JPS6190045A - Mri device - Google Patents

Abstract

PURPOSE:To correct the attenuation of a magnetic field automatically and to produce a static magnetic field with high uniformity by providing a control means which the controls the excitation of a correcting coil which corrects the static magnetic field established by a main coil on the basis of a magnetic field detecting means. CONSTITUTION:An MR (magnetic resonance) phenomenon is caused at the expected tomographic surface part of an object body P arranged in an uniform static magnetic field produced by the main coil 1 and a shim coil and an induced MR signal is detected to obtain projection information. Then,a the magnetic field sensor consisting of a detection part 11, coupling support rod 12, and rotary driving device 13 is fitted in a groove 10 for magnetic sensor storage formed in the internal surface of the transmitting and receiving coil container 4 of a high-frequency transmitter and receiver 4. The device 13, on the other hand, incorporates a storage position sensor 14 and a measurement position detection sensor 15 which detect the position of the magnetic sensor, and the detection part 11 is coupled electrically; with the magnetic field sensor transmitting and receiving device 16. Further, a controller 17 which controls the correction of the attenuation of the magnetic field, the device 16, the device 13, and a Zo shim coil power unit 7a are coupled electrically with one another.

Description

Detailed description of the invention (Technical field 1 of the invention)
Resonance; 1] Identification of i-sample using the phenomenon (referred to as IR)! J atom (for example, as a length,
The spin of the hydrogen nucleus, the time constant distribution, and the chemical shift meter ff1lj value are measured from the outside of the above specimen at 9% heat immersion, and the cross-sectional image information is M
RI (tvl agnetic Reso-11an
Regarding the Ce l magi njl) device, in particular,
This relates to a klRIY device that automatically corrects the attenuation of the magnetic field to generate a highly uniform static field.

[Technical Police of Invention] What is the MR phenomenon? ! It is known that the intensity of the magnetic field at the position where the two specimens are placed, that is, the position where the IR current 9 is generated, is exactly proportional to the strength of the magnetic field, and that the magnetic field resonates in a rounded and narrow range. It is being

Therefore, in order to obtain a clear angle of view due to the NIR phenomenon, it is necessary to
A magnetic uniformity of 100 ppm + l (cm) and stability of about 10 -8 hours are required inside the cm sphere.

For this reason, a long air-core solenoid or a double I\Lumholtz coil configuration is used as the static magnetic field generating coil to achieve high uniformity, and a persistent current switch etc. is used to achieve high stability. <I am trying to operate from high current mode 1.

On the other hand, the static field Kogyo coil may not be as accurate as specified due to the dimensional accuracy when making the WI or the positional accuracy between the coil and the coil, and therefore the magnetic field j uniformity of about r1m is It can't be achieved. Furthermore, when a static magnetic field generating coil is constructed from a superconducting coil, there is a 5!1 field strength attenuation. That is, since superconducting coils are manufactured by splicing ordinary conductive wires together, Joule loss occurs as the persistent current flows in these joints, and 10-8.・Current loss of about an hour occurs. When the magnetic field strength attenuates in about 1Q-11,/hour, the magnetic field strength decreases to 1 D in about 4 days.
rum attenuates from the initial first shift, resulting in blurring of the image.

Upper i! In order to solve problems with the uniformity and stability of the magnetic field, it has traditionally been necessary to provide a shim coil (correction coil) for f1 field correction in addition to the static magnetic field generating coil as the main coil. There is.

Also, this shim coil can be installed at the location where the main coil is installed! It also corrects disturbances in the uniformity of the magnetic field due to the presence or absence of strong-field objects in the surrounding area.

This shim coil is made up of 18 plurality of coils such as ZO shim coils in order to adjust the three-dimensional Efi jQ. This shim coil adjusts the F1 field generated by the main coil, and can correct the attenuation of the central magnetic field strength by several hundred ppm.

[Problems in the Background Art] In conventional M and RI devices, the above-mentioned (11) attenuation correction is performed by an operator who performs the 11-field attenuation correction of the Ti R'A position for the shim coil when acquiring images (during operation of the MRI device). By manually adjusting the volume, you can adjust the current value flowing through the shim coil and eliminate blurred images! I am correcting myself.

In this case, the operator must perform the above manual x1 adjustment at each time of standardization and acquisition based on the past adjustment t1, and if the operator is a doctor, he or she must perform the [Objective of the Invention] The present invention was made based on the above circumstances, and its purpose is to generate a highly uniform static n-field by automatically correcting the attenuation of the magnetic field. We would like to share the MRI equipment that has been made possible.

[IQ essential point of explanation] In order to achieve the above object, the MRI equipment according to the present invention has a main coil that generates a static Ta field and a correction coil that corrects the Ffi 7% due to this main coil. ■
(1. Center of the field [!! Magnetic field detection means for measuring the field strength,
this! The present invention is characterized by comprising a control means for controlling the excitation of the correction coil based on the output of the first boundary detection means.

[Embodiment of the Invention] An MRI apparatus according to the present invention will be described below according to an embodiment shown in FIG.

That is, 1 is the super-m l as the main coil that generates the static magnetic field.
2 is a shim coil (Zo shim coil).
! Subject P was placed in the room.

3 is a gradient magnetic field coil that superimposes a gradient magnetic field on the above-mentioned static Fu field. 4 is a high frequency transmitter/receiver (probe head) having a transmitting coil and a receiving coil, which applies an excitation rotating magnetic field to the static magnetic field formed by the gradient magnetic field,
? ! 2. MR current drop is generated on the planned fault plane part of P-body, and the constructed \1R signal is detected to calculate the projection information of the planned fault plane part. 5 is the projection information of the above planned fault plane part. A computer that generates uniform information that reflects at least one of, for example, the spin density distribution of hydrogen nuclei and the time constant distribution, etc., on the tomographic plane of the subject P by subjecting the information to pre-image processing (S acid treatment, etc.) It is a fault device.

6 is a power supply device for the superconducting coil 1, 7 is a power supply device for the shim coil 2, 7a is a power supply device for the 70 shim coil, 8 is a power supply device for the gradient magnetic field coil, and 9 is a power supply for the high frequency transceiver 4. It is a device.

The combinations up to this point are the same as those of the conventional device, and in this embodiment, the 1m combination described below is added. That is, a groove 10 for storing a magnetic field sensor is provided on the inner surface of the transmitting/receiving coil container 4a of the high frequency transmitter/receiver 4, and within this groove 10, an F! Install the iYang sensor.

The rotary drive device 13 includes two position sensors for detecting the position of the F1 Yang sensor, namely, an R beat position same detection sensor 1.
4, F, 11 Stereotaxic stomach detection sensor 15 is built into the detection unit 11 (well! I-field sensor transmission/reception @ 冑16 and electrically connected. F! 1-field) Controller 17 that performs representative correction control And magnetic field sensor transmitter/receiver 16, rotation drive! J
] The mounting 13 and the ZO shim coil haze source device 7a are electrically connected.

Next, the operation of the MRI apparatus of this embodiment configured as described above will be explained with reference to FIG. 1 and FIG. It is a flowchart of control of a present Example.

That is, the timer T1 is turned on at the time when the initial magnetic field strength is adjusted at Sl. In S2, the timer T1 times out (for example, if the TO' of the superconducting coil 1 is 14% and the decay rate is 10-'' hours, it takes 4 days), and in S3, the subject P is placed at a predetermined position in the IRI device. If so, the operator or doctor turns on the start push m switch for magnetic field attenuation correction control in S4.Then, in S5, the drive! restart signal is input from the controller 17 to the rotation drive device @13. In S5, the magnetic field sensor is rotated and set at a predetermined measurement position.The measurement position is where the detection unit 11 coincides with the center of the static magnetic field applied by the electroconduction coil 1.

When the measurement position is set, the measurement position detection sensor 15 outputs a setting completion signal in step S6.
1 is input. When this setting completion signal is input, S
At step 7, the magnetic field sensor transmitting/receiving device 16 and the detecting section 11 start to determine the center magnetic field strength, and the measured magnetic field strength B is inputted to the controller 17.

Then, in S8, the arithmetic circuit of the controller 17 calculates the f stock attenuation ΔBtfi, and in S9, the increase ΔI in the excitation F1 current of the ZO shim coil 2 corresponding to this one turn is calculated. Then, in S10, the controller 17 sends 20 shim coils 11ii in the shim coil power supply device 7! Device 7a
An excitation current increase command is input to , and the zo shim coil 2 is excited by the excitation current increased by ΔI. This ZO shim coil 2 allows the static Ft! The field is incremented by ΔB. For example, when the central magnetic field strength is 15,000 Gauss, the magnetic field attenuation rate is 10-8. /hour, 8B is 0.015 Gauss.

Again, in S11, set the central magnetic field using the ti magnetic field sensor.
and compare it with the required magnetic field strength Bo. And 312
The difference between B and BO is 0. If it is less than lppm, it is considered that the correction is completed and the process proceeds to 813 and thereafter. If not, the process returns to S8 and the controller 17 and the 70 shim coil electric 1i1
At 7a, adjust the magnetic shielding current of Zo shim coil 2 to
! Perform 1-field measurement.

vi jq When the damping correction is completed, a rotation command is given from the controller 17 to the rotary drive device 13 in 813, and S
At step 14, the magnetic field sensor is stored in the original position, that is, in the sensor storage groove 1o.When the magnetic field sensor is stored in the above position, the storage position detection sensor 14
The setting completion signal is sent to the controller 17 (by two people, three
In response to this, at step 15, an interlock signal enabling image collection is input from the controller 17 to the computer image clinic apparatus 5. At this time, timer T1 is turned on again and S
Return to the initial control state of l.

As explained above, this embodiment has a similar effect.

■ The magnetic field attenuation valve can be automatically corrected, so S〕'
Clear images with good N ratio can be obtained.

t21 At the time of image collection, magnetic field correction is performed in advance, and there is no need to adjust image blur, so the image collection time can be shortened.

(2) Since the operator does not have to manually correct the Pl field attenuation, the operator's working time is reduced accordingly, labor costs are reduced, and as a result, N and IRI operating costs are reduced.

■ The Ei magnetic field sensor is not exposed to the outside due to the magnetic field sensor housing groove 10. ′! Even if it is placed inside the P-body high frequency transmitter/receiver 4, it will not cause any interference.

(2) If the f1 field sensor is made of a non-magnetic material, it will not have any adverse effect on the F1 field uniformity.

Next, a second embodiment of the present invention will be described.

The m* attenuation characteristic of a superconducting coil in persistent current mode is uniquely determined by the coil components and installation environmental conditions, and the attenuation characteristic after a long period of operation (for example, one month) is stable and reaches a constant value (for example, 10- 8 hours), and there are no fluctuations due to disturbances.

Taking advantage of this characteristic, the RTL field sensor and the transmitting/receiving device 16 shown in FIG. 1 are not used or removed, and the
The q-attenuation characteristic is measured in advance and the characteristic field is input into the controller 7. Since the excitation current value of the ZO shim coil 2 that should be increased in accordance with this magnetic field attenuation rate is determined,
This is ZO shim coil 74il! It is input to the i-device 7a and the ZO shim coil 2 is excited and adjusted.

The excitation adjustment of the ZO shim 2 may be performed continuously in response to the magnetic field attenuation, or may be performed every attenuation of about 1 ppm, similar to the first actual excitation.

In the case of this embodiment, compared to the first embodiment, the magnetic field sensor and the transmitting/receiving device 16 are unnecessary, which has the effect of reducing costs.

Next, a third embodiment of the present invention will be described.

That is, instead of the detecting section 11 of the magnetic field sensor, a phantom is installed in which the main component is sealed in a non-Eft container such as plastic.

Next, the operation of this embodiment will be explained. When measuring the magnetic field strength B, as in the first embodiment, the phantom is placed at the magnetic field measurement position using the rotation 1 calling device 13. At this time, in the same manner as when acquiring images of the subject P, a high frequency is applied to the phantom using the high frequency transmitter/receiver 4 and the high frequency power supply 9 to give an excitation rotating magnetic field, The emitted IR signal is received and inputted to the controller 17. After this, the first
Magnetic field attenuation correction is performed in the same way as signal processing and shim coil adjustment similar to those in the embodiment shown in FIGS.

According to the above, the detection unit 11 of the magnetic field sensor. and [n+
Since the three-sensor transmitting/receiving device 16 is not required, this embodiment has the effect of being more compact than the embodiment shown in FIG.

In each of the above embodiments, the case where a superconducting coil is used as the main coil is described, but it goes without saying that the present invention can also be applied to a case where a normal normal conducting coil is used as the main coil.

[Effects of the Invention] As described above, according to the present invention, the main coil that generates a static magnetic field and the F! It has a correction coil for correcting the field, and the static I41'! and a control means for controlling the excitation of the correction coil by detecting the output of the field detection means, so that the attenuation of the magnetic field can be automatically corrected. An MRI apparatus capable of generating a highly uniform static magnetic field can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the MRI apparatus according to the present invention, and FIG. 2 is a flowchart of the magnetic field attenuation correction plate of the same embodiment. 1...Superconducting coil, 2...Shim coil, 3...
Slope [! ! Field coil 4...high frequency transmitter/receiver, 5...
・Computerized tomography diagnostic device, 6.7, 8.9... Power supply device, 10... Pl field sensor groove, 11... Detection section, 12... Continuous support rod, 13... Rotation drive device surface,
14... Beat beat position detection sensor, 15... 1 fixed position detection sensor. 16...Magnetic field sensor transmitting/receiving device, 17...Con(
·roller.

Claims (1)

[Claims] A specimen is placed in a static magnetic field to generate a magnetic resonance phenomenon, and the spin density distribution of a specific atomic nucleus within the tomographic plane of the specimen is determined.
An MRI apparatus that measures relaxation time constant distribution and chemical shift measurement values, which has a main coil that generates the static magnetic field and a correction coil that corrects the magnetic field generated by the main coil, and measures the center magnetic field strength of the static magnetic field. An MRI apparatus comprising: a magnetic field detecting means for detecting a magnetic field; and a control means for controlling excitation of the correction coil based on the output of the magnetic field detecting means.