JP3972236B2 - Magnetic resonance imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic resonance imaging apparatus, and more particularly, to a technique for monitoring an invasive device such as a catheter inserted into a living body of a patient as a subject while performing continuous imaging.
[0002]
[Prior art]
A magnetic resonance imaging apparatus (MRI apparatus) irradiates a living body with a high-frequency magnetic field pulse in a state where a uniform static magnetic field acts on the living body, excites nuclei such as hydrogen and phosphorus in the living body, and generates nuclear magnetic resonance generated by this excitation. It is an apparatus that contributes to medical diagnosis by measuring a signal (NMR signal) and imaging a measurement region in a living body based on magnetic resonance information such as the density distribution or relaxation time distribution of hydrogen and phosphorus.
[0003]
As an imaging apparatus that contributes to such medical diagnosis, an X-ray imaging apparatus is widely known in addition to an MRI apparatus. In recent years, X-ray imaging devices adopt IV-R (InterVentional Radiology) method, which performs examination and treatment under fluoroscopy in order to reduce the invasiveness of patients and improve the quality of life (QOL) of patients. Has been. In such examination or treatment by the IV-R method, biopsy using a biopsy needle, treatment using a laser, treatment using a catheter, and the like are performed.
[0004]
On the other hand, also in the field of MRI apparatuses, the spread of open-type apparatuses that open the space around the imaging region of the patient as much as possible and make it easy for the operator to access the patient has progressed, and I perform examinations and treatments under MRI fluoroscopy. -MRI (Interventional MRI) has come to be used clinically. However, although I-MRI has the merit that there is no problem of X-ray exposure, there is a point that should be improved in terms of the spatial resolution, temporal resolution, or artifacts of the obtained image.
[0005]
For example, in I-MRI, a coil is attached to the tip of an invasive device such as a catheter, and the coil also receives an NMR signal to form an image, which is superimposed on the image of the NMR signal received by a normal receiving coil. There is known an active tracking method in which the tip of an invasive device is displayed with high luminance by displaying. In addition, by disturbing the static magnetic field near the tip of the invasive device by mixing a magnetic substance into the tip of the invasive device formed of resin or the like, thereby causing the NMR signal near the tip of the invasive device to be lost, A passive tracking method in which an image of the tip of an invasive device is lost is known.
[0006]
With such an invasive device, in I-MRI, the state of the subject, the position of the inserted invasive device, and the like are monitored in real time. For I-MRI that realizes real-time monitoring, a high-speed fluoroscopy method is usually employed. In fluoroscopy, an imaging sequence with a repetition time of several milliseconds (several ms) is executed, and an image is acquired at an image update interval of about 1 second (s) or 1 second or less. Furthermore, an echo sharing method has also been proposed in which MR measurement is partially performed and an image is created by reusing previously acquired image data for a portion where image data is insufficient, thereby shortening the image acquisition time. According to this, the image update interval can be shortened to several tens of milliseconds.
[0007]
[Problems to be solved by the invention]
Usually, the operation of inserting the invasive device into the living body must be performed with care, but there are cases where it must be performed with particular care depending on the part of the living body. In other words, since the internal structure of the subject is locally changed, for example, when the device passes through a branch portion, a bent portion, or a stenosis portion of a blood vessel or in a treatment site, a particularly careful operation is required. In such a region or region, it is necessary to shorten the image update interval or increase the spatial resolution, in particular, in order to improve the imaging ability of the invasive device.
[0008]
However, the conventional I-MRI fluoroscopy method does not consider changing the image update interval and spatial resolution in accordance with changes in the body part where the invasive device is located. Therefore, if the image update interval is long or the spatial resolution is set to a low value, the imaging ability of the invasive device may be poor and careful operation may be difficult.
