JP4632535B2 - MRI equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to magnetic resonance imaging that images the inside of a subject based on the magnetic resonance phenomenon of spins (nuclear spins), and obtains an arteriovenous phase image without using a contrast agent.MRI (magnetic resonance imaging) equipmentAbout.
[0002]
[Prior art]
Magnetic resonance imaging is an imaging method in which a nuclear spin of a subject placed in a static magnetic field is magnetically excited with a high-frequency signal of its Larmor frequency, and an image is reconstructed from an MR signal generated by the excitation. .
[0003]
In the field of magnetic resonance imaging, when an blood flow image of a lung field or abdomen is obtained, clinically, MR angiography in which a contrast medium is administered to a subject and angiography is started. However, this contrast-enhanced MR angiography method involves the administration of a contrast agent, and therefore requires invasive treatment. First of all, the burden on the patient's mental and physical strength is great. Also, the inspection cost is high. Furthermore, the contrast agent may not be administered depending on the patient's constitution.
[0004]
On the other hand, time-of-flight (TOF) method, phase contrast (PC) method, and the like are known as alternatives to contrast MR angiography.
[0005]
Among these, the time-of-flight method and the phase contrast method are methods that utilize the effect of a flow such as blood flow. The flow effect is caused by one of two properties of the moving spin. One is that the spin simply moves its position, and the second depends on the phase shift of the transverse magnetization caused by the movement of the spin in the gradient magnetic field. Among them, the method based on the former position movement is the TOF method, and the method based on the latter phase shift is the phase contrast method.
[0006]
[Problems to be solved by the invention]
However, since the TOF method and the phase contrast method described above are methods that use the effect of the flow of fluid such as blood, depending on the performance of the MRI apparatus, the speed is generally 2 to 2. Only a blood flow of 3 cm / s or more could be depicted, and a flow at a velocity lower than this could hardly be detected. For example, the flow of peripheral veins, lymphatic vessels, CSF (spinal fluid), pancreatic ducts, etc. of a patient (person) is slow and most speeds are 1 cm / s or less. In addition, since there is an influence of displacement due to pulsation or the like, the flow of these low-speed fluids cannot be detected conventionally.
[0007]
Even in the above-described TOF method or phase contrast method, it is necessary to image a slice perpendicular to the blood flow direction. That is, it is necessary to take an axial image with the slice direction aligned with the vertical direction. For this reason, in the case of a two-dimensional slice image, the image does not follow the blood flow. For this reason, when trying to obtain a three-dimensional image, there is a problem that the number of slices increases, and the entire imaging time becomes longer.
[0008]
  The present invention was made in order to overcome the current state of the art, and reliably displays a low flow rate flow seen in a fluid such as a blood flow of the lower limb with high image quality without administering a contrast medium. To doTheObjective.
[0010]
[Means for Solving the Problems]
  The MRI apparatus of the present invention sets two cardiac time phases of a subject placed in a static magnetic field, and performs the first and second scans based on a magnetic resonance imaging pulse sequence including a readout gradient magnetic field pulse. A signal collecting unit that collects an echo signal from the subject by executing it in two cardiac phases, and an image generating unit that generates an image of fluid in the subject based on the echo signal, Is provided. In the MRI apparatus of the present invention, the readout gradient magnetic field pulse has a pulse main body for reading out the echo signal, and a control pulse for controlling the phase behavior of the magnetization spin of the fluid. , The control pulse of the readout gradient magnetic field pulse of the pulse sequence used for the first scan in one cardiac phase is formed by a pulse responsible for the dephasing of the magnetization spin, and the second in the other cardiac phase The control pulse of the readout gradient magnetic field pulse of a pulse sequence used for scanning is formed of a pulse that is responsible for rephasing the magnetization spin.The
[0014]
  For example,As the one cardiac phase, the subject'sContractionPhase belonging to the periodButSettingIsWhenBothAnd saidThe otherAs a mental phase ofAboveSubject'sExpansionPhase belonging to the periodButSettingIsThe
[0015]
  For example, the signal acquisition means is means for sequentially executing the first and second scans within the imaging of the same slice or slice encoding amount.
[0016]
Preferably, the fluid is a blood flow in the subject. In this case, the blood flow is an arterial vein of the lower limb of the subject with a slow flow velocity, and the image generation unit is an arteriovenous image generation unit that generates an image obtained by separating the arterial vein.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below.
[0024]
(First embodiment)
A first embodiment will be described with reference to FIGS.
[0025]
A schematic configuration of an MRI (magnetic resonance imaging) apparatus according to this embodiment is shown in FIG.
[0026]
(1.1) Device configuration
The MRI apparatus includes a bed unit on which the 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, a transmission / reception unit that transmits and receives high-frequency signals, A control / arithmetic unit responsible for overall system control and image reconstruction, and an electrocardiogram measurement unit that measures an ECG signal as a signal representing the cardiac time phase of the subject P are provided.
[0027]
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 an axial direction of a cylindrical opening (diagnostic space) into which the subject P is loosely inserted. Static magnetic field H in the Z-axis direction₀Is 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 removably insert the top plate on which the subject P is placed into the opening of the magnet 1.
[0028]
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-axis direction, the Y-axis direction, and the Z-axis direction 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 gradient magnetic fields to the x, y, z coils 3x to 3z under the control of a sequencer 5 described later.
[0029]
By controlling the pulse current supplied to the x, y, z coils 3x to 3z from the gradient magnetic field power source 4, the gradient magnetic fields in the three axes (X axis, Y axis, Z axis) directions which are physical axes are synthesized. , Slice direction gradient magnetic field G orthogonal to each other_S, Phase encoding direction gradient magnetic field G_E, And readout direction (frequency encoding direction) gradient magnetic field G_RThe logical axis direction consisting of can be set and changed arbitrarily. Each gradient magnetic field in the slice direction, phase encoding direction, and readout direction is a static magnetic field H.₀Is superimposed on.
[0030]
The transmission / reception unit includes an RF coil 7 disposed in the vicinity of the subject P in the imaging 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 exciting nuclear magnetic resonance (NMR). The receiver 8R takes in an MR signal (high frequency signal) such as an echo signal received by the RF coil 7, and performs various signal processing such as preamplification, intermediate frequency conversion, phase detection, low frequency amplification, and filtering. After that, A / D conversion is performed to generate digital data (original data) of the MR signal.
[0031]
Further, the control / arithmetic unit includes a sequencer (also called 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 stored software procedure (not shown) and supervising the operation of the entire apparatus.
[0032]
This MRI apparatus is characterized by performing MR scan based on an electrocardiographic synchronization method based on a synchronization timing (cardiac time phase) of a preselected value. As shown in FIG. 2, the host computer 6 performs a preparation scan (hereinafter referred to as an ECG-prep scan) for executing a preparation pulse sequence for determining synchronization timing in advance, and electrocardiographic synchronization based on the synchronization timing. Two imaging scans (hereinafter referred to as imaging scans) for executing the imaging pulse sequence are performed while executing a main program (not shown). An example of the ECG-prep scan execution routine is shown in FIG. 3, and examples of the first and second imaging scan execution routines based on ECG synchronization are shown in FIGS.
[0033]
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.
[0034]
The pulse sequence may be a two-dimensional (2D) scan or a three-dimensional scan (3D) as long as the Fourier transform method is applied. In addition, as a pulse train, the SE method, the fast SE method, the EPI (Echo Planar Imaging) method, the FASE (Fast Asymmetric SE) method (that is, the fast SE method combined with the half Fourier method) SE series pulse trains are suitable.
