JPH02261430A - Magnetic resonance-imaging apparatus - Google Patents

Abstract

PURPOSE:To make it possible to shift a center of a field of view of a figure by setting a point where the amplitude of an inclined magnetic field becomes zero as the center of a field of view and adding an offset phase surroundings on each an encode both in the X and Y directions. CONSTITUTION:X and Y directions are divided into a frequency encode direction and a phase encodic direction, respectively and in an MRi apparatus, a figure wherein a center of a field of view is fitted on a body axis and a point of intersection of X-Y axes is a center is obtd. To take a photograph under such a condition that the center of the field of view is moved as much as D in the X direction from the point of intersection of X-Y axes, a phase rotation occurs when a magnetic field strength at a point D is P and the amt. of the phase rotation theta is given by an equation I (wherein gamma is a magnetic rotation ratio and Tx is a charging time of an inclined magnetic field in the X direction). To correct this amt. of an offset phase rotation to zero, an operation of an equation II is performed as a complex number Z' after correction of the phase. In a spin-echo-sequence where a phase encodic number is M, the correction of the phase on each encode is performed by adding a phase rotation as much as the amt. of an equation III wherein phase correction angles in the X and Y directions are thetax and thetay, respectively. A phase addition corresponding to the inclined magnetic field strength at each time is performed on the corrected measured data at each time on each encode. Therefore, FFT treatments are performed M times in the phase encodic direction. A figure on an arbitrary center of the field of view is obtd., as the phase correction is done in such a way that the phase rotation is zero.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a magnetic resonance imaging apparatus (MRI) that obtains a tomographic image of an object to be inspected using the nuclear magnetic resonance (NMR) phenomenon.
In particular, the present invention relates to an MHI apparatus that obtains tomographic images with the imaging center moved.

[Conventional technology]

In the conventional apparatus, as described in Japanese Patent Application Laid-open No. 62-197048, Nuclear Magnetic Resonance Tomography Apparatus, the center frequency was changed during data collection to shift the center of the image.

[Problem to be solved by the invention]

In imaging using the two-dimensional Fourier transform method,
For example, frequency encode in the X direction.

In the X direction, a two-dimensional space is encoded using gradient magnetic fields in two directions called phase encoding.

That is, while changing the 5-phase encode amount by a fixed amount, a frequency encode pulse is applied during data collection to read out the signal.

In the above-mentioned conventional technology, signals are read by moving the center frequency during data collection, and the center of the image can be shifted in the X direction. However, the movement of the image center in the X direction (phase encoding direction) is not taken into account6. Therefore, if the subject is located at a position shifted from the center of the field of view in the X direction (phase encoding direction), the image will shift in the X direction. There was a problem that it would separate (fold back).

The present invention aims to shift the center of the image in both the X direction (frequency encoding direction) and the Y direction (phase encoding direction).

[Means to solve the problem]

When a gradient magnetic field having a first-order gradient centered around the resonant frequency of the static magnetic field is applied, the point where the amplitude of the gradient magnetic field becomes 0 becomes the center of the field of view. Shifting the center of the field of view of the image means shifting the center of the encoding gradient magnetic field in the X and Y directions. In other words, it is sufficient to apply the gradient magnetic field with an offset. Therefore, providing an offset to the gradient magnetic field will affect the measurement data. This can be achieved by adding an offset phase correction, and can be achieved by adding an offset phase around each encode in both the X direction and the Y direction.

[Effect]

Adding phase correction for each encode corresponds to giving an offset to the encoding gradient magnetic field and moving the center of the gradient magnetic field. Therefore, the center of the visual field can be moved, and the center of the visual field can be freely moved in both the X and Y directions according to the amount of offset phase, so an image with an arbitrary center of the visual field can be obtained on the XY plane. Similar to X-ray CT images, in oblique images, multi-slice images in which the center of the field of view is always on the coordinate axis can also be obtained by applying offset phase correction to each slice.

