JP4090619B2 - MRI equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to magnetic resonance imaging for imaging the inside of a subject based on the magnetic resonance phenomenon of the subject. In particular, even without using a contrast agent, MRI (MR) for MR angiography, which collects echo signals in a short imaging time by applying an ECG gate (electrocardiogram gating) with an optimal delay time, and visualizes blood flow. ) Apparatus and MR imaging method.
[0002]
As used herein, “blood (or blood flow)” is used to mean “fluid” representing cerebral spinal fluid, blood (blood flow), and the like flowing in the subject.
[0003]
[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. .
[0004]
In the field of magnetic resonance imaging, when an blood flow image of a lung field or abdomen is obtained, clinically, MR angiography is being performed in which a contrast medium is administered to a subject to perform angiography. However, this contrast-enhanced MR angiography method requires an invasive treatment because a contrast agent is administered, and 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.
[0005]
When contrast agents cannot be administered, other imaging methods can only be used, but time-of-flight (TOF) and phase contrast (PC) methods are known as alternative methods. It has been. The flow effect in magnetic resonance imaging 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, even when the above-described TOF method or phase contrast method is used, an MR image of the lung field or the abdomen is obtained, and if an attempt is made to depict the flow in the superior-inferior direction of a large blood vessel such as the aorta, blood It is necessary to take an image perpendicular to the flow direction. That is, an axial image is taken with the slicing direction set in the vertical direction, and when a 3D (three-dimensional) image is obtained, the number of images to be captured increases, and the entire imaging time becomes considerably long.
[0007]
The present invention has been made to break down the state of the art as described above, and one of its purposes is to obtain an MRA image non-invasively without administering a contrast agent, This is to greatly reduce the imaging time.
[0008]
Another object of the present invention is to be able to depict blood pumped from the heart in a non-invasive manner without administering a contrast agent, and to significantly reduce the imaging time for collecting data necessary for this visualization. It is to be.
[0009]
In addition, another object of the present invention is that a non-invasive, arterial and vein-separated image can be suitably depicted without administering a contrast agent, and the imaging time required for collecting the data necessary for this rendering is greatly increased. To shorten it.
[0011]
[Means for Solving the Problems]
  In order to solve the above-described problem, the invention according to claim 1 represents the cardiac time phase of the subject collected by the time phase detection means in the MRI apparatus that generates the MRA image of the imaging region of the subject. An imaging scanning means for executing a three-dimensional scan in which an echo signal corresponding to a predetermined slice encoding amount is collected in a diastole in synchronization with the signal, and an echo signal obtained by the three-dimensional scan. And generating means for generating a three-dimensional MRA image of the imaging region of the subject that does not use a contrast agent.
  According to a tenth aspect of the present invention, in the MRI apparatus for generating the MRA image of the imaging region of the subject, the first delay time is delayed from the reference waveform representing the cardiac time phase of the subject for a predetermined slice encoding amount. A first three-dimensional scan that repeats the operation of collecting echo data for each of a plurality of heartbeats is performed, and an operation of collecting echo data for a predetermined slice encoding amount by delaying a second delay time from the reference waveform is performed for a plurality of heartbeats. An imaging scanning unit that performs a second three-dimensional scan that repeats every time, and a first three-dimensional that does not use a contrast agent in the imaging region of the subject based on an echo signal obtained by the first three-dimensional scan A second 3 that generates an MRA image and does not use a contrast agent in an imaging region of the subject based on an echo signal obtained by the second three-dimensional scan Generating means for generating an original MRA image, it is characterized in that it comprises a data processing means for subtracting the first and second three-dimensional MRA image.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below.
[0030]
(First embodiment)
A first embodiment will be described with reference to FIGS.
[0031]
A schematic configuration of an MRI (magnetic resonance imaging) apparatus according to this embodiment is shown in FIG.
[0032]
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.
[0033]
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.
[0034]
The gradient magnetic field generator includes a gradient magnetic field coil unit 3 incorporated in the magnet 1. The gradient coil unit 3 includes three sets (types) of x, y, and z coils 3x to 3z for generating gradient magnetic fields in the X, Y, and Z axis directions orthogonal to each other. The gradient magnetic field unit also includes a gradient magnetic field power supply 4 that supplies current to the x, y, and z coils 3x to 3z. The gradient magnetic field power supply 4 supplies a pulse current for generating a gradient magnetic field to the x, y, z coils 3x to 3z under the control of a sequencer 5 described later.
[0035]
By controlling the pulse current supplied from the gradient magnetic field power source 4 to the x, y, z coils 3x to 3z, the gradient magnetic fields in the three axes X, Y, and Z, which are physical axes, are synthesized and slices orthogonal to each other. The logical axis directions of the direction gradient magnetic field Gs, the phase encode direction gradient magnetic field Ge, and the readout direction (frequency encode direction) gradient magnetic field Gr can be arbitrarily set and changed. Each gradient magnetic field in the slice direction, the phase encoding direction, and the readout direction is represented by a static magnetic field H.₀Is superimposed on.
[0036]
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 the MR signal (high frequency signal) received by the RF coil 7 and performs various signal processing such as preamplification, intermediate frequency conversion, phase detection, low frequency amplification, filtering, etc. Digital data (original data) of MR signal is generated by / D conversion.
[0037]
The control / arithmetic unit further includes a sequencer (also referred to as a sequence controller) 5, a host computer 6, an arithmetic unit 10, a storage unit 11, a display device 12, an input device 13, and a sound generator 16. Among these, the host computer 6 has a function of instructing the pulse sequence information to the sequencer 5 according to the stored software procedure (not shown) and supervising the operation of the entire apparatus.
[0038]
This MRI apparatus is characterized by performing a 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. An imaging scan for executing the imaging pulse sequence (hereinafter referred to as an imaging scan) is performed while executing a main program (not shown). An example of an ECG-prep scan execution routine is shown in FIG. 3, and an example of an imaging scan execution routine based on electrocardiogram synchronization is shown in FIGS.
[0039]
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.
[0040]
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, and the pulse train may have a high-speed SE method. The EPI (Echo Planar Imaging) method, the FASE (Fast Asymmetric SE) method (that is, an imaging method in which the fast SE method is combined with the half Fourier method), and the like are suitable.
[0041]
Further, the arithmetic unit 10 inputs the digital data (original data) output from the receiver 8R through the sequencer 5, and the original data (also referred to as raw data) in the Fourier space (also referred to as k space or frequency space) in the internal memory. The original data is subjected to a two-dimensional or three-dimensional Fourier transform for each set and reconstructed into real space image data. The arithmetic unit is adapted to perform data composition processing and difference calculation processing on the image. This composition processing includes processing for adding image data of a plurality of frames for each corresponding pixel, maximum value projection (MIP) processing for selecting a maximum value for each corresponding pixel between the image data of a plurality of frames, 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.
[0042]
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.
[0043]
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.
[0044]
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 is used by the sequencer 5 when executing each of the ECG-prep scan and the electrocardiographic synchronization imaging scan. Accordingly, the synchronization timing of the electrocardiographic synchronization method can be set appropriately, and data can be collected by performing an electrocardiographic imaging scan based on the set synchronization timing.
[0045]
Next, synchronization timing determination processing for an imaging scan based on electrocardiogram synchronization will be described with reference to FIGS.
[0046]
The host computer 6 starts executing 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).
[0047]
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 condition includes a scan type, a pulse sequence, a phase encoding direction, 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.
[0048]
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.
[0049]
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.
[0050]
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
[0051]
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 be the same as the imaging pulse sequence described later, and is, for example, the FASE (Fast Asymmetric SE) method in which the fast SE method is combined with the 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 the main scan (imaging scan) for collecting image data is a three-dimensional (3D) method, or according to the area of the main scan. Alternatively, a three-dimensional scan may be performed.
[0052]
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.
[0053]
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."
[0054]
When the above-described processes are sequentially executed, as an example, a 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. 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 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.
[0055]
  Then, when the number counter CNT has not reached the predetermined value, the processing from step S5 to step S11 is 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. When this scan is finished and the next R wave appears, the delay time TDL = 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, when this scan is finished and the next R wave appears, the delay time T_DL= T₀+ 3 · T_inc= After 600 msec, the fourth timeScan IMG _prep4 ButThe echo signal is collected in the same manner for a predetermined time. 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.
[0056]
The echo data is sequentially sent to the arithmetic unit 10 via the receiver 8R and the sequencer 5. The arithmetic unit 10 reconstructs k-space echo data into real-space image data by a two-dimensional Fourier transform method. This image data is stored in the storage unit 11 as MRA image data. For example, in response to an operation signal from the input unit 13, the host computer 6 sequentially displays the MRA images in cine.
[0057]
FIGS. 5A to 5E show display examples of a plurality of MRA images obtained by collecting and reconstructing echo data in a state where the electrocardiographic synchronization delay signal (synchronization timing) is dynamically changed. These figures show the 2D-FASE method (effective TE (TE_eff) = 40 ms, echo interval (ETS) = 5 ms, number of shots = 1, slice thickness (ST) = 40 mm, number of slices (NS) = 1, number of added images (NAQ) = 1, matrix size = 256 × 256, FOV = 40 × 40 cm, actual scan time = about 500 ms), and phase encode direction = vertical direction of the figure (body axis direction). The blood flow as the target entity in this image is the descending aorta. In the figure, each of the delay times TDL is T in (a)._DL= 300 msec, (b) T_DL= 400 msec, (c) T_DL= 500 msec, (d) T_DL= 600 msec, (e) T_DL= 700 msec.
[0058]
When these cine display images are visually observed, the echo signal from the aortic flow appears most strongly in the MRA image in FIG. In the other MRA images (a) to (d), the range in which the aortic flow is reflected is very small or short compared to (e), and the velocity of blood flow accompanying pulsation is high. Due to factors such as low, the intensity of the echo signal is relatively low, and it is close to the flow void phenomenon. That is, when obtaining an MRA image of the aortic flow in the lung field, in this experiment, the state shown in FIG._DL= 700 msec is optimal. As a result, the synchronization timing of the electrocardiogram synchronization is determined by the delay time T from the R wave peak arrival time._DLIt turns out that the time is 700 msec later.
[0059]
Therefore, the operator determines the optimum image, that is, the optimum delay time TDL by visual determination from the plurality of MRA images picked up by dynamically changing the delay time TDL in this manner, and performs the delay time parameter continuously. Perform the process to be reflected in the scan.
[0060]
Furthermore, in the ECG-prep scan described above, the phase encoding direction is intentionally set to a direction (body axis direction) along the traveling direction of the aortic flow. As a result, compared with the case where the phase encoding direction is set to other directions, it is possible to capture more clearly without missing or dropping the traveling direction (directionality) of the aortic flow, and the imaging performance is excellent. Yes. The reason for this will be described below.
[0061]
In general, blood flow represented by pulmonary blood vessels and liver blood vessels (portal veins) is T₂Time is slightly shorter (T₂= 100 to 200 ms). This T₂The shorter blood flow is T₂CSF and joint fluid (T₂It has been found that the full width at half maximum of the signal is wider than (> 2000 ms). This can be seen, for example, in the literature “R. TodCons-table and John C. Gore,“ The loss of small objects in Variable TE imaging: Implications for FSE ” 1992 ". According to the document, T₂As shown in FIG. 6, the spread of signal values for substances having different times is represented by “point spread function”. The graph of the figure shows a static magnetic field = 1.5 T, TE_eff = 240 ms, echo interval (ETS) = 12 ms, the horizontal axis represents the number of pixels on the image in the phase encoding direction, and the vertical axis represents the signal intensity in arbitrary units. According to this, T₂= T compared to 2000ms CSF and synovial fluid₂= 200 ms of blood (artery) has its full width at half maximum. This is T₂= 200 ms of blood (artery) is apparently equivalent to the fact that the width of the phase encoding direction per pixel is extended more than CSF and joint fluid. Therefore, T₂= 200 ms of blood (artery) indicates that the entire image is more blurred in the phase encoding direction than CSF or synovial fluid.
