modulated high-frequency pulse. The electromagnetic wave is applied to the irradiation coil 34 to irradiate the subject 100 with electromagnetic waves.

The static magnetic field generating magnet 4 is for generating a uniform static magnetic field in a predetermined direction in a space for accommodating the subject 100, and a magnet of a superconducting type, a normal conducting type or a permanent magnet type is used. Can be done. The gradient magnetic field generation system 5 is composed of a gradient magnetic field power supply 51 and three sets of gradient magnetic field coils 52 connected to the gradient magnetic field power supply 51, and supplies a current to the gradient magnetic field power supply 51 from the gradient magnetic field power supply 51. By so doing, a gradient magnetic field is generated, whereby the static magnetic field and the gradient magnetic field are superposed to generate a gradient magnetic field. The three sets of gradient magnetic field coils are used in correspondence with the slice direction, the phase encoding direction, and the frequency encoding (reading) direction.

The receiving system 6 is an NM generated from the subject 100.
A receiving coil 61 that receives the R signal, an amplifier 62 that amplifies the output signal of the receiving coil 61, a quadrature phase detector 63 that quadrature detects the output signal of the amplifier 62 with a reference signal from the synthesizer 31, and the quadrature phase detector. And an A / D converter 64 for A / D converting the output signal of the device 63,
The detected NMR signal is Fourier-transformed by the signal processing / display system 7 so that the image can be reconstructed and output.

The signal processing / display system 7 includes a part of the CPU 1, an external storage device 70 such as a magnetic disk 71 and an optical disk 72, and a display 73 such as a CRT. Is displayed on the display 73 and stored in the external storage device 70.
The console 8 has a keyboard 81 and a mouse 82.
And an input device including various push button switches and a display.

Next, the relationship between the image quality parameter and the photographing parameter will be described. First, of the pulse sequences used in the MRI apparatus, the most representative pulse sequence of the spin echo method (SE method) will be described with reference to FIG. In the SE method, a high-frequency pulse (RF pulse) 101 having a frequency and a band corresponding to a slice position and a slice thickness (Thickness) is applied to a subject 100 placed in a static magnetic field while applying a slice-direction gradient magnetic field 201. Apply. R
The F pulse 101 is called a 90 ° RF pulse, and its application amount is an amount by which the nuclear spin in the subject is tilted by 90 ° with respect to the static magnetic field direction by the RF pulse. As a result, only nuclear spins within the set slice of the subject 100 are selectively excited.

Subsequent to this slice selection, a slice direction gradient magnetic field 202 is applied in order to align the phase of the selectively excited nuclear spins in the slice direction. The applied amount of the gradient magnetic field 202 is said to be equal to the applied amount of the gradient magnetic field 201a. Next, gradient magnetic fields 301 and 401 orthogonal to the slice direction are applied. The gradient magnetic field 301 is a gradient magnetic field applied in one of two directions orthogonal to each other in the slice plane. Since the gradient magnetic field 301 is applied for the purpose of giving a phase difference to the nuclear spins in that direction at the end of application, it is called a phase encoding gradient magnetic field. be called. This phase encoding gradient magnetic field 301
Is applied by changing the intensity stepwise according to the repetition of the pulse sequence. The number of steps corresponds to the number of pixels in the phase encoding direction. That is, in order to obtain an image of 256 pixels in the phase encoding direction, it is necessary to perform phase encoding in 256 steps. On the other hand, the gradient magnetic field 401 is a gradient magnetic field applied in a direction perpendicular to the phase encode direction in the slice plane, and a phase shift (Dephasi
ng) is applied. This gradient magnetic field 40
Since the direction in which 1 is applied is the read direction, it is also called a read direction gradient magnetic field or a frequency encode gradient magnetic field for identifying the read signal by frequency.

