JP5508697B2 - MRI equipment - Google Patents

Description

  The present invention relates to an MRI apparatus, and more particularly to an MRI apparatus that suppresses MR signals generated from adipose tissue by applying a fat signal suppression method.

  In magnetic resonance imaging (MRI), nuclear spins of an object placed in a static magnetic field are excited by a high-frequency signal (RF pulse) having the Larmor frequency, and a magnetic resonance signal (MR signal) generated by the excitation is excited. ) Based on the imaging method.

  An MRI apparatus is an image diagnostic apparatus that generates image data based on MR signals detected from within a living body, and obtains a lot of diagnostic information such as biochemical information and functional diagnostic information as well as anatomical diagnostic information. Therefore, it has become indispensable in the field of diagnostic imaging today.

  In an examination using an MRI apparatus (MRI imaging), an MR signal generated from a water tissue constituting a living tissue (that is, an MR signal resulting from resonance of a hydrogen nuclear spin in the water tissue) and an MR signal generated from a fat tissue are usually used. When image data is generated by mixing MR signals from clinically effective water tissue, it may be difficult to generate high-quality image data due to mixing of MR signals generated from adipose tissue. .

  For such a problem, the inversion recovery method (IR: Inversion Recovery) using the fact that the longitudinal relaxation time of the hydrogen nucleus spin of the water tissue is different from the longitudinal relaxation time of the hydrogen nucleus spin of the adipose tissue, or Fats such as so-called chemical shift selective (CHESS), which excites only the magnetization of adipose tissue using the difference in resonance frequency of hydrogen nucleus spin in each tissue and extinguishes its transverse magnetization component by a spoiler pulse. A method of suppressing MR signals generated from adipose tissue by applying a signal suppression method has been developed (see, for example, Patent Document 1).

  In addition, in order to further suppress the MR signal generated from the fat tissue, a fat saturation pre-saturation pulse (hereinafter referred to as a fat suppression pulse) in which the MR signal generated from the fat tissue substantially disappears. A fat signal suppression method in which a flip angle is set in accordance with imaging conditions has also been proposed (see, for example, Patent Document 2).

JP 05-285116 A US Pat. No. 6,272,369

  As described above, image data based on the MR signal from the water tissue is generated by substantially completely suppressing the MR signal generated from the fat tissue by applying the fat signal suppression method such as the chemical shift selection method. Can do. However, in an actual clinical setting, image data in which water tissue and adipose tissue are mixed, that is, image data based on MR signals from water tissue and MR signals from adipose tissue suppressed to a desired size is required. May be.

  For example, when imaging bone and ligament tissue by MRI imaging of a joint, MR signals collected from the ligament tissue are inherently weak, and when the fat signal suppression method is applied to this MRI imaging, MR signals collected from bones containing a large amount of are suppressed and become extremely small signals. For this reason, it becomes difficult to clearly distinguish and display bone and ligament tissue.

  As described above, the MRI imaging to which the conventional fat signal suppression method is applied includes a tissue having a low density of hydrogen nuclei or a tissue in which a small MR signal is collected due to the relationship between the relaxation time and the pulse sequence and a large amount of fat components. It has a problem that it cannot be displayed separately from the organization.

  The present invention has been made in view of the above-described problems, and its object is to suppress the MR signal generated from the adipose tissue of the subject to a desired magnitude, thereby suppressing the MR signal of the water tissue. Another object of the present invention is to provide an MRI apparatus capable of generating image data having a suitable inter-contrast contrast based on MR signals of fat tissue.

In order to solve the above-described problems and achieve the object, the MRI apparatus of the present invention includes a fat suppression degree selection unit for selecting and setting a desired fat suppression degree from a plurality of preset fat suppression degrees. When transmission and reception to generate the flip angle setting unit for setting the flip angle of the fat suppression pulse based on the imaging condition and the fat suppression degree of MRI imaging to which the fat signal suppression method, the fat saturation pulse having the flip angle And a sequence control unit that controls irradiation of the fat suppression pulse and application of a spoiler gradient magnetic field to the imaging target region of the subject, and suppresses an MR signal generated from the fat tissue of the imaging target site to a predetermined magnitude; An image based on an MR signal acquired by applying a predetermined pulse sequence to the region to be imaged in which MR signals from the fat tissue are suppressed. Comprising an image data generation unit for generating data.

In addition, the MRI apparatus of the present invention receives an input from an operator and adjusts the fat suppression degree of MRI imaging to which the fat signal suppression method is applied within a predetermined range of fat suppression degrees. An input unit, an imaging parameter setting unit for setting parameters of fat suppression conditions for fat suppression based on the adjusted degree of fat suppression, and fat suppression of the parameters set for the imaging target region of the subject controls morphism irradiation pulses, and the photographing MR signals generated from the adipose tissue of a subject site in a predetermined suppressing the magnitude sequence control unit with respect to the imaging target portion MR signal is suppressed from the adipose tissue An image data generation unit that generates image data based on MR signals collected by applying a predetermined pulse sequence.

According to the present invention, the MR signal generated from the adipose tissue of the subject is suppressed to a desired magnitude, so that a suitable tissue contrast based on the MR signal of the water tissue and the suppressed MR signal of the adipose tissue is obtained. The generated image data can be generated. For this reason, it is possible to clearly distinguish and display adipose tissue, which has been difficult in the past, and other tissues with low MR signal intensity, and the diagnostic performance of the apparatus is improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the embodiments of the present invention described below, first, the flip angle of the fat suppression pulse is set based on the imaging conditions and the fat suppression degree of MRI imaging to which the fat signal suppression method is applied. Next, in a fat suppression sequence for the purpose of suppressing MR signals generated from adipose tissue (hereinafter referred to as fat signals), irradiation of a fat suppression pulse having the flip angle with respect to the imaging target region of the subject; The spoiler gradient magnetic field is applied to suppress the fat signal to a desired magnitude. Next, in the MR signal acquisition sequence subsequent to the fat suppression sequence, irradiation of an RF pulse and application of a gradient magnetic field to the imaging target site are performed according to a predetermined pulse sequence, and the MR signal (water signal) generated from the water tissue is suppressed. The fat signal is detected. Then, the obtained water signal and fat signal are processed to generate image data.

  In the following embodiments, an MR signal (that is, a water signal and a suppressed fat signal) generated from a region to be imaged of the subject by applying an SE (Spin Echo) method using a 90 degree pulse and a 180 degree pulse. Signal) is collected, but the present invention is not limited to this. Other methods such as FSE (Fast Spin Echo) method, FE (Field Echo) method, and EPI (Echo Planar Imaging) method are also used. It doesn't matter.

(Device configuration)
The configuration of the MRI apparatus in the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the overall configuration of the MRI apparatus in this embodiment.

  The MRI apparatus 100 shown in FIG. 1 includes a static magnetic field generation unit 1 that generates a static magnetic field for a subject 150, a gradient magnetic field generation unit 2 that generates a gradient magnetic field, and irradiation of an RF pulse to the subject 150. A transmission / reception unit 3 that receives MR signals; a top 4 on which the subject 150 is placed; an image data generation unit 5 that reconstructs MR signals received by the transmission / reception unit 3 to generate image data; A sample image data storage unit 6 in which a plurality of sample image data corresponding to various types of fat suppression is stored in advance, and a sample image data storage unit based on the image data and the fat suppression level generated in the image data generation unit 5 6 is provided with a display unit 7 for displaying the sample image data read out from 6.