〔Example〕

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

FIG. 2 is a block diagram showing an example of the overall configuration of a nuclear magnetic resonance imaging apparatus according to the present invention. This nuclear magnetic resonance imaging apparatus uses a nuclear magnetic resonance (NMR) phenomenon to obtain a tomographic image of a subject 1, and uses a static magnetic field generating magnet 1.
0, a central processing unit (hereinafter referred to as CPU) 11, a sequencer 12, a transmission system 13, a magnetic field gradient generation system 14, a reception system 15, and a signal processing system 16. The static magnetic field generating magnet 10 generates a strong and uniform static magnetic field around the subject 1 in the body axis direction or in a direction perpendicular to the body axis, and has a certain extent around the subject 1. A permanent magnet type, normal conduction type, or superconducting type magnetic field generating means is arranged in the space. The sequencer 12 operates under the control of the CPU 11 and sends various commands necessary for data collection of tomographic images of the subject 1 to the transmission system 13, magnetic field gradient generation system 14, and reception system 15. The transmission Wt system 13 includes a high-frequency oscillator 17, a modulator 18, a high-frequency amplifier 19, and a high-frequency coil 20a on the transmission side. Amplitude modulation is performed, and this amplitude modulated high frequency pulse is sent to a high frequency amplifier 1.
The high magnetic wave is amplified in step 9 and then supplied to a high frequency coil 20a disposed close to the object 1 to be inspected, so that the object 1 to be inspected is irradiated with high magnetic waves.

The magnetic field gradient generation system 14 includes gradient magnetic field coils 21 wound in the three axes of X, Y, and Z, and a gradient magnetic field power supply 22 that drives each coil.
Gradient magnetic field power source 2 of each coil according to instructions from
2, gradient magnetic fields Gx, Gy in the x, y, and z directions are generated.

Gz is applied to the object 1 to be inspected.

Depending on how this gradient magnetic field is applied, a slice plane for the object 1 to be inspected can be set. The receiving system 15 includes a receiving-side high-frequency coil 20b, an amplifier 23, a quadrature phase detector 24, and an A/D converter rif 25. Electromagnetic waves (NMR signals) are detected by a high frequency coil 20b placed close to the object to be inspected 1, and sent to an A/D converter 25 via an amplifier 23 and a quadrature phase detector 24.
It is input into the digital quantity, and then sent to sequencer 1.
Two series of collected data are sampled by the quadrature phase detector 24 at the timing according to the command from 2, and the signals are sent to the signal processing system IG.

This (No. 3 processing system 16) consists of a CPtJll, a storage device such as a magnetic disk 26 and a magnetic tape 27, and a display 28 such as a CRT. performs processing such as artifact removal and image reconstruction.

The signal intensity distribution of a low cross section or the distribution obtained by performing appropriate calculations on multiple signals is converted into an image and displayed on the display 2.
8. In addition, in FIG. 2, the high-frequency coils 20a, 20b and the gradient magnetic field coil 21 on the transmitting side and the receiving side are arranged in the magnetic field space of the static magnetic field generating magnet 10 arranged in the space around the test object 1. There is.

FIG. 3 schematically represents a time sequence in a typical spin echo measurement. In FIG. 3, RF indicates the timing of irradiation of radio frequency signals and an envelope for selective excitation. Gz indicates the timing of applying a gradient magnetic field in the slice direction. ay
indicates that measurement is performed by changing the timing and amplitude of the gradient magnetic field application in the phase encoding direction. Gx indicates the timing of application of the frequency encode gradient magnetic field, and Si and nal indicate the NMR signal to be measured. The bottom row shows the time sequence divided into sections 1 to 6.

Note that the three axes X, Y, and Z are Cartesian coordinate axes that are orthogonal to each other. In section 1 in Figure 3.

A 90 degree selective excitation pulse is irradiated and a gradient magnetic field in the slice direction is applied. In section 2, a gradient magnetic field in the phase encoding direction is applied to add position-dependent rotation of the nuclear spins in the Y direction.

Furthermore, in section 2, a frequency encoding gradient magnetic field is applied. This measures the NMR signal in section 6.
This is for dephasing (dephasing + inverting the phase) the nuclear spin in advance so that the time origin is at the center of section 6 when the time is shifted. In section 3, no signal is issued. In section 4, a 180 degree selective excitation pulse is irradiated and a gradient magnetic field in the slice direction is applied.

In section 5, no signal is issued. In section 6, a frequency encoding gradient magnetic field is applied and an NMR signal is measured. To perform NMR imaging,
As described above, an RF pulse is irradiated with a gradient magnetic field applied to the static magnetic field, and a gradient magnetic field is applied to encode the NMR signal emitted from the inspection area of the object 1 as spatial information, and the NMR signal is After measuring, one image is reconstructed.

To encode space, a gradient magnetic field is used, which takes advantage of the fact that the nuclear magnetic resonance frequency ω has a linear relationship with the magnetic field strength. In other words, if the linearity of the gradient magnetic field is maintained spatially, the relationship between the spatial amplitude and frequency in the target region will be linear, and the NMR signal, which is time information, can be Fourier transformed and replaced with the frequency axis. The image is reconstructed by utilizing the fact that the position information of the body 1 is obtained.

Specifically, the image is reconstructed using a two-dimensional Fourier transform method, but below we will explain how to encode the space after the nuclear spins in a region with a certain thickness in the slice direction are excited by selective excitation. do.

In order to add rotation to the nuclear spin of a two-dimensional plane region with a certain thickness by an amount corresponding to the spatial coordinates,

It is encoded separately in two directions of Y. If you follow Figure 3.

The X direction is divided into a frequency encoding direction, and the Y direction is divided into a frequency encoding direction.

In the frequency encoding direction, when reading a spin echo signal, the phase must be shifted by Nπ at both ends of the field of view, and if the frequency encoding time is Tx, y Gx-D-Tx:=N π-( 9) The following relationship must be satisfied. Here, γ: gyromagnetic ratio of proton, which is the target nucleus (2,6751X lO'rad/
See/Causs) Gx Two Same frequency encoding direction gradient magnetic field strength D: Field of view diameter N: Number of measurement samples.

In addition, in the phase encoding direction, if phase encoding is performed M times, the phase at both ends of the field of view is at most Mπ
So it just needs to be off.

When the phase encode pulse application time is Ty, γGy
-D-Ty=Mπ...(1o) must be satisfied. here.

Gy: Maximum value of gradient magnetic field in phase encoding direction M: Number of phase encodes. In addition, the field of view was a square area.

The gradient magnetic field in the frequency encoding direction is applied with the same intensity for each phase encode, and the spatial coordinate in the X direction is encoded on the frequency axis. On the other hand, in the phase encoding direction,
One phase encoding amount γGy-D −'ry is set so that the gradient Bi field strength becomes γGY-D・Ty for each encode.
The spin echo signal is measured by changing Gy so that it changes by π.

In this way, N samples in the X direction and M samples in the X direction.
Two-dimensional measurement data with samples is collected. usually,
QPD (Quadrature P) is used for NMR signal measurement.
Since the real part and the imaginary part are collected simultaneously using a method (hase detection), NXM sample data is obtained, and when this is subjected to two-dimensional Fourier transformation, an image is obtained.

By the way, in an MRI apparatus, an oblique image at an arbitrary slice section can be obtained by combining and applying gradient magnetic fields in the X, Y, and X directions. FIG. 4 shows the field of view for oblique image capturing.

In FIG. 4, the coordinate axes determined by the gradient magnetic field fixed to the MRI apparatus are indicated by x, y, and z, and the coordinate axes fixed to an arbitrary inclined cross section 51 to be imaged are indicated by u, v, and s axes. It shows. Now, if we take the S axis as the slice axis and image a tilted cross section using a combination of gradient magnetic fields in the X, Y, and X directions, then u, v
A plane is obtained.

If the origins of the coordinate axes u, v, s are the same as the origin of the coordinate axes XYZ, the resonant frequency of selective excitation remains the same, and x,
By combining the application of gradient magnetic fields in the y and x directions, an inclined cross section 51 is formed.
can be imaged. Further, an inclined cross section 52 which is a distance d away from the S axis E and parallel to the inclined cross section 51 can be obtained by irradiating the resonant frequency of selective excitation according to the distance d on the slice direction axis S. . At this time, the center of the field of view of the obtained image is on the intersection with the S axis. The amplitude center of the gradient magnetic field is determined by the arrangement of the coils, and is in the X direction.

The point O of the gradient magnetic field in both the Y direction and the X direction cannot be geometrically moved, the origin in the three-dimensional space is fixed, and the center of view in the slice plane is at the intersection of perpendicular lines passing from the origin through the slice plane.

Figure 5 shows an MRI device and an X-ray CT in oblique cross-sectional imaging.
This shows the differences in the imaging methods used by the devices. As already shown in Figure 4, the center of the field of view of the imaging plane in the MRI apparatus is the normal to the imaging plane that passes through the origin, and the dotted line shown in Figure 5(a) passes through the center of the field of view of each imaging plane. . The dotted line shown in Fig. 5(b) also indicates the normal line of the inclined cross-section passing through the origin, but since the X-ray CT apparatus captures images by moving the bed, the center of the field of view of each inclined cross-section is the normal line. The difference is that the point is on the X axis parallel to the direction of the bed shift axis. FIG. 5(a) is a side view of the imaging area during eight multi-slices in cross-sectional imaging of a human head with an oblique. It can be seen that in the third slice, where the parietal side is the first slice, the origin coincides with the center of the visual field, but in the other slices, the center of the visual field is shifted from the X and Y axes. On the other hand, FIG. 5(b) shows the imaging area of the cross-sectional image in the X-ray CT apparatus. In X-ray CT, oblique measurement is performed by tilting the gantry, and multi-slice measurement is performed sequentially by moving the table. Therefore, if the X-axis is the table movement direction, the center of the field of view is always on the X-axis.

