JPH09187436A - Three-dimensional blood flow velocity image projection method in magnetic resonance diagnosing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a projection method which obtains a flow velocity image with limited error by using three-dimensional data acquired by employing a multiple phase sensitivity measuring method in a magnetic resonance diagnosing apparatus. SOLUTION: A three-dimensional data with multiple phase sensitivities is measured by a multiple phase sensitivity measuring method using a magnetic resonance diagnosing apparatus. Angio images 102 of slides are formed by using a complex difference to accomplish a maximum projection with respect to the visual axis of projection 101. In the maximum projection, the position 105 of a point at which the maximum value is reached in the direction of the visual axis is detected and a flow velocity at the maximum point is calculated to obtain a flow velocity projection image 106. A calculation of the flow velocity is performed by evaluating the phase of each phase sensitivity image and a correct flow velocity can be obtained. But it has the shortcoming that the error of a noise part is substantial. As the angio images 102 have a low value at the noise part, a blood vessel can be recognized stably. Thus, the position of a blood vessel part is recognized by the angio images 102 to evaluate the phase thereby reducing errors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional blood flow velocity image projection method for obtaining a blood flow velocity image in a magnetic resonance diagnostic apparatus.

[0002]

2. Description of the Related Art Conventionally, the following documents describe a blood vessel imaging method. (1) CLDumoulin, SPSouza, MFWalker, and W.Wa
gle, "Three-DimensionalPhase Contrast Angiography",
Magnetic Resonance in Medicine, Vol.9, pp.139-149
(1989). (2) Y.Machida, N.Ichinose, H.Sugimoto, T.Goro, a
nd J. Hatta, "DualVelocity Sensitive Tetrahedral Flo
w Encoding MR Angiography ", Proceedings of Society
of Magnetic Resonance in Medicine, eleventhAnnual
Scientific Meeting, p2810 (1992). (3) MFWalker, SPSouza, and CLDumoulin, "Qu
antitative FlowMeasurement in Phase Contrast MR An
giography ", Journal of ComputerAssisted Tomography,
vol.12, no.2, pp304-313 (1988). The above prior art (1) uses one set of flow encode pulses having different polarities in the three axis directions, and the total is 6
Acquire signals corresponding to three-dimensional flow velocity in three directions by measuring types 6
The method of measuring the phase sensitivity is described. Obtained 6
Based on the measurement signals of the types, the difference between the measurement signals forming a pair is calculated to create three types of signals including flow velocity information in the x, y, and z3 directions, and the images are reconstructed by the two-dimensional Fourier transform method. , Three types of three-dimensional image data reflecting the flow velocity in each direction are created, and three-dimensional angio data (angiography data) reflecting the magnitude of the flow velocity is obtained based on these three types of three-dimensional image data. The three-dimensional angio data is used for observing the image of each slice and performing projection processing to create a projection image. There are various projection methods, such as integrated projection and maximum intensity projection (ma).
ximum pixel project, in general, the Maximum Intensity project
Ction (MIP)) and the like.

Incidentally, FIG. In 2,
Although only three types of signal data with flow velocity sensitivity are described, in reality signal data with flow velocity sensitivity in one direction is signal data obtained by applying a (+) flow encode pulse in that direction. It is created as a difference signal of the signal data obtained by applying the flow encode pulse of (-). Therefore, in view of the method of applying the flow encode pulse in the above-mentioned document (1), a total of 6 types of signal measurement are performed in 2 ways and 3 axes in order to obtain the velocity sensitivity signal data of 1 axis, and 6 times of phase measurement. We call it sensitivity measurement method. Next, the above-mentioned related art (2) describes a four-time phase sensitivity measuring method in which four types of flow encode pulse patterns are measured, images are reconstructed, and then a value approximately proportional to the flow velocity is calculated. . It is shown that three-dimensional angio data reflecting the magnitude of the flow velocity can be obtained even with the four phase sensitivity measurements, as in the six times measurement method in (1) above. The related art (3) reconstructs images of a plurality of measurement data with different flow encode pulse patterns,
The method of obtaining the flow velocity using the phase information is described. For a flow with a constant velocity and no velocity distribution in the cross section,
The flow velocity can be accurately obtained using the phase information. A detailed analysis has also been conducted for the case where there is a flow velocity distribution in the cross section, and a correction formula for obtaining the average flow velocity has been derived. In addition, an analysis has been made for unsteady flow with a non-constant velocity.

[0004]

The above prior art (1)
Describes a method of maximally projecting three-dimensional angio data obtained by taking a complex difference between data when the flow encode is positive and data when the flow encode is negative to form an angio image. If three-dimensional flow velocity data that is well proportional to the flow velocity is created using the phase described in the above-mentioned conventional technique (3) and maximum value projection is performed as in the above-mentioned conventional technique (1), two problems will occur. The first problem is that the result becomes unstable when using the phase. That is, in the area where the noise value is larger than the object value on the image, data having almost random phase values different from the original due to the effect of noise and completely devoid of the meaning of flow velocity can be obtained. Therefore,
A commonly used method is to set a threshold value and regard a pixel having a value equal to or less than the threshold value as having no object and having a phase of 0. However, even if the method using the threshold value is used, the two-dimensional flow velocity image can be easily seen, and unless the threshold value is carefully set for each image, a large error point is scattered. When the maximum intensity projection of the three-dimensional data is performed in that state, a point with a large error is recognized as the maximum value, so the instability of the flow velocity image after projection is extremely large.
Even with pixels that should originally display the blood flow velocity of the blood vessel, bad luck may cause an erroneous display of almost random values due to the influence of noise.

