JP5319835B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention relates to a magnetic resonance imaging apparatus suitable for observing the dynamics of moving substances in the body such as blood and cerebrospinal fluid (CSF).

  By applying an inversion pulse, the observation target at a certain time is labeled (labeled) in the form of longitudinal magnetization, and an MRI image is captured after a certain period of time, whereby the distribution of the labeled observation target Is known (see Non-Patent Document 1, for example).

  When this method is used, RF excitation and echo for imaging are performed at a time when a certain time has elapsed from the time at which a characteristic electrocardiogram waveform such as an R wave of the heart appears using the ECG synchronization method. Signal collection is often performed. This utilizes the fact that changes in the flow rate of blood, cerebrospinal fluid, and the like often have the property of having a high correlation with the cardiac phase. By adopting such a synchronization method, artifacts due to pulsation can be reduced, and the rendering ability and signal intensity of blood vessels and cerebrospinal fluid are stabilized, and the image quality is improved.

  Furthermore, a method is known in which longitudinal magnetization is labeled by a selective excitation method before acquisition for imaging, and a plurality of images are captured while changing the time TI from the labeling time to imaging. (For example, see Patent Document 1). By continuously displaying a plurality of images obtained by this method with a certain time interval, the dynamics of moving substances in the body such as blood and cerebrospinal fluid can be observed.

  FIG. 24 is a diagram showing a pulse sequence of this conventional example. The waveforms shown in FIG. 24 are, in order from the top, ECG (electrocardiograph) as a synchronous waveform, a high-frequency pulse (RF) applied to the imaging target, a gradient magnetic field waveform (Gss) in the slice direction, and a gradient magnetic field waveform in the readout direction ( Gro), a gradient magnetic field waveform (Gpe) in the phase encoding direction, and a deviation (Δf) from the center frequency of the carrier wave when a high frequency pulse is applied. The period P1 is a tag sequence part for labeling blood and cerebrospinal fluid, and the period P2 is a pulse sequence part of the main body for imaging. In both periods P1 and P2, the gradient magnetic field strength combination and Δf can be set independently during selective excitation, and the direction and position of the excitation plane can be set independently. In this example, an example of the fast spin echo method is shown, but any imaging method such as a coherent gradient echo method (TrueSSFP method, TrueFISP, balancedFFE method) can be used. The number of shots necessary for reconstructing one image at the same time TI is collected. This imaging is repeated while changing the time TI. The cerebrospinal fluid dynamics are observed by continuously displaying a plurality of captured images having different times TI. Of the portion excited by the labeling pulse in the period P1, the portion that moves is moved according to the flow velocity during the time TI, so that the portion other than the labeled region on the image is reduced in signal. Thereby, the movement of blood and cerebrospinal fluid can be observed. Further, by adding another non-selective IR pulse before or after the RF pulse in the period P1, the longitudinal magnetization of the labeled portion becomes almost the initial state, and the movement of blood and cerebrospinal fluid is increased. An example of imaging as a signal is also shown.

  In addition, as a measurement method related to the movement of cerebrospinal fluid, other methods such as injecting a radioisotope into the spinal cavity and tracking the movement in the body by means of a scintillation counter in several hours, or a contrast agent (Metrizamide) There is a method of performing the same measurement using X-ray CT (computed tomography). These methods have the advantage of being able to observe long-term cerebrospinal fluid movement called bulk motion, but all of them are highly invasive to the subject, and the internal pressure of cerebrospinal fluid changes due to injection. There is a problem that there is a fear and affects the observation target.

JP 2001-252263 A

“Considerations of Magnetic Resonace Angiography by Selecitve Iversion Recovery”, D.G.Nishimura et al., Magnetic Resonance in Medicine, Vol. 7,472-484,1988

  Problem: In order to perform imaging using labeling, the device user needs clinical knowledge about the cerebrospinal fluid and blood circulation pathways, and it is difficult to set imaging conditions appropriately. It was.

  An object of the present invention is to enable easy and appropriate setting of imaging conditions.

  The present invention provides a magnetic resonance imaging apparatus for imaging cerebrospinal fluid for the purpose of observing cerebrospinal fluid of a subject. In the magnetic resonance imaging apparatus, a labeling unit, an acquisition unit, a control unit, a reconstruction unit, a display unit, and a reception unit are provided. Prepare. The labeling means labels the spins contained in the cerebrospinal fluid in a part of the labeling region in the imaging region of the subject. The acquisition unit acquires an echo signal related to spins included in the imaging region by a predetermined pulse sequence. The control unit controls the labeling unit and the acquisition unit so that the acquisition cycle of the echo signal is performed a plurality of times from the time when the labeling is performed. The reconstruction unit reconstructs a plurality of images in the imaging region based on echo signals acquired in each of a plurality of cycles. The display means displays at least one of the plurality of images as a positioning image. The accepting unit accepts designation of an imaging section on the positioning image.