[0009]
An object of the present invention is to improve the ability to depict an invasive device for a real-time monitor image.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, a magnetic resonance imaging apparatus of the present invention includes a control unit that executes an imaging sequence that performs measurement by adding spatial position information to a nuclear magnetic resonance signal generated by exciting a subject, and the nucleus. An image constructing unit that generates a magnetic resonance image of the subject based on the magnetic resonance signal, a monitor that displays an image created by the image constructing unit, and a mark at an arbitrary position on the image displayed on the monitor And an input unit for setting the imaging sequence, and the control unit has a function of changing the imaging sequence when the distance between the invasive device displayed in the image and the mark is within a setting range. And In this case, the imaging sequence is preferably changed by changing at least one of the image frame rate (the reciprocal of the image update interval) and the spatial resolution to, for example, a high value.
[0011]
With this configuration, the problem of the present invention is solved as described below. First, when an invasive device is inserted into a living body, an operator should carefully look at an MR image displayed on a monitor, for example, a region such as a branching portion or a stenosis portion of a blood vessel image, and carefully insert in that region. And a mark is set in the region (region of interest) via the input means. When treatment is required, a mark is set with the treatment site as a region of interest. Then, the control means tracks the position of the invasive device displayed in the image, and when the invasive device is inserted within the set range of the mark, the imaging sequence is changed, and the frame rate and spatial resolution of the image are changed. Change at least one to a higher value. As a result, when the invasive device moves and reaches the region of interest, the imaging speed is automatically increased or the spatial resolution is increased, so that the operator can move the invasive device finely and accurately position it with the blood vessel. Relationships can be accurately monitored with images.
[0012]
The mark is preferably set as a point or a circle. When setting with a point, it is preferable to set a certain range around the point as a region of interest. When setting a circle, the radius of the circle can be set freely.
[0013]
In order to change the frame rate and the spatial resolution, a plurality of imaging sequences having different frame rates and spatial resolutions of images can be set in advance, and the imaging sequence can be switched and changed by the control means. Alternatively, the imaging sequence can be changed by changing parameters related to the frame rate and spatial resolution of the imaging sequence. An example of improving the spatial resolution can be realized by setting the photographing field of view small.
[0014]
The determination as to whether or not the position of the invasive device is within the set range with respect to the mark can be realized by providing a tracking means described below. In other words, the tracking unit determines the invasive device in the image based on the difference in luminance. The position change of the invasive device is detected every time the image is updated, and the position is tracked. On the other hand, the position of the mark set on the image is determined, and the interval between the mark and the invasive device is obtained by calculation. When the obtained interval is within a preset range, it is determined that the invasive device is present in the region of interest, and the imaging frame rate is changed to a high value or the spatial resolution is changed to a high value. Thus, the visibility is improved by increasing the visibility of the movement of the invasive device. In this case, both the frame rate and the spatial resolution may be changed to high values.
[0015]
In this way, when entering the region of interest where the invasive device must be carefully operated, the frame rate is automatically shortened or the spatial resolution is improved, so that the detailed movement of the invasive device can be captured. Can do. As a result, the insertion operation of the invasive device is facilitated.
[0016]
In the above, the mark is set in the region of interest on the image, but instead, the advancing speed of the invasive device is obtained based on the change in the position of the invasive device obtained by the tracking means. When is smaller than the set value, at least one of the image frame rate and the spatial resolution may be changed to a high value. In other words, when an invasive device comes to a region of interest such as a bifurcation of a blood vessel, the surgeon naturally becomes careful and the insertion speed decreases, so this can be used to change the frame rate and spatial resolution. Even if it does, the same effect is acquired.
[0017]
Further, the attention area can be set in a plurality of stages such as up, inside, and down according to the degree of attention. Then, the frame rate and the spatial resolution can be made different according to the degree of attention.