A second problem is that when the phase is evaluated to obtain the flow velocity, not only the magnitude of the flow velocity but also the flow velocity direction is desired to be obtained, so that the flow velocity image in the X-axis direction and the flow velocity image in the Y-axis direction are obtained. , When the flow velocity image in the Z-axis direction is obtained and the flow velocity image in each axis direction is projected, the flow velocity direction has a positive value or a negative value. There is a problem that blood vessels cannot be correctly recognized. A method of projecting one with a large absolute value in consideration of the absolute values of the maximum value and the minimum value is also possible, but there is no guarantee that points at the same position on each axis will be projected as a point with a large absolute value, There is a problem that points with errors appear in some places. The above-mentioned conventional technique (2) describes a method for obtaining imaging data reflecting the flow velocity similarly to the above-mentioned conventional technique (1). However, when the phase is evaluated to obtain the flow velocity image, the same is true. The above two problems appear. Therefore, an object of the present invention is to solve the above two problems, accurately recognize the position of a blood vessel, evaluate the phase, and obtain a projection image of a flow velocity with little error in a three-dimensional magnetic resonance diagnostic apparatus. It is to provide a blood flow velocity image projection method.

[0006]

In order to achieve the above object, in the three-dimensional blood flow velocity image projection method in the magnetic resonance diagnostic apparatus of the present invention, projection processing is performed by the following method. That is, in the case of the six-time phase sensitivity measurement method described in the above-mentioned related art (1), first, the complex difference described in the above-mentioned related art (1) is performed to create three-dimensional angio data which is image-reconstructed. In addition, the position of the point having the maximum value by projecting the above-mentioned three-dimensional angio data from the desired projection line of sight is stored for each projection line of sight, and finally, regarding the position of each point having the maximum value, As described in the prior art (3), the phase was evaluated, the flow velocity value was calculated, and the flow velocity image was obtained. In the case of the four-time phase sensitivity measurement method described in the above-mentioned related art (2), similarly, the calculation applying the complex difference as described in the above-mentioned related art (2) is performed to create the three-dimensional angio data to obtain the maximum value. The flow velocity image was obtained by projecting and evaluating the phase at the position of the maximum point.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An operation is performed based on a complex difference as described in the above-mentioned prior art (1) and the above-mentioned prior art (2),
The three-dimensional image data obtained by image reconstruction has a large value in a region where the blood flow is fast, and a small value such as a noise level in a region without flow. In particular, there is no object and only the noise area has a small value of about the noise level. When the maximum value projection is performed, a region where the blood flow is fast is stably depicted. Therefore, the three-dimensional image data in which the blood flow portion has a large value and the noise portion is stable to the noise level by using the complex difference in this manner is referred to as three-dimensional angio data here. Three-dimensional angio data has the advantage that a stable blood vessel image can be obtained by maximum intensity projection, but on the other hand,
It only has a value that is approximately proportional to the flow velocity, and has the drawback that there are too many errors for quantitative evaluation of the flow velocity. In the case of the method of evaluating the phase to obtain the flow velocity as described in the above-mentioned conventional technique (3), there is an advantage that in a region where an object exists, a value that can withstand quantitative evaluation well proportional to the flow velocity is obtained, and there is no object. In the noise region, the phase becomes random due to the effect of noise, and the error of the flow velocity value is large.
In order to overcome the drawback, even if a threshold value is introduced, the result becomes unstable at the boundary between the part with the object and the part without the object, and it is difficult to set the threshold value. In particular, in the case of projecting three-dimensional data, the instability of the boundary has a great influence on the image after projection, and there remains a drawback that the error of the flow velocity value is large. It should be noted that obtaining the flow velocity by evaluating the phase is simply referred to as flow velocity calculation here, and the three-dimensional data thus obtained is referred to as three-dimensional flow velocity data. The flow velocity data includes data that simply indicates the magnitude of the flow velocity, but in order to express the direction of the flow velocity, flow velocity data in the X axis direction, flow velocity data in the Y axis direction, flow velocity data in the Z axis direction, etc. There is also azimuth angle data such as the Euler angle indicating the direction of. Here, they are collectively referred to as flow velocity data. As described above, the flow velocity data has an advantage of having a value that is well proportional to the flow velocity, but has a drawback that the value of a portion without an object is unstable. In addition, since the three-dimensional flow velocity data representing the direction of the flow velocity has a sign, it has a feature that a blood vessel cannot be recognized only by performing maximum value projection.

In the present invention, the blood vessel can be stably recognized by storing the position where the maximum value is projected by using the three-dimensional angio data capable of stably obtaining the blood vessel image and the maximum value is stored. It is possible to solve the two problems described in the above-mentioned problem section. That is, when the conventional maximum intensity projection method is applied to the three-dimensional flow velocity data simply representing the magnitude of the flow velocity, the phase of the noise part other than the blood vessel part is affected by noise and the incorrect flow velocity is evaluated. Although there was a portion for obtaining the value, in the present invention, the position of the blood vessel is stably recognized, and the flow velocity at that position is calculated using the phase, so that the correct flow velocity of the blood vessel portion can be evaluated, and the above two problems Especially the former of the points can be eliminated. Further, in the present invention, since the position of the blood vessel is recognized and the flow velocity at that position is calculated using the phase, since there is a sign even when handling three-dimensional flow velocity data having a sign representing the direction of the flow velocity, there is a sign. The latter of the two problems that have appeared can be solved.