  The MRI apparatus 100 further includes an input unit 8 for inputting subject information, selecting an imaging mode, setting imaging conditions, setting a fat suppression degree, inputting various command signals, and the like, and imaging parameters corresponding to the various imaging conditions. Of the fat suppression pulse based on the setting information of the fat suppression degree supplied from the input unit 8 and the information of the imaging parameter supplied from the shooting parameter storage unit 9. A flip angle calculation unit 10 that calculates an angle and a control unit 11 that comprehensively controls each unit in the MRI apparatus 100 are provided.

  The static magnetic field generation unit 1 includes a main magnet 101 composed of a normal conducting magnet or a superconducting magnet, and a static magnetic field power source 102 for driving the main magnet 101. The static magnetic field power source 102 is connected to the main magnet 101. By supplying a predetermined current, a strong static magnetic field is formed on the subject 150 arranged in the imaging field of the gantry (not shown). The main magnet 101 described above may be constituted by a permanent magnet.

  On the other hand, the gradient magnetic field generator 2 includes a plurality of gradient magnetic field coils 21 that form gradient magnetic fields in the X axis direction, the Y axis direction, and the Z axis direction orthogonal to each other, and a pulse current for each of the gradient magnetic field coils 21. Is provided.

  The gradient magnetic field power supply 22 in the fat suppression sequence for the purpose of suppressing the fat signal uses a gradient magnetic field as a pulse current for applying the spoiler gradient magnetic field Gp to the irradiation region of the fat suppression pulse irradiated from the transmission coil 31 described later. The coil 21 is supplied. The macroscopic transverse magnetization component of the magnetization vector of the adipose tissue that has been tilted by the flip angle α by irradiation with the fat suppression pulse is extinguished (saturated) by the application of the spoiler gradient magnetic field.

  On the other hand, the gradient magnetic field power supply 22 in the MR signal acquisition sequence encodes the imaging field of the gantry in which the subject 150 is arranged. That is, the gradient magnetic field power supply 22 controls the pulse current supplied to the gradient magnetic field coil 21 in the X-axis direction, the Y-axis direction, and the Z-axis direction based on the sequence control signal supplied from the control unit 11 to thereby change the direction of each direction. To form a gradient magnetic field. The gradient magnetic fields in the X-axis direction, the Y-axis direction, and the Z-axis direction are combined to form a slice selection gradient magnetic field Gs, a phase encode gradient magnetic field Ge, and a readout (frequency encode) gradient magnetic field Gr that are orthogonal to each other. The That is, these gradient magnetic fields Gs, Ge, and Gr and the above-described spoiler gradient magnetic field Gp are superimposed on the static magnetic field formed by the main magnet 101 and applied to the subject 150.

  Next, the transmission / reception unit 3 transmits a transmission coil 31 and a transmission unit 32 that irradiate the subject 150 with RF pulses, and a reception coil 33 that receives MR signals (water signal and fat signal) generated in the subject 150. And a receiving unit 34. However, a transmission / reception coil having the function of the transmission coil 31 and the function of the reception coil 33 in one coil may be used.

  Based on the sequence control signal supplied from the control unit 11, the transmission unit 32 has the same frequency as the magnetic resonance frequency (Larmor frequency) of the hydrogen nuclear spins in the fat tissue and the water tissue determined by the static magnetic field strength of the main magnet 101. A pulse current having a carrier wave and modulated with a predetermined selective excitation waveform is generated. FIG. 2 shows the magnetic resonance frequency f0w of the water tissue and the magnetic resonance frequency f0f of the fat tissue. When the magnetic resonance frequency f0w of the water tissue is used as a reference (0 ppm), the magnetic resonance frequency f0f of the fat tissue is Present at −3.5 ppm on the frequency axis.

  In this case, the transmission unit 32 in the fat suppression sequence generates a pulse current for generating a fat suppression pulse having a predetermined frequency band Δf0f with the magnetic resonance frequency f0f of the fat tissue as the center frequency. Similarly, the transmission unit 32 in the MR signal acquisition sequence generates, for example, a pulse current for generating a 90 degree RF pulse and a 180 degree RF pulse having a predetermined frequency band Δf0w with the magnetic resonance frequency f0w of the water tissue as a center frequency. Is generated.

  Next, the transmission coil 31 shown in FIG. 1 is driven by the pulse current supplied from the transmission unit 32 described above, and irradiates the imaging target region of the subject 150 in the fat suppression sequence with a fat suppression pulse. A 90-degree RF pulse and a 180-degree RF pulse are irradiated to the imaging target site in the MR signal acquisition sequence.

  On the other hand, the receiving coil 33 detects MR signals (water signal and fat signal) generated from the water tissue and adipose tissue in the imaging target region of the subject 150 by the irradiation of the 90 degree RF pulse and the 180 degree RF pulse. The receiving coil 33 is usually constituted by a so-called array coil in which a plurality (N) of small-diameter coils are arranged in order to detect MR signals with high sensitivity.

  The receiving unit 34 includes an N channel amplification circuit, an intermediate frequency conversion circuit, a detection circuit, a filtering circuit, and an A / D converter (not shown), and amplifies, intermediate frequency conversion, and a minute MR signal detected by the reception coil 33. A / D conversion is performed after performing signal processing such as phase detection and filtering. However, the amplifying circuit is usually provided in the vicinity of the receiving coil 33 in order to amplify the MR signal detected by the receiving coil 33 with high S / N.

  The main magnet 101, the gradient magnetic field coil 21, the transmission coil 31, and the reception coil 33 are provided in a gantry (not shown) of the MRI apparatus 100, and an imaging field is formed at the center of the gantry. That is, an imaging field in which the subject 150 is inserted together with the top 4 is provided at the center of the gantry, and the reception coil 33, the transmission coil 31, the gradient magnetic field coil 21, and the main magnet 101 are Z-axis around the imaging field. Are arranged concentrically with the axis as the axis.

  Next, the top plate 4 is slidably mounted in the Z-axis direction on the upper surface of a bed (not shown) installed in the vicinity of the gantry, and the subject 150 placed on the top plate 4 is moved in the body axis direction (Z-axis direction). ) To set the imaging target region of the subject 150 at a desired position in the imaging field. In this case, the top plate 4 is moved by the top plate movement mechanism unit and the top plate movement control unit (not shown) so that the imaging target part faces the receiving coil 33 provided in the vicinity of the imaging field.

  The image data generation unit 5 includes an MR signal storage unit 51, a high-speed calculation unit 52, and an image data storage unit 53. The MR signal storage unit 51 includes intermediate frequency conversion, phase detection, and further by the reception unit 34 of the transmission / reception unit 3. Are sequentially stored together with the imaging position information (that is, slice encoding information, phase encoding information, etc.) supplied from the control unit 11 with the N-channel MR signal subjected to A / D conversion.