Therefore, images obtained with the MR4 device and images obtained with the X-ray CT device have different visual field centers and cannot be directly compared. Therefore, one object of the present invention is to capture an image in which the center of the field of view is aligned with the body axis, as shown in FIG. 5(b), in an MRI apparatus. FIG. 6 shows the relationship between the imaging field of view and the encoding gradient magnetic field. In the X direction (-
) to (+) by applying an X-direction gradient magnetic field with the following gradient: Measurement is performed centered on the X-Y axis, and an image centered on the intersection of the X-Y axes is obtained. Further, even if the slice positions differ in two directions (perpendicular to the plane of the paper), the slice plane only moves in parallel in the two directions, and the center of the field of view is always on the two axes. Here, consider imaging by moving the center of the field of view by D in the X direction from the intersection of the X-Y axes, as indicated by the field of view 2 surrounded by dotted lines in FIG. In order to make position D the center of the field of view, it is necessary to apply an X-direction gradient magnetic field so that the amplitude strength of the gradient magnetic field becomes 0 at position D, as shown by the dotted line. However.

It is generally difficult to move the amplitude center of a gradient magnetic field, that is, to apply a gradient magnetic field with an offset. Therefore, when applying a gradient magnetic field in the X direction, at position D, if the magnetic field strength at point D in FIG.
: Magnetic rotation ratio Tx: Given by the time of application of the gradient magnetic field in the X direction.

The present invention aims to correct this offset phase rotation amount to O. For phase correction, complex number data is
Letting the real part be α and the imaginary part β, then 2=α+iβ...(13) For the complex number data, the complex number data Z' after phase correction rotated by the phase angle θ is z' = If α'+iβ' .multidot.(14), then the calculation given by can be performed.

Now, as mentioned above, encoding of a two-dimensional slice plane is performed by applying an encoding gradient magnetic field of frequency in the X direction and phase in the Y direction, for example. When trying to move the visual field center by dX in the frequency encoding direction (X direction), the amount of phase rotation θ is calculated from equation (15) as follows: θ = γGxdxTsGx2 (same frequency encoding direction (X direction)) Gradient magnetic field strength Tx = frequency It is given by the gradient magnetic field application time in the encoding direction (X direction). Similarly, when trying to shift the visual field center by dy in the phase encoding direction (Y direction), the amount of phase rotation θ is 0 = γGydyTy (16) from equation (11), and the phase is shifted every time in M encodings. The amount of rotation is different.

Therefore, it is necessary to perform phase correction for each encode.

Now, regarding phase correction, it is sufficient to restore the phase rotation so that the phase rotation at the center of the field of view is O in both the X and Y directions, so the phase correction angle is the value obtained by adding a (-) to the amount of phase rotation. Become. However, in the spin/echo sequence, as shown in Figure 2, in the phase encoding direction, the phase rotation due to the encoding gradient magnetic field in section 2 is reversed by the 480° RF pulse in section 4 when reading the signal in section 6. ing. Therefore, in the spin echo sequence, if the phase correction angle in the X direction is θ and the phase correction angle in the Y direction is θ, then the following equation is obtained (17), and it is sufficient to add phase rotation by this amount. FIG. 1 shows the reconstruction process according to the present invention of signal data measured by a two-dimensional Fourier transform method using several frequency encodes and M phase encodes. FIG. 1 shows the reconstruction process according to the present invention, but in the frequency encoding direction.

Fast Fourier transform (F F T
), phase correction is performed before processing. First, phase addition 31 is performed in the frequency encoding direction. At this time, it is sufficient to add the phase by θX to all measurement data. Thereafter, frequency encoding direction FET processing 32 is performed the same number of times as phase encoding. continue.