Following the application of the gradient magnetic field in these two directions, the slice direction gradient magnetic field 203 is applied again, and the RF pulse 102 is applied together with the application. RF pulse 10
2 further increases the nuclear spin in the slice excited by 90 ° by 18
Excitation (reversal) at 0 °. Then, following this 180 ° RF pulse 102, a read direction gradient magnetic field 402 is applied. The read direction gradient magnetic field 402 is applied with twice the amount of the normal gradient magnetic field 401, and the echo signal becomes maximum at the center thereof. Application of RF pulse 101 to gradient magnetic field 4
The elapsed time to the center of 02 is called the echo time TE.
In addition to the application of the read-out direction gradient magnetic field 402, in the receiving system shown in FIG. 6, the receiving coil 61 detects the NMR signal, and the A / D converter 64 samples the signal.
The number of pixels in the image reading direction corresponds to the number of signals sampled by the A / D converter.

After measuring the echo signal, 90 ° RF again
The pulse 103 is applied together with the slice direction gradient magnetic field 204. This is the second start of the pulse sequence. The application time interval between 101 and 103 of the 90 ° RF pulse is referred to as a pulse sequence repetition time TR. To obtain one image by the SE method, the pulse sequence is executed multiple times. The number of times of execution is related to the number of pixels in the phase encoding direction of the image and the SN ratio. Here, the SN ratio is related to the number of times,
This is because the SN ratio can be improved by averaging the signals obtained by the pulse sequences of the same phase encoding. Therefore, according to the addition of 2 times and the addition of 3 times, SN
The ratio improves, but with it, the number of times the pulse sequence is performed increases proportionally. Assuming that the average number of additions is NSA and the number of steps of phase encoding is N, the measurement time (Time) for obtaining one image is Time = TR.N.NSA (1).

Next, the structure of the apparatus for displaying the relationship between the image quality parameter and the photographing parameter according to the present invention will be described with reference to FIG. In FIG. 1, 11 is a measurement data memory for sequentially storing the output signal of the A / D converter 64 in FIG. 6, that is, the digitized NMR signal, and 12 is a microprocessor unit (hereinafter referred to as MPU and Note.)
Then, the software stored in the built-in memory performs a Fourier transform on the stored contents of the measurement data memory 11 and calculates image quality parameters and shooting parameters. 13 is an image memory, which stores the image data output from the MPU 12. What is to be stored, 14 is a graphic memory, and the ID of the subject is added to the image output from the image memory
And a memory for superimposing and displaying characters and numbers of photographing conditions and the like, 15 is an image synthesizing circuit for synthesizing images of the contents of the image memory 13 and the graphic memory 14,
Reference numeral 3 denotes a CRT display shown in FIG. 6, which displays the image by inputting the output of the image synthesizing circuit 15 into an analog signal by the D / A converter 74.

Reference numeral 8 denotes a console shown in FIG. 6, which is equipped with a keyboard 81 and a mouse 82 as well as various switches and indicators which are omitted in the drawing, and
A display switch 83 is provided for switching between a screen displayed on the display 73 as an image of a subject imaged or a screen showing the relationship between image quality parameters and imaging parameters.

Reference numeral 84 denotes a parameter display memory, which preferably comprises a plurality of frame memories, stores the relationship between the image quality parameter and the photographing parameter in a predetermined format, and reads the contents by an external input, In addition, it can be rewritten and read. In order to selectively supply / display the contents of the parameter display memory 84 to the display 73,
A changeover switch 85 is provided. The measurement data memory 11, MPU 12, image memory 13, and graphic memory 14 are components of the CPU 1 of FIG.

Next, FIG. 2 shows a display format showing the relationship between the image quality parameter and the photographing parameter stored in the parameter display memory 84. In FIG. 2, 81
0 is an image quality parameter, SN ratio (S / N) 811, contrast (Contrast) 812, spatial resolution (Resolution)
813. In the present embodiment, the time resolution is the spatial resolution of the resolution, which is not an image quality parameter, but the imaging time (Time) 814 which is deeply related to the imaging parameter is arranged in the same row as the image quality parameter. Each of the image quality parameters and the shooting time are displayed by letters of the alphabet and a circular display portion 811a on the left side of the display portion 811a.
814a.

