JP4136783B2 - Magnetic resonance imaging system - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a magnetic resonance imaging apparatus (MRI apparatus), and more particularly to an MRI apparatus that performs synchronous imaging using a biological monitor signal such as an electrocardiogram.
[0002]
[Prior art]
As in cardiovascular system imaging, in the imaging of a region where the state changes due to heartbeat, generally, electrocardiographic synchronization is used and the time phase of signal measurement is made constant to improve the image quality. For example, in the electrocardiogram synchronization, as shown in FIG. 9, a measurement window is provided with an appropriate delay within a cardiac cycle (RR interval), and a plurality of echo signals acquired during the measurement window are used to make a constant. Create an image of the time phase. As the imaging sequence, for example, an SSFP sequence is used in which an echo signal is measured by Steady State Free Precession (SSFP) by a short TR gradient echo method. At this time, the plurality of echo signals acquired in the measurement window are assigned different phase encodings, and are arranged in the k space according to the phase encoding amount. By repeating this over a plurality of cardiac cycles, an echo signal that fills the entire k-space can be measured, and one image is reconstructed by Fourier transforming this.
[0003]
Here, the method of filling the k space with the echo signal, that is, the method of adding the phase encoding to the echo signal, is roughly divided into two types. As shown in FIGS. 10 (a) and 10 (b), the k-space is equally divided into a plurality of (6) regions corresponding to the number of echoes obtained in one measurement (here, 6). Echo signals are equally arranged in these areas. In the other method, as shown in FIGS. 3C and 3D, a plurality of echo signals obtained by one measurement are arranged in one of k-space regions. In any case, the filling order of the k space is determined by the centric ordering (a), (c) from the center of the k space toward the periphery, and the sequential ordering from one periphery of the k space through the center to the other periphery ( b) and (d). In general, the vicinity of the center of the k-space is an area for determining the image contrast. In the conventional MRI apparatus, the division method and ordering of these k-spaces are appropriately selected according to the target imaging target and imaging method.
[0004]
In circulatory system imaging using a contrast agent, it is necessary to focus on data near the center of k-space that determines the image contrast in a time zone when the contrast agent concentration is high in the target blood vessel (eg, artery) after administration of the contrast agent There is. Therefore, for example, as shown in FIG. 11, centric ordering is employed in which the phase encoding amount monotonously increases from the center of the k space with the contrast agent concentration peak in the target blood vessel as the start of imaging. However, synchronous measurement is not considered here.
[0005]
By the way, in circulatory system imaging, in order to suppress a signal from fat, a signal suppression pulse called a preparation pulse is often applied prior to a sequence for imaging. The effect of the preparation pulse is higher as the time from the preparation pulse application is shorter, and decreases with time. In the example of FIG. 9 described above, the effect of the preparation pulse is high from echo1 to echo4, but the effect is low at echo5 and echo6. Therefore, in order to obtain an image with an excellent SN ratio and a high contrast, it is preferable to select an ordering that measures a signal arranged in the low frequency region of k-space while the elapsed time from the preparation pulse application is short.
[0006]
On the other hand, when the imaging sequence is repeated in synchronization with the electrocardiogram as described above, it becomes more susceptible to body movement (respiration movement) as the number of repetitions increases. For example, assuming a case where a sequence of measuring 6 echoes in one cardiac cycle (RR) is repeated 6R-R (acquiring 36 echoes) and one image is reconstructed, 5 cardiac cycles, 6 cardiac cycles Then, it becomes easy to be affected by body movement. Therefore, in order to eliminate the influence of body movement as much as possible, it is preferable to arrange echoes obtained in a cardiac cycle with a fast imaging time in the k-space low frequency region. Also in dynamic imaging using a contrast agent, it is necessary to acquire k-space low frequency data in a time zone in which the contrast agent concentration is high as described above.