[0035]
Further, the arithmetic unit 10 inputs the digital data (also referred to as original data or raw data) output from the receiver 8R through the sequencer 5, and the digital data is input to the k space (also referred to as Fourier space or frequency space) by its internal memory. Data is arranged, and this data is subjected to two-dimensional or three-dimensional Fourier transform for each set to reconstruct image data in real space. In addition, the arithmetic unit can execute data composition processing and difference calculation processing (including weighted difference processing) as necessary. This synthesis processing includes processing for adding each pixel, maximum value projection (MIP) processing, and the like. As another example of the above synthesis process, the axes of a plurality of frames may be aligned in Fourier space, and the original data may be synthesized into one frame of original data. The addition processing includes simple addition processing, addition averaging processing, weighted addition processing, and the like.
[0036]
The storage unit 11 can store not only the reconstructed image data but also the image data that has been subjected to the above-described combining process and difference process. The display device 12 displays an image. Further, parameter information for selecting a synchronization timing desired by the surgeon, scan conditions, pulse sequences, information relating to image synthesis and difference calculation can be input to the host computer 6 via the input unit 13.
[0037]
The voice generator 16 can issue a breath holding start message and a breath holding end message as voice when instructed by the host computer 6.
[0038]
Further, the electrocardiogram measurement unit attaches to the body surface of the subject and detects an ECG signal as an electrical signal, and performs various processing including digitization processing on the sensor signal to perform the host computer 6 and the sequencer. And an ECG unit 18 for outputting to the PC. The measurement signal from the electrocardiogram measurement unit can be used as required by the sequencer 5 when performing each of the ECG-prep scan and the electrocardiographic synchronization imaging scan. Thereby, the synchronization timing of the electrocardiographic synchronization method can be set appropriately, and data can be collected by performing an electrocardiographic synchronization imaging scan based on the synchronization timing.
[0039]
(1.2) ECG-prep scan
Next, the optimum synchronization timing determination process by ECG-prep scan will be described with reference to FIGS.
[0040]
The host computer 6 starts the ECG-prep scan shown in FIG. 3 in response to a command from the input device 13 while executing a predetermined main program (not shown).
[0041]
First, the host computer 6 reads scan conditions and parameter information for executing the ECG-prep scan from the input device 13 (step S1 in the figure). The scan conditions include the type of scan, the pulse sequence, the application direction of the readout gradient magnetic field pulse, and the like. The parameter information includes an initial time T for determining the synchronization timing (time phase) of ECG synchronization.₀(Here, the elapsed time from the peak value of the R wave in the ECG signal), the time increment includes the step size Δt, the upper limit value of the number counter CNT, etc., and these parameters can be arbitrarily set by the operator.
[0042]
Next, the host computer 6 counts the number of times of execution of the sequence counter CNT and the time increment parameter T for determining the synchronization timing._incIs cleared (CNT = 0, T_inc= 0: Step S2). Thereafter, the host computer 6 sends message data to the sound generator 16 to cause the subject (patient) to perform a breath holding command such as “please hold your breath” (step S3). This breath holding is preferably performed in order to suppress the body movement of the subject during the execution of the ECG-prep scan. However, in some cases, the ECG-prep scan is executed without performing the breath holding. Also good.
[0043]
When the preparation is completed in this way, the host computer 6 sequentially executes the processes after step S4. Thereby, it shifts to scan execution while changing the synchronization timing of electrocardiogram synchronization.
[0044]
Specifically, the delay time T from the peak arrival time of the R wave_DLBut T_DL= T₀+ T_inc(Step S4). Next, the ECG signal processed by the ECG unit 18 is read, and it is determined whether or not the peak value of the R wave in the signal has appeared (step S5). This determination process is repeated until the R wave appears. When an R wave appears (step S5, YES), the delay time T at that time calculated in step S4_DLIs subsequently determined whether or not the R wave peak time has elapsed (step S6). This determination process is also delayed time T_DLContinue until
[0045]
R wave peak time to delay time T_DL(Step S6, YES), the sequencer 5 is instructed to start each pulse sequence (step S7: see FIG. 4). This pulse sequence is preferably set to the same type as an imaging pulse sequence described later, and is, for example, a 2D-FASE (Fast Asymmetric SE) method in which a high-speed SE method is combined with a half Fourier method. Of course, various sequences such as a high-speed SE method and an EPI method can be adopted for this sequence. In response to this command, the sequencer 5 starts executing the type of pulse sequence commanded by the operator, so that the region of the desired part of the subject is scanned. This ECG-prep scan may be performed by a two-dimensional (2D) scan, for example, when an imaging scan (main scan) for collecting image data is a three-dimensional (3D) method, or according to the region of the imaging scan. A three-dimensional scan may be performed. In this embodiment, the imaging scan is executed as a three-dimensional scan, but the ECG-prep scan is executed as a two-dimensional scan from the viewpoint of reducing the scan time. In view of the mission of ECG-prep scanning, a two-dimensional scan is sufficient.
[0046]
After the above sequence execution start command, the number counter CNT = CNT + 1 is calculated (step S8), and the time increment parameter T_inc= ΔT · CNT is calculated (step S9). As a result, the count value of the number counter CNT is incremented by 1 each time the execution of the pulse sequence is commanded, and the increment parameter T for adjusting the synchronization timing._incIncreases in proportion to the count value.
[0047]
Next, it waits as it is until a predetermined period (for example, about 500 to 1000 msec) necessary for execution of each pulse sequence elapses (step S10). Further, it is determined whether or not the number counter CNT has reached a predetermined upper limit value (step S11). In order to optimize the synchronization timing, the delay time T_DLFor example, when five two-dimensional images are taken while changing the time to various time values, the number counter CNT = 5 is set. If the number counter CNT has not reached the upper limit value (step S11, NO), the process returns to step S5 and the above-described process is repeated. On the other hand, when the number counter CNT reaches the upper limit value (step S11, YES), a command for releasing the breath holding is issued to the sound generator 16 (step S12), and the subsequent processing is returned to the main program. For example, the breath-holding voice message is "You can breathe."
[0048]
When the above-described processes are sequentially executed, for example, the preparation pulse sequence is executed at the timing shown in FIG. For example, the initial time T₀= 300 msec and time step ΔT = 100 msec is commanded, delay time T for the first sequence_DL= 300 msec, delay time T for the second time_DL= 400 msec, delay time T for the third time_DL= Delay time T for determining synchronization timing such as 500 msec,..._DLIs adjusted.
[0049]
Therefore, when the first R wave after the breath holding command reaches the peak value, the delay time T_DL(= T₀) Later, for example, the first scan IMG based on the two-dimensional FASE method_prep1Continues for a predetermined time (500 to 1000 msec), and echo signals are collected. Even when the next R wave appears during the continuation of the sequence, the sequence is continued without being involved in the appearance of the R wave because there is a standby process in step S10 of FIG. That is, the execution process of the sequence started in synchronization with a certain heartbeat is continued over the next heartbeat, and echo signals are collected.
