JP4316078B2 - MRI equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention images the inside based on the magnetic resonance phenomenon of spin (nuclear spin) in a subject. MRI ( Magnetic resonance imaging )apparatus Therefore, T1 (longitudinal relaxation) time and T2 (lateral relaxation) time of a vascular disease site can be easily measured without using a contrast medium. MRI equipment About.
[0002]
[Prior art]
Magnetic resonance imaging is an imaging method in which a nuclear spin of a subject placed in a static magnetic field is magnetically excited with a high-frequency signal of its Larmor frequency, and an image is reconstructed from an MR signal generated by the excitation. .
[0003]
In the field of magnetic resonance imaging, when an blood flow image of a lung field or abdomen is obtained, clinically, MR angiography in which a contrast medium is administered to a subject and angiography is started. However, this contrast-enhanced MR angiography method 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.
[0004]
When a contrast agent cannot be administered or is not administered, time-of-flight (TOF) method, phase contrast (PC) method, and the like are known as alternative methods.
[0005]
Among these, the time-of-flight method and the phase contrast method are methods that utilize the effect of a flow such as blood flow. The flow effect is caused by one of two properties of the moving spin. One is that the spin simply moves its position, and the second depends on the phase shift of the transverse magnetization caused by the movement of the spin in the gradient magnetic field. Among them, the method based on the former position movement is the TOF method, and the method based on the latter phase shift is the phase contrast method.
[0006]
[Problems to be solved by the invention]
By the way, for example, when there is bleeding in a lesion such as a tumor or thrombosis progresses, the blood properties (such as viscosity) change depending on the progression process (stage) of the lesion, and the blood It is known that T1 time and T2 time also change. For this reason, if the T1 time and T2 time of the blood are known, it is possible to estimate the progress state of the lesion.
[0007]
In addition, even if a T1-weighted image or a T2-weighted image is captured by a normal method, such as when there is bleeding around the tumor, the values of the T1 time and T2 time of the bleeding site are changed. It is very difficult to draw a clear distinction from a region. Also in this case, if the values of T1 time and T2 time that may change according to the progress of the lesion are accurately known, an effective T1 weighted image or T2 weighted image is captured and the lesion portion is captured. It is possible to obtain an image that clearly distinguishes the area of bleeding and bleeding, which can be useful for diagnosis.
[0008]
However, according to the above-described conventional imaging method for blood flow visualization, it is not necessary to use a contrast medium, but the T1 time and T2 time of a lesion part of a vascular disease accompanied by bleeding, thrombus, etc. can be easily and shortly shortened. No specific imaging technique has been proposed yet for measuring over time or grasping the state of such a lesion.
[0009]
The present invention was made in order to break down the current state of the prior art, and the first object of the present invention is to perform T1 time and T2 time of a lesion part associated with bleeding, thrombus, etc. without administering a contrast medium. Is to be able to measure easily and in a short time.
[0010]
The second object of the present invention is to easily and quickly measure the T1 time and T2 time of a lesion part accompanied by bleeding, thrombus, etc. without administering a contrast medium, and accurately reflects the measurement result. A T1-weighted image and a T2-weighted image of a lesion can be obtained, whereby a lesion such as a tumor and the surrounding bleeding portion are differentiated by contrast, and an image in which the boundary is clearly distinguished is provided. It is.
[0011]
[Means for Solving the Problems]
In order to achieve the first object described above, the MRI apparatus of the present invention uses the same slice at the scan site of the subject. , A measurement scan based on a pulse sequence is synchronized with a reference wave of a signal representing a cardiac time phase of the subject. Repeating multiple times for multiple heartbeats, and changing the value of the physical quantity related to the spin behavior during the repetition And collecting means for collecting a plurality of frames of image data, and a measuring means for automatically measuring the spin relaxation time from the plurality of frames of image data.
[0012]
For this reason, a single shot type pulse sequence such as the FASE method is used for the same slice of the scan region by the collecting means, for example, the inversion time TI and the effective echo time TE _eff The dynamic scanning is performed while changing the value of the physical quantity related to the spin behavior for each shot. As a result, a plurality of pieces of image data reflecting the physical values related to spin behavior having different values are collected. Therefore, for example, a signal value represented by a pixel at a desired position of the image data is obtained for each image by the measuring means, and the plurality of signal values and the plurality of physical quantity values at the time of image data collection are associated with each other by natural logarithm calculation. Thus, the longitudinal relaxation time T1 and the lateral relaxation time T2 are calculated.
[0013]
As described above, since a plurality of images are obtained by one imaging, the imaging time is short, and the relaxation time can be provided by a relatively simple calculation process. Therefore, the T1 time and T2 time of the vascular disease part can be measured easily and quickly. For this reason, even in the case where thrombosis or the like in which T1 time or T2 time changes in accordance with the stage of the disease state progression in the diseased part (for example, aneurysm or the like), It is also easy to estimate the degree.
[0014]
In order to achieve the second object, the MRI apparatus of the present invention further includes an imaging means for imaging the scan site based on the relaxation time measured by the measuring means in addition to the above-described configuration. And
[0015]
As a result, the imaging means can perform imaging under imaging conditions suitable for the measured T1 time and T2 time, so that the ability to draw the measurement part of the relaxation time is improved. Therefore, by setting the measurement site to the lesion part of the vascular disease, a contrast is established between the bleeding site and the surrounding bleeding site. Therefore, the boundary between the lesion site and the bleeding site is clearly displayed, and diagnosis can be performed. Great contribution.
[0016]
Specific configurations for the two aspects of the MRI apparatus described above are provided as follows.
[0017]
For example, the relaxation time is the longitudinal relaxation time T1 or the lateral relaxation time T2.
[0018]
Further, for example, the pulse sequence is a single shot type pulse train including a FASE (Fast Asymmetric SE) method or an EPI (Echo Planar Imaging) method.
[0019]
Preferably, the pulse sequence is a pulse sequence using an inversion pulse, the physical quantity is an inversion time TI due to the inversion pulse, and the relaxation time is a longitudinal relaxation time T1. The physical quantity is an effective echo time TE. _eff And the relaxation time may be the longitudinal relaxation time T2. Further, the physical quantity may be an echo interval ETS, and the relaxation time may be a longitudinal relaxation time T2. Further, the physical quantity may be a repetition time TR, and the relaxation time may be a longitudinal relaxation time T1.
[0020]
In addition, the acquisition means includes a time phase detection means for detecting a signal representing a cardiac time phase of the subject, and a synchronization timing for a reference wave in the signal detected by the time phase detection means. It is also possible to provide timing determination means for determining a value that is optimally rendered, and execution command means for executing the measurement scan at the synchronization timing determined by the timing determination means. In this case, for example, 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.
[0021]
Further, in each configuration described above, the measurement unit includes a display unit that displays image data of at least one frame of the image data of the plurality of frames as an image, and a ROI (region of interest) at a desired position on the image. A signal value calculating means for calculating a signal value of a pixel related to the position of the ROI for each of the image data of the plurality of frames, and the signal calculated for each of the image data of the plurality of frames. It is desirable to provide relaxation time calculation means for calculating the relaxation time from the correspondence between the value and the physical quantity value used when collecting the image data of the plurality of frames.
[0022]
Furthermore, in each configuration described above, it is desirable that the collection unit includes a physical quantity setting unit that allows an operator to set in advance at least one of the type of the physical quantity and a value that changes the physical quantity.
[0025]
Also The above reference The synchronization timing for the wave is determined to the optimum value from the image obtained by performing a preparatory scan in advance. Provide timing determination means You may do it.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below.
[0029]
(First embodiment)
A first embodiment will be described with reference to FIGS.
[0030]
A schematic configuration of an MRI (magnetic resonance imaging) apparatus according to this embodiment is shown in FIG.
[0031]
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.
[0032]
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.
[0033]
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.
[0034]
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.
[0035]
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.
[0036]
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.
[0037]
One feature of this MRI apparatus is that it can execute 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 prepares a preparatory scan (hereinafter referred to as ECG-prep scan) for executing a preparatory pulse sequence for determining a synchronous timing (delay time from the R wave) in advance, and the synchronous timing thereof. A main program (not shown) is executed for a dynamic scan for measurement based on the electrocardiographic synchronization method based on the ECG and an imaging scan (hereinafter referred to as an imaging scan) based on the electrocardiographic synchronization method based on the synchronization timing. To do in. The imaging scan is executed by reflecting the measurement result of the longitudinal relaxation time T1 or the transverse relaxation time T2 measured through the measurement dynamic scan.
[0038]
In some cases, it is also possible to measure the longitudinal relaxation time and lateral relaxation time, which will be described later, from the image data of the scan result after finishing the scan by the dynamic scan for measurement without performing the imaging scan.
[0039]
An example of an ECG-prep scan execution routine is shown in FIG. 3, and an example of a measurement dynamic scan execution routine based on the ECG synchronization method is shown in FIGS.
[0040]
In this way, the ECG-prep scan determines the optimal synchronization timing of ECG synchronization, and the subsequent echo data acquisition scan is performed at this ECG synchronization timing, so that blood flow can be reliably captured and discharged from the heart. You can always scan for fresh blood.
[0041]
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.
[0042]
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. Various forms such as EPI (Echo Planar Imaging) method and FASE (Fast Asymmetric SE) method (that is, an imaging method in which the fast SE method is combined with the half Fourier method) can be employed.
[0043]
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.
[0044]
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.
[0045]
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.
[0046]
Further, the electrocardiogram measurement unit attaches to the body surface of the subject and detects an ECG signal as an electrical signal, and performs various processing including digitization processing on the sensor signal to perform the host computer 6 and the sequencer. And an ECG unit 18 for outputting to the PC. The measurement signal from the electrocardiogram measurement unit can be used as required by the sequencer 5 when performing each of the ECG-prep scan and the electrocardiographic synchronization imaging scan. Thereby, the synchronization timing of the electrocardiographic synchronization method can be set appropriately, and data can be collected by performing an electrocardiographic synchronization imaging scan based on the synchronization timing.
[0047]
Next, the optimum synchronization timing determination process by ECG-prep scan will be described with reference to FIGS.
[0048]
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).
[0049]
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.
[0050]
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. _inc Is 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.
[0051]
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.
[0052]
Specifically, the delay time T from the peak arrival time of the R wave _DL But T _DL = T ₀ + T _inc (Step S4). Next, the ECG signal subjected to signal processing by the ECG unit 18 is read, and it is determined whether or not an R wave peak value appears in the signal (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 _DL Is subsequently determined whether or not the R wave peak time has elapsed (step S6). This determination process is also delayed time T _DL Continue until
[0053]
R wave peak time to delay time T _DL (Step S6, YES), the sequencer 5 is instructed to start each pulse sequence (step S7: see FIG. 4). This pulse sequence is preferably set to the same type as the imaging pulse sequence described later, and is, for example, a 2D-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 an imaging scan (main scan) for collecting image data is a three-dimensional (3D) method, or according to the region of the imaging scan. A three-dimensional scan may be performed. In this embodiment, since the imaging scan is executed as a two-dimensional scan, the ECG-prep scan is also executed as a two-dimensional scan.
[0054]
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. _inc Increases in proportion to the count value.
[0055]
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 _DL For 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 contrary, if the number counter CNT has reached the upper limit value (step S11, YES), a breath holding release command 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."
[0056]
When the above-described processes are sequentially executed, for example, the preparation pulse sequence is executed at the timing shown in FIG. For example, the initial time T ₀ = 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,... _DL Is adjusted. Therefore, when the first R wave after the breath holding command reaches the peak value, the delay time T _DL (= T ₀ ) Later, for example, the first scan IMG based on the FASE method _prep1 Continues 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, there is a standby process in step S10 in 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.
[0057]
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 = T ₀ + T _inc = When the 400 msec has elapsed, the second scan IMG _prep2 Continues for a predetermined time, and echo signals are collected as well. When this scan ends and the next R wave appears, the delay time T _DL = T ₀ + 2 · T _inc = 500 msec has passed and the third scan IMG _prep3 Continues 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 = T ₀ + 3 · T _inc = After 600 msec, the 4th scan IMG _prep3 Continues for a predetermined time, and echo signals are collected as well. This scan is continued a desired number of times, for example, 5 times, and echo data of the same cross section for a total of 5 frames (sheets) is collected.
[0058]
The echo data is sequentially sent to the arithmetic unit 10 via the receiver 8R and the sequencer 5. The arithmetic unit 10 reconstructs echo data in k space (frequency space) into real space image data by a two-dimensional Fourier transform method. This image data is stored in the storage unit 11 as 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.
[0059]
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, the delay time T _DL Respectively, 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.
[0060]
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 case of the MRA images shown in (a) to (d) of the figure, the range in which the aortic flow is reflected is limited to a part or a short range as compared with (e), and the blood flow accompanying pulsation is reduced. Due to factors such as low speed, the intensity of the echo signal is relatively low and 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 _DL It turns out that the time is 700 msec later.
[0061]
Therefore, the operator can thus delay time T _DL From the plurality of MRA images picked up dynamically, that is, the optimum delay time T _DL Is determined by visual determination, and processing for reflecting this delay time parameter in the subsequent imaging scan is performed.
[0062]
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 any other direction, it is possible to capture more clearly without missing information on the traveling direction (direction) of the aortic flow, and the rendering ability is excellent. It becomes a thing.
[0063]
Next, the measurement dynamic scan operation of this embodiment will be described with reference to FIGS. Using the image data obtained by this scan, the T1 relaxation time is calculated (measured) after the scan.
[0064]
The host computer 6 executes a predetermined main program (not shown), and executes the process shown in FIG. 6 while corresponding to the operation information from the input device 13.
[0065]
In detail, the host computer 6 firstly determines the optimum delay time T determined by the operator through the ECG-prep scan described above. _DL Is input via the input device 13, for example (step S20). 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 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).
[0066]
Next, the host computer 6 automatically determines the type of physical quantity used in T1 (T2) measurement described later by a method of referring to a table, for example, according to the type of pulse sequence (step S21A). This physical quantity is a physical quantity that is changed for each shot when the image data necessary for the measurement of T1 time or T2 time is collected multiple times for each shot. Depending on the type of the pulse sequence, the inversion time TI, There are an echo time TEeff, a repetition time TR, an echo interval ETS, and the like. Note that the physical quantity may be determined interactively with the operator.
[0067]
Next, a plurality of default values are read from the memory as the determined physical quantity values (step S21B). For example, if the inversion time TI is determined as a physical quantity, TI = t1, t2,..., T5 (t1 <t2 <,..., <T5). Next, the host computer 6 inquires of the operator whether the default value is acceptable, and accepts the value when the operator manually sets (or selects) another value (steps S21C, 21D). Thereby, the type and value of the physical quantity for T1, T2 measurement are set.
[0068]
Next, when the host computer 6 can determine that there is a notification of completion of preparation before scanning (step S22), it outputs a breath holding start command to the sound generator 14 in step S23 (step S23). As a result, the voice generator 14 issues a voice message such as “please hold your breath” in the same way as in the ECG-prep scan, so that the patient who hears it stops breathing (see FIG. 8). .
[0069]
Thereafter, the host computer 6 instructs the sequencer 5 to start a dynamic scan for measurement (step S24 and FIG. 7). This command includes information on the physical quantities for T1, T2 measurement set in steps S21A to S21D.
[0070]
When the sequencer 5 receives a measurement dynamic scan start command (FIG. 7; step S24-1), the sequencer 5 starts reading the ECG signal (step S24-2), and the peak value of the R wave (reference waveform) in the ECG signal. 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 _DL Only waiting processing is performed (step S24-4). This delay time T _DL As 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.
[0071]
This optimum delay time T _DL The sequencer 5 executes the measurement dynamic scan (step S24-5), assuming that the time at which elapses is the optimum ECG synchronization timing. Specifically, the transmitter 8T and the gradient magnetic field power source 4 are driven according to the pulse sequence information that has already been stored, and for example, the first scan based on the pulse sequence of the two-dimensional FASE method using inversion pulses is performed. 8 is executed under the electrocardiographic synchronization method (the phase encoding direction gradient magnetic field is not shown in the figure).
[0072]
According to the pulse sequence of FIG. 8, a 180 ° RF pulse is first applied as an inversion pulse by slice selection, and the nuclear spin in the selected slice of the subject is inverted in the −z′-axis direction. After that, during the inversion time TI = t1, after the T1 relaxation, the 90 ° RF pulse is selectively applied as a slice as an excitation pulse. As a result, the spin is flipped to the x′-y ′ plane, and a predetermined number of echo signals are collected by the echo collection pulse train by the subsequent refocus pulse.
[0073]
At this time, as shown in FIG. 9, the phase encoding direction PE is made to substantially coincide with the designated direction, for example, the direction of blood flow (artery AR or vein VE). Further, the echo interval in this pulse sequence is set to a short value of about 5 msec.
[0074]
As a result, echo signals are collected from a two-dimensional imaging region set in the thoracoabdominal region, for example, with a scan time of about 600 msec under the first inversion time TI = t1.
[0075]
In this embodiment, this inversion time TI is used as a measurement parameter for the T1 relaxation time described later, and as will be described subsequently, a plurality of scans are dynamically executed by changing the length of the inversion time TI. Is done.
[0076]
When the first measurement dynamic scan is completed, the sequencer 5 determines whether or not the final measurement dynamic scan is completed (FIG. 7; step S24-6), and this determination is NO (the final scan has been completed). In the case of (not), while monitoring the ECG signal, for example, two R heartbeats (2R-R) from the R wave used for the dynamic scan for measurement, for example, are waited until a shorter set period elapses (step S24-7). ). That is, this standby period becomes the repetition time TR.
[0077]
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. _DL The next inversion time TI = t ₂ (> T ₁ Accordingly, the second measurement dynamic scan is executed in the same manner as described above, and echo signals are collected from the two-dimensional imaging region (steps S24-4 and S5). Similarly, the final inversion time TI = t _n (> Tn-1, ...,> t ₂ > T ₁ : For example, echo signals are collected up to n = 5).
[0078]
Inversion time TI = t _n When the final measurement dynamic scan in step S24 ends, the determination in step S24-6 becomes YES, and a scan completion notification 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.
[0079]
Upon receiving the scan completion notification from the sequencer 5 (step S25), the host computer 6 outputs a breath holding release command to the voice generator 16 (step S26). Therefore, the voice generator 16 issues a voice message such as “It is fine to breathe” to the patient, and the breath holding period ends (see FIG. 8).
[0080]
In this way, as schematically shown in FIG. 8, the measurement dynamic scan based on the electrocardiographic synchronization method is performed n times (for example, every 2R-R based on the 2D-FASE method using inversion pulses). For example 5 times).
[0081]
The eco-signal generated from the patient P is received by the RF coil 7 and sent to the receiver 8R for each collection. 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 two-dimensional k-space formed in the memory. Since the half Fourier method is employed, k-space data not collected is obtained by calculation, and echo data is arranged in the entire k-space. Thereafter, two-dimensional Fourier transform is executed for each k space, and echo data is converted into real space image data. The tomographic image data is stored in the storage unit 11 and displayed on the display unit 12 as necessary.
[0082]
The image data collected by the measurement dynamic scan as described above forms a plurality of two-dimensional images obtained by dynamically capturing the same slice of the scan site as schematically shown in FIG. Therefore, after the dynamic scan for measurement, the arithmetic unit 10 uses, as an example, a process for measuring the relaxation time T1 or T2 using this image data and a process for reflecting the measurement result in the imaging scan, based on FIG. Do it.
[0083]
In FIG. 10, the arithmetic unit 10 first displays a representative image of a plurality of (for example, five) two-dimensional images collected by the dynamic scan for measurement on the display 12 (step S31). . The representative image may be the oldest first collected image over time, or an appropriate image may be selected while scrolling.
[0084]
Next, the arithmetic unit 10 displays the representative image I _REP An ROI is set for the upper lesion (step S32). For example, as shown in FIG. 9, this ROI is set so as to be contained within the aneurysm as a lesion. Thereby, the contamination from parts other than an aneurysm is prevented as much as possible. Next, it is visually confirmed on the screen whether or not the position and size of this ROI are satisfactory (step S33).
[0085]
Thereafter, the arithmetic unit 10 adds the signal value of the pixel position, for example, for the pixels that fall within the set ROI, and calculates the average value of the signal values as the entire ROI (step S34). This average value calculation is repeated with respect to the region corresponding to the above-mentioned ROI with respect to all the plural (for example, five) two-dimensional images (step S35). Thereby, an average value of a plurality (for example, five) of signal values corresponding to the number of images is obtained.
[0086]
Next, the arithmetic unit 10 obtains the longitudinal relaxation time T1 or the lateral relaxation time T2 by logarithmic calculation using the average value of the plurality of calculated signal values (step S36). In the first embodiment, since a plurality of two-dimensional images having different inversion times TI are obtained, the longitudinal relaxation time T1 is calculated. Specifically, as shown in FIG. 11, when the average value of the signal values is S, the inversion time TI is plotted on the horizontal axis, and lnS (ln is a natural logarithm) is plotted on the vertical axis. The slope represents the value for T1 time.
[0087]
When the relaxation time T1 or T2 is obtained in this way, this time value is passed to the host computer 6. The host computer 6 appropriately adjusts the imaging parameters (inversion time TI, repetition time TR, etc.) executed in the imaging scan according to the obtained relaxation time T1 or T2, and obtains a T1-weighted image or a T2-weighted image. (Step S37). Then, the host computer 6 determines whether or not to continue the imaging scan from the operation information or the like, and if it is determined that such a scan is to be performed, instructs the sequencer 5 to perform an imaging scan using the updated imaging parameters ( Steps S38 and S39).
[0088]
Thus, as an example, imaging is performed with the same pulse sequence (two-dimensional FASE method pulse train using an inversion pulse based on the electrocardiogram synchronization method) used in the measurement dynamic scan, and an image of the lesion is obtained. .
[0089]
According to the present embodiment, as described above, the longitudinal relaxation time T1 of a vascular disease can be measured easily (that is, simply and in a short time) using image data obtained by one measurement dynamic scan. Can do. For this reason, by observing the degree of the measured T1 time value, it is possible to easily grasp the stage of the degree of bleeding of a vascular disease that changes its properties depending on the time, such as a thrombus, and can be used for diagnosis. .
[0090]
Further, based on the measurement result of the T1 time value, an imaging scan of the T1-weighted image can be performed on the lesion with the optimal imaging parameter. For this reason, for example, the contrast between the tumor portion and the surrounding bleeding portion is different, and the boundary between the two can be more clearly differentiated and depicted. As a result, various information useful for diagnosis can be obtained, such as the size and spread of the tumor can be clearly determined.
[0091]
Further, since the physical quantity (inversion time TI in this embodiment) necessary for the measurement of the T1 time is set automatically or in an interactive form with the operator, as represented by steps S21A to S21D in FIG. It is possible to provide a device that is easy to use and easy to use.
[0092]
Furthermore, when the T1 time is measured as described above and a T1-weighted image is scanned based on the measurement result as necessary, an electrocardiographic synchronization method based on an optimal synchronization timing (delay time) is assumed. For this reason, it is possible to set in advance the optimal synchronization timing for the depiction of blood flow in accordance with the pulsation of the heart, thereby reliably capturing the blood flow and obtaining clearer image data of the vascular disease site. Can be used for measurement. For this reason, more accurate and stable T1 measurement can be performed, and the T1 enhancement degree of subsequent imaging can be further ensured.
[0093]
(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. The MRI apparatus of this embodiment measures the lateral relaxation time T2 as in the first embodiment, and can capture a T2-weighted image according to the measurement result. In this embodiment as well, the ECG synchronization timing is determined using ECG-prep scanning. For this reason, as shown in FIG. 2 described above, T2 time measurement and imaging are performed in the order of ECG-prep scan, measurement dynamic scan, and imaging scan.
[0094]
The hardware configuration of the present embodiment is the same as or equivalent to that described in the first embodiment. The ECG-prep scan, the measurement dynamic scan, and the imaging scan have the same processing flow as that of the first embodiment. However, in this embodiment, since the lateral relaxation time T2 is measured, the variable parameter required for this measurement is set to the effective echo time TE. _eff (In the first embodiment, this takes the inversion time TI).
[0095]
After the same ECG-prep scan as described above, the host computer 6 and the sequencer 5 command the measurement dynamic scan using the pulse sequence shown in FIG. 12 (see FIG. 6, step 24 and FIG. 7).
[0096]
This pulse sequence is performed based on the electrocardiographic synchronization method, and the synchronization timing, that is, the delay time T from the R wave of the ECG signal. _DL Is a value determined by the ECG-prep scan. As an example, the type of the pulse sequence is a pulse train based on the two-dimensional FASE method.
[0097]
In the dynamic scan for measurement, this pulse sequence is activated a plurality of times every 2R-R, and the effective echo time TE is _eff Is changed from t1 to tn. For example, t1 <t2 <t3 ... <tn. Effective echo time TE _eff Is a period from the time of RF excitation to the central time of collecting echo signals arranged at the position of phase encoding amount = 0 in k-space. For this reason, the effective echo time TE _eff Can be varied by adjusting the number of echoes. Therefore, after the measurement dynamic scan is completed, image data of a plurality of (for example, five) two-dimensional images obtained by dynamically imaging the same slice of the scan region is generated.
[0098]
Therefore, the arithmetic unit 10 measures the time T2 using the ROI in the same manner as the processing in FIG. 10 described above. In this measurement, the transverse relaxation time T2 is obtained by logarithmic calculation using an average value obtained by averaging signal values in the ROI for each image. Specifically, as shown in FIG. 13, when the average value of the signal values is S, the horizontal axis represents the effective echo time TE. _eff When lnS (ln is a natural logarithm) is plotted on the vertical axis, the slope of the straight line represents the value of T2 time.
[0099]
When the relaxation time T2 is obtained in this way, this time value is passed to the host computer 6. The host computer 6 performs imaging parameters (effective echo time TE) to be executed in the imaging scan. _eff , Repetition time TR, etc.) is appropriately adjusted in accordance with the obtained value of relaxation time T2, so that a T2-weighted image is obtained. If the host computer 6 determines that an imaging scan is to be performed, the host computer 6 instructs the sequencer 5 to perform an imaging scan using the updated imaging parameters.
[0100]
Thereby, as an example, imaging is performed with the same pulse sequence as that used in the dynamic scan for measurement (a pulse train of a two-dimensional FASE method employing an electrocardiogram synchronization method), and an image of a lesion is obtained.
[0101]
Therefore, the same effect as that obtained in the first embodiment can be obtained for the lateral relaxation time T2. Furthermore, in combination with the first embodiment, it is possible to easily measure either the T1 time or the T2 time. By designing in such a manner, depending on the type of vascular disease, either T1 time or T2 time can be quickly selected and measured on the spot, and an enhanced image reflecting the measurement result is easily provided. Will be able to. As a result, the MRI apparatus can be multi-functional and its versatility can be improved.
[0102]
In the second embodiment, the effective echo time TE _eff The image data of T2 time measurement is collected by performing a dynamic scan while changing the effective echo time TE. _eff Instead of this, an echo interval ETS (Echo Train Spacing) may be taken as a measurement parameter, and the echo interval ETS may be dynamically changed to collect data. In this case, the horizontal axis of FIG. 13 is represented by the echo interval ETS.
[0103]
(Third embodiment)
A third embodiment of the present invention will be described with reference to FIG. The present embodiment shows an example in which the vertical relaxation time T1 is measured and a T1-weighted image is obtained, as in the first embodiment.
[0104]
However, the main difference from the first embodiment is that the electrocardiographic synchronization method is not used for the dynamic scan for measurement as shown in FIG. The pulse sequence of this scan is a pulse train based on the two-dimensional FASE method using an inversion pulse, as in the first embodiment. In this scan, with the repetition time TR of the shot (RF excitation) set to an arbitrary value, the inversion time TI is changed for each shot, and a plurality of images corresponding to the number of shots from the inversion time TI = t1 to tn. Get the data.
[0105]
Subsequent measurement processing and imaging scan are performed in the same manner as in the first embodiment. Thus, T1 time measurement not based on the electrocardiogram synchronization method is possible, and measurement is diversified.
[0106]
In the third embodiment, the repetition time TR itself may be used as a measurement parameter, and the measurement dynamic scan may be similarly performed by changing the repetition time TR to measure and image T1.
[0107]
Note that the types of pulse sequences that can be used in the first to third embodiments described above are not limited to pulse trains based on the FASE method, and may be one-shot two-dimensional scans, which are ultra-high speed scan methods. An EPI (echo planar imaging) method, a hybrid EPI method (GRASE method), or the like may be used.
[0108]
(Fourth embodiment)
A fourth embodiment of the present invention will be described with reference to FIG. The present embodiment shows an example in which a lateral relaxation time T2 is measured to obtain a T2-weighted image, as in the second embodiment.
[0109]
However, the main difference from the second embodiment is that, as shown in FIG. 15, the electrocardiographic synchronization method is not used for the measurement dynamic scan, while the two-dimensional scan EPI method is used as the scan pulse sequence. is there. In this scan, the effective echo time TE is set with the repetition time TR of the shot (RF excitation) set to an arbitrary value. _eff For each shot, change TE _eff = A plurality of pieces of image data corresponding to the number of shots from t1 to tn are obtained.
[0110]
Subsequent measurement processing and imaging scan are performed in the same manner as in the second embodiment. In this way, T2 time measurement not based on the electrocardiogram synchronization method is possible, and measurement is diversified.
[0111]
In the fourth embodiment, the echo interval ETS may be taken as a measurement parameter, and the dynamic scan for measurement may be similarly performed by changing the echo interval ETS, and the measurement and imaging for T2 time may be performed.
[0112]
In addition, the type of pulse sequence that can be used in this embodiment is not limited to the pulse train based on the EPI method, and may be a one-shot two-dimensional scan, such as a hybrid EPI method (GRASE method). .
[0113]
Furthermore, as a scanning method for classifying in the order of echo data collection of the pulse sequence employed in each of the above-described embodiments, even in the case of line scan (linear order data collection order), spurious scan (spiral order data collection order) It may be.
[0114]
Furthermore, in each of the above-described embodiments, only the T1 time and T2 time measurement functions are mounted, and the imaging scan is a conventional single scan (that is, an imaging scan that is not linked to the measurement function is performed). An apparatus can also be provided.
[0115]
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.
[0116]
【The invention's effect】
As explained above, the present invention MRI equipment According to the method, it is possible to easily and quickly measure the T1 time and T2 time of a lesion part associated with bleeding, thrombus, etc. without administering a contrast medium, and estimate the progress of the disease state of the lesion part from the measurement result. Thus, it is possible to provide a diagnostic function associated with a vascular disease, which is not present in the past.
[0117]
In addition, according to the MRI apparatus of the present invention, a T1-weighted image or a T2-weighted image of a lesion such as a tumor that accurately reflects the above measurement result can be obtained. Can be distinguished and contrasted. This makes it possible to provide useful diagnostic information such that the boundary between the two becomes clear and the true spread of the lesion can be reliably grasped.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a configuration example of an MRI apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining temporal relationships of an ECG-prep scan, a dynamic scan for measurement, and an imaging scan 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 schematic flowchart showing an example of control of a measurement dynamic scan executed by a host computer.
FIG. 7 is a schematic flowchart showing an example of control of measurement dynamic scan executed by the sequencer.
FIG. 8 is a rough timing chart of a measurement dynamic scan based on an electrocardiogram synchronization method according to the first embodiment;
FIG. 9 is a diagram schematically illustrating a plurality of slice images obtained by a measurement dynamic scan.
FIG. 10 is a flowchart showing an outline of processing related to T1 (T2) measurement and subsequent imaging scan commands;
FIG. 11 is a schematic diagram illustrating the principle of T1 measurement.
FIG. 12 is a rough timing chart of a dynamic scan for measurement based on an electrocardiogram synchronization method according to the second embodiment.
FIG. 13 is a schematic diagram illustrating the principle of T2 measurement.
FIG. 14 is a rough timing chart of a dynamic scan for measurement in the third embodiment.
FIG. 15 is a rough timing chart of a dynamic scan for measurement in the fourth embodiment.
[Explanation of symbols]
1 Magnet
2 Static magnetic field power supply
3 Gradient magnetic field coil unit
4 Gradient magnetic field power supply
5 Sequencer
6 Host computer
7 RF coil
8T transmitter
8R receiver
10 Arithmetic unit
11 Storage unit
12 Display
13 Input device
17 ECG sensor
18 ECG units

Claims (13)

For the same slice of the scan region of the subject, the measurement scan based on the pulse sequence is repeated a plurality of times in synchronization with the reference wave of the signal representing the cardiac time phase of the subject. And collecting means for collecting image data of a plurality of frames by changing the value of a physical quantity related to the behavior of the spin, and a measuring means for automatically measuring the relaxation time of the spin from the image data of the plurality of frames. An MRI apparatus characterized by The MRI apparatus according to claim 1,
An MRI apparatus comprising imaging means for imaging the scan region based on the relaxation time measured by the measuring means. The MRI apparatus according to claim 1 or 2,
The MRI apparatus, wherein the relaxation time is a longitudinal relaxation time T1 or a lateral relaxation time T2. The MRI apparatus according to claim 1 or 2,
The MRI apparatus, wherein the pulse sequence is a single shot type pulse train including a FASE (Fast Asymmetric SE) method or an EPI (Echo Planar Imaging) method. The MRI apparatus according to claim 4, wherein
The MRI apparatus, wherein the pulse sequence is a pulse sequence using an inversion pulse, the physical quantity is an inversion time TI due to the inversion pulse, and the relaxation time is a longitudinal relaxation time T1. The MRI apparatus according to claim 4, wherein
The MRI apparatus, wherein the physical quantity is an effective echo time TEeff, and the relaxation time is a longitudinal relaxation time T2. The MRI apparatus according to claim 4, wherein
The MRI apparatus, wherein the physical quantity is an echo interval ETS, and the relaxation time is a longitudinal relaxation time T2. The MRI apparatus according to claim 4, wherein
The MRI apparatus, wherein the physical quantity is a repetition time TR, and the relaxation time is a longitudinal relaxation time T1. The MRI apparatus according to claim 4, wherein
The collection means detects the signal representing the cardiac time phase of the subject, and the target of the scan region optimizes the synchronization timing for the reference wave in the signal detected by the time phase detection means. An MRI apparatus comprising: timing determination means for determining a value to be rendered in the image; and execution command means for executing the measurement scan at a synchronization timing determined by the timing determination means. The MRI apparatus according to claim 9, wherein
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. apparatus. The MRI apparatus according to any one of claims 1 to 10,
The measurement unit includes a display unit that displays image data of at least one frame of the image data of the plurality of frames as an image, a setting unit that sets a ROI (region of interest) at a desired position on the image, Signal value calculation means for calculating a pixel signal value related to the position of the ROI for each of the plurality of frames of image data, the signal value calculated for each of the plurality of frames of image data, and the plurality of frames of image data An MRI apparatus comprising relaxation time calculation means for calculating the relaxation time from a correspondence relationship with the value of the physical quantity used when collecting each. The MRI apparatus according to any one of claims 1 to 10,
The MRI apparatus, wherein the collection means includes physical quantity setting means in which an operator can set in advance at least one of a type of the physical quantity and a value to change the physical quantity. The MRI apparatus according to claim 1,
An MRI apparatus comprising timing determination means for determining an optimum value for a synchronization timing with respect to the reference wave from an image obtained by performing a preparatory scan in advance.

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