[0007]
Thus, in circulatory system imaging, echoes with a high effect of preparation pulses are arranged in the k-space low frequency region, and echoes measured in the cardiac cycle as early as possible from the start of imaging are arranged in the k-space low frequency region. There are two requests. However, the combination of the conventional k-space division method and ordering cannot realize both of them. For example, when an echo signal is acquired by the method shown in FIG. 10 (a), as shown in FIG. 12, in each cardiac cycle, a trajectory in which the distance from the center of the k space is evenly separated is drawn. Can be placed in the area that determines the image contrast, and the fat suppression effect by the preparation pulse is high, but the time required to acquire all the areas that determine the image contrast It becomes longer and more susceptible to body movements and respiratory movements that can occur in the second half of the measurement. In addition, since the echo acquisition of the area that determines the image contrast is dispersed in time, dynamic imaging that increases the image contrast for a certain period of time when the contrast medium is present by contrast medium injection can provide sufficient image quality. Absent.
[0008]
When the echo signal is acquired by the method shown in FIG. 10 (c), a trajectory is drawn in which the distance from the center of the k space increases as the heart rate increases as shown in FIG. The area that determines the image contrast can be acquired, and the effects of body movements and respiratory movements that can occur in the latter half of the measurement can be reduced, but the echo signal acquired when the effect from the preparation pulse is reduced also increases the image contrast. Since it is arranged in the area to be determined, the effect of the preparation pulse is reduced.
[0009]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide an MRI apparatus that is not easily affected by body movement or the like in synchronous imaging using a preparation pulse and that can make the most of the effect of the preparation pulse.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the MRI apparatus of the present invention divides a plurality of echo signals acquired in the measurement window into two or more groups according to the elapsed time from the preparation pulse, and performs phase encoding control of the echo signals of each group. By doing so, the k-space low-frequency region can be composed of signals that are highly effective due to preparation pulses, and that are not significantly affected by body movements, etc., which results in higher contrast and higher image quality in electrocardiographic synchronization Is realized.
[0011]
That is, the MRI apparatus of the present invention includes a magnetic field generating unit that applies a high-frequency magnetic field and a gradient magnetic field to a space in which a subject is placed, a receiving unit that measures a nuclear magnetic resonance signal generated by the subject as an echo signal, and a high-frequency magnetic field. And a control means for controlling the application of the gradient magnetic field and the acquisition of the echo signal, and a signal processing means for reconstructing the image of the subject using the echo signal, wherein the control means is a biological monitor signal generated periodically In synchronism with the above, a means for setting a measurement window for measuring an echo signal within each cycle, and a plurality of echo signals measured within the measurement window are divided into two or more groups, and according to the signal measurement time of each group And means for controlling phase encoding so as to occupy a predetermined area of k-space. Alternatively, in synchronization with a periodically generated biological monitor signal, a means for setting a measurement window for measuring an echo signal within each period and a plurality of echo signals measured in the measurement window are acquired in the first half. The echo signal occupies a low frequency region in the k space, and the phase encoding is controlled so that the echo signal acquired in the second half occupies a high frequency region in the k space.
[0012]
In the MRI apparatus of the present invention, it is preferable that the control means phase the echo signals acquired in the first half of the plurality of echo signals measured in the measurement window in order from the center of the k space toward the high frequency region. Control the encoding.
[0013]
According to such an MRI apparatus of the present invention, the k-space low frequency region data for determining the image contrast is converted into a signal (for example, a signal whose contrast is enhanced depending on the measurement time among echo signals measured in the measurement window. Signal obtained in the first half of the measurement window), an image with excellent image contrast can be obtained. In addition, by arranging the echo signals acquired in the first half from the center of k-space toward the high-frequency region in the order of acquisition, signals that are not affected by temporal changes such as body movements are disposed in the center of k-space and regions close to it. Therefore, it is possible to prevent image quality deterioration due to body movement or the like. Also in imaging using a contrast agent, the center of the k-space and an area close thereto can be measured while the concentration of the contrast agent is high, so that the target blood vessel can be imaged with high rendering ability.
[0014]
The MRI apparatus of the present invention is suitable for imaging including a step of applying a preparation pulse for suppressing a signal from a specific tissue, particularly in the previous stage of the measurement window, and the signal suppression effect by the preparation pulse ( High contrast).
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. FIG. 1 is a diagram showing an overall outline of an MRI apparatus to which the present invention is applied.
[0016]
This MRI apparatus includes a magnet 102 that generates a uniform static magnetic field in a space where the subject 101 is placed, a gradient magnetic field coil 103 that applies a magnetic field gradient to the static magnetic field generated by the magnet 102, and a tissue that forms the subject 101. An RF coil 104 that generates a high-frequency magnetic field that causes nuclear magnetic resonance to occur in the nucleus, an RF probe 105 that detects a nuclear magnetic resonance signal (echo signal) generated from the subject 101, and the subject 101 into the static magnetic field space And a bed 112 for carrying out.
[0017]
The static magnetic field generating magnet 102 is a permanent magnet, a normal conducting type or a superconducting type magnet device, and generates a predetermined uniform static magnetic field in the space where the subject 101 is placed. The gradient magnetic field coil 103 is composed of gradient magnetic field coils in three directions of x, y, and z, each connected to a gradient magnetic field power supply 109, and generates a gradient magnetic field in response to a signal from the gradient magnetic field power supply 109. The gradient magnetic field gives positional information to the echo signal, and the slice excited by the high-frequency magnetic field is determined and the echo signal can be phase-encoded according to the application method. The RF coil 104 is connected to an RF transmission unit 110 that includes a high-frequency oscillator, a synthesizer, and the like, and generates a high-frequency magnetic field having a predetermined frequency, phase, and intensity according to a signal from the RF transmission unit 110.
[0018]
The RF probe 105 is connected to a signal detection unit 106 having a quadrature phase detection circuit, an A / D conversion circuit, and the like, and a signal detected by the RF probe 105 is detected by the signal detection unit 106 and A / D converted. The signal is processed by the signal processing unit 107 and converted into an image signal by calculation. The image is displayed on the display unit 108. The operations of the gradient magnetic field power source 109, the RF transmission unit 110, and the signal detection unit 106 are controlled by the control unit 111 according to a predetermined pulse sequence determined by the imaging method. The pulse sequence is pre-installed as a program in a storage device attached to the control unit 111. The user selects a desired one via the input / output device attached to the control unit 111, and sets the necessary shooting conditions (parameters). Can be set.
[0019]
In the MRI apparatus of the present invention, an electrocardiogram synchronous imaging sequence using a preparation pulse is incorporated as one of the imaging sequences, and is characterized by a gradient magnetic field control method (phase encoding control method) in its execution. The gradient magnetic field control method uses, for example, a predetermined ky value as a table in accordance with the number of repetitions of electrocardiogram synchronous imaging (the number of cardiac cycles necessary for imaging) and the number of echo signals measured in one measurement window. 111 can be stored. In addition, the control unit 111 includes a port for taking in a biological monitor signal from a biological monitor signal measuring device such as an electrocardiograph provided separately from the MRI apparatus in order to perform an electrocardiogram synchronous imaging sequence.
[0020]
Hereinafter, electrocardiographic synchronous imaging executed by the MRI apparatus of the present invention will be described.
[0021]
FIG. 2 is a diagram showing an embodiment of ECG synchronization imaging according to the present invention. In the figure, the horizontal axis is the time axis, the upper R indicates the input timing of the R wave signal from the biological monitor signal measuring device (here, the electrocardiograph), the lower indicates the execution timing of the imaging sequence, It shows that the preparation pulse 203 is applied and the echo signal in the measurement window 204 is measured during one cardiac cycle (RR).
[0022]
The preparation pulse 203 applied immediately before the measurement window 204 selectively excites an unnecessary tissue signal and suppresses the signal from the tissue, or T1 at the time of applying an excitation pulse (α pulse). Alternatively, it is a pulse that gives a difference in the strength of magnetization for tissues having different T2 and increases the contrast difference of the tissue, and a selective excitation pulse having a fat proton frequency can be adopted as the former example. In the latter case, for example, in the case of blood vessel rendering, a non-selective 180 ° pulse that increases the contrast of the blood vessel image, or a 90 ° -180 ° -90 ° pulse that obtains T2-weighted contrast depending on the target site. Can be adopted.
[0023]
The measurement window 204 is set by a predetermined time (delay time) and time width (number of echoes to be measured) from R201. The measurement window is usually a short time of 100 to 200 ms. As the imaging sequence, for example, a gradient echo pulse sequence is used in which echo signals (echo1 to echo6) are measured in a steady state by repeating excitation with a high frequency excitation pulse (RF) with a short repetition time TR. An example of such a pulse sequence is shown in FIG. In FIG. 3, RF is the application timing of the high-frequency pulse, Gs, Gp, and Gr are the slice direction gradient magnetic field, the phase encode direction gradient magnetic field, and the readout direction gradient magnetic field application pattern, and A / D and echo are the sampling time and echo signal. Indicates the measurement timing.
[0024]
This imaging sequence is an SSFP sequence that has a gradient magnetic field application pattern symmetrical to the echo signal that is generated while the excitation pulses are alternately reversed in polarity as shown in the figure. After applying an excitation pulse 302 with a flip angle α together with 301, a phase encode gradient magnetic field 303 and a read gradient magnetic field 304 are applied, a read gradient magnetic field 305 with reversed polarity is applied, and an echo signal 307 is applied within the sampling window 306. measure. Then, after applying the phase encoding gradient magnetic field 308 and the read gradient magnetic field 309 for rephasing, the excitation pulse 310 with the flip angle −α is applied together with the slice gradient magnetic field after the repetition time TR. Thereafter, the next echo signal is measured by applying the phase encode gradient magnetic field and the read gradient magnetic field in the same manner. In the embodiment shown in FIG. 2, 6 echoes are measured at 6 repetition times TR in the measurement window 204 of one cardiac cycle. Although not shown, excitation (empty shot) is performed at the same repetition time TR as the echo signal measurement until the echo signal measurement after the preparation pulse is applied so that the echo signal can be measured in a steady state in the measurement window. ) Is preferably repeated.
[0025]
In the echo signal generated in the measurement window 204, the intensity of the phase encoding gradient magnetic field 303 (308) is controlled so that the phase encoding differs for each echo. In the phase encoding control in this embodiment, 1) a plurality of signals measured in one cardiac cycle are divided into a plurality of n groups according to the time interval from the preparation pulse application, and the time interval from the preparation pulse application is shorter. The echo signal occupies a lower frequency region in the k space, and a set of echo signals having a longer time interval from the preparation pulse application occupies the higher frequency region in the k space. 2) One image is measured over a plurality of cardiac cycles. At this time, two conditions are satisfied: a signal measured in the early cardiac cycle from the start of imaging occupies the low frequency side, and a signal measured in the cardiac cycle that has elapsed from the start of imaging is on the high frequency side.
[0026]
Specifically, for example, assuming that six echoes are measured in a measurement window 204 of one cardiac cycle and this is performed in six cardiac cycles, as shown in FIG. Divided into a low frequency region 401 and 1/6 high frequency regions 402 and 402 ′ on both sides thereof, the echo signal acquired in the first cardiac cycle has a relatively short time interval from the preparation pulse application. The center of k-space and the subsequent low frequency range 401 are acquired with a short echo (echo1 to echo4), and the high frequency range 402, 402 ′ is acquired with an echo (echo5, echo6) having a relatively long time interval from the preparation pulse application. To. In this case, the shorter the time interval from the preparation pulse application, the closer to the center of the k space. In the subsequent measurement of the second cardiac cycle, the outside of the region measured in the first cardiac cycle of the low frequency region 401 is acquired with four echoes (echo7 to echo10) having a relatively short time interval from the preparation pulse application, and the preparation pulse is obtained. The outside of the region measured in the first cardiac cycle of the high-frequency region 402 is acquired with two echoes (echo11, echo12) having a relatively long time interval from the application. Similarly, in the third, fourth,... Cardiac cycles, measurement is sequentially performed toward the high frequency region of the k space, and finally an echo signal of all phase encoding necessary for image reconstruction is acquired.
[0027]
FIG. 5 shows the phase encoding control according to this embodiment. In FIG. 5, the vertical axis represents the phase encoding amount, and a range of ± 6 with the phase encoding amount 0 interposed therebetween is a region 501 that determines image contrast, and the outside thereof is a middle-high region 502. The horizontal axis indicates the echo number (number in the acquisition order), and the larger the echo number, the greater the influence of body movement. In addition, a region where the effect of the preparation pulse is low within one cardiac cycle is shown surrounded by a hatched line 503.
[0028]
As is clear from comparison with FIGS. 11 to 13 showing the conventional phase encoding control, according to the embodiment shown in FIG. 5, the region 501 for determining the k-space image contrast has a high effect of the preparation pulse. Moreover, it is measured when there is little influence of body movement (up to 3 cardiac cycles), and it can be seen that an image with excellent SN due to the fat suppression effect and without image quality deterioration due to body movement can be obtained.
[0029]
Next, a second embodiment of electrocardiogram synchronous imaging executed by the MRI apparatus of the present invention will be described.
[0030]
FIG. 6 is a diagram showing a second embodiment. Here, R indicates an R wave signal from the electrocardiograph, and a measurement window 604 is set to RR and a preparation pulse 603 is applied immediately before that. Is the same as in the first embodiment. The imaging sequence executed in the measurement window is the SSFP sequence as shown in FIG. 3 as in the first embodiment, but here, 20 echoes are acquired in one measurement window, and one image is taken in 6 heart cycles. It is assumed that echoes (120 echoes) of the image are acquired.
[0031]
In the present embodiment, 20 echoes measured in the measurement window are divided into three groups of 12 echoes having a relatively short elapsed time from the preparation pulse application, 6 echoes having a relatively long time, and 2 echoes having a long time. The k-space is divided into three regions in the phase encoding direction (low regions 701 and 701 on both sides of the center, middle regions 702 and 702 on the outside, and high regions 703 and 703 on the outside), and each region is a preparation pulse. Acquired by three sets of echoes with different elapsed times from application. That is, in the first cardiac cycle, the low range 701 of k space is acquired sequentially from the center with echo1 to echo12, the midrange 702 is acquired from the low range side to the high range side with echo13 to echo18, and high with echo19 and echo20. The area 703 is acquired in order from the low frequency side. In the next second cardiac cycle, the outside of the region acquired in the first cardiac cycle within the same region is sequentially acquired toward the high frequency side. Thereafter, measurement is similarly performed up to the sixth cardiac cycle, and finally, the number of echo signals necessary for one image reconstruction is obtained.
[0032]
The state of phase encoding control in this embodiment is shown in FIG. Again, the vertical axis represents the phase encoding amount, and the horizontal axis represents the echo number. In addition, an echo that has the effect of the preparation pulse but has elapsed since the appropriate ECG delay is indicated by a diagonal line 714, and an echo that has a low effect of the preparation pulse and has elapsed since the ECG delay is indicated by the shaded line 715. Respectively.
[0033]
Also in this embodiment, the region 711 for determining the image contrast is acquired when the effect of the preparation pulse is high and hardly affected by body movement, and the effect of the preparation pulse is low or affected by body movement. The easy signal is on the high side 713. As a result, an image with a good SN ratio and a good image quality can be obtained.
[0034]
As described above, as an embodiment of the present invention, the echo signal acquired in the measurement window is divided into a predetermined number (2 or 3) according to the elapsed time from the preparation pulse, and based on the echo number and the cardiac cycle number in the measurement window. Although the example of controlling the phase encoding has been described, the number of divisions within the measurement window and the division method (uniform division, non-uniform division, ratio in the case of non-uniformity, etc.) are not limited to the above-described embodiment, and various changes are possible. It is. Further, although the above embodiment has been described on the assumption of two-dimensional measurement, the MRI apparatus of the present invention can also measure the above-mentioned electrocardiogram synchronous imaging three-dimensionally.
[0035]
In the three-dimensional measurement, since encoding is performed in both the phase encoding direction and the slice encoding direction, the number of encodings is large, the number of cardiac cycles required for acquiring echo signals necessary for image reconstruction is increased, and the imaging time is several minutes. Therefore, it is difficult to maintain a stationary state with the cooperation of the patient until the end of the measurement, and the influence of body movement is likely to occur. In order to eliminate the influence of such body movement, in the three-dimensional measurement, it is preferable to perform the phase encoding control not only in the phase encoding direction but also in the slice encoding direction.
[0036]
FIGS. 8A and 8B show an embodiment in which gradient magnetic field control is performed in the phase encoding direction (ky direction) and the slice encoding direction (kz direction). In the illustrated embodiment, a ky-kz space determined by phase encoding and slice encoding is a region (low region) 801 surrounded by a square or circle (ellipse) centered on the origin, and a square or circle outside the low region. It is divided into a region (middle region) 802 surrounded by (ellipse) and a region (high region) 803 outside the middle region.
[0037]
Also in this embodiment, setting a measurement window with a predetermined delay from the R wave and providing a preparation pulse application immediately before the measurement window are the same as in the case of two-dimensional measurement. The plurality of echoes measured in the measurement window are divided into three groups in the order of measurement corresponding to the ratio of the number of data (number of echoes) occupying each of the three areas as shown in FIG. An echo with a short elapsed time from the application of the preparation pulse is a low frequency 801 in the ky-kz space, and an echo obtained with the effect of the preparation pulse with a relatively long elapsed time is obtained in the middle region 802. Phase encoding and slice encoding are assigned so that an echo whose effect is reduced becomes a high frequency band 803. Further, as the echo number increases (as it progresses from the first cardiac cycle to the second and third), it is directed toward the periphery of the ky-kz space in order.
[0038]
Also in this embodiment, since the low frequency data for determining the image contrast is acquired at the initial stage of imaging when the effect of the preparation pulse is high, body motion that can occur in the latter half of the measurement without impairing the effect of the preparation pulse. And the effects of respiratory motion can be reduced.
[0039]
As described above, the electrocardiogram synchronous imaging has been described as an embodiment of the imaging method employed in the MRI apparatus of the present invention. It can be applied to an MRI apparatus. The present invention is suitable for the case where a preparation pulse application step is provided in front of the measurement window, but the feature of the present invention is the phase encoding control of the echo signal measured in the measurement window, and an imaging sequence that does not use a preparation pulse. It is also possible to apply to.
[0040]
For example, when angiography (contrast MRA) using a contrast medium is performed by electrocardiographic synchronization, a predetermined measurement window is set between RR as shown in FIG. 9, and a specific time phase of the cardiac cycle ( For example, signal measurement is performed during diastole. Here, when a certain width (for example, 100 ms) is set as a measurement window in order to prevent a long shooting time, echoes measured in the latter half of the measurement window are out of the target time phase. By assigning echoes measured in the latter half of the measurement window to the high frequency region in the k space and making echoes measured in the first half of the measurement window in the low frequency region in the k space, the shooting time is increased. The state of the target time phase can be accurately imaged without any problems. Also, by filling the echoes measured in the first half in order from the center of the k space, the low frequency region of the k space can be filled in the time zone that is the contrast agent peak (with a small cardiac cycle). A high-contrast blood vessel image can be obtained.
[0041]
【The invention's effect】
According to the present invention, in imaging using a preparation pulse that repeatedly performs measurement in synchronization with a biological monitor signal and enhances image contrast, the unnecessary signal suppression effect due to the preparation pulse is not impaired and the shooting time elapses. It is possible to effectively eliminate the influence of body movement and the influence of changes in contrast medium concentration. As a result, a high-quality image with a good SN can be obtained. According to the present invention, even when electrocardiogram synchronous imaging is performed in contrast MRA, a high-accuracy and high-contrast image can be obtained without increasing the imaging time.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall outline of an MRI apparatus to which the present invention is applied.
FIG. 2 is a diagram showing an embodiment of an imaging method employed by the MRI apparatus of the present invention.
3 is a diagram showing an example of a shooting sequence used in the shooting method of FIG.
FIG. 4 is a diagram for explaining phase encoding gradient magnetic field control in the imaging method of FIG. 2;
FIG. 5 is a graph showing the phase encoding gradient magnetic field control of FIG.
FIG. 6 is a diagram showing another embodiment of an imaging method employed by the MRI apparatus of the present invention.
7 is a graph showing phase encoding gradient magnetic field control in the imaging method of FIG. 6;
FIG. 8 is a diagram showing an embodiment of phase encoding gradient magnetic field control in the case of three-dimensional measurement by the MRI apparatus of the present invention.
FIG. 9 is a diagram showing conventional ECG synchronous measurement
FIG. 10 is a diagram showing phase encoding gradient magnetic field control in conventional electrocardiographic synchronization measurement;
FIG. 11 is a diagram showing phase encoding gradient magnetic field control in conventional contrast imaging
FIG. 12 is a diagram showing phase encoding gradient magnetic field control in conventional electrocardiographic synchronization measurement;
FIG. 13 is a diagram showing phase encoding gradient magnetic field control in conventional electrocardiographic synchronization measurement;
[Explanation of symbols]
101 ... subject, 102 ... magnet, 103 ... gradient coil, 104 ... RF coil, 105 ... RF probe, 106 ... signal detector, 107 ... signal processor 111 ... Control unit

Claims (4)

Magnetic field generating means for applying a high-frequency magnetic field and a gradient magnetic field to the space where the subject is placed, receiving means for measuring a nuclear magnetic resonance signal generated by the subject as an echo signal, application of the high-frequency magnetic field and the gradient magnetic field, and an echo signal In a magnetic resonance imaging apparatus, comprising: a control means for controlling the acquisition of the signal; and a signal processing means for reconstructing an image of the subject using an echo signal.
The control means is configured to set a measurement window for measuring an echo signal within each period in synchronization with a periodically generated biological monitor signal; and two or more echo signals to be measured within the measurement window. Phase encoding control means for controlling the phase encoding so as to divide into groups and occupy a predetermined area of k-space according to the signal measurement time of each group,
The phase encoding control means arranges the echo signals of the group having the earliest signal measurement time among the two or more groups in order from the low range to the high range of the k space sequentially for each period. Magnetic resonance imaging device. Magnetic field generating means for applying a high-frequency magnetic field and a gradient magnetic field to the space where the subject is placed, receiving means for measuring a nuclear magnetic resonance signal generated by the subject as an echo signal, application of the high-frequency magnetic field and the gradient magnetic field, and an echo signal In a magnetic resonance imaging apparatus, comprising: a control means for controlling the acquisition of the signal; and a signal processing means for reconstructing an image of the subject using an echo signal.
The control means includes means for setting a measurement window for measuring an echo signal within each period in synchronization with a biological monitor signal generated periodically, and a plurality of echo signals measured within the measurement window. The phase encoding is controlled so that the echo signal acquired in the period 1 occupies the low frequency region of the k space and the echo signal acquired in the second period later than the first period occupies the high frequency region of the k space. Phase encoding control means for
The magnetic resonance imaging apparatus characterized in that the phase encoding control means arranges echo signals acquired in the first period sequentially from the low range to the high range of the k space . 3. The magnetic resonance imaging apparatus according to claim 1, wherein the control unit includes a step of applying a preparation pulse for suppressing a signal from a specific tissue before the measurement window. Magnetic resonance imaging apparatus. Magnetic field generating means for applying a high-frequency magnetic field and a gradient magnetic field to the space where the subject is placed, receiving means for measuring a nuclear magnetic resonance signal generated by the subject as an echo signal, application of the high-frequency magnetic field and the gradient magnetic field, and an echo signal In a magnetic resonance imaging apparatus, comprising: a control means for controlling the acquisition of the signal; and a signal processing means for reconstructing an image of the subject using an echo signal.
The control means performs control to repeat measurement for obtaining a plurality of echo signals after application of a preparation pulse for suppressing a signal from a specific tissue a plurality of times . Filling is controlled according to the elapsed time from the application of the preparation pulse, and echo signals acquired in the first half of one repetition are sequentially arranged from the low range to the high range of the k space. A magnetic resonance imaging apparatus.

Images