JP4406139B2 - MRI equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention images blood flow without using an MR contrast agent In particular to MRI equipment, Using the electrocardiogram synchronization method, the effect of blood flow inflow (ie, the effect of increasing MR signal value with the inflow of fresh blood flow into the imaging region: the inflow effect) has been maximized. MRA (MA angiography) can be performed For MRI equipment Related.
[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 for performing angiography by administering an MR contrast agent to a subject has begun to be performed. However, this contrast-enhanced MR angiography method requires an invasive treatment for administering a contrast agent, and above 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]
When a contrast agent cannot be administered or is not administered, a time-of-flight (TOF) method is known as one of alternative methods.
[0005]
This time-of-flight method is a technique that uses the effect of a flow such as blood flow. In general, the flow effect is caused by one of two properties of a 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 these, the method based on the former position movement is the TOF method.
[0006]
[Problems to be solved by the invention]
Incidentally, as an example of imaging using the conventional TOF method, three-dimensional imaging is performed by applying the TOF method to the head. However, in the blood flow image obtained by this, the contrast between the blood flow and the substantial part is not yet sufficient, and there is a demand from the clinical site to improve this contrast and increase the resolution. It had been.
[0007]
The present invention has been made to overcome such a conventional state of the art, and the object thereof is a blood flow in which blood flow can be imaged without administration of a contrast medium and the flow state can be changed. Also, it is to obtain an MRA image in which the contrast between the blood flow and the substantial part is improved by making the best use of the inflow effect of the blood flow.
[0008]
[Means for Solving the Problems]
As a result of earnestly examining, studying, and studying the above-described problems related to the conventional 3D-TOF method from various directions, the inventors have reached the following conclusions.
[0009]
The conventional TOF method, particularly the 3D-TOF method, is based on an imaging procedure that does not take into account the circumstances on the imaging target side, such as the speed of blood flow that is the imaging target and the state of pulsation. For this reason, only an image with a signal intensity averaged between a time phase having a large change in pulsation and a time phase in which the pulsation changes greatly affects the magnitude of the signal value. For example, when the conventional 3D-TOF method is applied to the head, images are captured in a state in which signal changes associated with the strength of pulsation are averaged, so blood flow signals appearing in the image of the head 3D-MRA are also averaged. It remained in the value that was converted. For this reason, the contrast between the blood vessel and the substantial part has not been sufficient yet.
[0010]
Therefore, in MR imaging according to the present invention, the signal from the blood flow in which the flow state changes, such as pulsation, becomes the highest signal using a preparation scan called an ECG-prep scan method (that is, Scanning for imaging (2D or 3D), which is the main scan, is measured by measuring the delay time (referred to as the timing of synchronization of the electrocardiogram synchronization method) from the optimal R wave (maximizing and effectively using the inflow effect due to the TOF effect). ) Employs a technique of reconstructing an image by arranging echo data obtained in the time phase exhibiting the high signal value in a low frequency region near the center of the k space (frequency space). As the pulse sequence based on the ECG-prep scan method, for example, a single slice at multiphase sequence having an echo time TE equivalent to that of an imaging scan sequence for collecting data is used.
[0011]
In this way, an image with high contrast between blood and noise can be obtained by reconstructing echo data obtained from the vicinity of the time phase with a high signal value in the center area in the phase encoding direction of the k space (frequency space). Can do.
[0012]
Preferably, signals collected in a time phase other than the time phase exhibiting the high signal value described above are arranged in the remaining high frequency region of the k space. Thereby, even when the ECG-synchronization (ECG-gating) method is used, it is possible to suppress an increase in the overall scan time (imaging time).
[0013]
The specific configuration of the present invention is as follows.
[0014]
The MRI apparatus of the present invention is an apparatus that performs imaging based on an electrocardiographic synchronization method on a desired region of a subject, and is used for an MR scan for imaging based on the electrocardiographic synchronization method and has a high signal value. Optimum delay time setting means for setting in advance optimum synchronization timing corresponding to the high signal time phase to be exhibited through execution of the preparatory MR scan, and collecting echo signals by executing the imaging MR scan synchronized with the optimum delay time An imaging scanning unit that arranges the echo signal in the k-space, and an image generation unit that generates an image by performing reconstruction processing on the arrangement signal, and the imaging scanning unit includes the high-signal time phase. To execute a pulse sequence set so that echo signals collected in a region are arranged in a desired low-frequency region in the center of the k-space. Equipped with a means The optimum delay time setting means collects a two-dimensional phase image (2D-PS) of the area by a single slice at multiphase method and creates a flow image at each synchronization timing; And means for determining the optimum synchronization timing based on a flow image exhibiting a peak flow from the plurality of flow images. It is characterized by that.
[0015]
Preferably, the optimum delay time setting means includes a signal collection means for collecting a signal representing a cardiac time phase of the subject, and a plurality of different delay times synchronized with a reference wave in the signal. Preparatory scanning means for executing the preparatory MR scan to collect echo signals, image acquisition means for obtaining a plurality of images corresponding to the plurality of delay times from the echo signals, and synchronization with the reference wave Determining means for determining the optimum delay time based on the plurality of images. The optimum delay time setting means includes a signal collection means for collecting a signal representing a cardiac time phase of the subject, and a plurality of different delay times synchronized with a reference wave in the signal, with respect to the region. Preparation scanning means for executing the preparation MR scan and collecting echo signals, image acquisition means for obtaining a plurality of images corresponding to the plurality of delay times from the echo signals, and the plurality of images as an operator Receiving means for receiving the optimum delay time synchronized with the reference wave determined by visual observation.
[0016]
For example, the preparation scanning means includes Based on the two-dimensional segmented FFE (seg. FFE) method The preparatory MR scan is performed by a pulse sequence of a single slice at multiphase system.
[0017]
Preferably, the pulse sequence executed by the execution means is a pulse sequence based on a two-dimensional or three-dimensional segmented FFE (seg. FFE) method. Further, the pulse sequence executed by the execution means is a phase encoding amount or a slice encoding amount in which echo signals collected by executing this pulse sequence are arranged in the k space in a centric order. You may have a gradient magnetic field pulse. For example, it is desirable that the echo times of the pulse sequence executed by the execution means and the pulse sequence executed by the preparation scanning means are substantially the same.
[0018]
Furthermore, the pulse sequence executed by the execution means may be a pulse sequence based on a three-dimensional segmented FFE (seg. FFE) method.
[0019]
The pulse sequence executed by the execution means includes a pulse train applied for collecting an echo signal in the high signal time phase region in synchronization with the optimum delay time, and a free time phase before reaching the optimum delay time. And a pulse train to be applied in the region. In this case, the pulse train applied in the empty time phase region may include a pulse train for collecting echo signals that are scrolled and arranged in a high frequency region that is a remaining region other than the low frequency region of the k space. In addition, the pulse train applied in the idle time phase region may include an idle pulse that excites a spin in a substantial part of the region. Furthermore, a configuration in which the pulse train applied in the idle time phase region includes an MT pulse that causes the MT effect in the echo signal collected from the region is also a preferable aspect.
[0021]
Further, the preparation scanning means is means for executing the preparation MR scan in a pulse sequence based on a two-dimensional field echo (FE) method of a single slice at multiphase method, The pulse sequence executed by the execution means may be a pulse sequence based on a field echo (FE) method that constitutes a two-dimensional or three-dimensional time-of-flight (TOF) method. In this case, the preparatory scanning means collects and arranges echo signals only in a central portion that forms a desired low-frequency region in k space corresponding to each of the plurality of synchronization timings using the pulse sequence, and Means for collecting and arranging echo signals in the remaining high-frequency region of the k space corresponding to at least one of the synchronization timings of the image acquisition means, wherein the image acquisition means is arranged such that the echo signals are arranged by the preparation scanning means. The k space having no high frequency region may have means for copying the signal value from the high frequency region of the k space where the echo signal is arranged.
[0023]
Further preferably, the signal representing the cardiac time phase is an ECG (electrocardiogram) signal, the reference wave is an R wave of the ECG signal, and the synchronization timing is a delay time from the R wave. Is provided.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below.
[0026]
(First embodiment)
A first embodiment will be described with reference to FIGS.
[0027]
A schematic configuration of an MRI (magnetic resonance imaging) apparatus according to this embodiment is shown in FIG.
[0028]
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.
[0029]
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 direction ₀ Is generated. In addition, the shim coil 14 is provided in this magnet part. The shim coil 14 is supplied with a current for homogenizing a static magnetic field from a shim coil power supply 15 under the control of a host computer to be described later. The couch portion can removably insert the top plate on which the subject P is placed into the opening of the magnet 1.
[0030]
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.
[0031]
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 _R The 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. ₀ Is superimposed on.
[0032]
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. With this operation, 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.
[0033]
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.
[0034]
While executing a main program (not shown), the MRI apparatus first performs a preparation scan (hereinafter referred to as an ECG-prep scan), and then performs an imaging scan (hereinafter referred to as an imaging scan). A two-stage scanning method is used. In the ECG-prep scan, a preparation pulse sequence is executed using the ECG signal, and the acquisition start timing at the cardiac time phase of echo data to be arranged in the low frequency region of the k space is determined optimally in the subsequent imaging scan. Here, the acquisition start timing is determined as a delay time from the peak value of the R wave of the ECG signal. In the imaging scan, an imaging pulse sequence based on an electrocardiographic synchronization method including a scan synchronized with the timing determined in this manner is executed.
[0035]
The sequencer 5 includes a CPU and a memory, stores pulse sequence information sent from the host computer 6, controls the operations of the gradient magnetic field power source 4, the transmitter 8T, and the receiver 8R according to this information, The digital data of the MR signal output from the receiver 8R is once inputted and transferred to the arithmetic unit 10. Here, the pulse sequence information is all information necessary for operating the gradient magnetic field power source 4, the transmitter 8T, and the receiver 8R according to a series of pulse sequences, for example, x, y, z coils 3x to 3z. Includes information on the intensity, application time, application timing, and the like of the pulse current applied to.
[0036]
The pulse sequence is a two-dimensional (2D) scan or a three-dimensional scan (3D), and the pulse train is in various forms such as a segmented FFE (high-speed FE) method and an FE method. Can be used.
[0037]
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. The arithmetic unit is also capable of executing data composition processing and difference arithmetic 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.
[0038]
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 12 is used for displaying a reconstructed image, for example. Also, parameter information desired by the surgeon, scan conditions, pulse sequences, information relating to image synthesis and difference calculation, and the like can be input to the host computer 6 via the input unit 13.
[0039]
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.
[0040]
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. This ECG measurement signal is used by the sequencer 5 when executing an ECG-prep scan and an imaging scan. Thereby, the synchronization timing for the ECG synchronization method can be set optimally, and data can be collected by performing an ECG synchronization imaging scan based on the synchronization timing.
[0041]
Subsequently, the ECG-prep scan will be described with reference to FIGS.
[0042]
While executing a predetermined main program (not shown), the host computer 6 starts execution of the ECG-prep scan process shown in FIG. 3 in response to a command from the input device 13, for example.
[0043]
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 a delay time T that determines the timing within the cardiac phase. _DL Etc. are included. These parameters can be arbitrarily set by the operator.
[0044]
Next, the host computer 6 sends message data to the voice generator 16 to cause the subject (patient) to give a breath holding command such as “please hold your breath” (step S2). This breath holding is preferably performed from the viewpoint of suppressing 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. May be.
[0045]
Thereafter, the host computer 6 starts reading the ECG signal (step S3).
[0046]
Next, the count value of the software timer T that measures the elapsed time from the peak value of the R wave as the reference wave in the ECG signal is cleared (T = 0) (step S4).
[0047]
Then, the host computer 6 determines whether or not an R wave peak value appears in the ECG signal (step S5). This determination is continued until the R wave peak value appears.
[0048]
If YES in step S5, that is, if an R wave peak value appears, the host computer further calculates the delay time T from the R wave peak value. _DL (= Α1, α2,..., Αn is determined based on the count value of the timer T (step S6), where the delay time T _DL = Α1, α2,..., Αn are set to α1 <α2,..., <Αn, as shown in FIG. 4, and the number of segments segmented for each cardiac cycle (segment number n = 1 to a predetermined number) It defines the start timing of a plurality of phases (here, the number of time phases m = 1 to 5; each time phase is composed of a plurality of scans; here, the number of scans p = 1 to 4). It is a time value. The determination in step S6 is also the set delay time T. _DL It continues until (= α1, α2,..., Αn) elapses.
[0049]
The determination in step S6 is YES, that is, the delay time T _DL When it is recognized that (= α1α2,..., Αn) has arrived, the host computer 6 is based on, for example, a two-dimensional segmented FFE method (hereinafter referred to as a seg.FFE method) with respect to the sequencer 5. The execution of a scan based on the number of time phases m for each segment number n and the number of scans p constituting each time phase is commanded (scan S7).
[0050]
This seg. The FFE method is a method of obtaining a lump of continuous data called a segment between RR waves of an ECG signal. This seg. The ECG-prep scan based on the FFE method is performed based on a method called “single slice multiphase”. According to this “single slice multiphase” method, the gradient magnetic field for slice G _S In addition, echo data of a plurality of time phases can be collected at a time for a single slice determined by the RF frequency. For this reason, in the present embodiment, as shown in FIG. 4 for example, the slice of the head is scanned by the ECG-prep scan, and the slice thickness is determined so that the imaging target blood vessel enters the slice.
[0051]
In this embodiment, the pulse sequence used for the ECG-prep scan is a two-dimensional scan, and that in an imaging scan described later is a three-dimensional scan. The purpose of the ECG-prep scan is not to obtain the image itself, but it is only necessary to find a cardiac time phase in which the blood flow portion is depicted with the highest signal value when performing the ECG synchronization method. A scan is sufficient. By executing the ECG-prep scan as a two-dimensional scan, the time for the ECG-prep scan can be shortened.
[0052]
However, it is desirable that the pulse sequences used for the ECG-prep scan and the imaging scan are of the same type. FFE method. If the type of pulse sequence changes, the image quality changes even in the same scan region, and this is natural. Further, the echo time TE of the pulse sequence used for the ECG-prep scan and the imaging scan (TE = TE in FIG. 5 and FIG. 7 described later). ₁ Are preferably the same. Thereby, the dephase component of the spin of blood flow can be made substantially the same.
[0053]
Note that this ECG-prep scan may be performed by a two-dimensional (2D) scan, for example, when the imaging scan (main scan) is a three-dimensional (3D) method, or a three-dimensional scan adapted to the region of the imaging scan. You may go on.
[0054]
On the other hand, regarding the correspondence between the ECG-prep scan and the ECG signal, as shown in FIG. 4 and FIG. 5 as an example, five time phases m for each cardiac cycle have a delay time T from the R wave. _DL = Is set to a value substantially corresponding to α1 to α5. For this reason, when the ECG-prep scan is executed, under the control of the sequencer 5, as shown in FIG. 5, four scans are executed for each time phase based on the FFE method. An echo signal is collected.
[0055]
As shown in FIG. 4, the k-space is divided into four regions in the phase encoding direction. And the phase encoding direction gradient magnetic field pulse G _E By appropriately setting the phase encoding amount by, the echo data of four scans in the constant time phase m in each cardiac cycle fill one two-dimensional k space. At this time, four echo signals collected at the time phase of m = 1 in the segment n = 1 are at the head phase encode position in each of the four divided regions, and then when m = 1 in the segment n = 2. The four echo signals collected in phase are sequentially arranged at the next phase encoding position in each of the four divided regions.
[0056]
Next, the host computer 6 determines whether or not scanning for the predetermined number of segments n has been completed. If NO, the process returns to step S4 and repeats the above-described processing (step S8).
[0057]
For this reason, when YES is determined in step S8, the scan for the predetermined number n of segments is completed. The echo signals related to these scans are received and processed by the receiver 8R, and sent as echo data to the arithmetic unit 10 via the sequencer. The echo data is filled in a total of five sets of two-dimensional k-spaces KS1 to KS5 corresponding to the number of time phases m = 5 in each segment n by the arithmetic unit 10. The echo data in which the five sets of k spaces KS1 to KS5 are filled with the delay time T from the R wave, respectively. _DL = Echo data group collected almost in synchronization with α1 to α5.
[0058]
When the determination of YES is made in step S8, since the ECG-prep scan is completed, the host computer 6 causes the voice generator 16 to output a breath holding release command (step S9). As a result, a voice-holding voice message is output from the voice generator 16 with the content of “breathing is fine”, for example.
[0059]
When the above processing is executed sequentially, the delay time T from the R wave _DL For example, T _DL = 5 frames of echo data of 50 msec, 150 msec, 250 msec, 350 msec, and 450 msec are prepared in the arithmetic unit 10. Therefore, these echo data are reconstructed into real space images by the arithmetic unit 10 and stored in the storage unit 11. For example, in response to an operation signal from the input device 13, the host computer 6 reads out the reconstructed image from the storage unit 11 and sequentially displays it as an MRA image.
[0060]
Therefore, the operator can determine the MRA image in which the blood flow portion is depicted with the highest signal by visually observing these cine display images.
[0061]
That is, the plurality of MRA images obtained by the ECG-prep scan are each delayed by a delay time T from the R wave. _DL Since the inflow effect when the pulsating blood flow flows into the head slice region is the largest, the blood flow of the reconstructed MRA image is rendered with a higher signal value. For this reason, the optimal delay time T can be determined by specifying an image in which the blood flow portion of the image is the clearest and the highest signal. _DL That is, it is possible to determine the synchronization timing that can reliably capture the unsaturated fresh inflow (blood flow) under the implementation of the ECG synchronization method.
[0062]
Note that the process of determining the synchronization timing of the electrocardiographic synchronization method from the plurality of MRA images is not necessarily limited to the visual observation of the image of the operator. An ROI is set on the blood flow portion on the display image, and the ROI is set. It may be performed by an automated process such as analyzing the signal intensity distribution in the signal and comparing the analysis results. In addition, if there are multiple images that are considered optimal as a result of visual observation or automation processing, that is, there are multiple delay times that are considered optimal, new processing such as interpolation is performed between these delay times. Time (synchronization timing) may be calculated.
[0063]
The synchronization timing optimally set through the ECG-prep scan is reflected in the subsequent imaging scan based on the electrocardiographic synchronization method.
[0064]
Subsequently, an imaging scan based on the electrocardiogram synchronization method will be described with reference to FIGS.
[0065]
The host computer 6 executes the processing shown in FIG. 6 in response to the operation information from the input device 13 while executing a predetermined main program (not shown).
[0066]
More specifically, the host computer 6 first determines the optimal delay time T of the electrocardiographic synchronization method determined through the execution of the ECG-prep scan described above. _DL Is read (FIG. 6, step S20). This time value may be read by receiving an input from the operator via the input device 13 or the optimum delay time T stored in the memory in the storage unit 11. _DL May be automatically read out to the work area.
[0067]
Next, the host computer 6 scans the scanning conditions (phase encoding direction, image size, number of scans, waiting time between scans, type of pulse sequence according to the scan site, etc.) designated by the operator from the input device 13 and the image processing method. (Addition processing or maximum value projection (MIP) processing, etc. In the case of addition processing, simple addition, addition averaging processing, weighted addition processing, etc.) is input, and the optimum delay time T _DL Is processed into control data, and the control data is output to the sequencer 5 and the arithmetic unit 10 (step S21).
[0068]
Next, when the host computer 6 can determine that there is a notification of preparation completion before the imaging scan (step S22), it outputs a breath holding start command to the sound generator 14 at step S23 (step S23). As a result, the voice generator 14 issues a voice message of “Please hold your breath” in the same manner as in the ECG-prep scan, and the patient who has heard this will stop breathing.
[0069]
Thereafter, the host computer 6 instructs the sequencer 5 to start an imaging scan (see step S27 and the process of FIG. 7).