Embodiments of the present invention will be described below in detail with reference to the drawings. The present invention is an invention relating to a means for obtaining a projection image corresponding to a flow velocity after imaging using a multiple flow velocity sensitivity method capable of obtaining three-dimensional data according to a flow velocity using a magnetic resonance diagnostic apparatus, and in particular, The invention is characterized by a projection method. The embodiment will be described by dividing it into sections (1) to (4). In section (1), the configuration of the magnetic resonance diagnostic apparatus embodying the present invention will be described. In section (2), the operation procedure of one embodiment of the present invention will be described in detail with respect to the projection method which is a feature of the present invention. In section (3), various flow velocity sensitivity measurement methods, which are methods of capturing data to be processed by the projection method of the present invention, will be described, and a specific flow velocity sensitivity measurement method will be described with reference to data processed by the projection method of the present invention. A method of creating certain three-dimensional angio data and a method of evaluating the phase and calculating the flow velocity will be described. Finally, in section (4), an application method in the case where it is desired to use asymmetric measurement in the multiple flow velocity sensitivity measurement method used in the present invention to improve image quality will be described.

(1) Configuration FIG. 2 is a block diagram of a magnetic resonance diagnostic apparatus to which the present invention is applied. The magnetic resonance diagnostic apparatus of FIG. 2 includes a static magnetic field generator 202, a gradient magnetic field generator 203, a high frequency magnetic field generator 204, a receiver 205, and a sequence controller 2.
06, a processing device 207, and a display device 208. The static magnetic field generator 202 generates a strong and uniform magnetic field to generate magnetization in the inspection object 201. The gradient magnetic field generator 203 has gradient magnetic field generators in the x, y, and z3 directions and can operate independently of each other. By setting the application timing and the applied intensity of the gradient magnetic field in each of the above directions, an arbitrary strength can be obtained at any time. Can generate a gradient magnetic field having a direction. When a gradient magnetic field is applied, the magnetic field strength changes according to the position in the direction of the gradient magnetic field, and the Larmor frequency of the magnetization of the inspection object 201 changes accordingly, and the inspection object 201 can be distinguished in position. The high-frequency magnetic field generator 204 is capable of generating a desired high-frequency magnetic field and, if necessary, resonantly excites the magnetization of the inspection object 201 to emit only electromagnetic waves satisfying the resonance condition. By combining the gradient magnetic field and the high frequency magnetic field, electromagnetic waves can be generated only from the slice area satisfying the resonance condition, and the slice area can be imaged. Receiver 205
Measures the electromagnetic wave generated by the resonance excitation of the magnetization of the inspection object 201, and passes it to the processing device 207 as signal data. The processing device 207 stores the signal data or reconstructs the image of the signal data to create image data. Display device 2
08 displays the image data. Sequence control device 2
Reference numeral 06 denotes a gradient magnetic field generating device 203, a high frequency magnetic field generating device 204, a receiving device 205, a processing device 207, and a display device 2.
08 operation control is performed. Sequence control device 206
Has a function of an ordinary computer, and has a program for sending a command to operate each device, and data describing an operation state of each device referred to by the program. Further, the processing device 20
7 consists of dedicated hardware that performs calculations at high speed,
The calculation of data processing is performed by creating and executing a program described in a programming language specific to the dedicated hardware. The processing device 207 can use an ordinary computer because of its function.

(2) Procedure The operation procedure of the present invention will be described with reference to step numbers in FIG. FIG. 4 is an operation flowchart of a three-dimensional blood flow velocity image projection method showing an embodiment of the present invention. Step 40
In 1, the three-dimensional data measurement is performed using the multiple flow velocity sensitivity measurement method. Three-dimensional data with multiple flow velocity sensitivities can be obtained. A specific measuring method will be described later in section (3). In step 402, three-dimensional angio data is created based on the three-dimensional data having a plurality of flow velocity sensitivities obtained in step 401. Three-dimensional angio data is
The two-dimensional angio image having a thin slice thickness is data obtained continuously for a plurality of slices.
How to create three-dimensional angio data depends on a specific measurement method, and will be described in detail later in section (3). In step 403, maximum intensity projection from a desired projection line of sight is performed using the three-dimensional angio data obtained in step 402. The maximum intensity projection is a method in which the value of the point having the largest value on each projection line of sight is used as the projection data of that projection line of sight. Here, not only the maximum value on each projection line of sight is found, but also the position of the point having the maximum value is stored. By step 403, two-dimensional position storage data in which the position of the maximum value is stored for each projection line of sight is obtained. In step 404, with reference to the two-dimensional position storage data stored in step 403, the flow velocity is obtained at the position of the point having the maximum value on the projection line of sight of interest, and a flow velocity image is obtained as the flow velocity value of the projection line of sight. . The method of calculating the flow velocity depends on the specific measurement method, and will be described later in section (3).

The operation procedure of one embodiment of the present invention has been described above. However, the present invention has various other implementation procedures. For example, in the above implementation procedure, in step 403, two-dimensional position data storing the position of the maximum point for each projection line of sight is created and stored, and then in step 404, the two-dimensional position data is referred to. The flow velocity value at that point was obtained, but this step 404 was abolished, and at step 403,
When performing maximum intensity projection for each projection line of sight, prepare a storage buffer to detect not only the maximum value but also the position of the point that is the maximum value on that line of sight, compare the maximum values, and project the maximum value. It is also possible to obtain the flow velocity image by repeating the calculation of the flow velocity at the position of the point having the maximum value obtained after the maximum value projection of the projection line of sight is finished for each projection line of sight. In addition, a flow velocity image can be obtained even if the flow velocity value is stored without determining the position detection storage buffer and determining the flow velocity at each point when large data appears when comparing the maximum values. Also, for example, in step 4 above.
In 04, the flow velocity calculation of the corresponding position is performed for the first time here. In step 402, the flow velocity calculation is performed on all the three-dimensional data points to create the three-dimensional flow velocity data, and in step 404, the flow velocity of the corresponding position is calculated. The flow velocity image can also be obtained by referring to the flow velocity value of the three-dimensional flow velocity data.