[0062]
Therefore, by making the phase encoding direction substantially coincide with the blood flow direction, T₂The degree of spread (blurring) on the pixel of the signal value in the phase encoding direction of blood with a short time is expressed as T₂The fact that the time is larger than the long one can be actively used, and the direction of blood flow is emphasized. Therefore, as described above, when selecting an optimal MRA image (that is, optimal delay time) for ECG synchronization, the selection is facilitated.
[0063]
Next, the operation of the imaging scan of this embodiment will be described with reference to FIGS.
[0064]
The host computer 6 executes a predetermined main program (not shown), and as a part thereof, executes the processing shown in FIG. 7 in response to operation information from the input device 13.
[0065]
More specifically, the host computer 6 first inputs the optimum delay time TDL determined by the operator through the ECG-prep scan described above, for example, via the input device 13 (step S20). Next, the host computer 6 scans information specified by the operator from the input device 13 (phase encoding direction, image size, number of scans, waiting time between scans, pulse sequence corresponding to the scan region, etc.) and image processing method information. (Addition processing or maximum value projection (MIP) processing, etc. In the case of addition processing, any of simple addition, addition averaging processing, weighted 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).
[0066]
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 manner as in the ECG-prep scan, so that the patient who hears it stops breathing (see FIG. 9). .
[0067]
Thereafter, the host computer 6 instructs the sequencer 5 to start an imaging scan (step S24).
[0068]
When the sequencer 5 receives a command to start an imaging scan (step S24-1), the sequencer 5 starts reading an ECG signal (step S24-2), and a predetermined n-th peak value of the R wave (reference waveform) in the ECG signal. Appearance 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_DLOnly waiting processing is performed (step S24-4). This delay time T_DLAs described above, the ECG-prep scan is optimized to a value that has the highest echo signal intensity when imaging a blood flow or tissue of interest, and has excellent entity rendering capability.
[0069]
This optimum delay time T_DLThe sequencer 5 executes an imaging scan on the assumption that the time at which elapses is the optimal ECG synchronization timing (step S24-5). Specifically, the transmitter 8T and the gradient magnetic field power source 4 are driven according to the pulse sequence information already stored, and for example, the first scan based on the pulse sequence of the three-dimensional FASE method is performed as shown in FIG. The process is executed synchronously (in the figure, the phase encoding direction gradient magnetic field is not shown). At this time, the phase encoding direction PE is made to substantially coincide with the designated direction, for example, the direction of blood flow (artery AR, vein VE) as shown in FIG. Further, the echo interval in this pulse sequence is shortened to about 5 msec. As a result, echo signals are collected from the three-dimensional imaging region Rima set in the lower abdomen, for example, as shown in the figure, with a scan time of about 600 msec based on the first slice encoding amount SE1.
[0070]
When this first imaging scan is completed, the sequencer 5 determines whether or not the final imaging scan has been completed (step S24-6). 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 suppresses positively (step S24-7). That is, this standby period becomes the repetition time TR.
[0071]
The repetition time TR is set shorter than the repetition time (about 5000 ms to 8000 ms) by the FASE method when imaging by MRCP or the like. Thereby, relaxation of the longitudinal magnetization of the spin in the stationary substantial part can be intentionally made insufficient. In contrast with the conventional method, the repetition time TR is set to 4 heartbeats (4R-R) or less.
[0072]
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._DLAt the time when elapses, the second imaging scan is executed in the same manner as described above in accordance with the next slice encoding amount SE2, 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).
[0073]
When the last imaging scan with the slice encoding amount SEn is completed, the determination in step S24-6 becomes YES, and the completion notification of the imaging scan is output from the sequencer 5 to the host computer 6 (step S24-8). As a result, the processing is returned to the host computer 6.
[0074]
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. 9).
[0075]
Therefore, as schematically shown in FIG. 9, for example, every 2R-R, an electrocardiographic imaging scan is performed n times (for example, 8 times) based on, for example, the 3D-FASE method.
[0076]
The eco signal generated from the patient P is received by the RF coil 7 and sent to the receiver 8R for each scan. The receiver 8R performs various preprocessing on the echo signal and converts it into a digital quantity. The digital amount of echo data is sent to the arithmetic unit 10 through the sequencer 5 and is arranged in a three-dimensional k-space formed by a memory. Since the half Fourier method is adopted, k-space data that has not been collected is obtained by calculation and buried in the k-space. When the echo data is arranged in the entire k space in this way, a three-dimensional Fourier transform is executed, and the echo data is converted into image data in the real space. This image data is further converted into two-dimensional tomographic image data by MIP processing. This tomographic image data is stored in the storage unit 11 and displayed on the display 12.
[0077]
In order to confirm the effect of the above-described configuration, the present inventor performed imaging of a coronal image depicting the abdominal aorta. The static magnetic field is O.D. 5T, and the pulse sequence used is a 3D-FASE sequence (TE_eff= 24.8 ms, ETS = 6.2 ms), a 256 × 256 matrix was executed with an 8-slice encoding amount every 3 heartbeats (3R-R), and a coronal image of the abdomen was obtained by MIP processing. The phase encoding direction was set up and down (the patient's body axis direction). The ECG delay time was 600 ms. The entire imaging time was about 23 seconds, and one breath was held. As a result, an excellent blood vessel rendering ability was confirmed.
[0078]
In this way, by setting the repetition time TR for each slice encoding to a short value such as 2R-R or 3R-R, the longitudinal magnetization relaxation of the stationary substantial part is positively insufficient, and the signal value from the substantial part Can be suppressed.
[0079]
In addition, blood with a relatively high flow rate that flows every heartbeat can be depicted by ECG synchronization. Optimum delay time T for executing the scan in the diastole when the blood flow is stable for each slice encoding._DLTherefore, the blood flow can be reliably captured and fresh blood discharged from the heart can always be scanned. The present inventor named this MR angiography technique “FBI (Fresh Blood Imaging) method”.
[0080]
A turbulent time zone that occurs immediately after the appearance of the R wave can be avoided, and a time zone in which the blood flow state is relatively stable can be selected and scanned. As a result, the influence of the turbulent blood flow can be eliminated, and the echo signal in a stable blood flow state can be arranged in the center area in the phase encoding direction of the k space, and the contrast of the reconstructed image can be increased.
[0081]
Therefore, it is possible to provide MR angiography having excellent blood flow rendering ability.
[0082]
In addition, the repetition time TR and the echo interval are set short, the phase encoding direction is made to substantially coincide with the blood vessel running direction, and the slice direction is set to the front and back of the patient's coronary direction (from the front to the back). Compared to a method of photographing perpendicularly to the blood flow such as, the entire scan time is shortened. Furthermore, since the imaging range (length) in the slice direction is shortened and the number of application times of slice encoding is reduced, the entire imaging time is significantly shortened compared to the conventional TOF method and phase encoding method. This reduces the burden on the patient and increases patient throughput.
[0083]
Concomitantly, since the entire imaging (multiple imaging scans) can be completed within one breath holding period, the burden on the patient is significantly reduced.
[0084]
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.
[0085]
Furthermore, since the phase encoding direction matches or substantially matches the traveling direction of the blood vessel, pixel blurring can be used positively, and thereby, the ability to depict the traveling direction of the blood vessel is excellent. By changing the phase encoding direction according to the blood vessel traveling direction of the imaging region, various regions can be easily dealt with.
[0086]
In addition, since a high-speed SE system pulse sequence is used, it is possible to naturally enjoy advantages in terms of susceptibility and distortion of form.
[0087]
Furthermore, since the synchronization timing of ECG synchronization is optimized in advance, there is almost no need to perform imaging again, the burden on the operator is reduced, patient throughput can be improved, and patient The burden is also reduced or suppressed.
[0088]
Further, in the case of the above-described embodiment, all the imaging scans are completed in one breath holding period. For this reason, it is possible to suppress the occurrence of body movement artifacts due to periodic movements of the lungs and the like, and to reduce the generation of body movement artifacts due to the positional deviation of the patient's body itself when performing breath-hold imaging multiple times. . As a result, a high-quality image with less artifacts can be provided.
[0089]
By the way, according to the present embodiment, a new composite image can be obtained from a plurality of images of echo data collected by changing the phase encoding direction. This composite image is based on the control of changing the encoding direction.₂Excellent ability to draw blood flow in a short time.
[0090]
(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. The MRI apparatus according to this embodiment is a further development of the configuration of the above-described embodiment. The MRI apparatus performs imaging by changing the delay time of ECG synchronization, and a plurality of MRA original images obtained by this imaging are mutually differentiated to obtain a specific blood vessel. It is characterized by drawing only.
[0091]
Note that the hardware configuration of this embodiment is the same as or equivalent to that described in the first embodiment.
[0092]
As schematically shown in FIG. 11, when the host computer 6 is instructed to draw a specific blood vessel such as an aorta (step S31), the ECG delay time T is sent to the sequencer 5._DL= Α1 (for example, 100 ms) and T_DL= Α2 (≠ α1: for example, 500 ms) is commanded for imaging scan (steps S32 and S33). These multiple types of delay times T_DLCan be set to an appropriate value as long as the values are different, and may be stored in advance by ECG-prep scanning or the like according to the type of blood vessel to be rendered. The operator may be allowed to input.
[0093]
These multiple types of delay times T_DLThe original data captured a plurality of times based on each is stored in the arithmetic unit 10 and the image reconstruction calculation is performed (step S34), as described above. Next, the host computer 6 instructs the arithmetic unit 10 to perform a weighted difference calculation for each pixel between the reconstructed sets of image data (step 35).
[0094]
Thus, as schematically shown in FIG. 12 as an example, for example, an ECG delay time T_DL= 100 ms 3D image data set and T_DL= A weighted difference calculation is performed with a set of 3D image data of 500 ms. As shown in FIG. 4A, the ECG delay time T_DLIf 100 ms is short, the pumped blood is turbulent, resulting in a flow void, the signal value of the arterial AR becomes almost zero (shown black in the actual image), and the vein VE Only the signals are collected. On the other hand, as shown in FIG._DL= 500 ms, which is an appropriate value, both the signals of the arterial AR and the vein VE are collected with appropriate strength. Therefore, the image data in FIGS. 7A and 7B are weighted and differentiated for each pixel, thereby obtaining three-dimensional image data in which only the artery AR is depicted as shown in FIG. In the case of the figure, the difference calculation using the weighting coefficient k of “(b) −k · (a)” is performed on the image data of FIGS. The weighting coefficient k is determined so that the image data of the vein VE is satisfactorily canceled by the difference calculation.
[0095]
Next, the host computer 6 instructs the arithmetic unit 10 to perform MIP processing on the differenced image data (step S36), and then displays it (step S37). Thereby, an MRA image that suitably depicts the artery AR is provided.
[0096]
As a result, the same operational effects as those of the first embodiment described above can be obtained, and in addition, only a desired blood vessel can be reliably depicted. It can contribute to improvement.
[0097]
In the difference calculation described above in the present invention, the difference calculation may be performed between two sets of three-dimensional original data (k-space data) having different ECG delay times, and then the reconstruction / MIP process may be performed. .
[0098]
(Third embodiment)
A third embodiment of the present invention will be described with reference to FIG.
[0099]
The MRI apparatus of this embodiment relates to another example of an imaging scan based on an electrocardiogram synchronization method, and is particularly characterized by the application of an MT pulse. With respect to the FBI method according to the present invention, the settings and configurations unique to the FBI method described above are inherited.
[0100]
The hardware configuration and imaging processing are the same as or similar to those in the first or second embodiment described above.
