JPH02295546A - Nuclear magnetic resonance image diagnosing device - Google Patents

Abstract

PURPOSE:To prevent the missing of the image occurring in SAT by adopting the constitution consisting in generating a 90 deg. pulse and 180 deg. pulse at prescribed timing to selectively excite a tilted slice surface after the generation of 1st and 2nd selective excitation signals. CONSTITUTION:A sequence memory circuit 6 generates the 1st selective excitation signal to impress the SAT pulse in the region having a prescribed thickness in the direction parallel with the body axis direction and adjacent to the slice surface at the time of obtaining the tomographic image of the specific section of the tilted object to be inspected in care of a multislice scanning by impressing the RF pulse and gradient magnetic field to the object to be inspected according to predetermined sequence. The above-mentioned circuit generates the 2nd selective excitation signal to impress the SAP pulse to the region having the prescribed thickness in the direction parallel with the slice direction and adjacent to the above-mentioned slice surface. The slice surface excited by generating the 90 deg. pulse and 180 deg. pulse at the prescribed timing after the generation of the 1st and 2nd selective excitation signals is selectively excited to generate the signal for collection of NMR signals.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a nuclear magnetic resonance imaging apparatus that obtains a tomographic image of a specific part of a tilted subject during multi-slice scanning. PRESATURATION PU outside
The present invention relates to a nuclear magnetic resonance imaging diagnostic apparatus that uses LSB (hereinafter referred to as SAT) to obtain a tomographic image of a specific part of a subject without causing any defects in the reconstructed image. (Prior Art) A nuclear magnetic resonance imaging diagnostic apparatus includes a magnet section that includes a static magnetic field coil that creates a uniform static magnetic field and a gradient magnetic field coil that creates a magnetic field that has linear gradients in each of the x, y, and z directions. A transmitting/receiving unit that applies an RF pulse to a subject placed within a magnetic field formed by the subject, detecting an NMR signal from the subject, and controlling the operation of the transmitting/receiving unit and the magnet unit; It has a control image processing unit centered on a computer that processes detected data and displays images. In the above configuration, a subject is placed, and a static magnetic field coil forms a quiet magnetic field of a predetermined strength in a predetermined space. On the other hand, under the control of the control image processing section, the transmitting/receiving section generates a selective excitation pulse sequence (SAT is 90 ``This is to remove influences from outside the image plane by applying pulses to saturate the blood entering the image plane in advance.'' and Figure 4 (
(c) Gradient magnetic fields Gx, Gy as shown in (2)
, Gz are generated at a predetermined timing, and the NMR at that time is
The signal (see FIG. 4 (e)) is detected.

