JP2859264B2 - Magnetic resonance imaging equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention applies a gradient magnetic field and an excitation high-frequency magnetic field to a subject arranged in a static magnetic field in accordance with a predetermined excitation / detection procedure. By applying the magnetic field, a magnetic resonance phenomenon occurs in a specific portion of the subject, and the excited magnetic resonance signal is detected and subjected to signal processing to thereby provide anatomical information and quality of the specific portion of the subject. The present invention relates to a magnetic resonance imaging apparatus for imaging at least one of target information, and more particularly to a magnetic resonance imaging apparatus and method capable of efficiently obtaining information at different time phases of a moving organ such as a heart. (Prior Art) As a diagnostic device capable of obtaining anatomical information, particularly tomographic image information of a subject, a magnetic resonance imaging apparatus and an X-ray CT scanner apparatus have an imaging mode called a heartbeat synchronous imaging mode. In this heartbeat synchronous imaging mode, for example, an electrocardiograph is used to obtain an electrocardiographic waveform signal of a subject, and, for example, slice images of different cardiac phases are obtained on the basis of, for example, the R wave of the electrocardiographic waveform signal, and a systolic phase of the heart is obtained. It is a clinically useful information that accurately informs the diagnostician of the dynamic morphological changes of the myocardium, ventricles, and valves during diastole. Here, an example of a conventional magnetic resonance imaging apparatus capable of performing heartbeat synchronous imaging will be described. That is, a superconducting or normal conducting static magnetic field coil, a gradient magnetic field coil, and a transmitting / receiving coil are provided as a static magnetic field generating device in the cylindrical main body. A subject placed on a couch top is introduced with a diagnosable magnetic field generation region in the main body. Then, in a state where a static magnetic field is applied to the subject, the gradient magnetic field coil and the transmission / reception coil are driven in accordance with an excitation / detection procedure for performing a predetermined pulse sequence, and a gradient magnetic field and an excitation high-frequency magnetic field are applied. This causes a magnetic resonance phenomenon at a specific site of the subject. The excited magnetic resonance signal is detected by the transmission / reception coil, introduced into a computer system, and subjected to signal processing, for example, to image a slice tomographic image as anatomical information of a specific site of the subject, and display the image on a monitor. I am trying to do it. The above is the configuration of the normal apparatus. In addition, the apparatus is provided with an electrocardiograph or a phonograph so that heart rate synchronized imaging can be performed.
Then, as shown in FIG. 5, the slice plane with the heart CA
In response to S1, as shown in FIG. 6, an electrocardiographic waveform signal or an electrocardiographic signal Sh from an electrocardiograph or a soundcardiograph indicates that the time T1
By executing the above-described excitation / detection procedure at T4, tomographic images D1 to D4 of slice planes of the heart CA at different time phases can be obtained. In the above, it is essential that the repetition time Tr of the RF pulse sequence is equal to or longer than the relaxation time Tr min required for relaxation recovery in order to obtain a sufficient contrast. Therefore, the number of images that can be obtained per unit time T is the number determined depending on the repetition time Tr and the number of encoding steps required to construct one magnetic resonance image,
Compared to an X-ray CT scanner that is often compared as a device for obtaining this kind of cardiac temporal slice image, the number of acquired images per unit time T is extremely small, and there is a problem that efficient image acquisition cannot be performed. Was. (Problems to be Solved by the Invention) As described above, in the magnetic resonance imaging apparatus according to the related art, the signal does not wrap around within the time interval defined by the repetition time Tr in the relaxation recovery of the pulse sequence. A time phase image of a moving organ such as the heart cannot be obtained, and the number of acquired images per unit time T is extremely small, so that there is a problem that efficient image acquisition cannot be performed. Therefore, an object of the present invention is to provide a magnetic resonance imaging apparatus and method capable of efficiently obtaining a time-phase image of a moving organ such as a heart without a signal wraparound. [Structure of the Invention] (Means for Solving the Problems) The present invention has a structure in which the following means are taken in order to solve the above problems and achieve the object. That is, the present invention applies a gradient magnetic field and a high-frequency magnetic field for excitation to a subject arranged in a static magnetic field in accordance with a predetermined procedure, thereby causing a magnetic resonance phenomenon in a specific portion of the subject, thereby generating the magnetic resonance phenomenon. A magnetic resonance imaging apparatus for detecting a magnetic resonance signal to be obtained and obtaining a magnetic resonance image of a specific part of the subject, a detecting means for detecting a periodic body movement of the subject, and a detection from the detecting means Based on the signal, in each cycle, the procedure is repeatedly performed on the first cross section at a predetermined time phase in the periodic body motion and at a predetermined repetition time, and further in each cycle, 1