[0018]
[Embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 2 schematically shows the overall configuration of a typical magnetic resonance imaging apparatus (MRI apparatus). As illustrated, the MRI apparatus includes a magnet 22 that generates a static magnetic field in a space (measurement space) in which the subject 21 is placed, a gradient coil 23 that generates a gradient magnetic field in the same measurement space, and a high frequency in the same measurement space. A high-frequency coil (RF coil) 24 that generates a magnetic field and a high-frequency probe (RF probe) 25 that receives an NMR signal generated from a subject are configured. The subject is inserted into the static magnetic field so that the imaging region is positioned in the measurement space while lying on the bed 26.
[0019]
The gradient magnetic field coil 23 is composed of a plurality of gradient magnetic field coils that generate magnetic fields inclined in orthogonal three-axis (X, Y, Z) directions, and a desired gradient is generated by a pulsed excitation current supplied from the gradient magnetic field power supply 27. A magnetic field is generated. The RF coil 24 generates a high frequency magnetic field corresponding to the high frequency magnetic field pulse supplied from the RF transmitter 28. The NMR signal received by the RF probe 25 is input to the signal detection unit 29 and subjected to processing such as amplification detection. The NMR signal output from the signal detection unit 29 is subjected to signal processing by the image construction unit 30 and converted into an image signal. The image signal output from the image construction unit 30 is displayed on the monitor 31. The gradient magnetic field power supply 27, the RF transmission unit 28, and the signal detection unit 29 are controlled by the control unit 33 based on a sequence called an imaging sequence or a pulse sequence. The control unit 33 controls the image forming unit 30 and the monitor 31 and takes in the image information of the image forming unit 30 or the monitor 31 to perform various types of analysis. Store the necessary data. The input unit 34 is used by an operator to input various setting information to the control unit 34.
[0020]
A method for imaging an MR image of a subject using the MRI apparatus configured as described above will be described. Currently, the measurement targets that are widely used in clinical practice are the spatial distribution of the density of protons, which are the main constituents of the subject, and the spatial distribution of the relaxation phenomenon of the excited state. By imaging these spatial distributions, the form or function of the human head, abdomen, quadrilateral, etc. can be imaged two-dimensionally or three-dimensionally to contribute to diagnosis.
[0021]
Imaging is performed according to an imaging sequence called a pulse sequence. FIG. 3 shows a gradient echo sequence as an example of a general imaging sequence. The figure shows a high-frequency pulse RF, a slice gradient magnetic field Gs, a phase encoding gradient magnetic field Gp, a readout gradient magnetic field Gr, a sampling window AD, and an NMR signal (echo signal) Echo in order from the top. The horizontal axis indicates time. First, a slice gradient magnetic field pulse 42 corresponding to a desired slice position is generated together with the high-frequency pulse 41 and applied to the subject. Thereby, for example, protons in the subject are excited, and an echo signal is generated from the subject. In order to give phase information and frequency information, which are spatial position information, to this echo signal, a phase encoding gradient magnetic field pulse 43 is first applied, and then a readout gradient magnetic field pulse 44 is applied. The echo signal 46 is sampled in accordance with the sampling window 45 within the application period of the readout gradient magnetic field pulse 44.
[0022]
By repeating such a pulse sequence a plurality of times while sequentially changing the intensity of the phase encoding gradient magnetic field pulse 43, a two-dimensional image can be captured. In FIG. 3, reference numeral 47 is a pulse sequence repetition interval, reference numeral 48 is an image update interval of a two-dimensional image, and reference numeral 49 is a fluoroscopy imaging time. For example, the number of phase encodings is generally selected from 64, 128, 256, 512, etc. per image. The echo signal is usually sampled as a time-series signal by 128, 256, 512, and 1024 sampling windows. These echo signals are two-dimensionally Fourier transformed to create one MR image.
[0023]
MR images created in this way are obtained every repetition time 48 of the pulse sequence of FIG. 3, and in I-MRI, images obtained continuously during fluoroscopic imaging are displayed on a monitor as needed. Thereby, the state of the subject, the position of the invasive device inserted into the subject, and the like can be monitored.
[0024]
Next, with reference to FIG. 1, an embodiment in which the image rate of the invasive device is improved by changing the frame rate and the like according to the position of the invasive device, which is a feature of the present invention, will be described. In this embodiment, a case where a catheter is inserted into a blood vessel as an invasive device and an aneurysm is used as a treatment target will be described as an example. First, prior to fluoroscopy, a tomographic image 1 of a desired site as shown in FIG. 1 is taken. In the image 1 displayed on the monitor 31, a blood vessel 2, a blood vessel branching portion 3, a blood vessel stenosis portion 4, and a target 5 that is an aneurysm to be treated are displayed. Usually, when a catheter is inserted into a blood vessel, it is necessary to carefully operate the catheter at a bent portion or a narrowed portion of the blood vessel. Accordingly, the operator sets the circular marks 6, 7, and 8 on the monitor image by operating the input unit 34 with the branch portion 3, the narrowed portion 4, and the target 5 as the region of interest. The size of this mark can be variably set for each region of interest.
[0025]
After setting the region of interest in this manner, fluoroscopy imaging is started while inserting the catheter. As a result, time-series images captured continuously are displayed on the monitor 31. FIG. 4A shows an example of the time series image 9. As shown in the drawing, a mark 6 of the attention area and the catheter 10 are displayed on the monitor. The control unit 33 detects the position of the catheter 10 in the image from time-series images taken continuously. Since the receiving coil or magnetic material is mixed in the catheter 10, the control unit 33 can easily detect the catheter 10 because the catheter 10 is displayed with a luminance different from that of a normal body part. The position of the catheter 10 is detected in correspondence with coordinates set in advance in the image. And the control part 33 calculates | requires the linear distance L of the center 11 of the mark 6 and the center of the catheter 10 at any time by calculation. That is, the control unit 33 has a function of tracking the position of the catheter 10.
[0026]
FIG. 4B shows an example in which the position of the catheter 10 is tracked in this way and the linear distance L to the nearby mark 6 is obtained. As shown in the figure, the catheter 10 approaches the mark 6 as time elapses, and the catheter 10 enters the mark 6 having the radius R at time t1, and passes further through the center position of the mark 6 as time elapses. It is shown. The fluoroscopy image update interval FR at this time is shown in FIGS. FIG. 4 (C) shows an image taken with a constant image update interval FR1 as in conventional fluoroscopy. FIG. 4 (D) shows the image update interval between the catheter 10 and the mark 6 by applying the present invention. In this case, the image is changed to an image update interval FR2 shorter than FR1 in accordance with the positional relationship. That is, since a careful operation is necessary in the vicinity of the region of interest, the control unit 33 changes the imaging sequence so that the image update interval is shortened as the catheter 10 approaches the center of the mark 6. The change of the image update interval may be obtained by calculation at any time using an expression having the distance L as a function. In addition, when setting the mark of the attention area, a table in which the image update interval is set in advance corresponding to the distance L may be created and changed according to this table. The change of the imaging sequence may be set in a different manner for each region of interest, that is, for each mark. For example, the image update interval may be changed according to the radius R of the attention area. Further, the image update interval may be directly input and set when setting the mark. Furthermore, at the time of mark setting, the degree of attention can be set for each mark, and the image update interval can be changed in, for example, three stages according to the degree of attention and the distance L.
[0027]
Here, the modification of this embodiment is demonstrated using FIG. Examples of 5, when the catheter 10 enters into the mark, by enlarge the attention area imaging field with a small fence, an example of changing the spatial resolution to a higher value. That is, when the catheter 10 is in the outer region of the mark 6, the image 12 shown in FIG. 5A is displayed by performing imaging with an imaging sequence having a large field of view. When the catheter 10 enters the inside of the mark 6, an image 13 shown in FIG. 5B is displayed by changing the imaging sequence so that the imaging field of view is reduced and performing imaging. Thereby, the surgeon can perform an insertion operation while confirming a fine movement in the catheter 10. Note that the spatial resolution may be increased by changing the imaging sequence without reducing the imaging field of view. That is, the spatial resolution is improved by increasing the number of phase encodes and the number of samples of the echo signal.
[0028]
In addition, when monitoring an invasive device such as a catheter by imaging a blood vessel, it is preferable to inject a contrast medium into the blood vessel to enhance the contrast of the blood vessel. For example, when performed in combination with the present invention, it is preferable to automatically inject a contrast medium when a device enters the mark.
[0029]
As described above, according to the embodiment or the modification of FIG. 1, when the catheter 10 moves and reaches the range of the mark of the attention area, the imaging speed is automatically increased or the spatial resolution is increased. The operator can accurately monitor the detailed movement of the catheter 10 and the accurate positional relationship with the blood vessel with images.
[0030]
Next, another embodiment according to the features of the present invention will be described with reference to FIG. In this example, the image update interval FR and the spatial resolution of the time-series image are changed according to the insertion speed of the invasive device. FIG. 6A is an image 14 in which the positions 15 and 16 of the catheter 10 detected from two images with different imaging times captured by fluoroscopy are displayed simultaneously. The figure shows that the catheter 10 has moved from position 15 to position 16 by the insertion operation. The average traveling speed V1 of the catheter 10 at this time is obtained by dividing the distance L2 between the position 15 and the position 16 by the difference ΔT1 between the imaging times of the two images. That means
V1 = L2 / ΔT1
It is obtained by Similarly, when the time further elapses, the catheter 10 advances the distance L3 from the position 16 to the position 17 in FIG. 6B. The average traveling speed V2 of the catheter 10 at this time is expressed as ΔT2 when the image capturing time difference from the position 16 to the position 17 is set as ΔT2.
V2 = L3 / ΔT2
It is obtained by
[0031]
As described above, the surgeon naturally becomes cautious in the vicinity of the region of interest, so the catheter speed is slow. Therefore, in this embodiment, when the insertion speed of the catheter is slow, the image update interval is shortened, or the spatial resolution is increased to improve the rendering ability of the catheter 10. FIG. 7 shows an example in which the image update interval FR is changed according to the average traveling speed of the catheter 1. FIG. 3A shows a change in the traveling speed V of the catheter 10. Then, the traveling speed is compared with two set threshold values Vr1 and Vr2, and when Vr2 <V ≦ Vr1, the image update interval FR3 is set, and when V ≦ Vr2, the image update interval FR4 is changed. . In FIG. 2A, the traveling speed V of the catheter 10 decreases to a threshold value Vr1 or less at t2, and further decreases to a threshold value Vr2 or less at t2. FIG. 6B shows a case where monitoring is performed at a constant image update interval FR1 during fluoroscopy imaging as in the conventional case, and FIG. 6C shows the image update interval according to the traveling speed of the catheter 10 according to this embodiment. The case where it changed into FR1->FR3-> FR4 is shown.
[0032]
According to the present embodiment, the same effect can be obtained except that the trouble of setting the mark of the attention area can be saved as compared with the embodiment. Similarly to the above-described embodiment, the spatial resolution of the image can be changed alone or in combination with the image update interval according to the traveling speed of the catheter 10. As described above, as a method of increasing the spatial resolution of an image, any of a method of changing to a pulse sequence in which the number of phase encodes and the number of sample points are increased in addition to changing the pulse sequence so as to reduce the visual field can be used.
[0033]
The present invention is not limited to the above-described embodiment, and can take various forms based on the gist of the present invention. For example, in the above-described embodiment, the gradient echo method is used as an imaging sequence used for fluoroscopy. However, the present invention is not limited to this, and an echo planar imaging (EPI) method which is one of high-speed imaging methods can be applied. It can also be combined with the echo sharing method described above.
[0034]
【The invention's effect】
As described above, according to the present invention, the ability to draw a real-time monitor image of an invasive device can be improved, and the operability of the invasive device can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment of a mark setting method according to a feature of the present invention.
FIG. 2 is a block configuration diagram of an embodiment of a magnetic resonance imaging apparatus to which the present invention is applied.
FIG. 3 is a diagram showing an example of an imaging sequence applicable to the present invention.
4 is a diagram showing an example of a monitor image by fluoroscopy according to the embodiment of FIG. 1, a diagram showing a change in distance between a catheter and the center of a region of interest, and a diagram showing changes in image update intervals according to the prior art and the present invention.
FIG. 5 is a diagram illustrating a case where the field of view is changed to be small instead of changing the image update interval of the monitor image of FIG. 4;
FIG. 6 is an example of a monitor image obtained by fluoroscopy according to another embodiment of the present invention.
7 is a diagram showing a change in the advancing speed of the catheter of the embodiment of FIG. 6, and a diagram showing a change in an image update interval according to the prior art and the present invention.
[Explanation of symbols]
1 Image 2 Blood vessel 3 Bifurcation 4 Stenosis 5 Target 6, 7, 8 Mark 10 Catheter

Claims (9)

  Control means for executing an imaging sequence for measuring by adding spatial position information to a nuclear magnetic resonance signal generated by exciting a subject, and generating a magnetic resonance image related to the subject based on the nuclear magnetic resonance signal Image forming means, display means for displaying an image created by the image forming means, and input means for setting a mark at an arbitrary position on the image displayed on the display means, the control means, A magnetic resonance imaging apparatus having a function of changing the imaging sequence when a distance between an invasive device displayed in the image and the mark is within a set range.   Control means for executing an imaging sequence for measuring by adding spatial position information to a nuclear magnetic resonance signal generated by exciting a subject, and generating a magnetic resonance image related to the subject based on the nuclear magnetic resonance signal An image constructing means; and a display means for displaying an image created by the image constructing means, wherein the control means is configured to select a desired image on the invasive device and the image when the invasive device is inserted into the subject. A magnetic resonance imaging apparatus comprising: means for acquiring a distance to an area, and imaging at least one of the image update period and the spatial resolution according to the acquired distance. An input unit for setting a mark in a desired area on the image displayed on the display unit;
The distance acquisition means acquires a distance between the invasive device displayed in the image and the mark,
3. The magnetic resonance imaging apparatus according to claim 2, wherein the control unit changes at least one of an update period and a spatial resolution of the image when the distance acquired by the distance acquisition unit is within a set range.   The magnetic resonance imaging apparatus according to claim 2, wherein the control unit changes at least one of an update period and a spatial resolution of the image by changing the imaging sequence.   The magnetic resonance imaging apparatus according to claim 2, wherein the control unit increases the spatial resolution by reducing a field of view.   The said control means changes the said update period based on the relationship preset between the distance acquired by the said distance acquisition means, and the said update period, The Claim 2 thru | or 5 characterized by the above-mentioned. Magnetic resonance imaging apparatus.   The magnetic resonance imaging apparatus according to claim 2, wherein the control unit changes the spatial resolution to a high value when the distance acquired by the distance acquisition unit is within a set range.   The magnetic resonance imaging apparatus according to claim 1, wherein the control unit includes a tracking function that detects an invasive device in the image and tracks its position. Control means for executing an imaging sequence for measuring by adding spatial position information to a nuclear magnetic resonance signal generated by exciting a subject, and generating a magnetic resonance image related to the subject based on the nuclear magnetic resonance signal Image forming means, and display means for displaying an image created by the image forming means, wherein the control means detects an invasive device in the image and tracks its position to detect the invasive device and the image on the image. desired to get the distance between the region, the acquired magnetic resonance imaging device including a to that function changes the imaging sequence in accordance with the distance.

Images