Performs phase addition in the phase encoding direction. At this time, since the amount of phase correction is different for each encode in ~1 phase encode, the phase is added to the measurement data collected at that time for each encode according to the gradient magnetic field strength at that time. After that, FFT processing in one phase encoding direction is performed M times. In this way, a two-dimensional slice image with IXM matrices is obtained. Since the phase is corrected so that the phase rotation becomes 0 at dx and dy, the center of the encoding gradient magnetic field is at dx and dy. Therefore, an image centered on dx and dy can be obtained. dx and dy can be taken at arbitrary positions on the X-axis and Y-axis, respectively, and by adding the phase correction given by equation (17), an image with an arbitrary center of the field of view can be obtained.

Next, the imaging of an image in which the center of the field of view is always on the X-axis as shown in FIG. 5(b) will be specifically explained using the imaging of a transformer image. FIG. 7 shows the flow of multi-slice image measurement. As shown in FIG. 7, first, a positioning image capturing process 41 is performed. In an X-ray CT device, this is the imaging of a scanogram image, and in an MRi device, this is imaging in a sagittal plane or a coronal plane orthogonal to the target transformer plane. Since it is only necessary to know the positional relationship of the ML weave at this time, the measurement is usually performed in a short measurement time. Further, only one image is required for measurement, and then first positioning processing is performed on the measured image. As positioning parameters, the oblique angle from the slice position to the axis is determined based on the number of multi-slices, slice thickness, and slice interval selected according to the imaging conditions. 6 Figure 8 shows the positioned state. . The center of each slice is at the center of the slice thickness, and if the parietal side is the first slice, then in the first slice, the point indicated by the dashed line is the center line of the slice, and the perpendicular line including the symbol drawn from this point to the origin is the center line of the slice. The length is the slice order [, d. Further, the oblique angle α from the horizontal axis is also determined as shown in FIG.

Figure 9 is a diagram showing only the slice positions in Figure 8.
sl to 85 indicate the slice positions from the first slice to the fifth slice, and ul to u6 indicate the visual field movement distance from the first slice to the fifth slice. Here, if the slice position in the i-slice is Sj and the visual field center position is Ll+, then u+=stTanα −(1
8) α niobium leak angle.

Next, the transformer image is not measured at the located slice position and oblique angle. At this time, measurements are taken in the a-a' force direction frequency encoding direction in FIG. When measuring, there is no need to be aware of the center of the visual field. The measurement data thus obtained is reconstructed according to the reconstruction flow shown in FIG. Here, since the visual field center was moved in the frequency encoding direction, dx in equation (17) was changed to ul in equation (18).
is substituted and phase addition is performed at each slice position to perform F, F, and T processing in the frequency encoding direction. Since the visual field center is not moved in the phase encoding direction, the amount of rotation in the phase encoding direction is 0 degrees. After that, FFT processing in the phase encoding direction is performed to obtain an image whose field of view is centered on the Y axis. Here, the direction shown in Fig. 8 is taken as the frequency encoding direction, but what can be done by switching the frequency encoding direction and the phase encoding direction? 1I11 and the amount of phase rotation in the 8-frequency encoding direction is set to 0 degrees, and the amount of rotation in the phase encoding direction and dy in equation (17) are replaced by u in equation (18).
A similar image can be obtained by substituting t to obtain the amount of phase rotation, performing phase addition, and performing reconstruction.

The image obtained in this way always has the center of view on the Y axis,
There is no deviation between the image obtained by the X-ray CT device and the field of view. Therefore, it can be easily compared with an X-ray CT image, which has the effect of increasing diagnostic efficiency. Furthermore, in the present invention, since the field of view can be moved in both the frequency encoding direction and the phase encoding direction, the center of the field of view can be specified in both directions during positioning. FIG. 10(a) shows positioning of the trans image from the coronal image. As shown in FIG. 10, the image is closer to the measurement because it is set off from the center of the subject. Therefore, the transformer image attempts to shift the center of the field of view to the left and bring it to the center of the image.
Perform positioning by shifting d to the left of the center. In this coronal image, the transformer image is measured with the a-a′ force direction (left and right direction of the human head) as the frequency encoding direction, and by adding a phase in the frequency encoding direction during reconstruction, the transformer image is created in the center of the image. can be obtained.

Furthermore, a similar image can be obtained by performing measurement by taking a-a15 in the phase encoding direction and performing phase addition in the phase encoding direction.

Further, if the subject is extremely shifted from the imaging field of view and is removed from the imaging field of view, a curvature will occur on the reconstructed image as shown in FIG. 10(b). This occurs because the fast Fourier transform stabilizes the periodic function. In this case as well, by adding phase rotation and shifting the center of the field of view by d, an image without aliasing can be obtained. In addition, since this processing is performed during the reconstruction process, if raw data exists for the already reconstructed image, the field of view movement distance is determined from the reconstructed image, the corresponding phase rotation is added, and the reconstruction is performed again. This makes it possible to obtain an image without aliasing.

In this way, the center of the visual field can be set freely.

Even if the subject is placed off the center of the imaging space, there is an effect that an image centered on the subject can always be obtained.

FIG. 11 shows the positioning for cross-sectional imaging at the knee. When a cross-sectional image is taken of a region including bending joints such as the anus and knees, the center position of the subject on the image differs for each slice image depending on the slice position in multi-slice imaging.

Therefore, consider imaging in which the center position of the subject is always at the center of the image. In FIG. 11, horizontal bars 61 to 65
indicates the positioning of the slice position of the cross-sectional image to be captured. The center of the bar indicates the center of the field of view to be imaged. The dotted line in FIG. 11 connects the visual field centers of each slice.

After subtraction, the center of the subject can always be aligned with the center of the reconstructed image by performing phase addition according to the deviation amounts u1 to u5 from the imaging center determined from the gradient magnetic field during reconstruction.

In addition, as shown in Figure 11, by positioning and capturing images of areas including bending joints such as elbows and knees, the subject is always aligned to the center of the image. be able to.

〔Effect of the invention〕

According to the present invention, since the center of the field of view of a slice image can be moved to an arbitrary position, imaging can be performed so that the subject is located at the center of the image even if the subject is shifted from the center of the imaging space. Furthermore, if the subject is far off the center of the imaging space compared to the imaging field of view, the subject will be separated vertically or horizontally. imaging can be performed.

Also, in oblique images, X! Similar to 1ACT images, it is also possible to perform imaging by aligning the center of the field of view with the horizontal axis, and there is no shift in the center of the field of view between MRiii images and X-ray CT images, and they can be easily compared with X-ray CT images, improving diagnostic efficiency. It has the effect of increasing

[Brief explanation of drawings]

FIG. 1 is a diagram showing a flow of reconstruction processing according to an embodiment of the present invention, FIG. 2 is a diagram showing an overall configuration diagram of an embodiment of the present invention, and FIG. 3 is a diagram showing a pulse to be measured. FIG. 3 is a diagram showing an example of a sequence. FIG. 4 is a diagram showing the imaging field of view of an oblique image,
Fig. 5 is a side view of the imaging field of view in 1 to 1-lance image imaging of MR1 images and X-ray CT images, and Fig. 6 is a diagram showing the relationship between the imaging field of view and the gradient magnetic field. Figure 7 is a diagram showing the imaging flow in measurement, Figure 8 is a diagram showing the positioning screen when trans-image positioning, and Figure 9 is a diagram showing the positioning parameters of Figure 8. FIG. 10 shows a coronal image, and FIG. 11 shows the positioning of the bent part. DESCRIPTION OF SYMBOLS 1... Test object, 10... Static magnetic field generating magnet, 11.
...Central processing unit, 12...Sequencer, 13...Transmission system, 14...Magnetic field gradient generation system, 15...Reception system,
16...Signal processing system, 17...High frequency oscillator, 18...
・Modulator. 19... High frequency amplifier, 20a... Transmitting side high frequency coil, 20b... Receiving side high frequency coil, 21... Gradient magnetic field coil, 22... Gradient magnetic field power supply, 23... Amplifier. 24... Quadrature phase detector, 25... A/D converter,
26...Magnetic disk, 27...Magnetic tape, 28 Display 31-34.41-43--Processing, 51.5
2...Oblique cross section, 61-65...Horizontal bar Fig. 3 Fig. 5 (and 2.N Haku Ri picture UP) 4 Yen 2 θ゛ et al. (OL) Origiriku) Yoto-5! PA I3 and <b> Fig. 8 Fig. 9 Fig. Bent f- sound Y E no I device

Claims (1)

[Claims] 1. A means for applying a static magnetic field and a gradient magnetic field to an object to be inspected, a means for applying a high frequency pulse to cause nuclear magnetic resonance in the atomic nuclei constituting the tissue of the object to be inspected, and a means for applying a signal due to the nuclear magnetic resonance. In a nuclear magnetic resonance imaging apparatus comprising a nuclear magnetic resonance detection means for detection and a means for Fourier transforming the nuclear magnetic resonance signal detected by the detection means to reconstruct an image, imaging is performed prior to signal measurement. A magnetic resonance imaging apparatus comprising processing means for positioning the center of the field of view at a desired position.