Magnetic resonance imaging apparatus and control method therefor

Abstract

To provide an MRI device that can acquire images with excellent discrimination ability between tissues with inflammation and normal tissues by eliminating influence on a T1 contrast and a T2 contrast as much as possible while suppressing fat.SOLUTION: In imaging using a fat-suppression IR pulse, an MSDE sequence is added immediately before a data collection sequence to suppress the blood flow. A desired contrast is estimated based on the imaging conditions and imaging parameters of the data collection sequence, and the duration TMSDE of the MSDE sequence and the delay time TD of the data collection sequence that starts after the MSDE sequence are adjusted so as to obtain the desired contrast.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a magnetic resonance imaging apparatus, and more particularly to a fat suppression imaging technique. [Background technology]

[0002] One of the imaging methods using a magnetic resonance imaging device (hereinafter referred to as an MRI device) is a method (fat suppression imaging) that suppresses signals from fat and enhances the imaging ability of tissues other than fat. As a method for suppressing signals from fat, various methods have been proposed (Patent Document 1, Patent Document 2, etc.), such as a method of applying an RF pulse (called a Fat-Sat pulse or a CHESS pulse) at the magnetic resonance frequency of fat to saturate signals from fat and then executing a pulse sequence for data collection, and a method (STIR method) of applying an IR pulse that inverts spins, utilizing the difference in inversion recovery speed between fat tissue and other tissues, and executing a pulse sequence for data collection at the point in time TI (null point) when signals from fat become zero (Patent Document 1, Patent Document 2, etc.).

[0003] Patent Document 1 discloses that after applying a fat suppression pulse, a pulse sequence for data acquisition is executed twice after TI to acquire low-frequency region data and high-frequency region data of k-space. In the technology described in Patent Document 1, the decrease in fat suppression effect caused by the inversion pulse is suppressed by acquiring low-frequency region data at a timing when the nuclear spin (also called nuclear magnetization) of hydrogen atoms constituting fat has not yet recovered to T1.

[0004] In addition to fat suppression, a method for removing the influence of blood flow has also been developed. For example, Patent Document 2 discloses a method for performing two pulse sequences for data collection at different timings from an IR pulse and taking the difference between the pulse sequence signal acquisitions that start from the two pulse sequences. Patent Document 1 also describes applying a pre-pulse (MSDE) that reduces the signal intensity of blood flow after applying a fat suppression pulse. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6420583 [Patent Document 2] JP 2018-202122 A Summary of the Invention [Problem to be solved by the invention]

[0006] When an IR pulse is applied, at the null point where the nuclear magnetization of fat becomes zero, the nuclear magnetization of tissues other than fat remains, but the contrast of the image obtained from the data collected in this state is strongly affected by the increase in blood, and slight changes in the T1 and T2 values ​​of cells are buried in the contrast change caused by the increase in blood. In addition, the T1 and T2 values ​​change depending on the pathology of inflammation and non-inflammatory tissues such as cancer, but for the same reason, it is difficult to distinguish between them and visualize them clearly. In response to this, by using the MSDE (Motion Sensitized Driven Equilibrium) method, which reduces the signal intensity of blood flowing through blood vessels, it is possible to obtain contrast that shows changes in cells that have leaked into inflammation.

[0007] MSDE uses an MSDE pulse group or MSDE sequence that combines RF pulse groups and diffusion weighted gradient pulses (MPG), which has the effect of strengthening the T2 contrast. The longer the time (duration) that the MSDE pulse group is executed, the stronger the T2 contrast becomes. Therefore, adding MSDE creates the problem that it becomes difficult to obtain the desired T1 contrast. It is possible to control the T2 contrast to some extent by lengthening the time between the end of MSDE and the start of the data acquisition sequence, but if this time is too long, the blood flow suppression effect of MSDE is reduced.

[0008] In addition, iron tends to be deposited in inflamed tissues, and the T2 value is shortened in such tissues. As a result, even if the duration of MSDE is the same, there is an issue that the T2 contrast is too strong and deviates from the desired T2 contrast.

[0009] When adding MSDE in this way, adjustments that take into account the target contrast are necessary, but conventional fat suppression imaging techniques that take into account blood flow suppression do not address the issue of MSDE adjustment.

[0010] An object of the present invention is to provide an MRI apparatus that can obtain images with excellent discrimination between inflamed tissue and normal tissue while suppressing fat and minimizing the influence on T1 contrast and T2 contrast as much as possible. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention adds a sequence (blood flow suppression sequence) for suppressing blood flow signals by the MSDE method prior to a data collection sequence when performing imaging using an IR pulse as a fat suppression pulse, and controls the length (duration) of the blood flow suppression sequence and the time from the end of the blood flow suppression sequence to the start of the data collection sequence (hereinafter also referred to as delay time).The control is performed by estimating a desired contrast based on the imaging conditions and imaging parameters of the data collection sequence, so that the desired contrast can be obtained.

