JP2961373B2 - Nuclear magnetic resonance imaging system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a nuclear magnetic resonance imaging apparatus for obtaining a tomographic image of a specific part of a subject tilted during a multi-slice scan, and more particularly, to an FOV region. Pre-saturation pulse (PRESATURATION PULSE, hereafter referred to as SAT) applied outside to obtain a tomographic image of a specific part of the subject without causing any loss in the reconstructed image. Related to the device.

(Prior Art) A nuclear magnetic resonance imaging diagnostic apparatus includes a magnet unit including a static magnetic field coil that generates a uniform static magnetic field and a gradient magnetic field coil that generates a magnetic field having each linear gradient in each of x, y, and z directions. Applying an RF pulse to the subject installed in the magnetic field formed by the magnet unit, a sending / receiving unit for detecting an NMR signal from the subject, or controlling the operation of the sending / receiving unit and the magnet unit, It has a control image processing unit centered on a computer that processes detected data and displays an image.

In the above configuration, the subject is placed, and a static magnetic field having a predetermined strength is formed in a predetermined space by the static magnetic field coil. On the other hand, under the control of the control image processing unit, the transmitting / receiving unit
Selective excitation pulse sequence that generates 90 ° pulse and 180 ° pulse at predetermined timing as shown in Fig. (A) (STA applies 90 ° pulse to pre-saturate blood and the like entering the image plane) To remove the influence from outside the plane.), And FIG. 4 (b)
(C) A gradient magnetic field Gx, Gy, Gz as shown in (d) is generated at a predetermined timing, and an NMR signal at that time (see FIG. 4 (e)) is detected.

Conventionally, when obtaining a large number of tomographic images (multi-slice scan) in which the angle θ is tilted with respect to a plane perpendicular to a coordinate axis (body axis direction) determined by hardware such as a magnet in accordance with the above sequence (multi-slice scan), a period 0, a period 0 in FIG. And, as shown in 1, since the slice gradient is distributed in the Gx direction according to the tilt angle θ of the plane to be sliced and the Gz direction, and the SAT position outside the FOV region is set for each moving plane in the body axis direction,
The STA area overlaps the moving planes a, b, and c, causing image loss. (See FIG. 5) (Problems to be Solved by the Invention) The present invention has been made in view of the above circumstances, and has as its object to provide a nuclear magnetic resonance image that does not cause image loss due to STA. It is to provide a diagnostic device.

(Means for Solving the Problems) A nuclear magnetic resonance imaging diagnostic apparatus of the present invention that achieves the above object is a nuclear magnetic resonance imaging diagnostic apparatus that obtains a tomographic image of a subject placed in a static magnetic field. First excitation means is a region extending in a direction parallel to the body axis direction of the specimen and adjacent to a plurality of slice planes arranged along the body axis direction of the subject. And a plurality of slice planes are excited by the second excitation means, and a nuclear magnetic resonance image is formed by the image construction means on the slice plane based on the NMR signal obtained by the excitation of the second excitation means. It is an image diagnostic apparatus.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram of a nuclear magnetic resonance imaging diagnostic apparatus embodying the present invention. In the figure, reference numeral 1 denotes a space having a space for inserting a subject therein, and a static magnetic field coil for applying a constant static magnetic field to the subject and a gradient magnetic field for generating a gradient magnetic field surrounding the space. The magnet assembly includes a coil, an RF transmission coil for applying an RF pulse for exciting nuclear spins in the subject, a receiving coil for detecting an NMR signal from the subject, and the like. The static magnetic field coil, the gradient magnetic field coil, the RF transmitting coil, and the receiving coil are connected to a static magnetic field power supply 2, a gradient magnetic field driving circuit 3, an RF power amplifier 4, and a preamplifier 5, respectively. The sequence storage circuit 6 operates the gate modulation circuit 8 (modulates the RF output signal of the RF oscillation circuit 9 at a predetermined timing) in accordance with a command from the computer 7, and converts the RF pulse signal from the RF power amplifier 4
Apply to RF transmit coil. In addition, the sequence storage circuit 6 also operates the gradient magnetic field drive circuit 3 and the AD converter 11 in response to a command from the computer 7 by a sequence signal based on FIG. That is, the sequence storage circuit 6 extends in a direction parallel to the body axis direction and excites a region adjacent to the slice plane.
Selective excitation signal, and has a predetermined thickness in a direction parallel to the slice plane direction, and the area adjacent to the slice plane SA
A second selective excitation signal applied with a T pulse, a 90 ° pulse, and 18 pulses after the first and second selective excitation signals are generated.
A means for generating a 0 ° pulse at a predetermined timing to selectively excite a tilted slice plane and generating a signal for collecting an NMR signal from the slice plane is provided. 10 is RF
This is a phase detector that performs phase detection on the output of the received signal of the preamplifier 5 using the output of the oscillation circuit 9 as a reference signal. This power signal is converted into a digital signal by the AD converter 11 and input to the computer 7. Reference numeral 12 denotes an operation console for inputting instructions for realizing various pulse sequences and various setting values to the computer 7, and 13 denotes a display device for displaying an image reconstructed by the computer 7.