  On the other hand, the high-speed calculation unit 52 reads the MR signal and imaging position information once stored in the MR signal storage unit 51, and performs image reconstruction processing by two-dimensional Fourier transform to generate image data. The obtained image data is stored in the image data storage unit 53. However, instead of reconstructing the two-dimensional MR signal supplied from the receiving unit 34 to generate two-dimensional image data, a three-dimensional Fourier transform is performed on the three-dimensional MR signal supplied from the receiving unit 34. The volume data (three-dimensional data) may be generated by performing reconstruction processing according to the above, and three-dimensional image data or MPR image data may be generated based on the volume data. In this case, the high-speed calculation unit 52 performs, for example, a function of rendering volume data to generate three-dimensional image data such as volume rendering image data and surface rendering image data, and MPR (Multi Planar Reconstruction) has a function to generate image data.

  In the sample image data storage unit 6, a plurality of image data collected from the subject 150 or other subjects at various fat suppression degrees is stored in advance as sample image data. In addition, information on imaging conditions such as an imaging part, an imaging purpose, and image contrast in the collection of the image data, and information on the fat suppression degree are also stored in the sample image data storage unit 6 as incidental information of the sample image data.

  Next, the display unit 7 includes a display data generation circuit and a monitor (not shown), and the display data generation circuit generates image data of the subject 150 at a desired degree of fat suppression generated by the image data generation unit 5, or The sample image data read from the sample image data storage unit 6 is converted into a predetermined display format based on the fat suppression degree and imaging condition information supplied from the input unit 8 to generate display data. The displayed display data is displayed on the monitor.

  Further, the display data generation circuit has an image data calculation unit (not shown) that performs calculation between image data. For example, when sample image data having a desired fat suppression degree does not exist in the sample image data storage unit 6 Sample image data (first sample image data) in the imaging condition corresponding to each of a plurality of fat suppression degrees set in the input unit 8 or automatically set in the control unit 11 is stored in the sample image data storage unit 6, sample image data (second sample image data) having a desired degree of fat suppression is generated by weighting and adding these image data.

  Next, the input unit 8 is an interface provided with various input devices such as switches, a keyboard, a mouse, a slide lever, and a display panel on the console, and an imaging mode selection unit that selects normal imaging mode / fat suppression imaging mode. 81, an imaging condition setting unit 82 for setting an imaging condition for the MRI imaging, and a fat suppression degree setting unit 83 for setting a fat suppression degree in the fat suppression imaging mode. Furthermore, input of object information, setting of image data generation conditions and image data display conditions, input of various command signals, and the like are performed using the above-described input device and display panel.

  3 and 4 show a specific example of the fat suppression degree setting unit 83 that is used after the fat suppression imaging mode is selected by the imaging mode selection unit 81, and FIG. Severe fat suppression imaging mode that generates image data with almost 100% suppression of fat signals and a mild fat suppression imaging mode that generates image data while suppressing fat signals to a desired size are possible A fat suppression degree setting unit 83. For example, a light fat suppression imaging mode is selected by selecting the radio button “ON” provided in the fat suppression degree setting unit 83, and a heavy fat suppression imaging mode is selected by selecting the radio button “OFF”. Is done. When a light fat suppression imaging mode is selected by the above-described method, for example, a fat suppression degree of 70% set in advance for the fat suppression imaging mode is set.

  Also, the fat suppression degree setting unit 83 shown in FIG. 3B has a radio button “high” for selecting a severe fat suppression imaging mode, a radio button “medium” for selecting a moderate fat suppression imaging mode, and a mild And a radio button “low” for selecting a fat suppression imaging mode, and is used when a desired fat suppression degree is selected from three preset fat suppression degrees. For example, the selection of the radio button “high” indicates 100% fat suppression, the selection of the radio button “middle” indicates 70% fat suppression, and the selection of the radio button “low” indicates 30% fat suppression. Are set respectively. In FIG. 3B, by selecting one of the radio buttons “high”, “medium” and “low”, three types of fat suppression degrees “100%”, “70%” and “30%” The case of selecting a desired fat suppression degree from among the above has been described, but the type and value of the fat suppression degree are not limited to these.

  In contrast to the fat suppression degree setting unit 83 in FIGS. 3A and 3B that selects and sets a desired fat suppression degree from a plurality of preset fat suppression degrees, FIG. The specific example of the fat suppression degree setting part 83 which can set a degree to arbitrary values is shown. That is, the fat suppression degree setting unit 83 of FIG. 4 has a lever 83a that is slidable in the left-right direction, and moves the lever 83a to a desired position on the fat suppression degree scale 83b provided below the lever 83a. It becomes possible to set the suppression degree to an arbitrary value. Then, the set value of the fat suppression degree is displayed on the fat suppression degree display portion 83c. Moreover, the same effect can be acquired by inputting the value of a fat suppression degree using the keyboard provided in the input part 8. FIG.

  Next, the fat suppression degree set in the fat suppression degree setting unit 83 in FIG. 3 or FIG. 4 is supplied to the flip angle calculation unit 10 via the control unit 11 together with the imaging conditions of the MRI imaging supplied from the imaging condition setting unit 82. Supplied. Then, the flip angle calculation unit 10 calculates the flip angle of the fat suppression pulse for realizing the fat suppression degree.

  Returning to FIG. 1, the imaging parameter storage unit 9 stores in advance imaging parameters corresponding to various imaging conditions including an imaging part, an imaging purpose, an image contrast, and the like. FIG. 5 shows a specific example of the imaging parameter corresponding to the imaging condition. For example, the imaging region is “head”, the imaging purpose is “head screening”, and the image contrast is “T2 weighted image”. Various imaging parameters (sequence type (pulse sequence name), repetition time TR, echo time TE, number of slices M, imaging area FOV, image matrix, etc.) preset for the conditions are stored.

  Similarly, imaging sites such as `` chest '', `` cervical '', `` abdominal '', `` pelvic part '', `` brain tumor '', `` pulmonary disease '', `` abdominal tumor '', `` cervical spine abnormality '', etc. Imaging parameters set for imaging conditions such as an image contrast such as “T1-weighted image” are also stored in the imaging parameter storage unit 9. Then, an imaging parameter corresponding to the imaging condition information supplied from the imaging condition setting unit 82 of the input unit 8 is read from the imaging parameter storage unit 9 and supplied to the flip angle calculation unit 10 via the control unit 11. .

  Returning to FIG. 1 again, the flip angle calculation unit 10 includes an arithmetic circuit and a storage circuit (not shown), and realizes a desired fat suppression degree based on the above-described imaging parameters supplied from the imaging parameter storage unit 9. Calculate the flip angle of the pulse.

  Next, a flip angle calculation method performed by the flip angle calculation unit 10 will be described with reference to FIG. FIG. 6 shows a pulse sequence of MRI imaging using a fat suppression pulse of flip angle α that realizes a desired degree of fat suppression as a pre-pulse. This pulse sequence applies a fat suppression pulse to the imaging target region of the subject 150. A fat suppression sequence that suppresses a fat signal generated from the imaging target region to a desired magnitude by irradiation, and an MR signal from water tissue by applying the SE method to the imaging target site in which the fat signal is suppressed ( And an MR signal acquisition sequence for acquiring MR signals (fat signals) from the suppressed fat tissue.

