JP3907944B2 - Magnetic resonance imaging method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic resonance imaging method and apparatus for obtaining a tomographic image of a desired part of a subject using a nuclear magnetic resonance phenomenon.
[0002]
[Prior art]
First, a configuration of a typical MRI apparatus (magnetic resonance imaging apparatus) will be described with reference to FIG.
[0003]
In FIG. 7, an MRI apparatus includes a magnet 302 that generates a static magnetic field around a subject 301, a gradient magnetic field coil 303 that generates a gradient magnetic field in this static magnetic field space, and an RF coil that generates a high-frequency magnetic field in this spatial region. 304 and an RF probe 305 that detects an MR signal generated by the subject 301.
[0004]
The gradient magnetic field coil 303 is composed of gradient magnetic field coils in three directions of X, Y, and Z, and each generates a gradient magnetic field in response to a signal from the gradient magnetic field power supply 309. The RF coil 304 generates a high frequency magnetic field in accordance with the signal from the RF transmission unit 310.
[0005]
The signal of the RF probe 305 is detected by a signal detection unit 306, signal processed by a signal processing unit 307, and 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, and the control time chart is generally called a pulse sequence. The bed 312 is for the subject to lie down.
[0006]
The imaging target of the MRI apparatus in the current technology is a proton that is a main constituent material of a subject as widely used clinically. By imaging the spatial distribution of the proton density and the spatial distribution of the relaxation phenomenon in the excited state, the form or function of the human head, abdomen, limbs, etc. is photographed two-dimensionally or three-dimensionally.
[0007]
Next, a photographing method will be described. Different phase encodings are given depending on the gradient magnetic field, and echo signals obtained by the respective phase encodings are detected. As the number of phase encodings, values such as 128, 256, and 512 are usually selected per image.
[0008]
Each echo signal is usually obtained as a time-series signal composed of 128, 256, 512, and 1024 sampling data. These data are two-dimensionally Fourier transformed to create one MR image.
[0009]
In the case of obtaining an image with an MRI apparatus, it is possible to obtain images having various tissue contrasts by changing parameters such as TE and TR or performing image computation. In clinical practice, an image in which MR signals due to fat are suppressed is often required.
[0010]
Typical methods for obtaining an image with suppressed fat include (1) a method by frequency selective excitation, (2) a method by inversion excitation, and (3) a method by image calculation.
[0011]
In the method (1), the uniformity of the static magnetic field generated by the magnet 302 in the space around the subject 301 needs to be extremely high. Further, in the method (2), the uniformity of the static magnetic field is not required, but the signal value of the tissue having a T1 value comparable to that of fat is reduced as well as the signal due to fat. In addition, the overall SNR is reduced.
[0012]
A typical method of (3) is the Dixon method, which is described in ““ Simple Proton Spectroscopic Imaging ”; W. Thomas Dixon et al .; RADIOLOGY, Vol, 153, 189-194 (1984)”. ing.
[0013]
The Dixon method is a water / fat image separation method using a difference in chemical shift between water protons and fat protons. Since the water proton and the fat proton precess at different resonance frequencies fow and fof, the relative directions of the magnetization vectors of the water proton and the fat proton shift with time.
[0014]
If the difference in resonance frequency between water protons and fat protons is Δf, and 2τ = 1 / Δf, then the water protons and fat protons facing in the same direction at the time of excitation are then reversed in each τ (180 ° ), Facing in the same direction (360 °),
Fat protons and water protons differ in precession frequency by 3.5 ppm. When the resonance frequencies of water protons and fat protons are respectively fow and fof, the difference Δf can be expressed by the following equation.
[0015]
Δf (= fow−fof) to γB₀× 3.5 × 10^-6
Where γ is the gyromagnetic ratio of proton, B₀Is the static magnetic field strength.
[0016]
In the Dixon method, water protons and fat protons have the same phase, opposite phase,... For each τ. That is, it utilizes the fact that the MRI signal of water and the MRI signal of fat change in phase, opposite phase,.
[0017]
FIG. 8 shows the principle of the 2point Dixon (2PD) method. In the 2PD method, imaging is performed twice while changing TE in a gradient echo (GE) sequence. In FIG. 8, 101 is a high frequency excitation pulse. When TE for the first imaging is TE1, TE1 is set to an integral multiple of 2τ, and the readout gradient magnetic field pulse 102 is applied. The TE and TE2 for the second imaging are longer than τ than the TE1 for the first imaging, and the readout gradient magnetic field pulse 103 is applied.
[0018]
In FIG. 8, the water signal is indicated by a black arrow and the fat signal is indicated by a white arrow. During the first imaging, the water signal 105 and the fat signal 104 are in phase. On the other hand, during the second imaging, the water signal 107 and the fat signal 106 are in opposite phases. If the magnitudes of the water signal and the fat signal at the (x, y) coordinate position of the image are W (x, y) and F (x, y), respectively, the first and second signals S1 (x, y) and S2 (x, y) are expressed as the following equations (1) and (2), respectively.
[0019]
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), as an added image of these formulas (1) and (2), a water image is obtained from S1 (x, y) + S2 (x1, y) = 2W (x, y). As a subtraction image, a fat image is obtained from S1 (x, y) −S2 (x, y) = 2F (x, y).
[0020]
Although FIG. 8 depicts a GE sequence, it is also possible to use a spin echo (SE) sequence.
[0021]
FIG. 9 shows a case where the SE sequence is used. When this SE sequence is used, the application timings of the high frequency excitation pulse 201 and the high frequency inversion pulse 202 are the same in the two imaging operations.
[0022]
In the first imaging, a readout gradient magnetic field pulse is applied as in 203 to acquire a signal in TE1, and in the second imaging, a readout gradient magnetic field pulse is applied as in 204 and from the TE1 during the first imaging. A signal is acquired at TE2 after τ.
[0023]
In the 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 is distorted, the generated static magnetic field itself may have nonuniformity.
[0024]
In addition, when the subject is inserted into the static magnetic field space, nonuniformity may occur in the static magnetic field due to different magnetic susceptibility for each part of the subject. The non-uniformity of the static magnetic field in the MRI field of view (Field of View: FOV) changes the frequency of the MR signal and causes image quality deterioration such as displacement and flow in the obtained image.
[0025]
In addition, since the phase of an image changes due to non-uniformity of a static magnetic field, a correct result cannot be obtained when performing a complex operation between images. When the static magnetic field is not uniform, the above formulas (1) and (2) are expressed as the following formulas (3) and (4).
[0026]
S1 (x, y) = (W (x, y) + F (x, y)) exp (iα (x, y))
---- (3)
S2 (x, y) = (W (x, y) −F (x, y)) exp (i (α (x, y) + α ′ (x, y))) −−− (4)
Α (x, y) and α ′ (x, y) in Equation (4) are both components of phase rotation due to non-uniform static magnetic field and depend on the position. Α (x, y) occurs at time 2τ × n (= TE), α ′ (x, y) occurs at time τ, and α (x, y) becomes α ′ (x , Y) is 2n times.
[0027]
As described above, when there is non-uniform static magnetic field, a phase difference occurs between the water signal at the first imaging and the water signal at the second imaging, and the water signal and the fat signal are obtained by simple addition / subtraction. Cannot be separated.
[0028]
Therefore, auto shimming is performed by directly correcting non-uniformity of the static magnetic field in the FOV using an additional coil (shim coil), or post-processing is performed on the image to correct the influence of the non-uniformity of the static magnetic field.
[0029]
The latter method, that is, a method in which a signal phase correction process is added to the Dixon method using a static magnetic field inhomogeneous distribution map is called a 3point Dixon (3PD) method. The principle of this 3PD method is shown in FIG.
[0030]
In the 3PD method, imaging is performed three times by changing TE. The first and second imaging are the same as in the 2PD method. In the first imaging, TE1 is set to an integer multiple of 2τ and a readout gradient magnetic field pulse is applied as in 402. .
[0031]
In the second imaging, TE2 is set longer than 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 further extended by τ (2τ from the first imaging) from the second imaging TE2, and a readout gradient magnetic field pulse is applied as indicated by 404.
[0032]
The signal S3 (x, y) at the time of the third imaging is expressed as the following equation (5).
S3 (x, y) = (W (x, y) + F (x, y)) exp (iα (x, y) + 2α ′ (x, y)) −−− (5)
During the first imaging, the water signal 406 and the fat signal 405 have the same phase and a phase 407. This value is α. Similarly, during the second imaging, the water signal 409 and the fat signal 408 are in opposite phases.
[0033]
The phase of the water signal is 410 and its value is α + α ′. At the time of the third imaging, the phase is again the same as that of the water signal 412 fat signal 411, and the value of the phase 413 is α + 2α ′.
[0034]
Since the water signal and the fat signal have the same phase during the first and third imaging, the phase of S3 (x, y) / S1 (x, y) is obtained as in the following equation (6). Thus, the amount of phase rotation due to non-uniform static magnetic field can be obtained.
arg (S3 (x, y) / S1 (x, y)) = 2α '(x, y) --- (6)
However, arg () means obtaining the phase.
[0035]
The value of the above equation (6) is obtained for all (x, y), subjected to an unwrap process (described later) for removing around the principal value, and then divided by 2 to obtain a phase rotation amount α ′ ( x, y).
[0036]
The following equations (7) and (8) are executed using the obtained α ′ (x, y).
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)
When the above equations (7) and (8) are calculated, a water image is obtained from S1 ′ (x, y) + S2 ′ (x, y) = 2W (x, y) as an added image, and S1 ′ as a subtracted image. A fat image is obtained from (x, y) −S2 ′ (x, y) = 2F (x, y).
[0037]
  Of course, not only the GE sequence but also the SE sequence can be used in the 3PD method. In this case, until the second imaging,FIG.In the third imaging, the readout gradient magnetic field pulse is further delayed by τ (2τ from the first imaging) to acquire a signal.
[0038]
There is also a method of obtaining a water / fat separated image by obtaining a phase rotation amount due to non-uniform static magnetic field from only two signals obtained by TE and TE + τ. The 2PD method with static magnetic field correction is described in the following document. Literature “Two-Point Dixon Technique for Water-Fat Signal Decomposition with B0 Inhomogeneity Correction”; Bernard D. Cooms et al .; Magnetic Resonance in Medicine, Vol. 38, 884-889 (1997) ”.
[0039]
When obtaining the amount of phase rotation due to static magnetic field inhomogeneity in 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.
[0040]
Hereinafter, the unwrap process will be described.
If the phase is a value from −π to + π, it is uniquely determined. However, when the static magnetic field inhomogeneity is large or the time interval between TE1 and TE2 is widened and the phase at a certain position is -π or less, or + π or more, the phase value at that position is folded. As a result, values from −π to + π are obtained.
[0041]
This is shown in FIG. In FIG. 11, the horizontal axis indicates the position, and the vertical axis indicates the amount of phase rotation due to the static magnetic field inhomogeneity. Reference numeral 501 denotes a distribution of the amount of phase rotation due to non-uniform static magnetic field in the FOV.
[0042]
As shown in FIG. 11, the portion 502 where the phase value is + π or more is folded back and takes the value 503. Further, portions 504 and 505 that are equal to or less than −π are folded back to become 506 and 507, respectively, and discontinuous jumps (dotted lines in the figure) occur in the phase values. However, discontinuous jumps cannot occur in an actual magnetic field.
[0043]
Therefore, in order to remove discontinuous jumps and obtain a smooth static magnetic field nonuniform distribution map, an unwrapping (rewinding) process is performed. The method of unwrap processing is mentioned in the above-mentioned documents, but in addition to these, it is described in the following documents.
[0044]
Literature “Direct Calculati on of Wrap-Free Phase Image”; M. Patel and X. Hu; Proceedings of Annual Meetings of the Society of Magnetic Resonance in Medicine (= SMRM), No. 721, 1993 ”,“ Phase unwrapping in the Three-point Dixon Method for Fat Suppresion MRI Imaging ”; Jerzy Szumowski et al .; Radiology, Vol, 192, 555-561 (1994)”.
[0045]
This unwrapping (rewinding) process is easily affected by noise, and thus requires a device such as making a mask to remove the influence of noise, and is complicated and takes a long calculation time. According to preliminary studies by the inventors of the present application, in order to stably perform a water / fat separation process on a 256 × 256 original image using a workstation, a computation time of about 20 s to 30 s is required.
[0046]
[Problems to be solved by the invention]
As described above, in order to obtain a water / fat separation processed image from the original image, a computation time of 20 s to 30 s is required. However, static magnetic field correction such as unwrap processing is easily affected by noise, and particularly the subject's Noise generated at a non-existing location or at the boundary between tissues in the subject deteriorates the image quality of the entire image, and it is difficult to obtain an accurate water-fat separation image.
[0047]
Further, when a water-fat separated image is obtained by calculation such as the Dixon method, the length of the processing time is also a problem. In particular, in the 3PD method, it is necessary to obtain the distribution of the amount of phase rotation due to non-uniform static magnetic fields, which is a very time-consuming operation.
[0048]
Therefore, the image processing time is further extended. The reduction in processing time is especially true when water fat separation technology is applied to dynamic imaging in which the same part of the subject is imaged at a certain time interval, and a series of images are captured to capture the time change. is important.
[0049]
That is, if a processing time of 20 s to 30 s is required to obtain a water / fat separated image, it is difficult to obtain a water / fat separated processed image at an appropriate timing for each obtained image in dynamic imaging. Reduction of processing time is important.
[0050]
As clinical use of dynamic imaging, for example, in open MRI with relatively large static magnetic field inhomogeneity, monitoring when puncturing a tumor in fatty liver is conceivable. This is because in order to depict a tumor with high contrast, it is desirable to suppress fat signals in the image and update the image at a rate of 1 to 2 images per second.
[0051]
There is also a demand for dynamic imaging of coronary arteries to depict coronary arteries with high contrast to surrounding fat.
[0052]
In addition, in order to examine the motor function of the limbs, there are cases where it is desired to repeat imaging while moving the joint, and in this case also, there is a demand for monitoring water-fat separation images in near real time.
[0053]
However, in the prior art, it takes a long time to obtain a water / fat separation image, and it has been difficult to apply to dynamic imaging.
[0054]
An object of the present invention is to realize a magnetic resonance imaging method and apparatus capable of obtaining a water / fat separation image with improved image accuracy and shortening the water / fat separation processing time.
[0055]
[Means for Solving the Problems]
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 acquired and a water / fat separated image is obtained by calculation, a partial region to be subjected to water / fat separation processing is designated in the original image data. Only the designated partial area is set as a water / fat separation calculation target, and a water image or a fat image of only the area is obtained.
[0056]
(2) Preferably, in the above (1), the acquired original image data having different echo times is at least two.
[0057]
(3) Preferably, in the above (1), a plurality of partial areas for performing the water / fat separation process can be designated.
[0058]
(4) Preferably, in the above (1), the original image is displayed by a display means, a partial region for performing the water / fat separation process is designated by the displayed original image, and the original image is displayed. Only the designated partial area is displayed with an image separated by water and fat, and the other portion is displayed with an image not separated by water and fat.
[0059]
(5) A signal detection unit that detects a magnetic resonance signal from the subject, a signal processing unit that performs image processing on the detected signal, a display unit that displays a signal-processed image, the signal detection unit, and the signal processing unit And a control unit for controlling the operation of the display unit, acquiring a plurality of original image data with different image echo times, and obtaining a water / fat separated image by calculation, in the original image data, A partial region for performing water / fat separation processing is designated by the display unit, and only the designated partial region is subjected to water / fat separation calculation by the signal processing unit, and the calculated water image or fat image is displayed on the display unit. .
[0060]
(6) Preferably, in the above (1), an area of the original image obtained by dynamic imaging is designated, and water fat separation processing calculation is performed only on the designated area, and an image is displayed.
In the magnetic resonance imaging method of the present invention, an original image before water / fat separation processing is first displayed on the display unit. Then, the operator sets an area where water / fat separation processing is necessary. Thereafter, the water / fat separation process is performed using only the data included in the set area. Further, such a region-selected water / fat separation processing display is applied to dynamic imaging to enable real-time water / fat separation image display.
[0061]
According to the above method, unnecessary data in the original image is not used in the water / fat separation processing calculation, so the absolute amount of noise and the like mixed in the calculation is reduced, and the water / fat separation processing such as phase unwrapping work is performed. You can reduce time mistakes. In addition, since the number of data to be processed is reduced, the processing time can be reduced.
[0062]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
First, an example in which one embodiment of the present invention is applied to the 3PD method will be described. In the 3PD method, TE is set to TE1, TE2, and TE3 in the SE sequence or the GrE sequence, and imaging is performed three times.
[0063]
Also, if Δf is the difference in resonance frequency due to chemical shift between water and fat and 2τ = 1 / Δf, for example, the difference between TE2 and TE1 is set to (2n + 1) τ, where n is a natural number.
[0064]
On the other hand, the difference between TE3 and TE1 is set to 2nτ, where n is also a natural number. However, the signal is T2, T2^*In the normal case, TE2 and TE3 are set to TE1 + τ and TE1 + 2τ, respectively.
[0065]
Further, instead of performing the imaging three times, it is possible to generate three echoes with a multi-echo type SE and GrE sequence and complete the imaging once.
[0066]
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, the photographing time is shortened to 1/3, so the effect of shortening the computation time is further increased.
[0067]
Now, as shown by reference numerals 601, 602, and 603 in FIG. 1, signals 604, 605, and 606 are obtained for TE = TE 1, TE 2, and TE 3 by alternately inverting the polarity of the read gradient magnetic field pulse, respectively. The MR signals obtained by TE = TE1, TE2, and TE3 are respectively shown as s1, s2, and s3 in common in the case of performing the imaging three times and in the case of completing the single imaging with the multi-echo type. To do.
[0068]
In FIG. 1, reference numerals 604, 605, and 606 correspond to the MR signals s1, s2, and s3. When Fourier transform is applied to the MR signals s1, s2, and s3, image data S1, S2, and S3 are obtained. The obtained image data S1, S2, and S3 are complex data.
[0069]
In one embodiment of the present invention, first, the absolute value display images of the image data S1, S2, and S3 are displayed on the display unit 308 of the MR imaging apparatus shown in FIG. The image displayed here may be any of image data S1, S2, and S3, or a combination of a plurality of them.
[0070]
FIG. 2 shows an example in which only the image 701 of the image data S1 is displayed. The operator draws a processing target area 702 that is a partial area of the image 701 on the previously displayed image 701 by using a pointing tool such as a mouse pointer or a pen, and sets the water fat separation processing target area. decide.
[0071]
At this time, the number of processing target regions is not limited to one, and a plurality of processing target regions may be drawn. In this case, the processing regions are read in the drawing order or the priority order is specified separately.
[0072]
FIG. 3 shows an example in which two images of image data S 1 and S 2 are displayed on the display unit 308. In such a case, as shown in FIG. 3A, it is also possible to select a plurality of processing regions for one image as two water fat separation processing target regions 801 and 802. Also, as shown in FIG. 3B, it is possible to draw on the other image, such as water / fat separation target regions 803 and 804.
[0073]
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 are drawn, or are read according to a separately specified priority order, as described above. In the examples shown in FIG. 2 and FIG. 3, the selection of the water / fat separation processing target area is shown as an example of freehand selection, but the configuration is such that a rectangular processing target area is selected by specifying diagonal points. It is also possible to do. Moreover, it may be circular and a known technique can be used.
[0074]
FIG. 4 is a diagram showing an example of an image obtained by subjecting the designated processing target region 702 in the image 701 to water / fat separation processing, and FIG. 4 (A) shows a water image. (B) shows a fat image.
[0075]
In addition, when applying one Embodiment of this invention to dynamic imaging (after-mentioned), you may apply the process target area set here to the several image image | photographed continuously. In the case of multi-slices, the same water / fat separation target region may be set for all slices, or may be set for each slice. This selection can be configured so that the user can switch arbitrarily.
[0076]
Next, the determined water / fat separation target region is sent to the signal processing unit 307. The signal processing unit 307 performs the water / fat separation processing calculation described above only for the pixels corresponding to the transmitted water / fat separation processing target region.
[0077]
That is, a static magnetic field inhomogeneous distribution map is created from the image data S1 and S3 only for pixels corresponding to the water / fat separation target region, and the phase of the image data S2 is corrected. This phase correction is also performed only for the water fat separation target region specified previously.
[0078]
Assuming that the image data S2 is subjected to phase correction is S2 ', addition / subtraction processing of the image data S1 and S2' is performed in the water / fat separation target region to obtain a water / fat separation image.
[0079]
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 either a water image or a fat image, or both. For parts other than the water / fat separation processing target region, for example, when an image before processing is displayed with reduced contrast, the relationship between the position of the water / fat separation processing part and the whole is desirable.
[0080]
Similarly, an example of applying the present invention to the 2PD method with static magnetic field correction will be described. In this example, as in the 3PD method, imaging is performed using the SE sequence or the GrE sequence, but TE is set to TE1 and TE2 and imaging is performed twice. The difference between TE2 and TE1 is set to (2n + 1) τ, where n is a natural number. In normal cases, TE2 is set to TE1 + τ.
[0081]
That is, a signal is acquired by the same method as the 2PD method shown in FIG. Further, instead of performing the imaging twice, it is also possible to generate two echoes by a multi-echo type SE and GrE sequence and complete the imaging once.
[0082]
That is, in FIG. 1, the readout gradient magnetic field pulse 603 is not applied. At that time, the echo signal 606 is not generated. The imaging that acquires two echoes by a single scan has a particularly large user merit because the processing time is particularly short.
[0083]
Now, MR signals obtained by imaging TE = TE1 and TE2 are denoted by s1 and s2, respectively. When Fourier transform is applied to these MR signals s1 and s2, image data S1 and S2 are obtained. The obtained image data S1 and S2 are complex data.
[0084]
Therefore, an absolute value display image of the image data S1 and S2 is displayed on the display unit 308. The image to be displayed here is one or both of the image data S1 and S2. Next, the operator uses a pointing tool such as a mouse pointer or a pen to draw and determine a water / fat separation target region on the previously displayed image.
[0085]
In accordance with the 2PD method with static magnetic field correction described above, a water / fat separation image of the water / fat separation processing target region is obtained and displayed on the display unit 308 in the same manner as when applied to the 3PD method. In the case of the 2PD method with static magnetic field correction, processing is generally complicated and processing time is longer than that of the 3PD method.
[0086]
Therefore, the effect of shortening the time according to the present invention is particularly great. For example, if each side of the rectangular processing target area is ½ of the original image, the processing time can be reduced to almost ¼.
[0087]
The above technique can also be applied to dynamic photography. As described above, this dynamic imaging is a method of imaging the same portion of the subject at a certain time interval, obtaining a series of images, and imaging the time change. In this dynamic shooting, an absolute value image is displayed only for the first image, and a water / fat separation target region is determined using this absolute value image. In the second and subsequent images, an image (for example, a water-fat separation image as shown in FIG. 4) that is partially water-fat separated in real time at a high speed in the water-fat separation processing target region selected in the first time. indicate.
[0088]
For dynamic imaging, an example in which processing according to an embodiment of the present invention is combined with a 2-echo GrE sequence with a short imaging time has the highest real-time performance.
[0089]
In the conventional technique, since the water fat separation processing time is as long as 20 s to 30 s in dynamic shooting, it was difficult to obtain a water fat separated image corresponding to the obtained image on a one-to-one basis. According to one embodiment of the present invention, since the water / fat separation processing time can be executed in a few seconds, it is possible to obtain a water / fat separation image corresponding to the obtained image on a one-to-one basis even in dynamic imaging.
[0090]
Note that if the processing target area can be reset from the GUI as necessary, it is possible to cope with the case where the position of the examination region is shifted and it is easy to use.
[0091]
5 and 6 are diagrams showing another embodiment of the present invention.
In the above-described embodiment of the present invention, the designated area of the original image 701 is subjected to water / fat separation processing, and only the area subjected to water / fat separation is displayed on the display unit 308.
[0092]
On the other hand, in another embodiment of the present invention shown in FIG. 5 and FIG. 6, water fat separation processing is performed on a specified area of the original image 701 and water fat separation is performed on a partial area. Is displayed, and other parts that are not separated from water and fat are also displayed together.
[0093]
That is, as shown in FIG. 5, when only the region 702 in the original image 701 is a water image, the other part displays an image 703 in the state of the original image on the display unit 308.
[0094]
As shown in FIG. 6, when only the area 702 in the original image 701 is a fat image, the other portion displays an image 703 in the original image state on the display unit 308.
[0095]
In the other embodiments of the present invention described above, the same effect as that of the embodiment can be obtained, and the position where the water fat separation display is located in the entire image can be confirmed at a glance. It is possible to obtain an effect that the separated portion can be easily compared with the portion that is not.
[0096]
【The invention's effect】
As described above, the present invention provides a magnetic resonance imaging method and apparatus for acquiring a plurality of original image data having different echo times and obtaining a water / fat separated image by calculation. A designated area is designated, and water fat separation processing is performed for the designated area.
[0097]
As a result, the noise component included in the specified area is less than the noise component included in the original image data, and errors during calculation such as phase unwrapping due to this noise component can be reduced, so that deterioration in image quality can be suppressed, and image quality can be reduced. An improved water / fat separation image can be obtained.
[0098]
In addition, since the amount of data to be subjected to the water / fat separation process is reduced, the water / fat separation processing time can be significantly reduced.
[0099]
Therefore, it is possible to obtain a water / fat separation image with improved image accuracy and to realize a magnetic resonance imaging method and apparatus with a shortened water / fat separation processing time.
[Brief description of the drawings]
FIG. 1 is a data acquisition time chart according to a 3PD method in 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 an image with a region selected displayed on a display unit according to an embodiment of the present invention.
FIG. 4 is a diagram showing an example of a water / fat separation image in an embodiment of the present invention.
FIG. 5 is a diagram showing an example of a water / fat separation image according to another embodiment of the present invention.
FIG. 6 is a diagram showing 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 a GE sequence.
FIG. 9 is a data acquisition time chart in the 2PD method using an SE sequence.
FIG. 10 is a data acquisition time chart in the 3PD method using a GE sequence.
FIG. 11 is a diagram showing an example of a static magnetic field inhomogeneous distribution in the FOV.
[Explanation of symbols]
301 Subject
302 Static magnetic field magnet
303 gradient coil
304 RF coil
305 RF probe
306 Signal detection unit
307 Signal processor
308 display
309 Gradient magnetic field power supply
310 RF transmitter
311 Control unit
312 beds

Claims (6)

To a plurality of original image data having different between the echo time, a magnetic resonance imaging method for obtaining a water-fat separation images by computation,
In the original image data, specify the partial area for water fat separation processing,
Run the phase unwrapping process for correcting the phase error due to the static magnetic field inhomogeneity with respect to only the designated partial region,
A magnetic resonance imaging method characterized in that a water / fat separation process is performed on a partial area on which the phase unwrapping process has been performed to obtain a water image or a fat image of only that area.   The magnetic resonance imaging method according to claim 1, wherein the original image data having different echo times is at least two.   2. The magnetic resonance imaging method according to claim 1, wherein a plurality of partial regions for performing the water / fat separation process can be designated. The magnetic resonance imaging method according to claim 1, wherein said original image, and displayed by the display means, from the displayed original image specifies a partial region for the water-fat separation process, the original image and the partial region A magnetic resonance imaging method, comprising combining and displaying an image separated from water and fat in correspondence with each other . A signal detector detecting the magnetic resonance signals from the subject, a signal processing unit for image processing the detected signals, and a display unit for displaying the signal processed image, the signal detection unit, a signal processing unit and a display A magnetic resonance imaging apparatus that obtains a plurality of original image data having different echo times and obtains a water-fat separated image.
A specifying means for specifying one or a plurality of regions in the original image data to be subjected to the water / fat separation process,
The signal processing unit, the water for the specified for only in the region running phase unwrapping process for correcting the phase error due to the static magnetic field inhomogeneity, the phase unwrapping process is performed partial regions by said specifying means A magnetic resonance imaging apparatus characterized by performing fat separation calculation and displaying the calculated water image or fat image. 6. The magnetic resonance imaging apparatus according to claim 5, wherein the original image data is continuously acquired, and the water / fat separated image is displayed on the display unit in real time.

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