[0050]
Then, when the number counter CNT has not reached the predetermined value, the processes of steps S5 to S11 are executed again. For this reason, in the example of FIG. 4, when the third R wave appears and reaches the peak value, the delay time T_DL= T₀+ T_inc= When the 400 msec has elapsed, the second scan IMG_prep2Continues for a predetermined time, and echo signals are collected as well. At the end of this scan, the next R wave appears and the delay time T_DL= T₀+ 2 · T_inc= 500 msec has passed and the third scan IMG_prep3Continues for a predetermined time, and echo signals are collected as well. Further, after this scan is finished, the next R wave appears and the delay time T_DL= T₀+ 3 · T_inc= After 600 msec, the 4th scan IMG_prep4Continues for a predetermined time, and echo signals are collected as well. This scan is continued a desired number of times, for example, 5 times, and echo data of the same cross section for a total of 5 frames (sheets) is collected.
[0051]
The echo data is sequentially sent to the arithmetic unit 10 via the receiver 8R and the sequencer 5. The arithmetic unit 10 reconstructs echo data in k space (frequency space) into real space image data by a two-dimensional Fourier transform method. This image data is stored in the storage unit 11 as blood flow image data. For example, in response to an operation signal from the input unit 13, the host computer 6 sequentially displays the blood flow image in a cine.
[0052]
That is, as schematically shown in FIG. 5, for example, n two-dimensional coronal images having different time phases of the lower limbs are displayed. In this coronal image, an artery AR and a vein VE that flow in the vertical direction in the lower limb are positioned. However, the timing of imaging, that is, “delay time T from R wave_DL= Initial time T₀+ Tinc · Δt ”differs for each image. The operator visually observes these images, and selects an image in which the artery AR and vein VE appear in the highest signal and an image in which only the vein appears in the highest signal. Among these, a delay time T corresponding to an image in which only the vein VE appears in a relatively high signal._DL1The synchronous timing T of the systole_DL= T_DL1Is decided. Further, a delay time T corresponding to an image in which the artery AR and the vein VE appear in a relatively high signal._DL2As a result, the expansion timing T_DL= T_DL2Is decided.
[0053]
Therefore, the surgeon can thus determine the delay time T_DLVisual observation of a plurality of blood flow images picked up by dynamically changing the rhythm, and the optimal delay time T in each systole and diastole as two cardiac phases_DL= T_DL1, T_DL2(Synchronization timing) is determined, and this delay time T_DLFor example, the process of reflecting in the subsequent imaging scan is performed manually.
[0054]
When an image determined by visual observation is designated, the delay time T given to the designated image is designated._DLIs automatically stored as the optimum synchronization timing, and this timing T_DLSoftware may be constructed and installed to automatically read out images during imaging scans. As a result, the ECG synchronization timing automatic designation processing can be performed.
[0055]
(1.3) Imaging scan
Next, the operation of two imaging scans (that is, two imaging operations) in this embodiment will be described with reference to FIGS.
[0056]
The host computer 6 executes a predetermined main program (not shown), and as part of that, executes the imaging scan process shown in FIG. 6 in response to the operation information from the input unit 13.
[0057]
Assume that the first imaging scan (imaging) is assigned to the systole. In this case, the host computer 6 firstly sets the optimum delay time T for the systole determined by the operator through the ECG-prep scan described above._DL(= T_DL1Or T_DL2> T_DL1) Is input, for example, via the input device 13 (step S20).
[0058]
Next, the host computer 6 scans the conditions specified by the operator from the input unit 13 (application direction of readout gradient magnetic field pulse, image size, number of scans, standby time between scans, pulse sequence corresponding to the scan region, etc.) and image processing Information on the method (MIP processing, difference processing, etc. In the case of difference processing, simple difference, weighted difference processing, addition processing, etc.) is input, and the delay time T_DLIs processed into control data, and the control data is output to the sequencer 5 and the arithmetic unit 10 (step S21).
[0059]
Next, when it is determined that there is a notice of completion of preparation before scanning (step S22), a command to start breath holding is output to the sound generator 14 in step S23 (step S23). As a result, the voice generator 14 issues a voice message such as “please hold your breath” in the same way as in the ECG-prep scan, so that the patient who hears it stops breathing (see FIG. 9). .
[0060]
Thereafter, the host computer 6 instructs the sequencer 5 to start the first (or second) imaging scan (step S24).
[0061]
When the sequencer 5 receives this imaging scan start command (FIG. 7, step S24-1), the sequencer 5 starts reading the ECG signal (step S24-2), and determines the peak value of the R wave (reference waveform) in the ECG signal. The occurrence of the predetermined nth time is determined from the ECG trigger signal synchronized with the peak value (step S24-3). Here, the reason for waiting for the appearance of the R wave n times (for example, twice) is to estimate the time when the shift to breath holding is surely made. When a predetermined n-th R wave appears, the set delay time T_DL1Only waiting processing is performed (step S24-4).
[0062]
This optimum delay time T_DL1(Or T_DL2), The sequencer 5 executes the first imaging scan (step S24-5). Specifically, the transmitter 8T and the gradient magnetic field power source 4 are driven according to the pulse sequence information that has already been stored, and the first imaging scan (imaging) based on, for example, a three-dimensional FASE pulse sequence is shown in FIG. As shown in (a) and (c), it is executed in synchronization with the electrocardiogram (the phase encoding direction gradient magnetic field is not shown in FIG. 10 (c)).
[0063]
According to this pulse sequence, the readout gradient magnetic field pulse G_RFor example, as shown in FIG. 10, the application direction RO is set so as to substantially coincide with the flow direction of the blood flow (artery AR, vein VE) for imaging purposes.
[0064]
Further, the readout gradient magnetic field pulse G included in this pulse sequence_R8 (c) and FIGS. 9 (a) to 9 (c), a pulse body P for frequency encoding for collecting echo signals._bodyAnd this pulse body P_bodyTwo dephasing pulses P as control pulses added continuously before and after_dephaseIt consists of. This dephase pulse P_dephaseIs the pulse body P for frequency encoding._bodyThis has the function of promoting dephasing of the moving magnetic spin.
[0065]
Dephase pulse P_dephaseHardly exerts the dephase function on the magnetized spin that has hardly moved. For this reason, the readout gradient magnetic field pulse G_RIt is important that the voltage is applied almost in accordance with the direction of movement of the fluid (blood or lymph) for imaging purposes.
[0066]
Preferably, the dephase pulse P_dephaseThe intensity can be changed or controlled according to the speed of the lymph or blood flow as the fluid to be imaged. 9A to 9C show the dephasing pulse P in this order._dephaseThe example which reduces the intensity | strength of is illustrated. In general, as the blood flow velocity increases, the dephase pulse P_dephaseIt is changed or controlled so as to reduce the intensity.
[0067]
When the velocity of the fluid to be imaged (blood flow or the like) is relatively high, as shown in FIG._bodyA total of two rephase pulses P as control pulses continuously before and after_rephaseIs added. This rephase pulse P_rephaseIs the pulse body P for frequency encoding._bodyThe polarity is opposite to the above, and in order to suppress excessive dephasing, it has a function of rephasing the magnetized spin to suppress artifacts. This rephase pulse P_rephaseIt is preferable that the intensity | strength of is also changed according to a flow rate.
[0068]
In the first embodiment, therefore, the readout gradient magnetic field pulse G is used in both the first and second (described later) imaging scans._RHas a dephase pulse P_dephaseOr rephase P_rephaseIs added.
[0069]
For this reason, by executing the above-described three-dimensional FASE pulse sequence, echo signals energized by the excitation 90 ° RF pulse and the refocus 180 ° RF pulse are collected for each slice encoding and each phase encoding. The This echo signal includes a dephase pulse P_dephasePhase demagnetization or rephase P of magnetized spin due to_rephaseThe rephasing effect of the phase of the magnetized spin due to the above is reflected.
[0070]
This will be described in detail together with the display operation described later, and the outline thereof will be described as follows.
[0071]
That is, for the fluid flowing along the application direction of the readout gradient magnetic field pulse, the dephase pulse P_dephaseThe dephasing effect due to the flow leads to the promotion of the flow void effect. For this reason, the intensity of the echo signal is reduced by the dephasing pulse. On the other hand, in the case of a fluid that hardly flows in that direction, the dephasing pulse P_dephaseThe degree of acceleration of the flow void effect due to the noise is low, and the intensity of the echo signal does not decrease so much.
[0072]
Rephase pulse P_rephaseIn this case, due to the rephasing action, the effect of dephasing is suppressed according to the flow of the fluid.
[0073]
The echo interval in the above pulse sequence is shortened to about 5 msec. Thus, echo signals are collected from the three-dimensional imaging region Rima set on the lower limb, for example, as shown in FIG. 10 with a scan time of about 600 msec based on the first slice encoding amount SE1.
[0074]
When the scan based on the first slice encoding is completed, the sequencer 5 determines whether or not the scan for the final slice encoding is completed (step S24-6), and this determination is NO (the scan based on the final slice encoding is performed). In the case of not completed), while monitoring the ECG signal, for example, from the R wave used in the previous imaging scan, for example, 2 heartbeats (2R-R) and wait until a shorter set period elapses (step S24- 7). The repetition time TR is set to 4 heartbeats (4R-R) or less.
[0075]
Thus, for example, after waiting for a period corresponding to 2R-R, for example, when the third R wave appears (step S24-7, YES), the sequencer 5 returns the process to step S24-4 described above. As a result, the specified delay time T from the ECG trigger signal synchronized with the third R wave peak value is obtained._DL1At the time when elapses, scanning based on the next slice encoding amount SE2 is executed in the same manner as described above, and the three-dimensional imaging region R_imaEcho signals are collected from (step S24-4, 5). Similarly, echo signals are collected up to the final slice encoding amount SEn (for example, n = 8).
[0076]
When the final scan based on the slice encoding amount SEn is completed, the determination in step S24-6 is YES, and the completion notification of the first (or second) imaging scan is output from the sequencer 5 to the host computer 6 (step S24-6). S24-8). As a result, the processing is returned to the host computer 6.
[0077]
Upon receiving the scan completion notification from the sequencer 5 (step S25), the host computer 6 outputs a breath holding release command to the voice generator 16 (step S26). Therefore, the voice generator 16 issues a voice message such as “It is fine to breathe” to the patient, and the breath holding period ends (see FIG. 8).
[0078]
Thereby, the 1st (or 2nd) imaging scan (imaging) by an electrocardiogram synchronization is performed for every 2R-R based on 3D-FASE method, for example.
[0079]
The echo signal generated from the patient P is a slice gradient magnetic field pulse G._sIs received by the RF coil 7 and sent to the receiver 8R. The receiver 8R performs various preprocessing on the echo signal and converts it into a digital quantity. This digital amount of echo data is sent to the arithmetic unit 10 through the sequencer 5 and is arranged at a position corresponding to the encoded amount of the three-dimensional k-space formed by the memory.
[0080]
Next, as shown in FIG. 2, the second imaging scan (imaging) for the diastole is performed in the same manner as the first time with an appropriate time interval. However, in the second case, the optimum delay time T for determining the predetermined time phase of the expansion period set in advance through the ECG-prep scan described above._DL2Is read (FIG. 6, steps S20 and S21), and this delay time T_DL2ECG synchronization based on the above is taken (FIG. 7, step S24-4).
[0081]
For this reason, in the case of the second imaging scan, as shown in FIGS._DL2A three-dimensional FASE method scan based on each phase encoding amount SE is executed at an expansion period synchronization timing delayed by a certain amount. Also in this case, the readout gradient magnetic field pulse G_RThe application direction is made to almost coincide with the direction of movement of the imaging fluid such as blood flow. Also, the readout gradient magnetic field pulse G_RIncludes a control pulse (dephase pulse P) for controlling the behavior (dephase or rephase) of the magnetized spin._dephaseOr rephase pulse P_rephase) Is added.
[0082]
Therefore, the readout gradient magnetic field pulse G is obtained by the second imaging scan, as in the first._RDephase pulse P added to_dephaseOr rephase pulse P_rephaseThe image data of the expansion period reflecting the spin control function is obtained.
[0083]
(1.4) Data processing and image display
When the collection of echo data is completed in this way, the host computer 6 causes the arithmetic unit 10 to execute the processing shown in FIG.
[0084]
As shown in the figure, in response to the command from the host computer 6, the arithmetic unit 6 causes both the systolic k-space and the diastole k-space to calculate echo data based on the half Fourier method (step S31). . That is, the data of the remaining area of the k space for which the echo data has not been collected is calculated according to the complex conjugate relation and arranged. As a result, both the k spaces are filled with echo data.
[0085]
Thereafter, the arithmetic unit 10 performs image reconstruction by performing three-dimensional Fourier transform on the echo data of the systolic k-space and the diastole k-space, respectively (steps S32 and S33). As a result, as shown in FIGS. 12A and 12B, the delay time T in the systole._DL1Time phase image (systolic image) IM_sysAnd delay time T in diastole_DL2Time phase image (diastolic image) IM_dia3D data is obtained.
[0086]
According to this image data, the systolic image IM_sysOnly the vein VE is reflected in the image, and the artery AR is hardly reflected. Meanwhile, diastolic image IM_diaIn FIG. 5, the arterial AR and the vein VE are reflected to some extent.
[0087]
Here, such a systolic image IM_sysAnd diastolic image IM_diaIs the principle of the readout gradient magnetic field G described above._RApplication direction and dephase pulse P_dephaseThe functions are described in detail below.
[0088]
The phase of magnetization spins of components such as blood flow flowing in the direction in which the read gradient magnetic field pulse is applied is more easily dispersed by the dephase pulse. In other words, for the flowing component, this is equivalent to the promotion of the flow void effect due to the flow itself. On the contrary, the rephasing function acts on the phase of the magnetized spin such as blood flow due to the rephasing pulse.
[0089]
For example, the lower limb of the subject is taken as an example. In the case of the lower limb, the artery in the systole usually has a low flow rate of 1 cm / s or less, and the flow velocity is low enough to be considered that the vein in the systole and the artery and vein in the diastole are hardly moving. For this lower limb, as shown in FIG._dephaseGradient magnetic field pulse G added with_RThe imaging scan (imaging) is performed at each desired time phase of the systole and the diastole.
[0090]
These imaging scans excite the arteriovenous magnetization spins and collect echo signals. At this time, since the arterial and venous flow velocities are slightly different from each other, the difference in the flow velocities is reflected in the promotion of the flow void effect due to the rephasing pulse, and appears as a relative change in the signal value of the echo signal.
[0091]
Specifically, the systole is as follows. Since the vein flows very slowly, the echo signal is slightly reduced by the dephasing pulse, but the flow void effect is small, and the blood is depicted in a bright blood with a relatively high signal value. On the other hand, the systolic artery flows at a higher flow rate than the vein, so that the flow void effect promoted by the dephasing pulse is greater than that of the vein. As a result, the signal value of the artery is greatly reduced, and is rendered in black blood. This state is schematically shown in FIG. In the figure, the hatched portion is bright blood and the dotted line portion is black blood.