  Then, at the time t1 of the fat suppression sequence, as already described in FIG. 2, the fat suppression pulse having the band Δf0f with the magnetic resonance frequency f0f of the fat tissue lower by 3.5 ppm than the magnetic resonance frequency f0w of the water tissue as the center frequency. Then, a relatively wide area of the imaging target region determined by the size of the transmission coil 31 is irradiated, and the magnetization vector of the adipose tissue existing in this irradiation area is tilted by a flip angle α degrees.

  Next, at the time t2 of the fat suppression sequence subsequent to the irradiation of the fat suppression pulse, for example, by applying a spoiler gradient magnetic field Gp in the phase encoding direction, a phase difference is given to the transverse magnetization component of the magnetization vector tilted by α degrees. The macroscopic transverse magnetization component of this magnetization vector is extinguished (saturated).

  Next, at the time t3 of the MR signal acquisition sequence after the time interval Td has elapsed from the irradiation of the fat suppression pulse, the application of the 90-degree RF pulse and the application of the slice selection gradient magnetic field Gs for selecting the slice cross-section are applied to the above-described imaging target region. The magnetization vector of the water tissue consisting of a plurality of selected slice sections is tilted by 90 degrees.

  Further, at the time t4 after TE / 2 from the irradiation of the 90 degree RF pulse, the same imaging target region is irradiated with the 180 degree RF pulse, and the magnetization vector in the water tissue that has been expanded in the period [t3-t4]. The phase difference is gradually reduced by the irradiation of the 180 degree RF pulse. Then, at time t5 after TE / 2 from irradiation of the 180 degree RF pulse, the phase of the magnetization vector coincides to generate an MR signal, and this MR signal is generated in the presence of the readout gradient magnetic field Gr applied at time t5. It is detected by the receiving coil 33 and supplied to the receiving unit 34. MR signals for one phase encoding direction are collected by the above-described procedure, and further, MR signals for one slice necessary for generating image data are collected by repeating the same procedure while sequentially updating the phase encoding gradient magnetic field Ge. Is done.

  At this time, if the repetition time TR is sufficiently longer than the longitudinal relaxation time T1 of the adipose tissue, the longitudinal magnetization component of the magnetization vector in the adipose tissue saturated in the fat suppression sequence is almost completely recovered and is irradiated after the TR. It is defeated again by α degrees by the next fat suppression pulse. Here, when the time interval Td from the irradiation of the fat suppression pulse at the time t1 to the irradiation of the 90-degree RF pulse at the time t3 is sufficiently shorter than the longitudinal relaxation time T1 of the adipose tissue, immediately before the 90-degree RF pulse is irradiated. The longitudinal magnetization component of the magnetization vector in the fat tissue is substantially equal to the longitudinal magnetization component immediately after the fat suppression pulse is irradiated. Therefore, MR signals in which the fat signal is suppressed are collected from the imaging target region of the subject 150 based on the fat suppression pulse with the flip angle α.

When MR signals are continuously collected for different phase encoding while irradiating a fat suppression pulse with a flip angle α at a repetition time TR, longitudinal magnetization of a magnetization vector in a fat tissue immediately after the irradiation of the fat suppression pulse is performed. The longitudinal magnetization component M0 of the magnetization vector in the initial state before irradiation with the component Mz + and the first fat saturation pulse has a relationship represented by the following formula (1) when the longitudinal relaxation time of the fat tissue is T1.

即ち、脂肪抑制度（１−Ｍｚｆ／Ｍ０）は、繰り返し時間ＴＲ、脂肪組織の縦緩和時間Ｔ１、脂肪抑制パルス照射時刻ｔ１から９０度ＲＦパルス照射時刻Ｔ３までの時間間隔Ｔｄ、脂肪抑制パルスのフリップアングルαの関数となり、例えば、ＴＲ＝２０００ｍｓｅｃ、Ｔ１＝２６０ｍｓｅｃ、Ｔｄ＝１０ｍｓｅｃの場合、脂肪抑制パルスのフリップアングルαに対するＭｚｆ／Ｍ０は上式（１）及び（２）を用いることにより図７にようになる。そして、この図７によれば、脂肪抑制度を７０％（即ち、Ｍｚｆ／Ｍ０＝０．３）にしたい場合には脂肪抑制パルスのフリップアングルαを約７５度に設定すればよいことがわかる。尚、脂肪組織の縦緩和時間Ｔ１や時間間隔Ｔｄは、通常、撮像条件等に依存することなく設定されるため、フリップアングルαは、繰り返し時間ＴＲによって略決定される。 Further, the longitudinal magnetization component Mzf in the magnetization vector just before irradiation with the 90-degree RF pulse and the longitudinal magnetization component M0 in the magnetization vector in the initial state are relaxed in the longitudinal magnetization component Mz + performed in the period [t1-t3]. By considering the process, the following equation (2) is obtained.

That is, the degree of fat suppression (1-Mzf / M0) is the repetition time TR, the longitudinal relaxation time T1 of fat tissue, the time interval Td from the fat suppression pulse irradiation time t1 to the 90-degree RF pulse irradiation time T3, and the fat suppression pulse. For example, when TR = 2000 msec, T1 = 260 msec, and Td = 10 msec, Mzf / M0 with respect to the flip angle α of the fat suppression pulse is obtained by using the above equations (1) and (2). It becomes like. According to FIG. 7, it is understood that the flip angle α of the fat suppression pulse may be set to about 75 degrees when the fat suppression degree is desired to be 70% (that is, Mzf / M0 = 0.3). . Since the longitudinal relaxation time T1 and the time interval Td of the adipose tissue are normally set without depending on the imaging conditions and the like, the flip angle α is substantially determined by the repetition time TR.

  And the arithmetic program based on Formula (1) and Formula (2) is stored beforehand by the said memory circuit with which the flip angle calculation part 10 is provided. On the other hand, the arithmetic circuit of the flip angle calculation unit 10 repeats the imaging parameter supplied from the imaging parameter storage unit 9 based on the imaging condition of the MRI imaging set by the imaging condition setting unit 82 of the input unit 8. TR, the longitudinal relaxation time T1 and time interval Td of the preset fat tissue, and the desired fat suppression degree supplied from the fat suppression degree setting unit 83 of the input unit 8 via the control unit 11 are stored in the storage circuit. The flip angle α for realizing the fat suppression degree is calculated by inputting the calculation program read from the above.

  In the typical pulse sequence such as the spin echo (SE) method, the fast spin echo (FSE) method, the field echo (FE) method, etc., MR signals are collected for a plurality of slice sections during the repetition time TR. A multi-slice method is applied. FIG. 8 schematically shows the acquisition of MR signals by the multi-slice method. For example, when acquiring MR signals for M slice cross sections during the repetition time TR, each of the slices 1 to M is shown. MR signals are collected by the fat suppression sequence and the MR signal collection sequence in the same manner as in FIG.

この場合、フリップアングル算出部１０の前記演算回路は、入力部８の撮像条件設定部８２にて設定される当該ＭＲＩ撮影の撮像条件に基づいて撮像パラメータ保管部９から供給される撮像パラメータの繰り返し時間ＴＲ及びスライス数Ｍ（図５参照）とから脂肪抑制パルス間隔Ｔｆを算出する。そして、得られた脂肪抑制パルス間隔Ｔｆと予め設定された脂肪組織の縦緩和時間Ｔ１及び時間間隔Ｔｄ、更には、入力部８の脂肪抑制度設定部８３から制御部１１を介して供給される所望の脂肪抑制度を前記記憶回路から読み出した演算プログラムに入力することにより前記脂肪抑制度を実現するためのフリップアングルαを算出する。 If the MR signal acquisition repetition time for the slice cross section with the number of slices M is TR, the MR signal acquisition time (ie, fat suppression pulse interval) Tf for each slice cross section is represented by Tf = TR / N. The flip angle α of the fat suppression pulse in such a multi-slice method can be calculated based on the following equation (3) in which the repetition time TR in the equations (1) and (2) is replaced with the fat suppression pulse interval Tf. Is possible.

In this case, the arithmetic circuit of the flip angle calculation unit 10 repeats the imaging parameters supplied from the imaging parameter storage unit 9 based on the imaging conditions of the MRI imaging set by the imaging condition setting unit 82 of the input unit 8. The fat suppression pulse interval Tf is calculated from the time TR and the slice number M (see FIG. 5). Then, the obtained fat suppression pulse interval Tf, preset longitudinal relaxation time T1 and time interval Td of fat tissue, and further supplied from the fat suppression degree setting unit 83 of the input unit 8 via the control unit 11. A flip angle α for realizing the fat suppression degree is calculated by inputting a desired fat suppression degree to the calculation program read from the storage circuit.

  FIG. 9 shows Mzf / M0 with respect to the flip angle α of the fat suppression pulse for various fat suppression pulse intervals Tf. For example, many MR signals are shortened by irradiating the RF pulse a plurality of times continuously. In the FSE method that can be collected in time, when all MR signals for one slice cross section are collected during the repetition time TR, Tf = TR, and as described above, when Tf is 2000 msec, By setting the flip angle of the fat suppression pulse to 75 degrees, image data with a fat suppression degree of 70% can be obtained.

  However, in order to shorten the MR signal acquisition time for many slice cross sections, for example, when the number of phase encoding directions is reduced and the MR signal acquisition time for one slice cross section, that is, the fat suppression pulse interval Tf is set to 100 msec. In order to obtain a fat suppression degree of 70%, it is necessary to set the flip angle α of the fat suppression pulse to about 55 degrees. In other words, when the flip angle α of the fat suppression pulse is kept at 75 degrees, image data in which the fat signal is excessively reduced is generated.

  Further, in the SE method and the FE method, for example, when the MR signal acquisition time for one slice cross section is further reduced and the fat suppression pulse interval Tf is shortened to 20 msec, in order to obtain a fat suppression degree of 70%, The flip angle α must be set to 35 degrees.

  In order to simplify the explanation in the equations (2) and (3) and FIGS. 7 and 9 showing these, only the influence of the fat suppression pulse is used in the calculation of the longitudinal magnetization, and the RF pulse in the MR signal acquisition sequence is used. The effect of is not considered. However, if the type of pulse sequence, imaging conditions, etc. are determined, the longitudinal magnetization in the steady state can be obtained in the same manner.

  Next, the control unit 11 in FIG. 1 includes a main control unit 111 and a sequence control unit 112. The main control unit 111 includes a CPU and a storage circuit (not shown) and has a function of controlling the MRI apparatus 100 in an integrated manner. The memory circuit of the main control unit 111 includes a preset longitudinal relaxation time of fat tissue and water tissue, a time interval Td from a fat suppression pulse to a 90-degree RF pulse, and magnetic resonance frequencies f0f and f0w of fat tissue and water tissue. Various pulse sequence data applicable to the MR signal acquisition sequence (for example, the center frequency and band of pulse current supplied to the transmission coil 31 in various pulse sequences, the magnitude, the supply time, the supply timing, etc.) are stored. The subject information input / set / selected by the input unit 8, the imaging mode, the imaging conditions, the fat suppression degree, and the like are stored. The CPU of the main control unit 111 controls each unit of the MRI apparatus 100 based on the above-described various information stored in the storage circuit, and performs MRI imaging on the subject 150.

  On the other hand, the sequence control unit 112 of the control unit 11 includes a CPU (not shown), and generates a sequence control signal based on the fat suppression sequence and the pulse sequence data of the MR signal acquisition sequence supplied from the main control unit 111. Then, by supplying this sequence control signal to the gradient magnetic field power source 22 of the gradient magnetic field generation unit 2 and the transmission unit 32 of the transmission / reception unit 3, the pulse currents for the gradient magnetic field coil 21 and the transmission coil 31 are controlled.

(MRI imaging procedure)
Next, the procedure of MRI imaging in the present embodiment will be described along the flowchart shown in FIG. Although the case where image data for one slice section is generated by applying the SE method will be described here, the present invention is not limited to this.

  Prior to MRI imaging of the subject 150, the operator of the MRI apparatus 100 moves the subject 150 placed on the top 4 in the Z-axis direction to place the imaging target region in the imaging field of the gantry, and then input The unit 8 performs initial settings such as input of object information, setting of image data generation conditions, setting of image data display conditions, and the like (step S1 in FIG. 10).

  Next, the operator selects the fat suppression imaging mode in the imaging mode selection unit 81 of the input unit 8, and then in the imaging condition setting unit 81, imaging conditions for the MRI imaging of the subject 150 (imaging site, imaging purpose, image contrast). Etc.) (step S2 in FIG. 10), and a desired fat suppression degree is set in the fat suppression degree setting unit 83 (step S3 in FIG. 10).

  When setting the fat suppression degree, the operator tentatively sets a desired fat suppression degree by using an input device provided in the fat suppression degree setting unit 83, and sets the setting information and the imaging conditions described above to the control unit 11. The display data generation circuit of the display unit 7 received via the main control unit 111 reads sample image data corresponding to these pieces of information from the sample image data storage unit 6 and displays the sample image data on the monitor of the display unit 7.

  When the sample image data corresponding to the above-described fat suppression degree does not exist in the sample image data storage unit 6, the display data generation circuit is configured to correspond to each of the plurality of fat suppression degrees set in the input unit 8. Sample image data under the imaging conditions (first sample image data) is read from the sample image data storage unit 6. Then, by weighting and adding these image data, sample image data (second sample image data) corresponding to the provisional fat suppression degree is generated and displayed on the display unit 7. Then, the operator determines the validity of the fat suppression degree provisionally set by observing the sample image data displayed on the display unit 7, and based on the determination result, the operator sets the formal setting of the fat suppression degree. Do.