On the right side of the display area of the image quality parameter 810, a display area of the photographing parameter 820 is provided. The imaging parameter 820 is the imaging field of view (FOV) 82.
1, pulse sequence repetition time (TR) 822, echo time (TE) 823, slice thickness (Thickness) 8
24, the number of projections (Projection) 825, and the number of signal additions (NSA) 826. The alphabetic character display and the circular display portions 821a to 826a on the left side of the alphabetic character display.
And numerical display parts 821b to 826b.
The above display format is stored in the parameter display memory 84 of FIG.

Next, a display related to the image quality parameter 810 and the shooting parameter 820 will be described. The operator turns on the power of the MRI apparatus, turns on the display changeover switch 83 of the console 8, and inputs the imaging region, the type of pulse sequence, and the like from the keyboard 81. Then, the display format shown in FIG. 2 including the input imaging region and standard imaging parameters 830 in the used pulse sequence is displayed on the display 73. The displayed standard parameters are supplied to the sequencer 2 via the MPU 12, and if measurement is started in this state, an image of the displayed shooting parameters can be obtained.

It is assumed that the operator is supposed to shoot an image prioritizing the SN ratio prior to shooting. In this case, the operator uses the mouse 82 to move the cursor to the S / N of the display screen.
Take to 811 and click. Then, as shown in FIG. 3A, the inside of the frame of the S / N 811 is displayed with a brightness difference or a hue added to the other portions, and displayed from 811a to 811a.
Similarly, the inside of all the circles on the left side of 16a are displayed as if the lamp were lit with a brightness difference or a hue from other parts.
This display is performed by inputting a signal from the mouse 82 to the MPU 12, processing by software installed in the MPU 12, and inputting the output to the parameter display memory 84. As a result, the SN ratio is (FOV) 821, (TR) 822, (TE) 823, (T
hickness) 824, (Projection) 825 and (NS
A) being related to all parameters of 826,
Recognized by the operator.

Next, it is assumed that the operator desires to give priority to the contrast of the image and photograph it. At this time, the operator uses the mouse 82 to select (Contrast) 812. Then, as shown in FIG. 3B, the inside of the frame of (Contrast) 812 and the inside of the circle on the left of (TR) 822 and (TE) 823 are displayed with a brightness difference or a hue with respect to other parts. It This allows the operator to see that the image contrast is related to the pulse sequence repetition time and the echo time.

Further, when the operator wants to know which photographing parameter the image resolution is related to, the mouse 82
(Resolution) 813 is selected. Then, FIG. 3 (c)
As shown in, inside the frame of (Resolution) 813 and (FO)
V) 821 and (Projection) 825 are displayed in the circle on the left with a brightness difference or hue. From this, it can be seen that the resolution of the image is related to the FOV and the number of projections.

In the above description, the image quality parameter is designated, and the photographing parameter related to the image quality parameter is displayed so that the operator can recognize it. On the contrary, each photographing parameter is related to which image quality parameter. If it can be displayed, it is more convenient for the operator. That is, although each shooting parameter can be arbitrarily set by the operator within the specifications of the apparatus, it is difficult for the operator to instantly determine which image quality parameter each shooting parameter relates to.
The embodiment described below takes account of this.

The format shown in FIG. 2 is the display 7
Until it is displayed in step 3, the procedure proceeds as in the above-described embodiment. Here, the operator selects (FOV) 8 from the standard photographing parameter value group 830 shown in FIG. 2 as an example.
If you try to set 21 again, the shooting parameter F
An OV that allows the display to know which of the image quality parameters is to be photographed will be described with reference to FIG.

The operator selects and specifies the photographing parameter (FOV) 821 by using the mouse 82 while looking at the display screen of FIG. The output signal of the mouse 82 is input to the parameter display memory 84 and the MPU 12.
Then, the MPU 12 obtains the image quality parameter related to the FOV of the shooting parameter from the built-in software based on the input signal, and (S / N) 811 and (Resolution)
A signal for distinguishing the portion within the circle on the left of 813, that is, 811a and 813a from other portions by the difference in luminance or the hue is output. Similarly, a luminance difference or a hue is given to the inside of the frame of (FOV) 821. As a result, the format of FIG. 4 is displayed on the screen of the display 73.

In the above example, the display of the image quality parameter with respect to the shooting parameter of the FOV has been explained, but the same display is possible with other shooting parameters, and (S / N) with respect to (TR). And (Contrast) and (Time), which is not an image quality parameter, but for (TE), (S / N) and (Cont
rast), (S / N) for (Thickness), and (Rr
(S / N) and (Resolution) and (Time) for ojection, and (S / N) and (Time) for (NSA).
Are displayed in association with each other. These associations can be performed by software installed in the MPU 12.

As described above, since it is possible to display the relation between the image quality parameter and the photographing parameter, it is apparent that the convenience for the operator is improved as compared with the conventional apparatus. However, it is not clear from the above embodiment what happens to the image quality when the shooting parameters are changed with respect to the set values. Therefore, an example of displaying how the image quality changes when the shooting parameter is changed will be described below.

FIG. 5 shows a parameter display format in this embodiment. In the upper part of FIG. 5, an image quality parameter item display unit 810 and a bar graph display unit qualitatively showing its height are shown.
40 shows an image quality parameter display format consisting of 40 and a shooting parameter display format in which a bar graph display section 850 of shooting parameters is added to the shooting parameter display formats 820 and 830 similar to those in the above embodiment. The device configuration for displaying these formats is similar to that of the above-described embodiment, and the parameter display memory 84, MPU 12, and software are the main components.

Next, the operation and display operation of this embodiment will be described. The operator turns on the power of the MRI apparatus, turns on the display changeover switch 83 of the console 8, and inputs the imaging region, the type of pulse sequence, and the like from the keyboard 81. Then, the format shown in FIG. 5 is read from the parameter display memory 84 and displayed on the display 73. At this time, for each of the imaging parameters, standard numerical values for the set imaging region and pulse sequence type are displayed. These displayed shooting parameters are not only displayed but also set in the device so that the actual shooting can be started.

Each bar graph (81
1c to 814c) has a partition line 815 at the center thereof. The partition line 815 indicates the image quality level according to the initially set shooting parameter. Therefore, for the default shooting parameters, the bar graphs are shown in the partition lines. As this display mode, the partition line 81
5 may be displayed with a certain thickness, or a bar-shaped object having a certain length centered on the partition line 815 may be displayed.

On the other hand, a bar graph 8 in the photographing parameter display section
Reference numeral 50 indicates a settable range of each imaging parameter due to restrictions from the specifications of the MRI apparatus, for example, (FOV) 8
FOV of 5 is 50 and 300 in the bar graph 821c of 21.
It is shown that it can be set in the range of 0 × 50 (mm) to 300 × 300 (mm), and the initial setting value 250 indicates that it is within that range.

Next, in order to change the image quality parameter,
A case when the shooting parameter is operated will be described. When the operator wants to obtain an image having a spatial resolution better than the initial setting value, first, the mouse 82 of the console 8 is operated to select and specify (Resolution) 813 on the screen. Then, as shown in FIG. 5, the inside of the circle on the left of (FOV) 821 and (Projection) 825 of the photographing parameter display unit 820 is displayed with the brightness difference or hue given to the other portions.

The spatial resolution R is the phase direction resolution R _p ,
It is represented by the resolution in the frequency direction R _f and the resolution in the slice direction R _s, and in the calculation formula, it is expressed as R = R _p · R _f · R _s (2), and these are R _p = Projection / FOV (3) R _f = Sample / FOV (4) R _s = k / Thickness (5) Here, Sample can be expressed as the number of samples.

Therefore, the MPU 12 calculates the spatial resolution R using the equations (2), (3), (4), and (5) for the initial setting values of the imaging parameters, and holds the value. There is. From this state, the operator changes the spatial resolution,
Each data of (FOV), (Projection), (Thickness) is input using the keyboard 81 and the mouse 82 with reference to the settable range on the right. As an example, (FOV) is 200 (mm) and (Projection) is 25
It is assumed that 3 (mm) is input for (Thickness) while keeping 6.
It is assumed that the number of samplings is a device-specific setting value and does not change. These set values are updated and displayed on the display screen and input to the CPU 1. And MP of CPU1
In U12, the spatial resolution R is calculated based on the calculation formulas (2) to (5). In this case, the spatial resolution R is improved by (250/200) ² × (5/3) from the initial setting value. The MPU 12 compares the calculated result with the held value, and the MPU 12 rewrites the bar graph 813c corresponding to (Resolution) in the parameter display memory 84 so that the bar graph 813c is stretched to the right and displayed. The contents of the rewritten parameter display memory 84 are read out and displayed on the display 73 as shown in FIG.