[0092]
On the other hand, in the diastole, both the arteries and veins move only at a very low flow rate, so that both the arteries and veins are depicted in bright blood, although there is a slight signal value decrease due to the dephasing pulse. This state is schematically shown in FIG.
[0093]
Returning to the explanation of FIG._ARTo obtain the systolic image IM_sysAnd diastolic image IM_diaThe difference calculation “IM_dia-ΒIM_sysIs performed for each pixel (step S34). Here, β is a weighting coefficient. Accordingly, as shown in FIG. 12, by appropriately setting the weighting coefficient β, the image data of the vein VE becomes almost zero, and the arterial phase image IM showing only the artery AR._AR3D image data is obtained.
[0094]
Furthermore, the vein phase image IM_VETo obtain the difference operation “IM_dia-IM_ARIs performed for each pixel (step S35). Image data IM_ARIs image data calculated by the above-described weighting difference. Thereby, as shown in FIG. 13, the image data of the artery AR becomes almost zero, and the vein phase image IM in which only the vein VE is shown._VE3D image data is obtained. Note that this difference calculation may also be performed using a weighted difference.
[0095]
When the difference calculation is completed in this way, the calculation unit 10 determines both arterial phase images IM._ARAnd vein phase image IM_VEFor each of them, MIP (maximum value projection) processing is performed to create data of a two-dimensional image (for example, coronal image) when those blood vessels are observed from a desired direction (step S36).
[0096]
Two-dimensional image IM of the arterial phase and the venous phase_ARAnd IM_VEFor example, as shown in FIG. 14, the image data is displayed on the display 12 and the image data is stored in the storage unit 11 (step S39).
[0097]
In this display, the arterial phase image IM_ARAnd vein phase image IM_VEIn addition to the systolic image IM_sysAnd diastolic image IM_diaMay be displayed on the same screen or on a separate monitor screen.
[0098]
(1.5) Effect
As described above, in the MRI apparatus of the present embodiment, the readout gradient magnetic field pulse G is applied during the imaging scan._RIs applied almost in accordance with the flow direction of a low flow rate fluid (blood flow, etc.) found in the lower limb blood vessels. At the same time, the gradient magnetic field pulse G_RDephase pulse P_dephaseOr rephase pulse P_rephaseIs added.
[0099]
As a result, the relative signal value difference between the flowing fluid and the fluid flowing only at a lower velocity is calculated as the dephasing pulse P._dephaseOr rephase pulse P_rephaseCan be increased. Therefore, for example, when the dephasing pulse is used, even in the lower limb blood vessel whose flow velocity is lower than that of the abdomen or chest, the arteriovenous vein is clearly separated from the relative signal value difference as shown in FIG. It can be displayed with high rendering ability.
[0100]
In this way, in order to give a relative difference in the signal value between the arteriovenous vein, the read gradient magnetic field pulse is applied in the same direction as the flow direction, and the dephasing and rephasing of the magnetized spin are actively used. The technique for controlling the flow void effect is a novel technique first developed by the present inventors.
[0101]
In this embodiment, since the optimal ECG synchronization timing for the systole and the diastole is set in advance by the ECG-prep scan, the target blood flow is reliably captured in each time phase of the systole and the diastole. be able to. Furthermore, the optimal setting of the electrocardiogram synchronization timing eliminates the need for re-imaging, thereby reducing the operational burden on the operator and the physical and mental burden on the patient.
[0102]
In addition, since the slice direction or slice encode direction can be taken in directions other than the patient's vertical direction, the entire scan time is compared with a method of imaging in the vertical direction perpendicular to the blood flow, such as the TOF method. It's short. This reduces the burden on the patient and increases patient throughput.
[0103]
Furthermore, since it is not necessary to administer a contrast medium, non-invasive imaging can be performed, and the mental and physical burden on the patient is remarkably reduced from this point. At the same time, it is freed from the troublesomeness inherent in contrast methods, such as the need to measure the timing of contrast effects, and unlike contrast methods, it enables repeated imaging as required.
[0104]
(Modification of the first embodiment)
In the above-described embodiment, as shown in FIG. 8, the read gradient magnetic field pulse G is used for both the first and second imaging scans._RDephase pulse P_dephaseOr rephase pulse P_rephaseIt explained in the aspect which adds.
[0105]
As a modified example of this mode, a dephase pulse P as shown in FIG._dephaseOn the other hand, the rephase pulse P shown in FIG. 5B is added to the second imaging scan performed in the time phase of the systole._rephaseMay be added.
[0106]
That is, the type of control pulse that additionally controls the behavior of the magnetized spin is changed according to the systole and the diastole. Thereby, the signal value can be increased by reflecting the effect of rephase (flow compensation) in the expansion period, and the S / N can be improved.
[0107]
(Second Embodiment)
Next, a second embodiment according to the present invention will be described with reference to FIGS. Note that the hardware configuration of the MRI apparatus used in this embodiment is the same as or equivalent to that of the first embodiment.
[0108]
In the second embodiment, the first imaging scan and the second imaging scan executed in the first embodiment are executed in one imaging scan, and the systolic and diastolic phases of the cardiac cycle are performed. In addition, the present invention relates to a configuration in which the aforementioned dephasing pulse and rephasing pulse are used properly.
[0109]
Assume that a separated image of the arteries and veins of the lower limb is obtained as a low-speed fluid. As shown in FIG. 16, an ECG-prep scan is first performed, and then one imaging scan is performed under the electrocardiographic synchronization method. The ECG-prep scan is performed by the method described in the first embodiment, whereby the delay time T from the R wave that provides the most visualization capability in the systole and the diastole._DL1And T_DL2Are set respectively.
[0110]
Next, this delay time T_DL1And T_DL2An imaging scan based on the electrocardiographic synchronization method based on is performed as one imaging. The procedure of this imaging scan is illustrated in FIGS. 17 and 18, and the pulse sequence used for this scan is illustrated in 19.
[0111]
(2.1) Imaging scan
While executing a predetermined main program (not shown), the host computer 6 executes the processing shown in FIGS. 17 and 18 in response to operation information from the input device 13 as part of it.
[0112]
More specifically, the host computer 6 first determines that the optimal two delay times T determined by the operator through the ECG-prep scan described above are used._DL(That is, the optimal delay time T of the systole_DL1And the optimal delay time T of the diastole_DL2(> T_DL1)) Is input, for example, via the input device 13 (step S120). This optimum delay time T_DL1And T_DL2This information may be stored in advance in the storage unit 11, for example.
[0113]
Next, the host computer 6 inputs information on the scanning conditions and the image processing method, and the delay time T_DL1And T_DL2Is processed into control data, and the control data is output to the sequencer 5 and the arithmetic unit 10 as necessary (step S121).
[0114]
Next, as in the first embodiment, when the host computer 6 determines that preparation before scanning is completed, the host computer 6 is instructed to start breath holding and is instructed to start an imaging scan (steps S123 to S124).
[0115]
When the sequencer 5 receives a command to start an imaging scan (FIG. 18: Step S124-1), the sequencer 5 starts reading the ECG signal (Step S124-2), and determines a predetermined peak value of the R wave (reference waveform) in the ECG signal. The appearance of the nth time is determined from the ECG trigger signal synchronized with the peak value (step S124-3).
[0116]
When a predetermined n-th R wave appears, first, a delay time T set for a specific time phase of systole_DL1Only waiting processing is performed (step S124-4).
[0117]
This optimum delay time T_DL1The sequencer 5 performs a scan for the systole, assuming that the time point after the elapse is the optimal ECG synchronization timing (step S124-5).
[0118]
Specifically, the transmitter 8T and the gradient magnetic field power source 4 are driven according to the pulse sequence information that has already been stored, and for example, the first slice encode amount SE1 based on the pulse sequence of the first three-dimensional FASE method is used. Scan SN_sys1Is executed by an electrocardiographic synchronization method as shown in FIG.
[0119]
This first scan SN_sys1Then, the readout gradient magnetic field pulse GR is applied in the body axis direction substantially along the arteriovenous veins of the lower limbs. Also, this readout gradient magnetic field pulse G_RIncludes a dephase pulse P that disperses the phase of the magnetized spin._dephaseAs shown in the figure, the front and rear are added continuously in time. Further, the echo interval in this pulse sequence is shortened to about 5 msec.
[0120]
The first scan SN for this systole_sysnAs shown in FIG. 19, the number of echoes is set to be short, and the pulse sequence used for is finished within a short time within one heartbeat from the start of scanning. As schematically shown in FIG. 20, the number of echoes is set so as to be sufficient to collect the echo data arranged only in the central portion (low frequency region) in the phase encoding ke direction of the k space for each slice encoding amount. . For this reason, the second scan SN for the diastole_dian19 and 20, the first scan SN for systole_sysnYou can start within the same heartbeat. Also, systolic k-space (first k-space) K_sysThe echo data that is lacking in is the expansion k space (second k space) K described later._diaAnd a calculation based on the half Fourier method (see FIG. 20).
[0121]
As a result, echo signals are collected from the three-dimensional imaging region Rima (see FIG. 10) set on the lower limbs with a short scan time of about several hundreds msec under the initial slice encoding amount SE1.
[0122]
Next, the sequencer 5 shifts to scan control in the expansion period. Specifically, the delay time T set for the specific time phase of the diastole_DL2Only waiting processing is performed (step S124-6).
[0123]
This optimum delay time T_DL2The sequencer 5 executes the second scan for the diastole (step S124-7), assuming that the time at which elapses is the optimum ECG synchronization timing (step S124-7). Specifically, the transmitter 8T and the gradient magnetic field power source 4 are driven according to the pulse sequence information that has already been stored, and for example, the second slice encoding amount SE1 based on a pulse sequence of the first three-dimensional FASE method is used. Scan SN_dia1Is executed by an electrocardiographic synchronization method as shown in FIG.
[0124]
This second scan SN_dia1Also, the readout gradient magnetic field pulse GR is applied in the body axis direction substantially along the arteriovenous veins of the lower limbs. Also, this readout gradient magnetic field pulse G_RIncludes a rephasing pulse P for rephasing the magnetized spin._rephaseAs shown in the figure, the front and rear are added continuously in time. The echo interval in this pulse sequence is also shortened to about 5 msec.
[0125]
The second scan SN in this expansion period_dianAs shown in FIG. 19, the pulse sequence used for is set to collect more echoes than the systole, but to collect fewer echoes than the number of echoes that fill the entire k space by using the half Fourier method. . As schematically shown in FIG. 20, the number of echoes is collected for each slice encode amount by collecting echo data arranged only in the center (low frequency region) and one end (high frequency) of the phase encoding ke direction in the k space. It is set to be sufficient. Expansion space k-space K_dia, The missing echo data is obtained by calculation based on the half Fourier method, as will be described later. Scan SN in this diastole_dia1As shown in FIGS. 19 and 20, scanning is usually performed over the next heartbeat.
[0126]
Thus, echo signals are collected from the three-dimensional imaging region Rima (see FIG. 10) set on the lower limbs with a scan time of about 600 msec based on the first slice encoding amount SE1.
[0127]
When these first imaging scans are completed, the sequencer 5 determines whether or not the final scan has been completed (step S124-8). If this determination is NO (the final scan has not been completed), the ECG signal Monitoring, for example, from the R wave used in the imaging scan, for example, 2 heartbeats (2R-R), and wait for a short period of time to elapse, and recover the longitudinal magnetization of the stationary part of the spin. It actively suppresses (step S124-9).
[0128]
Thus, for example, after waiting for a period corresponding to 2R-R, for example, when the third R wave appears from the start of scanning (YES in step S124-9), the sequencer 5 performs the process in step S124-4 described above. return.
[0129]
As a result, the delay time T is calculated from the third R wave peak value._DL1At the time when elapses, the first scan SN for the second systole according to the next slice encoding amount SE2_sys2Is executed in the same manner as described above, and the three-dimensional imaging region R_imaEcho signals are collected from (step S124-4, 5). Furthermore, the delay time T is calculated from the third R wave peak value._DL2At the time when elapses, the second scan SN for the second diastole according to the slice encoding amount SE2_dia2Is executed in the same manner as described above, and the three-dimensional imaging region R_imaEcho signals are collected from (step S124-6, 7).
[0130]
Similarly, echo signals are collected for the systole and the diastole until the final slice encoding amount SEn (for example, n = 8).
[0131]
Last scan SN with slice encoding amount SEn_sysn, SN_dianWhen the process is completed, the determination in step S124-8 is YES, and an imaging scan completion notice is output from the sequencer 5 to the host computer 6 (step S124-10). As a result, the processing is returned to the host computer 6.
[0132]
Upon receiving the scan completion notification from the sequencer 5 (FIG. 17: step S125), the host computer 6 outputs a breath holding release command to the voice generator 16 (step S126).
[0133]
Therefore, as schematically shown in FIG. 19, in one imaging scan (imaging), for example, every 2R-R, the electrocardiographic scan for the systole and the diastole is performed by n 3D-FASE method, for example. It is executed for the slice encoding amount.
[0134]
The echo signal generated from the patient P is converted into digital amount of echo data as in the first embodiment. This echo data is sent to the arithmetic unit 10 through the sequencer 5 and is formed by a memory in a three-dimensional k-space K for systole and diastole._sysAnd K_diaThey are arranged corresponding to the phase encoding amount and the slice encoding amount, respectively.
[0135]
(2.2) Data processing and image display
When the echo data collection is thus completed, the host computer 6 instructs the arithmetic unit 10 to execute the processing shown in FIG.
[0136]
As shown in FIG. 21, the arithmetic unit 6 responds to a command from the host computer 6 and uses the systolic k-space K._sysAnd expansion space k-space K_diaAll the data arrangements are completed (steps S131 and S132). Specifically, in step S131, as shown in FIG._diaThe echo data of one high-frequency region Re in the phase encoding direction (echoes of numbers h to n in FIG. 20) is the systolic k-space K._sysIs copied to the corresponding position. This echo data is data of an area that was not collected by the systolic scan. Next, the process proceeds to step S132, and the systolic k-space K_sysAnd expansion space k-space K_diaThe half Fourier method is individually applied to both, and the data of the remaining area where the echo data has not been collected is calculated according to the complex conjugate relation and arranged. Therefore, both k-spaces K are processed through the processing of steps S131 and S132._sysAnd K_diaAre all filled with data.