[0101]
In this embodiment, the delay time T of the ECG synchronization method_DLAfter (synchronization timing) is set to an optimum value using an image collected by the ECG-prep scan, an imaging scan shown in FIG. 13 is commanded by the sequencer 5 in the same procedure as described above. A breath-holding method is also used in this imaging scan.
[0102]
The sequence of the pulse sequence shown in FIG. 13 includes a predetermined delay time T for the R wave of the ECG signal for each sequence._DLSynchronize with. The pulse sequence for each shot (RF excitation) is the pre-sequence SQ applied first._preAnd the subsequent data collection sequence SQ_acqConsists of.
[0103]
Pre-sequence SQ_preIs the MT pulse train P causing the MT effect_MTAnd this MT pulse train P_MTGradient magnetic field spoiler pulse SP applied after application_S, SP_R, SP_EIncluding. MT pulse train P_MTAre a plurality of excitation RF pulses P sequentially applied as MT pulses.₁ , P₂ , P_Three , ..., P_nAnd a gradient magnetic field pulse G for slicing applied in parallel with these MT pulses._SIt consists of.
[0104]
Gradient magnetic field pulse G for slicing_S Applied intensity = G_S1Is set so that application of the MT pulse results in off-resonance RF excitation for the target imaging region. As an example, this gradient magnetic field pulse G for slicing_SThe selected area depending on the imaging area (G_S= G_S2(G_S1) And a position with a gap or a gap different from the above.
[0105]
Each MT pulse P₁ (P₂ , P_Three , ..., P_n) Is formed by a SINC function as an example, and the intensity is set so that the spin flip angle FA accompanying this pulse application is, for example, 90 °. MT pulse P₁ , P₂ , P_Three , ..., P_nThe total number is set to 10 as an example.
[0106]
That is, in this embodiment, instead of the conventional configuration in which one MT pulse having a large flip angle FA (for example, 500 ° to 1000 °) is applied by slice selection, this MT pulse is divided into a plurality of pieces, and sequentially. The configuration of the MT pulse train to be applied is adopted.
[0107]
Each MT pulse P₁ (P₂ , P_Three , ..., P_n) Is a value (a preferable example is 90 ° to 100 °) divided so as to cause a desired MT effect in the entire MT pulse train, and the number thereof is also the MT effect of the entire MT pulse train. In addition, the number is appropriately determined (5 to 10) depending on the balance with the imaging time. The application time of each divided MT pulse is about 1300 μsec, which is shorter than the conventional slice selection MT pulse by the divided amount.
[0108]
Furthermore, the time interval Δt between the divided MT pulses in the MT pulse train is set to a value that can optimize the MT effect of water / fat in the substantial part of the MT pulse application region. This time interval Δt varies depending on the measurement site, and in some cases, Δt = 0 can be set.
[0109]
On the other hand, the gradient magnetic field spoiler pulse SP placed in three directions of the slice direction, readout direction, and phase encode direction_S, SP_R, SP_EIs the pre-sequence SQ_preUsed as an end spoiler. For this reason, gradient magnetic field spoiler pulse SP_S, SP_R, SP_EIn each of the above, after applying a plurality of divided MT pulses, the spin phase is dispersed in each direction, so that interference of the spin phase between the pre-sequence and the data acquisition sequence is eliminated, and generation of pseudo echoes is prevented. I have to. The spoiler pulse may be applied only in one arbitrary direction or two directions.
[0110]
Data collection sequence SQ_acqIs the same as that of FIG.
[0111]
Thus, the pre-sequence SQ_preA plurality of divided MT pulses P₁ , ..., P_n, The echo signal from the substantial part (stationary part) of the imaging region is reduced by the MT effect, and the MT effect generated in the blood flow (arteries and / or veins) flowing into the imaging region is reduced ( Reduce). That is, due to the short MT pulse divided into a plurality of times, the apparent longitudinal relaxation T1 time of the flowing or tumbling blood flow is shortened, and the effect of the MT effect is reduced. Since the substantial part (stationary part) has a signal value reduction effect corresponding to the sum of a plurality of divided MT pulses, the image contrast between the blood flow flowing into the imaging region (blood) and the substantial part has been conventionally The MT effect using one MT pulse (with a long application time and a large flip angle) is significantly improved.
[0112]
Therefore, according to the present embodiment, in addition to the effects based on the FBI method described above, there are few artifacts, and the image contrast between the inflow blood flow / substantial portion is significantly improved compared to the case where the conventional MT pulse is used. An MRA image can be provided.
[0113]
Note that the method of applying a plurality of divided MT pulses is not limited to the one shown in FIG. 13, but can be modified as shown in FIGS.
[0114]
According to the application method shown in FIG. 14, the gradient magnetic field G for slicing is applied when a plurality of divided MT pulses are applied._SInstead of a configuration in which a plurality of pulses are also applied, a slice gradient magnetic field G is applied while a plurality of divided MT pulses are being applied._S One pulse is applied continuously. As a result, the MT pulse train P_MTThe time required for the application of is sufficient, and the entire imaging time can be shortened. In the case of the MT pulse application method shown in FIG. 15, the gradient magnetic field pulse is not applied in any direction, and the divided MT pulse is applied alone. Thereby, a plurality of divided MT pulse spaces are applied in a non-selective manner. For this reason, the divided MT pulse is applied over a wide area and is not limited to a slice or a slab. 14 and 15, the gradient magnetic field axes in the reading direction and the phase encoding direction are not shown.
[0115]
(Fourth embodiment)
A fourth embodiment of the present invention will be described with reference to FIGS.
[0116]
The MRI apparatus according to this embodiment is characterized by using respiratory synchronization together with the ECG synchronization method described above.
[0117]
For this reason, as shown in FIG. 16, the MRI apparatus includes a respiratory sensor (electrode) 19 that detects a signal that is in contact with the chest of the subject and that is proportional to the rib cage motion, and respiratory curve data from the detection signal of the sensor 19. And a respiratory synchronization unit 20 that outputs a synchronization signal synchronized with a desired period (for example, exhalation period) of the subject's respiratory cycle. The respiratory sensor and the respiratory synchronization unit may have other configurations, for example, a configuration in which a respiratory cycle is detected by detecting abdominal muscle movement as an optical variable, and a gas flow associated with breathing It may be an apparatus using a configuration for detecting by.
[0118]
The respiratory synchronization signal output from the respiratory synchronization unit 20 is sent to the sequencer 5. The sequencer 5 executes the imaging scan described in each of the above-described embodiments using both the ECG signal and the respiratory synchronization signal. Other configurations of the MRI apparatus are the same as those described above.
[0119]
As shown in FIG. 17, the sequencer 5 performs a predetermined delay time T from the start of the breathing exercise, for example, the expiration period._kMonitor the progress of And this delay time T_kAfter the elapse of time, the delay time T from the R wave of the ECG signal generated thereafter_DLMonitor the timing of elapse. When this timing arrives, as described above, the scan for each slice encoding amount is executed.
[0120]
In this way, a three-dimensional scan based on the FBI method using both the ECG synchronization method and the breath synchronization method can be executed. For this reason, in addition to the various functions and effects based on the FBI method described above, the subject does not need to hold his / her breath, so that the burden on the subject is reduced. In addition, the operational burden on the operator accompanying the breath-holding command is reduced.
[0121]
(Fifth embodiment)
A fifth embodiment of the present invention will be described with reference to FIGS.
[0122]
This embodiment is characterized in that various reagents are administered to a subject, and the contrast effect of the reagent or the function of a target stimulated by the reagent is imaged.
[0123]
The reagent used in the present invention is not a conventionally used MR contrast agent such as Gd-DTPA, but a beverage containing physiological saline, injections such as glucose, and acetic acid, that is, an orally administered reagent. . When the former injection is used, imaging is performed by the contrast effect. As the latter beverage, a beverage obtained by mixing other components with acetic acid is preferable so that the patient can easily drink it.
[0124]
An example of a basic sequence of an imaging method incorporating this reagent administration and an image generation flow is shown in FIG. This sequence is executed by the sequencer 5 and the arithmetic unit 10 under the control of the host computer 6. The execution of scanning related to this sequence and the data processing related to image generation are the same as or equivalent to those described in the above-described embodiments.
[0125]
First, the above-described ECG-prep scan is performed, and the optimum delay time T for ECG synchronization_DHIs required. Thereafter, an electrocardiogram-gated imaging scan (1) before reagent administration is performed based on the FBI method described above. This imaging scan (1) is commanded to hold the breath.
[0126]
A reagent is then administered to the subject. When this reagent is physiological saline or glucose, as an example, about 100 cc is administered by injection. As an example, when the reagent is a beverage containing acetic acid, about 10 cc is orally administered. Wait for an appropriate time after this administration. Thereafter, an electrocardiogram-synchronized imaging scan (2) after reagent administration is similarly performed based on the FBI method described above. A breath-holding method is used in combination with this imaging scan (1).
[0127]
The pulse sequence used for the two imaging scans is preferably a three-dimensional scan method based on the above-described sequence that can enhance the T2 value by the blurring, for example, FSE method, FASE method, EPI method.
[0128]
In addition, the structure which images by a TOF method or PS method in the state which administers a reagent is also possible.
[0129]
When physiological saline or glucose is injected and administered as a reagent, the T2 value of blood increases, that is, the T2 relaxation time becomes longer, and the contrast effect is exhibited. As a result, the intensity of the echo signal detected from the blood is increased and the SNR is improved. On the other hand, when a beverage containing acetic acid is used as a reagent, the acetic acid component in the administered beverage stimulates the vascular system, particularly the portal vein (reflection), and dilates the blood vessel. As a result, the blood flow volume increases, the intensity of the echo signal detected from the blood flow increases, and the SNR improves.
[0130]
Echo signals generated by these imaging scans are collected by the arithmetic unit 10 via the receiver 8R and the sequencer 5, respectively, and reconstructed as three-dimensional image data (FIG. 18, steps S51a, S51b, S52a, S52b). Thereafter, the two sets of three-dimensional image data are subjected to differential processing for each pixel, for example, by the arithmetic unit 10 (step S53). Next, the difference result data is displayed and stored after being subjected to MIP processing (steps S54 and S55).
[0131]
On the other hand, FIG. 19 shows a sequence flow when a dynamic scan is performed after reagent administration. After administration of the reagent or after the start of administration, imaging is performed by a three-dimensional scan of the volume region at regular intervals, and time change data in the body related to the reagent is specified. For this three-dimensional scan, the pulse sequence of the FBI method based on the three-dimensional Fourier transform method or the multi-slice method of the FBI method based on the two-dimensional Fourier transform method (same ECG synchronization delay time for each slice) is applied Is done.
[0132]
The present inventor applied this reagent administration to the FBI method and confirmed the effect by actual experiments. In one experiment, about 150 cc of physiological saline was injected and images of lung fields before and after that were imaged with a 1.5 T (static magnetic field) MRI apparatus and compared. The pulse sequence used in this experiment is a 3D-FASE sequence, and its imaging parameter is TE_eff= 60 ms, TR = 3R-R, TI = 180 ms, matrix size = 256 × 256, ETS = 5 ms, FOV = 37 cm × 37 cm²Resolution = 1.4 mm (RO) × 1.4 mm (PE) / 2 mm (slice). This confirmed a clear signal intensity difference in the pulmonary artery and an improvement in the ability to depict fine blood vessels. This is considered to be due to the fact that the influence of T2 value blurring was reduced by the administration of the water component into the blood vessel, and the blood vessel could be sharply depicted.
[0133]
In another experiment, about 20 cc of acetic acid was orally administered, and images of the chest and abdomen before and after that were imaged with a 0.5 T (static magnetic field) MRI apparatus and compared. The pulse sequence used in this experiment is a 3D-FASE sequence, and its imaging parameter is TE_eff= 62 ms, TR = 3R-R, TI = 140 ms, matrix size = 256 × 256, ETS = 6.2 ms, FOV = 37 cm × 37 cm²Resolution = 1.4 mm (RO) × 1.4 mm (PE) / 2 mm (slice). FIGS. 20A and 20B schematically show these images by hand. FIG. 4A is a copy image before acetic acid administration, and FIG. 4B is a copy image after acetic acid administration. As can be seen by comparing these, it was confirmed that the post-administration image significantly improved the signal difference of the blood vessels and the ability to depict the interpulse system compared to the pre-administration image. This is because the acetic acid component stimulated the portal vein as described above. This stimulation also rendered the blood vessels in the stomach. Thus, it was found that the function of blood vessels can be measured by the stimulant (reagent) to be administered.
[0134]
In particular, in the image after administration in FIG. 5B, a very thin blood vessel B that did not appear at all in the image before administration in FIG._thinI was able to confirm. In the case of MT angios to which the MR contrast agent Gd-DTPA is administered, thin blood vessels such as collateral blood vessels do not depend on temporal changes in the contrast effect. For this reason, when there is a stenosis in a blood vessel and a collateral circulation is created, such a circulation cannot be depicted with contrast angiography. On the other hand, according to the imaging of the FBI method in which acetic acid is administered according to the present invention, it can be expected that such collateral circulation can also be depicted.
[0135]
Conventionally, as in the BOLD (Blood Oxygen Level Dependent) method, T2^*A method of performing functional MRI based on a change in (apparent T2 value) has been known. However, this method is not an imaging method that can directly observe the function of blood vessels as an image. Such direct observation is possible with the present invention.
[0136]
In addition, by using a reagent containing acetic acid as described above, the function of blood vessels can be imaged. Changes in vascular function of patients with vascular dysfunction or vascular disease that could not be visualized until now can also be imaged.
[0137]
As one of the reagent administration methods described above, when imaging a vascular disease site, a vasodilator or blood pressure control reagent can also be used as a reagent according to the present invention. As a result, it is possible to depict the interstitial network when there is a collateral circulation due to functional MRA before or after reagent administration to a patient such as varicose veins or stenosis.
[0138]
By the way, in the case of the CE-MRA method of Gd-DTPA administration, it has been reported that stenosis is underestimated (Nikkei Medical Journal 17: 4; 115-124, 1995). As an imaging method for avoiding such underestimation, the FBI method of the present invention can be used. That is, imaging based on the FBI method may be performed simply in a state where physiological saline is administered. Thereby, the physiological saline functions as a contrast agent, slightly increases the T2 value of blood, and reduces T2 value blurring. As a result, a situation in which stenosis is underestimated can be eliminated as much as possible.
[0139]
In addition, although the said embodiment is the structure which implements the imaging method using a reagent by FBI method, in this structure, respiratory synchronization can also be used together.
[0140]
In the present invention, in the above-described pulse sequence for three-dimensional scanning, inversion recovery is performed in order to suppress the collection of MR signals from fat in the imaging region before executing the imaging data acquisition sequence as shown in FIG. IR pulse and / or fat suppression pulse F_satMay be applied.
[0141]
The description of the present embodiment is as described above. However, the present invention is not limited to the configuration described in the embodiment, and those skilled in the art do not depart from the gist described in the claims. These can be changed or modified as appropriate, and their configurations are also included in the present invention.
[0142]
【The invention's effect】
  Claim 1According to the MRI apparatus according to the present invention, an operation for collecting a signal representing the cardiac phase of the subject and collecting an echo signal for a predetermined slice encoding amount in the diastole in synchronization with the signal representing the cardiac phase, Perform a 3D scan that repeats every multiple heartbeats, non-invasive without administering contrast agent,Blood flowCan provide a 3D MRA image of the imaging region of a subject with high imaging ability. In addition, according to the MRI apparatus of claim 3,An image obtained by separating the arteriovenous can be suitably depicted.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing an example of the configuration of an MRI apparatus according to an embodiment of the present invention.
FIG. 2 is a view for explaining the temporal relationship between an ECG-prep scan and an imaging scan based on an electrocardiogram synchronization method in the embodiment.
FIG. 3 is a schematic flowchart illustrating an ECG-prep scan procedure executed by a host computer.
FIG. 4 is a timing chart showing an example of an ECG-prep scan.
FIG. 5 is a diagram schematically showing a lung field MRA image obtained by ECG-prep scan when the delay time is dynamically changed.
FIG. 6 is a diagram for explaining the spread of signal values in the phase encoding direction.
FIG. 7 is a schematic flowchart showing an example of imaging scan control executed by the host computer.
FIG. 8 is a schematic flowchart showing an example of control of an imaging scan executed by a sequencer.
FIG. 9 is a rough timing chart showing the timing of an imaging scan based on the electrocardiogram synchronization method in the first embodiment.
FIG. 10 is a diagram illustrating a positional relationship between a three-dimensional imaging region and each encoding direction.
FIG. 11 is a rough flowchart showing an outline of imaging can processing according to the second embodiment;
FIG. 12 is a view for explaining weighted difference calculation according to the second embodiment.
FIG. 13 is a rough timing chart showing the timing of an imaging scan based on an electrocardiogram synchronization method according to the third embodiment of the present invention.
FIG. 14 is a partial timing chart showing another application method of a divided MT pulse.
FIG. 15 is a partial timing chart showing still another application method of a divided MT pulse.
FIG. 16 is a functional block diagram showing an example of the configuration of an MRI apparatus according to a fourth embodiment of the present invention.
FIG. 17 is a rough timing chart showing the timing of an imaging scan in which the electrocardiographic synchronization method and the respiratory synchronization method are combined in the fourth embodiment.
FIG. 18 is a diagram illustrating an overview of an imaging procedure and acquired data processing according to a fifth embodiment of the present invention.
FIG. 19 is a diagram for explaining an outline of an imaging procedure in another embodiment.
FIG. 20 shows a copy of an experimental example in the fifth embodiment.
FIG. 21 is a timing chart showing another example of the pulse sequence of the present invention.
[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
16 Sound generator
17 ECG sensor
18 ECG units
19 Respiration sensor
20 Respiratory synchronization unit

Claims (20)

In an MRI apparatus that generates an MRA image of an imaging region of a subject,
Synchronized with the signal representing the cardiac time phase of the subject collected by the time phase detection means, a three-dimensional scan is executed in which the echo signal for a predetermined slice encoding amount is collected in the diastole for every multiple heartbeats. Scanning means for imaging,
An MRI apparatus comprising: generating means for generating a three-dimensional MRA image of the imaging region of the subject not using a contrast agent based on an echo signal obtained by the three-dimensional scan. The MRI apparatus according to claim 1,
The three-dimensional scan is an MRI apparatus in which a repetition time is set to any one of 2 to 4 heartbeats. The MRI apparatus according to claim 2,
The three-dimensional scan is an MRI apparatus including a gradient magnetic field in a slice direction for collecting data based on slice encoding in a direction substantially parallel to a running direction of blood flow. The MRI apparatus according to claim 3, wherein
The three-dimensional scan is an MRI apparatus including a phase encoding direction gradient magnetic field for applying phase encoding in a direction substantially coinciding with a traveling direction of the blood flow. The MRI apparatus according to claim 1,
The imaging scanning means collects echo signals for the predetermined slice encoding amount in an SE-based data acquisition sequence that generates a plurality of echo signals for one spin excitation based on the excitation RF magnetic field. Configured MRI apparatus. The MRI apparatus according to claim 5, wherein
The SE pulse sequence is an MRI apparatus that is a FASE sequence combined with a half Fourier method. In the invention of claim 1,
The time phase detecting means is a means for collecting an ECG signal of the subject as a signal representing the cardiac time phase, and the imaging scanning means is synchronized with an R wave appearing in the ECG signal. MRI apparatus which is means for executing In the invention of claim 7,
Based on the plurality of sets of echo signals, preparation scanning means for performing a preparation scan on the imaging region of the subject at different delay times from the R wave of the ECG signal and collecting a plurality of sets of echo signals Preparation image generating means for generating a plurality of preparation images having different delay times,
The MRI apparatus, wherein the imaging scanning unit includes a preparation information reflecting unit that reflects a delay time in which a specific preparation image of the plurality of preparation images is collected as the expansion period on the imaging scanning unit. In the invention of claim 1,
Preparation scanning means for collecting a plurality of sets of echo signals by performing a preparation scan for the imaging region of the subject for each of a plurality of cardiac time phases having different delay times from the reference waveform representing the cardiac time phase, and the echo Preparation image generating means for generating a plurality of preparation images having different delay times based on a signal,
The MRI apparatus, wherein the imaging scanning means includes preparation information reflecting means for reflecting a delay time in which a specific preparation image of the plurality of preparation images is collected to the imaging scanning means as the expansion period. In an MRI apparatus that generates an MRA image of an imaging region of a subject,
While performing a first three-dimensional scan that repeats an operation for collecting echo data for a predetermined slice encoding amount by delaying a first delay time from a reference waveform representing a cardiac time phase of the subject, the reference waveform A scanning means for imaging that performs a second three-dimensional scan that repeats an operation of collecting echo data for a predetermined slice encoding amount with a delay of a second delay time from a plurality of heartbeats;
Based on the echo signal obtained by the first three-dimensional scan, a first three-dimensional MRA image not using a contrast agent in the imaging region of the subject is generated, and obtained by the second three-dimensional scan. Generating means for generating a second three-dimensional MRA image that does not use a contrast agent in the imaging region of the subject based on the echo signal;
Data processing means for subtracting the first and second three-dimensional MRA images;
An MRI apparatus characterized by comprising: In the invention of claim 10,
The data processing means includes a difference calculation means for obtaining a difference image by subtracting the first and second three-dimensional MRA images, and a generation means for generating a final image for rendering an artery from the difference image. apparatus. In the invention of claim 11,
The data processing means is an MRI apparatus which is a process of projecting a maximum value (MIP) from the difference image data. The invention according to any one of claims 1 to 12,
An MRI apparatus comprising breath holding command means for commanding the subject to perform breath holding at least while the imaging scanning means is executing the three-dimensional scan. In the invention of claim 1,
Comprising a respiratory cycle detection means for detecting the respiratory cycle of the subject;
The MRI apparatus, wherein the imaging scanning unit is a unit that executes the three-dimensional scan in synchronization with a signal detected by the time phase detection unit and a respiratory cycle detected by the respiratory cycle detection unit. In the invention of claim 10,
A preparatory scanning means for performing a preparatory scan on the subject;
The MRI apparatus according to claim 1, wherein the imaging scanning unit performs the first and second three-dimensional scans of the imaging region at a delay time determined based on data obtained by the preparation scan. In the invention of claim 15,
The preparatory scanning means performs a two-dimensional scan of the same cross section for each of a plurality of cardiac time phases having different delay times from a reference waveform representing the cardiac time phase of the subject collected by the time phase detecting means, and a plurality of sets of echo signals It has been made to collect,
The imaging scanning unit is configured to acquire the first and second images in the imaging region in a delay time in which specific preparation images are collected from the plurality of preparation images having different delay times generated based on the echo signal . An MRI apparatus characterized by performing a three-dimensional scan. In the invention of claim 16 ,
The MRI apparatus, wherein the two-dimensional scan is the same type of pulse sequence as the three-dimensional scan. In the invention of claim 17 ,
The two-dimensional scan and the three-dimensional scan are executed in a pulse sequence in which a half-Fourier method is combined with a high-speed SE method that generates a plurality of echo signals for one spin excitation based on an excitation RF magnetic field. MRI equipment. The invention according to any one of claims 1 to 18,
The MRI apparatus that applies a fat suppression pulse that suppresses collection of echo signals from fat in the imaging region before the imaging scanning unit performs the three-dimensional scan. The invention according to any one of claims 1 to 18,
The imaging scanning unit is an MRI apparatus that applies a reverse recovery IR pulse before executing the three-dimensional scan.

Images