Next, the case of contrast will be described. The contrast is equal to TR and T as described in the above embodiment.
Related to E. This is explained as follows. The image contrast C is C∝ [S ₁ −S ₂ ] / [S ₁ + S ₂ ] ... (6) where S ₁ : signal intensity of tissue 1 S ₂ : signal intensity of tissue 2 []: by absolute value symbol Represented. Further, again, S ₁ ∝Sd ₁ · P _X · P _Y · P _Z ··· (7) S ₂ ∝Sd ₂ · P _X · P _Y · P _Z ··· (8) where Sd ₁ : tissue 1 by pulse sequence Signal Sd ₂ : signal of tissue 2 by pulse sequence P _X : X direction pixel size P _Y : Y direction pixel size P _Z : Z direction pixel size. Furthermore, if the pulse sequence is the SE method, Sd ₁ and Sd ₂ can be expressed as follows. Sd ₁ ∝ρ ₁ · exp (-TE / T ₂₁ ) ・ [1-exp (-TR / T ₁₁ )] (9) Sd ₂ ∝ρ ₂・ exp (-TE / T ₂₂ ) ・ [1-exp (-TR / T _12)] ... (10) here, [rho _1: organization 1 proton density [rho _2: tissue 2 of proton density T _11: organization 1 longitudinal relaxation time T _12: longitudinal relaxation time of the tissue 2 T ₂₁ : Transverse relaxation time of organization 1 T ₂₂ : Transverse relaxation time of organization 2

Therefore, the proton density ρ of the tissue, the longitudinal relaxation time T ₁ of the tissue, and the transverse relaxation time T ₂ of the tissue are measured and stored in advance for typical tissues of the living body, such as muscle and fat. Therefore, Sd ₁ and Sd ₂ corresponding to the input TR and TE are estimated, and S ₁ and S ₂ are estimated, and whether or not the contrast is increased by changing TR and TE according to the equation (6). Can be calculated by the MPU 12. Based on this result, the MPU 12 rewrites the bar graph in the parameter display memory 84, and the rewritten contents are displayed on the display 73.

Furthermore, in the case of the SN ratio, the following display is made. The SN ratio is as described in the above-mentioned embodiment,
(FOV), (TR), (TE), (Thickness), (Projecti
on), (NSA). This can be explained as follows. That is, firstly, the S / N ratio is S / N ratio ∝S ... (11), where S is the signal strength, and S is S∝Sd · P _X · P _Y · P _Z … (12). here, Sd: a signal of a tissue by the pulse sequence P _X: X-direction pixel size P _Y: Y-direction pixel size P _Z: represented by Z-direction pixel size. If the pixel size in the X, Y, and Z directions is X
Direction is slice direction, Y direction is phase encode direction, Z
When the direction is the frequency encoding direction, P _X ∝Thickness (13) P _Y ∝FOV / Projection (14) P _Z ∝FOV / Sample (15) If the pulse sequence is the SE method,
Similarly to the expressions (9) and (10), Sd∝ρ · exp (−TE / T ₂ ) · [1-exp (−TR / T ₁ )] (16) where ρ: Proton density T _It is expressed as ₁ : longitudinal relaxation time T ₂ : lateral relaxation time TR: repetition time TE: echo time. Further, as explained before, the SN ratio is ∝NSA (17).

Therefore, whether or not the SN ratio when only the desired photographic parameters are input and changed is higher than the SN ratio for the photographic parameter group having the initial setting value is determined as described above.
The determination can be performed using the calculation formula related to the changed parameter in (11) to (17). This calculation and display method can also be performed in the same manner as the above-mentioned spatial resolution and contrast.

