JP2000189398A - Magnetic resonance imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the shading of an aspirating needle to a desired width by providing a means for switching an image pickup condition during radioscopic image pickup operation for continuously displaying an image in real time to control the shading of a specified object in a tested body to a desired width, and displaying plural images different in shading width. SOLUTION: A CPU 7 and an operating part 8 are provided with a function of switching an image pickup contition during image pickup operation and controlling the shading of a specified object in a tested body to a desired width. The advance of an aspirating needle is monitored, and simultaneously radioscopic image pickup operation is conducted. When the width of shading of the aspirating needle is too thick, during the radioscopic image pickup operation, the sequence type is switched from GrE(gradation echo) method to SE(spin echo) method, or the read inclined magnetic field intensity of the radioscopic image pickup sequence is increased. When the shading width is too thin, switching from SE method to GrE method is performed or the read inclined magnetic field intensity of the radioscopic image pickup sequence is decreased. Thus, it is possible to display an image different in shading width according to the advance state of the aspirating needle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus (hereinafter, referred to as an MRI apparatus) for displaying an image of an arbitrary cross section of a subject by utilizing a nuclear magnetic resonance phenomenon. Reconstruction and image display are performed continuously, and a puncture needle or biopsy needle is displayed with a desired shading width on a specific target within the subject, for example, a lesion of the subject during fluoroscopic imaging that displays a continuous image in real time. M that can do
Related to an RI device.

[0002]

2. Description of the Related Art In recent years, a technique (IVMR) for confirming a puncture position and a direction in real time using MRI when a puncture needle or a biopsy needle is advanced to a lesion of a subject has been developed.
Puncture is used for the purpose of biopsy of a lesion, drug injection, laser treatment, and the like. In this IVMR, imaging, image reconstruction,
A fluoroscopic imaging method in which display is performed continuously (fluorocopy) is used.

[0003] A puncture needle on an MR image is displayed as a shadow because the magnetic field is distorted due to the influence of the magnetic susceptibility of the puncture needle and the collected signal (measurement data) is lost. Thereby, the position of the puncture needle can be known.

[0004]

SUMMARY OF THE INVENTION By the way, IVMR
When the puncture needle or biopsy needle is advanced at the start of puncture or while the puncture needle is in progress, it is better that the shade of the puncture needle is thick in order to improve the visibility of the puncture needle, but the puncture needle is oriented in the direction of the lesion. The thinner the shadow, the better if it is to check whether the needle tip is proceeding accurately or if it is to check whether the needle tip is exactly at the desired position when the needle tip reaches the lesion.

However, in the conventional fluoroscopic imaging method, the width of the shadow of the puncture needle is always constant, and if the width of the shadow of the puncture needle on the image during fluoroscopic imaging is too large, the position of the puncture needle can be accurately determined. I could not confirm. Also, if the width of the shadow is too narrow,
It was difficult to see the puncture needle. Accordingly, an object of the present invention is to provide a fluoroscopic imaging method capable of controlling such a problem and controlling the shading of a puncture needle to a desired width.

[0006]

In order to achieve the above object, the present inventor examines conditions affecting the shadow of a puncture needle in imaging with an MRI apparatus, and switches these conditions during fluoroscopic imaging. The desired shade width can be controlled.

That is, the MRI apparatus of the present invention comprises a means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field in a space where a subject is placed, and a nuclear magnetic resonance (NM) generated from the subject.
R) a means for detecting a signal, a means for reconstructing an image of a subject based on an NMR signal, a means for displaying an image, and setting and controlling conditions of imaging, reconstruction, and image display by each of these means. In the MRI apparatus provided with the control unit, the control unit continuously performs imaging, reconstruction, and image display of tomographic images of the subject, and switches imaging conditions during fluoroscopic imaging in which continuous image display is performed in real time. Means for controlling a shadow of a specific object in the subject to a desired width, and displaying a plurality of images having different shadow widths.

In the MRI apparatus of the present invention, imaging, reconstruction, and image display of a tomographic image of a subject are continuously performed, and when performing continuous image display in real time, the fluoroscopic imaging conditions are switched during fluoroscopic imaging. The shading of a specific object in the subject is controlled to a desired width, and a plurality of images having different shading widths are displayed.

The imaging conditions that affect the width and shape of the puncture needle shadow include: 1) the type of imaging sequence, 2) the readout direction (frequency code direction), the intensity of the gradient magnetic field, and 3) the direction of the static magnetic field. There is an angle between the sequence readout direction and 4) an angle between the direction of the static magnetic field and the direction of the puncture needle.

[0010] The puncture needle has a narrower shade when it is imaged by an imaging method based on the spin echo method than when it is imaged by an imaging method based on the gradient echo method. Also, when the intensity of the gradient magnetic field in the readout direction of the sequence is increased, the width of the shadow is reduced, and when the intensity is reduced, the width of the shadow is increased. Further, when the direction of the static magnetic field and the reading direction of the sequence are parallel, the width of the shadow becomes large, and when the direction is vertical, the width of the shadow becomes thin.

In the MRI apparatus of the present invention, among the above-mentioned imaging conditions, the conditions 1) to 3) which can be switched and changed by the setting of the apparatus can be switched. Therefore, for example, at the start of the fluoroscopy and during the progress of the puncture needle, the type of the fluoroscopic imaging sequence is set to the gradient echo (GrE) method, and the puncture needle with a relatively thick shade is displayed, so that the puncture needle can be easily confirmed. When the target approaches the target lesion, spin echo (SE) from GrE method
By switching to the method and displaying the puncture needle with a relatively thin shadow, the direction and position can be confirmed accurately.

Alternatively, without changing the type of the imaging sequence, the intensity of the readout direction gradient magnetic field is set to be relatively small at the start of imaging during fluoroscopic imaging, and then increased. In this case as well, it is possible to switch from the display of relatively thick shadows to the display of thin shadows as in the case of switching the type.
Alternatively, the phase encoding direction and the reading direction of the fluoroscopic imaging sequence may be switched without changing the type of the imaging sequence.

The switching of the condition is performed in accordance with the progress of the puncture needle, and depending on the situation visually recognized, the condition is changed to either side between the condition in which the shadow is shown thick and the condition in which the shadow is displayed thin. , And can be switched any number of times.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing the overall configuration of an MRI apparatus to which the present invention is applied. This MRI apparatus uses the nuclear magnetic resonance phenomenon to measure the nuclear spin density distribution and relaxation time distribution at a desired examination site in a subject, and displays an image of an arbitrary cross section of the subject from the measurement data. A static magnetic field generating magnet 1, a gradient magnetic field generating system 2, a sequencer 3, a transmitting system 4, a receiving system 5, a signal processing system 6, a central processing unit (CPU) 7,
An operation unit 8 is provided.

The static magnetic field generating magnet 1 generates a uniform static magnetic field around the subject 9 in a body axis direction or a direction orthogonal to the body axis, and has a certain space around the subject 9. A permanent magnet type, normal conduction type or superconducting type magnetic field generating means is disposed.

The gradient magnetic field generation system 2 includes a gradient magnetic field coil 10 in three axial directions of X, Y and Z, and a gradient magnetic field power supply 11 for driving each coil. By driving the gradient magnetic field power supply 11, the gradient magnetic field G
s (Gradient magnetic field in slice direction), Gp (Gradient magnetic field in phase encoding direction), Gf (Gradient magnetic field in frequency encoding direction)
Is applied to the subject 9. The slice position and the cross section with respect to the subject 9 can be set by the method of applying the gradient magnetic field.

The sequencer 3 is a control means for repeatedly applying a high frequency pulse and a gradient magnetic field for causing nuclear magnetic resonance to the nuclei of the atoms constituting the living tissue of the subject 9 in a predetermined pulse sequence, and collecting measurement data. , CPU7
And sends various commands necessary for data collection of tomographic images of the subject 9 to the transmission system 4, the gradient magnetic field generation system 2, and the reception system 5.

The transmission system 4 irradiates a high-frequency pulse to cause nuclear nuclei of the nuclei of the atoms constituting the living tissue of the subject 9 by a high-frequency pulse commanded by the sequencer 3. The modulator 13 includes a modulator 13, a high-frequency amplifier 14, and an irradiation coil 15. The high-frequency pulse output from the high-frequency oscillator 12 is amplitude-modulated by the modulator 13 in accordance with a command from the sequencer 3. After amplification, the electromagnetic wave is applied to the irradiation coil 15 arranged close to the subject 9 to irradiate the subject 9 with electromagnetic waves.

The receiving system 5 is an echo signal (NMR signal) emitted by magnetic resonance of atomic nuclei of the living tissue of the subject 1.
It comprises a receiving coil 16, an amplifier 17, a quadrature detector 18 and an A / D converter 19, and the electromagnetic wave (NMR signal) of the response of the subject 9 due to the electromagnetic wave emitted from the irradiation coil 15 is , Are detected by a receiving coil 16 disposed in close proximity to the subject 9, are converted into two series of collected data via an amplifier 17 and a quadrature detector 18,
The signal is input to the converter 19, converted into a digital quantity, and the signal is sent to the signal processing system 6.

The signal processing system 6 includes a CPU 7, a recording device such as a magnetic disk 20 and an optical disk 21, and a display 22 such as a CRT. The CPU 7 performs processing such as Fourier transform, correction coefficient calculation, and image reconstruction. An appropriate operation is performed on the measured data of the nuclear spin density distribution and relaxation time distribution of an arbitrary cross section of the subject 9, and the obtained distribution is imaged and displayed on the display 22 as a tomographic image.

The CPU 7 controls the gradient magnetic field generation system 2, the transmission system 4 and the reception system 5 via the sequencer 3 in addition to the above-described operations for image reconstruction, and performs image capturing and image Reconstruct and display. The imaging method, its conditions, and control information of processing performed by the signal processing system 6 are input and set from the operation unit 8 having input means such as the keyboard 23.

In the present invention, when the perspective imaging method is adopted as the imaging method, the imaging conditions are switched during the imaging,
The CPU 7 and the operation unit 8 have a function of controlling the shading of a specific object in the subject to a desired width. Such a function can be performed, for example, in the operation unit 8 independently of individual commands of 1) switching of imaging type, 2) change of readout gradient magnetic field intensity, 3) change of axes of readout gradient magnetic field and phase encoding gradient magnetic field. You can make it selectable with a tree structure, or change the width of the puncture needle (make it thicker,
May be selected. In the case of using a tree structure, for example, first, 1) the imaging type is switched, 2) the readout gradient magnetic field intensity is changed or not changed for the selected imaging type, and 3) selection is made.
Next, select whether to change the axis or not. 1) ~
Step 3) may be performed in any order.

Next, a method of performing fluoroscopic imaging using such an MRI apparatus while advancing a puncture needle to a subject will be described with reference to FIG.
This will be described with reference to FIGS. FIG. 2 is a flowchart showing one embodiment of the perspective imaging method according to the present invention.
3A and 3B are diagrams showing two types of pulse sequences executed in the present embodiment, wherein FIG. 3A shows a pulse sequence based on the GrE method, and FIG. 3B illustrates a pulse sequence based on the SE method. FIG. 4 is a view schematically showing an image 40 of the subject displayed by executing the fluoroscopic imaging method. FIGS. 4A and 4B show images in which the widths of the puncture needles are different.

First, when imaging starts (step 24),
A pulse sequence according to the GrE method shown in FIG. 3A is executed (step 25). That is, the slice selection magnetic field Gs
, A high-frequency pulse is applied, then a phase encoding gradient magnetic field Gp is applied, and a readout gradient magnetic field Gf is applied.
And measure the echo signal. While changing the intensity of the phase encoding gradient magnetic field Gp, the process from application of a high-frequency pulse to measurement of an echo signal is repeated at a predetermined repetition time, and the number of echo signals required for image reconstruction is measured. C
The PU 7 reconstructs an image using the set of echo signals obtained by such repetition, and displays the reconstructed image on the display 22.
(Steps 26 and 27).

In the displayed image, the puncture needle 44 loses the collected signal (measurement data) and becomes a shadow. Gr
The shadow captured by the E method is relatively wide as shown in FIG. 4B, and its position and direction can be easily checked at the start of puncturing or at the stage when the puncture needle is advanced. The moving puncture needle is monitored while continuously repeating such imaging, image reconstruction, and display.

When imaging and image reconstruction are repeated, measurement data is shared between a plurality of temporally consecutive images according to a known fluoroscopic imaging method, or only low-phase encoding amount data is repeatedly obtained. May be updated.

When the puncture needle 44 further advances and approaches the lesion 42, it is necessary to more accurately grasp the positional relationship between the tip of the puncture needle 44 and the lesion 42, and the thinner the shadow, the better. Therefore, the imaging sequence is set to SE through the operation unit 8.
Switch to the modal pulse sequence. When the switching command is input, the sequencer 3 waits for the elapse of the repetition time of the pulse sequence in FIG. 3A or the end of the repetition of the pulse sequence necessary to reconstruct one image. Then, the imaging sequence is switched to the pulse sequence of the SE method in FIG. 3B (steps 28 and 2).
9). If you switch immediately after the repetition time elapses,
Although a part of the measurement data is wasted, the image can be switched with good response to the command.

In the pulse sequence of the SE method, a high-frequency pulse for inverting spin is applied after excitation of a selected slice by a high-frequency pulse, and an echo signal is measured.
Here, the steps from the application of the high-frequency pulse to the measurement of the echo signal are repeated for each repetition time TR while changing the intensity of the phase encoding gradient magnetic field Gp, and the echo signal necessary for image reconstruction is measured. As a result, unlike the image obtained by the GrE method, the display shown in FIG.
As shown in FIG. 7, an image in which the width of the shadow of the puncture needle 43 is small is displayed. Thus, even when the puncture needle 43 has advanced to a position overlapping the image of the lesion 41, the position and direction of the puncture needle 43 can be accurately confirmed, and the image of the lesion 41 is not difficult to see.

FIG. 3 shows the basic pulse sequences of the GrE method and the SE method. However, various pulse sequences using these pulse sequences can be adopted. For example, the shadow width of the puncture needle is relatively large. As an imaging sequence displayed thickly, an echo planar (EPI) method for measuring a plurality of echo signals by one excitation, a divided EPI method, a spiral scan method, or the like can be adopted. In addition, as an imaging sequence in which the shadow width of the puncture needle is displayed relatively thick, a high-speed spin echo method that repeats spin inversion by an inversion pulse or the like can be adopted.

The switching of the imaging sequence is as follows.
If necessary, the method can be switched from the SE method to the GrE method (steps 30 and 31), and switching between these sequences may be performed a plurality of times.

Next, when the shadow of the puncture needle is not sufficiently thinned only by switching the imaging sequence, or when the shadow of the puncture needle is too thin to visually recognize the shadow of the puncture needle, the readout gradient magnetic field intensity is reduced. Change (step 32,
33). The read gradient magnetic field strength (38, 39 in FIG. 3) may be set by a numerical value, or a thick shadow or a thin shadow may be selected. When the shadow of the puncture needle is to be made thicker than the displayed image, the readout gradient magnetic field strength is set to be smaller, and when it is desired to be thinner, the readout gradient magnetic field strength is set to be larger. When such a change in the read gradient magnetic field strength is set, the sequencer 3 changes the read gradient magnetic field strength to the specified strength after the elapse of the repetition time of the pulse sequence in FIG. In this case, since the type of the imaging sequence has continuity, the conditions can be switched without wasting the measurement data.

As described above, after changing the read gradient magnetic field strength or without changing the read gradient magnetic field strength,
The width of the shadow of the puncture needle may be further controlled by changing the axis of the gradient magnetic field (steps 34 and 35). For example, in the pulse sequence shown in FIG. 3, assuming that the phase encoding gradient magnetic field Gp is a gradient magnetic field in the x direction and the readout gradient magnetic field Gf is a gradient magnetic field in the same z direction as the static magnetic field direction, the phase encoding gradient is changed by changing the axis. The magnetic field Gp is changed in the z direction, and the readout gradient magnetic field Gf is changed in the x direction.

Such settings are also set via the operation unit 8, and when such a command is issued, the sequencer 3 waits for the elapse of the repetition time or the pulse necessary for reconstructing one image. Wait for the end of the sequence repetition,
The axes of the gradient magnetic fields Gp and Gf are exchanged.

The width of the shadow of the puncture needle becomes large when the direction of the readout gradient magnetic field Gf is parallel to the direction of the static magnetic field.
When the direction of the readout gradient magnetic field Gf is perpendicular to the direction of the static magnetic field, the width of the shadow becomes narrow. Therefore, the shadow width of the puncture needle is controlled to be further narrowed by the above change. Of course, when the readout gradient magnetic field Gf is perpendicular to the static magnetic field direction in the initial setting state, the shade width of the puncture needle can be controlled to be wide by exchanging the axis with the phase encoding gradient magnetic field parallel to the static magnetic field direction. .

When the slice gradient magnetic field is parallel to the static magnetic field direction, the phase encoding gradient magnetic field and the readout gradient magnetic field are both perpendicular to the static magnetic field direction. No change. Therefore, the control of the shadow width of the puncture needle by changing the axis is effective when imaging a cross section that is not parallel to the direction of the static magnetic field.

As described above, in the MRI apparatus of the present invention, the fluoroscopic imaging is executed while monitoring the progress of the puncture needle. If the width of the shadow of the puncture needle is too large, the type of fluoroscopic imaging sequence is performed during the fluoroscopic imaging. Is switched from the GrE method to the SE method, or the readout gradient magnetic field strength of the fluoroscopic imaging sequence is increased. Conversely, if the width of the shadow is too narrow, the SE method is switched to the GrE method, or the readout gradient magnetic field strength of the fluoroscopic imaging sequence is reduced. Further, the phase encoding direction and the reading direction of the fluoroscopic imaging sequence are switched during the fluoroscopic imaging depending on the angle between the direction of the static magnetic field and the reading direction of the fluoroscopic imaging sequence. While seeing the images displayed continuously in this manner, fluoroscopic imaging is performed while arbitrarily controlling the shade width of the puncture needle, and the imaging ends (steps 36 and 37).

In the above embodiment, the case where the type of the imaging sequence is switched first and then the readout gradient magnetic field intensity is set has been described. However, after the readout gradient magnetic field intensity is changed and set, the type of the imaging sequence is further switched. You may do so. Further, only one of the three conditions for determining the shade width of the puncture needle may be settable,
These can be independently selected and set. 3
When the two conditions are combined, it is possible to control the shadow width most finely. Such setting and switching can be performed as many times as necessary during imaging.

[0038]

The MRI apparatus of the present invention is provided with means for switching imaging conditions during imaging such as fluoroscopic imaging and controlling the shading of a specific object in a subject to a desired width. When the puncture needle is advanced to the subject, images having different shade widths can be displayed according to the progress of the puncture needle, and the position and direction of the puncture needle can be accurately confirmed. Further, the visibility of the puncture needle can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of an MRI apparatus to which the present invention is applied.

FIG. 2 is a flowchart showing one embodiment of a fluoroscopic imaging method in the MRI apparatus of the present invention.

3A and 3B are diagrams showing different pulse sequences used in the fluoroscopic imaging method, wherein FIG. 3A shows a pulse sequence of the GrE method,
(B) is a pulse sequence of the SE method.

4A and 4B are diagrams schematically showing two types of images having different shadow widths obtained by fluoroscopic imaging, wherein FIG. 4A is an image in which the puncture needle has a narrow shadow width, and FIG. 4B is a diagram in which the puncture needle has a wide shadow width. Each image is shown.

[Explanation of symbols]

 Reference Signs List 1 static magnetic field generating magnet (magnetic field generating means) 2 gradient magnetic field generating system (magnetic field generating means) 3 sequencer (control means) 4 transmitting system (magnetic field generating means) 5 receiving system (detecting means) 6 signal processing system 7 CPU (control means) ) 8 Operation unit 9 Subject

Claims (1)

[Claims] A means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field in a space where an object is placed; a means for detecting a nuclear magnetic resonance signal generated from the object; A magnetic resonance imaging system comprising: means for originally reconstructing the image of the subject; means for displaying the image; and control means for setting and controlling conditions for imaging, reconstruction, and image display by each of these means. In the apparatus, the control unit continuously performs imaging, reconstruction, and image display of a tomographic image of the subject, and switches the imaging conditions during fluoroscopic imaging in which continuous image display is performed in real time. A magnetic resonance imaging apparatus comprising: means for controlling a shadow of a specific object to have a desired width, and displaying a plurality of images having different shadow widths.