JP4693227B2 - Magnetic resonance imaging apparatus and scan synchronization method of magnetic resonance imaging - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to magnetic resonance imaging (MRI) that images the inside of an imaging target based on a magnetic resonance phenomenon, and more particularly to MR imaging called a black blood method.
[0002]
[Prior art]
Currently, magnetic resonance imaging is widely used as one of medical imaging methods. In this magnetic resonance imaging, the nuclear spin of the imaging target placed in a static magnetic field is magnetically excited with a high-frequency signal of its Larmor frequency, and the image inside the imaging target is reconstructed from the MR signal generated by this excitation. This is an imaging method. There are various types of magnetic resonance imaging, and the types differ depending on the pulse sequence used for magnetic excitation and signal acquisition.
[0003]
In the case of magnetic resonance imaging that images the heart region, ghost-like artifacts (blood flow artifacts) from the part with a lot of blood flow toward the phase encoding direction on the reconstructed image due to the influence of blood pulsation It is likely to occur. In order to suppress this artifact, an electrocardiographic synchronization imaging method in which RF excitation and echo collection are synchronized with an electrocardiogram waveform is generally used. Thereby, the fluctuation | variation of the echo signal for every shot (excitation) can be suppressed, and the above-mentioned blood flow artifact can be reduced.
[0004]
Furthermore, the paper “Edelman RR et al., Fast selective black block MR imaging, Radiology 1991 Dec. 181 (3): 655-60, 1991”, “Edelman RR et alc. angiography, Radiology 1990 Oct. 177 (1): 45-65, 1990 ", etc., with the main purpose of improving the myocardial rendering ability, prepulse for suppressing the collection of MR signals of blood. A so-called black blood method has been proposed which is added before the pulse train of normal RF excitation and echo acquisition. As a pulse train for RF excitation and echo collection, a pulse train such as a pulse train based on a field echo method, a fast field echo method, a fast spin echo method, or the like is used.
[0005]
Furthermore, in recent years, a selective inversion pulse that inverts and excites substantially the same region as the imaging cross section and a non-selective inversion pulse that inverts and excites the entire imaging target are continuously applied, and after 400 to 700 ms from the application, For example, a black blood method using so-called double inversion pulses for performing RF excitation and echo acquisition is also reported (for example, the document “Simonetti OP et al.,“ Black Blood ”T2-lighted inversion-recovery MR imaging). of the heart, Radiology 1996 Apr. 199 (1): 49-57, 1996 "," Stehling MK et al., Single-shot T1- and T2-weighted magneto ". etic resonance imaging of the heart with black blood: preliminary experience, MAGMA 1996 Sep Dec, 4 (3-4):. 231-40, 1996 "," Arai AE et al, Visualization ofaortic valve leaflets using black blood MRI, J Magn Reson Imaging 1999 Nov., 10 (5): 771-7, 1999 ”).
[0006]
The black blood method using this double inversion pulse is attracting attention because of its high blood signal suppression effect and low signal degradation in other tissues, and is expected to become increasingly popular. The shape of the prepulse varies from report to report. Since the prepulse is basically intended to reduce the longitudinal magnetization of the blood signal to zero or sufficiently small, in any case, the time from the application of the prepulse to the application of the excitation pulse for imaging is about 400 to 700 ms. This time is longer than the pre-pulse applied for other purposes.
[0007]
For this reason, even when a prepulse is applied immediately after detecting an R wave using the electrocardiographic synchronous imaging method, the cardiac time phase that can be actually imaged is the second half of the cardiac cycle, that is, the diastole. Therefore, for example, as described in the above-mentioned paper “Simonetti OP et al.,“ Black Blood ”T2-lighted inversion-recovery MR imaging of the heart, Radiology 1996 Apr. 199 (1): 49-57, as seen in this document. When using the black blood method, it is common to collect diastole images.
[0008]
Here, FIG. 6 shows a pulse sequence of a black blood method using a conventional double inversion pulse. As shown in the figure, a double inversion pulse DIV as a pre-pulse for suppressing blood is applied in synchronization with a predetermined time td from the R wave of the ECG (electrocardiogram) signal. After time BBTI, imaging pulse train SEQ _ima Is applied to collect echo signals. In the figure, RF represents an RF pulse, Gs represents a slice direction gradient magnetic field, Gr represents a read direction gradient magnetic field, Ge represents a phase encode direction gradient magnetic field, and Echo represents an echo signal.
[0009]
Of the two RF pulses of the double inversion pulse DIV, one is applied with the intensity of the gradient magnetic field Gs in the slice direction being zero, and the other is exciting the same region as the slice that is selectively excited in the pulse sequence for imaging. In order to achieve this, a slice direction gradient magnetic field Gs having a required strength is applied in addition. The waiting time BBTI is usually about 500 to 600 ms, and is set to a time at which the longitudinal magnetization of blood becomes substantially zero.
[0010]
[Problems to be solved by the invention]
However, when using the conventional black blood method, it is difficult to collect systolic images that are close to the R wave in time, or a series of images with a delay time that changes at regular intervals, such as cine mode display. There is a problem that it is difficult to do.
[0011]
Therefore, since a long time: BBTI (inversion time of the black blood method) is required from the application of the prepulse to the echo collection, in order to collect a systolic image, one or more of the heart cycles actually collected is collected. The R wave of the previous cardiac cycle must be used as a synchronous trigger. This is shown in FIG. That is, as shown in the figure, in order to collect an image of the systole between R2 and R3, a predetermined delay time is added to R wave: R1 in a preceding cardiac cycle, for example, cardiac cycle R1-R2. It is necessary to synchronize with td.
[0012]
Even in a healthy person, the heartbeat cycle fluctuates by about 10 to 20%. That is, the position of the R wave is shifted on the time axis for each heartbeat. For this reason, even if an image is collected after a certain time “td + BBTI” from an R wave more than one cardiac cycle before, the myocardial position at the time of echo collection fluctuates for each shot, and the image quality deteriorates significantly. Images that can withstand the diagnosis are not obtained. FIG. 8 schematically shows FIG. 7 divided into two conditions, that is, when the cardiac cycle is long and when it is short. As shown in FIG. 8, in the conventional case, since the delay time td1 and the inversion time BBTI are fixed and the start timing of the imaging pulse train SQima is controlled, the delay time td2 having a strong correlation with the actual myocardial movement is It changes in the same way due to fluctuations in the cardiac cycle.
[0013]
For this reason, conventionally, as described above, it has been limited to collecting images in the expansion period.
[0014]
The present invention was made in order to overcome the current situation faced by the prior art, and after applying a pre-pulse, such as imaging based on the black blood method using a double inversion pulse, until application of an imaging pulse train. MR imaging using a pulse sequence in which the waiting time is longer than the cardiac cycle provides an imaging method that can reliably capture an image in the systolic phase of the cardiac cycle even when the cardiac cycle varies from cycle to cycle That is the purpose.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, in the magnetic resonance imaging of the present invention, in the imaging based on the black blood method, the time BBTI from the application of the pre-pulse to the application of the imaging pulse train is relatively longer than one cardiac cycle. Is based on the knowledge of the present inventor that the difference in blood signal suppression effect due to fluctuations in the range of approximately 400 to 700 ms is small and the influence on the image quality is almost negligible. .
[0016]
Therefore, for the pre-pulse and imaging pulse train of the pulse sequence used in the magnetic resonance imaging of the present invention, a plurality of predetermined waveforms (for example, R waves) arranged in time series of signals representing the cardiac time phase (for example, ECG signals), The gist is to apply synchronization separately.
