JPH03276082A - Measuring device for magnetic field - Google Patents

Abstract

PURPOSE:To improve a working efficiency for magnetic field measurement by providing plural magnetic field detecting elements, supporting rod with specified length on which the aforementioned plural magnetic field detecting elements are fixedly arranged in specified positions at the tip side, and position adjusting mechanism to support the back end side of this supporting rod so as adjustable for the position. CONSTITUTION:The device is furnished with the plural magnetic field detecting elements C10-C14, supporting rod 22 with specified length on which those plural magnetic field detecting element C10-C14 are fixedly arranged in the specific positions at the tip side, and position adjusting mechanism 23 to support the back end side of this supporting rod so as adjustable for the position. Consequently, the position adjusting mechanism 23 is possible to be arranged in the position away from the center of a gradient magnetic field coil 2 to the axial direction of the gradient magnetic field coil 2 by the length of supporting rod 22, then the position adjustment for plural magnetic field detecting elements C10-C14 can be easily performed. Further, the measurement for magnetic field in the specified position can be easily made by the plural magnetic field detecting elements C10-C14.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention is a method for measuring a linear gradient magnetic field generated by a gradient magnetic field coil used in a magnetic resonance imaging apparatus (hereinafter referred to as an "rMRI apparatus"). The present invention relates to a magnetic field measuring device.

(Prior art) An MRI apparatus places a subject in a static magnetic field formed inside a cylindrical gradient magnetic field coil, and pulses a linear gradient magnetic field in the X, Y, and Z directions orthogonal to each other from the gradient magnetic field coil. At the same time, an excitation pulse is output to the subject and is superimposed on the static magnetic field, and an MR multiplied signal generated from within the subject is detected by irradiating the subject with an excitation pulse to obtain a tomographic image of the subject.

The linear gradient magnetic field provides coordinate information for forming an MR multiplied signal tomographic image obtained from the subject, and requires a highly accurate magnetic field. For this purpose, a linear gradient magnetic field is measured using a magnetic field measuring device 1 shown in FIG. 8, and the center of the coil 2 is aligned with the center of the eddy current. If the linear gradient magnetic field is not a predetermined magnetic field, that is, if the magnetic field waveform is dulled by eddy current, the current flowing through the gradient magnetic field coil 2 is adjusted so that a predetermined linear gradient magnetic field is formed. There is.

The magnetic field measuring device 1 shown in FIG. 8 includes two search coils C.
,, C2 has a structure that can slide within the groove 3,
This device 1 is placed on a top plate T, and the top plate T is moved into a gradient magnetic field coil 2 to measure a linear gradient magnetic field near the center of the gradient magnetic field coil 2.

When measuring the linear gradient magnetic field generated by the gradient magnetic field coil 2, as shown in FIG.
and each direction x, y from this center O.

Points X, , X-, Y, , Y- that are apart from Z by a predetermined distance.

2. Magnetic field measurements are usually performed at a total of eight points.

When measuring the magnetic field at the above measurement points, before measurement, one end of the top plate T is pulled out from inside the gradient magnetic field coil 2, and the search coils C, C2 are moved within the groove 3, After that, the top plate T is moved into the gradient magnetic field coil 2 to measure the magnetic field.

(Problem to be Solved by the Invention) Since the conventional device is configured as described above, the top plate T must be pulled out from within the gradient magnetic field coil 2 every time a measurement is performed, which makes measurement time-consuming and makes magnetic field measurement difficult. There was a problem that the work efficiency was poor.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetic field measuring device that can improve the working efficiency of magnetic field measurement.

[Configuration of the Invention (Means for Solving the Problems) To achieve the above object, the present invention provides a magnetic field measurement device that measures a linear gradient magnetic field formed inside a cylindrical gradient magnetic field coil. A plurality of magnetic field detection elements to be detected, a support rod of a predetermined length formed by fixing the plurality of magnetic field detection elements at predetermined positions on the tip side, and a position that supports the rear end side of the support rod in an adjustable manner. It is characterized by having an adjustment mechanism.

(for production) The operation of the device having the above configuration will be explained.

The position adjustment mechanism of this device can be placed at a position away from the center of the gradient magnetic field coil in the axial direction of the gradient magnetic field coil by the length of the support rod, making it possible to easily adjust the position of multiple magnetic field detection elements. . Furthermore, magnetic field measurement at a predetermined position can be easily performed using a plurality of magnetic field detection elements.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 shows an overall block diagram of an apparatus 10 according to an embodiment of the present invention.

