JP2010131200A - Mri apparatus and photography trigger signal generating unit for mri apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate trigger signals without influence of a gradient magnetic field or RF pulse. <P>SOLUTION: A pickup part 911 of a biological signal detecting part 91, disposed in the periphery of the chest of a subject to which the gradient magnetic field and RF pulse necessary for the MRI photography are applied, collects the cardiac sound and respiration sound of the subject as acoustic biological signals. A flexible guide tube 913 formed of an insulating material such as resin feeds the acoustic biological signals to a transducer 912 disposed in an area where the gradient magnetic field or RF pulse is not applied. Next, the transducer 912 converts the acoustic biological signals fed via the guide tube 913 into electric biological signals, and a trigger signal generating part 932 of a photography trigger signal generating part 93 generates trigger signals synchronized with the heartbeat time-phase or respiration time-phase of the subject based on the electric biological signals. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an MRI apparatus and an imaging trigger signal generation unit for an MRI apparatus, and more particularly to an MRI apparatus and an imaging trigger signal generation unit for an MRI apparatus that can collect image data synchronized with a heartbeat time phase or a respiratory time phase. .

  In magnetic resonance imaging (MRI), a nuclear spin in a subject tissue placed in a static magnetic field is excited by a high-frequency signal (RF pulse) having the Larmor frequency, and a magnetic resonance signal ( This is an imaging method for reconstructing image data from MR signals.

  An MRI apparatus is an image diagnostic apparatus that generates image data based on MR signals detected from within a living body, and obtains a large amount of information such as biochemical diagnostic information and functional diagnostic information as well as anatomical diagnostic information. This makes it indispensable in today's diagnostic imaging.

  In recent years, functional analysis of the brain and heart has become possible due to the development of high-speed MRI imaging methods. In particular, when imaging an organ with rapid movement such as the heart, it is required to shorten the imaging time. For example, EPI (Echo-planar-imaging) method which is one of high-speed imaging methods is used. According to this, the imaging time of one image is 100 msec or less, and image data at a desired heartbeat time phase of the heart can be collected. In MRI imaging of the heart, conventionally, a method has been adopted in which an electrocardiographic waveform of a subject is simultaneously collected during imaging and MRI imaging of a desired slice section is performed based on, for example, an R wave of the electrocardiographic waveform (for example, (See Patent Document 1).

  In addition, in order to prevent image quality deterioration due to respiratory movement, for example, the respiratory time phase is measured based on the degree of elasticity of the tube attached to the abdomen of the subject, and image data in the respiratory time phase with less respiratory movement. There are also ways to collect them.

  By the way, in MRI imaging synchronized with a heartbeat time phase, it is necessary to apply an RF pulse or a gradient magnetic field to a subject based on an imaging trigger pulse generated using an electrocardiographic waveform or the like. When collecting electrocardiogram waveforms from a subject undergoing MRI imaging, a plurality of signal lines connecting a plurality of ECG electrodes mounted on the subject's body surface and the electrocardiograph body are arranged on the body surface. A closed loop is formed by capacitive coupling between the signal line and the ECG electrode. For example, when an RF pulse or a gradient magnetic field is switched at high speed as in EPI imaging, the magnetic flux crossing this closed loop changes greatly, so that an induced current (induced noise) is generated between the signal line and the electrode on the body surface. When this induced current is mixed into the electrocardiographic waveform, it is difficult to obtain an accurate imaging trigger signal. In addition, there is a problem that the above-described induced current may cause injury such as burns or electric shock to the subject by flowing into the body surface or the body.

In order to deal with such problems, a method has been proposed in which heart sounds are collected by a heart sound microphone attached to the body surface of a subject and an imaging trigger signal is generated based on the heart sounds (see, for example, Patent Document 2). .
JP-A-8-182661 JP-A-2-63011

  According to the method described in Patent Document 2 described above, the induced current mixed into the heart sound waveform collected by the heart sound microphone is reduced as compared with the case where the electrocardiogram waveform is used. However, in this method, since the electrical heart sound waveform is supplied to the heart sound meter main body via the signal line disposed in the gradient magnetic field or RF pulse application region, the signal line has a shield structure. Even in such a case, it is difficult to suppress the generation of the induced current below an allowable level.

  The present invention has been made in view of the above-described problems, and its purpose is to provide a heartbeat time phase and breathing without being affected by a gradient magnetic field or an RF pulse applied to a subject during MRI imaging. An object of the present invention is to provide an MRI apparatus and an imaging trigger signal generation unit for an MRI apparatus that can generate good image data synchronized with the time phase.

  In order to solve the above-described problems, the MRI apparatus imaging trigger signal generation unit according to the first aspect of the present invention is an MRI apparatus imaging trigger signal generation unit that generates an imaging trigger signal synchronized with a biological signal of a subject. A biological signal pickup means that is disposed in the vicinity of the subject to which a gradient magnetic field and RF pulse necessary for MRI imaging are applied and collects at least one of a heart sound and a respiratory sound generated from the subject as an acoustic biological signal A transducer disposed in a region where the gradient magnetic field and RF pulse are not applied and converting the acoustic biological signal into an electrical biological signal; and the acoustic biological signal collected by the biological signal pickup means A lead pipe for supplying to the transducer, and the electrical biological signal obtained by the transducer. A trigger signal generating means for generating a trigger signal Zui is characterized by comprising an imaging trigger signal output means for outputting the trigger signal as an imaging trigger signal.

  The MRI apparatus imaging trigger signal generating unit according to the third aspect of the present invention is an MRI apparatus imaging trigger signal generating unit that generates an imaging trigger signal synchronized with a biological signal of a subject, and is necessary for MRI imaging. A biological signal pick-up means that is disposed in the vicinity of the subject to which a gradient magnetic field and an RF pulse are applied and collects at least one of a heart sound and a respiratory sound generated from the subject as an acoustic biological signal; A transducer for converting a biological signal into an electrical biological signal; a transmitting means disposed in the vicinity of the transducer for transmitting the electrical biological signal in the air; and an aerial transmission disposed in a region to which the gradient magnetic field and RF pulse are not applied. Receiving means for receiving the received electrical biological signal, and the electrical biological signal received by the receiving means A trigger signal generating means for generating a trigger signal based, is characterized by comprising an imaging trigger signal output means for outputting the trigger signal as an imaging trigger signal.

  On the other hand, the MRI apparatus of the present invention according to claim 10 is an MRI apparatus that performs MRI imaging based on an imaging trigger signal synchronized with a biological signal of a subject, and is any one of claims 1 to 9. The MRI imaging of the subject is performed based on the imaging trigger signal supplied from the imaging trigger signal generation unit for the MRI apparatus described in 1).

  According to the present invention, it is possible to reliably generate good image data synchronized with a heartbeat time phase or a breathing time phase without being affected by a gradient magnetic field or an RF pulse applied to a subject during MRI imaging. Can do. For this reason, diagnostic accuracy and diagnostic efficiency for the subject are greatly improved.

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

  The imaging trigger signal generation unit provided in the MRI apparatus of the present embodiment described below collects the heart sound and breathing sound of the subject as an acoustic biological signal, and converts the acoustic biological signal into an electrical signal obtained. A pick-up unit arranged near the chest of the subject to which a gradient magnetic field and an RF pulse are applied when collecting an imaging trigger signal necessary for MRI imaging based on the biological signal; and a gradient magnetic field And a transducer that is arranged in a region where no RF pulse is applied and converts an acoustic biological signal into an electrical biological signal, and a guide tube that is formed of an insulating material such as a resin and that can propagate acoustic biological signals. The imaging trigger pulse synchronized with the heartbeat time phase and the breathing time phase is generated without being influenced by the gradient magnetic field or the RF pulse.

(Device configuration)
The configuration of the MRI apparatus in the embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing the overall configuration of the MRI apparatus in the present embodiment, and FIG. 4 is a block diagram showing a specific configuration of an imaging trigger signal generating unit provided in the MRI apparatus.

  An MRI apparatus 200 shown in FIG. 1 includes a static magnetic field generation unit 1 and a gradient magnetic field generation unit 2 that generate a magnetic field with respect to a subject 150, and a transmission / reception unit that performs RF pulse irradiation and MR signal reception on the subject 150. 3, a top plate 4 on which the subject 150 is placed, and a top plate moving mechanism unit 5 that moves the top plate 4 in the body axis direction of the subject 150.

  Further, the MRI apparatus 200 includes an image data generation unit 6 that reconstructs MR signals received by the transmission / reception unit 3 to generate image data, a display unit 7 that displays the generated image data, and MR signal collection. An input unit 8 for setting conditions and display conditions for image data, inputting various command signals, and the like, and an imaging trigger signal generating unit 9 for generating an imaging trigger signal based on heart sounds and respiratory sounds detected from the subject 150 The control unit 10 that controls each of the units provided in the MRI apparatus 200 is provided.

  The static magnetic field generating unit 1 includes a main magnet 11 composed of a normal conducting magnet or a superconducting magnet and a static magnetic field power source 12 for supplying current to the main magnet 11, and is arranged in a gantry imaging field (not shown). A strong static magnetic field is formed on the specimen 150. The main magnet 11 may be constituted by a permanent magnet.

  On the other hand, the gradient magnetic field generator 2 supplies a pulse current to each of the gradient magnetic field coil 21 that forms a gradient magnetic field in the X axis direction, the Y axis direction, and the Z axis direction orthogonal to each other, and the gradient magnetic field coil 21. A gradient magnetic field power source 22 is provided.

  The gradient magnetic field power source 22 encodes the imaging field in which the subject 150 is placed based on the sequence control signal and the imaging trigger signal supplied from the control unit 10. That is, the gradient magnetic field power source 22 controls the pulse current supplied to the gradient magnetic field coil 21 in the X-axis direction, the Y-axis direction, and the Z-axis direction based on the sequence control signal and the imaging trigger signal, and thereby for each direction. To form a gradient magnetic field. The gradient magnetic fields in the X-axis direction, the Y-axis direction, and the Z-axis direction are combined to form slice selection gradient magnetic fields, phase encoding gradient magnetic fields, and readout (frequency encoding) gradient magnetic fields that are orthogonal to each other in the desired directions. The gradient magnetic field is applied to the subject 150 while being superimposed on the static magnetic field formed by the main magnet 11.

  Next, the transmission / reception unit 3 irradiates the subject 150 with an RF pulse and also has an RF coil unit 31 having an RF coil for detecting an MR signal generated from the subject 150, and an RF drive signal for the RF coil. And a receiver 33 that performs predetermined processing on the MR signal detected by the RF coil.

  FIG. 2 shows the RF coil unit 31 used during MRI imaging in a cross section (XY cross section) perpendicular to the body axis direction (Z direction in FIG. 1) of the subject 150. The unit 31 is disposed above the subject 150 and performs an RF pulse irradiation and MR signal detection, and an upper RF coil 311 and a coil support 312 for holding the upper RF coil 311 at a suitable position above the subject. And a lower RF coil 313 that is disposed between the subject 150 and the top plate 4 and irradiates the subject 150 with RF pulses and detects MR signals.

  Next, a specific example of the lower RF coil 313 is shown in FIG. 3A shows a plan view of the lower RF coil 313, and FIG. 3B shows an A-A ′ cross section of the lower RF coil 313 of FIG. 3A. The lower RF coil 313 includes a coil cover 313b having holes two-dimensionally arranged in the XZ plane, and a coil 313a arranged in a loop around these holes. The coil 313a is flexible. It is covered with a coil cover 313b made of a resin having

  Furthermore, a pickup unit 911 (to be described later) provided in the photographing trigger signal generation unit 9 is provided on the surface or inside of the coil cover 313b. 3 shows the lower RF coil 313 in which three holes are two-dimensionally arranged in the X direction and the Z direction, respectively, the number of holes and the arrangement method are not limited thereto. Further, one or a plurality of rectangular or loop-shaped coils may be arranged in the XZ plane without having a hole.

  Returning to FIG. 1, the transmission unit 32 of the transmission / reception unit 3 has a magnetic resonance frequency (Larmor frequency) determined by the static magnetic field strength of the main magnet 11 based on the sequence control signal and the imaging trigger signal supplied from the control unit 10. And a pulse current modulated with a predetermined selective excitation waveform. Then, the above-described pulse current is supplied to the upper RF coil 311 and the lower RF coil 313 of the RF coil unit 31 in synchronization with the imaging trigger signal.

  On the other hand, the receiving unit 33 includes an amplification circuit, an intermediate frequency conversion circuit, a detection circuit, an A / D converter, and a filtering circuit (not shown), and the minute amount detected by the upper RF coil 311 and the lower RF coil 313 of the RF coil unit 31. The MR signal is amplified, and further, A / D conversion is performed after performing signal processing such as intermediate frequency conversion, phase detection, and filtering. However, the amplifier circuit is usually installed in the vicinity of the RF coil unit 31 in order to amplify MR signals detected by the upper RF coil 311 and the lower RF coil 313 with high S / N.

  When MRI imaging of the subject 150 is performed, an imaging field is formed in the central portion of the gantry (not shown) of the MRI apparatus 200 by the main magnet 11 and the gradient magnetic field coil 21 described above, and the upper RF coil 311 and the lower portion of the RF coil unit 31. The subject 150 in which the RF coil 313 is arranged is moved in the body axis direction together with the top 4 so that the imaging target site is arranged in the imaging field.

  Next, the top plate 4 is slidably attached in the body axis direction of the subject 150 on the upper surface of a bed (not shown) installed in the vicinity of the gantry, and the subject 150 placed on the top surface of the top plate 4 is attached to Z. By moving in the axial direction, the region to be imaged is set to a desired position in the field. The top plate moving mechanism unit 5 is attached to the above-described bed, for example, and generates a top plate moving drive signal based on a control signal supplied from the control unit 10, and the top plate 4 is driven by this top plate moving drive signal. Is moved at a predetermined speed in the Z-axis direction.

  Next, the image data generation unit 6 includes a data storage unit 61 and a high-speed calculation unit 62. The data storage unit 61 includes an MR signal storage unit 611 that stores MR signals and an image data storage unit 612 that stores image data. I have. The MR signal storage unit 611 sequentially stores MR signals that have been subjected to intermediate frequency conversion, phase detection, and A / D conversion by the receiving unit 33 in accordance with the movement of the subject 150. The shooting position information supplied from the control unit 10 is added to the signal as supplementary information. On the other hand, the image data storage unit 612 stores image data generated by the high-speed calculation unit 62 by reconstructing the MR signal. Then, the high-speed calculation unit 62 of the image data generation unit 6 reads the MR signal and imaging position information once stored in the MR signal storage unit 611 and performs image reconstruction processing such as two-dimensional Fourier transform to generate image data. To do.

  The display unit 7 includes a display data generation circuit, a conversion circuit, and a monitor (not shown). The display data generation circuit includes image data supplied from the image data storage unit 612 of the image data generation unit 6 and a control unit from the input unit 8. Display data is generated by synthesizing incidental information such as subject information supplied via 10. The conversion circuit converts the display data into a predetermined display format, and further displays a video signal generated by performing D / A conversion and television format conversion on the monitor including a CRT or a liquid crystal panel.

  On the other hand, the input unit 8 includes various input devices such as switches, a keyboard, and a mouse on a console, and a display panel. The input unit 8 inputs subject information, sets MR signal collection conditions and image data generation conditions, and first based on heart sounds. Setting of threshold for second biological signal based on biological signal and breathing sound, setting of filter characteristic when separating biological signal into first biological signal and second biological signal, setting of dead time, and various Inputs command signals.

  Next, a specific configuration of the photographing trigger signal generation unit 9 will be described with reference to FIG. The imaging trigger signal generation unit 9 includes a biological signal detection unit 91 that detects a heart sound and a respiratory sound of the subject 150 as a biological signal, an environmental sound removal unit 92 that removes an environmental sound mixed in the biological signal, and a biological signal. An imaging trigger signal generation unit 93 that generates a synchronized imaging trigger signal is provided.

  The biological signal detection unit 91 includes a pickup unit 911, a transducer 912, and a guiding pipe 913. The pickup unit 911 has a function of collecting heart sounds and breathing sounds generated by the subject 150 as acoustic biological signals, and includes a gradient magnetic field generated by the gradient magnetic field coil 21 of the gradient magnetic field generation unit 2 and an upper part of the transmission / reception unit 3. In order to eliminate the influence of the RF pulse generated by the RF coil 311 and the lower RF coil 313 (for example, induced current caused by application of a gradient magnetic field or RF pulse), an insulating material such as a resin is used.

  The pickup unit 911 is provided, for example, in the coil cover 313b of the lower RF coil 313 disposed above the top plate 4 as already described with reference to FIG. 3, and the chest (heart) of the subject 150 is located in the vicinity of the pickup unit 911. The subject 150 is placed on the top 4 so that is positioned. By disposing the pickup unit 911 near the heart of the subject 150, heart sounds and breathing sounds can be collected with high sensitivity.

  On the other hand, the transducer 912 is provided in another region that is not affected by the gradient magnetic field or RF pulse applied to the chest region of the subject 150 including the above-described pickup unit 911, and the heart sound collected by the pickup unit 911 and Respiratory sound (acoustic biological signal) is converted into an electrical biological signal. A piezoelectric element is usually used as a detection element (sensor) included in the transducer 912, but other materials having a function of converting an acoustic signal into an electric signal may be used.

  The guiding tube 913 is a flexible hollow tube that supplies the heart sound and breathing sound detected by the pickup unit 911 to the transducer 912, and the gradient magnetic field of the gradient magnetic field generation unit 2 is the same as the pickup unit 911. The insulating material is not affected by the gradient magnetic field generated by the coil 21 or the RF pulses generated by the upper RF coil 311 and the lower RF coil 313 of the transmission / reception unit 3.

  FIG. 5 shows the gradient magnetic field and RF pulse application region and the arrangement positions of the pickup unit 911 and the transducer 912. The gradient magnetic field by the gradient magnetic field coil 21 and the RF pulse application region by the RF coil unit 31 are shown in FIG. A region to be imaged including the chest of the subject 150 is disposed, and a pickup unit 911 made of an insulating material attached to the lower RF coil 313 is disposed in the vicinity of the chest. On the other hand, the transducer 912 is disposed in a region that is separated from the gradient coil 21 and the RF coil unit 31 by a predetermined distance and is not affected by the gradient magnetic field or the RF pulse, and the pickup unit 911 and the transducer 912 are connected by the guiding pipe 913. .

  As described above, when the heart sound and breathing sound (acoustic biological signal) of the subject 150 collected by the pickup unit 911 are converted into an electrical biological signal by the transducer 912, a gradient magnetic field or an RF pulse is applied. Heart sounds and breathing sounds are collected using a pickup unit 911 made of an insulating material arranged in the vicinity of the chest of the subject 150, and these heart sounds and breathing sounds are collected through a guiding tube 913 made of an insulating material through a gradient magnetic field and an RF pulse. By supplying to the transducer 912 disposed in a region not affected by the above, it is possible to prevent the generation of an induced current due to the application of a gradient magnetic field or an RF pulse.

  Returning to FIG. 4, the environmental sound removal unit 92 is an environmental sound mixed in the electrical biological signal detected by the biological signal detection unit 91 (for example, the vibration sound of the gradient magnetic field coil 21 or the vibration sound of the refrigerator). And a function of removing ambient noise caused by BGM in the examination room, the voice of the operator, and the like, and a microphone 921, a gain adjustment unit 922, and a subtraction processing unit 923.

  The microphone 921 has a function of collecting ambient noise of the MRI apparatus 200 as an electrical environmental sound, and is disposed in a region where a gradient magnetic field or an RF pulse is not applied. On the other hand, the gain adjustment unit 922 adjusts the amplitude (gain) of the environmental sound supplied from the microphone 921 to a suitable value, and the subtraction processing unit 923 is an electrical unit supplied from the transducer 912 of the biological signal detection unit 91. The environmental sound mixed in the biological signal is eliminated by subtracting the biological signal from the environmental sound after gain adjustment output from the gain adjusting unit 922. In this case, the gain adjustment unit 922 adjusts the environmental sound gain so that the environmental sound remaining in the output signal of the subtraction processing unit 923 is minimized.

  Next, the imaging trigger signal generation unit 93 includes a biological signal separation unit 931, a trigger signal generation unit 932, a trigger signal storage unit 933, a signal determination unit 934, and an imaging trigger signal output unit 935.

  The biological signal separation unit 931 includes two filter circuits (not shown) having different frequency characteristics, and the first signal based on the heart sound is selected from the electrical biological signals output from the subtraction processing unit 923 of the environmental sound removal unit 92. It has a function of separating the second biological signal based on the biological signal and the respiratory sound.

  FIG. 6 shows a specific example of the frequency characteristics of the filter circuit. For example, the filter circuit having the frequency range [200 Hz to 2000 Hz] as shown in FIG. The biological signal is collected, and the second biological signal is collected by a filter circuit having a frequency range [20 Hz to 200 Hz] as shown in FIG. 6B.

  Returning to FIG. 4 again, the trigger signal generation unit 932 processes the first biological signal and the second biological signal obtained by the biological signal separation unit 931, and synchronizes with the first trigger signal and the heartbeat time phase. A second trigger signal synchronized with the breathing time phase is generated. The first biological signal based on the heart sound and the first trigger signal generated by processing the first biological signal will be described with reference to FIGS.

  FIG. 7 shows an electrocardiogram waveform (FIG. 7 (a)) used in conventional MRI imaging or the like synchronized with heartbeat and an electrocardiogram (FIG. 7 (b)) used in MRI imaging of this embodiment. When an electrocardiogram waveform is used, an R wave having the maximum value is detected by comparing the electrocardiogram waveform Se with a predetermined threshold Te, and a trigger pulse is generated at the generation timing of the R wave.

  On the other hand, when using a cardiac sound waveform as in the present embodiment, the S1 wave and the S2 wave having a value larger than the threshold value Tp are detected by comparing the cardiac sound waveform Sp with a predetermined threshold value Tp. A trigger pulse is generated at the generation timing of the S1 wave or S2 wave detected by paying attention that the period T12 indicating the time interval with the S2 wave is shorter than the period T21 indicating the time interval between the S2 wave and the S1 wave.

  FIG. 8 shows a case in which a trigger signal is generated based on the S1 wave of the heart sound waveform Sp. The trigger signal generation unit 932 of the imaging trigger signal generation unit 93 includes a preset threshold value Tp and a heart sound waveform Sp. (FIG. 8A), and trigger pulses P1 and P2 are generated at the timing when the S1 wave and S2 wave of the heart sound waveform Sp exceed the threshold value Tp (FIG. 8B). Next, the trigger pulse P2 based on the S2 wave is excluded based on the dead time Tx information supplied from the input unit 8 (FIG. 8C).

  In this case, since the time interval T12 from the S1 wave to the S2 wave and the time interval T21 from the S2 wave to the S1 wave are always in a relationship of T12 <T21, the dead time Tx is set to satisfy T12 <Tx <T21. By setting, the first trigger signal (FIG. 8 (d)) constituted by the trigger pulse P1 based on the S1 wave is generated. Further, by subtracting the trigger pulse P1 shown in FIG. 8D from the trigger pulses P1 and P2 shown in FIG. 8B, a first trigger signal constituted by the trigger pulse P2 may be generated. Is possible. Further, a second imaging trigger pulse is generated by applying the same procedure to the second biological signal based on the respiratory sound collected from the subject 150.

  Next, the trigger signal storage unit 933 illustrated in FIG. 4 includes a trigger signal (first trigger signal and first trigger signal) generated by the trigger signal generation unit 932 and determined to have good characteristics by a signal determination unit 934 described later. The second trigger signal) is stored sequentially. On the other hand, the signal determination unit 934 includes a reference data storage unit (not shown) in which reference data for the above-described trigger signal is stored in advance, and the trigger signal generated in the trigger signal generation unit 932 and the reference read from the reference data storage unit The quality of the trigger signal generated by the trigger signal generation unit 932 is determined by comparing the data.

  The shooting trigger signal output unit 935 shoots either the trigger signal generated by the trigger signal storage unit 933 based on the determination result supplied from the signal determination unit 934 or the trigger signal already stored in the trigger signal storage unit 933. Output as a trigger signal. That is, when the signal determination unit 934 determines that the characteristics of the trigger signal generated by the trigger signal generation unit 932 are good, the imaging trigger signal output unit 935 that has received the determination result controls the trigger signal as an imaging trigger signal. To the unit 10. On the other hand, when it is determined that the characteristics of the trigger signal generated by the trigger signal generation unit 932 are poor, the imaging trigger signal output unit 935 uses the trigger signal already stored in the trigger signal storage unit 933 instead of the imaging trigger signal. Is output to the control unit 10 as a shooting trigger signal.

  Next, the control unit 10 in FIG. 1 includes a main control unit 101, a sequence control unit 102, and a top board movement control unit 103. The main control unit 101 includes a CPU and a storage circuit (not shown) and has a function of controlling the MRI apparatus 200 in an integrated manner. The storage circuit of the main control unit 101 includes subject information input or set by the input unit 8, MR signal collection conditions, image data generation conditions, threshold values Te and Tp for biological signals, and filter characteristics in biological signal separation. Information such as dead time Tx is stored.

  On the other hand, the CPU of the main control unit 101 generates pulse sequence information generated based on the above-described input information and setting information (for example, the magnitude of the pulse current supplied to the gradient magnetic field coil 21 and the RF coil unit 31, the supply time, the supply timing) And the imaging trigger signal supplied from the imaging trigger signal generation unit 9 is supplied to the sequence controller 102.

  The sequence control unit 102 of the control unit 10 includes a CPU and a storage circuit (not shown). After the pulse sequence information supplied from the main control unit 101 is temporarily stored in the storage circuit, the pulse sequence information and the above-described imaging trigger signal are stored. Thus, a sequence control signal is generated to control the gradient magnetic field power source 22 of the gradient magnetic field generator 2 and the transmitter 32 of the transmitter / receiver 3. The top plate movement control unit 103 of the control unit 10 generates a top plate movement control signal for the purpose of moving the top plate 4 based on the control signal supplied from the main control unit 101, and the top plate movement mechanism unit. 5 is supplied.

(Shooting trigger signal generation procedure)
Next, a procedure for generating a shooting trigger signal by the shooting trigger signal generating unit 9 of this embodiment will be described with reference to the flowchart of FIG.

  When an imaging trigger signal used for MRI imaging is generated, the pickup unit 911 of the biological signal detection unit 91 provided on the coil cover 313b of the lower RF coil 313 acoustically generates a heart sound and a respiratory sound generated by the subject 150. Signals are collected (step S1 in FIG. 9), and the obtained acoustic biological signal is provided in a region that is not affected by a gradient magnetic field or an RF pulse through a guiding tube 913 formed of an insulating material. It is supplied to the transducer 912 and converted into an electrical biological signal (step S2 in FIG. 9).

  On the other hand, the microphone 921 of the environmental sound removal unit 92 collects the vibration sound generated by the MRI apparatus 200, the voice of the operator, and the like as electrical environmental sound (step S3 in FIG. 9), and the gain adjustment unit 922 includes the microphone. The amplitude (gain) of the environmental sound supplied from 921 is adjusted to a suitable value (step S4 in FIG. 9).

  The subtraction processing unit 923 of the environmental sound removal unit 92 performs subtraction processing between the electrical biological signal supplied from the transducer 912 of the biological signal detection unit 91 and the environmental sound after gain adjustment output from the gain adjustment unit 922. The environmental sound mixed in the biological signal is removed (step S5 in FIG. 9).

  Next, the biological signal separation unit 931 of the imaging trigger signal generation unit 93 receives the biological signal after removal of the environmental sound output from the subtraction processing unit 923 of the environmental sound removal unit 92, and based on the heart sound included in the biological signal. The first biological signal and the second biological signal based on the respiratory sound are separated by filtering processing (step S6 in FIG. 9). Then, the trigger signal generation unit 932 processes the first biological signal and the second biological signal separated by the biological signal separation unit 931 and is synchronized with the first trigger signal and the respiratory time phase synchronized with the heartbeat time phase. The generated second trigger signal is generated (step S7 in FIG. 9).

  On the other hand, the signal determination unit 934 determines the quality of the trigger signal by comparing the trigger signal generated by the trigger signal generation unit 932 with the reference data read from its own reference data storage unit. When it is determined that the characteristics of the trigger signal are good, the imaging trigger signal output unit 935 that has received the determination result outputs the trigger signal as the imaging trigger signal to the main control unit 101 of the control unit 10 (FIG. 9 step S8).

  On the other hand, if the signal determination unit 934 determines that the characteristics of the trigger signal generated by the trigger signal generation unit 932 are poor, the imaging trigger signal output unit 935 reads the trigger read from the trigger signal storage unit 933 instead of the trigger signal. The signal is output to the main control unit 101 as a shooting trigger signal (step S9 in FIG. 9).

  The configuration of the MRI apparatus in the present embodiment has been described above. Specific examples of MRI imaging using the imaging trigger signal described above are disclosed in Japanese Patent Application Laid-Open Nos. 2004-24637, 2004-329669, and further described above. Detailed description thereof is omitted.

(Modification)
Next, a modification of the imaging trigger signal generation unit 9 provided in the MRI apparatus 200 of the present embodiment will be described.

  The biological signal detection unit 91 of the imaging trigger signal generation unit 9 in the above-described embodiment includes the pickup unit 911 that collects heart sounds and breathing sounds generated by the subject 150 as acoustic biological signals, and the influence of gradient magnetic fields and RF pulses. The transducer 912 is provided in a region that is not subjected to the signal and converts the acoustic biological signal collected by the pickup unit 911 into an electrical biological signal, and the acoustic biological signal collected by the pickup unit 911 is supplied to the transducer 912. It has a guiding tube 913, and the pickup portion 911 and the guiding tube 913 are formed using an insulating material such as resin, thereby preventing the generation of an induced current due to a gradient magnetic field or an RF pulse.

  In contrast, the biological signal detection unit of the present modification includes a pickup unit that detects a heart sound and a respiratory sound generated by the subject 150 as an acoustic biological signal, and a heart sound and a respiratory sound (acoustic signal) detected by the pickup unit. A transducer that converts a biological signal) into an electrical biological signal, a transmitter that transmits the electrical biological signal to a receiver that is not affected by a gradient magnetic field or an RF pulse, The above-described pickup unit, transducer, and transmission unit, which have a reception unit and are arranged in a gradient magnetic field or RF pulse application region, are integrated, and the biological signal is supplied from the transmission unit to the reception unit by a wireless method. Thus, the generation of induced current caused by a gradient magnetic field or an RF pulse is reduced.

  FIG. 10 is a block diagram showing a specific configuration of the imaging trigger signal generation unit in this modification. However, in FIG. 10, the same reference numerals are given to units having the same configuration and function as the units included in the imaging trigger signal generation unit 9 shown in FIG.

  That is, the imaging trigger signal generation unit 9a shown in FIG. 10 includes a biological signal detection unit 91a that detects a heart sound and a respiratory sound of the subject 150 as biological signals, and an environmental sound removal that removes environmental sounds mixed in the biological signals. And an imaging trigger signal generator 93 that generates an imaging trigger signal synchronized with the biological signal. The biological signal detector 91a includes a pickup unit 911a, a transducer 912a, a transmitter 914, and a receiver 915. Yes.

  The pickup unit 911a collects heart sounds and respiratory sounds generated by the subject 150 as acoustic biological signals, and the transducer 912a electrically converts the heart sounds and respiratory sounds (acoustic biological signals) collected by the pickup unit 911a. Convert to biological signal. The transmission unit 914 modulates the electrical biological signal supplied from the transducer 912a with a predetermined carrier frequency and transmits it to the reception unit 915 in the air. In this case, the pickup unit 911a, the transducer 912a, and the transmission unit 914 are integrated and provided, for example, in the coil cover 313b of the lower RF coil 313 to which a gradient magnetic field or an RF pulse is applied or in the vicinity thereof.

  On the other hand, the receiving unit 915 is provided in a region that is not affected by the gradient magnetic field or the RF pulse and demodulates the radio wave transmitted in the air by the transmitting unit 914 to reproduce an electrical biological signal. Then, the obtained biological signal is supplied to a subtraction processing unit 923 provided in the environmental sound removal unit 92.

  According to the embodiment of the present invention and the modification thereof described above, when the imaging trigger signal used for MRI imaging is generated based on the biological signal of the subject, it is applied to the subject during MRI imaging. Biological signals can be collected without generating an induced current caused by a gradient magnetic field, an RF pulse, or the like. Therefore, it is possible to generate a high-quality imaging trigger signal by using a biological signal in which no induced current is mixed, and it is possible to reliably generate image data synchronized with the heartbeat time phase and the respiratory time phase by using this imaging trigger signal. it can.

  In particular, according to the above-described embodiment, an imaging trigger signal is generated based on an acoustic biological signal such as a heart sound and a respiratory sound collected using a pickup unit and a guiding tube formed of an insulating material such as a resin. Therefore, it is possible to collect a biological signal without being affected by a gradient magnetic field or an RF pulse, and the pickup unit used for collecting an acoustic biological signal such as a heart sound or a respiratory sound Since it is not necessary to directly contact the body surface, it is possible to prevent inductive current from flowing into the subject, which has been a major problem when collecting electrocardiographic waveforms as biological signals. Safe MRI imaging that does not cause harm such as electric shock becomes possible.

  Further, according to the above-described modification, the biological signal obtained by the pickup unit and the transducer is supplied to the receiving unit provided in the region where the gradient magnetic field or the RF pulse is not irradiated by the wireless method, and based on this biological signal. Since the imaging trigger signal is generated, it is possible to generate an imaging trigger signal that is not affected by a gradient magnetic field, an RF pulse, and the like. Further, since the inflow of induced current to the subject can be reduced, On the other hand, safe MRI imaging that does not cause harm such as burns or electric shock is possible.

  On the other hand, according to the above-described embodiment and its modification, MRI imaging can be performed based on the first imaging trigger signal based on the heart sound and the second imaging trigger signal based on the respiratory sound. A period with less respiratory movement is set by the second imaging trigger signal, and image data in a desired heartbeat time phase during this period can be generated based on the first imaging trigger signal. Therefore, it is possible to collect good image data with less influence of respiratory movement in a desired heartbeat time phase.

  Furthermore, acoustic biological signals such as heart sounds and breathing sounds can be collected using a common pickup unit, and it is not necessary to directly bring the pickup unit into contact with the body surface of the subject as described above. Since it is possible to collect biological signals, the degree of freedom with respect to the arrangement of the pickup section is increased. For example, the biological signals can be collected without being conscious of the subject by being integrated with the top plate, the lower RF coil, etc. Is possible.

  In addition, since the opening of the pickup unit that collects heart sounds and breathing sounds is smaller than the mounting area of a plurality of electrode groups that collect electrocardiographic waveforms, it has been difficult to attach electrode groups conventionally, such as newborns Furthermore, since the pickup portion is formed of an inexpensive resin or the like, it can be easily replaced.

  Further, according to the above-described embodiment and its modification, the environment for removing the vibration sound of the MRI apparatus and the environmental sound such as BGM in the examination room collected together with the acoustic biological signals such as heart sounds and breathing sounds in the pickup unit. Since the sound removal unit is provided, it is possible to generate a high-quality shooting trigger signal that is not affected by the environmental sound.

  Furthermore, when the trigger signal generated by the trigger signal generation unit has a poor characteristic, a trigger signal collected in advance can be output as an imaging trigger signal instead of the trigger signal. Even when the trigger signal is greatly disturbed due to coughing, sneezing, body movement, etc., it is possible to stably output an imaging trigger signal effective for MRI imaging.

  As mentioned above, although the Example of this invention and its modification were described, this invention is not limited to the above-mentioned Example and modification, It can change and implement further. For example, the imaging trigger signal generation unit 9 in the above-described embodiment and the imaging trigger signal generation unit 9a in the modification have the first imaging trigger signal and the second imaging based on the heart sound and the respiratory sound collected from the subject 150. Although the case where the trigger signal is generated has been described, only one of them may be used.

  Moreover, although the case where the heart sound and the breathing sound are collected simultaneously using the common detection element provided in the pickup unit 911 (911a) of the biological signal detection unit 91 (91a) has been described, The pickup units may be used independently. According to this method, the biological signal separation unit 931 of the imaging trigger signal generation unit 93 is not necessary.

  On the other hand, the pickup unit 911 (911a) in the above-described embodiment is described as being provided in the lower PF coil 313. However, the present invention is not limited to this. For example, the mat 41 (see FIG. 2), or may be provided in the upper RF coil 311.

  Further, in the subtraction process between the biological signal and the environmental sound, the case where the gain is adjusted with respect to the environmental sound collected by the microphone 921 of the environmental sound removing unit 92 has been described. However, the transducer 912 of the biological signal detecting unit 91 (91a) is described. Gain adjustment may be performed on the electrical biological signal obtained in (912a).

  Further, FIG. 8 shows the case where the first trigger signal is generated at the timing of the trigger pulse P1 based on the S1 wave of the heart sound or the trigger pulse P2 based on the S2 wave. The first trigger signal may be generated at a delayed timing.