[0012] That is, the MRI apparatus of the present invention includes an imaging unit that executes a fat suppression pulse sequence including an IR pulse and a data collection sequence, and a processor including an imaging control unit that controls the imaging unit. The imaging control unit controls the imaging unit to execute the fat suppression pulse sequence including a blood flow suppression sequence after application of an IR pulse and before the start of a data collection sequence. The processor includes a blood flow suppression sequence adjustment unit that adjusts at least one of the duration of the blood flow suppression sequence and a delay time from the end of application of a preparation pulse after the blood flow suppression sequence.

[0013] Furthermore, the control method for an MRI apparatus of the present invention is a control method for a magnetic resonance imaging apparatus equipped with an imaging unit that executes a fat suppression pulse sequence including an IR pulse and a data collection sequence, and executes a blood flow suppression sequence that suppresses signals from moving spins after application of an IR pulse and before start of the data collection sequence, and controls at least one of the duration of the blood flow suppression sequence and the delay time from the end of the blood flow suppression sequence to the start of the data collection sequence depending on the contrast of the image obtained in the data collection sequence. Effect of the Invention

[0014] According to the present invention, the duration of the blood flow suppression sequence (T MSDS ) and the delay time (TD) from the end of the sequence to data collection, it is possible to prevent the differences in the T1 and T2 values ​​of tissues from becoming difficult to distinguish due to the effects of blood flow, and to prevent the T2 contrast from becoming too strong, thereby obtaining an image with the desired contrast.

[0015] In addition, according to the present invention, the duration of the blood flow suppression sequence (T MSDS Since the system can automatically control the time delay (TD) and the time of the blood flow suppression sequence, fat suppression imaging can be optimized by adding a blood flow suppression sequence without burdening the operator. [Brief description of the drawings]

[0016] [Figure 1] Diagram showing the overall configuration of an MRI device [Diagram 2] Functional block diagram of a computer (processor) [Diagram 3] A diagram showing a fat suppression pulse sequence using an IR pulse. [Figure 4] FIG. 4 is a diagram for explaining the behavior of spins in the pulse sequence of FIG. 3. [Diagram 5] FIG. 1 is a diagram showing an example of a fat suppression pulse sequence with an MSDE sequence used in this embodiment. [Figure 6]Figure showing an example of an MSDE pulse train [Figure 7] Figure explaining the behavior of spins in the pulse sequence of FIG. 5 [Figure 8] Figure showing the flow of the process of Embodiment 1 [Figure 9] Figure showing an example of a UI screen for setting imaging conditions [Figure 10] Figure explaining an algorithm for determining the optimum value of the MSDE sequence [Figure 11] Figure explaining the effect of Embodiment 1 [Figure 12] Figure showing an example of a UI screen displaying diagnostic support information [Figure 13] Figure showing the fat suppression pulse sequence of Embodiment 2 [Figure 14] Figure showing an example of k-space data acquisition in Embodiment 2

Best Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the MRI apparatus and its control method according to the present invention will be described with reference to the drawings.

[0018] First, the overall configuration of the MRI apparatus to which the present invention is applied will be described. <Configuration of MRI Apparatus> As shown in FIG. 1, the MRI apparatus 1 of the present embodiment includes a static magnetic field generation unit such as a static magnetic field coil 11 that generates a static magnetic field in a space where a subject is placed, a transmission high-frequency coil 12 (hereinafter simply referred to as a transmission coil) and a transmitter 16 that transmit a high-frequency magnetic field pulse (RF pulse) to a measurement region of the subject, a reception high-frequency coil 13 (hereinafter simply referred to as a reception coil) and a receiver 17 that receive a nuclear magnetic resonance signal generated from the subject, a gradient magnetic field coil 14 that applies a magnetic field gradient to the static magnetic field generated by the static magnetic field coil 11 and its drive power source, a gradient magnetic field power supply 15, a sequencer 18, and a computer 20. The respective parts of the MRI apparatus 1 excluding the computer 20 are collectively referred to as an imaging unit 10.

[0019] The MRI apparatus 1 may be of a vertical magnetic field type or a horizontal magnetic field type depending on the direction of the static magnetic field generated, and various types of static magnetic field coils 11 are adopted depending on the type. The gradient magnetic field coil 14 is made up of a combination of multiple coils that generate gradient magnetic fields in three mutually orthogonal axial directions (x-direction, y-direction, and z-direction), and each is driven by a gradient magnetic field power supply 15. By applying a gradient magnetic field, position information can be added to the nuclear magnetic resonance signal generated from the subject.

[0020] In the illustrated example, the transmitting coil 12 and the receiving coil 13 are separate, but a single coil may be used that functions as both the transmitting coil 12 and the receiving coil 13. The high frequency magnetic field emitted by the transmitting coil 12 is generated by a transmitter 16. The nuclear magnetic resonance signal detected by the receiving coil 13 is sent to a computer 20 via a receiver 17.

[0021] The sequencer 18 controls the operation of the gradient magnetic field power supply 15, the transmitter 16, and the receiver 17, controls the application of the gradient magnetic field and the radio frequency magnetic field, and the timing of receiving the nuclear magnetic resonance signal, and executes the measurement. The control time chart is called a pulse sequence, and various pulse sequences that differ depending on the imaging method are stored in advance in a storage device or the like provided in the computer 20. When the imaging method and the imaging part are determined, the sequencer 18 reads out a predetermined pulse sequence, calculates the imaging sequence to be used for imaging using the imaging conditions set by the user, and controls the imaging unit 10 to collect the nuclear magnetic resonance signal according to this imaging sequence.

[0022] The computer 20 is an information processing device equipped with a CPU, a memory, a storage device, etc., and controls the operation of each part of the MRI apparatus via the sequencer 18, and performs various arithmetic processing including image reconstruction using measurement data collected by the imaging unit 10. For this reason, the computer 20 is equipped with functional units such as an imaging control unit 21 and an image reconstruction unit 23, as shown in Fig. 2. These functions are executed by the computer 20 reading a program stored in the storage device. However, it is also possible to realize some of the functions using a programmable IC such as an ASIC or FPGA.

[0023] Furthermore, the computer 20 of this embodiment has a function of adjusting the duration of the blood flow suppression sequence and the start timing of the data collection sequence (delay time from the blood flow suppression sequence) in accordance with the desired contrast in the data collection sequence when executing a data collection sequence including an IR pulse and a blood flow suppression sequence. As the blood flow suppression sequence, a known pulse train including a high-intensity gradient magnetic field pulse (MPG pulse) having the effect of diffusing mobile spins can be used. In this embodiment, as an example, a case where an MSDE pulse group, which is a typical blood flow suppression sequence having the effect of suppressing extracellular diffusive blood flow, is used, and in FIG. 2, a sequence adjustment unit that adjusts the blood flow suppression sequence is called an MSDE adjustment unit 25. However, the present invention does not exclude the case where a blood flow suppression sequence other than MSDE is used. For example, it is also possible to use an MPG pulse train such as a bipolar MPG such as velocity encoding (VENC) that does not include an RF pulse.

[0024] Furthermore, the computer 20 can also include a function of estimating or calculating information that assists diagnosis using images obtained by a fat suppression pulse sequence, and an assistance information generating unit 27. The functions of the computer 20 will be described in detail later.

[0025] The computer 20 is connected to a display device 30, an input device 40, an external storage device 50, and the like. The display device 30 is an interface that displays the results obtained by the arithmetic processing to the user (operator). The input device 40 is an interface through which the user inputs the conditions, parameters, and the like required for the measurement and arithmetic processing performed in this embodiment. The display device 30 and the input device 40 are also collectively referred to as a UI unit. The user can input scan parameters (imaging conditions) such as the number of echoes to be measured, the echo time TE, and the echo interval ITE, for example, via the UI unit. The external storage device 50, together with the storage device inside the computer 20, holds data used in various arithmetic processing executed by the computer 20, data obtained by the arithmetic processing, input conditions, parameters, and the like.

[0026] Based on the above configuration, an overview of the operation of the MRI apparatus of this embodiment will be described. When imaging, the examination site is specified, and imaging method and imaging conditions are set, and imaging is started. If the imaging method and imaging conditions are set in advance as an examination protocol, they are read. By setting the imaging method and imaging conditions, the pulse sequence used for imaging and its scan parameters TE (echo time), TR (repetition time), FOV, etc. are determined. In this embodiment, a fat suppression pulse sequence with blood flow suppression is set. Here, as an example, the blood flow suppression sequence is assumed to be MSDE. The user can further set the type of MSDE, b value, etc.

[0027] When a fat suppression pulse sequence with blood flow suppression is set, the MSDE adjustment unit 25 estimates the contrast intended for this imaging using the magnitude of the IR pulse and the T1 value and T2 value registered in advance for the tissues included in the examination region, and adjusts the duration of the MSDE applied after the IR pulse and the delay time TD from the MSDE to the start of the data acquisition sequence. In adjusting the duration and delay of the MSDE, the unit determines the range of the duration (minimum duration) and delay time (shortest delay time) that can be realized from the imaging conditions and MSDE conditions (type, b value, etc.) set by the user, and determines the duration and delay time within that range at which the ratio of the signal values ​​of each tissue included in the imaging region becomes the desired contrast. The calculation performed by the MSDE adjustment unit 25 will be described in detail in the embodiment described later.

[0028] After adjustment by the MSDE adjustment unit 25, the imaging control unit 21 controls the imaging unit 10 to execute the fat suppression pulse sequence under the adjusted conditions. Furthermore, as necessary, the imaging control unit 21 executes a fat suppression pulse sequence with a blood flow suppression sequence and a fat suppression pulse sequence without a blood flow suppression sequence for the same subject. The support information generation unit 27 uses the measurement data obtained by these two fat suppression pulse sequences or the images reconstructed by the image reconstruction unit 23 from the data to generate images (difference images or ratio images) showing the difference in the influence of blood flow, or data analyzing the images. The diagnostic support information generated by the support information generation unit 27 may be displayed on the display device 30, or may be sent to a database such as a PACS together with the image information.

[0029] According to this embodiment, imaging is performed by controlling the duration of the blood flow suppression pulse and the delay time of data collection, so that during the data collection period, the influence of fat signals can be suppressed and signals from blood in the extracellular space can be suppressed, and an image with the desired contrast can be obtained.

[0030] Before describing a specific embodiment of the function of the MSDE adjustment unit 25, a fat saturation pulse sequence will be described below.

[0031] As an example of a fat suppression pulse sequence (one that does not include MSDE), a pulse sequence 100 using 3D-RSSG (RF-spoiled steady state gradient-echo) as a data acquisition sequence is shown in Fig. 3. In Fig. 3, RF indicates the application timing of an RF pulse, and Gs, Gp, and Gr indicate the application timing of gradient magnetic field pulses in the slice direction, phase encoding direction, and readout direction.

[0032] 3D-RSSG is a data collection sequence in which a three-dimensional region (voxel) of a specified thickness is selected and an RF pulse is applied, then a phase encoding gradient magnetic field pulse is applied, and gradient echoes are generated and collected using a readout gradient magnetic field pulse, and this process is repeated while changing the strength of the phase encoding gradient magnetic field pulse, and this process is further repeated while changing the strength of the slice encoding gradient magnetic field pulse to collect three-dimensional k-space data. There are various methods for the order of phase encoding and slice encoding, and any of them can be adopted.

[0033] In this fat suppression pulse sequence 100, prior to this data acquisition sequence (3D-RSSG), an IR pulse is first applied, and data is acquired at or near the point where longitudinal magnetization of fat disappears (that is, the null point).

[0034] The behavior of the spin (longitudinal magnetization) of fat and the spin of other tissues at this time is shown in Figure 4. In the figure, the horizontal axis indicates the time axis, and the vertical axis indicates the magnitude of longitudinal magnetization. As shown in the figure, at the null point where the longitudinal magnetization of fat disappears, the longitudinal magnetization remains in tissues other than fat, such as normal tissue and inflamed tissue, which have a longer T1 than fat. By starting the data acquisition sequence from this point, it is possible to obtain an image in which fat is suppressed. Furthermore, since the T1 values ​​of normal tissue and inflamed tissue are different, a contrast difference occurs for them as well, and for example, a T1 weighted image with a contrast difference can be obtained. However, in inflamed tissue, there is a lot of blood flow near the cells, and the difference in T1 and T2 values ​​between tissues is buried due to the influence of the blood flow, making it difficult to obtain fine contrast of cells, especially in inflamed tissue.

[0035] The imaging sequence of this embodiment suppresses signals from the blood flow present in the extracellular space by adding a sequence consisting of a blood flow suppression pulse group (hereinafter referred to as an MSDE sequence) immediately before the data acquisition sequence. An example in which an MSDE sequence is added to the fat suppression pulse sequence shown in Fig. 3 is shown in Fig. 5 and Fig. 7 (fat suppression pulse sequences 200, 200A). As shown in the figures, the MSDE sequence is inserted between the application of an IR pulse and the null point TI of fat in the fat suppression pulse sequence.

[0036] The MSDE sequence is composed of a composite pulse (pulse group) that combines an RF pulse group and an MPG (Motion Probing Gradient) pulse, and various sequences are known. One example is shown in FIG. 6. The upper side (a) of FIG. 6 is the most basic sequence, in which a 180-degree pulse is placed between two 90-degree pulses, and an MPG pulse is placed on both sides of the 180-degree pulse of the RF pulse group. Furthermore, as shown in (b) and (c), there are three RF pulse groups, and five RF pulse groups with spoiler gradient magnetic fields placed on both sides of the sequence, and any of them can be adopted. However, the effect of blood flow suppression and the contrast of the obtained image differ depending on the number of RF pulse groups, the pulse interval PreTE, the strength of MPG, etc., and in this embodiment, the duration of the sequence and the delay time of the data acquisition sequence executed thereafter are adjusted according to the desired contrast.

[0037] The significance of adjusting the MSDE sequence will be described below with reference to the behavior of longitudinal magnetization shown in FIG.

[0038] In the fat suppression sequence 200A of FIG. 7 , the change in the longitudinal magnetization of fat and normal tissue is similar to that in the fat suppression pulse sequence of FIG. 3 . However, with respect to the longitudinal magnetization of inflamed tissue, which also contains the longitudinal magnetization of blood flow, by adding MSDE, only the longitudinal magnetization of blood flow approaches zero, and signals other than blood remain, and the contrast difference between the longitudinal magnetization of tissues other than blood and normal tissue becomes clear.

[0039] In such MSDE, the longer the duration, the greater the blood flow suppression effect, but the T2 contrast is enhanced due to signal attenuation according to the tissue's transverse relaxation time T2. If the data acquisition sequence with fat suppression is T1-weighted imaging, the desired T1 contrast cannot be obtained due to the enhanced T2 contrast. On the other hand, the increase in T2 contrast caused by MSDE can be suppressed by extending the time (delay time) until the data acquisition sequence is started after MSDE, but if the delay time is too long, the effect of blood flow suppression by MSDE decreases. It is extremely difficult for the user to adjust the duration and delay time of MSDE each time, both from the viewpoint of technology and imaging procedures.

[0040] In this embodiment, the MSDE adjustment unit 25 automatically adjusts the duration T of the MSDE in accordance with the contrast of the image that the user is trying to obtain. MSDE By adjusting the TD, imaging with the desired contrast with fat suppression and blood flow suppression is possible. As described above, the duration of the MSDE can be adjusted by the number of RF pulse groups, the application time of the MPG pulse, and the interval between pulses shown as PreTE in FIG.

[0041] Hereinafter, an embodiment of a specific adjustment process by the MSDE adjustment unit 25 will be described.

[0042] <Embodiment 1> In this embodiment, an example will be described in which the data acquisition sequence is the 3D-RSSG shown in Fig. 7. The flow of processing up to the start of imaging is shown in Fig. 8.

[0043] First, the operator sets the subject information, the imaging region, etc., selects a fat suppression pulse sequence with an MSDE sequence as shown in FIG. 4 as an imaging sequence, and sets imaging conditions such as scan parameters other than MSDE (S1). The imaging conditions can be set, for example, via a parameter setting block 303 on a UI screen 300A as shown in FIG. 9. The imaging conditions may include information such as 2D imaging or 3D imaging, image type (T1 weighted image, T2 weighted image, PD image), in addition to scan parameters (TE, TR, FA, TI, FOV). When MSDE application is set in the setting of the imaging conditions, the operator sets the conditions of the MSDE sequence such as the type of MSDE and the b value, which is an index of the strength of the MPG pulse. For example, the settings are made by the block 304. The type of MSDE and the number of RF pulse groups may be set to standard values ​​by default, and the user may adjust them.

[0044] The MSDE adjustment unit 25 reads the set imaging conditions and calculates the length and delay time TD of the optimal MSDE sequence in accordance with the time conditions of the MSDE, that is, the contrast desired by the operator.

[0045] For this reason, the MSDE adjustment unit 25 first judges the contrast to be used as the basis for the calculation from the set conditions, that is, whether it is T1 weighted, PD weighted, or T2 weighted (S2). For example, if the set information includes the type of contrast image, the judgement method can use the information. The judgement may also be made by referring to the TE (echo time) and TR (repetition time) set as scan parameters. Generally, in an SE sequence, if the TR is shorter than the T1 value of the tissue, the difference in the T1 value of each tissue is reflected in the image, and if the TE is much shorter than the T2 value, an image with little influence of the T2 value of each tissue is obtained. That is, if both the TR and TE are short, a T1 weighted image is obtained. Therefore, the TE is compared with a predetermined threshold, and if it exceeds the threshold, it is judged to be T2 weighted imaging, and if the TE is equal to or less than the predetermined threshold, the TR is compared with the predetermined threshold, and if it is equal to or less than the threshold, it is judged to be T1 weighted imaging. The result of the judgement in this way is used in the judgement step of the subsequent processing.

[0046] Next, the MSDE adjustment unit 25 determines the duration T of the MSDE based on the desired contrast and the set imaging conditions. MSDE and the delay time TD until the start of the data collection sequence are determined in the following procedure (S3 to S5).

[0047] <s3> First, the shortest possible duration of the MSDE, T MSDEmin and the shortest delay time TD min Determine the shortest duration T MSDEmin is the duration T of the shortest MSDE sequence that can achieve the set b value based on the instrument specifications and the type of MSDE set (wave number, etc.). MSDEmin Calculate T MSDEmin ≦ T MSDE It becomes.

[0048] In addition, a spoiler pulse is required between the end of MSDE and the start of the data collection sequence, so the application time of this spoiler is set to the shortest value of TD, TD min Let us assume that.

[0049] <s4> Furthermore, the MSDE adjustment unit 25 determines the T1 and T2 values ​​of the substances A and B to be imaged from the imaging region set in S1. The T1 and T2 values ​​of each substance may be stored in advance as a table in the system (or in the external storage device 50), or may be input by the operator via the UI (input device 40).

[0050] Next, the T1 and T2 values ​​of each substance were used to calculate the duration of MSDE, T MSDE The expected signal value S when the delay time TD is changed A , S B Calculate the signal ratio SIR of each substance A and substance B using formula (1). A / B is calculated using formula (2).

[0051]

number

[0052] The signal ratio SIR expressed by equation (2) A / B is the duration of MSDE T MSDE For example, as shown in FIG. 10, the signal ratio SIR A / B has a given distribution. Figure 10 shows the T 1A = 680 ms, T 2A = 100 ms, T of substance B 1B = 320 ms, T 2B This is an example calculated with TD = 20 ms, and the minimum value of TD min (=0) and the minimum duration of the usable MSDE (T calculated in step S3) MSDEmin ) is shown by a dotted line, and the range defined by this dotted line is the achievable duration and delay time for the set MSDE.