  On the other hand, the flip angle calculation unit 10 that has received the imaging condition and fat suppression degree setting information supplied by the imaging condition setting unit 82 and the fat suppression degree setting unit 83 of the input unit 8 via the main control unit 111 of the control unit 11 is First, an imaging parameter corresponding to the imaging condition is extracted from various imaging parameters stored in the imaging parameter storage unit 9 (step S4 in FIG. 10). Next, the repetition time TR included in the imaging parameter, the fat suppression degree supplied from the fat suppression degree setting unit 83, and 90 degrees from the preset longitudinal relaxation time T1 of the fat tissue and the fat suppression pulse. By inputting the time interval Td to the RF pulse into the calculation program read from its own storage circuit, the flip angle α of the fat suppression pulse for realizing the fat suppression degree is calculated (step S5 in FIG. 10).

  Then, when the calculation result of the flip angle α is supplied to the main control unit 111, MRI imaging in the fat suppression imaging mode is started.

  At the time of MRI imaging in the fat suppression imaging mode, the sequence control unit 112 of the control unit 11 suppresses the fat signal based on the calculated flip angle α and generates an MR signal based on the SE method set in the sequence type of the imaging parameter described above. Collect. That is, the transmission unit 32 of the transmission / reception unit 3 generates a predetermined pulse current based on the control signal supplied from the sequence control unit 112 at time t1 of the fat suppression sequence. The transmission coil 31 to which this pulse current is supplied takes an image in which a fat suppression pulse of a flip angle α having a predetermined band Δf0f with a magnetic resonance frequency f0f of fat tissue as a center frequency is determined by the size of the transmission coil 31. The target site is irradiated, and the magnetization vector of the adipose tissue existing in this irradiation region is tilted by a flip angle α degrees.

  Next, by applying a spoiler gradient magnetic field Gp in the phase encoding direction at time t2 of the fat suppression sequence following the fat suppression pulse irradiation, a phase difference is given to the transverse magnetization component in the above-described magnetization vector that has been tilted by α degrees. Then, the macroscopic transverse magnetization component of this magnetization vector is extinguished (saturated) (step S6 in FIG. 10).

  Next, at the time t3 of the MR signal acquisition sequence after the time interval Td has elapsed from the irradiation of the fat suppression pulse, the irradiation of the 90-degree RF pulse and the application of the slice selection gradient magnetic field Gs for setting a predetermined slice cross section are performed as described above The magnetization vector of the water tissue and the suppressed fat tissue existing in the selected slice cross-section is tilted by 90 degrees.

  Further, irradiation of 180 degree RF pulse and application of slice selective gradient magnetic field Gs are performed at time t4 after TE / 2 from irradiation of 90 degree RF pulse. At this time, the phase difference of the magnetization vector in the water tissue and the fat tissue of the slice cross-section that was expanding in the period [t3-t4] is gradually reduced by the irradiation of the 180 RF pulse, and from the irradiation of the 180 degree RF pulse, the TE / Two times later at time t5, the phases of the magnetization vectors coincide and are detected as MR signals. This MR signal is detected by the receiving coil 33 in the presence of the readout gradient magnetic field Gs applied at time t5, and the detected MR signal is amplified, intermediate frequency converted, phase detected, filtered, A / D converted. Through signal processing such as the above, the image data is stored in the MR signal storage unit 51 of the image data generation unit 5 together with imaging position information such as slice encoding information and phase encoding information (step S7 in FIG. 10).

  The MR signal is collected and stored for one phase encoding direction necessary for generating image data by the above procedure, and the MR signal is collected at the repetition time TR while updating the magnitude of the phase encoding gradient magnetic field by the same procedure. By repeating the above, MR signals necessary for generating image data for one slice are collected and stored (steps S6 to S7 in FIG. 10).

  On the other hand, the high-speed calculation unit 52 of the image data generation unit 5 reads the MR signals and shooting position information once stored in the MR signal storage unit 51, and performs image reconstruction processing on these MR signals based on the shooting position information. Data is generated (step S8 in FIG. 10). The obtained image data is displayed on the display unit 7 via the image data storage unit 53 (step S9 in FIG. 10).

  According to the embodiments of the present invention described above, the MR signal generated from the fat tissue of the subject is suppressed to a desired magnitude, and thus based on the MR signal of the water tissue and the MR signal of the suppressed fat tissue. Image data having suitable contrast between tissues can be generated. For this reason, it is possible to clearly distinguish and display adipose tissue, which has been difficult in the past, and other tissues with low MR signal intensity, and the diagnostic performance of the apparatus is improved.

  In particular, according to the above-described embodiment, when setting the fat suppression degree, the operator determines the validity of the fat suppression degree set by observing sample image data corresponding to the provisionally set fat suppression degree in advance. Since the determination can be made, it is possible to accurately and easily set the fat suppression degree that enables generation of image data having a suitable contrast between tissues.

  Further, the sample image data corresponding to the provisional fat suppression degree can be easily obtained from a plurality of sample image data collected in advance under various fat suppression degrees and various imaging conditions. When sample image data corresponding to the degree of suppression does not exist in the plurality of sample image data, it can be generated by adding a plurality of sample image data having different degrees of fat suppression. For this reason, it is possible to easily obtain the sample image data of the fat suppression degree set provisionally based on a plurality of sample image data collected in advance.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified. For example, the MRI apparatus 100 in the above-described embodiment includes the flip angle calculation unit 10, the fat suppression degree set by the fat suppression degree setting unit 83 of the input unit 8, and the imaging parameters supplied from the imaging parameter storage unit 9. In the above description, the flip angle of the fat suppression pulse for realizing the fat suppression degree is calculated and automatically set by inputting the value into a predetermined calculation program, but instead of the automatic setting, the calculated flip angle is displayed. It is also possible to allow the operator to check and correct the flip angle.

  Further, for example, as shown in FIG. 11, the imaging parameters (that is, the sequence type, repetition time TR, echo time TE, and slice of FIG. 5) have already been described with respect to flip angles suitable for the heavy, medium and light fat suppression imaging modes. (The number M, the imaging area FOV, and the image matrix) may be stored in the imaging parameter storage unit 9 in advance. According to this method, the flip angle read together with other imaging parameters based on the imaging conditions set in the imaging condition setting unit 82 of the input unit 8 is corrected as it is or by the input unit 8 as necessary. By using it, MRI imaging in the fat suppression imaging mode can be performed. Therefore, complicated calculations based on the above formulas (1) and (2) or the above formula (3) are not required, and the time required for setting the flip angle is greatly reduced.

  Furthermore, as shown in FIG. 12, flip angles suitable for heavy, medium, and light fat suppression imaging modes may be stored in advance for various pulse sequences. For example, in the FSE method, if the number of MR signals is constant, the time interval Tf of fat suppression pulses is constant under the condition that the number of slices is maximum even if the repetition time TR and the number of slices M change. Therefore, the flip angle of the fat suppression pulse corresponding to a predetermined fat suppression degree (severe, medium and mild fat suppression degrees) is obtained with the pulse sequence classified based on the time required for acquiring MR signals in one slice cross section as a unit. By storing in advance, the flip angle of the fat suppression pulse that realizes the fat suppression degree based on the maximum number of slices that can be imaged at the repetition time TR set by the operator prior to MRI imaging and the desired fat suppression degree Can be set.

  On the other hand, in the above-described embodiment, an MR signal (that is, water signal and suppressed fat) generated from the imaging target region of the subject 150 by applying the SE (Spin Echo) method using the 90-degree pulse and the 180-degree pulse. (Signal) is described, but other methods such as an FSE (Fast Spin Echo) method, an FE (Field Echo) method, and an EPI (Echo Planar Imaging) method may be used.