Next, the operation of this embodiment will be described with reference to FIG. 2 and FIG. Here, as shown in FIG. 3, the angle θ with respect to the X axis
It is assumed that three slice planes a, b, and c are imaged, and an imaging method of the slice plane a will be described first. FIG. 2 is a diagram showing a pulse sequence in the sequence storage circuit 6. In FIG. 2, Gy is a gradient magnetic field for applying a magnetic field to the Y axis. The warp gradient applied to the Y axis is for applying phase information in the Y axis direction by applying a magnetic field having a different phase each time in the Y axis direction. Gx is a gradient magnetic field applied to the X axis, and Gz is a gradient magnetic field applied to the Z axis. The slice gradient applied to the X axis and the Z axis is for exciting only spins in a specific plane, and the read gradient is for observing a spin echo signal. The gradient magnetic field applied to the X-axis and the Y-axis during the period 5 is for removing a phase difference generated at the time of slicing in each direction and for giving phase information in each direction. Is applied. RF is a high-frequency rotating magnetic field applied in a direction perpendicular to the static magnetic field, and applies a 90 ° pulse and a 180 ° pulse to selectively excite a desired slice plane. TR is the pulse repetition cycle, and a 90 ° pulse is applied again after TR,
Start the next view (VIEW). FIG. 3 is a diagram for explaining an imaging method according to the present invention. First,
In the periods 0 and 1, the region extending in the direction parallel to the body axis direction and adjacent to the slice plane is excited.
An SAT pulse and a slice gradient magnetic field in the Gx direction are applied. In periods 2 and 3, the SAT pulse and Gx have a predetermined thickness in a direction parallel to the slice plane direction and are selectively excited in regions adjacent to slice planes a and c. , And a slice gradient is applied in the Gz direction.
The distribution ratios of the gradients in the Gx and Gz directions for slicing when the SAT pulse is applied in the periods 2 and 3 are changed according to the tilt angle θ of the plane to be sliced. Similarly, the gradient in each direction during the period described below is also distributed according to the tilt angle θ. In period 4, a 90 ° pulse and a slice gradient are applied, and spins on slice plane a are selectively excited. In period 5, the spin phase disturbed by the slice gradient due to the rephase gradient is restored, while the dephase gradient and
A phase difference corresponding to the coordinates is given to the spin in order to observe the NMR signal later by the warp gradient. 180 ° in period 6
The pulse and the slice gradient are applied, and the spin on the slice plane a is selectively excited. In the period 7, a read gradient is applied to the slice plane a defined by the slice gradients in the period 4 and the period 6, and a large number of spin and echo signals are collected.
Data from the entire slice plane a is obtained.

Similarly, after the TR, a 90 ° pulse is applied to start imaging of the next slice plane b, and thereafter, the slice plane c is isoseated.

As described above, in the nuclear magnetic resonance imaging diagnostic apparatus according to the present embodiment, an image without missing images can be obtained.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the claims. For example, SA
The T region may be selected in any order, and can be applied to a case where the angle θ is tilted with respect to the Y direction. Further, in the above description, the spin and echo method is used, but the present invention can be applied to other Fourier methods such as a field echo (FIELD ECHO) method.

(Effects of the Invention) As described above, according to the nuclear magnetic resonance imaging diagnostic apparatus of the present invention, in the multi-scan when the tilted surface moves in the body axis direction, the SAT region is not perpendicular to the slice surface but is not perpendicular to the slice surface. Since the setting is made parallel to the axial direction, it is possible to obtain a tomographic image of a specific part of the subject without causing image loss due to the SAT. Further, according to the present invention, the present invention can also be applied when performing a zoom scan (ZOOM SCAN).

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a pulse sequence of an embodiment of the present invention, and FIG.
FIG. 4 is a diagram for explaining an imaging method according to the present invention, FIG. 4 is a diagram showing a pulse sequence in which an image is lost due to an STA pulse, and FIG. 5 is a diagram for explaining a SAT region. DESCRIPTION OF SYMBOLS 1 ... Magnet assembly, 2 ... Static magnetic field power supply, 3 ... Gradient magnetic field drive circuit, 4 ... RF power amplifier, 5 ... Preamplifier, 6
... Sequence storage circuit, 7 ... Calculator, 8 ... Gate modulation circuit, 9 ... RF oscillation circuit, 10 ... Phase detector, 11 ... AD converter, 12 ... Operation console, 13 ... Display device,

Continuation of the front page (56) References JP-A-62-197048 (JP, A) JP-A-60-152942 (JP, A) JP-A-63-122439 (JP, A) JP-A-63-206231 (JP) , A)

Claims (1)

(57) [Claims] 1. A tomographic image of a specific portion of a subject placed in a static magnetic field by setting a plurality of slice planes parallel to each other in a specific portion of the subject along a body axis direction of the subject. A nuclear magnetic resonance imaging diagnostic apparatus for obtaining a first excitation means for exciting an area that extends in a direction parallel to a body axis direction of the subject and that is in the vicinity of the specific site A second excitation unit that tilts the plurality of slice planes to excite nuclear spins of the slice plane; and constructs a tomographic image of the slice plane based on the NMR signal obtained by the second excitation unit. A nuclear magnetic resonance imaging diagnostic apparatus comprising: