JP2002200056A - Method and apparatus for magnetic resonance imaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for magnetic resonance imaging, which can provide a water-fat separation image in improved precision and is reduced in water-fat separation treatment time. SOLUTION: The method and apparatus for magnetic resonance imaging provide plural original image data with different echo times and calculates a water-fat separation image. A partial area is designated in the original image data and the water-fat separation treatment is executed on the designated area. Thus the noise component included in the designated area is smaller than the noise component included in the original image data. Accordingly misses such as phase unwrap, etc., by the noise component in calculation are reduced to suppress deterioration of image quality to enable to obtain a water fat separation image with improved quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a magnetic resonance imaging method and apparatus for obtaining a tomographic image of a desired portion of a subject by utilizing a nuclear magnetic resonance phenomenon.

[0002]

2. Description of the Related Art First, the configuration of a typical MRI apparatus (magnetic resonance imaging apparatus) will be described with reference to FIG.

In FIG. 7, an MRI apparatus includes a subject 30.
1, a magnet 302 for generating a static magnetic field, a gradient coil 303 for generating a gradient magnetic field in this static magnetic field space, and an RF coil 304 for generating a high-frequency magnetic field in this space region
And an RF probe 305 for detecting an MR signal generated by the subject 301.

[0004] The gradient magnetic field coil 303 has three X, Y, and Z coils.
And a gradient magnetic field power supply 309.
A gradient magnetic field is generated in accordance with the signals from RF
The coil 304 generates a high-frequency magnetic field according to the signal of the RF transmission unit 310.

[0005] The signal of the RF probe 305 is detected by a signal detection unit 306 and processed by a signal processing unit 307.
It is converted into an image signal by calculation. The converted image is displayed on the display unit 308. The gradient magnetic field power supply 309, the RF transmission unit 310, and the signal detection unit 306 are controlled by the control unit 311. The control time chart is generally called a pulse sequence. The bed 312 is for the subject to lie down.

[0006] An object to be imaged by the MRI apparatus in the current technology is proton which is a main constituent substance of a subject as being widely used clinically. By imaging the spatial distribution of the proton density and the spatial distribution of the relaxation phenomenon of the excited state, the form or function of the human head, abdomen, limbs, etc. is two-dimensionally or three-dimensionally photographed.

Next, a photographing method will be described. Different phase encoding is given by the gradient magnetic field, and the echo signal obtained by each phase encoding is detected. As the number of phase encoding, a value such as 128, 256, 512 or the like is usually selected for one image.

Each echo signal is usually 128, 256, 5
It is obtained as a time-series signal composed of 12,1024 sampling data. These data are subjected to two-dimensional Fourier transform to create one MR image.

When an image is obtained by an MRI apparatus, TE or TR
By changing parameters such as the above and performing image calculation, images having various tissue contrasts can be obtained. In clinical practice, an image in which an MR signal due to fat is suppressed is often required.

Representative methods for obtaining an image with reduced fat include (1) a method using frequency selective excitation,
(2) a method by inversion excitation, and (3) a method by image calculation.

The method (1) requires that the uniformity of the static magnetic field generated by the magnet 302 be extremely high in the space around the subject 301. In the method (2), the uniformity of the static magnetic field is not required, but the signal value is reduced not only to the signal due to fat but also to the signal value of the tissue having the same T1 value as fat. In addition, a decrease in the overall SNR also occurs.

As a typical method of (3), Dixo
The Dixon method is described in "" Simp
le Proton Spectroscopic Imaging ”; W. Thomas Dixon
RADIOLOGY, Vol, 153, 189-194 (1984) ".

The Dixon method is a water / fat image separation method utilizing the difference in chemical shift between water protons and fat protons. Since the water proton and the fat proton perform precession at different resonance frequencies fow and fof, the relative directions of the magnetization vectors of the water proton and the fat proton are shifted with time.

If the difference between the resonance frequencies of water protons and fat protons is プ ロ ト ン f and 2τ = 1 / △ f, the water protons and fat protons that are oriented in the same direction at the time of excitation will
The opposite direction (180 °), the same direction (360 °) for each τ,
The fat protons and the water protons have a precession frequency different by 3.5 ppm. Assuming that the resonance frequencies of the water proton and the fat proton are fow and fof, respectively, the difference Δf can be expressed by the following equation.

Δf (= fow−fof) to γB ₀ × 3.5 × 10 ^-6 where γ is the gyromagnetic ratio of protons, and B ₀ is the static magnetic field strength.

In the Dixon method, water protons and fat protons have the same phase, opposite phases,... That is, the fact that the MRI signal of water and the MRI signal of fat change in phase, opposite phase,... Is used.

FIG. 8 shows 2 point Dixon (2P
D) The principle of the method is shown. In the 2PD method, imaging is performed twice while changing TE in a gradient echo (GE) sequence. In FIG. 8, reference numeral 101 denotes a high-frequency excitation pulse.
Assuming that TE for the first imaging is TE1, TE1 is set to an integral multiple of 2τ, and a read gradient magnetic field pulse 102 is applied. TE and TE2 of the second imaging are T at the time of the first imaging.
Read gradient magnetic field pulse 103
Is applied.

In FIG. 8, a water signal is indicated by a black arrow, and a fat signal is indicated by a white arrow. At the time of the first imaging, the water signal 105 and the fat signal 104 have the same phase. On the other hand, at the time of the second imaging, the water signal 107 and the fat signal 106 have opposite phases. The magnitudes of the signal due to water and the signal due to fat at the position of (x, y) coordinates of the image are W (x, y),
Assuming that F (x, y), the first and second signals S1
(X, y) and S2 (x, y) are represented by the following equations (1) and (2), respectively.

S1 (x, y) = W (x, y) F (x, y) (1) S2 (x, y) = W (x, y) -F (x, y) --- (2) From the above formulas (1) and (2), these formulas (1),
As the added image of (2), S1 (x, y) + S2 (x
A water image is obtained from (1, y) = 2W (x, y), and S1 (x, y) -S2 (x, y) = 2F as a subtraction image
A fat image is obtained from (x, y).

Although FIG. 8 illustrates a GE sequence, a spin echo (SE) sequence may be used.

FIG. 9 shows a case where the SE sequence is used. When this SE sequence is used, the high-frequency excitation pulse 201 and the high-frequency inversion pulse 2
02 is applied at the same timing.

In the first imaging, a readout gradient magnetic field pulse is applied as shown at 203 to obtain a signal at TE1, and
In the second imaging, a readout gradient magnetic field pulse is applied as indicated by 204, and a signal is acquired at TE2 τ after TE1 at the first imaging.

In an MRI apparatus, it is ideal that the static magnetic field generated by the magnet 302 is uniform in the space around the subject 301. However, when the magnet 302 has a distortion, the generated static magnetic field itself may have non-uniformity.

When the subject is inserted into the static magnetic field space, the static magnetic field may be non-uniform due to the different magnetic susceptibility of each part of the subject. MRI field of view (F
The non-uniformity of the static magnetic field in the field of view (FOV) changes the frequency of the MR signal and causes image quality deterioration such as displacement or flow in the obtained image.

Further, since the phase of the image changes due to the non-uniformity of the static magnetic field, a correct result cannot be obtained when performing a complex operation between the images. When the static magnetic field has inhomogeneity, the above equations (1) and (2) are expressed as the following equations (3) and (4).

S1 (x, y) = (W (x, y) + F (x, y)) exp (ia (x, y)) --- (3) S2 (x, y) = (W (x , Y) -F (x, y)) exp (i (α (x, y) + α ′ (x, y))) --- (4) α (x, y), α ′ in equation (4) Both (x, y) are phase rotation components due to non-uniformity of the static magnetic field, and depend on the position. Α (x, y) is time 2τ × n (= TE), α ′
(X, y) occurs at time τ, and if the rotation around the main value is removed, α
(X, y) is 2n times α '(x, y).

As described above, when the static magnetic field is inhomogeneous, 1
A phase difference occurs between the water signal at the time of the second imaging and the water signal at the time of the second imaging, and the water signal and the fat signal cannot be separated by simple addition / subtraction.

In view of this, auto-simming for directly correcting the non-uniformity of the static magnetic field in the FOV is performed by using an additional coil (shim coil), or post-processing is performed on the image to correct the effect of the non-uniform static magnetic field. I do.

The latter method, that is, a method in which signal phase correction processing is added to the Dixon method using a distribution map of non-uniform static magnetic field, is referred to as a 3 point Dixon (3PD) method. FIG. 10 shows the principle of the 3PD method.

In the 3PD method, imaging is performed three times while changing the TE. The first and second imagings are the same as in the case of the 2PD method. For the high-frequency excitation pulse 401, TE1 is set to an integral multiple of 2τ in the first imaging, and a readout gradient magnetic field pulse is applied as in 402. .

In the second imaging, TE2 is made longer by τ than TE1 in the first imaging, and a readout gradient magnetic field pulse is applied as indicated by 403. In the third imaging, TE3 is set to 2
The readout gradient magnetic field pulse is applied as indicated by 404 by extending τ from the second imaging TE2 by 2τ (2τ from the first imaging).

The signal S3 (x, y) at the time of the third imaging is
It is expressed as in the following equation (5). S3 (x, y) = (W (x, y) ten F (x, y)) exp (iα (x, y) + 2α ′ (x, y)) --- (5) At the time of the first imaging , Water signal 406 and fat signal 405 have the same phase and phase 407. This value is α. Similarly, at the time of the second imaging, the water signal 409 and the fat signal 40
8 has the opposite phase.

The phase of the water signal is 410 and its value is α
+ Α ′. At the time of the third imaging, the water signal 412 has the same phase as the fat signal 411 again, and the phase 413 has a value of α +
2α ′.

At the time of the first and third imagings, since the water signal and the fat signal have the same phase, S3 (x, y) / S1 (x, y) is calculated as in the following equation (6). By determining the phase, the amount of phase rotation due to the non-uniformity of the static magnetic field can be determined. arg (S3 (x, y) / S1 (x, y)) = 2α ′ (x, y) (6) where arg () means to obtain the phase.

The value of the above equation (6) is obtained for all (x, y), subjected to an unwrapping process (described later) for removing the rotation around the main value, and then divided by 2 to obtain the phase rotation amount due to the non-uniformity of the static magnetic field. α ′ (x, y) is obtained.

Using the obtained α ′ (x, y), the following equations (7) and (8) are executed. S1 ′ (x, y) = S1 (x, y) exp (−i2nα ′ (x, y)) −−− (7) S2 ′ (x, y) = S2 (x, y) exp (−i ( 2n + 1) α '(x, y)) --- (8) By calculating the above equations (7) and (8), S
A water image is obtained from 1 ′ (x, y) + S2 ′ (x, y) = 2W (x, y), and S1 ′ (x, y) −
A fat image is obtained from S2 ′ (x, y) = 2F (x, y).

Of course, in the 3PD method, not only the GE sequence but also the SE sequence can be used.
In this case, up to the second imaging, the same as the SE sequence in FIG. 7 is performed. In the third imaging, the readout gradient magnetic field pulse is further set to τ (2 from the first imaging).
τ) to acquire the signal.

Further, the phase rotation amount due to the non-uniformity of the static magnetic field is obtained from only the two signals obtained by TE and TE + τ,
There is also a method of obtaining a fat separation image. This 2PD method with static magnetic field correction is described in the following document. Document "" Two-Point Dixon Technique for Water-Fat Sign
al Decomposition with B0 Inhomogeneity Correctio
n ”; Bernard D. Cooms et al; Magnetic Resonance in Medic
ine, Vol. 38, 884-889 (1997) ".

When the amount of phase rotation due to the non-uniformity of the static magnetic field is determined by the 3PD method or the 2PD method with static magnetic field correction, it is necessary to perform a process called unwrapping or rewinding as described above.

Hereinafter, the unwrapping process will be described.
The phase is uniquely determined if the value is between -π and + π. However, the static magnetic field inhomogeneity is large, or the time interval between TE1 and TE2 is large, and the phase at a certain position is -π.
If the value is equal to or less than + π or more, the phase value at that position is turned back, and a value from -π to + π is obtained.

FIG. 11 shows this state. However, FIG.
In the graph, the horizontal axis indicates the position, and the vertical axis indicates the amount of phase rotation due to the non-uniformity of the static magnetic field. Reference numeral 501 denotes a distribution of the amount of phase rotation due to the non-uniformity of the static magnetic field in the FOV.

As shown in FIG. 11, a portion 502 having a phase value of + π or more is folded to take a value 503. Also, portions 504 and 505 which are equal to or less than -π are folded back to 506 and 507, respectively, and a discontinuous jump (dotted line in the drawing) occurs in the phase value. However, discontinuous jumps cannot occur in an actual magnetic field.

Therefore, in order to remove discontinuous jumps and obtain a smooth static magnetic field non-uniform distribution diagram, an unwrapping (rewinding) process is performed. The unwrapping method is described in the above-mentioned documents, but is described in the following documents in addition to them.

Reference "" Direct Calculati on of Wrap-Fr
ee Phase Image ”; M.Patel and X.Hu; Proceedings of A
nnual Meetings of the Society of Magnetic Resonanc
e inMedicine (= SMRM), No.721,1993 ”,” ”Phase unwrappi
ng in the Three-point Dixon Method for Fat Suppres
ion MRI Imaging ”; Jerzy Szumowski et al .; Radiolog
y, Vol, 192, 555-561 (1994). "

This unwrapping (rewinding) process is complicated and requires a lot of calculation time because it is susceptible to noise and requires some measures such as making a mask to remove the effect of noise. According to preliminary studies by the inventors of the present application, it is required to stably process a water-fat separation process on a 256 × 256 original image using a workstation in 20 to 30 seconds.
This required a certain amount of calculation time.

[0046]

As described above, in order to obtain a water / fat separation processed image from an original image, it takes 20 s to 3 s.
Although a calculation time of 0 s is required, the static magnetic field correction such as the unwrapping process is easily affected by noise. In particular, noise generated at a portion where the subject does not exist or at a boundary portion of the tissue in the subject is reduced. As a result, the image quality deteriorates, and it is difficult to obtain an accurate water fat separated image.

When a water fat separated image is obtained by a calculation such as the Dixon method, the length of the processing time also becomes a problem. In particular, in the 3PD method, it is necessary to find the distribution of the amount of phase rotation due to the non-uniformity of the static magnetic field.

Therefore, the image processing time is further extended. The reduction in processing time is particularly important when applying water fat separation technology to dynamic imaging in which the same part of a subject is imaged at certain time intervals, a series of images are obtained, and the time change is imaged. is important.

That is, if the processing time for obtaining the water-fat separated image requires a long time of 20 s to 30 s, it is difficult to obtain a water-fat separated image at an appropriate timing for each obtained image in dynamic imaging. Therefore, it is important to reduce the processing time.

Clinical applications of dynamic imaging include, for example, open M with relatively large inhomogeneity in static magnetic field.
In RI, monitoring when puncturing a tumor in fatty liver is considered. Suppress fat signals in images to visualize tumors with high contrast, and 1 per second
This is because it is desired to update an image at a speed of about two images.

In dynamic imaging of the coronary arteries, there is a demand to draw the coronary arteries with high contrast with respect to the surrounding fat.

There are also cases where it is desired to repeat imaging while moving a joint in order to examine the motor function of the limb. In this case, too, there is a demand to monitor a water fat separated image in near real time.

However, in the conventional technique, it takes a long time to obtain a water fat separation processed image, and it is difficult to apply the technique to dynamic imaging.

It is an object of the present invention to provide a magnetic resonance imaging method and apparatus capable of obtaining a water fat separated image with improved image accuracy and shortening the water fat separation processing time.

[0055]

In order to achieve the above object, the present invention is configured as follows. (1) In a magnetic resonance imaging method in which a plurality of original image data having different echo times are obtained and a water / fat separation image is obtained by calculation, a partial region in which water / fat separation processing is performed is designated in the original image data. Then, only the designated partial area is subjected to the water / fat separation calculation, and a water image or a fat image of only that area is obtained.

(2) Preferably, in the above (1),
The acquired original image data with different echo times is at least two.

(3) Preferably, in the above (1), a plurality of partial areas for performing the water fat separation processing can be designated.

(4) Preferably, in the above (1), the original image is displayed by a display means, a partial area for performing the water / fat separation process is specified by the displayed original image, and the displayed original image is displayed. Among the images, an image in which only a specified partial region is separated from water and fat is displayed, and the other portions are images in which water and fat are not separated.

(5) A signal detecting section for detecting a magnetic resonance signal from the subject, a signal processing section for performing image processing on the detected signal, a display section for displaying a signal-processed image, the signal detecting section, A magnetic resonance imaging apparatus comprising a signal processing unit and a control unit for controlling the operation of the display unit, acquiring a plurality of original image data having different image echo times, and obtaining a water / fat separation image by calculation; Among them, the partial area for performing the water / fat separation process is specified by the display unit, only the specified partial area is subjected to the water / fat separation calculation by the signal processing unit, and the calculated water image or fat image is displayed on the display unit. Is displayed.

(6) Preferably, in the above (1), an area of the original image obtained by dynamic shooting is designated, a water fat separation processing operation is performed only on the designated area, and the image is displayed. In the magnetic resonance imaging method of the present invention, first, the original image before the water fat separation processing is performed is displayed on the display unit. Then, the operator sets an area where the water / fat separation process is required. Thereafter, the water / fat separation process is performed using only the data included in the set area. Also,
Applying the water fat separation processing display of such area selection to dynamic imaging enables real-time water fat separation image display.

According to the above method, unnecessary data in the original image is not used in the water / fat separation processing operation, so that the absolute amount of noise and the like mixed in this operation is reduced, and the water amount in the phase unwrapping operation is reduced. The mistake at the time of fat separation processing can be reduced. Further, since the number of data to be processed is reduced, the processing time can be reduced.

[0062]

Embodiments of the present invention will be described below. First, an example in which one embodiment of the present invention is applied to a 3PD method will be described. In 3PD method, SE sequence or
Alternatively, in the GrE sequence, TE is set to TE1, TE
2. Set to TE3 and shoot three times.

If Δf is the difference between the resonance frequencies due to the chemical shift between water and fat, and 2τ = 1 / Δf, for example, the difference between TE2 and TE1 is expressed as (2)
n + 1) Set to τ.

On the other hand, the difference between TE3 and TE1 is n
Is a natural number, it is set to 2nτ. However, since the signal is attenuated by the relaxation time such as T2 and T2 ^* , in the normal case, TE2 and TE3 are TE1 + τ and TE1 respectively.
+ 2τ.

Instead of performing three times of photographing, it is also possible to generate three echoes in a multi-echo type SE, GrE sequence to complete one time of photographing.

FIG. 1 is a time chart of an example in which one embodiment of the present invention is applied to a multi-echo type SE sequence. In such a single scan sequence, since the photographing time is reduced to 1/3, the effect of shortening the calculation time is further enhanced.

In FIG. 1, reference numerals 601, 60
As shown by 2, 603, TE = TE1, TE2,
Signals 604, 605 and 606 are obtained at TE3, respectively. Three shots and one for the multi-echo type
TE = TE1,
The MR signals obtained by the imaging of TE2 and TE3 are respectively represented by s
1, s2, and s3.

In FIG. 1, reference numerals 604, 605, 60
6 corresponds to the MR signals s1, s2, s3. When Fourier transform is performed on the MR signals s1, s2, and s3, image data S1, S2, and S3 are obtained. Obtained image data S
1, S2 and S3 are complex data.

In one embodiment of the present invention, first, the absolute value display image of the image data S1, S2, S3 is displayed on the MR data shown in FIG.
The information is displayed on the display unit 308 of the imaging device. The image displayed here may be any of the image data S1, S2, and S3, or may be a combination of a plurality of data.

FIG. 2 shows an example in which only the image 701 of the image data S1 is displayed. The operator uses a pointing tool such as a mouse pointer or a pen to display the previously displayed image 701 on the image 701.
Processing target area 70 which is a partial area of this image 701
2, the water fat separation processing target area is determined.

At this time, the number of processing target areas is not limited to one, and a plurality of processing areas may be drawn. In this case, the processing areas are read in the order in which they are drawn, or the priority is specified separately.

FIG. 3 shows that the display unit 308 displays the image data S
1 shows an example in which two images of S1 and S2 are displayed. In such a case, as shown in FIG. 3A, it is also possible to select two of the water fat separation processing target areas 801 and 802 and a plurality of processing areas for one image. Further, as shown in FIG. 3B, the water-fat separation processing target area 803,
As in 804, it is also possible to draw on the other image.

When a plurality of water / fat separation processing target areas are selected, the water / fat separation processing target areas are read in the order in which they were drawn, or read in accordance with a separately specified priority order, as described above. In the example shown in FIGS. 2 and 3, the selection of the water fat separation processing target area is performed by freehand selection, but a configuration in which a rectangular processing target area is selected by specifying a diagonal point is configured. It is also possible. Also,
The shape may be circular, and a known technique can be used.

FIG. 4 is a diagram showing an example of an image obtained by subjecting a designated processing target area 702 of an image 701 to a water / fat separation process. FIG. 4A shows a water image. FIG.
(B) shows a fat image.

When the embodiment of the present invention is applied to dynamic photographing (described later), the processing target region set here may be applied to a plurality of continuously photographed images. In the case of multi-slice, the same fat / oil separation processing target region may be set for all slices, or may be set for each slice. This selection can be configured to be arbitrarily switched by the user.

Next, the determined water fat separation processing target area is sent to the signal processing unit 307. Signal processing unit 307
Performs the above-described water / fat separation processing operation only on the pixels corresponding to the sent water / fat separation processing target area.

That is, a static magnetic field non-uniform distribution map is created from the image data S1 and S3 only for the pixels corresponding to the water fat separation processing target area, and the phase correction of the image data S2 is performed. This phase correction is also performed only on the previously specified water fat separation processing target region.

Assuming that the image data S2 obtained by performing the phase correction is S2 ′, the addition / subtraction processing of the image data S1 and S2 ′ is performed in the water / fat separation processing target area,
Obtain a fat separation image.

The obtained water / fat separation image of the processing target area is displayed on the display unit 308. The image to be displayed may be only the water image, the fat image, or both. For a part other than the water fat separation processing target area, for example, if the image before the processing is displayed with reduced contrast, the relationship between the position of the water fat separation processing part and the whole is desirable, which is desirable.

Similarly, an example in which the present invention is applied to the 2PD method with static magnetic field correction will be described. In this example, 3PD
Similar to the method, imaging is performed in the SE sequence or the GrE sequence, but TE is set to TE1 and TE2, and two imagings are performed. The difference between TE2 and TE1 is set to (2n + 1) τ, where n is a natural number. In a normal case, TE2 is set to TE1 + τ.

That is, a signal is obtained by the same method as the 2PD method shown in FIG. Instead of performing two imagings, a multi-echo type SE, GrE sequence is used.
It is also possible to generate one echo and perform only one imaging.

That is, in FIG. 1, the read gradient magnetic field pulse 603 is not applied. At that time, no echo signal 606 is generated. Since the imaging time for acquiring two echoes in a single scan is particularly short, the reduction of the processing time is particularly advantageous to the user.

Now, MR signals obtained by imaging at TE = TE1 and TE2 are s1 and s2, respectively. These MRs
When Fourier transform is performed on the signals s1 and s2, the image data S
1, S2 is obtained. The obtained image data S1 and S2 are complex data.

For this reason, the absolute value display image of the image data sets S1 and S2 is displayed on the display unit 308. The image displayed here is either or both of the image data S1 and S2. Next, the operator draws and determines a water-fat separation processing target area on the previously displayed image using an instruction tool such as a mouse pointer or a pen.

According to the above-described 2PD method with static magnetic field correction, a water / fat separation image of the water / fat separation processing target area is obtained and displayed on the display unit 308 as in the case of applying the 3PD method. In the case of the 2PD method with static magnetic field correction, processing is generally complicated and the processing time is longer than that of the 3PD method.

Therefore, the effect of time reduction according to the present invention is particularly large. For example, if each side of the rectangular processing target area is の of the original image, the processing time can be reduced to almost １ ／.

The above technique can be applied to dynamic photography. As described above, the dynamic imaging is a method of imaging the same part of the subject at a certain time interval, obtaining a series of images, and imaging the change over time. In this dynamic imaging, an absolute value image is displayed only for the first image taken, and a water fat separation processing target region is determined using the absolute value image. In the second and subsequent images, 1
In the water fat separation processing target area selected at the time, an image (for example, a water fat separation image as shown in FIG. 4) in which water fat is partially separated is displayed at high speed in real time.

For dynamic photography, the photography time is short 2
An example in which the processing according to the embodiment of the present invention is combined with the echo GrE sequence has the highest real-time property.

In the conventional technique, in the dynamic photographing, since the water fat separation processing time is as long as 20 s to 30 s, it is difficult to obtain a water fat separated image corresponding to the obtained image on a one-to-one basis. However, according to one embodiment of the present invention, the water fat separation processing time can be performed in a few seconds,
Also in dynamic imaging, it is possible to obtain a water fat separated image corresponding to the obtained image on a one-to-one basis.

The processing target area may be changed by a GUI as necessary.
If the setting can be reset from the above, it is possible to cope with a shift in the position of the inspection part, and it is easy to use.

FIGS. 5 and 6 show another embodiment of the present invention. In one embodiment of the present invention described above, the designated area of the original image 701 is subjected to the water / fat separation processing, and only the area where the water / fat is separated is displayed on the display unit 30.
8 to display an image.

On the other hand, in another embodiment of the present invention shown in FIG. 5 and FIG.
The apparatus is configured to perform a water / fat separation process on a designated area, display a partial area where the water / fat is separated, and also display an image of other parts where the water / fat is not separated.

That is, as shown in FIG.
If only the area 702 is a water image, the other part displays the image 703 in the state of the original image on the display unit 308.

As shown in FIG. 6, when only the area 702 of the original image 701 is a fat image, the other part displays an image 703 in the original image state on the display unit 308.

In the above-described other embodiment of the present invention, the same effect as that of the embodiment can be obtained. In addition, it is possible to confirm at a glance which position of the whole image where the water fat separated and displayed is located. In addition, it is possible to easily obtain a comparison between the portion separated from the water fat and the portion not separated.

[0096]

As described above, the present invention relates to a magnetic resonance imaging method and apparatus for acquiring a plurality of original image data having different echo times and obtaining water / fat separated images by calculation. Are configured to specify a partial area, and to perform water fat separation processing on the specified area.

As a result, the noise component contained in the designated area is smaller than the noise component contained in the original image data, and errors in the calculation such as phase unwrap due to this noise component can be reduced, and the deterioration of the image quality can be suppressed. Thus, it is possible to obtain a water-fat separation-processed image with improved image quality.

Further, since the amount of data for performing the water fat separation processing is reduced, the water fat separation processing time can be greatly reduced.

Therefore, it is possible to obtain a water fat separation image with improved image precision and to realize a magnetic resonance imaging method and apparatus in which the water fat separation processing time is shortened.

[Brief description of the drawings]

FIG. 1 is a data acquisition time chart according to a 3PD method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of region selection of an image displayed on a display unit according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a region-selected image displayed on a display unit according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a water fat separated image according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating an example of a water fat separated image according to another embodiment of the present invention.

FIG. 6 is a diagram illustrating another example of a water fat separated image according to another embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of an MRI apparatus to which the present invention is applied.

FIG. 8 is a data acquisition time chart in the 2PD method using the GE sequence.

FIG. 9 is a data acquisition time chart in the 2PD method using the SE sequence.

FIG. 10 is a data acquisition time chart in a 3PD method using a GE sequence.

FIG. 11 is a diagram showing an example of a non-uniform distribution of a static magnetic field in a FOV.

[Explanation of symbols]

 301 Subject 302 Static magnetic field magnet 303 Gradient magnetic field coil 304 RF coil 305 RF probe 306 Signal detection unit 307 Signal processing unit 308 Display unit 309 Gradient magnetic field power supply 310 RF transmission unit 311 Control unit 312 Bed

Claims (5)

[Claims] 1. A magnetic resonance imaging method for acquiring a plurality of original image data having different echo times and obtaining a water / fat separated image by calculation, comprising: A magnetic resonance imaging method comprising specifying a designated partial region as a subject of water / fat separation calculation, and obtaining a water image or a fat image of only that region. 2. The magnetic resonance imaging method according to claim 1, wherein at least two pieces of the acquired original image data having different echo times are obtained. 3. The magnetic resonance imaging method according to claim 1, wherein a plurality of partial areas for performing the water fat separation processing can be designated. 4. The magnetic resonance imaging method according to claim 1, wherein said original image is displayed by a display means, and a partial area in which said water-fat separation process is to be performed is specified by said displayed original image. Magnetic resonance imaging method, wherein an image in which only a specified partial region is separated from water and fat is displayed, and an image in which other portions are not separated from water and fat is displayed. 5. A signal detector for detecting a magnetic resonance signal from a subject, a signal processor for image-processing the detected signal,
A display unit for displaying a signal-processed image, and a control unit for controlling the operations of the signal detection unit, the signal processing unit, and the display unit are provided. In the magnetic resonance imaging apparatus that obtains a water / fat separation image by using the display unit, a partial region in the original image data where the water / fat separation process is performed is designated by the display unit, and only the designated partial region is subjected to water by the signal processing unit. A magnetic resonance imaging apparatus wherein a fat separation calculation is performed and the calculated water image or fat image is displayed on a display unit.