1 is a block diagram showing the overall configuration of an MRI apparatus in an embodiment of the present invention. The figure which shows the structure of RF coil unit with which the MRI apparatus of the Example was equipped. The figure which shows the structure of the lower RF coil provided in the RF coil unit of the Example. The block diagram which shows the specific structure of the imaging | photography trigger signal generation unit with which the MRI apparatus of the Example is provided. The figure which shows the arrangement | positioning position of the application area | region of a gradient magnetic field and RF pulse, a pickup part, and a transducer in the Example. The figure which shows the frequency characteristic of the filter circuit provided in the biosignal separation part of the Example. The figure which shows the electrocardiogram used by MRI imaging of the Example, and the electrocardiogram waveform used by the conventional MRI imaging. The figure which shows the production | generation method of the trigger signal in the imaging | photography trigger signal generation part of the Example. 6 is a flowchart showing a procedure for generating a shooting trigger signal in the embodiment. The block diagram which shows the modification of the imaging | photography trigger signal generation unit with which the MRI apparatus of the Example is provided.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Static magnetic field generation part 2 ... Gradient magnetic field generation part 3 ... Transmission / reception part 31 ... RF coil unit 313 ... Lower RF coil 313a ... Coil cover 313b ... Coil cover 4 ... Top plate 5 ... Top plate movement mechanism part 6 ... Image data generation part DESCRIPTION OF SYMBOLS 7 ... Display part 8 ... Input part 9 ... Shooting trigger signal generation unit 91 ... Biological signal detection part 911 ... Pickup part 912 ... Transducer 913 ... Guide pipe 92 ... Environmental sound removal part 921 ... Microphone 922 ... Gain adjustment part 923 ... Subtraction Processing unit 93 ... Imaging trigger signal generation unit 931 ... Biological signal separation unit 932 ... Trigger signal generation unit 933 ... Trigger signal storage unit 934 ... Signal determination unit 935 ... Imaging trigger signal output unit 10 ... Control unit 200 ... MRI apparatus

Claims (10)

An imaging trigger signal generation unit for an MRI apparatus that generates an imaging trigger signal synchronized with a biological signal of a subject,
A biological signal pickup means that is arranged in the vicinity of the subject to which a gradient magnetic field and an RF pulse necessary for MRI imaging are applied and collects at least one of a heart sound and a respiratory sound generated from the subject as an acoustic biological signal;
A transducer disposed in a region to which the gradient magnetic field and RF pulse are not applied and converting the acoustic biological signal into an electrical biological signal;
A guiding tube for supplying the acoustic biological signal collected by the biological signal pickup means to the transducer;
Trigger signal generating means for generating a trigger signal based on the electrical biological signal obtained by the transducer;
An imaging trigger signal generating unit for an MRI apparatus, comprising: an imaging trigger signal output means for outputting the trigger signal as an imaging trigger signal.   The imaging trigger signal generation unit for an MRI apparatus according to claim 1, wherein the guiding pipe is made of an insulating material. An imaging trigger signal generation unit for an MRI apparatus that generates an imaging trigger signal synchronized with a biological signal of a subject,
A biological signal pickup means that is arranged in the vicinity of the subject to which a gradient magnetic field and an RF pulse necessary for MRI imaging are applied and collects at least one of a heart sound and a respiratory sound generated from the subject as an acoustic biological signal;
A transducer for converting the acoustic biological signal into an electrical biological signal;
Transmitting means disposed in the vicinity of the transducer for transmitting the electrical biosignal in the air;
Receiving means for receiving the electrical biological signal transmitted in the air and disposed in a region where the gradient magnetic field and RF pulse are not applied;
Trigger signal generating means for generating a trigger signal based on the electrical biological signal received by the receiving means;
An imaging trigger signal generating unit for an MRI apparatus, comprising: an imaging trigger signal output means for outputting the trigger signal as an imaging trigger signal.   4. The biological signal pick-up means is provided on either an RF coil arranged around the subject or a top plate on which the subject is placed. An imaging trigger signal generation unit for the described MRI apparatus.   The imaging trigger signal generation unit for an MRI apparatus according to claim 1 or 3, wherein the biological signal pickup means collects a heart sound and a breathing sound generated from the subject simultaneously using a common detection element. .   Biological signal separation means for separating a first biological signal based on the heart sound and a second biological signal based on the respiratory sound constituting the electrical biological signal, and the trigger signal generating means includes the biological signal 6. An imaging trigger signal generation unit for an MRI apparatus according to claim 5, wherein the trigger signal corresponding to each of the first biological signal and the second biological signal separated by the signal separation means is generated.   The imaging trigger signal generation unit for an MRI apparatus according to claim 6, wherein the biological signal separation means separates the first biological signal and the second biological signal by a filter circuit having different frequency characteristics.   An environmental sound removing unit, wherein the environmental sound removing unit converts the electrical biological signal obtained by the transducer and the environmental sound collected around the subject into a subtraction process to the electrical biological signal. The imaging trigger signal generation unit for an MRI apparatus according to claim 1 or 3, wherein mixed environmental sounds are removed.   A trigger signal storage unit that stores a trigger signal generated by the trigger signal generation unit; and a signal determination unit that determines whether the trigger signal generated by the trigger signal generation unit is good or bad. The imaging trigger signal output unit includes the signal determination unit. The trigger signal generated by the trigger signal generation unit based on the determination result of the unit or the trigger signal stored in advance in the trigger signal storage unit is output as the imaging trigger signal. The MRI apparatus imaging trigger signal generation unit according to claim 3. An MRI apparatus that performs MRI imaging based on an imaging trigger signal synchronized with a biological signal of a subject,
An MRI apparatus for performing MRI imaging on the subject based on an imaging trigger signal supplied from the imaging trigger signal generation unit for an MRI apparatus according to any one of claims 1 to 9.

Images