[0137]
Thereafter, the arithmetic unit 10 determines the k-space K for systole._sysAnd expansion space k-space K_diaRespectively, image reconstruction by three-dimensional Fourier transform is performed (steps S133 and S134). As a result, as shown in FIGS. 12 (a) and 12 (b), the delay time T in the systole._DL1Image (systolic image) IM_sysAnd delay time T in diastole_DL2Images (diastolic images) IM_dia3D data is obtained. According to this image data, the systolic image IM_sysOnly the vein VE is reflected in the image, and the artery AR is hardly reflected. Meanwhile, diastolic image IM_diaIn FIG. 5, the arterial AR and the vein VE are reflected to some extent.
[0138]
Therefore, the arithmetic unit 10, as in the first embodiment (see FIGS. 12 to 14), calculates the difference calculation “IM_dia-ΒIM_sysPhase image IM_ARGeneration (step S135), the difference calculation “IM_dia-IM_ARVenous phase image IM_VEGeneration (step S136), arterial phase image IM_ARAnd vein phase image IM_VEEach MIP (maximum value projection) process (step S137), two-dimensional image display of arterial phase and vein phase, and storage of image data (step S138) are sequentially executed.
[0139]
(2.3) Effects
As described above, in the MRI apparatus of the present embodiment, the readout gradient magnetic field pulse G is applied during the imaging scan._RIs applied in accordance with the flow direction of the lower limb blood vessel, and the gradient magnetic field pulse G applied during the systole._RDephase pulse P_dephaseAnd rephase pulse P applied to that applied in diastole_rephaseAre added.
[0140]
As a result, similar to the behavior control of the magnetization spin described in the first embodiment, the signal value can be lowered by giving a flow void promoting effect to the artery, particularly in the systole, while the diastole. The flow compensation effect can be positively given to the arteries and the arterial flow.
[0141]
Therefore, the relative signal value difference between the flowing blood flow and the blood flow flowing only at a lower speed is made significant by the dephasing pulse and the rephasing pulse, and the flow velocity is higher than that of the abdomen and the chest. Even in a low limb blood vessel, the arteriovenous vein can be clearly separated and displayed with high rendering ability based on the relative signal value difference.
[0142]
Further, according to the MRI apparatus of the present embodiment, the optimum scan start timing (delay time from the R wave) is set for each systole and diastole within one cardiac cycle. Then, the two-shot scans of the systole and the diastole for one slice encoding are alternately executed sequentially in one imaging scan. Moreover, the first systolic scan within one cardiac cycle shortens the data acquisition time (number of echoes) so that subsequent diastolic scans do not take time, and the collected echo data is used for the systolic phase. It is arranged in a low frequency region that is most important in terms of improving contrast in the k space. Data deficient in systolic k-space is supplemented by copying data obtained in subsequent diastolic scans that can perform echo acquisition relatively long. In addition, the half-Fourier method is adopted for each scan for systole and diastole, and the scan time is set as short as possible.
[0143]
For this reason, the two-shot scan for the systole and the diastole for one-slice encoding usually falls within about two heartbeats. Thus, by repeating these scans alternately one after another, echo data of systolic and diastolic blood flows is collected within one breath holding continuation period in one imaging. That is, three-dimensional data of systolic and diastolic blood flows are collected individually and at optimum timing by one imaging.
[0144]
Therefore, it is not necessary to individually perform imaging scans for the systole and the diastole (that is, to perform imaging twice in total), and only one imaging is necessary. Therefore, imaging time is significantly reduced and patient throughput is increased. In particular, the effect of shortening the imaging time becomes significant when performing three-dimensional imaging. In addition, since misregistration due to patient movement and the like can be greatly reduced, the quality of the presented image is improved. Further, since a blood flow image (MRA image) obtained by separating the arterial phase and the venous phase can be obtained from the two-phase echo data collected by one imaging, the imaging efficiency is good and the blood to be provided is provided. The flow information is also abundant.
[0145]
Moreover, according to this 2nd Embodiment, the other effect obtained in 1st Embodiment can be enjoyed similarly.
[0146]
(Modification of the second embodiment)
In the first and second imaging scans of the second embodiment described above, as shown in FIG. 19, a dephasing pulse is added to the readout gradient magnetic field pulse for systole, and the readout for diastole. A rephase pulse was added to the gradient magnetic field pulse. On the other hand, only the dephasing pulse may be added to the readout gradient magnetic field pulses for systole and diastole. As a result, as in the first embodiment (see FIG. 8), it is possible to reflect the degree of promotion of the flow void effect due to different blood flow velocities for each time phase in the intensity of the signal value. Can be reliably separated.
[0147]
(Modification common to each embodiment)
In addition, this invention is not limited to the structure as described in each embodiment mentioned above, Furthermore, various deformation | transformation structures and applications are possible.
[0148]
For example, in the above-described embodiment, both the arterial phase image and the venous phase image are presented. However, for this, only the arterial phase image may be calculated and displayed. That is, the difference calculation for the vein phase image in step S136 of FIG. 21 can be omitted. On the contrary, although the difference calculation of the images of the arterial phase and the venous phase is performed together, the displayed image may be only the arterial moving image.
[0149]
Further, in each of the above-described embodiments, the scan method using the half Fourier method is adopted for each of the scans for the systole and the diastole, but the half Fourier method is not necessarily adopted. Good. In this case, it is preferable that the k space is fully collected by the diastolic scan, and the echo data in the high frequency region at both ends of the slice encoding direction is copied to the corresponding region in the systolic k space.
[0150]
Furthermore, although the above-described embodiment has been described with respect to the case where the three-dimensional scan is performed, this can be similarly applied to the two-dimensional scan imaging. The employed pulse sequence is not limited to the FASE method, and a sequence of FSE method or FASE method using an inversion recovery (IR) pulse may be employed.
[0151]
Further, the post-processing of the echo data according to the above-described embodiment is configured to convert the echo data into real-space image data once, and then perform a difference calculation to obtain images of the arterial phase and the venous phase. However, such a difference calculation may be performed with the echo data on the k-spaces Ksys and Kdia having the same matrix size, and the echo data as the difference result may be reconstructed to obtain a blood flow image.
[0152]
Further, as a configuration for detecting a signal representing the heartbeat of the subject, for example, a detection signal called PPG (peripheral gating) for detecting a pulse wave of a fingertip with an optical signal is used instead of the above-described ECG signal detection. You may do it.
[0153]
Furthermore, the MRI apparatus according to each of the above-described embodiments and modifications thereof is configured to create one image data from two cardiac phase image data. However, according to another aspect of the present invention, this is not necessarily the case. It is not limited to. For example, a readout gradient magnetic field pulse to which a dephasing pulse or a rephasing pulse is added is applied so that it substantially coincides with the flow direction of the fluid (blood, lymph, etc.), and one imaging scan is performed regardless of the cardiac phase. A single image may be obtained by going. In this image, the fluid reflecting the degree of promotion of the flow void effect is reflected in bright or black, so that flow information regarding the fluid can be given.
[0154]
Furthermore, means for controlling the intensity of the aforementioned dephasing pulse or rephasing pulse according to the flow velocity of the fluid to be imaged can be provided. This means comprises, for example, the input device 13, the host computer 6, and / or the storage unit 11. When the operator inputs information specifying the imaging region and the fluid from the input device 13, the host computer 6 refers to a table (stores the pulse intensity for each fluid) stored in the storage unit 11 in advance, and according to the reference result. Thus, the intensity of the dephase pulse or rephase pulse may be output to the sequencer 5. In addition, the operator can directly give the pulse intensity via the input device 13.