The figure which shows the structure of the magnetic resonance imaging apparatus which concerns on the 1st thru | or 7th embodiment of this invention. The figure which shows the pulse sequence in 1st Embodiment. The figure which shows the flowchart of the process of the host computer 6 in FIG. 1 for condition setting. The figure which shows the modification of the pulse sequence in 1st Embodiment. The figure which shows the pulse sequence in 2nd Embodiment. The figure which shows the pulse sequence for a trigger detection in the period P11 in FIG. The figure which shows an example of the waveform of the echo signal obtained by the pulse sequence for trigger detection, and the absolute value and phase profile of the readout direction obtained by one-dimensional Fourier-transforming this echo signal. The figure which plotted the phase change (theta) (ro, i) measured by the pulse sequence for trigger detection in time order. The figure which shows the example of a setting of the excitation area | region and observation object area | region in 2nd Embodiment. The figure which shows another example of a setting of the excitation area | region and observation object area | region in 2nd Embodiment. The figure which shows the pulse sequence in 3rd Embodiment. The figure which shows a mode that the image IM1, IM2 ..., IMm is average-processed, and the average image IMave is produced. The figure which shows a mode that the dispersion | distribution image IMvar proportional to dispersion | distribution of image IM1, IM2 ..., IMm is produced. The figure which shows the pulse sequence in 4th Embodiment. The figure which shows the example of a setting of the labeling area | region in 4th Embodiment. The figure explaining an example of a suitable cross section in order to obtain the image for positioning for setting the labeling area | region in 4th Embodiment. The figure which shows the example of a setting of the two-dimensional image imaged about the cross section S1 shown by FIG. 16, and a labeling area | region in this image. The figure which shows an example of the image imaged by the pulse sequence of 4th Embodiment in the state in which labeling area | regions R11 and R12 were set as shown in FIG. The figure which shows an example of the image for positioning in 5th Embodiment. The figure which shows the example of a setting of the imaging cross section on the image for positioning shown in FIG. The figure which shows an example of the two-dimensional image imaged regarding the imaging cross section S11 shown in FIG. The figure which shows an example of the image obtained by imaging after labeling the labeling area | region R23 as shown in FIG. It is a flowchart which shows the procedure of the characteristic process in 6th Embodiment of the host computer 6 in FIG. The figure which shows the pulse sequence disclosed by patent document 1. FIG.

  Hereinafter, first to seventh embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) according to the first to seventh embodiments.

  This MRI apparatus includes a bed unit on which a patient P as a subject is placed, a static magnetic field generating unit for generating a static magnetic field, a gradient magnetic field generating unit for adding position information to the static magnetic field, and transmission and reception for transmitting and receiving high-frequency signals. Unit, a control / arithmetic unit responsible for overall system control and image reconstruction, an electrocardiogram measurement unit that measures an ECG signal as a signal representing the cardiac time phase of the subject P, and commands the patient P to hold his / her breath And a breath-hold command unit.

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 (diagnosis space) into which the subject P is loosely inserted. A static magnetic field H ₀ is generated in the (Z-axis direction). 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.

  The gradient magnetic field generator includes a gradient magnetic field coil unit 3. The gradient magnetic field coil unit 3 includes three sets of coils 3x, 3y, and 3z for generating gradient magnetic fields in the X, Y, and Z axis directions orthogonal to each other. The gradient magnetic field generation unit also includes a gradient magnetic field power supply 4 that supplies current to the coils 3x to 3z. The gradient magnetic field power supply 4 supplies a pulse current for generating a gradient magnetic field to the coils 3x to 3z under the control of a sequencer 5 described later.

By adjusting the pulse current supplied from the gradient magnetic field power supply 4 to the coils 3x to 3z, the gradient magnetic fields in the X, Y, and Z directions, which are physical axes, are synthesized and slice direction gradient magnetic fields Gs orthogonal to each other. The logical axis directions of the phase encoding direction gradient magnetic field Ge and the readout direction (frequency encoding direction) gradient magnetic field Gr can be arbitrarily set. Each gradient magnetic field in the slice direction, the phase encoding direction, and the readout direction is superimposed on the static magnetic field H ₀ .

  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 pulse having a Larmor frequency for causing nuclear magnetic resonance (NMR). The receiver 8R takes in an echo 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. A digital amount of echo data (original data) corresponding to the echo signal is generated by / D conversion.

  The control / arithmetic unit includes a sequencer (also referred to as a sequence controller) 5, a host computer 6, an arithmetic unit 10, a storage unit 11, a display device 12, an input device 13, and a sound generator 16. Among these, the host computer 6 has a function of commanding the pulse sequence information to the sequencer 5 according to the stored software procedure and overseeing the operation of the entire apparatus.