Conventionally, when a large number of tomographic images are obtained by tilting the angle θ with respect to a plane perpendicular to the coordinate axis (body axis direction) determined by hardware such as a magnet according to the above sequence (multi-slice scan), the period 0, as well as,
As shown in 1, the slice gradient was distributed in the Gx and Gz directions according to the tilt angle θ of the plane to be sliced, and the SAT position outside the FOV area was set for each plane of movement in the body axis direction. The moving planes a, b, and c overlap, resulting in missing images. (See Figure 5) (Problems to be Solved by the Invention) The present invention has been made in view of the above circumstances, and its purpose is to provide nuclear magnetic resonance images that do not cause image deletions caused by SAT. The purpose is to provide diagnostic equipment. <Means for Solving the Problems> A nuclear magnetic resonance imaging apparatus of the present invention that achieves the above object applies an RF pulse and a gradient magnetic field to a subject according to a predetermined sequence, and performs a multi-slice scan. When obtaining a tomographic image of a specific part of a tilted subject,
The sequence memory circuit SAs a region having a predetermined thickness in a direction parallel to the body glaze direction and adjacent to the slice surface.
A first selective excitation signal applied with a T pulse, and a second selective excitation signal applied with a SAT pulse to a region having a predetermined thickness in a direction parallel to the slice plane and adjacent to the slice plane. After generating the first and second selective excitation signals, a 90' pulse and a 180' pulse are generated at predetermined timings to selectively excite the tilted slice plane, thereby eliminating images caused by SAT. It has a means for generating a signal for collecting an NMR signal from the slice surface without any loss. (Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a configuration diagram of a nuclear magnetic resonance imaging diagnostic apparatus that implements the present invention. In the figure, reference numeral 1 has a space for inserting the subject, a static magnetic field coil that surrounds this space and applies a constant static magnetic field to the subject, and a gradient that generates a gradient magnetic field. This is a magnet assembly that includes a magnetic field coil, an RF transmitting coil that provides RF pulses to excite nuclear spins within the subject, and a receiving coil that detects NMR signals from the subject. The static magnetic field coil, gradient magnetic field coil, RF transmitting coil, and receiving coil are each composed of a static magnetic field power supply 2, a gradient magnetic field drive circuit 3, and an RF
It is connected to a power amplifier 4 and a preamplifier 5. The sequence recording circuit 6 operates the gate modulation circuit 8 according to instructions from the computer 7 (modulates the RF output signal of the RF oscillation circuit 9 at a predetermined timing), and converts the RF pulse signal into an RF signal.
t is applied from the force amplifier 4 to the RF transmitting coil. In addition, the sequence storage circuit 6 stores the gradient magnetic field II according to a sequence signal based on FIG.
The controller #13 and the AD converter 11 are also operated. That is, the sequence storage circuit 6 has a predetermined thickness in a direction parallel to the body axis direction, and a first selective excitation signal that applies a SAT pulse to a region adjacent to the slice plane, and a direction parallel to the slice plane direction. a second selective excitation signal that has a predetermined thickness and applies a SAT pulse to a region adjacent to the slice surface;
After generation of the second selective excitation signal, a 90° pulse and a
A 80" pulse is generated at a predetermined timing to selectively excite the tilted slice surface, and NMR from the slice surface is detected.
It has means for generating signals for collecting signals. 1
0 is a phase detector that detects the phase of the received signal output of the preamplifier 5 using the output of the RF 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. 12 is an operation console for inputting instructions and various setting values for realizing various pulse sequences to the computer 7; 13 is the computer 7;
A display device that displays the reconstructed image! It is. Next, the operation of this embodiment will be explained using FIGS. 2 and 3. Here, as shown in Fig. 3, three slice planes a. Let us assume that images b and C are to be imaged, and first explain the imaging method for slice plane a. FIG. 2 is a diagram showing the pulse sequence in the sequence storage circuit 6. In Figure 2, GV is a gradient magnetic field that applies a magnetic field to the Y axis. The warp gradient applied to the Y-axis is to provide phase information in the Y-axis direction by applying a magnetic field with a different phase each time in the Y-axis direction.Gx is a gradient magnetic field applied to the X-axis,
GZ is a gradient magnetic field applied to the Z axis. X axis and Z
The slice gradient applied to the axis is used to excite only the spins in a specific plane, and the lead gradient is used to observe the Subin echo signal. Also period 5
The gradient magnetic field applied to the X-axis and Y-axis is
A vector sum of a rephase gradient, which is used to remove the phase difference that occurs when slicing in each direction, and a dephase gradient, which is used to provide phase information in each direction, is applied.RF is a static magnetic field. It is a high frequency rotating magnetic field applied in the direction perpendicular to the 90° pulse and 180° pulse.
The desired slice plane is selectively excited by applying 0 pulse. TR is a pulse repetition period, and after TR, a 90° pulse is applied again to start the next view. FIG. 3 is a diagram for explaining the imaging method according to the present invention. First, in periods 0 and 1, a SAT pulse and a slice gradient in the Gx direction are applied so that a region having a predetermined thickness in a direction parallel to the body axis direction and adjacent to the slice plane is selectively excited. is applied. Period 2,
3, the SAT pulse and Gx are applied so that the regions having a predetermined thickness in the direction parallel to the slice plane direction and adjacent to slice plane a and slice plane C are selectively excited.
, and a slice gradient is applied in the Gz direction. The distribution ratio of the gradients in the Gx and Gz directions for slicing during the application of the SAT pulses in periods 2 and 3 is 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;
Spins on slice plane a are selectively excited. In period 5, the rephase gradient restores the spin phase disturbed by the slice gradient, while the defase gradient and
The warp gradient gives the spins a phase difference according to their coordinates in order to later observe the NMR signal. 18 in period 6
A 0° pulse and a slice gradient are applied to selectively excite spins on slice plane a. In period 7, the slice plane a is limited by the slice gradients of periods 4 and 6.
A lead gradient is applied to , a large number of spin echo signals are collected, and data from the entire slice plane a is obtained. Thereafter, in the same manner, after TR, a 90° pulse is applied to start imaging the next slice plane b, and then imaging of the slice plane C is performed. In this manner, the nuclear magnetic resonance imaging apparatus of this embodiment can obtain images without image deletion. Note that the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the claims. For example, S.A.
The selection order of the T area may be arbitrary, and it is also applicable to cases where the T area is tilted at an angle θ with respect to the Y direction. Furthermore, although the above explanation uses the spin echo method, it can also be applied to other Fourier methods such as the field echo (FIELD ECHO) method. <<Effects of the Invention>> As explained above, according to the nuclear magnetic resonance imaging apparatus of the present invention, in multi-scanning when the tilted plane moves in the body axis direction, the SAT region is not perpendicular to the slice plane but is Since it is set parallel to the axial direction, it is possible to obtain a tomographic image of a specific part of the subject without image loss caused by SAT. Furthermore, according to the present invention, it can also be applied when ZOOM SCAN is performed.

[Brief explanation of the drawing]

・Figure 1 is a configuration diagram representing an embodiment of the present invention, Figure 2 is a diagram representing a pulse sequence of an embodiment of the present invention, and Figures 3 are diagrams for explaining the imaging method according to the present invention. , Figure 4 is a diagram showing a pulse sequence that causes image loss due to the SAT pulse, and Figure 5 is a diagram showing the SA pulse sequence.
FIG. 3 is a diagram for explaining a T distribution area. 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... Computer, 8... Gate modulation circuit, 9...
RF oscillation circuit, 10...phase detector, 11...AD
Converter, 12...Operation console, 13...Display device, Yokogawa Medical Systems Co., Ltd.

Claims (1)

[Claims] RF pulses and gradient magnetic fields are applied to a subject placed in a static magnetic field according to a predetermined sequence, and the object is scanned from a tilted slice plane during a multi-slice scan that moves in the body axis direction. a sequence storage circuit for generating a signal for collecting NMR signals;
In a nuclear magnetic resonance imaging diagnostic apparatus that obtains a tomographic image of a subject based on signals, the sequence storage circuit stores an area having a predetermined thickness in a direction parallel to the body axis direction and adjacent to a slice plane in SAT. a first selective excitation signal that is applied as a pulse; a second selective excitation signal that has a predetermined thickness in a direction parallel to the slice plane and that is applied to a region adjacent to the slice plane as a SAT pulse; After generating the first and second selective excitation signals, a 90° pulse and a 180° pulse are generated at predetermined timing to selectively excite the tilted slice plane, and collect NMR signals from the slice plane. A nuclear magnetic resonance imaging diagnostic apparatus, characterized in that it is configured to generate a signal for the purpose of: