JPH0237172B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an NMR imaging device that displays an NMR image of an arbitrary cross section of an object to be imaged.

Recently, research has been actively conducted to visualize the proton spin density of biological cross sections using NMR technology. Normal NMR equipment detects resonance signals while applying a uniform magnetic field to the sample.
In imaging the proton spin density, a gradient magnetic field with spatially different strengths is applied to the object to be imaged, superimposed on the uniform magnetic field, and the resonance signal generated in this state is processed by an electronic computer. An image of an arbitrary cross section of the imaged object is obtained.

The present invention relates to an improvement of an NMR imaging device for obtaining a cross-sectional image of an object to be imaged as described above, and provides an NMR imaging device that can easily determine information such as the size of the obtained cross-sectional image. The purpose is to

The NMR imaging device based on the present invention obtains an NMR signal from an object to be imaged while applying a gradient magnetic field having spatially different intensities to the object, and displays an image of a cross section of the object on a display means based on the signal. In an NMR imaging device configured to display marks on the direction axis of the gradient magnetic field applied to the object, marks generated at each predetermined magnetic flux density or on the direction axis of the gradient magnetic field applied to the object, The present invention is characterized in that a mark having a length corresponding to a predetermined unit magnetic flux density range is displayed on the display means together with the image.

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

In FIG. 1, 1 is a superconducting magnet that generates a uniform magnetic field, and an object 2 to be imaged is placed in the uniform magnetic field generated by the magnet. Gradient magnetic fields of different strengths in the X direction are further applied to the object 2 in accordance with the current applied from the power supply 3 to the pair of X direction gradient coils 4 . Further, the object 2 is configured such that a gradient magnetic field in the Y direction and a gradient magnetic field in the Z direction are applied to the object 2 by a combination of a power source 5 and a Y direction gradient coil 6, and a combination of a power source 7 and a Z direction gradient coil 8, respectively. has been done. Each of the coils has a structure similar to a shim coil that is normally used to homogenize the magnetic field, and the strength of the gradient (inclination of the gradient) changes depending on the current value applied to the coil. ing. Note that the current value supplied from each power source to each coil is changed according to a command from the electronic computer 9, and a magnetic field of arbitrary gradient strength is applied to the object 2 to be imaged. A coil 10 is further wound around the object 2, and a high frequency pulse from a transmitter 11 is applied to the coil 10. A free induction decay (FID) signal generated with the application of a high-frequency pulse to the coil 10 is detected by a receiver 12, detected by a detector 13, and then detected by an A-D converter 14. The signal is then A-D converted and supplied to the electronic computer 9. The electronic computer 9 performs predetermined processing including Fourier transformation on a large number of supplied FID signals, and creates a video signal of the proton spin density of an arbitrary cross section of the object 2. The video signal obtained by the electronic computer is supplied to the cathode ray tube 15, and the image of the object 2 is sent to the cathode ray tube.
An NMR image is displayed. The cathode ray tube 15 is supplied with a mark signal from a mark signal generator 16 as well as a video signal from the computer 9.
This mark signal generator 16 includes X, Y, and Z axis direction conversion tables 17X, 17Y, and 17Z, and a multiplier 1.
8X, 18Y, 18Z, marker signal generation circuit 19
It is composed of X, 19Y, 19Z, and a synthesis circuit 20.

In the configuration as described above, each power source 3, 5, 7
The transmitter 11 irradiates the object 2 with high-frequency pulses many times through the coil 10 while controlling the current supplied to each coil 4, 6, and 8.
If the FID signal is processed by the electronic computer 9, an NMR image of the object can be displayed on the cathode ray tube 15. Here, the resonance conditions for NMR can be expressed as ω ₀ =γ·H 0 , where ω ₀ is the resonance frequency, H ₀ is the uniform magnetic field strength, and _γ is the gyromagnetic ratio. That is, under these conditions, the sample shown in FIG. 2 (sample tube 2 with an inner diameter of d)
The resonance signal of the water (water added to the water) has a sharp waveform as shown in FIG. Next, a uniform magnetic field is applied to the sample 20.
A magnetic field with a spatial linear gradient in the X direction in addition to H ₀
When GX is applied, the resonance condition becomes ω ₀ =γ·H ₀ +γ·GX, and the line width of the resonance signal depends on the magnitude of GX. That is, the resonance signal obtained from the sample in Figure 2 has a width W (mm) as shown in Figure 4.
The width W corresponds to the magnitude (Gauss/mm) of the applied gradient magnetic field in the X direction and the width d (mm) of the sample in the X direction. The magnitude of the gradient magnetic field is determined by the number of turns of the gradient coil and the magnitude of the current applied to the coil. In other words, if the strength of the uniform magnetic field and the size of the sample are constant, the line width of the resonance signal when a gradient magnetic field is applied is proportional to the magnitude of the current applied to the gradient coil.

Now, if a signal with a line width of 5kHz is obtained from a sample having a width of 10mm in the X direction under the application of a gradient magnetic field, the gradient strength of the gradient magnetic field is 5kHz/10mm=
500Hz/mm, which means that the magnetic field strength is
When the measurement target is protons with a resonance condition of 4.7 Tesla and a frequency of 200 MHz, the result is 117.5 mG/mm.
If the current value flowing through the gradient coil at this time is 3A, then if the current value is halved to 1.5A, the gradient strength of the gradient magnetic field will be 58.75mG/mm, and the line width of the obtained resonance signal will be 2.5kHz. becomes. This means, on the contrary,
The linewidth of the signal from the unknown sample obtained under a current of 1.5 A, that is, a gradient strength of 58.75 mG/mm, is 2.5 kHz.
, it becomes clear that the width of the sample is 10 mm, and the line width of the obtained signal is
At 10kHz, the width of the sample turns out to be 40mm. Although the explanation so far has mainly been about the X direction, the Y direction and the Z direction can also be handled in the same way as the X direction.

In this way, there is a proportional relationship between the current applied to the coil, that is, the gradient strength of the gradient magnetic field, and the line width of the signal.
NMR obtained when measuring a sample with a diameter of 10 mm) at a certain gradient strength and twice that gradient strength.
Comparing the images, when the gradient strength is doubled, the line width is also doubled, and the length of the sample in the X direction on the displayed NMR image is also doubled. Therefore, marks (scales) are generated on the direction axis of the gradient magnetic field at predetermined magnetic flux densities corresponding to the reference length on the actual size, or marks (scales) are generated on the direction axis of the gradient magnetic field on the actual size. A mark with a length corresponding to a predetermined range of unit magnetic flux density corresponding to the standard length is NMR
If displayed superimposed on the image, the interval between markers (scales) indicating the reference length will change according to changes in gradient strength.
Alternatively, since the length of the marker indicating the reference length expands or contracts in response to changes in gradient strength, the actual dimensions of the unknown sample can be accurately determined by comparing the NMR image with the marker indicating the reference length on the actual dimension. can be grasped.

In the embodiment shown in FIG. 1, a signal corresponding to a control signal specifying the current value to be passed through each coil supplied from the computer 9 to each coil power source 3, 5, 7, that is, each of X, Y, Z Signals Bx, By, and Bz corresponding to the gradient strength in the direction are sent to the mark signal generation circuit 16.
The data is supplied to conversion tables 17X, 17Y, and 17Z within. Each conversion table contains gradient strength values and
At that time, a table indicating how long the marker should be displayed on the screen indicating the reference length on the actual size is created and stored in advance based on the above-mentioned proportional relationship or based on actual measurements. ing.

Then, when the signals Bx, By, and Bz corresponding to the gradient strength are supplied to each conversion table, information Lx, By, and Bz indicating the length of the marker to be displayed are obtained from the angle conversion table.
Ly and Lz are output. Marker signal generation circuit 19
X, 19Y, and 19Z create marker signals based on this information Lx, Ly, and Lz. The created marker signal is sent to the cathode ray tube 15 via the synthesis circuit 20, and as a result, the marker is displayed on the screen 15a of the cathode ray tube 15 superimposed on the NMR image.

FIG. 5 shows a display example, in which marks M ₁ and M ₂ in two orthogonal directions are combined and displayed together with the NMR image I on the screen 15a. This FIG. 5 shows an example of displaying an NMR image I showing a cross section along the X-Y plane perpendicular to the Z axis, where M ₁ is a mark in the X direction,
_M2 is a mark in the Y direction. In this case, since there is no need to display the mark in the Z direction, the signal Bz is not supplied from the computer 9 to the conversion table 17Z. Therefore, a Z-direction marker signal is not created, and only the X-direction and Y-direction marker signals created by the marker signal creation circuits 19X and 19Y are combined in the combining circuit 20.

The above marks M ₁ and M ₂ are marked with a scale C representing the unit length, and are
Since the length of the mark and the interval between the scales C change in accordance with the change in the size of the NMR image I, the size of the imaged object can be correctly recognized.

In addition, when the magnification of the image displayed on the cathode ray tube is changed by processing within the electronic computer 9 without changing the gradient magnetic field, the information m of the magnification is determined by the multiplication within the mark signal generator 16. The information Lx, Ly, Lz indicating the length of the marker output from the conversion table is multiplied by the multiplication factor m and sent to the marker signal generation circuits 19X to 19Z, so it is always displayed. A mark corresponding to the size of the image will be displayed on the screen.

When displaying an NMR image showing a cross section along the When showing an NMR image showing a cross section along the Y-Z plane,
It goes without saying that it is sufficient to display a mark that is a combination of direction and Z direction mark signals.

As detailed above, in the present invention, along with the NMR image on the display means, marks are generated at each predetermined magnetic flux density on the directional axis of the gradient magnetic field, or on the directional axis of the gradient magnetic field applied to the object. By displaying a mark with a length corresponding to a predetermined unit magnetic flux density range, the interval or length changes depending on the gradient strength of the gradient magnetic field, and the reference length on the actual size of the imaged object is always displayed. Since a mark indicating the size of the elephant is displayed, the operator can always correctly recognize the size of the displayed elephant.

Note that the present invention is not limited to the embodiments described above, and can be modified in many ways. For example, in the above embodiment, the mark M ₁ whose total length corresponds to the reference length,
Although M ₂ and the scale whose interval corresponds to the reference length are displayed at the same time, only one of them may be displayed. Further, in the above embodiment, a desired mark is placed on the display device using a mark signal generator, but the mark signal is created in the process of signal processing within the computer, and the mark signal is generated in the process of signal processing within the computer. A mark signal may be included in the video signal.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIGS. 2 to 4 are diagrams for explaining the embodiment of FIG. 1,
FIG. 5 is a diagram showing an NMR image and marks displayed on a cathode ray tube. 1... superconducting magnet, 2... object to be imaged,
3, 5, 7... Coil power supply, 4, 6, 8... Gradient coil, 9... Electronic computer, 10... Coil, 1
1... Transmitter, 12... Receiver, 13... Detector, 14... A-D converter, 15... Cathode ray tube,
16...Mark signal generator.

Claims (1)

[Claims] 1 Obtain an NMR signal from the object while applying a gradient magnetic field with spatially different strengths to the object,
In an NMR imaging device that displays an image of a cross section of the object on a display means based on the signal,
A mark generated at each predetermined magnetic flux density on the direction axis of the gradient magnetic field applied to the object, or a length corresponding to a range of a predetermined unit magnetic flux density on the direction axis of the gradient magnetic field applied to the object. An NMR imaging device configured to display a mark given an image on the display means together with the image.