Control means for repeatedly executing the procedure on the second cross section at the repetition time at a timing shifted from the execution timing of the procedure on the cross section by a time shorter than the repetition time. It is assumed that. (Operation) According to the present invention, the first section is repeatedly photographed (excited and magnetic resonance signals are collected), for example, N times at a predetermined repetition time, and the N times photographing is performed for the body movement of the subject. It is repeatedly executed at a predetermined time phase in each cycle. Similarly, for the second section, for example, at a predetermined repetition time at a timing shifted from the execution timing of the imaging procedure for the first section by a time shorter than the predetermined repetition time, like the first section, for example. Photographs are repeated M times. For example, N magnetic resonance images having different body motion time phases with respect to the first cross section are generated from the magnetic resonance signals for, for example, 256 cycles collected by such imaging, and the body motion is similarly performed with respect to the second cross section. M magnetic resonance images with different time phases are generated. As described above, according to the present invention, it is possible to efficiently collect a plurality of magnetic resonance images (multi-time phase images) having different body motion time phases with respect to each of the first and second cross sections. That is, according to the present invention, a multi-phase image for a specific cross section can be obtained within a short time, and it is possible to cope with a plurality of cross sections. (Embodiment) An embodiment of a magnetic resonance imaging apparatus according to the present invention will be described below with reference to FIG. In FIG. 1, a superconducting or normal conducting static magnetic field coil 2, an X-axis, a Y-axis, a Z-axis gradient magnetic field coil 3, and a transmitting / receiving coil 4 are provided in a cylindrical normal body 1 as a static magnetic field generating device. The subject P placed on the top board 6 of the bed 5 is introduced into the diagnosable magnetic field generation region DSV in the main body 1. The static magnetic field coil 2 is driven by a static magnetic field power supply 7, and the X-axis, Y-axis, and Z-axis gradient magnetic field coils 3 are respectively driven by an X-axis gradient magnetic field power supply 8, a Y-axis gradient magnetic field power supply 9, and a Z-axis gradient magnetic field power supply 10. When activated, the transmit / receive coil 4 is driven by a transmitter 11 for excitation and by a receiver 12 for detection. The X-axis gradient magnetic field power supply 8, the Y-axis gradient magnetic field power supply 9, the Z-axis gradient magnetic field power supply 10, and the transmitter 12 are driven by a sequencer 13 in accordance with a predetermined excitation procedure. For example, the X-axis gradient magnetic field Gx shown in FIG. , Y-axis gradient magnetic field Gy, Z-axis gradient magnetic field Gz, and 90 ° -180
高周波 Generate high-frequency pulses in a pulse sequence. FIG. 2 shows a pulse sequence of one encoding step in the spin echo method. In order to obtain one magnetic resonance image, while changing the gradient magnetic field Gy as shown by the arrow, that is, the phase encoding amount is changed. This pulse sequence is repeated while changing. Computer system 14
Drives and controls the sequencer 13 and introduces a magnetic resonance signal obtained from the receiver 12 to perform signal processing, thereby generating a tomographic image of a certain slice portion and displaying it on a monitor. The computer system 14 also controls the bed 5. Further, in this embodiment, an electrocardiograph 15 is provided. That is, the subject P is provided with an electrocardiograph electrode 15a, and the signal line of the electrocardiograph electrode 15a is introduced into the electrocardiograph main body 15b, where signal processing is performed, for example. The electrocardiographic waveform signal Sh as shown in FIG.
And used as a control signal for heart-rate synchronous imaging. Here, in order to perform heart-rate synchronous imaging, the subject P is introduced into the diagnosable magnetic field generation region DSV, and an electrocardiographic signal Sh shown in FIG. 4 is obtained while a static magnetic field is applied. Then, as shown in FIG. 3, the slice time S1 of the heart CA is timed by the electrocardiographic waveform signal Sh shown in FIG.
At T1, the pulse sequence (excitation / detection procedure) of FIG. 2 is executed at least once. As a result, the gradient coil 3,
The transmitting / receiving coil 4 is driven, and the X-axis and the Y-axis as shown in FIG.
A magnetic resonance phenomenon is generated in the slice site S1 of the subject P by applying the axis- and Z-axis gradient magnetic fields Gx, Gy, Gz and the high-frequency pulse magnetic field for excitation. A phase-encoded magnetic resonance signal D1 having a time phase is obtained. At time T3 delayed by Tr from time T1, a phase-encoded magnetic resonance signal D3 having a heartbeat time phase different from time T1 on the same slice plane S1 is obtained. Similarly, at time T5 delayed by Tr from time T3, a phase-encoded magnetic resonance signal D5 having a heartbeat time phase different from time T1 and time T3 on the same slice plane S1 is obtained. Thereafter, the process moves to the next heart cycle.
In the next heartbeat cycle, at time T7 corresponding to the same heartbeat time phase as time T1, the phase encoding is changed for the same slice plane S1 to obtain a magnetic resonance signal D7. Thus, for each repetition of the heartbeat cycle, magnetic resonance signals D1, D7..., D3. With respect to S1, a magnetic resonance image of a heartbeat phase corresponding to time T1, a magnetic resonance image of a heartbeat phase corresponding to time T3, and a magnetic resonance image of a heartbeat phase corresponding to time T5 are obtained. Next, the slice plane S2, which is a position that is not affected by excitation and detection mutually with the slice plane S1, is moved from the time T1 to the time T2 which is delayed by the time Tr / 2 from the pulse sequencer (excitation /
(Detection procedure) at least once. By executing the above-described excitation / detection procedure, the gradient magnetic field coil 3 and the transmission / reception coil 4 are driven, and the X-axis, Y-axis, and Z-axis gradient magnetic fields Gx, Gy, Gz and the excitation high-frequency pulse as shown in FIG. A magnetic field is applied. As a result, a magnetic resonance phenomenon occurs in the slice site S2 of the subject P, and a magnetic resonance signal D2 of a certain phase encoding is obtained at time T2 with respect to the slice plane S2. At time T4 which is delayed by Tr from time T2, the same slice plane
A phase-encoded magnetic resonance signal D4 having a heartbeat time phase different from time T2 in S2 is obtained. Similarly, at time T6 which is delayed by Tr from time T4, a phase-encoded magnetic resonance signal D6 having a heartbeat time phase different from time T2 and time T4 on the same slice plane S2 is obtained. Thereafter, the process moves to the next heart cycle. In this next heartbeat cycle, at the time corresponding to the same heartbeat time phase as time T2, the phase encoding is changed for the same slice plane S2 to obtain a magnetic resonance signal. Thus, for each repetition of the heartbeat cycle, magnetic resonance signals D2,..., D4,..., D6...
Regarding, a magnetic resonance image of a heartbeat phase corresponding to time T2,
Magnetic resonance image of heartbeat phase corresponding to time T4, and time
A magnetic resonance image of the heartbeat phase corresponding to T6 is obtained. Next, the slice surface S1 is again subjected to time Tr from time T2.
At time T3 delayed by / 2, the excitation / detection procedure of FIG. 2 is executed. As described above, at times T1, T3, T5, and T7 where the repetition time Tr without signal wraparound is set with respect to the slice surface S1.
By executing the excitation / detection procedure of FIG. 2, magnetic resonance signals D1, D3, D5, D7 relating to the slice plane S1 can be obtained. By performing signal processing for each of a plurality of magnetic resonance signals having different phase encodings obtained in the same heartbeat phase with respect to the same slice plane S1, a plurality of magnetic resonance images having different heartbeat phases with respect to the slice plane S1 can be obtained. Further, at times T2, T4, and T6 at which a repetition time Tr without signal wraparound is set with respect to the slice surface S2, which is a position that is not affected by excitation and detection mutually with the slice surface S1, the excitation shown in FIG. By executing the detection procedure, the magnetic resonance signals D2, D4, D6 relating to the slice plane S2 can be obtained. By performing signal processing for each of a plurality of magnetic resonance signals having different phase encodings obtained in the same heartbeat phase with respect to the same slice plane S2, a plurality of magnetic resonance images having different heartbeat phases with respect to the slice plane S2 can be obtained. As described above, according to the present embodiment, the number of images that can be obtained per unit time T is about twice as large as that of the related art per unit time T, and there is an operational effect that image collection can be performed efficiently. In the above embodiment, two slice planes are scanned during the repetition time Tr (two scans). However, the present invention is not limited to this.
Scan three or more slice planes during (3
The above scan) may be performed. In this case, it is a condition that three or more slice planes are positions that are not mutually affected by excitation and detection. In the above embodiment, an electrocardiograph is used as a means for obtaining a heartbeat synchronization signal.
Although 15 is used, a heartbeat synchronization signal may be obtained by deriving a heart sound to a position that is not affected by a magnetic field using a pipe or the like. If such a means is used, no mutual influence is exerted on the magnetic field, so that the generated image is prevented from deteriorating. Further, as a signal which is a basis of the heartbeat synchronization signal, a heart sound waveform signal may be used in addition to the electrocardiogram waveform signal. Further, the target of diagnosis may be a moving organ other than the heart. The present invention can be variously modified and implemented without departing from the gist of the present invention. [Effects of the Invention] As described above, according to the present invention, the first section is repeatedly photographed (excited, for example) N times with a predetermined repetition time.
Magnetic resonance signals are collected), and the N times of imaging are repeatedly performed at a predetermined time phase in each cycle of the body movement of the subject. Similarly, for the second section, for example, at a predetermined repetition time at a timing shifted from the execution timing of the imaging procedure for the first section by a time shorter than the predetermined repetition time, similarly to the first section, for example. Photographs are repeated M times. For example, N magnetic resonance images with different body motion time phases with respect to the first section are generated from the magnetic resonance signals for, for example, 256 cycles collected by such imaging, and similarly with respect to the second section, body motion is also performed. M magnetic resonance images with different time phases are generated. As described above, according to the present invention, it is possible to efficiently collect a plurality of magnetic resonance images (multi-time phase images) having different body motion time phases with respect to each of the first and second cross sections. That is, according to the present invention, a multi-phase image of a specific cross section can be obtained within a short time, and a plurality of cross sections can be handled.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one embodiment of a magnetic resonance imaging apparatus according to the present invention, and FIG.
FIG. 3 is a view showing an example of a detection procedure, FIG. 3 is a view showing a slice plane and a tomographic image in the embodiment, FIG. 4 is a view showing scan timing in the embodiment, and FIG. FIG. 6 is a diagram showing an image, and FIG. 6 is a diagram showing scan timing in the conventional example. DESCRIPTION OF SYMBOLS 1 ... Body, 2 ... Static magnetic field coil, 3 ... Gradient magnetic field coil, 4 ... Transmission / reception coil, 5 ... Bed, 6 ... Top plate, 7
... static magnetic field power supply, 8 ... X axis gradient magnetic field power supply, 9 ... Y axis gradient magnetic field power supply, 10 ... Z axis gradient magnetic field power supply, 11 ... transmitter, 12 ... receiver, 13 ... sequencer, 14 ... Computer system, 15 ... Electrocardiograph.

Claims (1)

(57) [Claims] By applying a gradient magnetic field and a high-frequency magnetic field for excitation to a subject arranged in a static magnetic field according to a predetermined procedure, a magnetic resonance phenomenon occurs at a specific portion of the subject, and a magnetic resonance signal generated thereby is generated. In a magnetic resonance imaging apparatus that detects and obtains a magnetic resonance image of a specific part of the subject, a detecting unit that detects a periodic body movement of the subject, and based on a detection signal from the detecting unit, In each cycle, the procedure is repeatedly performed on the first cross section at a predetermined time phase in the periodic body motion and at a predetermined repetition time, and further in each cycle, the procedure for the first cross section is performed. Control means for repeatedly executing the procedure with the repetition time for the second cross section at a timing shifted from the execution timing of the procedure by a time shorter than the repetition time; Magnetic resonance imaging apparatus characterized by comprising.