The parameter display format of FIG.
The number of slices 827, which is not in the example shown in FIG. 3, and an imaging time [Time] 814 that cannot be called an image quality parameter are also included. This shooting time also becomes longer or shorter depending on the shooting parameters. This is also clear from the equation (1). In the present embodiment, when a shooting parameter that determines the image quality and is related to shooting time is changed,
According to the equation (1), the MPU 12 calculates whether the shooting time is longer or shorter than that before the change, and the bar graph is displayed. Since it is clear that this calculation and display method can be performed in the same manner as the above-mentioned method, detailed description will be omitted.

The present invention has been described above based on the embodiments, but the present invention can be variously modified without departing from the scope of the invention. For example, in the embodiment shown in FIG. 5, the change state of the image quality parameter with respect to the changed photographing parameter may be displayed numerically, for example, quantitatively such as percentage display, instead of qualitatively like the bar graph. It is possible. Further, in the case where a single subject is repeatedly photographed with the photographing parameters changed, the change state of the image quality parameters regarding the photographing parameters after the change from the initial setting is displayed for a predetermined time and changed after the predetermined time. The following parameters may be regarded as initial settings, and a bar graph of image quality parameters may be displayed on the partition line portion so as to be prepared for the next change of shooting parameters.

In the present embodiment, the FOV, TR, TE, the slice thickness, the number of projections, the number of signal additions, and the like have been described as the imaging parameters, but the imaging parameters may be related to image quality other than these. However, it is possible to add more. Further, as the calculation formula for estimating the relationship between the image quality parameter and the photographing parameter, it is possible to use other formulas than those shown in (2) to (17).

[0049]

As described above, according to the present invention, when the image quality parameter and the photographing parameter are displayed on the display in a predetermined format and a certain parameter is selected and designated, the parameter related to the designated parameter can be identified. Is displayed on the screen, the operator can easily set the parameters. Further, the image quality parameter and the shooting parameter are displayed on the display in a predetermined format, and when the shooting parameter is changed, it is possible to display how the image quality parameter is changed by the change. It is possible to grasp the change in the image quality of the image to be picked up even without looking at it.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration related to parameter display according to an embodiment of the present invention.

FIG. 2 is a diagram showing a display format of a first embodiment of the parameter display method of the present invention.

FIG. 3 is a diagram showing a screen during operation of the display format shown in FIG.

FIG. 4 is a diagram showing a screen during operation in the opposite mode of the display shown in FIG.

FIG. 5 is a diagram showing a display format and a screen during operation of a second embodiment of the parameter display method of the present invention.

FIG. 6 is a block diagram showing a schematic configuration of an MRI apparatus.

FIG. 7 is an SE method pulse sequence diagram used in the MRI apparatus.

[Explanation of symbols]

8 consoles 12 MPU 73 display 81 keyboard 82 mice 83 Display changeover switch 84 Parameter display memory

Continuation of front page (56) References JP-A-3-37044 (JP, A) JP-A-6-90926 (JP, A) JP-A-5-176911 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) A61B 5/055

Claims (2)

(57) [Claims] 1. Storage means for storing a shooting parameter necessary for shooting an MR image and an image quality parameter indicating an image quality characteristic of the MR image in a predetermined format, and a display means for displaying the contents read from the storage means. An input means for selectively designating and inputting at least any one of the image quality parameter or the photographing parameter displayed on the display means, and the parameter related to the parameter designated by the input means, and the related parameter A magnetic resonance imaging apparatus, comprising: identification information giving means for giving identification information to the contents of the storage means so that only one another can be identified. 2. A photographing parameter input means for inputting setting of a parameter value necessary for photographing an MR image and a change of the setting value, and the photographing parameter value and an image quality parameter indicating an image quality characteristic of the MR image in a predetermined format. Storage means for storing, display means for displaying the contents read from the storage means, calculation software for the relationship between the shooting parameter and the image quality parameter, and the image quality parameter for the set shooting parameter and the shooting parameter after change And an image quality parameter for the changed shooting parameter, a change state obtained by comparing the image quality parameter for the changed shooting parameter with a setting time, and a signal for writing the change state in the format in the storage means. And a magnetic resonance imaging apparatus.