[0070]
FIG. 8 shows an outline of the pulse sequence of this imaging scan, the temporal relationship with the blood flow signal intensity (beat) for each cardiac cycle, and an example of the arrangement of echo signals, and FIG. 9 shows a detailed example of the pulse train of this pulse sequence. Shown in
[0071]
Note that the processing of the echo signals collected by this imaging scan is the same as in the ECG-prep scan described above. That is, the echo signal is received by the RF coil 7, and then sent to the receiver 8R for reception processing. The processed signal is sent as echo data to the arithmetic unit 10 via the sequencer 5 and is arranged in the three-dimensional k space according to the slice encoding amount and the phase encoding amount. For this reason, in the following description, the detailed description from reception of an echo signal to arrangement | positioning is abbreviate | omitted.
[0072]
As shown in FIGS. 8 and 9, the imaging scan is performed using a three-dimensional seg. Based on the FFE method, for example, the three-dimensional region Rima of the head is implemented as an imaging region (see FIG. 10). This three-dimensional seg. In the FFE method, as shown in FIGS. 8 and 9, for each cardiac cycle, a plurality of segmented field echo collection scans (segment n) and MT ( Magnetic transfer (pulse): Pmt, CHESS (chemical shift selective) pulse: Pches, and spoiler pulses: SPs, SPr, SPe are used. The three-dimensional seg. Echo time TE = TE in pulse train of FFE method ₁ Is set to be the same as that of the ECG-prep scan described above.
[0073]
Specifically, when the sequencer 5 receives a scan start command, the sequencer 5 executes a first group scan S1 based on several FFE methods at a predetermined timing after the appearance of the R wave for each cardiac cycle (FIG. 7). Steps S24-1 to 24-5). As shown in FIG. 8, the echo signal collected by the first group scan S1 is a slice encoding G having a three-dimensional k-space. _E2 High-frequency region R against _H1 Phase encoding G as arranged in _E1 Is set (see FIG. 9).
[0074]
This high frequency region R _H1 And the high frequency region R of the target position. _H2 In the example of FIG. 8, the 128 phase encode amounts are divided into 8 regions by 16 lines, and three regions from the upper and lower sides toward the center of the phase encode amount = 0 are indicated. For this reason, the remaining two divided regions located in the center of the phase encoding direction are low frequency regions R important for image contrast. _L Is set as
[0075]
For the first group scan S1, the phase encoding amount S _E1 By setting the value of, the echo signal collected in the first scan is a high-frequency region R for a slice encoding amount in k space. _H1 Echo signals collected in the second scan are in the first divided region of the same high frequency region R in the same space _H1 Echo signals collected in the second divided region and in the third scan are in the high frequency region R of the same space. _H1 Are arranged in the third divided area. Moreover, the echo signals collected by the first cardiac cycle scan in the first group scan S1 are the high frequency region R _H1 Are arranged at the position of the first phase encoding amount in each of the three divided regions, and are subsequently arranged at the position of the next phase encoding amount in order for each cardiac cycle.
[0076]
Also, in each cardiac cycle, MT pulse: Pmt, CHESS pulse: Pches, and spoiler pulses: SPs, SPr, SPe are sequentially applied at appropriate timing following the first group scan S1 (step S24- in FIG. 7). 6-24-11). The MT pulse is applied to cause an MT (Magnetic Transfer) effect and suppress a signal value from a substantial part. The CHESS pulse is applied for fat suppression. Furthermore, the spoiler pulse is applied in order to sufficiently dephase the phase of the nuclear spin so that the application of the MT pulse or the CHESS pulse does not affect the subsequent echo signal acquisition. Here, the spoiler pulse is applied in three directions: a slice direction, a phase encoding direction, and a reading direction.
[0077]
Thereafter, at an appropriate timing, the scan S2 of the latter half group is seg. This is executed by the FFE method (see FIG. 7, steps S24-12 to 24-13 and FIG. 9). This scan S2 is a low frequency region R located at the center of k-space. _L And the remaining high frequency region R _H2 This is for collecting echo signals to be arranged on the screen.
[0078]
In particular, among the scans S2 of the latter half group, the start timing of the scan to be executed first is set to the optimum delay time T through the ECG-prep scan as described above. _DL Is matched. The echo signals collected in each scan of the second half group scan S2 are in the low frequency region R in the scan order. _L And the remaining high frequency region R _H2 Is arranged for each region.
[0079]
That is, the echo signal collected by the first scan in the second half group scan S2 is the low frequency region R. _L The echo signal collected by the second scan appears in the low frequency region R. _L Echo signals collected by the third scan appear in the high frequency region R. _H2 In the first divided region, the echo signal collected by the fourth scan is the high frequency region R. _H2 It is arranged such as in the next divided area. Moreover, the echo signal collected by the first cardiac cycle scan in the latter half group scan S2 is arranged at the position of the first phase encoding amount in each divided region. Are arranged at the position of the phase encoding amount.
[0080]
As described above, the optimally set delay time T _DL The electrocardiographic synchronization timing matched with is the timing at which the blood flow signal is most highly rendered in the imaging region Rima. Therefore, by collecting as described above, the echo signals collected by the initial scan (particularly the first and second scans) in the scan S2 of the latter half group are always preferentially low frequency region R. _L Will be placed.
[0081]
The above seg. The execution of the scan based on the FFE method and the application of other MT pulses are repeated for each cardiac cycle, for example, “16 cycles (n = 16) × slice encoding amount”. As a result, the arrangement of the echo data in the three-dimensional k space is completed (FIG. 7, step S24-14).
[0082]
Thereafter, the sequencer 5 notifies the host computer 6 of the scan completion notification (step S24-15).
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.
[0083]
Thereafter, the host computer 6 issues an image reconstruction and display command to the arithmetic unit 10 (step S27). In response to this, the arithmetic unit 10 performs, for example, three-dimensional Fourier transform on the k-space data to generate real-space three-dimensional image data, and stores this data in the storage unit 11. The arithmetic unit 10 further generates two-dimensional image data by performing, for example, MIP (maximum value projection) processing on the three-dimensional image data, and displays it on the display 12.
[0084]
According to the above image generation method, the optimal delay time T obtained by the ECG-synchronization timing in advance through the ECG-prep scan is obtained. _DL And an echo signal having a high signal intensity collected in the vicinity of the synchronization timing is preferentially arranged in the center portion in the phase encoding direction of the k space, that is, in the low frequency region. This data collection / arrangement method is achieved by the above-mentioned second group scan S2, and considering this group scan S2 as a center, it becomes a centric order data collection / arrangement method. ing.
[0085]
Therefore, the blood flow can be imaged without using an MR contrast agent, and even in the case of pulsating blood flow, the contrast between the substantial part and the blood flow in the reconstructed image is very high and stable. . That is, it is possible to perform echo data collection and k-space arrangement by making maximum use of such an inflow effect of blood flow, and to provide an image generation method excellent in entity (blood flow) rendering ability. Can do.
[0086]
In addition, according to a comparative experiment on the MRA image of the head conducted by the present inventor, 3Dseg. In the case of an FFE imaging scan, the blood flow signal intensity of the obtained image is improved by about 1.5 times compared to an imaging scan based on a normal 3DTOF method for the head, and the rendering performance is reliably improved. Has been confirmed.
[0087]
In this embodiment, a three-dimensional seg. When an imaging scan is executed according to the FFE method, echo data to be mapped to a high-frequency region in the k space is collected by a scan S1 of the first half group in a vacant time before reaching the ECG synchronization timing for each cardiac cycle. By collecting data without wasting idle time in this way, the entire imaging time can be shortened as much as possible. This also keeps the breath holding period during the imaging scan as short as possible and reduces the burden on the patient.
[0088]
Furthermore, since the ECG synchronization timing is measured by the “single slice / multiphase” method as described above, images of a plurality of time phases can be obtained at one time by one ECG-prep scan. That is, it is not necessary to perform a plurality of ECG-prep scans, the entire imaging time can be shortened, and patient throughput is improved.
[0089]
Various modifications can be further made to the MRI apparatus of the present embodiment. Hereinafter, this modification will be described.
[0090]
(First variant)
The scan S1 of the first half group using the above-mentioned idle time is not necessarily executed. After applying the MT pulse, CHESS pulse, and spoiler pulse for each cardiac cycle, a series of echo data collections starting at the optimal synchronization timing is performed. Of course, the scanning may be continued.
[0091]
(Second variant)
In addition, as shown in FIG. 11, an imaging scan using the above-described electrocardiographic synchronization method is a two-dimensional seg. You may carry out based on FFE method. This imaging method omits application of the gradient magnetic field for slice encoding in the pulse train shown in FIG. _E Only is applied. Also in this two-dimensional imaging scan, it is possible to suitably use the above-described method of presetting the optimum synchronization timing and collecting and arranging centric order data.
[0092]
In this case, the slice of the ECG-prep scan and the slice (imaging region) of the imaging scan may be different.
[0093]
(Third variant)
This modification is characterized in that the collection and arrangement of echo data is performed by the scroll method. ECG synchronization timing (delay time T _DL ) Depending on the imaging conditions such as the number of phase encodings in the k space, there may not be enough space to perform another scan between the start timing of the scan S2 in the latter half group and the R wave. In such a case, scanning is started immediately at the set synchronization timing (corresponding to the scan S2 of the latter half group in the above-described embodiment), and the echo signals are collected and arranged based on the centric order method. In this case, the echo signal due to the later scan in the series of started scans is scrolled and arranged in the high frequency region of the k space as shown by the arrows in FIG. An encoding gradient magnetic field pulse is set. This can also shorten the imaging time.
[0094]
(Fourth modification)
Further, in the above-described embodiment, an excitation pulse (empty pulse) that does not collect echo signals may be applied instead of the scan S1 of the first half group. In this way, since the idle pulse is always applied in the idle time from the appearance of the R wave to the scan S2 by the centric order method, the signal value from the substantial part of the imaging region is suppressed and slice encoding is performed. It is possible to reduce signal variations between slices or slices.
[0095]
(5th modification)
This variant relates to the application of MT pulses. As shown in FIG. 14, a plurality of divided MT pulses are continuously applied as MT pulse: Pmt. Each of the divided MT pulses has a small flip angle, but the pulse waveform area is set so that a predetermined flip angle can be secured as a whole of the plurality of divided MT pulses. The signal value of the substantial part of the imaging region can also be suppressed by the MT effect even with the plurality of divided MT pulses, and at the same time, by adjusting the number of application of the plurality of MT pulses, between slice encoding or between slices The variation of the signal can be adjusted.
[0096]
(Sixth variation)
This modification relates to the start control of the imaging scan. The outline of this control is shown in FIG. 15 (the processing in FIG. 15 is performed jointly by a sequencer, a host computer, and an arithmetic unit). When this imaging scan is carried out, as the previous scan, electrocardiogram synchronization is not used and no encoding gradient magnetic field is applied. Echo signals are collected from the entire imaging region (voxel) in real time by the pulse sequence of the FFE method (FIG. 15, step S41). When the intensity of the echo signal exceeds a certain threshold, 3Dseg. An imaging scan based on the FFE method is executed in the same manner as described above (steps S42 to S44). Thereby, the start timing of the dynamic scan can be automatically set to the optimum value.
[0097]
(Seventh variation)
This modification is characterized in that the above-described pre-optimal setting of the synchronization timing of the electrocardiographic synchronization method and the data collection / placement method based on the centric order method are implemented in the normal TOF method, that is, the FE method. In this case, for example, the ECG-prep scan is executed by the 2D-FE method (normal 2D-TOF method), and the imaging scan is executed by the 3D-FE method (normal 3D-TOF method). Of course, you may perform an imaging scan by 2D-FE method (normal 2D-TOF method). Data collection and arrangement by the imaging scan is performed by the centric order method as described above.
[0098]
In this case, in particular, when the ECG-prep scan is the 2D-FE method, the scan time becomes long. Therefore, in order to avoid this, it is desirable to use a so-called keyhole imaging method in combination. That is, in this ECG-prep scan, only the central portion (low frequency region) in the phase encoding direction of the two-dimensional k-space is collected by the 2D-FE method, and the data once captured is copied to the remaining high frequency region. Then, each data collection is completed. Thereby, the time of the ECG-prep scan based on 2D-FE method can be shortened.
[0099]
(Eighth modification)
This modification is an example in which an ECG-prep scan is performed with a two-dimensional phase image (2D-PS image). The synchronization timing (delay time T of the ECG synchronization method described above _DL ) Is measured by taking a two-dimensional phase image based on a single slice / multiphase method and creating a flow image in each time phase for each cardiac cycle. When this flow image is comparatively observed, for example, it is possible to determine an image in which the flow peaks when time elapses from the R wave as a trigger. That is, the time phase at which this peak flow image is collected can be set as the optimum synchronization timing, and this synchronization timing can be reflected in the imaging scan as described above.
[0100]
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.
[0101]
For example, in the above-described embodiment and modifications thereof, the description has been made assuming that the synchronization timing (delay time) of the electrocardiographic synchronization method is synonymous with the start timing of the second-half group scan S2, but this synchronization timing is , It may be defined as a timing to collect data arranged at the phase encoding amount of k space = 0 through the ECG-prep scan. That is, it may be determined by calculation in consideration of conditions such as the optimum delay time obtained by ECG-prep scan, the number of phase encodings, and the range of the low frequency region.
[0102]
【The invention's effect】
As described above, according to the present invention, through the preparation MR scan called ECG-prep scan, the optimal synchronization timing of the electrocardiographic synchronization method capable of maximizing the blood flow inflow effect is determined, The MR scan for imaging combined with the electrocardiographic synchronization method based on this synchronization timing is executed based on the so-called centric order method, so that blood flow can be imaged without administering a contrast agent, and the flow state changes. Even in the case of blood flow, it is possible to provide an MRA image in which the contrast between the blood flow and the substantial part is improved by making the best use of the inflow effect of the blood flow.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a configuration example of an MRI apparatus according to embodiments and modifications of the present invention.
FIG. 2 is a diagram for explaining the temporal relationship between an ECG-prep scan and an imaging scan according to an embodiment and a modified embodiment.
FIG. 3 is a schematic flowchart illustrating an ECG-prep scan procedure executed by the host computer in the embodiment;
FIG. 4 is a timing chart illustrating the relationship between an ECG-prep scan and data arrangement in k-space.
FIG. 5 is a timing chart for explaining a pulse train of an ECG-prep scan.
FIG. 6 is a schematic flowchart of an imaging scan executed by a host computer.
FIG. 7 is a schematic flowchart of an imaging scan executed by a sequencer.
FIG. 8 is a timing chart illustrating the relationship between an imaging scan and data arrangement in k-space.
FIG. 9 is a timing chart for explaining a pulse train of an imaging scan.
FIG. 10 is a diagram illustrating a three-dimensional imaging region of an imaging scan.
FIG. 11 is a timing chart for explaining a pulse train of a two-dimensional imaging scan.
FIG. 12 is a diagram for explaining a concept of a scroll method applicable to data collection / arrangement.
FIG. 13 is a timing chart of a pulse sequence using a blank pulse for an imaging scan.
FIG. 14 is a timing chart of a pulse sequence using a plurality of divided MT pulses for an imaging scan.
FIG. 15 is a schematic flowchart showing control of the start timing of an imaging scan.
[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 (15)

In an MRI apparatus configured to perform imaging based on an electrocardiographic synchronization method on a desired region of a subject,
An optimum delay time setting means used in the MR scan for imaging based on the electrocardiogram synchronization method and setting an optimum synchronization timing corresponding to a high signal time phase region exhibiting a high signal value in advance through execution of the preparation MR scan;
An imaging scan means for acquiring an echo signal by executing an MR scan for imaging synchronized with the optimum delay time;
An image generating means for arranging the echo signal in the k space and generating an image by performing reconstruction processing on the arrangement signal;
The imaging scanning means includes execution means for executing a pulse sequence set so that echo signals collected in the high signal time phase region are arranged in a desired low frequency region in the center of the k space ,
The optimum delay time setting means is a means for collecting a two-dimensional phase image (2D-PS) of the region by a single slice multiphase method to create a flow image at each synchronization timing;
An MRI apparatus comprising: means for determining the optimum synchronization timing based on a flow image exhibiting a peak flow from the plurality of flow images . The MRI apparatus according to claim 1,
The optimum delay time setting means includes a signal collecting means for collecting a signal representing a cardiac time phase of the subject;
Preparatory scanning means for collecting the echo signal by executing the preparatory MR scan on the region at each of a plurality of different delay times synchronized with a reference wave in the signal;
Image acquisition means for obtaining each of a plurality of images corresponding to the plurality of delay times from the echo signal,
An MRI apparatus comprising: a determination unit that determines the optimum delay time synchronized with the reference wave based on the plurality of images. The MRI apparatus according to claim 1,
The optimum delay time setting means includes a signal collecting means for collecting a signal representing a cardiac time phase of the subject;
Preparatory scanning means for collecting the echo signal by executing the preparatory MR scan on the region at each of a plurality of different delay times synchronized with a reference wave in the signal;
Image acquisition means for obtaining each of a plurality of images corresponding to the plurality of delay times from the echo signal,
An MRI apparatus comprising: a receiving unit configured to receive the optimum delay time synchronized with the reference wave determined by visual observation of the plurality of images by an operator. The MRI apparatus according to claim 2 or 3,
The preparation scanning means is an MRI apparatus which is a means for executing the preparation MR scan with a single slice at multiphase pulse sequence based on a two-dimensional segmented FFE (seg. FFE ) method. . The MRI apparatus according to claim 4 , wherein
The MRI apparatus, wherein the pulse sequence executed by the execution means is a pulse sequence based on a two-dimensional or three-dimensional segmented FFE (seg. FFE) method. The MRI apparatus according to claim 5 , wherein
The pulse sequence executed by the execution means is a gradient magnetic field of a phase encoding amount or a slice encoding amount in which echo signals acquired by executing this pulse sequence are arranged in the k space in a centric order. MRI device with pulse. The MRI apparatus according to claim 5 or 6 ,
An MRI apparatus in which the echo times of the pulse sequence executed by the execution means and the pulse sequence executed by the preparation scanning means are substantially the same. 5. The MRI apparatus according to claim 4 , wherein the pulse sequence executed by the execution means is a pulse sequence based on a three-dimensional segmented FFE (seg. FFE) method. The MRI apparatus according to claim 4 , wherein
The pulse sequence executed by the execution means includes a pulse train applied for echo signal collection in the high signal time phase region in synchronization with the optimum delay time, and a free time phase region before reaching the optimum delay time. An MRI apparatus including a pulse train to be applied in the above. The MRI apparatus according to claim 9 , wherein
The MRI apparatus includes a pulse train for collecting echo signals to be scrolled and arranged in a high-frequency region that is a remaining region other than the low-frequency region of the k space, in which the pulse train applied in the empty time phase region. The MRI apparatus according to claim 9 , wherein
The MRI apparatus, wherein the pulse train applied in the idle time phase region includes an idle pulse that excites spins in a substantial part of the region. The MRI apparatus according to claim 9 , wherein
The MRI apparatus, wherein the pulse train applied in the empty time phase region includes an MT pulse that causes an MT effect on echo signals collected from the region. The MRI apparatus according to claim 2 or 3,
The preparation scanning means is means for executing the preparation MR scan with a pulse sequence based on a two-dimensional field echo (FE) method of a single slice at multiphase method,
The pulse sequence executed by the execution means is an MRI apparatus that is a pulse sequence based on a field echo (FE) method that forms a two-dimensional or three-dimensional time-of-flight (TOF) method. The MRI apparatus according to claim 13 , wherein
The preparatory scanning means collects and arranges echo signals only in a central portion forming a desired low-frequency region in k space corresponding to each of the plurality of synchronization timings using the pulse sequence, and the plurality of synchronization timings Means for collecting and arranging echo signals in the remaining high-frequency region of k-space corresponding to at least one of
The image acquisition means has means for copying a signal value from a high-frequency region of the k-space where the echo signal is arranged in a k-space having a high-frequency region where the echo signal is not arranged by the preparation scanning means. MRI equipment. The MRI apparatus according to any one of claims 1 to 14 ,
An MRI apparatus in which the signal representing the cardiac phase is an ECG (electrocardiogram) signal, the reference wave is an R wave of the ECG signal, and the synchronization timing is a delay time from the R wave.

Images