Further, although the three-dimensional angio data was created in the above step 402, the three-dimensional complex data corresponding to each phase sensitivity when each phase sensitivity measurement was performed before that,
3D angio data is created based on it, and step 4
At 04, the phase of the corresponding position of the three-dimensional complex data can be evaluated to obtain a flow velocity image. Similarly, three-dimensional complex data corresponding to each phase sensitivity at the time of performing each phase sensitivity measurement in step 402 is created, three-dimensional angio data is created based on the three-dimensional complex data, and the three-dimensional complex data is used. It is also possible to create three-dimensional flow velocity data and refer to the flow velocity at the corresponding position of the above three-dimensional flow velocity data in step 404 to obtain a flow velocity image. Note that how to create three-dimensional complex data corresponding to each phase sensitivity will be described later in section (3). In addition to the above, various concrete procedures according to the concept of stably recognizing a blood vessel position using three-dimensional angio data and calculating a flow velocity at that position, which is the most characteristic of the present invention, are possible.
For example, x, y, and
3D complex data reflecting the velocity information in the z3 direction is created, 3D angio data is created from the 3D complex data, and 3D velocity data approximately proportional to the velocity is obtained from the 3D complex data. You can also do it.

In order to clearly show the concept of the projection method, which is the most characteristic of the present invention, the concept that is the characteristic of the present invention will be described with reference to FIGS. 1 and 5, and the conventional extension method will be illustrated in FIG. Thus, the difference in technical idea from the present invention will be clarified. FIG.
FIG. 5 is an explanatory view of a projection method which is a feature of the present invention, FIG. 5 is a view explaining that the flow velocity has a direction in the projection method of FIG. 1, and FIG. 3 is a view showing an example of a conventional projection method. Is. Angio image 102 of each slice shown in FIG.
Is the three-dimensional angio data obtained in the above step 402, and the two-dimensional angio image having a thin slice thickness is continuously plural slices. Projected line of sight 101
Is a representative of one of the projection lines of sight having a desired projection direction, and the maximum-value projection process determines the value of the point having the largest value among the points on this projection line of sight. This is a process of creating an angio maximum intensity projection image 103 as a projection value. In the present invention, not only the maximum value is obtained at the time of maximum value projection, but also the point 104 having the maximum value on the projection line of sight.
Is obtained, and the flow velocity calculation 105 at the maximum point is performed to obtain a flow velocity projected image 106. FIG.
In FIG. 5, the idea that the flow velocity includes the direction is not well illustrated, but in FIG. 5, the flow velocity calculation 505 for each direction is performed, and the X-direction flow velocity projected image 506 and the Y-direction flow velocity projected image 5 are calculated.
07, the Z-direction flow velocity projected image 508 is illustrated so as to be obtained, and a specific example of the idea that the flow velocity has a direction is shown. FIG. 3 shows the conventional extension method, but the symmetry of the maximum intensity projection is as shown in FIG. 1 for the angio image 1 of each slice.
No. 02, but the flow velocity image 302 of each slice, that is, the three-dimensional flow velocity data is a big difference. In the extension of the conventional method, the flow velocity maximum intensity projection image 303 is obtained by evaluating the magnitude of the flow velocity and performing the maximum intensity projection. On the other hand, in the present invention, the angio image 10 of each slice is used.
A major feature is that the blood vessel position is stably recognized using two-dimensional or three-dimensional angio data.

(3) Phase sensitivity measuring method and angio
Velocity Calculation Method First, a general explanation of the phase sensitivity measurement method is given in Section (3-1), and then as a specific example of the phase sensitivity measurement method, (3-
Section 2) describes 6 times phase sensitivity measurement method, how to make 3D complex data corresponding to each phase sensitivity, 3D angio data, flow velocity calculation, and 4 times phase sensitivity measurement method in (3-3). The same explanation is given for an example of (3
In section -4), a similar explanation will be given for another example of the four-time phase sensitivity measurement method. (3-1) Phase Sensitivity Measuring Method FIG. 6 is a waveform diagram showing an application pattern of a gradient magnetic field called a flow encode pulse, which gives a phase to a region having a flow. When the positive direction flow encode pulse 601 is applied, the phase of the obtained image has a positive phase proportional to the flow velocity value in the direction of the gradient magnetic field to which the flow encode pulse is applied. When the negative direction flow encode pulse 602 is applied, the phase of the obtained image also has a negative phase proportional to the flow velocity value in the direction of the gradient magnetic field to which the flow encode pulse is applied. With no flow encode pulse 603, the phase of the obtained image does not change according to the velocity.