  The host computer 6 performs an imaging scan following a preparatory work such as a positioning scan. The imaging scan is a scan that collects a set of echo data necessary for image reconstruction, and is set to a two-dimensional scan here. The imaging scan can be performed using an ECG gate method based on an ECG signal. This ECG gate method may not be used in some cases.

  The pulse sequence is a three-dimensional (3D) scan or a two-dimensional (2D) scan. The pulse train forms include the SE (spin echo) method, the FSE (fast spin echo) method, the FASE (fast asymmetric spin echo) method combining the fast SE method with the half Fourier method, and the EPI (echo planar imaging) method. Used.

  The sequencer 5 includes a CPU and a memory, stores pulse sequence information transmitted from the host computer 6, and controls the operations of the gradient magnetic field power source 4, the transmitter 8T, and the receiver 8R according to this information. At the same time, the echo data output from the receiver 8R is temporarily input and transferred to the arithmetic unit 10. 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, the intensity of the pulse current applied to the coils 3x to 3z, the application Includes information about time, application timing, etc.

  The arithmetic unit 10 inputs the echo data output from the receiver 8 </ b> R via the sequencer 5. The arithmetic unit 10 arranges echo data in a Fourier space (also referred to as k space or frequency space) on its internal memory, and applies this echo data to a two-dimensional or three-dimensional Fourier transform for each group in real space. To reconstruct the image data. In addition, the arithmetic unit can perform data composition processing, difference calculation processing, and the like as necessary.

  In the synthesis process, an addition process that adds image data of two-dimensional plural frames for each corresponding pixel, a maximum value projection (MIP) process that selects a maximum value or a minimum value in the line-of-sight direction for the three-dimensional data, or minimum Value projection processing and the like are included. As another example of the synthesis process, the axes of a plurality of frames may be matched in the Fourier space and synthesized into one frame of echo data as it is. The addition processing includes simple addition processing, addition averaging processing, weighted addition processing, and the like.

  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 displays an image under the control of the host computer 6. Information relating to imaging conditions, pulse sequences, image composition and difference calculation desired by the operator can be input to the host computer 6 via the input unit 13.

  The sound generator 16 is provided as one element of the breath holding command unit. The voice generator 16 can emit a breath holding start message and a breath holding end message as voices under a command from the host computer 6.

  The electrocardiograph measures the ECG sensor 17 that attaches to the body surface of the subject and detects the ECG signal as an electrical signal, and performs various processing including digitization on the sensor signal to the host computer 6 and the sequencer 5. ECG unit 18 to output. The measurement signal from the electrocardiogram measurement unit is used by the sequencer 5 when executing an imaging scan. Thereby, the synchronization timing by the ECG gate method (electrocardiogram synchronization method) can be set appropriately, and the ECG gate method imaging scan based on this synchronization timing can be performed to collect data.

  Next, the operation of the MRI apparatus configured as described above will be described in detail.

(First embodiment)
The first embodiment will be described below.

  FIG. 2 is a diagram showing a pulse sequence in the first embodiment. The waveforms shown in FIG. 2 are, in order from the top, an ECG (electrocardiograph) as a synchronous waveform, a radio frequency pulse (RF) applied to an imaging target, a gradient magnetic field waveform (Gss) in a slice direction, and a gradient magnetic field waveform in a readout direction ( Gro), a gradient magnetic field waveform (Gpe) in the phase encoding direction, and a deviation (Δf) from the center frequency of the carrier wave when a high frequency pulse is applied. The period P1 is a tag sequence part for labeling blood and cerebrospinal fluid, and the period P2 is a pulse sequence part of the main body for imaging. In this example, the fast spin echo method is adopted, but any imaging method such as a coherent gradient echo method (TrueSSFP method, TrueFISP, balancedFFE method) can be used.

  As can be seen by comparing FIG. 2 and FIG. 24, the pulse sequence in the first embodiment is based on the pulse sequence disclosed in Patent Document 1. That is, a plurality of imaging cycles including labeling in the period P1 and echo collection in the period P2 are changed while changing the magnitude of the time TI from the excitation by the labeling pulse LP to the start of the pulse sequence for echo collection. Repeat once. The pulse sequence in the first embodiment is different from the pulse sequence shown in FIG. 24 in that the time TDtag from the reference time phase to the excitation by the labeling pulse LP is set to the time TI for each imaging cycle. It is in the point of changing contradictoryly. Here, the time phase in which the R wave occurs in the ECG is set as the reference time phase.

  FIG. 3 is a diagram showing a flowchart of processing of the host computer 6 for setting conditions.

In step Sa1, the host computer 6 inputs, for example, the value of the time TI _n specified by the operator for each of a plurality of imaging cycles, or the number of imaging cycles specified by the operator, for example, the first imaging cycle. The value of the time TI _{1 and} the amount of change ΔTI of the time TI are input, and the time TI _n for each of the second and subsequent imaging cycles is calculated based on a predetermined mathematical formula. As this formula, for example, the following formula can be applied.

