JP3537545B2 - Implantable artificial tube and magnetic resonance imaging apparatus using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial tube implanted in a body, that is, an artificial tube artificially installed in a body for flowing a body fluid such as bile, urine, cerebral fluid and the like, and uses the artificial tube. The present invention relates to a magnetic resonance imaging (MRI) device.

[0002]

2. Description of the Related Art In recent years, research on bioengineering materials (biomaterials) has been advanced, and research on various artificial organs has been conducted. Artificial skin has already begun to be used clinically, and its licensing and dissemination have been near. Research into creating artificial blood vessels and other intracorporeal vessels artificially is underway and has been clinically applied to a limited number of cases. These materials are artificially made, and are considered as foreign substances when considered at the cellular level. Cells may adhere to the surface of the material, and in the case of artificial blood vessels, thrombus may be formed. In recent years, the responsiveness of cells has been improved by immobilizing ligand proteins that bind biospecifically to cell surface receptors and their model polymers on the surface of artificial materials by adsorption or covalent bonding. It can be controlled to a considerable extent, and such ligand proteins and model macromolecules are called cell-specific materials.

As described above, research on materials that are easily recognized as foreign substances by cells is progressing, but it is very difficult to produce materials that are not completely recognized as foreign substances.
Therefore, it is necessary to take care of whether foreign matter such as thrombus adheres to the artificial blood vessel even after implantation in the body. Generally, an implantable artificial tube is used until it dies, so it must be checked repeatedly over a long period of about 10 to 30 years.

[0004]

As a method for examining the condition of the tube after implantation in the body, there is angiography using X-rays in the case of artificial blood vessels, but new thrombus due to exposure to X-rays and injection of a contrast agent. However, even if it is applied to the inspection immediately after implantation, it is not suitable for checking for many years thereafter.

[0005] Accordingly, an object of the present invention is to provide means capable of non-invasively examining the internal state of an artificial tube implanted in a body for an implanter. In particular, it is an object of the present invention to ensure the safety of an implanter by performing a long-term test continuously so that the tube can be replaced with a new artificial tube before the function is deteriorated.

[0006]

In order to achieve the above object, according to the present invention, an artificial tube implanted in a body is provided with an MR tube.
A receiving coil of I is provided. The receiving coil of the artificial tube functions as a receiving coil for detecting a nuclear magnetic resonance signal (hereinafter, referred to as an NMR signal) by being connected to a receiver of the MRI apparatus after the artificial tube is implanted. That is,
The MRI apparatus of the present invention uses an artificial tube incorporating a receiving coil as signal detection means for detecting an NMR signal. In the MRI method of the present invention, the NMR signal is detected by the receiving coil of the artificial tube after implantation. After receiving the NMR signal, perform signal processing and calculation for image reconstruction, image the inside of the artificial tube, or perform a function measurement such as a flow rate of a liquid flowing in the inside. It monitors the internal state of the artificial tube.

[0007] By applying a high-frequency magnetic field and a gradient magnetic field to a subject placed in the measurement space of the MRI apparatus, blood and bodily fluid flowing through the inner membrane formed on the inner wall of the artificial tube embedded in the subject and the inside thereof Etc. yield NMR signals. This NMR signal is detected by a receiving coil provided in the artificial tube. The receiving coil is connected to the receiver of the MRI apparatus, and the NMR signal detected by the receiving coil is imaged after being received at the receiver. That is, a tomographic image of the inside of the artificial tube can be obtained. Generally, in an MRI apparatus,
In the obtained image, the smaller the diameter of the receiving coil is, the more the sensitivity to the magnetic field and the resolution are improved. Since the diameter of the artificial tube is usually in the range of a few millimeters to a few centimeters, a receiving coil with a corresponding diameter is very sensitive and gives a good image. Also, in MRI, by measuring the NMR signal in a predetermined pulse sequence and performing an arithmetic operation, it is possible to measure the flow rate of a blood vessel or a bodily fluid flowing in the receiving coil, so that the function measurement of the artificial tube becomes possible.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an artificial blood vessel will be described below with reference to the drawings. FIG. 2 is a diagram showing an overall configuration of an MRI apparatus to which the present invention is applied. This MRI apparatus obtains a tomographic image of the subject 1 by utilizing an NMR phenomenon, and includes a static magnetic field generating magnet 2, A magnetic field gradient generating system 3, a transmitting system 4, a receiving system 5, a signal processing system 6,
Sequencer 7 and central processing unit (hereinafter referred to as CPU)
8 is provided.