[0053] <s5> The MSDE adjustment unit 25 calculates the signal ratio SIR A / B and the signal ratio SIR A / B For example, if the imaging is T1 weighted or PD imaging, the optimal point on the map (Fig. 10) is determined. min ≦ TD and T MSDEmin ≦ T MSDE In the range of TD+T, the SIR is below the allowable value ΔSIRmin of contrast change. MSDE If there are multiple points that satisfy this condition, TD+T MSDE Among the smallest MSDE is the smallest point.

[0054] For T2 weighted imaging, TD min ≦ TD and T MSDEmin ≦ T MSDE SIR is maximum and TD+T MSDE The point where is the smallest is the point where is the smallest, and if there are multiple points, the point where is the smallest is the point where is the smallest. Although the blood flow suppression pulse is described above as MSDE, the blood flow suppression pulse is not limited to MSDE. For example, blood flow signals can be suppressed in a similar manner by applying a bipolar gradient magnetic field such as velocity encoding (VENC). In that case, although the SNR is lower than that of MSDE, T MSDE It is possible to shorten the application time of the voltage Vcc.

[0055] The above process determines the MSDE conditions that can maintain the desired contrast. After the MSDE conditions are determined, imaging is started (S6). Since the process of the MSDE adjustment unit 25 is an internal process of the system, the imaging control unit automatically starts imaging when the above steps are completed.

[0056] Fig. 11 shows a schematic diagram of an image obtained by such imaging. In Fig. 11, the image on the left is an image with MSDE applied, the center is an image without MSDE applied, and the right is an SIR image (image calculated with MSDE applied / without MSDE applied) showing the ratio between the image with MSDE applied and the image without MSDE applied. Inflammatory tissue in an organ, which was unclear in the image without MSDE applied, is depicted with high contrast by applying MSDE optimized according to the method of this embodiment.

[0057] As described above, according to this embodiment, it is possible to prevent contrast changes that may occur due to the addition of MDSE in fat suppression imaging, particularly deviation from the desired contrast that occurs when appropriate blood flow suppression is not performed, and to improve tissue visualization ability due to blood flow suppression. Also, according to this embodiment, the adjustment of the time conditions of MSDE is automatically performed by reading the imaging conditions set by the user, so that high-quality images can be obtained while reducing the burden on the operator during examination.

[0058] <Application Examples> In the first embodiment, the adjustment of the time conditions of the MSDE pulse in fat suppression imaging has been described, but it is also possible to provide useful diagnostic information on inflamed areas such as joints based on this image. In this application example, the support information generating unit 27 provides diagnostic information using an image to which MSDE has been applied and an image captured without applying MSDE. An example of diagnostic information provided by the support information generating unit 27 will be described below.

[0059] As shown in Figures 4 and 7, when MSDE is not applied, blood signals are mixed in inflamed tissues, making it difficult to obtain fine contrast, but when MSDE is applied, an image of the inflamed tissue can be obtained in which blood signals are suppressed. Therefore, by taking the difference or ratio between an image with MSDE applied and an image without MSDE applied, it is possible to obtain information such as the extent to which blood has gathered in the extracellular space of the inflamed tissue, that is, the degree of edema of the inflamed tissue. Conversely, when inflammation progresses and iron deposition occurs, it is not suppressed as blood, but is depicted with a different contrast when MSDE is applied and not applied, so the progression of inflammation can be estimated from the change in contrast.

[0060] As a premise of this application example, it is assumed that the imaging control unit 21 controls the imaging unit 10 to acquire an image to which MSDE is not applied, and an image to which MSDE is not applied is obtained. The necessity of imaging to which MSDE is not applied may be instructed, for example, by the operator via a UI. The support information generating unit 27 calculates a difference or ratio using an MSDE image and an image to which MSDE is not applied acquired for the same subject, and generates a difference image or ratio image (SIR image) as shown on the right side of FIG. 11. Since the image to which MSDE is applied maintains substantially the same contrast as the contrast set in the image to which MSDE is not applied, the difference image or ratio image is an image that reflects only the effect of applying MSDE.

[0061] The support information generating unit 27 displays the generated image on the display device 30. In the difference image or ratio image, the pixel values ​​of the parts affected by MSDE, i.e., the parts where blood is collected, are high, so the operator can estimate the degree of inflammation from this image. Furthermore, the support information generating unit 27 can accept the setting of an ROI by the operator on the displayed image and analyze the degree of inflammation within the ROI. For example, it is possible to set a predetermined threshold value for pixel values ​​within the ROI, link values ​​above the threshold and values ​​below the threshold to diagnostic information related to blood flow (degree of edema), and present the diagnostic information.

[0062] FIG. 12 shows an example of a UI screen 300B for executing this application example. In this example, an image display block 301, a subject information display block 302, a block 303 for displaying scan parameters, etc. are provided, and an image obtained by imaging or an image generated by the support information generating unit 27 is displayed in the image display block 301. The display of the image may be switched by operating an image switching button (Image Switch), or may be changed to a thumbnail display. In addition, a button (Analize) 305 for instructing an analysis using a difference image or a ratio image may be provided, and an analysis of the image by the support information generating unit 27 may be performed, and the result may be displayed in the result display block 306. In addition, when a ratio is taken of an area with low signal intensity, noise may affect the interpretation, so that the influence may be reduced by applying a mask to remove noise when the signal value of the original image is below a threshold value. The threshold value is set in a filter block 308, and the result is reflected in the image display block 301.