[0017]
Specifically, as one aspect of the present invention, a pre-pulse is applied to an imaging target, and after a predetermined waiting time from the application, the imaging pulse train is applied to a desired region of the imaging target to perform scanning. In the resonance imaging apparatus, a collection unit that collects a signal representing a cardiac time phase of the imaging target and a predetermined waveform appearing at a certain timing of the signal collected by the detection unit are synchronized with a first delay time. A pre-pulse applying means for applying the pre-pulse, and a signal detected by the detecting means synchronized with the predetermined waveform appearing at a timing at least one cardiac cycle after the timing with a second delay time. And a scanning unit that performs scanning by applying an imaging pulse train.
[0018]
For example, the pre-pulse is a double inversion pulse forming part of a pulse sequence based on the black blood method. For example, the signal representing the cardiac phase is an ECG signal, and the predetermined waveform is an R wave of the ECG signal. Further, for example, the timing after the at least one cardiac cycle when the scanning unit starts scanning is a timing at which one cardiac cycle or two cycles have elapsed.
[0019]
Further, the predetermined waiting time is characterized by being long enough to occupy about half or more of one cycle of the heartbeat.
[0020]
Further, the second delay time is a time set in accordance with the systole of the heartbeat, and the first delay time is the second delay time, a desired value of the waiting time, and the heartbeat It is also desirable that the time is calculated from an average period.
[0021]
According to another aspect of the present invention, a pre-pulse is applied to an imaging target, and after a predetermined waiting time from this application, an imaging pulse train is applied to a desired area of the imaging target to perform scanning. In the resonance imaging apparatus, means for synchronizing the application of the pre-pulse and the imaging pulse train to two identical types of waveforms appearing at different timings in the signal representing the cardiac time phase of the imaging target is provided.
[0022]
According to still another aspect of the present invention, a magnetic resonance imaging pulse sequence including a pre-pulse and an imaging pulse train is applied to an imaging target in synchronization with a signal representing a cardiac time phase of the imaging target. In the scan synchronization method, the pre-pulse is applied in synchronization with a predetermined waveform appearing at a certain timing of the signal with a first delay time, and the signal appears at a timing at least one cardiac cycle after the timing. The scanning is performed by applying the imaging pulse train in synchronization with a predetermined waveform with a second delay time.
[0023]
Furthermore, in the present invention, a recording medium for magnetic resonance imaging in which a pulse sequence for magnetic resonance imaging composed of a pre-pulse and an imaging pulse train is applied to the imaging target in synchronization with a signal representing the cardiac time phase of the imaging target. A function of applying a pre-pulse to a computer in synchronization with a predetermined waveform appearing at a certain timing of the signal with a first delay time, and at least one cardiac cycle after the timing of the signal It is also possible to provide a computer-readable recording medium recording a program for realizing a function of performing scanning by applying the imaging pulse train in synchronization with the predetermined waveform appearing at timing with a second delay time. it can.
[0024]
Furthermore, a magnetic resonance imaging program for applying a pulse sequence for magnetic resonance imaging composed of a pre-pulse and an imaging pulse train to the imaging object in synchronization with a signal representing the cardiac time phase of the imaging object, A function of applying the pre-pulse in synchronization with a predetermined waveform appearing at a certain timing of the signal with a first delay time; and the predetermined waveform appearing at a timing at least one cardiac cycle after the timing of the signal In addition, a program for realizing a function of performing scanning by applying the imaging pulse train in synchronization with the second delay time can be provided.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, one embodiment according to the present invention will be described with reference to FIGS.
[0026]
A schematic configuration of a magnetic resonance imaging apparatus according to this embodiment is shown in FIG.
[0027]
The magnetic resonance imaging apparatus includes a bed unit on which an imaging target (subject) P is placed, a static magnetic field generation unit that generates a static magnetic field, a gradient magnetic field generation unit for adding position information to the static magnetic field, and a high-frequency signal. A transmission / reception unit for transmitting / receiving, a control / arithmetic unit responsible for overall system control and image reconstruction, an electrocardiogram measurement unit for measuring an ECG (electrocardiogram) signal representing a cardiac time phase of the imaging target P, and an imaging target A breath-hold command unit for commanding P to hold the breath.
[0028]
The static magnetic field generation unit includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 that supplies current to the magnet 1, and the axial direction of a cylindrical opening (diagnostic space) into which the imaging target P is loosely inserted. Static magnetic field H in the Z-axis direction ₀ Is generated. In addition, the shim coil 14 is provided in this magnet part. The shim coil 14 is supplied with a current for homogenizing a static magnetic field from a shim coil power supply 15 under the control of a host computer to be described later. The couch portion can be removably inserted into the opening of the magnet 1 with the top plate on which the imaging target P is placed.
[0029]
The gradient magnetic field generator includes a gradient magnetic field coil unit 3 incorporated in the magnet 1. The gradient coil unit 3 includes three sets (types) of x, y, and z coils 3x to 3z for generating gradient magnetic fields in the X, Y, and Z axis directions orthogonal to each other. The gradient magnetic field unit also includes a gradient magnetic field power supply 4 that supplies current to the x, y, and z coils 3x to 3z. The gradient magnetic field power supply 4 supplies a pulse current for generating a gradient magnetic field to the x, y, z coils 3x to 3z under the control of a sequencer 5 described later.
[0030]
By controlling the pulse current supplied from the gradient magnetic field power source 4 to the x, y, z coils 3x to 3z, the gradient magnetic fields in the three axes X, Y, and Z, which are physical axes, are synthesized and slices orthogonal to each other. The logical axis directions of the direction gradient magnetic field Gs, the phase encode direction gradient magnetic field Ge, and the readout direction (frequency encode direction) gradient magnetic field Gr can be arbitrarily set and changed. Each gradient magnetic field in the slice direction, phase encoding direction, and readout direction is a static magnetic field H. ₀ Is superimposed on.
[0031]
The transmission / reception unit includes an RF coil 7 disposed in the vicinity of the imaging target P in the diagnostic space in the magnet 1, and a transmitter 8T and a receiver 8R connected to the coil 7. The transmitter 8T and the receiver 8R operate under the control of the sequencer 5 described later. The transmitter 8T supplies the RF coil 7 with an RF current pulse having a Larmor frequency for causing nuclear magnetic resonance (NMR). The receiver 8R takes in the MR signal (high frequency signal) received by the RF coil 7 and performs various signal processing such as preamplification, intermediate frequency conversion, phase detection, low frequency amplification, filtering, etc. Digital data (original data) corresponding to the MR signal is generated by / D conversion.
[0032]
The control / arithmetic unit further includes a sequencer (also referred to as a sequence controller) 5, a host computer 6, an arithmetic unit 10, a storage unit 11, a display device 12, an input device 13, and a sound generator 16. Among these, the host computer 6 has a function of instructing the pulse sequence information to the sequencer 5 according to the procedure based on the stored software and overseeing the operation of the entire apparatus.
[0033]
Following the preparatory work such as the positioning scan (not shown), the host computer 6 performs the MR imaging scan based on the black blood method shown in FIG. Collect data sets. In this black blood method, a double inversion pulse DIV as a prepulse for suppressing a signal from blood and a predetermined waiting time (longitudinal magnetization of a magnetized spin reversed by the double inversion pulse is almost zero after application of this pulse. After BBTI, imaging pulse train SEQ _ima Is applied. This imaging pulse train SEQ _ima As such, any pulse train such as a two-dimensional scan or three-dimensional scan FE (field echo) system, SE (spin echo) system, or EPI (echo planar imaging) system may be used.
[0034]
In this black blood method, the feature corresponding to the present invention is that, as will be described later, a double inversion pulse DIV and an imaging pulse SEQ _ima It is to apply electrocardiogram synchronization separately to each other.
[0035]
The sequencer 5 includes a CPU and a memory, stores pulse sequence information sent from the host computer 6, controls the operations of the gradient magnetic field power source 4, the transmitter 8T, and the receiver 8R according to this information, The digital data of the MR signal output from the receiver 8R is once inputted and transferred to the arithmetic unit 10. Here, the pulse sequence information is all information necessary for operating the gradient magnetic field power source 4, the transmitter 8T, and the receiver 8R according to a series of pulse sequences, for example, x, y, z coils 3x to 3z. Includes information on the intensity, application time, application timing, and the like of the pulse current applied to.
[0036]
The arithmetic unit 10 inputs the digital raw data (also referred to as original data) output from the receiver 8R through the sequencer 5, and stores the raw data in the Fourier space (k space or frequency space) in the internal memory. This raw data is subjected to two-dimensional or three-dimensional Fourier transform for each set, and reconstructed into real space image data. The arithmetic unit can perform image data synthesis (addition) processing, difference calculation processing, and the like as necessary.
[0037]
The storage unit 11 stores not only computer programs necessary for signal control, data processing, and data calculation of the apparatus, and reconstructed image data, but also image data that has been subjected to the above-described synthesis processing and difference processing. can do. Therefore, an MR imaging program based on the black blood method according to the present invention is also stored in a recording medium (not shown) mounted in the storage unit 11 and is read by the host computer 6 and the sequencer 5.
[0038]
The display device 12 displays an image. Also, imaging conditions desired by the surgeon, pulse sequence information, calculation method parameters such as image synthesis and difference processing, and the like can be input to the host computer 5 via the input unit 13.
[0039]
Moreover, the sound generator 16 is provided as an element of the breath-hold command unit. Information related to computation can be input to the host computer 6. The voice generator 16 can emit a breath holding start message and a breath holding end message as voice when instructed by the host computer 6.
[0040]
Further, the electrocardiogram measurement unit attaches to the body surface of the imaging target P and detects an ECG (electrocardiogram) signal as a signal representing a cardiac time phase, and processes the ECG signal to process, for example, an R wave. And an ECG unit 18 for outputting a trigger signal synchronized with the peak value to the sequencer 5. This trigger signal is used by the sequencer 5 to execute black blood MR imaging in the electrocardiographic synchronization method.
[0041]
In the configuration of the present embodiment, the ECG sensor 17 and the ECG unit 18 constitute a signal collection unit that represents a cardiac phase according to the present invention. The magnet 1, the gradient magnetic field coil unit 3, the gradient magnetic field power source 4, the sequencer 5, the host computer 6, the RF coil 7, the transmitter 8T, and the storage unit 11 constitute the main parts of the prepulse applying means and the scanning means of the present invention. . Further, the storage unit 11 has memory means as a recording medium according to the present invention.
[0042]
Next, the operation of the magnetic resonance imaging apparatus of the present embodiment will be described with reference to FIGS.
[0043]
FIG. 2 shows a pulse sequence of a black blood method using a double inversion pulse, which is executed under the electrocardiographic synchronization method in this embodiment. This pulse sequence is executed by the sequencer 5 in the procedure of FIG. This procedure is transferred from the host computer 6 to the sequencer 5 as pulse sequence information.
[0044]
The sequencer 5 first determines whether or not the timing when the R wave of the ECG signal exhibits a peak value has been reached while trying to read the trigger signal from the ECG unit 18 (steps S1 and S2). This trigger signal is generated by the ECG unit 18. The ECG unit 18 repeats the operation of inputting the ECG signal from the ECG sensor 17, detecting the peak value of the R wave, and outputting a trigger signal at the time of detection (steps E1 to E3).
[0045]
When the sequencer 5 detects the appearance of the R wave peak value, the sequencer 5 starts measuring the time of a built-in software timer (step SS3). The R wave detected here is the first R wave: R1 shown in FIG.
[0046]
Next, the sequencer 5 determines whether or not the measured value CT of this timer coincides with a predetermined delay time td1 from the R wave shown in FIG. 2 (CT = td1) (step S4). This delay time td1 is a time for applying ECG synchronization to the double inversion pulse DIV as a pre-pulse, and corresponds to the first delay time of the present invention. The delay time td1 is set in advance as will be described later.
[0047]
If NO in the determination step of step S4, that is, if the measurement time has not yet reached the delay time td1, the time measurement is continued as it is. If YES, it is recognized that the delay time td1 has been reached, and the next step Proceed to processing. That is, the sequencer 5 commands the start of application of the double inversion pulse DIV as a pre-pulse (step S5). Thereafter, the measurement value of the software timer described above is cleared (step S6).
[0048]
Next, the sequencer 5 captures the imaging pulse train SEQ. _ima Shifts to ECG synchronization processing. That is, the trigger signal is read in the same manner as described above, and it is determined that the timing of the R wave peak value has arrived when the trigger signal is read (steps S7 and S8). The R wave detected by this is R wave: R2 shown in FIG.
[0049]
In response to the detection of the R-wave peak value, time measurement based on software time is started in the same manner as described above, and it is determined whether or not the measured value CT = delay time td2 (steps S9 and S10). . This delay time td2 is an imaging pulse train SEQ in an R wave (R2) different from the pre-pulse. _ima It is time to apply ECG synchronization. For example, the delay time td2 is given in advance so that data collection can be started at a desired timing in the diastole in one cardiac cycle.
[0050]
Therefore, when the determination in step S9 is YES (CT = td2), the imaging pulse train SEQ shown in FIG. _ima Is started (step S11). Next, when the timer is cleared and data is collected by the next phase encoding, the process returns to step S1 (steps S11 and S12).
[0051]
Here, a method for setting the above-described delay time td1 of the double inversion pulse DIV will be described. This delay time td1 (fixed value) is obtained from the delay time td2 (fixed value) given as described above, the inversion time BBTI required for the black blood method, and the average RR interval: RR of the ECG signal.
[Expression 1]
td1 = RR + td2-BBTI
It is calculated in advance based on the following formula.
[0052]
Therefore, a scan for MR imaging according to the black blood method shown in FIG. 2 is executed by the processing by the sequencer 5 described above.
[0053]
That is, when the R wave: R1 of the ECG signal at a certain time point appears, the double inversion pulse DIV is applied in synchronization with the preset delay time td1 from the point of the peak value. This pulse includes an inversion pulse that reversely excites spins of the entire imaging target without applying the slice gradient magnetic field Gs, and an inversion pulse that reversely excites spins of only the imaging cross section with the application of the slice gradient magnetic field Gs. Are continuously applied.
[0054]
After the application of the double inversion pulse DIV is started, the next R wave: R2 appears. When this R wave: R2 appears, when a preset delay time td2 elapses from the peak value, for example, an imaging pulse train SEQ according to the high-speed SE method is used. _ima Is started. As a result, echo signals are collected corresponding to a plurality of phase encoding amounts. These echo signals are converted into image data by the receiver 8R and sent to the arithmetic unit 10 for image reconstruction.
[0055]
For this reason, echo data can be collected almost without being affected by the fluctuation of the RR interval, that is, the cardiac cycle. For example, when the cardiac cycle changes from the state shown in FIG. 4 (a) to the state shown in FIG. 4 (b) where the cardiac cycle is small, the RR interval is shortened. This shortening is automatically performed by reducing the inversion time BBTI. Absorbed. On the contrary, when the cardiac cycle becomes large, the RR interval is enlarged, but this enlargement is automatically absorbed by the enlargement of the inversion time BBTI. In the case of the black blood method according to the present embodiment, the difference in the blood signal suppression effect is small as much as the time width of the inversion time BBTI is varied within a range of about 400 to 700 ms, and thus the influence on the image quality is ignored. It has been found that it can.
[0056]
In this way, since the change in the RR interval is absorbed by the change in the inversion time BBTI within the required range, the double inversion pulse DIV and the imaging pulse train SEQ _ima Are respectively synchronized with predetermined fixed delay times td1 and td2.
[0057]
That is, the imaging pulse train SEQ _ima Can synchronize the R wave independently of the double inversion pulse DIV. Therefore, considering only the delay time td2, the scan can be started at a desired timing of the systole within one cardiac cycle, and echo data of the systole can be collected. As a result, even in MR imaging using a pulse sequence with a long waiting time until data collection after pre-pulse application, such as the Black Blood method, echo collection is performed without being affected by fluctuations in the cardiac cycle. Can avoid a situation in which the position of the myocardium at the time of collection constantly fluctuates from shot to shot. Therefore, artifacts can be reduced, and high-quality MR images in the systole can be provided stably and reliably.
[0058]
Further, if imaging is performed while switching between the conventional method and the above-described method according to the present invention depending on the delay time, it is possible to perform cine mode imaging based on the black blood method, which has been substantially impossible in the past.
[0059]
In the embodiment described above, the double inversion pulse DIV and the imaging pulse train SEQ _ima The configuration has been described in which the two are synchronized separately with two different R waves: R1 and R2. However, the present invention is not necessarily limited to such a configuration. For example, as shown in FIG. 5, after the double inversion pulse DIV is synchronized with the R wave: R1, the next R wave: R2 is released. R wave: Imaging pulse train SEQ at R3 _ima May be synchronized. Two or more R waves may be generated. To achieve this, for example, a process for counting the desired number of R waves is interposed between steps S8 and S9 shown in FIG. 3, and when the count reaches the desired number, the process shown in step S9 is performed. What is necessary is just to make it move. With this configuration, in addition to the same effects as those of the above-described embodiment, the inversion time BBTI can be varied in the setting method.
[0060]
Furthermore, the present invention is not limited to the configurations of the above-described embodiments and modifications thereof, and can be implemented in still other forms without departing from the scope of the claims. For example, the method for detecting a signal representing a heartbeat described above is not limited to the method for detecting an ECG signal, but a method for detecting a pulse wave, a method for using the intensity of the MR signal itself, and a phase shift of an echo signal. A detection method, a method using a navigator echo, or the like may be used as appropriate.
[0061]
【The invention's effect】
As described above, according to the present invention, a predetermined waveform (R wave) in which a signal (ECG signal or the like) representing a cardiac time phase of an imaging target is different with respect to a prepulse and an imaging pulse train that form a pulse sequence such as a black blood method. Etc.) with different delay times, the application timing of the imaging pulse train for collecting the echo signals can always be kept constant even if the cardiac cycle varies. As a result, in MR imaging using a pulse sequence in which the waiting time between the pre-pulse and the imaging pulse train is longer than the cardiac cycle, even if there is a cycle-by-cycle variation in the cardiac cycle, the image in the systolic phase of the cardiac cycle Can be reliably imaged. Therefore, artifacts can be reduced and the image quality of MR images can be improved.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing an example of a schematic configuration of a magnetic resonance imaging apparatus according to an embodiment of the present invention.
FIG. 2 is a pulse sequence showing a black blood method used in the embodiment.
FIG. 3 is a flowchart showing an outline of an electrocardiogram synchronization process for executing the pulse sequence of FIG. 2;
FIG. 4 is a diagram for explaining a mechanism for absorbing fluctuations in the cardiac cycle.
FIG. 5 is a pulse sequence showing a black blood method used in a modified embodiment of the present invention.
FIG. 6 is a pulse sequence showing a conventional black blood method.
FIG. 7 is a pulse sequence showing an example of a synchronization method based on a conventional black blood method.
FIG. 8 is a pulse sequence for explaining inconveniences of the synchronization method based on the conventional black blood method.
[Explanation of symbols]
1 Magnet
2 Static magnetic field power supply
3 Gradient magnetic field coil unit
4 Gradient magnetic field power supply
5 Sequencer
6 Host computer
7 RF coil
8T transmitter
8R receiver
10 Arithmetic unit
11 Storage unit
12 Display
13 Input device
17 Sensor unit
18 ECG units

Claims (11)

In a magnetic resonance imaging apparatus that scans by applying a pulse sequence consisting of a pre-pulse and an imaging pulse train following the pre-pulse to an imaging target ,
Pre-pulse application for applying the pre-pulse in synchronization with a predetermined waveform appearing at a certain timing of a signal collected by a detecting means for collecting a signal representing a cardiac phase of the imaging target with a first delay time Means,
Scan means for performing a scan by applying the imaging pulse train in synchronization with the predetermined waveform appearing at a timing at least one cardiac cycle after the certain timing of the signal collected by the detection means with a second delay time And a magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 1.