FIG. 7 is a general pulse sequence diagram of the multiple phase sensitivity measurement method. The horizontal axis of FIG. 7 represents time, and the vertical axis represents the operating state of each device. The high frequency magnetic field 701 is generated by the high frequency magnetic field generator 202, and the X direction gradient magnetic field 70 is generated.
2, the Y-direction gradient magnetic field 703 and the Z-direction gradient magnetic field 704 are generated by the gradient magnetic field generator 203. Reception gate 705
Is issued to the receiving device 205 by the sequence control device 206, and is received in a gate-on state (a part where the upper side of the figure stands). The α-degree pulse 711 excites the magnetization in the imaging slice by α degrees. Although α can be arbitrarily selected, in the case of three-dimensional imaging, about 20 to 30 degrees is often used. The Z-direction encode 713 and the Y-direction encode 712 are gradient magnetic fields whose strength combinations change little by little each time. The flow encode pulse insertion unit 714 has X,
Independently of each of the Y, Z, and 3 axes, any one of the three pulse patterns shown in FIG. 6 is selected and applied. There are various methods for selecting a specific pulse pattern, and these will be described later in (3-2) to (3-4).
I explain in a section. The echo center 715 is the time at which the center of the echo signal exits. In the case of FIG. 7, the echo center 715 is located on the left side of the on-time of the reception gate 705. Thus, performing the asymmetrical measurement in which the echo center 715 is not in the center of the reception gate 705 is called asymmetrical measurement. In the case of symmetric measurement, the image reconstruction can be performed by the Fourier transform method, but in the case of asymmetric measurement, the unmeasured portion of the data is filled with 0 and the image reconstruction is performed by the Fourier transform method, or the half reconstruction is performed. Image reconstruction is performed by the Fourier method. As described above, when the asymmetrical measurement is performed and the half Fourier method is applied by the method of performing measurement with flow velocity sensitivity, the application method is limited and can be applied only in a very limited case. This will be described in Section (4). As described above, there are various methods in the multi-phase sensitivity measuring method depending on what kind of flow encode pattern is inserted in the flow encode inserting unit 714, which will be described below.

(3-2) Six-Time Phase Sensitivity Measurement Method As a pulse pattern to be inserted into the flow encode inserting section 714 of FIG. 7, a positive flow encode pulse 601 is represented by (+) and a negative flow encode pulse 602 is represented by (−). The flow encode pattern without flow encode pulse 603 is represented by 0, and the flow encode pattern to be inserted in each (X, Y, Z) axis is represented by the above symbol. In the 6-time phase sensitivity measurement method, the first measurement (+, 0, 0), 2
In the third measurement (-, 0, 0), in the third measurement (0, +,
0), the fourth time (0,-, 0), and the fifth time (0,0,
The measurement of (0), (-) is performed for the sixth time. 3D signal data of complex numbers obtained by each measurement expressed in S ₁ to S _6, the three-dimensional complex image data obtained it by complex Fourier transform and G ₁ ~G _6. The three-dimensional complex signal data reflecting the flow velocity sensitivity in the X direction is Sx, similarly in the Y direction, Z
The three-dimensional signal data in the directions are Sy and Sz. Similarly,
The three-dimensional complex image data reflecting the flow velocity sensitivities in the X, Y, and Z directions are represented by Gx, Gy, and Gz, and the three-dimensional image data representing the magnitude of the flow velocity is represented by Gv. Here, the Fourier transform is represented by F (•), and the above-mentioned values are measured signals S _{1 to} S
_The formula to calculate using ₆ is shown below

Gi = F (Si) (where 1 ≦ i ≦ 6) (Formula 1) Sx = S ₁ −S ₂ …………………………………… … (Equation 2) Gx = F (Sx) = F (S ₁ −S ₂ ) = F (S ₁ ) −F (S ₂ ) = G ₁ −G ₂ ……………………………… …………… (Equation 3) Sy = S ₃ −S ₄ ……………………………………… (Equation 4) Gy = F (Sy) = F (S _{3 -S 4) = F (S 3} ) -F (S 4) = G 3 -G 4 ................................................... ( equation ₅₎ Sz = S 5 -S ₆ ................................................... (equation 6) Gz = F (Sz) = F (S 5 -S 6) = F (S 5) -F (S 6) = G ₅ -G ₆ ................................................... (equation 7) Gv = √ (Gx * Gx + Gy * Gy + Gz * Gz) ................................. ( formula 8)

Here, an operation for obtaining a phase from complex image data is represented by Θ (·), and the phase is evaluated to obtain X.
The direction velocity data is θx, the Y direction velocity data is θy, the Z direction velocity data is θz, and the velocity data representing the magnitude of the velocity is θv. θx = (Θ (G ₁ ) −Θ (G ₂ )) / 2 ……………………………… (Equation 9) θy = (Θ (G ₃ ) −Θ (G ₄ )) / 2 …………………………………… (Equation 10) θz = (Θ (G ₅ ) −Θ (G ₆ )) / 2 …………………………………… (Equation 11) θv = √ (θx * θx ＋ θy * θy + θz * θz) …………………………… (Equation 12) In (Equation 9), θx is calculated from the phase of G ₁ by G
It was divided by 2 minus the _second phase, but the complex numbers regarded as a vector, there is a method of the θx divided by 2 obtains the angle between the complex vector of the complex vector and G ₂ G _1. Obtaining the angle between the vectors in this way has the advantage of being more resistant to the aliasing of the phase defined from −π to + π. As above, each calculation method has been described for the six-time measurement method. Gv is the three-dimensional angio data described in the section of the above (2) procedure, and (Expression 9) to (Expression 12) calculate the flow velocity. This is a method, and when each of the three-dimensional data is calculated from (Equation 9) to (Equation 12) and each three-dimensional data is created, the three-dimensional flow velocity data described in the section (2) above is obtained. Become. Further, G _{1 to} G ₆ shown in (Equation 1) are three-dimensional complex data corresponding to each phase sensitivity, and Gx, Gy,
Gz is three-dimensional complex data corresponding to the flow velocity in three directions. In addition, referring to FIG. 1, angio image 1 of each slice
02 indicates the three-dimensional angio data Gv.
That is, since FIG. 1 shows an example of projecting in the slice direction, the three-dimensional angio data Gv is decomposed and illustrated in the slice direction and called the angio data 102 of each slice. In this case, the flow velocity calculation 105 at the maximum point is a calculation for evaluating the phases shown in (Equation 9) to (Equation 12).

(3-3) 4 times phase sensitivity measurement method (example) (+, +, +), (-, +, +), (+,-, +), (+, +,-) 4
Each data can be calculated by the following equations by using the obtained three-dimensional measurement signals S _{1 to} S ₄ that are measured once and using the same symbols as in (3-2) above. Sx = S ₁ -S ₂ ................................................... (Equation 13) Gx = F (Sx) = F (S 1 -S 2) = F (S 1) - F (S ₂ ) = G ₁ −G ₂ …………………………………………… (Formula 14) Sy = S ₁ −S ₃ …………………………… .................. (equation 15) Gy = F (Sy) = F (S 1 -S 3) = F (S 1) -F (S 3) = G 1 -G 3 ..................... ………………………… (Equation 16) Sz = S ₁ −S ₄ …………………………………………… (Equation 17)

Gz = F (Sz) = F (S ₁ −S ₄ ) = F (S ₁ ) −F (S ₄ ) = G ₁ −G ₄ ………………………………………… ……… (Equation 18) Gv = √ (Gx * Gx + Gy * Gy + Gz * Gz) …………………………… (Equation 19) θx = (Θ (G ₁ ) −Θ (G ₂ )) / 2 …………………………………… (Equation 20) θy = (Θ (G ₁ ) −Θ (G ₃ )) / 2 …………………………………… (Equation 21) θz = (Θ (G ₁ ) -Θ (G ₄ )) / 2 …………………………………… (Equation 22) θv = √ (θx * θx ＋ θy * θy + θz * θz) …… (Equation 23) In this case, the angio image 102 of each slice in FIG. 1 is Gv similarly obtained by the calculation of (Equation 13) to (Equation 19), The flow velocity calculation 105 at the maximum point is
It is the calculation of (Equation 20) to (Equation 23).

(3-4) 4 times phase sensitivity measurement method (another method) (-,-,-), (-, +, +), (+,-, +), (+, +,-) Four
Each data can be calculated by the following equations by using the obtained three-dimensional measurement signals S _{1 to} S ₄ that are measured once and using the same symbols as in (3-2) above. Sx = -S ₁ -S ₂ + S ₃ + S ₄ …………………………………… (Equation 24) Gx = F (Sx) = F (-S ₁ -S ₂ + S ₃ + S _{4) = -F (S 1)} -F (S 2) + F (S 3) + F (S 4) = -G 1 -G 2 + G 3 + G 4 ................................. ( formula 25 _{) Sy = -S 1 + S 2} -S 3 + S 4 ................................................ ( equation 26) Gy = F (Sy) = F (-S 1 + S 2 -S 3 _{+ S 4) = -F (S} 1) + F (S 3) -F (S 1) + F (S 3) = -G 1 + G 2 -G 3 + G 4 ................................. ( formula 27) Sz = -S ₁ + S ₂ + S ₃ -S ₄ ………………………………………… (Equation 28)

[0023] Gz = F (Sz) = F (-S 1 + S 2 + S 3 -S 4) = -F (S 1) + F (S 3) + F (S 1) -F (S 3) = -G 1 + G ₂ + G ₃ −G ₄ ………………………………………… (Equation 29) Gv = √ (Gx * Gx + Gy * Gy + Gz * Gz) ………………………………… (Equation 30) θx = (− Θ (G ₁ ) −Θ (G ₂ ) + Θ (G ₃ ) + Θ (G ₄ )) / 4 (Equation 31) θy = (− Θ (G ₁ ) + Θ ( G ₂ ) −Θ (G ₃ ) + Θ (G ₄ )) / 4 (Equation 32) θz = (− Θ (G ₁ ) + Θ (G ₂ ) + Θ (G ₃ ) −Θ (G ₄ )) / 4 ……… (Equation 33) θv = √ (θx * θx ＋ θy * θy ＋ θz * θz) …………………………… (Equation 34)

Data Gv used for three-dimensional angio data
The method of making is not limited to the above (Equation 30), and other methods can be considered. For example, in the reference (2) cited in the section of the prior art above, if the symbols defined in this specification are used,
The following two formulas for obtaining Gv are described.

[Equation 1] Above, Gv, Gv ', G used for three-dimensional angio data
The method for obtaining v "is shown, but the above Gv, Gv ', Gv" are 0
Considering the above data, Gv * instead of Gv
It is conceivable that the data of Gv is made into three-dimensional angio data, and the square root is taken after the maximum value projection to make an angio data. The angio image 10 of each slice in FIG.
In this case, 2 is the same as Gv obtained by the calculation of (Formula 24) to (Formula 30), Gv ′ of (Formula 35), and (Formula 3).
7) Gv ″, and the flow velocity calculation 105 at the maximum point is the calculation of (Expression 31) to (Expression 34).

(4) When asymmetric measurement and half Fourier method are used Restrictions on application when the half Fourier method is applied by performing asymmetric measurement on the multiple flow velocity sensitivity measurement method briefly described in section (3-1) above. And how to apply. The half Fourier method is described in the following documents. (Reference 4) K.Sano, K.Suzuki, T.Yokoyama, and H.Koizu
mi, "ImageReconstructionfrom Half of the Data Usin
ga Phase Map ", Proceedings of Society of Magnetic
Resonance in Medicine, sixth Annual Scientific Mee
ting, p809 (1987). An example of performing the asymmetric measurement on the inflow angio and performing the half Fourier method is described in the following document. (Reference 5) Koichi Sano, "High-definition MR angiography-
Study on Image Quality ", IEICE Transactions DI
I, No. 4, (April 1994 issue) pages 874 to 881. However, in the above (Reference 5), only the principle that the phase changes with the flow velocity is described, and the reason why the asymmetric measurement and the half Fourier method are actually applied is that the inflow angio without the phase change (generally, TOF angio is used). Called)
Therefore, the asymmetric measurement and the half Fourier method are not applied to the multiple phase sensitivity measurement using the phase. In general, in order to be able to apply the half Fourier method, it is necessary to be able to estimate the phase of an image with data in a small area near the origin of k-space. In the TOF angio, since there is only a gentle phase change due to device distortion, the phase can be estimated and the half Fourier method can be applied. In the multiple phase sensitivity measurement method that changes the phase depending on the flow velocity, the phase estimation cannot be performed at first glance, and it seems that the half Fourier method cannot be applied. In fact,
In the four-time phase sensitivity measurement method, the phase change due to the flow velocity cannot be stably estimated by any calculation.
When the half Fourier method is applied forcibly, a pseudo image appears at the part where the phase estimation fails. However, in the 6-time phase sensitivity measurement method, the following difference signals Sx, Sy, Sz and sum signal Sxp,
When Syp and Szp are created, the portion having the phase sensitivity is canceled well and the phase can be estimated, and the half Fourier method can be applied.

Sx = S ₁ −S ₂ …………………………………………………… (Equation 38) Sy = S ₃ −S ₄ …………………… ……………………………………… (Equation 39) Sz = S ₅ −S ₆ ………………………………………………………… (Equation 40) Sxp = S ₁ + S ₂ …………………………………………………… (Equation 41) Syp = S ₃ + S ₄ ……………………………… ……………………………… (Equation 42) Szp = S ₅ + S ₆ …………………………………………………… (Equation 43)

Here, the calculation based on the half Fourier method is described as H (•), and the calculation formula for obtaining Gx and θx is shown below. Gx = H (Sx) θx = atan2 (H (Sx), H (Sxp)) ………………………… (Formula 44) Note that atan2 (a, b) is in the x-axis direction. b, a in the y-axis direction
Is a function for obtaining an angle formed by a vector having a length of x with the x axis. Similarly, Gy, Gz, θy, and θz can be obtained, and Gv and θv can be similarly obtained.

Although the embodiments of the present invention have been described above, in addition to the above, a threshold value may be introduced in the present invention to reduce the flow velocity error in the noise portion. That is, in the above-described embodiment, the phase of the peripheral portion of the blood vessel can be stably obtained, but even if the maximum value is projected in the background portion where there is no human body on the projection line of sight, noise is projected. The phase is evaluated and a random value with a large error is output as the flow velocity value. Therefore, the background part far from the blood vessel appears to flicker. Therefore, when a flow velocity is calculated by setting a predetermined threshold value, the phase is evaluated to calculate the flow velocity only when the predetermined data value for determining whether or not noise is larger than the threshold value If it is less than the value, it can be regarded as noise and the flow velocity value can be set to zero. There are various methods of creating the predetermined data value for determining whether or not it is noise. For example, density data may be calculated from complex image data that has been image-reconstructed in consideration of the measurement signal up to the phase and used as the predetermined data for noise determination. The density data is, for example, Go shown in (Expression 36).
That is. In addition, when the angio maximum intensity projection image 103 obtained by performing the maximum intensity projection is used as the noise determination data, as in the case of referring to the conductivity data, in the step of performing the flow velocity calculation 105 at the maximum point, It is also possible to judge whether or not to calculate the flow velocity by evaluating the phase by comparing the magnitude with the value, but once the angio maximum value projection image 103 and the flow velocity projection assisted image 106 are temporarily obtained, the angio maximum value is calculated. It is also possible to compare the magnitude of the projected image 103 with the threshold value and set the flow velocity value of the portion determined to be the noise portion to zero. In this case, the angio maximum intensity projection image 103
If the provisional flow velocity projection image 106 is obtained, it is easy to obtain the flow velocity image when the threshold value is changed, because the two-dimensional data are different from each other. Further, if the threshold value can be freely set any number of times, the flow velocity image for each threshold value can be interactively obtained. In addition, in the step of performing the flow velocity calculation 105 at the maximum point, if the calculation for obtaining Go shown in (Expression 36) is performed and the density projection image is created and used for the noise determination data, the threshold value can be freely set as many times as desired. It is also possible to interactively obtain the flow velocity image for each threshold value by setting to. Although the embodiments of the present invention have been described above, in the above claims, the data corresponding to the angio data of each slice of FIG. 1, that is, the three-dimensional angio data of the above embodiments, G
v, Gv ′, Gv ″, etc. will be referred to as three-dimensional angio data. Also, (Equation 9) to (Equation 12), (Equation 2)
The images obtained by evaluating the phases of 0) to (Equation 23) and (Equation 31) to (Equation 34) and calculating the flow velocity will be referred to as a flow velocity image.

[0029]

As described above, according to the present invention,
There is an effect that the position of the blood vessel is accurately recognized, the phase is evaluated, and a projection image of the flow velocity with less error can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a three-dimensional blood flow velocity image projection method in a magnetic resonance diagnostic apparatus of the present invention.

FIG. 2 is a configuration diagram of a magnetic resonance diagnostic apparatus to which the present invention is applied.

FIG. 3 is a diagram showing a case where a conventional projection method is applied.

FIG. 4 is an operation flowchart of a three-dimensional blood flow velocity image projection method showing an embodiment of the present invention.

5 is a diagram clearly showing that the flow velocity has a direction in the projection method of FIG.

FIG. 6 is a diagram showing a flow encode pulse pattern.

FIG. 7 is a general pulse sequence diagram of a multiple phase sensitivity measurement method.

[Explanation of symbols]

Reference numeral 101 ... Projection line of sight, 102 ... Angio image of each slice, 103 ... Angio maximum projection image, 104 ... Point having a maximum value in the projection line direction, 105 ... Flow velocity calculation at the maximum point, 106 ... Flow velocity projection image, 201 ... Inspection Target, 202
... static magnetic field generator, 203 ... gradient magnetic field generator, 204
... high-frequency magnetic field generator, 205 ... receiving device, 206 ... sequence control device, 207 ... processing device, 208 ... display device, 302 ... flow velocity image of each slice, 303 ... maximum flow velocity projection image, 401 ... steps 401, 402 ... Steps 402, 403 ... Steps 403, 404 ... Step 4
04, 505 ... Velocity calculation in each direction at the maximum point, 50
6 ... X direction flow velocity projection image, 507 ... Y direction flow velocity projection image, 508 ... Z direction flow velocity projection image, 601 ... Positive direction flow encode pulse, 602 ... Negative direction flow encode pulse, 603 No flow encode pulse, 701 ... High frequency magnetic field , 702 ... X direction gradient magnetic field, 703 ... Y direction gradient magnetic field, 704 ... Z direction gradient magnetic field, 705 ... Receiving gate, 711 ... α degree pulse, 712 ... Y direction encoding,
713 ... Encode in Z direction, 714 ... Flow encode pulse inserting section, 715 ... Echo center.

Claims (7)

[Claims] 1. A static magnetic field, a gradient magnetic field, a high-frequency magnetic field generation means, a detection means for measuring a magnetic resonance signal from an inspection object, a calculation means for performing various calculations on the detected signal, and each of the above means. In a velocity image projection method of a magnetic resonance diagnostic apparatus having a control means for controlling execution, (1) three-dimensional imaging using a multiple phase sensitivity measurement method in which imaging is performed by changing a combination of flow encode pulses; ) A step of reconstructing an image of the measurement signal obtained by the three-dimensional imaging to create three-dimensional angio data reflecting the flow velocity,
(3) Using the above three-dimensional angio data, maximum value projection is performed for each line of sight to project the value of the point having the maximum value when viewed from the desired projection line of sight, and each point having the maximum value at the time of maximum value projection Of the three-dimensional blood flow in the magnetic resonance diagnostic apparatus, including the steps of: (4) calculating the flow velocity at the position of each point having the maximum value, and obtaining a flow velocity image. Velocity image projection method. 2. The three-dimensional blood flow velocity image projection method in the magnetic resonance diagnostic apparatus according to claim 1, wherein the three-dimensional angio data of (2) above represents each phase sensitivity obtained by the multiple phase sensitivity measurement method. A method for projecting a three-dimensional blood flow velocity image in a magnetic resonance diagnostic apparatus, which is obtained based on a complex difference signal that is a complex difference of a measured signal that the user has. 3. The three-dimensional blood flow velocity image projection method in the magnetic resonance diagnostic apparatus according to claim 1, wherein the flow velocity calculation method in (4) above is a complex number obtained by image reconstruction in consideration of the measurement signal up to the phase. A method for projecting a three-dimensional blood flow velocity image in a magnetic resonance diagnostic apparatus, characterized in that the phase is evaluated for the image data of 1. 4. The three-dimensional blood flow velocity image projection method in the magnetic resonance diagnostic apparatus according to claim 1, wherein in the flow velocity calculation method of (4), a predetermined threshold value is provided and the measurement signal up to the phase is set. A three-dimensional magnetic resonance diagnostic apparatus characterized in that the flow velocity is calculated by evaluating the phase only when the value of the density data calculated from the image data of the complex number that has been image-reconstructed in consideration of it is larger than the threshold value. Blood flow velocity image projection method. 5. The three-dimensional blood flow velocity image projection method in the magnetic resonance diagnostic apparatus according to claim 1, wherein the flow velocity calculation method of (4) is provided with a predetermined threshold value, A three-dimensional blood flow velocity image projection method in a magnetic resonance diagnostic apparatus, characterized in that the phase is evaluated and the flow velocity is calculated only when it is larger than a threshold value. 6. A static magnetic field, a gradient magnetic field, a high frequency magnetic field generating means, a detecting means for measuring a magnetic resonance signal from an object to be inspected, a calculating means for performing various calculations on the detected signal, and each of the above means. In a velocity image projection method of a magnetic resonance diagnostic apparatus having a control unit for controlling execution, (1) three-dimensional imaging using a multiple phase sensitivity measurement method in which a combination of flow encode pulses is changed and (2) 3 above
(3) a step of reconstructing an image of the measurement signal obtained by three-dimensional imaging to create three-dimensional angio data reflecting the flow velocity;
Using the above-mentioned three-dimensional angio data, maximum value projection is performed for each line of sight to project the value of the point having the maximum value when viewed from the desired projection line of sight, and an angio maximum value projection image is obtained. The step of detecting the position of each point that has become, (4) the step of calculating the flow velocity at the position of the point where the maximum value has been obtained to create a temporary flow velocity image, and (5) the predetermined threshold value When the value of the angio maximum projection image is equal to or more than the threshold value, the corresponding value of the temporary flow velocity image is set as the flow velocity image value, and when the value is equal to or less than the threshold value, the flow velocity image value is 0. And a step of obtaining a flow velocity image as a method for projecting a three-dimensional blood flow velocity image in a magnetic resonance diagnostic apparatus. 7. The three-dimensional blood flow velocity image projection method in the magnetic resonance diagnostic apparatus according to claim 6, wherein the threshold value of (5) can be freely set any number of times so that each of the threshold values can be set. A three-dimensional blood flow velocity image projection method in a magnetic resonance diagnostic apparatus, characterized by interactively obtaining a flow velocity image with respect to a threshold value.