WO2015190508A1 - 磁気共鳴イメージング装置及び水脂肪分離画像作成方法 - Google Patents
磁気共鳴イメージング装置及び水脂肪分離画像作成方法 Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7235—Details of waveform analysis
- A61B5/7253—Details of waveform analysis characterised by using transforms
- A61B5/7257—Details of waveform analysis characterised by using transforms using Fourier transforms
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/74—Details of notification to user or communication with user or patient ; user input means
- A61B5/742—Details of notification to user or communication with user or patient ; user input means using visual displays
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/4828—Resolving the MR signals of different chemical species, e.g. water-fat imaging
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
- G01R33/56554—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by acquiring plural, differently encoded echo signals after one RF excitation, e.g. correction for readout gradients of alternating polarity in EPI
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
- G01R33/5659—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B2576/00—Medical imaging apparatus involving image processing or analysis
Definitions
- the present invention measures magnetic resonance (hereinafter referred to as “NMR”) signals of hydrogen nuclei (hereinafter referred to as “protons”) contained in a subject, and visualizes the density distribution, relaxation time distribution, etc. of protons.
- NMR magnetic resonance
- protons hydrogen nuclei
- the present invention relates to a resonance imaging (hereinafter referred to as “MRI”) apparatus, and more particularly to a technique for acquiring an image for quantitative evaluation of fat.
- the MRI device measures NMR signals generated by changes in the external magnetic field of the nuclear spins that make up the subject, especially human tissue, and forms the shape of the head, abdomen, limbs, etc. in two or three dimensions. It is a device that images.
- the NMR signal is subjected to phase encoding that varies depending on the gradient magnetic field, is frequency-encoded, and is measured as time-series data.
- the measured NMR signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.
- various tissue contrasts can be obtained by changing parameters such as echo time (hereinafter referred to as ⁇ TE '') and repetition time (hereinafter referred to as ⁇ TR '') and performing image computation.
- An image with can be obtained.
- an image in which signals from adipose tissue are suppressed is often required.
- a method for obtaining an image in which signals from adipose tissue are suppressed there is a method for obtaining a plurality of images having different TEs and obtaining an image in which water and fat are separated by calculation.
- DIXON method Non-Patent Document 1
- Non-Patent Document 2 discloses a two-point DIXON method with static magnetic field correction, in which a function for correcting the influence of static magnetic field inhomogeneity is added to the DIXON method.
- the influence of the reception frequency characteristic may occur in the positive and negative electrodes.
- the reception frequency characteristic is a characteristic of the receiver that the sensitivity (gain) varies depending on the reception frequency. Even if the generated echo signal has the same signal intensity, the magnitude of the echo signal changes depending on the reception frequency. This reception frequency characteristic varies depending on the connected reception coil and the object to be imaged.
- Non-Patent Document 2 does not disclose a function of correcting the influence of reception frequency characteristics. Therefore, in the DIXON method of Non-Patent Document 2, it is difficult to create a water-fat separated image from an image obtained from two TE signals to a level at which fat can be quantitatively evaluated.
- the imaging time must be extended and the number of imaging slices must be reduced. It is subject to restrictions such as having to.
- An object of the present invention is to provide a magnetic resonance imaging apparatus and a water / fat separation image capable of acquiring an image capable of quantitative evaluation of fat by removing the influence of the reception frequency characteristic of the image acquired by inverting the frequency encoding gradient magnetic field. It is to provide a creation method.
- an echo signal is acquired during application of a positive frequency encoding gradient magnetic field, and an echo signal is acquired during application of a negative frequency encoding gradient magnetic field.
- a correction amount for correcting the influence of the reception frequency characteristic is obtained from these signals, and using this correction amount, the signal intensity of the image derived from the TE signal obtained by inverting the polarity of the frequency encoding gradient magnetic field is corrected.
- the MRI apparatus of the present invention has the following characteristics.
- a static magnetic field magnet a high frequency generator for generating a high frequency magnetic field pulse, a receiver having a high frequency coil for receiving an echo signal generated by nuclear magnetic resonance, a gradient magnetic field coil, and the high frequency generator according to a predetermined pulse sequence
- a control unit for controlling the gradient magnetic field coil and the receiving unit, and a signal processing unit for processing the echo signal, the pulse sequence having different polarities at a plurality of echo times after excitation by the high-frequency magnetic field pulse.
- a multi-echo sequence for acquiring an echo signal during application of a frequency encoding gradient magnetic field, wherein the signal processing unit receives a pair of correction echo signals acquired during application of a positive and negative frequency encoding gradient magnetic field at the same echo time.
- Correction data is created using the frequency-encoded gradient magnetic field of the different polarity. Characterized in that it comprises a correction unit for correcting the over signal.
- the correction unit creates the correction data using an echo signal acquired by a correction data measurement sequence executed separately from the multi-echo sequence.
- the correction data measurement sequence is the same as the multi-echo sequence except for the application condition of the phase encoding gradient magnetic field.
- the pair of correction echo signals is an echo signal acquired in the execution of the multi-echo sequence and an echo signal acquired in a correction data measurement sequence executed separately from the multi-echo sequence.
- the pair of correction echo signals are signals acquired by applying a low-frequency phase encoding gradient magnetic field.
- the high-frequency coil includes a plurality of small coils, and the correction unit generates correction data for each of the small coils, and performs correction using the correction data on echo signals received by the small coils.
- the correction unit obtains the correction data from a ratio of data obtained by two-dimensional Fourier transform of the pair of correction echo signals for each small coil.
- the multi-echo sequence includes a first echo time in which an echo signal from water and an echo signal from fat are in phase in the frequency-encoded gradient magnetic fields of different polarities, an echo signal from water and the fat signal It is a water fat separation sequence in which an echo signal is acquired at a second echo time having an opposite phase to the echo signal.
- the echo signal for creating the correction data is an echo signal acquired at the same echo time as the first echo time or the second echo time.
- the water fat separation sequence is characterized in that the first echo time is set longer than the second echo time.
- the water / fat separation image creation method of the present invention has the following characteristics.
- a water / fat separation image creation method for creating a plurality of types of images using echo signals generated by nuclear magnetic resonance, wherein the echo signals are frequency encoded with different polarities at a plurality of echo times after excitation by a high-frequency magnetic field pulse.
- the pair of correction echo signals are signals acquired by applying a low-frequency phase encoding gradient magnetic field.
- the echo signal includes a first echo time in which an echo signal from water and an echo signal from fat are in phase, and a second echo in which the echo signal from water and the echo signal from fat are in reverse phase Using the first echo signal acquired at the first echo time and the second echo signal acquired at the second echo time to create a plurality of types of images. .
- the pair of correction echo signals are signals obtained by applying a low-frequency phase encoding gradient magnetic field at the same echo time as the first echo time or the second echo time.
- the fat distribution ratio is calculated using the plurality of types of images.
- an image acquired from an echo signal (hereinafter referred to as “positive echo signal”) acquired during application of the positive frequency encoding gradient magnetic field (hereinafter referred to as “positive image”).
- the influence of the reception frequency characteristics of the image (hereinafter referred to as the ⁇ negative image '') acquired from the echo signal (hereinafter referred to as the ⁇ negative echo signal '') obtained during application of the negative frequency encoding gradient magnetic field.
- the reception frequency characteristic for example, even when an image obtained by capturing an image of a region such as the liver at high speed under breathing stop is used, the accuracy of quantitative evaluation of fat can be improved. Further, in imaging for acquiring an image for quantitative evaluation of fat, the imaging time can be shortened or the number of imaging slices can be increased.
- the block diagram which shows the whole structure of the MRI apparatus with which this invention is applied The block diagram which shows the structure of the signal processing part of the MRI apparatus with which this invention is applied
- the figure which shows the gradient echo (GrE) type sequence used in the first embodiment and the second embodiment The figure which shows the example of the receiving frequency characteristic of the receiving coil Diagram explaining the effect of reception frequency characteristics on images
- the figure which shows the example of the correction data measurement sequence used by 1st embodiment Processing flowchart for correcting reception frequency characteristics Processing flow chart for channel composition and obtaining fat content image
- amendment data measurement sequence used by 2nd embodiment The figure which shows the gradient echo (GrE) type sequence used in the third embodiment
- FIG. 1 is a block diagram showing the overall configuration of an MRI apparatus to which the present invention is applied.
- An MRI apparatus to which the present invention is applied includes a static magnetic field magnet 102 that generates a static magnetic field around a subject 101, a gradient magnetic field coil 103 that generates a gradient magnetic field, and a high-frequency magnetic field pulse (hereinafter referred to as “RF”).
- An irradiation high-frequency coil hereinafter referred to as “irradiation coil”) 104, a reception high-frequency coil (hereinafter referred to as “reception coil”) 105 that receives an NMR signal from the subject, and a subject 101.
- a gradient magnetic field power source 107 that sends a signal to the gradient coil 103 to generate a gradient magnetic field
- an RF transmitter 108 that sends a signal to generate an RF pulse to the irradiation coil 104
- a reception coil 105 A signal detection unit 109 for detecting the received echo signal, a signal processing unit 110 for processing the signal detected from the signal detection unit 109, a display unit 111 for displaying an image and the like, and a control unit 112 for controlling imaging and the like And parameters necessary for imaging And an input unit 113 to force.
- the irradiation coil 104 and the RF transmission unit 108 are collectively referred to as a high frequency generation unit, and the reception coil 105 and the signal detection unit 109 are collectively referred to as a reception unit.
- the static magnetic field magnet 102 is a permanent magnet, a superconducting magnet, or a normal conducting magnet arranged in a wide space around the subject 101, and is parallel or perpendicular to the body axis of the subject 101. Generate a uniform static magnetic field in the direction.
- the gradient magnetic field coil 103 applies a gradient magnetic field in the X, Y, and Z axial directions to the subject 101 in accordance with a signal from the gradient magnetic field power source 107. By applying this gradient magnetic field, the imaging section of the subject is determined, and phase encoding and frequency encoding are applied to the signal.
- the irradiation coil 104 generates an RF pulse according to the signal from the RF transmitter 108.
- This RF pulse excites protons contained in the living tissue in the imaging cross section of the subject 101 set by the gradient magnetic field coil 103 to induce an NMR phenomenon.
- the receiving coil 105 receives an echo signal generated by the NMR phenomenon of protons contained in the subject 101 induced by the RF pulse irradiated from the irradiation coil 104.
- the receiving coil 105 may be a single coil, but may be a multi-channel coil (for example, a multiple array coil or a phased array coil) in which a plurality of small coils are combined, or a single multi-channel coil.
- the signal detection unit 109 detects an echo signal received through the reception coil 105 arranged close to the subject 101.
- the receiving coil has a plurality of coils (channels)
- an echo signal is detected for each channel.
- the signal processing unit 110 performs signal processing on the echo signal detected by the signal detection unit 109 to generate an image of the subject 101. Details of the signal processing unit 110 will be described below with reference to FIG.
- the display unit 111 displays images and shooting parameters generated by the signal processing unit 110.
- the input unit 113 is used for an operator to input parameters such as TR and TE necessary for imaging.
- the input parameters are displayed on the display unit 111 and sent to the control unit 112, and are used for imaging control.
- the control unit 112 Based on the parameters input from the input unit 113, the control unit 112 generates a predetermined pulse sequence for repeatedly generating each gradient magnetic field and RF pulse for performing slice selection, phase encoding, and frequency encoding, and the gradient magnetic field.
- the power source 107, the RF transmission unit 108, and the signal processing unit 110 are controlled.
- the pulse sequence includes a main measurement pulse sequence for main measurement and a correction data measurement sequence for measuring correction data.
- FIG. 2 shows the configuration of the signal processing unit 110 of the MRI apparatus of the present embodiment.
- the signal processing unit 110 includes a signal reception unit 201, an image conversion unit 204, an image processing unit 206, and an image transmission unit 207.
- the signal processing unit 110 includes a memory (k-space database 202, correction database 203, and image database 205) that stores data obtained by each of these units, and a memory (memory (memory (memory) that stores data acquired from the control unit). Parameter) 208).
- These parts can be composed of CPU and memory.
- a program for executing the function of each unit is stored in advance in the memory, and the CPU reads and executes the program in the memory. As a result, the operation of each part can be realized.
- a program as shown in the flow of FIG. 7 or FIG. 8 is stored in advance in the memory.
- the CPU reads the program shown in the flowchart of FIG. 7 and executes it, whereby the operation of the image conversion unit 204 is executed. Further, the CPU reads and executes the program shown in the flow of FIG. 8 from the memory, whereby the operation of the image processing unit 206 is executed.
- the description will be made assuming that the image conversion unit 204 and the image processing unit 206 are realized as software. This processing can also be realized by hardware such as ASIC or FPGA.
- the signal reception unit 201 stores the signal acquired by the main measurement among the echo signals detected by the signal detection unit 109 in the k-space database 202 based on the arrangement information in the k-space.
- the signal receiving unit 201 uses the pair of correction echo signals acquired by the correction data measurement from the echo signals detected by the signal detection unit 109 or the main measurement when using the signal acquired by the main measurement.
- the signal acquired by the low-frequency phase encoding and the signal acquired by the correction data measurement are stored in the correction database 203 based on the arrangement information in the k space.
- the image conversion unit 204 performs Fourier transform on the k-space data stored in the k-space database 202 to convert it into an image, corrects the reception frequency characteristics with the correction data stored in the correction database 203, and stores the correction in the image database 205. .
- This correction is performed for each coil. For example, when reception is performed by a receiving coil having a plurality of small coils (channels), the correction is performed for each small coil.
- the image processing unit 206 performs image processing on the image stored in the image database 205.
- Image processing includes, for example, processing for combining images for each channel of the receiving coil, processing for creating a water image and a fat image, processing for correcting unevenness in sensitivity of the receiving coil 105, and the like.
- the image processing unit 206 passes the processed image to the image transmission unit 207.
- the image transmission unit 207 transmits the image processed by the image processing unit 206 to the display unit 111.
- the transmitted images include In-phase images, Out-of-phase images, water images, fat images, and fat content images.
- Parameters stored in the memory 208 are necessary for the slice sequence, frequency encoding, and phase encoding information of the pulse sequence required by the signal reception unit 201, and the image conversion unit 204, the image processing unit 206, and the image transmission unit 207. It includes parameters such as an image matrix and filtering, and control information, and the memory 208 acquires these from the control unit 112.
- This measurement pulse sequence is a multi-echo sequence for measuring an echo signal for each inversion of a frequency encoding gradient magnetic field pulse and obtaining a plurality of images having different TEs.
- the correction data measurement sequence is to acquire correction data for removing the influence of the reception frequency characteristics included in each echo in the main measurement pulse sequence.
- This is a pulse sequence in which the polarity of the frequency encoding gradient magnetic field is reversed.
- a pair of correction echo signals acquired during application of frequency-encoded gradient magnetic fields of the same TE and different polarities to be used as correction data are the signals acquired in this measurement and the correction data measurement.
- the acquired echo signal is used.
- FIG. 3 shows an example of this measurement pulse sequence.
- This pulse sequence is a sequence for obtaining two types of image data having different TEs, and is a gradient echo (GrE) type sequence method.
- the frequency encoding gradient magnetic field is inverted from the positive electrode to the negative electrode to acquire two types of image data having different TEs.
- this pulse sequence is applied to water fat separation imaging.
- the control unit 112 performs the following control and executes this pulse sequence.
- the slice selective gradient magnetic field 302 is applied simultaneously with the irradiation of the RF pulse 301 to excite only the target tomographic plane.
- a phase encode gradient magnetic field 303 for encoding position information is applied, and at the same time, a frequency encode gradient magnetic field (prepulse) 304 in the negative direction is applied.
- a frequency encode gradient magnetic field 305 in the positive direction is applied to generate the first echo signal after TE1 has elapsed from the RF pulse.
- the frequency encode gradient magnetic field 306 in the negative direction is applied again to generate the next echo signal after TE2 has elapsed from the RF pulse.
- Such a sequence is repeatedly executed for the number of phase encodings while changing the application amount of the phase encoding gradient magnetic field 303, and echo signals for the number of phase encodings are acquired.
- the receiving coil has a plurality of channels, an echo signal is acquired for each channel.
- the k-space database 202 stores the echo signal data of TE1 and TE2. Two types of image data with different TEs are collected by Fourier transforming k-space data.
- this measurement may use a frequency encode gradient magnetic field having a polarity opposite to that of the frequency encode gradient magnetic field used in FIG. Specifically, after applying the frequency encode gradient magnetic field (pre-pulse) 304 in the positive direction, the frequency encode gradient magnetic field 305 may be applied in the negative direction, and then the frequency encode gradient magnetic field 306 may be applied in the positive direction.
- TE1 is the timing at which the phase of the echo signal from the water proton (water signal) and the echo signal from the fat proton (fat signal) are opposite
- TE2 is the phase of the water signal and the fat signal
- the timing can be the same phase.
- TE1 may have the water signal and the fat signal in the same phase and TE2 in the opposite phase.
- FIG. 4 is an example of the reception frequency characteristic of the reception coil, and shows the reception frequency characteristic of each channel of the two-channel coil.
- FIG. 5 is a diagram for explaining the influence of the reception frequency characteristic on the image.
- 401 is the reception frequency characteristic of channel number 1
- 402 is the reception frequency characteristic of channel number 2.
- the gain of 63.66 [MHz] is 15.3 [dB]
- the gain decreases as the reception frequency increases, and becomes 14.2 [dB] at 64.06 [MHz].
- the gain of 63.66 [MHz] is 11.7 [dB]
- the gain increases as the reception frequency increases, and becomes 12.2 [dB] at 64.06 [MHz].
- image 5 is an image of a positive electrode
- image 502 is an image of a negative electrode. Since the frequency encoding gradient magnetic field of images 501 and 502 is in the opposite direction, the frequency encoding of image 501 increases in frequency from left to right, whereas the frequency encoding of image 502 is frequency from left to right. Decrease.
- a case of an image based on a signal acquired with channel number 1 will be described. As described with reference to FIG. 4, in the reception frequency characteristic of channel number 1, the gain decreases as the reception frequency increases. That is, in the image 501, the gain of the reception frequency characteristic decreases from the left to the right.
- the gain of the reception frequency characteristic increases in the direction from left to right.
- the gain of channel number 1 is 15.0 [dB] at 63.76 [MHz] (point b) (see FIG. 4)
- the reception frequency increases from left to right (in other words, As it increases), the gain decreases to 14.4 [dB] (see Fig. 4) at 63.96 [MHz] (d point).
- the gain of channel number 1 increases from the left to the right (in other words, as the reception frequency decreases).
- the gain of the reception frequency characteristic of channel number 2 increases as the frequency increases.
- the signal value on the left side is lower in the image 501 than in the image 502
- the signal value on the right side is higher in the image 501 than in the image 502.
- the two channels have been described above. However, since each channel has different reception frequency characteristics, the influence of the reception frequency characteristics for each channel occurs differently.
- An image synthesized from signals acquired by a plurality of channels as described above is a result of synthesis of the influence of the reception frequency characteristics of each channel. As a result, the accuracy of the fat content image decreases due to the mixing of these effects.
- This correction data measurement pulse sequence is a pulse sequence in which the frequency encode gradient magnetic field of the measurement pulse sequence is reversed and a phase encode gradient magnetic field only in a low range is applied.
- FIG. 1 An example of the correction data measurement pulse sequence is shown in FIG.
- the polarity of the frequency encode gradient magnetic field 604, 605, 606 is opposite to the polarity of the frequency encode gradient magnetic field 304, 305, 306 of this measurement pulse sequence, respectively, and the phase encode gradient magnetic field 603 is low.
- This is the same as the main measurement pulse sequence of FIG. 3 except that only the phase encoding gradient magnetic field is used.
- Such a sequence is repeatedly executed for the number of times of phase encoding only in the low band while changing the application amount of the phase encoding gradient magnetic field 603. Either the TE1 signal or the TE2 signal acquired by the correction data measurement is used for correction.
- the echo signal used for correction is preferably acquired with the TE whose water and fat phases are closest to the same phase. It is preferable.
- the correction data measurement of FIG. 6 of the negative echo signal at TE2 of FIG. In the correction data measurement, the echo signal obtained from the same low-frequency phase encoding as the pulse sequence and the positive echo signal at TE2 in FIG. 6 are used as correction data.
- the main measurement pulse sequence of FIG. 3 when the timing at which the water signal and the fat signal are in phase is TE1, in the main measurement, among the positive echo signals at TE1 of FIG. 3, the correction data measurement of FIG.
- the echo signal acquired by the same low-frequency phase encoding as the pulse sequence and the negative echo signal at TE1 in FIG. 6 are used as correction data in correction data measurement.
- the correction data measurement pulse sequence shown in FIG. 6 is a sequence for obtaining two echo signals from excitation by one RF pulse irradiation. Although shown, the correction data measurement sequence may acquire one echo signal from one excitation.
- Correction data measurement is performed by applying a low-frequency phase encoding gradient magnetic field including a zero phase encoding gradient magnetic field.
- the application amount of the low-frequency phase encoding gradient magnetic field is preferably 8, more preferably 16, and further preferably 32.
- Correction data measurement is performed immediately before or immediately after the actual measurement at the same slice position as the actual measurement, the same imaging field (FOV (Field of View)), the same frequency encoding direction, the same frequency encoding sampling points, and the same reception bandwidth. May be. Further, the correction data measurement may be performed continuously or separately from the main measurement.
- FOV Field of View
- the correction data measurement preferably obtains a signal for each small coil. Moreover, it is preferable to perform correction data measurement for each object to be imaged.
- the echo signal obtained by the correction data measurement is stored in the correction database 203.
- the correction database 203 also stores an echo signal obtained by applying the same phase encode gradient magnetic field as the low phase phase encode gradient magnetic field of the correction data measurement pulse sequence among the signals obtained in this measurement in the k-space database. Stored separately from the received signal.
- Step S701 The k-space data stored in the k-space database 202 is converted into an image by two-dimensional Fourier transform.
- the converted image is an Out-of-phase image acquired by applying a positive frequency encode gradient magnetic field, and an In-phase image acquired by applying a negative frequency encode gradient magnetic field.
- Step S702 The echo data stored in the correction database 203 and having different polarities of the frequency encoding gradient magnetic field are each subjected to two-dimensional Fourier transform and converted into an image space.
- the correction data is an echo signal acquired with a phase encoding gradient magnetic field only for a low frequency with respect to one slice.
- Step S703 The ratio is obtained from the correction data of the positive electrode subjected to the two-dimensional Fourier transform and the correction data of the negative electrode subjected to the two-dimensional Fourier transform.
- one may be aligned with the other.
- a description will be given of how to obtain the ratio of correction data for correcting an In-phase image acquired by applying a negative frequency encoding gradient magnetic field so as to be aligned with the influence of the reception frequency characteristic included in the positive echo signal.
- Step S704 Fit the correction data ratio. Since the correction data includes noise, it is performed to remove the influence of noise. Prior to fitting, noise data is excluded by threshold processing. Further, since the influence of the reception frequency characteristic on the image is generated like a signal gradient of a linear or quadratic function, the correction data ratio may be fitted by a linear or quadratic function. The ratio of correction data after fitting is indicated by Fitting ⁇ Cr (x) ⁇ .
- Step S705 The two-dimensional Fourier-transformed image is corrected using the ratio Fitting ⁇ Cr (x) ⁇ of the corrected correction data.
- ⁇ Cr (x) ⁇ the corrected In-phase image Image In '(x, y)
- This corrected In-phase image In ′ (x, y) is aligned with the influence of the reception frequency characteristic included in the echo signal acquired during application of the positive frequency encoding gradient magnetic field.
- Steps S701 to S705 are performed for each reception coil and for each slice.
- the receiving coil is a coil having a plurality of small coils (channels)
- steps S701 to S705 are performed for each small coil (channel) and for each slice.
- the ratio of the correction data obtained in step S703 is the reciprocal of the right side of equation (1).
- the image conversion unit 204 fits the reciprocal.
- the image conversion unit 204 multiplies the reciprocal thus fitted by the image.
- the corrected image is aligned with the influence of the reception frequency characteristic included in the negative signal.
- the image processing unit 206 synthesizes the image for each channel using the image corrected by the image conversion unit 204 using a known method, creates a water image and a fat image, Can be processed. An example of such processing is shown in FIG.
- Step S801 A case where In ′ (x, y) that is an In-phase image corrected by the image conversion unit 204 is synthesized and Out (x, y) that is an Out-of-phase image is synthesized is shown.