[0155]
The description of the embodiment is as described above, but the present invention is not limited to the configuration described in the embodiment, and those skilled in the art can appropriately change the configuration without departing from the gist described in the claims. These can be modified, and their configurations are also included in the present invention.
[0156]
【The invention's effect】
  As described above, according to the MRI apparatus of the present invention,Without administering a contrast agent, it is possible to reliably depict a low flow rate flow seen in a fluid such as a blood flow in the lower limb with high image quality.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a configuration example of an MRI apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining a time series relationship between an ECG-prep scan and two imaging scans according to the first embodiment.
FIG. 3 is a schematic flowchart illustrating an ECG-prep scan procedure.
FIG. 4 is a timing chart illustrating a time series relationship with respect to an ECG signal in an ECG-prep scan.
FIG. 5 is a schematic image diagram obtained by ECG-prep scan when the delay time is dynamically changed.
FIG. 6 is a schematic flowchart showing an example of the first and second imaging scans.
FIG. 7 is a schematic flowchart showing an example of the first and second imaging scans.
FIG. 8 is a timing chart illustrating the timing of first and second imaging scans based on an electrocardiographic synchronization method in the first embodiment.
FIG. 9 is a diagram for explaining a dephasing pulse and a rephasing pulse to be added to a read gradient magnetic field.
FIG. 10 is a diagram for explaining the positional relationship between a three-dimensional imaging region and a blood vessel to be imaged.
FIG. 11 is a schematic flowchart for explaining echo data calculation and display processing in the first embodiment;
FIG. 12 is a schematic diagram illustrating an outline of difference calculation for obtaining an arterial phase image.
FIG. 13 is a schematic diagram illustrating an outline of difference calculation for obtaining a vein phase image.
FIG. 14 is a diagram illustrating a simultaneous display state of an arterial phase image and a venous phase image.
FIG. 15 is a pulse sequence of two imaging scans performed in a modification of the first embodiment.
FIG. 16 is a diagram for explaining a time-series relationship between an ECG-prep scan and one imaging scan according to the second embodiment of the present invention.
FIG. 17 is a schematic flowchart showing an example of an imaging scan.
FIG. 18 is a schematic flowchart showing an example of an imaging scan.
FIG. 19 is a timing chart illustrating the timing of an imaging scan based on the electrocardiogram synchronization method according to the first embodiment.
FIG. 20 is a diagram for explaining a state in which echo data collected during systole and diastole are arranged in k-space.
FIG. 21 is a schematic flowchart for explaining echo data calculation and display processing in the second embodiment;
[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 ECG sensor
18 ECG units

Claims (17)

Two cardiac time phases of a subject placed in a static magnetic field are set, and first and second scans based on a magnetic resonance imaging pulse sequence including a readout gradient magnetic field pulse are performed in the two cardiac time phases, respectively. Signal collecting means for collecting echo signals from the subject by performing ;
Image generating means for generating an image of fluid in the subject based on the echo signal ,
The readout gradient magnetic field pulse has a pulse body for reading out the echo signal, and a control pulse for controlling the phase behavior of the magnetization spin of the fluid,
Of the two cardiac time phases, the control pulse of the readout gradient magnetic field pulse of the pulse sequence used for the first scan in one cardiac time phase is formed by a pulse that bears the dephase of the magnetization spin, The MRI apparatus , wherein the control pulse of the readout gradient magnetic field pulse of the pulse sequence used for the second scan in the cardiac phase is formed by a pulse responsible for rephasing the magnetization spin . The MRI apparatus according to claim 1,
The signal collecting means sets a time phase belonging to the diastole of the subject as the one cardiac time phase and sets a time phase belonging to the systole of the subject as the other cardiac time phase. A featured MRI system. The MRI apparatus according to claim 1,
The signal collecting means sets a time phase belonging to the systole of the subject as the one cardiac time phase and sets a time phase belonging to the diastole of the subject as the other cardiac time phase. MRI apparatus shall be the feature. The MRI apparatus according to claim 1 ,
The signal acquisition means, said first and second scan, MRI device you being a means for sequentially performed in the image pickup is set to the same slice or slice encode amount. In the MRI apparatus according to any one of claims 1 to 4 ,
The fluid, MRI device you wherein a blood in the subject. The MRI apparatus according to claim 5, wherein
The blood is arteriovenous blood of the lower limb of the subject,
It said image generation means, MRI device you and generating an image separating the arteriovenous. In the MRI apparatus according to any one of claims 1 to 6 ,
It said first and second scan, MRI device you being a scan based on the half-Fourier method. The MRI apparatus according to claim 7, wherein
The first scan is a scan based on a pulse sequence for generating an echo signal for arranging echo data in a central region that forms a low frequency region in the phase encoding direction of the first k space,
The second scan is a pulse for generating an echo signal for arranging echo data in a central region forming a low frequency region and one of both end portions forming a high frequency region in the phase encoding direction of the second k space. MRI device you being a scan depends on the sequence. The MRI apparatus according to claim 8, wherein
The image generating means includes
In each of the first k space in which the echo data is collected by the first scan and the second k space in which the echo data is collected by the second scan, the echo data is calculated by the calculation according to the half Fourier method. Computing means for generating and arranging
Copy means for copying echo data of an area that is a part of the second k space and that corresponds to the uncollected area with respect to an uncollected area remaining on the first k space;
An MRI apparatus characterized by comprising: The MRI apparatus according to claim 9 , wherein
The image generation means performs an operation between the first k-space echo data or the image data thereof and the second k-space echo data or the image data thereof, so that echo data relating to the arterial phase image is obtained. Alternatively, an MRI apparatus comprising an arterial phase image generation means for obtaining the image data . The MRI apparatus according to any one of claims 1, 6 , and 10,
Wherein the operations performed by the image generating means, difference calculation, weighting the difference calculation, or, MRI device you being a summing operation. The MRI apparatus according to claim 10 , wherein
The image generation means performs a difference calculation between the echo data regarding the arterial phase image obtained from the arterial phase image generation means or the image data thereof and the echo data of the second k space or the image data thereof. in, MRI device you characterized as having echo data or venous phase image generating means for obtaining the image data regarding venous phase images. In the MRI apparatus according to any one of claims 7 to 12 ,
It said first and second scan, MRI device you being a two-dimensional scanning or three-dimensional scanning. In the MRI apparatus according to any one of claims 7 to 13 ,
A pulse sequence used for the first and second scans is a pulse train based on FASE (Fast Asymmetric SE) method, EPI (Echo Planar Imaging) method, FSE (Fast SE) method, or SE method. MRI apparatus you. In the MRI apparatus according to any one of claims 1 to 3 ,
The signal collecting means includes
A plurality of preparatory MR sequences are executed on the imaging region of the subject a plurality of times at different times from the periodic heartbeat reference wave that appears in the signal representing the cardiac time phase of the subject detected by the detecting means. Preparation means for obtaining one MR image;
Means for determining the two time phases from a plurality of MR images obtained by the preparation means;
MRI device further comprising a. The MRI apparatus according to claim 15 , wherein
The signal representing the cardiac phase is an ECG signal or a PPG signal of the subject,
The heartbeat reference wave, MRI device you being a R-wave of the ECG signal or the PPG signal. In the MRI apparatus according to any one of claims 1 to 4 ,
The fluid, MRI device you wherein a lymph in the subject.

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