TI _n = TI ₁ − (n−1) · ΔTI
In step Sa2, the host computer 6 inputs a value designated by the operator, for example, as a time TDseq from the reference time phase until the start of a pulse sequence for echo collection.

  In step Sa1 and step Sa2, various values may be input in any form such as a default value or a value selected by an operator from a plurality of default values. The order in which various values are input may be arbitrary.

In step Sa3, the host computer 6 calculates a time TDtag _n for each of a plurality of imaging cycles by the following equation.

TDtag _n = TDseq-TI _n
In general, TDtag _n must be 0 or a positive value for the control of the device. Therefore, if necessary, TDseq is equal to or greater than the maximum value of TI _n when TDseq is input. The input may be limited so that

In step Sa4, the host computer 6 executes scanning according to the pulse sequence shown in FIG. At this time, the host computer 6 instructs the sequencer 5 to apply the time TDtag _n and the time TI _n in the n-th imaging cycle. Based on this instruction, the sequencer 5 repeatedly executes the imaging cycle while changing the time TDtag and the time TI, respectively. In the example of Figure 2, but the first time TI ₂ at the second imaging cycle against time TI ₁ in the imaging cycle is small, this and the time TDtag ₁ in the first imaging cycle reciprocally is On the other hand, the time TDtag ₂ in the second imaging cycle is large.

  Information that is useful for observing the dynamics of blood and cerebrospinal fluid can be presented by continuously displaying multiple images reconstructed based on echo data collected for each imaging cycle. . That is, in the portion excited by the labeling pulse LP in the period P1, the portion that moves is moved according to the flow velocity during the time TI, so that the region that is not tagged on the image is reduced in signal. By tracking this part on each image, the movement of blood and cerebrospinal fluid can be observed.

  In the first embodiment, since the time TDtag is inversely proportional to the time TI, the time TDseq is the same in each imaging cycle. For this reason, the time TDseq from the reference time phase to the start of the pulse sequence for echo collection is uniform in each imaging cycle while the dynamics of blood and cerebrospinal fluid are depicted by changing the time TI. For this reason, since each imaging cycle synchronizes with ECG with high precision, the influence of the periodic fluctuation accompanying a pulsation is suppressed, and the fluctuation | variation and artifact of the image for every imaging can be suppressed.

  When the high-speed spin echo method using the CPMG pulse sequence is used as the pulse sequence of the main body, the image is constructed as a composite of a plurality of echo components having different phase change amounts due to the flow velocity. The image value changes drastically in response to. For this reason, according to the first embodiment, the reduction in image quality variation due to the uniform time TDseq in each imaging cycle is more significant than other pulse sequences, and is particularly effective.

  It is also possible to employ a pulse sequence that requires a plurality of shots in order to reconstruct one image. In this case, it suffices to repeat the procedure of echo collection for the number of shots necessary to reconstruct one image without changing the time TI, and further repeating such processing while changing the time TI.

  Further, as shown in FIG. 4, an IR pulse (180 degree pulse) A may be added before the labeling pulse LP in a non-slice state (the slice gradient magnetic field is 0 when RF is applied). As a result, the longitudinal magnetization of the labeled portion becomes almost the initial state, and the movement of blood or cerebrospinal fluid can be imaged as a high signal. That is, an image obtained by inverting the image obtained by the pulse sequence shown in FIG. 2 can be obtained.

(Second Embodiment)
Hereinafter, the second embodiment will be described.

  FIG. 5 is a diagram showing a pulse sequence in the second embodiment. The waveforms shown in FIG. 5 are, in order from the top, the cerebrospinal fluid pulsation waveform as a synchronous waveform, the high-frequency pulse (RF) applied to the imaging target, the gradient magnetic field waveform (Gss) in the slice direction, and the gradient magnetic field in the readout direction. A waveform (Gro), a gradient magnetic field waveform (Gpe) in the phase encoding direction, and a deviation (Δf) from the center frequency of the carrier wave when a high frequency pulse is applied are shown. The period P1 is a tag sequence part for labeling blood and cerebrospinal fluid, and the period P2 is a pulse sequence part of the main body for imaging. In this example, the fast spin echo method is adopted, but any imaging method such as a coherent gradient echo method (TrueSSFP method, TrueFISP, balancedFFE method) can be used.

  As can be seen by comparing FIG. 5 and FIG. 24, the pulse sequence in the second embodiment has the same periods P1 and P2 as the pulse sequence disclosed in Patent Document 1, and further prior to the period P1. It has a period P11. The period P11 is a period for detecting a trigger for starting the period P1. Then, an imaging cycle including labeling in the period P1 and echo collection in the period P2 is repeated a plurality of times, with the time phase in which the trigger is detected in the period P11 as the reference time phase.

  FIG. 6 is a diagram showing a pulse sequence for trigger detection in the period P11 in FIG. The waveforms shown in FIG. 6 are, in order from the top, a radio frequency pulse (RF) applied to the imaging target, a gradient magnetic field waveform (Gss) in the slice direction, a gradient magnetic field waveform (Gro) in the readout direction, and a gradient magnetic field in the phase encoding direction. A waveform (Gpe), a gradient magnetic field pulse (Gvenc) for flow encoding, and an echo signal waveform (Echo) are shown. The period P21 is a two-dimensional RF pulse for exciting a cylindrical region. This excitation by two-dimensional RF pulses is known from “Hardy, CJ, and Cline, HE, 1989. Broadband nuclear magnetic resonance pulses with two-dimensional spatial selectivity. J. Appl. Phys 66: 1513-1516.” .

  To increase the temporal resolution of the flow velocity, measure the flow velocity of cerebrospinal fluid or blood in a limited volume in a single time TR by limiting the imaging area by two-dimensional excitation in the slice direction and phase encoding direction. Can do. By applying a gradient magnetic field pulse Gvenc for flow encoding after excitation until echo collection, the echo signal undergoes a phase change proportional to the average flow velocity during the period. The time TR is about 10 to 200 ms, for example.

  For example, an echo signal having a waveform W shown in FIG. 7 is obtained by the above-described pulse sequence for trigger detection. Then, by performing one-dimensional Fourier transform (1DFT) on the echo signal by the host computer 6, absolute values and phase profiles PR1 and PR2 in the readout direction are obtained as shown in FIG.

  Before starting imaging in the second embodiment, an area to be excited in a pulse sequence for trigger detection (hereinafter referred to as an excitation area), an area to be observed for phase change (hereinafter referred to as an observation area) Is set in accordance with an instruction from the surgeon, for example.

FIG. 9 is a diagram illustrating an example of setting the excitation region and the observation target region. In this example, the operator designates a rectangular frame 21 representing an excitation area on the positioning image and two straight lines 22 and 23 orthogonal to the readout direction. Then, the host computer 6 sets a columnar (bar-shaped) region whose projection shape is a rectangular frame 21 as an excitation region, and the interval between the intermediate position r ₀ of the straight lines 22 and 23 in the readout direction and the straight lines 22 and 23. An observation target region is set as Δr.

FIG. 10 is a diagram illustrating another example of setting the excitation region and the observation target region. In this example, since the lead-out direction is different from the lead-out direction in the example of FIG. 9, the directions of the rectangular frame 24 and the straight lines 25, 26 are different, but the projected shape is a circle that looks like the rectangular frame 24. There is no difference in setting a columnar (bar-shaped) region as an excitation region and setting an observation target region by an intermediate position r _{0 in} the readout direction of the straight lines 25 and 26 and an interval Δr between the straight lines 25 and 26. Instead of the position r ₀ , the positions of the two straight lines in the lead-out direction may be used as observation area information.

  The positioning images in FIGS. 9 and 10 are sagittal cross-sectional images of the head. In this case, in the pulse sequence for trigger detection, the change in the flow rate of the cerebrospinal fluid in the head is directly and continuously obtained from the NMR signal to detect the trigger. In this case, as shown in FIG. 9 and FIG. 10, the excitation region is set so as to include a cerebral aqueduct portion having a high flow velocity and a large fluctuation, and the flow direction of cerebrospinal fluid It is desirable to match the direction of flow encoding. FIG. 9 shows an example in which the lead-out direction is aligned with the portion of the midbrain, and FIG. 10 shows an example in which the slice direction or the phase encoding direction is aligned with the portion of the midbrain. The example of FIG. 10 has a feature that the influence on the main imaging performed after the trigger detection is small because the range of exciting the cerebrospinal fluid portion to be observed with the pulse sequence for trigger detection is narrower.

  The host computer 6 measures an average phase change θ (ro, i) in the observation target region in the phase profile PR2. Here, i represents an index of the number of repetitions of time TR. By setting the observation target region as described above, the target voxel can be reduced, the partial volume effect can be reduced, and the phase change reflecting the change in flow velocity more faithfully can be measured.

  When the phase change θ (ro, i) measured at each time TR is plotted in time order, for example, the state of pulsation of cerebrospinal fluid appears as shown in FIG. Thus, if the time point at which the measured phase change θ (ro, i) matches a predetermined state is determined as the reference time phase, this reference time phase is synchronized with the cerebrospinal fluid pulsation with high accuracy. In the example of FIG. 8, an example is shown in which a time phase in which the phase change θ (ro, i) exceeds a threshold is defined as a reference time phase. In order to determine the reference time phase, for example, other methods such as a method of time-differentiating a waveform as shown in FIG. 8 to detect an inflection point can be employed. However, since the phase change θ (ro, i) can only collect a part of the data after the start of imaging, the trigger detection sequence is continuously executed before the imaging starts, and the average reference time phase (trigger) interval Alternatively, it may be necessary in some cases to determine a threshold value that can stably detect the reference time phase (trigger).

  Then, as shown in FIG. 5, the host computer 6 synchronizes the pulse sequence in the periods P1 and P2, that is, the main imaging so as to repeat the main imaging in synchronization with the reference time phase determined as described above in the period P11. Control. In the example of FIG. 5, the pulse sequence in the period P1 is immediately started with the trigger of reaching the reference time phase.

  As described above, according to the second embodiment, the pulsation of the cerebrospinal fluid is observed, and the reference time phase is determined based on the observation result. Therefore, the brain is more accurately compared to using ECG as a synchronous waveform. Echo collection can be performed in synchronization with the spinal fluid pulsation. As a result, the influence of periodic fluctuations associated with pulsation is suppressed, and fluctuations and artifacts in images for each imaging can be suppressed.

  It should be noted that the pulse sequence for trigger detection in the second embodiment can be applied to an imaging sequence in the first embodiment, the third embodiment, and the like.

  A part of the processing for trigger detection (for example, one-dimensional Fourier transform) may be performed by the arithmetic unit 10.

  Although an example in which a change in the local flow rate of cerebrospinal fluid is the target of trigger detection has been shown, it is also known that the cerebrospinal fluid moves the brain parenchyma due to pulsation. It is also possible to apply a high-intensity gradient magnetic field pulse (Gvenc) for flow encoding to make the minute motion of the brain parenchyma a target for trigger detection. It is also possible to make a change in blood flow the target of trigger detection.

(Third embodiment)
Hereinafter, a third embodiment will be described.

  FIG. 11 is a diagram showing a pulse sequence in the third embodiment. The waveforms shown in FIG. 11 are, in order from the top, an ECG (electrocardiograph) as a synchronous waveform, a radio frequency pulse (RF) applied to an imaging target, a gradient magnetic field waveform (Gss) in a slice direction, and a gradient magnetic field waveform in a readout direction ( Gro), a gradient magnetic field waveform (Gpe) in the phase encoding direction, and a deviation (Δf) from the center frequency of the carrier wave when a high frequency pulse is applied. The period P1 is a tag sequence part for labeling blood and cerebrospinal fluid, and the period P2 is a pulse sequence part of the main body for imaging. In this example, the fast spin echo method is adopted, but any imaging method such as a coherent gradient echo method (TrueSSFP method, TrueFISP, balancedFFE method) can be used.

  As can be seen by comparing FIG. 11 and FIG. 24, the pulse sequence in the third embodiment is based on the pulse sequence disclosed in Patent Document 1. That is, an imaging cycle including labeling in the period P1 and echo collection in the period P2 is repeated a plurality of times. The pulse sequence in the third embodiment is different from the pulse sequence shown in FIG. 24 in that the time TDtag and the time TI are constant in each cycle. In addition, although the sequence which makes time TDtag and time TI constant in each cycle is also shown in Patent Document 1, in Patent Document 1, the area to be labeled is different for each cycle. In the third embodiment, the labeling region is the same in each cycle. Such a pulse sequence can be realized by the control of the sequencer 5.

  By continuously displaying multiple images reconstructed based on echo data collected for each imaging cycle, it is possible to observe only image changes due to fluctuations in the movement of the observation target during individual imaging. . If necessary, the order of continuous display may be changed depending on the distance reached by the labeling portion on each image.

  Further, in order to reduce the influence of the fluctuation of the flow velocity every time, for example, as shown in FIG. 12, the averaged image IMave is generated and displayed by averaging the plurality of captured images IM1, IM2,. Also good. Alternatively, for example, as shown in FIG. 13, a dispersion image IMvar proportional to the dispersion of the images IM1, IM2,..., IMm may be created and displayed. Furthermore, the average image IMave and the dispersion image IMvar may be displayed with different colors.

  Furthermore, the above-described multiple times of image acquisition are performed while changing the time TI and the labeling region as necessary, and this series of processing called image averaging processing is performed for a plurality of different time TI and labeling regions having different positions. A plurality of obtained images after different average processing may be continuously displayed. In this case, it is possible to greatly reduce the influence of the fluctuation of the flow velocity, which is remarkable in each imaging, and to display the image change due to the difference in the time TI and the position of the labeling region more clearly.

  The display of various images as described above is performed on the display 12 under the control of the host computer 6, for example. Various image processing is performed by the host computer 6 or the arithmetic unit 10.

(Fourth embodiment)
Hereinafter, a fourth embodiment will be described. This fourth embodiment corresponds to the object of the present invention.

  FIG. 14 is a diagram showing a pulse sequence in the fourth embodiment. The waveforms shown in FIG. 14 are, in order from the top, an ECG (electrocardiograph) as a synchronous waveform, a high-frequency pulse (RF) applied to the imaging target, a gradient magnetic field waveform (Gss) in the slice direction, and a gradient magnetic field waveform in the readout direction ( Gro), a gradient magnetic field waveform (Gpe) in the phase encoding direction, and a deviation (Δf) from the center frequency of the carrier wave when a high frequency pulse is applied. The period P31 is a tag (label) sequence part for labeling blood and cerebrospinal fluid, and the period P2 is a pulse sequence part of the main body for imaging. In this example, the fast spin echo method is adopted, but any imaging method such as a coherent gradient echo method (TrueSSFP method, TrueFISP, balancedFFE method) can be used.

  In the pulse sequence in the fourth embodiment, an imaging cycle including labeling in the period P31 and echo collection in the period P2 is repeated a plurality of times. The pulse sequence for echo collection in the period P2 is the same as that shown in FIG.

In the period 31, three labeling pulses LP ₁ , LP ₂ , LP ₃ are continuously applied from the time when the time TDtag has elapsed from the reference time phase in which the R wave is generated in the ECG. When applying these labeling pulses LP ₁ , LP ₂ , LP ₃ , the gradient magnetic field waveforms are made different as shown in FIG. 14 in order to make the regions to be labeled different. Further, prior to applying the labeling pulse LP ₁ , the labeling pulse LP ₀ is applied. At this time, the labeling region is not selected without generating a gradient magnetic field. Such a pulse sequence can be realized by the control of the sequencer 5.

In the region excited by any of the labeling pulses LP ₁ , LP ₂ , LP ₃ , 180 ° inversion excitation is also performed by the labeling pulse LP ₀ . Since the time difference between the labeling pulse LP ₀ and the labeling pulses LP ₁ , LP ₂ , LP ₃ is sufficiently shorter than the T1 value of the labeling target such as cerebrospinal fluid, it is excited by the labeling pulses LP ₁ , LP ₂ , LP ₃ In this region, the longitudinal magnetization is almost in the initial state, as is the case with excitation of a flip angle of 360 degrees. On the other hand, in the region that is not excited by any of the labeling pulses LP ₁ , LP ₂ , LP ₃ , it is excited only by the labeling pulse LP ₀ , so that it is excited by 180 degrees and the longitudinal magnetization is inverted.

  Thus, according to the above pulse sequence in the fourth embodiment, it is possible to label three different regions. In the image reconstructed from the echoes collected in the period P2, only the portion labeled in the above three regions becomes a high signal. That is, according to the image picked up by the fourth embodiment, the dynamics of cerebrospinal fluid and blood over a wide range can be grasped on one image, and an efficient examination can be performed.

  In addition, since three independent regions can be labeled, an image effective for grasping the dynamics of cerebrospinal fluid and blood regarding different parts can be obtained.

  Note that the number of labeling regions may be two or four or more.

  A specific example of setting a plurality of labeling areas will be described below.

  Monro foramen, mesencephalic aqueduct and pontine cistern, or foramen magnum are known as sites of high clinical interest. These portions are portions where the flow of cerebrospinal fluid is narrow even in healthy subjects, and the flow velocity is relatively fast. Depending on the case, these sites may become narrower than normal subjects, or changes in cerebrospinal fluid flow may occur. Therefore, for example, as shown in FIG. 15, a region R1 including the Monroe groove, a region R2 including the middle brain aqueduct and the bridge tank, and a region R3 including the large occipital foramen can be set as labeling regions. In this way, using clinical knowledge about cerebrospinal fluid and blood circulation pathways, by setting the three labeling areas appropriately, it is possible to obtain very useful images suitable for clinical observation purposes. Is possible.

  Another area of clinical interest is the fossa lateralis cerebri. For the purpose of grasping the dynamics of cerebrospinal fluid in the lateral cerebral fossa (Fossa lateralis cerebri), for example, as shown in FIG. It is desirable to set a cross section S1 that passes through the vicinity of an anterior commisure or an optic chiasm with a cross section close to). FIG. 17 is a diagram showing a two-dimensional (2D) image captured for such a cross section S1. Then, as shown in FIG. 17, if labeling regions R11 and R12 are set on a two-dimensional image and imaging is performed by the above pulse sequence, for example, an image as shown in FIG. 18 is obtained. In a portion where the motion during imaging is sufficiently small, the labeling regions R11 and R12 themselves during imaging have a high signal. Due to the movement of the cerebrospinal fluid, the cerebrospinal fluid has a high signal with respect to the regions R13, R14, R15, R16, and R17. This indicates that cerebrospinal fluid moves back and forth in the lateral cerebrum fossa (movement called “to and fro motion”). On the other hand, in the regions R17 and R18, it is rare that high signal is normally observed. Information necessary for diagnosis can be collected by comparing the range of the high signal portion, the difference between the left and right sides, changes before and after some treatment, etc., so that a plurality of labeling regions such as the labeling regions R11 and R12 can be set. Is useful.

(Fifth embodiment)
The fifth embodiment will be described below.

  The host computer 6 displays, for example, an image as shown in FIG. 19 that has been imaged after labeling on the display 12 as a positioning image, and accepts designation of a cross section by the operator on this image. In FIG. 19, the region 21 is a labeling region, and the region R22 is depicted with a high signal. As the pulse sequence for capturing the positioning image, the pulse sequence shown in each of the above embodiments or the one shown in Patent Document 1 can be arbitrarily applied.

  Thus, for example, as shown in FIG. 20, the surgeon can determine an imaging section S11 that includes a portion where the flow rate of cerebrospinal fluid is fast.

  FIG. 21 is a two-dimensional image captured with respect to the imaging section S11. When such an image is imaged after labeling a labeling region R23 including a Monroe groove as shown in FIG. 21, for example, an image as shown in FIG. 22 is obtained. A region R24 represented by oblique lines is a portion where the cerebrospinal fluid has moved from the labeling region R23 after labeling and has a high signal. That is, the image shown in FIG. 22 is captured by a pulse sequence in which a non-selective IR pulse is applied before a labeling pulse, as shown in FIG.

  This makes it possible to make settings in a state where the cerebrospinal fluid flow information is known. The imaging cross section can be set.

(Sixth embodiment)
The sixth embodiment will be described below.

  FIG. 23 is a flowchart showing a characteristic processing procedure in the sixth embodiment of the host computer 6.

  The host computer 6 receives designation of a labeling area as preparation for inspection. At this time, it is desirable that the labeling region is designated appropriately according to the diagnostic purpose and other imaging conditions by making use of clinical knowledge about the cerebrospinal fluid and blood circulation pathways.

  If the labeling area is designated, the host computer 6 creates labeling position information relating to the designated labeling area in step Sb1. The labeling position information includes, for example, information such as offset, rotation information, width of the labeling region, RF pulse type and duration. In step Sb2, the host computer 6 stores the created labeling position information in the labeling position storage unit.

  The labeling position storage unit includes a storage unit 11, a storage medium managed by a hospital server connected to the MRI apparatus of the sixth embodiment via a hospital network, or the MRI apparatus of the sixth embodiment such as the Internet. Any storage medium such as a storage medium managed by a web server connected via the network can be used.

  At the time of actual inspection, in step Sc1, the host computer 6 reads the labeling position information from the labeling position holding unit. In step Sc2, the host computer 6 sets a labeling area based on the labeling position information.

  Thus, the setting of the labeling area at the time of actual examination can be performed easily and appropriately even by a device operator who does not have clinical knowledge about cerebrospinal fluid or blood circulation route, and depends on the skill level of the device operator. Variation in image quality can be reduced.

  Note that labeling position information about several labeling areas may be stored in the labeling position storage unit in advance, and the labeling position information may be selectively read out and used for setting the labeling area. In this way, it is not necessary to specify a labeling area as a preliminary preparation for inspection, and the operation is further simplified.

  Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1 ... Magnet, 2 ... Static magnetic field power supply, 3 ... Gradient magnetic field coil unit, 3x, 3y, 3z ... Coil, 4 ... Gradient magnetic field power supply, 5 ... Sequencer, 6 ... Host computer, 7 ... RF coil, 8R ... Receiver, 8T: Transmitter, 10: Arithmetic unit, 11: Storage unit, 12: Display, 13: Input device, 14: Shim coil, 15: Shim coil power supply, 16 ... Sound generator, 17 ... ECG sensor, 18 ... ECG unit.

Claims (2)

For the purpose of observing the dynamics of the cerebrospinal fluid of the subject, in the magnetic resonance imaging apparatus for imaging the cerebrospinal fluid,
Labeling means for labeling spins contained in cerebrospinal fluid in a part of the labeling region in the imaging region of the subject;
Acquisition means for acquiring an echo signal related to spins included in the imaging region by a predetermined pulse sequence;
Control means for controlling the labeling means and the acquisition means so as to perform a plurality of acquisition cycles of the echo signal from the time of the labeling;
Reconstructing means for reconstructing a plurality of images in the imaging region based on the echo signal acquired in each of the plurality of cycles;
Display means for displaying at least one of the plurality of images as a positioning image;
A magnetic resonance imaging apparatus comprising: an accepting unit that accepts designation of an imaging section on the positioning image.   The magnetic resonance imaging apparatus according to claim 1, wherein the labeling unit labels spins included in a region including a Monroe groove as the labeling region.

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