The static magnetic field generating magnet 2 generates a strong and uniform static magnetic field around the subject 1, and a permanent magnet system, a normal conducting system, or a superconducting system is provided in a certain wide space around the subject 1. Are provided.
The sequencer 7 operates under the control of the CPU 8 and sends various commands necessary for data collection of tomographic images of the subject 1 to the transmission system 4, the magnetic field gradient generation system 3, and the reception system 5.

The magnetic field gradient generating system 3 comprises a gradient magnetic field coil 9 wound in three directions of X, Y and Z, and a gradient magnetic field power supply 10 for driving each coil. Gradient magnetic field power supply 10 for coil
Are applied to apply a gradient magnetic field G _X , G _Y , G _Z in three axes of _X , _Y , _Z to the subject 1. A slice plane for the subject 1 can be set by adding the gradient magnetic field, and position information can be added to the NMR signal.

The transmission system 4 includes a high-frequency generator 11 and a modulator 1
2, a high-frequency amplifier 13 and a high-frequency coil 14a on the transmission side. The high-frequency pulse output from the high-frequency generator 11 is amplitude-modulated by the modulator 12 in accordance with a command from the sequencer 7, and the amplitude-modulated high-frequency pulse is transmitted to the high-frequency amplifier 1
After being amplified in 3, the specimen 1 is supplied to a high-frequency coil 14 a arranged in proximity to the subject 1, so that the subject 1 is irradiated with electromagnetic waves.

The receiving system 5 includes a receiving high-frequency coil (hereinafter referred to as a receiving coil) 21, a receiving circuit 15, a quadrature phase detector 16, and an A / D converter 17, and the receiving coil 21 is provided later. As described in detail, it is provided in an artificial blood vessel embedded in the subject 1. Further, the receiving coil 21 provided in the artificial blood vessel can be used together with the receiving high-frequency coil 14b conventionally used as the receiving coil.

The response electromagnetic wave in the artificial blood vessel due to the electromagnetic wave emitted from the high-frequency coil 14a on the transmitting side is detected by the receiving coil 21 incorporated in the artificial blood vessel, and the receiving circuit 1
5 and to an A / D converter 17 via a quadrature phase detector 16, which is converted into a digital quantity,
Are collected by the quadrature phase detector 16 at a timing according to a command from the system, and the collected data are sent to the signal processing system 6.

The signal processing system 6 includes a CPU 8, a recording device such as a magnetic disk 18 and a magnetic tape 19, and a CRT.
The CPU 8 performs processing such as Fourier transform, correction coefficient calculation, and re-image reconstruction by the CPU 8, and obtains a signal intensity distribution of an arbitrary cross section or a distribution obtained by performing an appropriate operation on a plurality of signals. The image is formed and displayed on the display 20. The high-frequency coils 14 on the transmission side and the reception side
a, 14 b and the gradient coil 9 are arranged in the magnetic field space of the static magnetic field generating magnet 2 arranged in the space around the subject 1.

Next, the receiving coil 2 incorporated in the artificial blood vessel
1 will be described. FIGS. 1A to 1C show artificial blood vessels 22 each having a receiving coil 21. Conventionally used artificial blood vessels 22 have little effect on cells and are stable for a long time. A tube (hereinafter, tube) 22 made of a biocompatible polymer material is used. As such a polymer material, a resin such as Teflon or silicon, which is processed in advance so that an inner film can be easily formed, is used. Further, the tube 1 may be provided with a reinforcing material so as not to be crushed by other organs or the like.

The receiving coil 21 is made of, for example, gold, platinum,
After winding a conductor such as copper with a polymer material such as Teflon around the tube 1 or winding the tube 1 into a two-layer structure consisting of an inner layer and an outer layer, winding the conductor around the inner layer, By forming an outer layer thereon, a layer of a conducting wire may be provided inside the tube 1. In any case, the portion of the conductive wire 21a drawn out of the tube is coated with a similar polymer material such as a tube, for example, Teflon.

The shape of the receiving coil 21 can be variously changed according to the site where the artificial blood vessel is to be implanted and according to the direction of the static magnetic field of the applied MRI apparatus. That is, M
In RI, if the direction of the static magnetic field and the winding direction of the coil are parallel to each other, the NMR signal cannot be detected, so that the winding direction of the coil needs to cross the static magnetic field direction. For example, in the MRI apparatus shown in FIG. 2, when the direction of the static magnetic field is the vertical direction, that is, the direction perpendicular to the body axis of the subject, many blood vessels run in the direction perpendicular to the static magnetic field. May be any direction as long as the direction in which the blood vessel runs (the longitudinal direction of the artificial blood vessel) as shown in FIG. However, in the case of an artificial blood vessel for a specific blood vessel flowing perpendicular to the body axis, it is necessary to make a winding perpendicular to the longitudinal direction of the artificial blood vessel as shown in FIG. 1 (b) or (c). . In addition, even when the direction of the static magnetic field is parallel to the body axis of the subject, the winding direction of the coil in the artificial blood vessel installed parallel to the body axis is as shown in FIG. 1 (b) or (c). The winding direction must be orthogonal to the longitudinal direction of the artificial blood vessel. Thus, depending on the direction of the static magnetic field of the MRI apparatus and the site where the artificial blood vessel is installed, FIGS.
What is necessary is just to use the artificial blood vessel of (c) properly. In addition, FIG.
In the receiving coil of No. 1, the number of turns of the coil is increased to increase the sensitivity.

The receiving coil 21 can be provided not only for one artificial blood vessel but also at a plurality of positions of the tube 22 according to the length and shape of the tube. For example, FIG.
When the tube 22 of the artificial blood vessel is long as shown in (a) or when the tube 22 is branched as shown in FIG. In addition, in the long artificial blood vessel, the conductive wires 21 and 21 ′ may be selectively disposed in a portion compressed by an organ or a bone or a bent portion. This makes it possible to reliably monitor a portion where a change in blood flow is likely to occur or a portion where a blood clot is likely to occur.

After the artificial blood vessel configured as described above is implanted as a substitute blood vessel for the subject, the receiving coil 21 is connected to the receiving circuit 15 of the MRI apparatus as shown in FIG.
Performs measurement for visualizing blood flow in the artificial blood vessel and measuring blood flow velocity. Next, a signal extracting means for extracting the NMR signal obtained from the receiving coil 21 to the outside of the body and connecting the signal to the receiving circuit 15 of the MRI apparatus will be described. FIG. 4 shows an example of such means. In this example, a connector 2 for extending a conductive wire 21a coated with Teflon or the like from a part of the skin 40 to the outside of the body and connecting to a receiving circuit is shown.
5 are connected. The connector 25 has a terminal (not shown) for connecting to a receiving circuit, and has a protection function of preventing a current from flowing from the outside to the inside. This protection function is provided by the transmitting high-frequency coil 14a.
The high-frequency coil 14a and the receiving coil are decoupled so that a current is not induced in the receiving coil 21 when a high-frequency magnetic field is applied from the antenna. In the example shown, the connector 2
5 is provided at a position away from the skin 40 via the cable 26, but it is also possible to attach the connector 25 directly to the skin 40. In this case, there is a possibility that the cut surface of the skin 40 becomes large, but since the cable can be eliminated, the cable 26 and the connector 2 can be used in daily life.
5 rarely hinders.

FIG . 5 shows another means for extracting an NMR signal from the receiving coil 21. A thin electrode 27 is buried immediately below the skin 40, and the receiving coil 21 is
Are connected. The electrode 27 is at the time of inspection by prick reception circuit electrically connected to the thin needle 28 of the MRI apparatus from the body surface, it can be connected to the receiving circuit. Signal extraction by such means
The procedure can be performed under a simple anesthesia, because the subject is not inconvenienced in life and the needle only needs to be stabbed subcutaneously during the examination. However, in this case, the high-frequency coil 1
It is necessary to provide a decoupling circuit with 4a on the receiving circuit side.

[0021] When the artificial blood vessel is installed in the shallow part of subcutaneously, by installing the coils in the vicinity of the body surface,
The NMR signal detected by the receiving coil of the artificial blood vessel can be detected by a coil near the body surface. In order to perform MRI imaging on a subject provided with the artificial blood vessel and the signal extraction means having the above-described configuration, an electrode 27 implanted under the skin of the subject is placed on a bed while the subject is placed on a bed.
Alternatively, the receiving coil 21 in the body and M
The receiver is connected to the receiving circuit 15 of the RI apparatus, and the bed is moved so that the portion where the artificial blood vessel is embedded is located substantially at the center of the measurement space. Next, a pulse sequence for obtaining a tomographic image under a predetermined imaging condition or a measurement sequence such as a blood flow velocity measurement is started.

As a pulse sequence for obtaining a tomographic image of the inner wall of the artificial blood vessel, generally, an imaging method using an MRI apparatus such as a high-speed imaging method such as a spin echo method, a gradient echo method, or an EPI (echo planar) method may be employed. For example, while selectively exciting a region where an artificial blood vessel is present by applying a high-frequency magnetic field and a slice selection gradient magnetic field, while repeating a predetermined sequence of applying a predetermined gradient magnetic field, the NMR signal detected by the reception coil 21 is changed. Receive. In addition, as a pulse sequence for measuring the blood flow velocity, generally, all the blood flow measurement sequences by the MRI apparatus can be adopted. For example, after selectively exciting a surface crossing the blood flow, it is parallel or orthogonal to the selective excitation surface. For example, a time-of-flight method of performing two selective excitations in the direction and measuring an echo signal from a fluid that has been excited twice is adopted.

In order to activate a pulse sequence for previously specifying and selectively exciting the position of the artificial blood vessel, it is necessary to determine the position of the artificial blood vessel in advance prior to the pulse sequence for imaging or measuring the function in the artificial blood vessel. A signal from a region where an artificial blood vessel is considered to be present may be received by the receiving high-frequency coil 14b, and the region may be imaged.

When the high-frequency coil 14a and the gradient magnetic field coil 9 are driven based on a pulse sequence for image measurement and a plurality of high-frequency magnetic fields and gradient magnetic fields are applied, the NMR signal detected by the reception coil 21 is output from the reception coil. ,
That is, a signal from a nuclear spin existing inside the artificial blood vessel and a signal from blood newly flowing into the imaging region can be made non-signal. After this signal is received by the receiving circuit 15 and is sampled for a predetermined sampling time, the CPU 8 of the signal processing system 6 performs processing such as Fourier transform, correction coefficient calculation, and re-image reconstruction to image an arbitrary cross section. can do.

FIG. 6 shows an MRI image of the inside of the artificial blood vessel acquired in this manner. The intima 31 and the thrombus 32 formed in the artificial blood vessel which are clearly distinguished from the blood flow portion 30 are shown.
Can be a clear image. In FIG. 7A, the intima 31 formed inside the artificial blood vessel in a normal state.
FIG. 3B shows the intima 31.
2 shows a cross-sectional image in which a thrombus 32 has occurred inside the inside of the slab.
By periodically performing MRI imaging on the subject in which the artificial blood vessel is implanted, the state inside the artificial blood vessel can be easily observed.

When a blood flow velocity measurement sequence such as the time-of-flight method is selected as the pulse sequence for applying the high-frequency magnetic field and the gradient magnetic field, the region in which the artificial blood vessel exists is set twice on the orthogonal plane. By selectively exciting, the blood flow voxel in the artificial blood vessel is excited, and by tracking the signal from this blood flow voxel, the blood flow velocity flowing through the artificial blood vessel can be obtained. Thus, it is possible to predict, for example, the state in which the artificial blood vessel is compressed by the thrombus 32 in FIG. 6B or the organs and bones as shown in FIG. You can know how much blood flow is maintained.

Thus, the state of formation of the intima in the artificial blood vessel,
Thrombus formation and the state of blood flow can be monitored non-invasively for a long time after installation. Although the embodiment in which the present invention is applied to an artificial blood vessel has been described above, the present invention is applicable not only to an artificial blood vessel but also to an artificial tube that is artificially installed in a body to flow a body fluid such as a ureter and a bile duct. Applicable,
Even in such a case, it is possible to monitor the stenosis in the artificial tube, the flow rate of the body fluid, and the like at any time. Especially in the case of the ureter, when ureteral stones occur, in the case of the ureter, it causes severe peristalsis and there is severe pain, so you can be aware of it, but in the case of an artificial tube,
If the passage of urine is only poor and mild,
If left as it is, stones may grow there and stop passing more and more. By installing the artificial tube according to the present invention, it is safe because the inside of the artificial ureter can be periodically observed.

It goes without saying that the shape of the artificial tube is not limited to a cylindrical shape, but can be appropriately changed according to the shape of a blood vessel or ureter to be applied, such as a rectangular shape or a tapered shape.

[0029]

According to the present invention, since the artificial tube is provided with the receiving coil of the MRI apparatus, the condition and function in the tube can be periodically measured non-invasively after the artificial tube is implanted in the body. Therefore, after the implantation, the function of the artificial tube is deteriorated, or some trouble can be detected at an early stage and the artificial tube can be replaced with a new artificial tube, so that the safety of the implanter can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment in which a receiving coil according to the present invention is applied to an artificial blood vessel, wherein (a), (b), and (c) are diagrams showing an artificial blood vessel provided with receiving coils having different shapes;

FIG. 2 is an MR for taking an internal image of an artificial blood vessel according to the present invention.
The figure which shows the structure of an I system.

FIG. 3 is a view showing another embodiment of the artificial blood vessel according to the present invention, wherein (a), (b) and (c) show an artificial blood vessel having a plurality of receiving coils, respectively.

FIG. 4 is a diagram showing an example of a unit for extracting a signal from a receiving coil provided in the artificial blood vessel.

FIG. 5 is a diagram showing another example of a means for extracting a signal from a receiving coil provided in the artificial blood vessel.

FIG. 6 is a view showing an image inside an artificial blood vessel acquired by the MRI method of the present invention, where (a) shows a normal state and (b)
FIG. 3 is a diagram showing a state in which a thrombus has been formed.

FIG. 7 is a view showing an image inside the artificial blood vessel acquired by the MRI method of the present invention, and showing a deformed artificial blood vessel.

[Explanation of symbols]

1 ... subject 2 ... Static magnetic field generating magnet 3 ... Gradient magnetic field generation system 4 ... Transmission system 5 ... Reception system 6 Signal processing system 7 Sequencer 8 Central processing unit (CPU) 21, 21 '... receiving coil 21a ... lead wire 22: Artificial blood vessel (tube) 25 Connector 27 ... electrode

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61B 5/055 A61F 2/04

Claims (5)

(57) [Claims] 1. An artificial tube for performing a function of a human body, wherein the artificial tube is provided with a receiving coil for receiving a nuclear magnetic resonance signal. 2. A magnetic field generating means for generating each of a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, a signal detecting means for detecting a nuclear magnetic resonance signal from a test object, and a receiving means for receiving the nuclear magnetic resonance signal Means, a signal processing means for image reconstruction based on a signal from the receiving means, a signal processing means for performing an operation, and an output means for outputting an operation result, wherein the signal detection means A magnetic resonance imaging apparatus using the artificial tube according to claim 1, wherein a receiving coil is incorporated. 3. The magnetic resonance imaging apparatus according to claim 2,
Wherein the receiving coil and the receiving means are electrically
Magnetic resonance image characterized by direct connection
Device. 4. The magnetic resonance imaging apparatus according to claim 2,
The receiving means may be a co-located body surface.
And the receiving coil detects through the coil.
Receiving a magnetic resonance signal in the form of a magnetic field.
Sound imaging device. 5. The artificial tube according to claim 1, further comprising a receiving coil.
Only to detect a nuclear magnetic resonance signal using the receiving coil.
Detecting means, and processing the nuclear magnetic resonance signal.
Perform an operation for image reconstruction in the inside of the artificial tube
Functional measurement such as flow velocity of liquid to be imaged or flowing inside
And a calculation means for performing
Mazing device.