[0063] According to this application example, the operator can confirm the effect of the MSDE and can also provide useful information that contributes to diagnosis.

[0064] <Embodiment 2> In the first embodiment, 3D-RSSG is used as a data acquisition sequence, but in the present embodiment, 2D-RSSG is used. In the present embodiment, the duration TMSDE and delay time TD of MSDE are controlled based on the T1 value, T2 value and desired contrast of tissue, similarly to the first embodiment. When performing 2D imaging, it is possible to simply replace the 3D data acquisition sequence (e.g., 3D-RSSG) with a 2D data acquisition sequence (e.g., 2D-RSSG) in the fat suppression pulse sequence 200A shown in FIG. 7, but in the present embodiment, multiple slices are measured simultaneously for one MSDE, and the slice measurements are performed in a nested manner to improve imaging efficiency.

[0065] In this embodiment, the configuration of the device is similar to that shown in FIGS. 1 and 2, so the following description of this embodiment will focus on the differences.

[0066] Hereinafter, the fat suppression pulse sequence 200B of this embodiment will be described with reference to Fig. 13. Here, the case where the 2D data acquisition sequence is 2D-RSSG is shown as an example. For simplicity of explanation, the case where the number of slices is 3 is shown, but the number of slices may be 2 or more than 3. This fat suppression pulse sequence 200B executes the sequence (1 shot) from IR pulse application to the data acquisition sequence at least twice (2 shots).

[0067] As shown in the figure, in one shot, first, multiple IR pulses with different slice positions are selected, IR S#1 , I.R. S#2 , I.R. S#3 is applied continuously, and the MSDE sequence is executed before TI is reached. Since MSDE has no slice selectivity, it acts on spins in all slices in the same way and suppresses blood flow signals. After the MSDE sequence is completed, a 2D data acquisition sequence, here 2D-RSSG, is executed continuously for each slice S#1, S#2, and S#3 at a predetermined delay time TD. The duration of the MSDE sequence T MSDE , and the delay time TD of the 2D-RSSG are determined by the method calculated in the step of the first embodiment based on the first IR pulse and the 2D-RSSG.

[0068] In the 2D-RSSG of each slice, which is performed consecutively within one shot, one or more echo signals are measured in one TR. At this time, the k-space data collected in each slice is divided into multiple (same number as the number of slices) equal-area segments, and each slice is controlled to collect data of a different segment. When the number of slices is three, the k-space is divided into, for example, 2D-k-space (ky-kz) into segment A in the low frequency region, segment B in the mid frequency region, and segment C in the high frequency region, as shown in FIG. 14. Note that FIG. 14 shows an example in which the k-space is divided along the kx axis, but depending on the k-space sampling method (for example, in the case of radial sampling, etc.), it may be divided concentrically from the center of the k-space to have equal areas.

[0069] After dividing the k-space in this manner, the slices from which data is collected immediately after application of the MSDE are looped for each shot to make the contrast constant for each slice.

[0070] That is, in the first shot (upper part of FIG. 13), data of segment A is collected in slice S#1 which is executed first, data of segment B is collected in slice S#2 which is executed second, and data of segment C is collected in slice S#3 which is executed third. Note that all data within the same segment may be collected in one TR, or may be collected in multiple times.

[0071] From the second time onwards (middle and bottom rows of Fig. 13), the order of slice selection is changed, and the same pulse sequence is executed. For example, in the second time, slice selection IR pulses are applied to slices S#3, S#1, and S#2 in that order, and the data acquisition sequence (2D-RSSG) is executed in that order. In this case too, the first 2D-RSSG executes acquires data for segment A, the second acquires data for segment B, and the third acquires data for segment C. In the third time, the order of slices is changed so that slice S#2 becomes the first, and data acquisition is performed in the same way. By going around these three shots, data can be acquired evenly for all segments in all slices.

[0072] As mentioned above, the duration of MSDE T MSDE The delay time TD of the 2D-RSSG is set based on the first slice, and the degree of diffusion and T2 emphasis by MSDE differs between the second and third slices. However, since data in the low-frequency region that contributes most to contrast is collected in the first slice of each shot, the effect can be reduced by shifting the delay time TD of the second and third data collection sequences from the set TD.

[0073] In the above description, data of each segment of k-space is collected by going around three shots, but when all k-space data of one slice is collected in one TR (all k-space data) by using EPI or the like as a data collection method, the slice measurement order is looped in the same way, and the k-space data collected by each shot is integrated. In the example of Fig. 13, each collected data when the measurement order is the first, second, and third for each slice is integrated, so that multiple data with different effects on diffusion and contrast due to differences in TD are averaged, and image quality between slices can be prevented from becoming uneven.

[0074] According to this embodiment, by performing measurements of multiple slices in a nested manner, it is possible to prevent a decrease in imaging efficiency caused by applying an IR pulse, which is a slice selection pulse, to each slice. In addition, by dividing the k-space and measuring data in the high frequency region of the k-space in a data acquisition sequence of a slice that starts with a set TD, it is possible to reduce the difference in the degree of diffusion and the influence on contrast caused by a shift in TD, and ensure the effectiveness of TMSDE and TD adjustment. [Explanation of symbols]

[0075] 1: MRI device, 10: imaging unit, 20: computer, 21: imaging control unit, 23: image reconstruction unit, 25: MSDE adjustment unit, 27: support information generation unit

Claims

1. An imaging unit that executes a fat suppression pulse sequence including an IR pulse and a data collection sequence, and a processor including an imaging control unit that controls the imaging unit, the imaging control unit controls the imaging unit to execute the fat suppression pulse sequence including a blood flow suppression sequence after application of the IR pulse and before start of the data collection sequence; A magnetic resonance imaging apparatus comprising: a blood flow suppression sequence adjustment unit configured to adjust at least one of a duration of the blood flow suppression sequence and a delay time from completion of application of a preparation pulse after the blood flow suppression sequence.

2. 2. The magnetic resonance imaging apparatus according to claim 1, A magnetic resonance imaging apparatus, wherein the blood flow suppression sequence is an MSDE sequence or a bipolar MPG pulse.

3. 2. The magnetic resonance imaging apparatus according to claim 1, the blood flow suppression sequence adjustment unit estimates a contrast of an image to be obtained by imaging from imaging conditions set for the fat suppression pulse sequence; A magnetic resonance imaging apparatus using the contrast to determine the duration and delay of the blood flow suppression sequence.

4. 4. The magnetic resonance imaging apparatus according to claim 3, a blood flow suppression sequence adjustment unit that uses scan parameters of the data collection sequence and T1 and T2 values ​​of tissues that constitute the imaging target site as the imaging conditions for estimating the contrast.

5. 4. The magnetic resonance imaging apparatus according to claim 3, The blood flow suppression sequence adjustment unit calculates a minimum duration of the blood flow suppression sequence that can be realized, and determines the duration of the blood flow suppression sequence using the minimum duration and the estimated contrast.

6. 6. The magnetic resonance imaging apparatus according to claim 5, a blood flow suppression sequence adjustment unit that calculates a minimum duration of the blood flow suppression sequence using a set type of the blood flow suppression sequence and a b-value of an MPG pulse included in the blood flow suppression sequence.

7. 2. The magnetic resonance imaging apparatus according to claim 1, A magnetic resonance imaging apparatus, wherein the data acquisition sequence is a 3D RSSG sequence.

8. 2. The magnetic resonance imaging apparatus according to claim 1, the data acquisition sequence is a 2D data acquisition sequence for acquiring measurement data for each two-dimensional slice, The imaging control unit performs control to repeat a one-shot sequence in which the IR pulses for selecting each slice are successively applied for a plurality of slices, the blood flow suppression sequence is executed, and after a determined delay time, the 2D data collection sequence for each slice is successively executed, with the IR application order and the data collection sequence execution order being different for each slice.

9. 9. A magnetic resonance imaging apparatus according to claim 8, The magnetic resonance imaging apparatus according to claim 1, wherein the imaging control unit cyclically changes the region of k-space data to be acquired for each slice depending on the execution order of the data acquisition sequence when repeating a one-shot sequence.

10. 2. The magnetic resonance imaging apparatus according to claim 1, the processor controls the imaging unit to execute a first fat suppression pulse sequence including the blood flow suppression sequence and a second fat suppression pulse sequence not including the blood flow suppression sequence; a support information generating unit configured to generate diagnostic support information using measurement data or an image obtained by the first fat suppression pulse sequence and measurement data or an image obtained by the second fat suppression pulse sequence.

11. 11. The magnetic resonance imaging apparatus according to claim 10, a first fat suppression pulse sequence for suppressing a fat distribution in a region of the image obtained by the first fat suppression pulse sequence and a second fat suppression pulse sequence for suppressing a fat distribution in the region of the image obtained by the second fat suppression pulse sequence;

12. 12. A magnetic resonance imaging apparatus according to claim 11, the support information generating unit estimates the presence or absence or a degree of edema in the imaging site by using, as the diagnostic support information, a ratio or a difference between measurement data obtained in the first fat suppression pulse sequence and measurement data obtained in a second fat suppression pulse sequence.

13. A method for controlling a magnetic resonance imaging apparatus having an imaging unit that executes a fat suppression pulse sequence including an IR pulse and a data acquisition sequence, comprising: After applying the IR pulse, a blood flow suppression sequence is performed to suppress signals from moving spins before the data acquisition sequence begins.

2. A method for controlling a magnetic resonance imaging apparatus, comprising: controlling at least one of a duration of the blood flow suppression sequence and a delay time from an end of the blood flow suppression sequence to a start of the data collection sequence in accordance with a contrast of an image obtained by the data collection sequence.

Images