The magnetic resonance imaging apparatus according to claim 1, wherein the pre-pulse is a double inversion pulse forming a part of a pulse sequence based on a black blood method. The magnetic resonance imaging apparatus according to claim 1.
The signal representing the cardiac time phase is an ECG signal, the predetermined waveform is an R wave of the ECG signal, and the scanning unit allows variation in time from the application of the pre-pulse to the start of the imaging pulse train. , Fixing the second delay time from the R wave immediately before the imaging pulse train to the start of the imaging pulse train,
Magnetic resonance imaging apparatus characterized by. The magnetic resonance imaging apparatus according to claim 1.
The magnetic resonance imaging apparatus according to claim 1, wherein the timing after the at least one cardiac cycle when the scanning unit starts scanning is a timing at which one cardiac cycle has elapsed. The magnetic resonance imaging apparatus according to claim 1.
The magnetic resonance imaging apparatus according to claim 1, wherein the timing after the at least one cardiac cycle when the scanning unit starts scanning is a timing at which two cardiac cycles have elapsed. The magnetic resonance imaging apparatus according to claim 1.
The magnetic resonance imaging apparatus characterized in that the time from the application of the pre-pulse to the start of the imaging pulse train is long enough to occupy about half or more of one cycle of the heartbeat . The magnetic resonance imaging apparatus according to claim 1.
The second delay time is a time set in accordance with the systole of the heartbeat, and the first delay time is the second delay time, the time from the application of the pre-pulse to the start of the imaging pulse train. And a time calculated from an average period of the heartbeat . In a magnetic resonance imaging apparatus that scans by applying a pulse sequence consisting of a pre-pulse and an imaging pulse train following the pre-pulse to an imaging target ,
2. A magnetic resonance imaging apparatus comprising: means for synchronizing the application of the pre-pulse and the imaging pulse train to two identical types of waveforms that appear at different timings in the signal representing the cardiac phase of the imaging object. In a magnetic resonance imaging scan synchronization method in which a pulse sequence for magnetic resonance imaging composed of a pre-pulse and a subsequent imaging pulse train is applied to the imaging target in synchronization with a signal representing a cardiac phase of the imaging target.
Applying the prepulse in synchronization with a predetermined waveform appearing at a certain timing of the signal with a first delay time;
Magnetic resonance imaging characterized in that scanning by applying the imaging pulse train is performed in synchronization with the predetermined waveform appearing at a timing after at least one cardiac cycle from the timing with a second delay time. Scan synchronization method. A recording medium for magnetic resonance imaging in which a pulse sequence for magnetic resonance imaging composed of a pre-pulse and a subsequent imaging pulse train is applied to the imaging target in synchronization with a signal representing a cardiac time phase of the imaging target,
A function of applying the pre-pulse to a computer in synchronization with a predetermined waveform appearing at a certain timing of the signal with a first delay time, and the signal appearing at a timing at least one cardiac cycle after the timing; A computer-readable recording medium on which a program for realizing a function of performing scanning by applying the imaging pulse train in synchronization with a predetermined waveform with a second delay time is recorded. A program for magnetic resonance imaging that applies a pulse sequence for magnetic resonance imaging composed of a pre-pulse and a subsequent imaging pulse train to the imaging object in synchronization with a signal representing a cardiac time phase of the imaging object,
A function of applying the pre-pulse to a computer in synchronization with a predetermined waveform appearing at a certain timing of the signal with a first delay time, and the signal appearing at a timing at least one cardiac cycle after the timing; A program for realizing a function of performing scanning by application of the imaging pulse train in synchronization with a predetermined waveform with a second delay time.

Images