- the image for each channel is synthesized by the following equation.
- In Comb (x, y) is an image obtained by synthesizing the corrected In-phase image In ′ (x, y).
- k indicates the channel number of the receiving coil, and N indicates the number of channels.
- M k (x, y) is a sensitivity map for channel synthesis, and is created by applying a low-pass filter to In ′ (x, y). * Indicates a complex conjugate.
- Out Comb (x, y) is an image obtained by synthesizing an Out-of-phase image Out (x, y).
- the sensitivity map used for synthesis is the same as that used when In Comb (x, y) is synthesized.
- Step S802 A phase map showing the phase change that occurs between different TEs due to the non-uniformity of the static magnetic field is created.
- TE1 in FIG. 3 is an Out-of-phase image
- TE2 is an In-phase image.
- the phase of the combined Out-of-phase image Out Comb (x, y) is subtracted from the combined In-phase image In Comb (x, y), the phase is doubled, and the initial phase map Create ⁇ (x, y).
- water and fat are in antiphase, so the antiphase of water and fat is eliminated by doubling.
- equation (5) is obtained.
- Arg indicates that the angle is obtained from complex data.
- the phase unwrapping process is performed on the initial phase map ⁇ (x, y).
- the phase unwrapping process is a process of eliminating a portion where the phase is spatially discontinuous because the range indicated by the phase is ⁇ to + ⁇ and making it spatially continuous. Since the initial phase map doubles the phase, the phase value ⁇ (x, y) is completed by halving the phase value after phase unwrapping.
- the equation (6) is obtained.
- Step S803 In-phase image In Comb (x, y) after composition, Out-of-phase image Out Comb (x, y) after composition, Water image Water (x, y) and Fat image Fat ( Create x, y).
- the formula (7) is obtained.
- Step S804 Using the water image Water (x, y) and the fat image Fat (x, y) or the In-phase image In Comb (x, y) and the fat image Fat (x, y), the fat content image FatRatio ( Create x, y). When expressed by the equation, the equation (8) is obtained.
- abs represents an absolute value. The same applies to the case where the In-phase image In (x, y) and the corrected Out-of-phase image Out ′ (x, y) are combined to create a water fat separation image and an image of fat content. It is.
- the image transmission unit 207 transmits the image-processed image to the display unit 111.
- the images include In-phase images, Out-of-phase images, water images, fat images, fat content images, and the like.
- FIG. 3 was used as the main measurement pulse sequence, and the pulse sequence shown in FIG. 6 was used as the correction data measurement sequence.
- FIGS. 1-10 the results will be described with reference to FIGS.
- Figure 9 shows an FOV 350mm, receiving bandwidth 360kHz, 256 sampling points in the frequency encoding direction, 128 sampling points in the phase encoding direction, and a nickel chloride aqueous solution phantom imaged in this measurement pulse sequence using a 4-channel receiving coil. It is an image.
- An image 901 is an image (TE1 echo image) acquired when the frequency encoding gradient magnetic field is positive (the frequency increases from left to right) and TE1 is 3.6 ms.
- the image 902 is an image (TE2 echo image) acquired when the frequency encoding gradient magnetic field is negative (the frequency decreases from left to right) and TE2 is 4.9 ms.
- Table 1 shows the ROI_A and ROI_B signal average values of the TE1 echo image 901, the ROI_A and ROI_B signal average values of the TE2 echo image 902, and the ROI_A and ROI_B signals in the TE2 echo image 902 corrected for the influence of the reception frequency characteristic.
- the average value is shown. Note that the coordinates of ROI_A and ROI_B of each echo image are the same.
- the value of ROI_A of the TE2 echo image 902 is smaller than that of the TE1 echo image 901.
- the value of ROI_B of the TE2 echo image 902 is larger than that of the TE1 echo image 901.
- the signal value of the TE2 echo image 902 having a TE of 4.9 ms must be smaller than the signal value of the TE1 echo image 901 having a TE of 3.6 ms. This is due to the influence of the reception frequency characteristic, and the TE2 echo image 902 needs to be corrected.
- FIG. 10 is an image for each channel of the receiving coil of the TE1 echo image 901 and the TE2 echo image 902 captured in this measurement.
- Image 1001 to image 1004 are images for each channel of the receiving coil of TE1 echo image 901.
- Image 1001, image 1002, image 1003, and image 1004 are images of 1 channel, 2 channels, 3 channels, and 4 channels, respectively. It is.
- images 1005 to 1008 are images for each channel of the TE2 echo image 902 receiving coil, and images 1305, 1306, 1307, and 1308 are 1 channel, 2 channels, 3 channels, and 4 channels, respectively. It is an image.
- Fig. 11 shows the correction data after two-dimensional Fourier transform.
- correction data data (images 1101 to 1104) obtained by measuring the main measurement pulse sequence and data (images 1105 to 1108) obtained by measuring the correction data measurement pulse sequence were used.
- An echo signal of TE TE1 was used.
- the correction data images 1101 to 1104 are correction data in which the frequency encoding gradient magnetic field created from the 16 phase encodings in the low band of the TE1 echo image acquired in this measurement is positive.
- An image 1101, an image 1102, an image 1103, and an image 1104 indicate 1 channel, 2 channels, 3 channels, and 4 channels, respectively.
- Images 1105 to 1108 are images of TE1 echoes acquired during application of the negative frequency encoding gradient magnetic field using the correction data measurement pulse sequence.
- An image 1105, an image 1106, an image 1107, and an image 1108 are 1 channel, 2 channels, 3 channels, and 4 channels, respectively.
- the phase encoding gradient magnetic field of the correction data measurement pulse sequence used 16 phase encodings in the low band.
- FIG. 12 shows the correction data ratio Cr (x) from the correction data shown in FIG. 11 and the correction data ratio Fitting ⁇ Cr (x) ⁇ fitted by a linear function.
- a graph 1201, a graph 1202, a graph 1203, and a graph 1204 indicate 1 channel, 2 channels, 3 channels, and 4 channels, respectively. Note that the correction data ratio Cr (x) in the graphs 1201 to 1204 indicates only data used for fitting by threshold processing.
- the TE2 echo channel image 1005 to 1008 is fitted with the correction data 1201 to 1204 ratio Fitting ⁇ Cr (x) ⁇ , and each channel composite image is created and the influence of the reception frequency characteristics is corrected.
- the values of ROI_A and ROI_B of the image 902 were calculated.
- the calculated values are shown as the average signal values of ROI_A and ROI_B in the TE2 echo image with the effect of the reception frequency characteristics corrected in Table 1.
- both ROI_A and ROI_B were reasonable signal values attenuated by 3% compared to the TE1 echo image. Therefore, the influence of the reception frequency characteristic can be removed by this embodiment.
- the water image, fat image, and fat content image obtained as described above from the out-of-phase image and the in-phase image whose reception frequency characteristic is corrected are frequency-encoded gradients. Since the influence of the reception frequency characteristic when the polarity of the magnetic field is reversed is corrected and removed, the accuracy is high and the error is reduced.
- this embodiment it is possible to remove the influence of the reception frequency characteristics of the positive and negative images acquired by reversing the frequency encoding gradient magnetic field.
- By removing the influence of the reception frequency characteristic it is possible to improve the accuracy of the quantitative evaluation of fat even when using an image acquired by imaging a region such as the liver at high speed while stopping breathing.
- imaging for acquiring an image for quantitative evaluation of fat it is not necessary to perform measurement with a frequency-encoded gradient magnetic field having the same polarity in order to avoid the influence of the reception frequency characteristic. Can be increased.
- the main measurement pulse sequence is the same as the main measurement pulse sequence (FIG. 3) described in the first embodiment.
- FIG. 13 shows an example of a correction data measurement sequence used in this embodiment.
- This correction data measurement sequence is a gradient echo (GrE) type sequence.
- the seed of the correction data measurement sequence is the same as the seed of this measurement pulse sequence.
- [Slice selective gradient magnetic field 1302 is applied simultaneously with the first RF pulse 1301 irradiation to excite only the intended tomographic plane. Then, a low-frequency phase encode gradient magnetic field 1303 for encoding position information is applied, and simultaneously a negative frequency encode gradient magnetic field 1304 is applied, followed by applying a positive frequency encode gradient magnetic field 1305 and an RF pulse.
- the echo signal generated after elapse of TE is obtained as the positive echo signal.
- the conditions after the irradiation of the next RF pulse 906 are the conditions for obtaining the above-described positive echo signal except that the negative frequency encode gradient magnetic field 1310 is applied after the positive frequency encode gradient magnetic field 1309 is applied. Similarly, a negative echo signal is obtained after TE.
- Correction data measurement is performed by applying a low-frequency phase encoding gradient magnetic field including a zero phase encoding gradient magnetic field.
- the application amount of the low-frequency phase encoding gradient magnetic field is preferably 8, more preferably 16, and further preferably 32.
- the correction data measurement is performed immediately before or immediately after the main measurement with the same slice position, the same imaging field (FOV (Field of View)), the same frequency encoding direction, the same frequency encoding sampling points, and the same reception bandwidth as the main measurement. May be executed. Further, the correction data measurement may be performed continuously or separately from the main measurement.
- FOV Field of View
- Measure correction data for each coil For example, when a signal is received by a coil having a plurality of small coils (channels), it is preferable to acquire a signal for each small coil (channel). Moreover, it is preferable to perform correction data measurement for each object to be imaged.
- a pair of positive and negative echo signals obtained by correction data measurement is stored in the correction database 203.
- the image conversion unit 204 uses the correction data to remove the influence of the reception frequency characteristic
- the image processing unit 206 uses the corrected image, synthesizes the images for each channel, creates a water image and a fat image
- the processing for obtaining the fat content and the processing in which the image transmission unit 207 transmits the image-processed image to the display unit 111 are the same as in the first embodiment.
- correction data is created using a pair of correction echo signals acquired during application of frequency-encoded gradient magnetic fields of different polarities with the same echo time, and the echo obtained by this measurement is measured. By correcting the signal, the same effect as in the first embodiment can be obtained.
- ⁇ Third embodiment> In the first and second embodiments, a sequence for acquiring two images with different TEs was used as the main measurement, but in the third embodiment, it can be applied to a sequence for acquiring three images with different TEs. To do.
- FIG. 14 shows an example of a sequence for acquiring three different TE images (this measurement pulse sequence of this embodiment). This sequence can be used, for example, in a three-point DIXON method.
- This measurement pulse sequence in FIG. 14 is the same except that the third frequency echo gradient magnetic field 1407 is applied again to generate the third echo signal and the third echo signal is generated after TE3 has elapsed from the RF pulse. This is the same as the main measurement pulse sequence shown in FIG. Three types of image data with different TEs can be obtained from the echo signal acquired from the main measurement pulse sequence of FIG.
- the correction data is acquired only for one set of the positive echo signal and the negative echo signal with the same TE as described in the first and second embodiments. That's fine. Then, as described in the first and second embodiments, the image conversion unit 204 uses the correction data to remove the influence of the reception frequency characteristic, and the image processing unit 206 uses the corrected image for each channel. These images are synthesized, a water image and a fat image are created, the processing for obtaining the fat content rate, and the processing for transmitting the image processed image to the display unit 111 by the image transmission unit 207 may be performed.
- the same effect as in the first and second embodiments can be obtained even in a sequence in which three images having different main measurements are acquired.
- the embodiments of the present invention have been described by taking the DIXON method as an example.However, if the pulse sequence acquires a plurality of signals having different TEs, the three-dimensional gradient echo method, the spin echo method, the fast spin echo method, etc.
- the present invention can be applied. Further, the present invention can be applied even when an image obtained by high-speed imaging of a region of another organ to which fat other than the liver adheres, such as fat around the heart or visceral fat.
- the present invention it is possible to remove the influence of the reception frequency characteristics of the positive and negative image obtained by reversing the frequency encoding gradient magnetic field.
- By removing the influence of the reception frequency characteristic it is possible to provide an MRI apparatus that can improve the accuracy of quantitative evaluation of fat even when using an image acquired by imaging a region such as the liver at high speed while stopping breathing.
- the influence of the reception frequency characteristics of the positive image and the negative image can be removed by inverting the frequency encoding gradient magnetic field.
- the influence of the reception frequency characteristic for example, even when an image obtained by capturing an image of a region such as the liver at high speed under breathing stop is used, the accuracy of quantitative evaluation of fat can be improved.
- the imaging time can be shortened or the number of imaging slices can be increased.
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Abstract
Description
画像処理には、例えば、受信コイルのチャンネル毎の画像を合成する処理や、水画像と脂肪画像を作成する処理や、受信コイル105の感度のムラを補正する処理などがある。画像処理部206は、処理した画像を画像送信部207に渡す。
本実施形態では、制御部112による制御のもと、本計測パルスシーケンスと、本計測で得たデータを補正するための補正データを計測する補正データ計測シーケンスを実行する。
k空間データベース202に格納されたk空間データを2次元フーリエ変換して画像に変換する。変換された画像は、正極の周波数エンコード傾斜磁場を印加して取得したOut-of-phase画像と、負極の周波数エンコード傾斜磁場を印加して取得したIn-phase画像となる。
補正データベース203に格納された、周波数エンコード傾斜磁場の極性が異なるエコーデータをそれぞれ2次元フーリエ変換し、画像空間に変換する。補正データは、1スライスに対して、低域だけの位相エンコード傾斜磁場で取得されたエコー信号である。
2次元フーリエ変換した正極の補正データと2次元フーリエ変換した負極の補正データから比を求める。正極及び負極の信号に含まれる受信周波特性の影響を取り除くためには、一方を他方にそろえればよい。例として、負極の周波数エンコード傾斜磁場印加に取得したIn-phase画像を正極のエコー信号に含まれる受信周波数特性の影響にそろえるように補正するための補正データの比の求め方を説明する。xを周波数エンコード方向、yを位相エンコード方向の座標とし、フーリエ変換した正極の補正データをCp(x,y)、フーリエ変換した負極の補正データをCm(x,y)とすると、比Cr(x)は
補正データの比をフィッティングする。補正データはノイズが含まれるためノイズの影響を除去するために行う。フィッティングに先立って、閾値処理によってノイズのデータを除外する。また、画像上における受信周波数特性の影響は1次または2次の関数の信号傾斜のように発生するため、補正データの比のフィッティングも1次もしくは2次の関数でフィッティングすればよい。フィッティング後の補正データの比はFitting{Cr(x)}で示す。
フィッティングした補正データの比Fitting{Cr(x)}を用いて、2次元フーリエ変換した画像を補正する。負極の周波数エンコード傾斜磁場を印加して取得したIn-phase画像を補正する場合、位相エンコード方向の座標をyとし、In-phase画像をIn(x,y)とすると、補正後のIn-phase画像In’(x,y)は
画像変換部204で補正されたIn-phase画像であるIn’(x,y)を合成し、Out-of-phase画像であるOut(x,y)を合成する場合を示す。それぞれのチャネル毎の画像の合成は以下の式で合成する。
静磁場の不均一によって、異なるTE間に発生する位相変化を示す位相マップを作成する。例えば、図3におけるTE1がOut-of-phase画像で、TE2がIn-phase画像とする。最初に、合成後のIn-phase画像InComb(x,y)から合成後のOut-of-phase画像OutComb(x,y)の位相を引き算し、位相を2倍して、初期位相マップΦ(x,y)を作成する。Out-of-phase画像では水と脂肪が逆位相のため、2倍することによって水と脂肪の逆位相を解消している。式で表すと式(5)となる。
合成後のIn-phase画像InComb(x,y)と合成後のOut-of-phase画像OutComb(x,y)、位相マップを用いて水画像Water(x,y)と脂肪画像Fat(x,y)を作成する。式で示すと式(7)となる。
水画像Water(x,y)と脂肪画像Fat(x,y)もしくは、In-phase画像InComb(x,y)と脂肪画像Fat(x,y)を用いて、脂肪含有率の画像FatRatio(x,y)を作成する。式で示すと式(8)となる。
なお、In-phase画像In(x,y)と補正後のOut-of-phase画像Out’(x,y)をそれぞれ合成し、水脂肪分離画像、脂肪含有率の画像を作成する場合も同様である。
画像1101、画像1102、画像1103、画像1104は、それぞれ、1チャンネル、2チャンネル、3チャンネル、4チャンネルを示す。
周波数エンコード傾斜磁場を印加中に取得したTE1エコーの画像である。画像1105、画像1106、画像1107、画像1108は、それぞれ、1チャンネル、2チャンネル、3チャンネル、4チャンネルである。補正データ計測パルスシーケンスの位相エンコード傾斜磁場は低域の16の位相エンコードを用いた。
第二実施形態でも、制御部112による制御のもと、本計測パルスシーケンスと、補正データ計測パルスシーケンスを実行することは第一実施形態と同じであるが、補正データとして、本計測で取得した信号を利用せずに、本計測とTEが同じで周波数エンコード傾斜磁場パルスの極性が異なる2種のエコー信号を別途取得して利用する点が異なる。
第一及び第二実施形態では、本計測として、TEの異なる2つの画像を取得するシーケンスを使用したが、第三実施形態では、TEの異なる3つの画像を取得するシーケンスにも適用できることを説明する。
Claims (15)
- 静磁場磁石と、高周波磁場パルスを発生する高周波発生部と、核磁気共鳴により発生するエコー信号を受信する高周波コイルを備えた受信部と、傾斜磁場コイルと、所定のパルスシーケンスに従い前記高周波発生部、前記傾斜磁場コイル及び前記受信部を制御する制御部と、前記エコー信号を処理する信号処理部と、を備えた磁気共鳴イメージング装置であって、
前記パルスシーケンスは、前記高周波磁場パルスによる励起後に、複数のエコー時間で異なる極性の周波数エンコード傾斜磁場の印加中にエコー信号を取得するマルチエコーシーケンスであり、
前記信号処理部は、同じエコー時間で正極及び負極の周波数エンコード傾斜磁場の印加中に取得した一対の補正用エコー信号を用いて補正データを作成し、前記異なる極性の周波数エンコード傾斜磁場の印加中に取得したエコー信号を補正する補正部を備えることを特徴とする磁気共鳴イメージング装置。 - 請求項1に記載の磁気共鳴イメージング装置であって、
前記補正部は、前記マルチエコーシーケンスとは別に実行される補正データ計測シーケンスで取得したエコー信号を用いて前記補正データを作成することを特徴とする磁気共鳴イメージング装置。 - 請求項2に記載の磁気共鳴イメージング装置であって、
前記補正データ計測シーケンスは、位相エンコード傾斜磁場の印加条件以外は、前記マルチエコーシーケンスと同種であることを特徴とする磁気共鳴イメージング装置。 - 請求項1に記載の磁気共鳴イメージング装置であって、
前記一対の補正用エコー信号は、前記マルチエコーシーケンスの実行において取得したエコー信号及び前記マルチエコーシーケンスとは別に実行される補正データ計測シーケンスで取得したエコー信号であることを特徴とする磁気共鳴イメージング装置。 - 請求項4に記載の磁気共鳴イメージング装置であって、
前記一対の補正用エコー信号は、低域の位相エンコード傾斜磁場を印加して取得した信号であることを特徴とする磁気共鳴イメージング装置。 - 請求項1に記載の磁気共鳴イメージング装置であって、
前記高周波コイルは、複数の小型コイルからなり、
前記補正部は前記小型コイル毎に補正データを作成し、前記小型コイルでそれぞれ受信したエコー信号に対し前記補正データを用いた補正を行うことを特徴とする磁気共鳴イメージング装置。 - 請求項6に記載の磁気共鳴イメージング装置であって、
前記補正部は、前記小型コイル毎に、前記一対の補正用エコー信号を2次元フーリエ変換して得たデータの比から前記補正データを求めることを特徴とする磁気共鳴イメージング装置。 - 請求項1に記載の磁気共鳴イメージング装置であって、
前記マルチエコーシーケンスは、前記異なる極性の周波数エンコード傾斜磁場において、水からのエコー信号と脂肪からのエコー信号とが同位相になる第一エコー時間と、前記水からのエコー信号と前記脂肪からのエコー信号とが逆位相になる第二エコー時間で、エコー信号を取得する水脂肪分離シーケンスであることを特徴とする磁気共鳴イメージング装置。 - 請求項8に記載の磁気共鳴イメージング装置であって、
前記補正データを作成するためのエコー信号は、前記第一エコー時間又は前記第二エコー時間と同じエコー時間に取得されたエコー信号であることを特徴とする磁気共鳴イメージング装置。 - 請求項8に記載の磁気共鳴イメージング装置であって、
前記水脂肪分離シーケンスは、前記第一エコー時間が前記第二エコー時間より長い時間に設定されていることを特徴とする磁気共鳴イメージング装置。 - 核磁気共鳴により発生するエコー信号を用いて複数種の画像を作成する水脂肪分離画像作成方法であって、
前記エコー信号は、高周波磁場パルスによる励起後に、複数のエコー時間で異なる極性の周波数エンコード傾斜磁場の印加中に取得され、
前記異なる極性の周波数エンコード傾斜磁場の印加中に取得したエコー信号を、同じエコー時間で正極及び負極の周波数エンコード傾斜磁場の印加中に取得した一対の補正用エコー信号を用いて補正することを特徴とする水脂肪分離画像作成方法。 - 請求項11に記載の水脂肪分離画像作成方法であって、
前記一対の補正用エコー信号は、低域の位相エンコード傾斜磁場を印加して取得した信号であることを特徴とする水脂肪分離画像作成方法。 - 請求項11に記載の水脂肪分離画像作成方法であって、
前記エコー信号は、水からのエコー信号と脂肪からのエコー信号とが同位相になる第一エコー時間と、前記水からのエコー信号と前記脂肪からのエコー信号とが逆位相になる第二エコー時間とで収集され、
前記第一エコー時間で取得された第一エコー信号と前記第二エコー時間で取得された第二エコー信号とを用いて、複数種の画像を作成することを特徴とする水脂肪分離画像作成方法。 - 請求項13に記載の水脂肪分離画像作成方法であって、
前記一対の補正用エコー信号は、前記第一エコー時間又は前記第二エコー時間と同じエコー時間で、低域の位相エンコード傾斜磁場を印加して取得した信号であることを特徴とする水脂肪分離画像作成方法。 - 請求項11に記載の水脂肪分離画像作成方法であって、
前記複数種の画像を用いて、脂肪分布率を算出することを特徴とする水脂肪分離画像作成方法。
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US15/311,630 US20170097400A1 (en) | 2014-06-12 | 2015-06-10 | Magnetic resonance imaging apparatus and method for generating water-fat separation image |
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CN107153169A (zh) * | 2017-07-04 | 2017-09-12 | 大连锐谱科技有限责任公司 | 一种稳态进动梯度多回波水脂分离成像方法 |
KR101844514B1 (ko) | 2016-09-02 | 2018-04-02 | 삼성전자주식회사 | 자기 공명 영상 장치 및 자기 공명 영상 획득 방법 |
KR20190121982A (ko) * | 2018-04-19 | 2019-10-29 | 광운대학교 산학협력단 | 정량적 자기 공명 영상 생성 방법 및 정량적 자기 공명 영상 생성 장치 |
JP2020199236A (ja) * | 2019-06-05 | 2020-12-17 | キヤノンメディカルシステムズ株式会社 | 磁気共鳴イメージング装置及び磁気共鳴イメージング方法 |
WO2022203273A1 (ko) * | 2021-03-24 | 2022-09-29 | 아주대학교산학협력단 | 신호강도기반 다중 에코 자기공명영상을 이용하여 고지방 복셀을 구별하고 지방분율맵을 생성하는 방법 및 장치 |
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CN104739409B (zh) * | 2013-12-31 | 2018-02-13 | 西门子(深圳)磁共振有限公司 | 磁共振成像方法和装置 |
US10338174B2 (en) * | 2016-02-11 | 2019-07-02 | The Board Of Trustees Of The Leland Stanford Junior Univesity | Robust dual echo Dixon imaging with flexible echo times |
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JP2020199236A (ja) * | 2019-06-05 | 2020-12-17 | キヤノンメディカルシステムズ株式会社 | 磁気共鳴イメージング装置及び磁気共鳴イメージング方法 |
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WO2022203273A1 (ko) * | 2021-03-24 | 2022-09-29 | 아주대학교산학협력단 | 신호강도기반 다중 에코 자기공명영상을 이용하여 고지방 복셀을 구별하고 지방분율맵을 생성하는 방법 및 장치 |
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