The MRI apparatus 4 includes a gradient magnetic field coil 2 formed in a cylindrical shape, a static magnetic field generator (not shown) that generates a static magnetic field inside the gradient magnetic field coil 2, and a vortex generator (not shown) that outputs a current to the gradient magnetic field coil 2 and generates a vortex to be described later. A gradient magnetic field power supply 5 equipped with a current compensation circuit (not shown) and an MRI system! [4] It has a system controller 13 that controls each part. The gradient magnetic field coil 2 of this MRI apparatus 4 includes an
It has a direction coil 2Y and a Z direction coil 2Z, and the positions of the coils 2x, 2y, and 2z are set in each direction X.

It has a moving mechanism (not shown) that can make fine adjustments independently in Y and Z.

Next, the present magnetic field measurement device 10 uses a plurality of (five in this example) magnetic field detection elements that measure linear gradient magnetic fields in the x, y, and z directions formed inside the gradient magnetic field coil 2 of the MRI device 4. Search coils CIO to CI4, a support section 20 that supports the search coils C, 10 to C14 from the top plate T, and a switch that selects and switches the electrical signals output by the search coils CIO to CI4 by detecting changes in the magnetic field. A switch SW, an integrator 11 that inputs and integrates an electrical signal selected by switching the changeover switch SW, and an integrator 1.
The MRI apparatus 1 has a digital oscilloscope 12 that records or displays output signals from the MRI apparatus 1, and a system controller 13 that controls each part of this apparatus 10 and is shared with the MRI apparatus 4.

FIG. 1 shows a perspective view of the support section 20. As shown in FIG.

This support section 20 supports the search coil CIO and other search coils C' l arranged at predetermined distances in the directions X and Y with the search coil C111 as the center.
1 to C14, and these search coils CIO to C1.
4, a support rod 22 having a predetermined length S and having the cross spar 21 fixedly disposed on the tip side;
It has a position adjustment mechanism 23 that supports the rear end side of the support rod 22 so that the position can be adjusted in the X direction and the Y direction.

When the search coils CtO to C14 detect a pulsed linear gradient magnetic field generated by the gradient magnetic field coil 2, an electromotive force is generated in the search coils CIO to C14 by this linear gradient magnetic field. This electromotive force is integrated by an integrator 11, and a voltage waveform Wi shown in FIG. 6 is output to a digital oscilloscope 12.

FIG. 2 is a perspective view of a main part of the position adjustment mechanism 23 of the support section 20 shown in FIG. 1.

This position adjustment mechanism 23 includes a movable nut 24 fixed to the rear end of the support rod 22, and a knob 25 that controls the movable nut 24.
A Y-direction moving screw 26 that can be moved in the direction Y by a knob 28, a frame member 27 that rotatably supports both ends of the Y-direction moving screw 26, and a frame member 27 that can be moved in the direction The X-direction moving screw 29 to be obtained and this X-direction moving screw 2
A frame member 30 rotatably supports both ends of the frame member 9 and supports the frame member 27 movably in the direction X, and this frame member 3
It has a fixing screw 31 disposed at the bottom of the 0.

This position adjustment mechanism 23 is fixed to the top plate T by screwing a fixing screw 31 into a female screw Ta provided on the tip side of the top plate T.

The system controller 13 controls the MR when measuring the magnetic field.
The gradient magnetic field coil 2 is controlled by controlling the gradient magnetic field power supply 5 of the I device 4.
The gradient magnetic field is output directly inside the coil 2 at predetermined intervals, and the control signals Sc and Sr are output to each part in synchronization with the timing of the linear gradient magnetic field output from the gradient magnetic field coil 2. ing.

Further, the system controller 13 outputs a switching signal Sc to the changeover switch SW, and selects the search coils CH to C14.
, outputs a reset signal Sr to the integrator 11, clears the offset voltage riding on the output voltage of the integrator 11, and allows the digital oscilloscope 12 to display an output voltage waveform Wi that is not affected by the offset voltage. There is.

It is preferable that the pulse current flowing through the gradient magnetic field coil 2 be rectangular and have a flat top because the area of the pulse current can be easily controlled. By the way, as shown in FIG. 4(a), a rectangular pulse current P is applied to the gradient magnetic field coil 2. Even if it outputs, the pulse current P flowing through this gradient magnetic field coil 2. As shown in the figure (b), a shield member placed near the gradient magnetic field coil 2 is
Eddy current Pw is generated. This eddy current Pw mixes into the gradient magnetic field coil 2, and the current flowing through the gradient magnetic field coil 2 becomes a distorted current waveform P' as shown in FIG.

Therefore, the eddy current compensation circuit of the gradient magnetic field power supply 5 of the MRI apparatus 4 arbitrarily changes the current waveform output to the gradient magnetic field coil 2 by the operator's operation, and the coil 2 is configured to have a rectangular shape that is not affected by eddy currents. Pulse current P. , is flowing. That is, the operator uses the digital oscilloscope 1
The eddy current compensation circuit is adjusted so that the top Wt of the voltage waveform Wi displayed in 2 becomes flat, and the gradient magnetic field power source 5
Current P after eddy compensation shown in figure (a). C is output to the gradient magnetic field coil 2. This causes the current P. Even if an eddy current Pw is mixed into C, this eddy current Pw is a current P. 0, the current waveform P has a flat top as shown in FIG. C.

Next, the operation of the embodiment device 10 configured as described above will be explained.

First, the operator sets the center of the gradient magnetic field coil 2.

The system controller 13 controls each part to perform x, y
, Start measuring the linear gradient magnetic field in the z direction.

The system controller 13 outputs a switching signal Sc to the changeover switch SW to select the search coil CIO shown in FIG.
Select.

The operator manipulates the top plate T on which the device 10 is fixedly arranged to install the search coil C. is placed at the center of the gradient magnetic field coil 2.

Next, the operator determines the voltage level V of the top Wt of the voltage waveform Wi displayed on the display screen of the digital oscilloscope 12.
Move the search coil CIO until t is close to zero,
Place the search coil CIQ at the center of the formed gradient magnetic field. Here, if the center of the gradient magnetic field and the center of the eddy current shift, a ripple waveform appears on the oscilloscope. The coil 2x of the MRI device 4 so that this ripple waveform disappears,
2y.

Finely adjust the position of 2z by operating the moving mechanism.

After setting the centers of the coils 2x, 2y, and 2z, the operator measures the magnetic fields of the search coils C1 to C14 with the search coil C1o positioned at the center O.

The system controller 13 outputs a switching signal Sr that sequentially selects search coils C11 to CI4 for each measurement to the changeover switch SW, and selects the search coils CI+ to C14.
The respective magnetic field waveforms detected by are integrated by an integrator 11 and displayed on a digital oscilloscope 12 as a voltage waveform Wi.

The operator then selects the voltage waveform W displayed on the digital oscilloscope 12 due to the influence of the eddy current.
If the top Wt of i is not flat but blunt, operate the eddy current compensation circuit of the gradient magnetic field power supply 5 of the MRI apparatus 4 to adjust the top Wt of the voltage waveform Wi to be a flat waveform without dullness. . In this way, the measurement point X shown in FIG.
+tx-y+, complete the measurement and adjustment of the magnetic field at y-.

Next, the operator selects a measurement point Z in the direction Z shown in FIG.

, 2-. The operator moves the top plate T in direction 2 and measures and adjusts the magnetic field in the same manner as described above.

In this way, the magnetic field can be measured without pulling out the top plate T each time a magnetic field is measured, thereby improving the measurement efficiency of linear gradient magnetic fields.

The present invention is not limited to the above-described embodiments, and may be modified without changing the gist thereof.

For example, the system controller may also perform automatic movement control of the top plate when measuring magnetic fields in two directions, thereby further automating magnetic field measurements. Further, as the magnetic field detection element, other elements than the search coil may be used as long as they can measure a magnetic field that changes in a pulsed manner.

Furthermore, the magnetic field detection element may have a number of elements corresponding to the number of measurement points desired to be measured. In this case, in this embodiment, the number of measurement points is seven, and the support rod may be curved so as not to interfere with the magnetic field detection element.

[Effects of the Invention] According to the present invention described in detail above, a plurality of magnetic field detection elements are provided at predetermined positions, and a position adjustment mechanism is used to detect a plurality of magnetic field detection elements at a predetermined distance ahead of the plurality of magnetic field detection elements. Since the position of the detection element can be adjusted, it is possible to provide a magnetic field measurement device that can improve work efficiency in magnetic field measurement.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a support part of an apparatus according to an embodiment of the present invention;
The figure is a perspective view of the main parts of the position adjustment mechanism of this device, FIG. 3 is an overall block diagram of this device, FIGS. 4(a) to (C) are current waveform diagrams before eddy current compensation, and FIG. 5(a) ) to (c) are current waveform diagrams after eddy current compensation, Figure 6 is a voltage waveform diagram displayed on the digital oscilloscope of this device, Figure 7 is a perspective view showing the magnetic field measurement points, and Figure 8 is a diagram of the voltage waveform displayed on the digital oscilloscope of this device. FIG. 2 is a perspective view of a main part of a conventional device. 2... Gradient magnetic field coil, 10... Magnetic field measuring device,
22... Support rod, 23... Position adjustment mechanism, CI
IJ to CI4...Search coil (magnetic field detection element).

Claims (1)

[Claims] A magnetic field measurement device that measures a linear gradient magnetic field formed inside a cylindrical gradient magnetic field coil includes a plurality of magnetic field detection elements that detect the magnetic field, and a plurality of magnetic field detection elements that are fixedly arranged at a predetermined position on the tip side. 1. A magnetic field measuring device comprising: a support rod having a predetermined length; and a position adjustment mechanism that supports the rear end of the support rod in a position-adjustable manner.