  Further, the case where the high-speed calculation unit 52 in the above-described embodiment generates the two-dimensional image data by reconstructing the two-dimensional MR signal supplied from the reception unit 34 has been described. Volume data may be generated by performing reconstruction processing by three-dimensional Fourier transform on the three-dimensional MR signal, and three-dimensional image data or MPR image data may be generated based on the volume data.

  In the above-described embodiments, the case of the SE method has been described. However, in the gradient echo method having a short repetition time, if a fat suppression pulse is added in front of each data collection unit, the entire imaging time cannot be extended. Therefore, a segment division type data acquisition method is used in which the k space is divided into a plurality of segments and one pre-pulse is applied to each segment. In the case of two-dimensional imaging, the number of data lines obtained by dividing the number of data lines necessary to fill the k space by the number of segments is acquired in one segment period, and this is multiplied by the repetition time TR. This is the time per segment, that is, the application interval of fat suppression pulses. Here, in the case of the spin warp method, the total number of data collection is a phase encoding matrix. The ratio of the longitudinal magnetization component Mz + of fat in each fat saturation pulse and the longitudinal magnetization component M0 in the initial state can be calculated in the same manner by replacing TR in the equation (1) with (number of phase encoding matrices / number of segments) * TR.

  Therefore, the flip angle of the fat suppression pulse that gives the same degree of fat suppression varies depending on the number of phase encoding matrices, the number of segments, and the TR of the pulse sequence. FIG. 13 shows an example of a segment division type pulse sequence using fat suppression pulses. In this example, the k space is divided into n segments. For example, if the phase encoding matrix is 128 and the number of segments n is 16, the number of data collections per segment is 8.

  In the case of three-dimensional imaging, phase encoding in the slice direction is added to this. The three-dimensional data collection order includes a method of collecting phase-encoded data in a plane first, a case of collecting phase-encoded data in a slice direction, and a method of collecting them in a mixed order. In any case, if the pulse sequence is assembled from the imaging conditions, the flip angle of the fat suppression pulse that gives the same degree of fat suppression can be obtained.

  In the above-described embodiment, the case of the CHESS method has been described. However, in the MRI fat suppression method, in addition to the CHESS method, the inversion recovery method is used, and the longitudinal magnetization component of fat is 0 after the inversion pulse. There is a method of collecting signals at the time when The inversion recovery (IR) method used in particular for fat suppression is called the STIR method. Unlike the CHESS method, this method also excites the water signal of the region of interest with an inversion pulse, so the signal value of the water is lower than when no IR is used. Therefore, there is an advantage that it is not affected by the uniformity of the static magnetic field, and it is used especially when uniform fat suppression is desired at a site where it is difficult to ensure the uniformity of the magnetic field.

  FIG. 14 shows a pulse sequence of the STIR method. The pulse sequence includes an inversion recovery unit 200 including an inversion pulse 201 that inverts the magnetization in the region of interest, followed by a data acquisition unit 210. The data collection unit 210 shows an example of the spin echo method. The flip angle of the inversion pulse is set to 180 degrees, and the polarity of the longitudinal magnetization component Mz is inverted. The transverse magnetization component in the xy plane due to the imperfection of the flip angle of the inversion pulse causes a phase difference depending on the location by the subsequent spoiler gradient magnetic field pulse 202 and loses the net macroscopic magnetization component. The longitudinal magnetization component whose polarity has been reversed by the inversion pulse is then recovered at a rate depending on the longitudinal relaxation time T1 of the tissue. In the process, excitation by a 90-degree pulse for data collection is performed after TI time, thereby relaxing the T1 relaxation. An image contrast enhanced with time can be obtained. In the case of STIR, the TI time is set so that the fat signal value becomes 0 in particular. The data collection unit 210 following the inversion recovery unit 200 shows a spin echo method in this example, and is the same as the fat suppression method using the CHESS pulse, and thus the description thereof is omitted.

When this method is executed, the ratio of the longitudinal magnetization component Mz immediately before the excitation pulse 211 in the steady state to the longitudinal magnetization component M0 in the initial state is set to TR as the repetition time, TI as the inversion recovery time, and T1 as the longitudinal relaxation time. Mz / M0 = 1−2 * exp (−TI / T1) + exp (−TR / T1) (4)
It is known to be given in

For example, if the repetition time of the pulse sequence is TR = 500 msec and the longitudinal relaxation time of fat at 1.5T is T1 = 230 msec, the fat signal immediately before excitation is set to 0 by Mz / M0 in the equation (4). By setting = 0, TI = T1 * ln (2 / (1 + exp (-TR / T1))) = 134.6 msec
It can be seen that it is.

Similarly, when collecting an image in which about 30% of the fat signal is left, TI = T1 * ln (2 // (1 + 0.3 + exp (−) where Mz / M0 = −0.3 in equation (4). TR / T1))) = 79.8msec
It can be seen that it is. Here, it was set to -0.3 instead of Mz / M0 = 0.3 for the following reasons.

  Longitudinal magnetization recovers from negative to positive after inverting the polarity by an inversion pulse. However, when considering that an image obtained by MRI is expressed by an absolute value, the signal intensity to be imaged is 0. The timing of excitation that becomes 3 may be Mz / M0 = −0.3 or +0.3. Among these, the TI time is shortened when Mz / M0 is −0.3, which has less influence on tissues having a longer longitudinal relaxation time than fat, and the pulse sequence time is shorter. This is because it becomes shorter.

  Furthermore, according to equation (4), it can be seen that these TI times also depend on the TR of the pulse sequence. For example, when the TR is extended from 500 msec to 1000 msec, the TI that sets Mz / M0 to 0 changes from 134.6 msec to 156 msec, and the TI that sets the fat signal to 30% changes from 79.8 msec to 96.8 msec. This state is shown in FIG.

  As described above, the fat signal suppression degree in the IR method also depends on other parameters of the pulse sequence. Therefore, in order to realize a desired fat suppression degree, calculation is performed each time based on imaging conditions, or TI time Is preferably stored for each imaging condition. When collecting multi-slice MR signals, a TI time is set for each slice.

1 is a block diagram showing the overall configuration of an MRI apparatus in an embodiment of the present invention. The figure which shows the magnetic resonance frequency of a water tissue and a fat tissue. The figure which shows the specific example of the fat suppression degree setting part with which the MRI apparatus in the Example of this invention was provided. The figure which shows the other specific example of the fat suppression degree setting part with which the MRI apparatus of the Example was provided. The figure which shows the specific example of the imaging parameter in the Example. The figure which shows the pulse sequence of the MRI imaging | photography used in the fat suppression imaging mode of the Example. The figure which shows the relationship between the flip angle of the fat suppression pulse and the fat suppression degree in the single slice method of the Example. The figure which shows typically the acquisition method of MR signal performed with the multi-slice method of the Example. The figure which shows the relationship between the flip angle of the fat suppression pulse and the fat suppression degree in the multi-slice method of the Example. 6 is a flowchart showing a procedure of MRI imaging in the same embodiment. The figure which shows the modification of the flip angle setting method in the Example. The figure which shows the other modification of the flip angle setting method in the Example. The figure which shows the example of a segment (segment) division type pulse sequence. The figure which shows the example of the pulse sequence of an inversion recovery method. The figure which shows the relationship between the longitudinal magnetization and TI time in a reverse recovery method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Static magnetic field generation part 101 Main magnet 102 Static magnetic field power supply 2 Gradient magnetic field generation part 21 Gradient magnetic field coil 22 Gradient magnetic field power supply 3 Transmission / reception part 31 Transmission coil 32 Transmission part 33 Reception coil 34 Reception part 4 Top plate 5 Image data generation part 51 MR Signal storage unit 52 High-speed calculation unit 53 Image data storage unit 6 Sample image data storage unit 7 Display unit 8 Input unit 81 Imaging mode selection unit 82 Imaging condition setting unit 83 Fat suppression degree setting unit 9 Imaging parameter storage unit 10 Flip angle calculation unit DESCRIPTION OF SYMBOLS 11 Control part 111 Main control part 112 Sequence control part 100 MRI apparatus 200 Repetitive recovery part 201 Inversion pulse 202 Spoiler gradient magnetic field pulse 210 Data acquisition part

Claims (22)

A fat suppression degree selection unit for selecting and setting a desired fat suppression degree from a plurality of preset fat suppression degrees;
A flip angle setting unit for setting a flip angle of a fat suppression pulse based on imaging conditions of MRI imaging using a fat signal suppression method and the fat suppression degree;
A transceiver for generating a fat suppression pulse having the flip angle;
A sequence controller that controls irradiation of the fat suppression pulse and application of a spoiler gradient magnetic field to the imaging target region of the subject, and suppresses an MR signal generated from the fat tissue of the imaging target site to a predetermined magnitude;
An image data generation unit that generates image data based on MR signals collected by applying a predetermined pulse sequence to the imaging target region in which MR signals from the adipose tissue are suppressed;
An MRI apparatus comprising: An imaging condition input unit for inputting imaging conditions of the MRI imaging;
An imaging parameter storage unit that stores imaging parameters corresponding to various imaging conditions is provided.
The flip angle setting unit includes the fat suppression pulse based on the desired fat suppression degree set by the fat suppression degree selection unit and an imaging parameter corresponding to the imaging condition extracted from the imaging parameter storage unit. The MRI apparatus according to claim 1, further comprising: a flip angle calculation unit that calculates a flip angle of the first and second flip angles. The flip angle calculation unit includes a storage unit in which a predetermined calculation program for calculating a flip angle of the fat suppression pulse is stored in advance.
The MRI apparatus according to claim 2, wherein the flip angle is calculated by inputting the desired fat suppression degree and the imaging parameter to the calculation program read from the storage unit. The flip angle setting unit includes:
The MRI apparatus according to claim 1, further comprising an imaging parameter storage unit that stores flip angles of fat suppression pulses and imaging parameters corresponding to various imaging conditions. The flip angle setting unit includes:
The MRI apparatus according to claim 2, further comprising an imaging parameter storage unit that stores flip angles and imaging parameters of fat suppression pulses corresponding to various imaging conditions. The flip angle setting unit includes:
The MRI apparatus according to claim 3, further comprising an imaging parameter storage unit that stores flip angles and imaging parameters of fat suppression pulses corresponding to various imaging conditions.   The MRI apparatus according to claim 4, wherein the imaging parameter storage unit stores flip angle information corresponding to various fat suppression degrees for each of the sequence types.   The MRI apparatus according to claim 5, wherein the imaging parameter storage unit stores flip angle information corresponding to various fat suppression degrees for each of the sequence types.   The MRI apparatus according to claim 2, wherein the imaging parameter is at least one of an imaging pulse sequence type, a repetition time TR, the number of slices, and a data collection time per slice.   The MRI apparatus according to claim 9, wherein the imaging parameter is a combination of two of an imaging pulse sequence type, a repetition time TR, the number of slices, and a data acquisition time per slice.   The MRI apparatus according to claim 4, wherein the imaging parameter is at least one of a type of imaging pulse sequence, a repetition time TR, the number of slices, and a data acquisition time per slice.   The MRI apparatus according to claim 11, wherein the imaging parameter is a combination of two of an imaging pulse sequence type, a repetition time TR, the number of slices, and a data acquisition time per slice. A fat suppression degree input unit for receiving the input from the operator and adjusting the fat suppression degree of MRI imaging to which the fat signal suppression method is applied, within a predetermined range of fat suppression degree;
An imaging parameter setting unit that sets parameters of fat suppression conditions for fat suppression based on the adjusted fat suppression degree;
A sequence control unit for controlling the irradiation of the fat suppression pulse of the set parameter to the imaging target region of the subject and suppressing the MR signal generated from the fat tissue of the imaging target region to a predetermined magnitude;
An image data generation unit that generates image data based on MR signals collected by applying a predetermined pulse sequence to the imaging target region in which MR signals from the adipose tissue are suppressed;
An MRI apparatus comprising:   The MRI apparatus according to claim 13, wherein the imaging parameter setting unit determines a parameter of the fat suppression condition according to a type of fat suppression method.   The imaging parameter setting unit employs a chemical shift selection method that excites only the magnetization of adipose tissue using the difference in resonance frequency of hydrogen nucleus spins in each tissue and extinguishes its transverse magnetization component by a spoiler pulse. The MRI apparatus according to claim 14, wherein a flip angle is determined as a parameter of the fat suppression condition.   When the inversion recovery method using the fact that the longitudinal relaxation time of the hydrogen nucleus spin of the water tissue and the longitudinal relaxation time of the hydrogen nucleus spin of the adipose tissue are different from each other, the imaging parameter setting unit performs the inversion recovery. The MRI apparatus according to claim 14, wherein time is determined as a parameter of the fat suppression condition.   The MRI apparatus according to claim 16, wherein the imaging parameter setting unit determines an inversion recovery time as a parameter of the fat suppression condition for each slice when collecting multi-slice MR signals. An imaging condition input unit for inputting imaging conditions of the MRI imaging;
A storage unit that stores the parameters of the fat suppression conditions together with the imaging parameters;
The MRI apparatus according to claim 13, wherein the imaging parameter setting unit reads and sets the fat suppression condition parameter and the imaging parameter corresponding to the imaging condition input by the imaging condition input unit.   The MRI apparatus according to claim 13, wherein the parameter of the fat suppression condition is a TI time from the inversion pulse to the application of the excitation pulse.   The MRI apparatus according to claim 13, wherein the parameter of the fat suppression condition is a TI time from the inversion pulse to the application of the excitation pulse.   The MRI apparatus according to claim 13, wherein the imaging parameter setting unit sets a parameter of the fat suppression condition based on an imaging parameter corresponding to the imaging condition of the MRI imaging. The fat suppression degree input unit is an interface for selecting a desired fat suppression degree from a predetermined range of fat suppression degrees, which is used after the fat suppression imaging mode to which the fat signal suppression method is applied is selected. The MRI apparatus according to claim 13.

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