JPS62231641A - Imaging surface variable type mri apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a variable image plane MHI device.

<Prior Art> An NMR signal excitation operation by an MHI device is performed based on, for example, a sequence as shown in the time chart of FIG. According to such a sequence, the magnetic field gradient (Gz) in two directions is 3.4 with the direction of the main static magnetic field for NMR as the two axes.
An imaging section in the subject perpendicular to the two axes is selected by , and the y-axis magnetic field gradient (Gy) 5 and the
By adding X) 6°7, the spin echo signal 8 is made to include two-dimensional information related to the above-mentioned cross-sectional layer.

By the way, the direction of the main static magnetic field for NMR, which is the z-axis direction, is
Due to the structure of the magnetic field generating coil, it is usually selected in the longitudinal direction of the subject (in the case of a human body, the height direction). In addition, the coils for generating magnetic field gradients have their coil axes aligned in the Z-axis direction and y-axis direction, respectively.
It is composed of three sets of coils oriented in the axial direction and the X-axis direction.

<Problems to be Solved by the Invention> Therefore, in the MRI apparatus according to the prior art, no matter how the combination of the directions of the three magnetic field gradients (Gz, Gy, Gx) is changed, the imaging cross section is x- It is limited to either the y plane+Y-2 plane or the z-x plane.

The present invention provides a solution to the above-mentioned drawbacks related to the selection of imaging sections in the prior art.

<Means for solving the problem> In order to solve the problem, the MRT device according to the present invention generates three sets of magnetic field gradients in which the coil axes are oriented in the z-axis direction, the y-axis direction, and the x-axis direction, respectively. By changing the combination of the magnitudes of the currents (pulse currents) to be supplied to the magnetic field coils, the direction of the principal axis of the magnetic field gradient tensor can be changed arbitrarily.

<Effect> Since the principal axis direction of the magnetic field gradient tensor can be changed arbitrarily,
By making the principal axis direction orthogonal to the cross-sectional layer in the object to be imaged, it becomes possible to image the cross-sectional layer in any direction.

<Example> Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a diagram showing a cross-sectional layer 13 to be imaged in a subject 11 and the direction of an axis ξ perpendicular to the cross-sectional layer 13.

If you want to image such a cross-sectional layer 13, first
The cross-sectional layer 12 perpendicular to the z-axis is imaged by the normal NMR signal excitation/detection sequence shown in the figure.
) A plurality of cross-sectional images as shown in (B), (C), and (D) are obtained. From these cross-sectional images, select two points where the axis ξ penetrates the cross-sectional layer 12 (for example, point P in FIG. 2(A) and point D in the same figure).
＞ Q point), from this we find the equation or direction cosine of the axis ξ and create a coordinate transformation matrix consisting of this value.
Combinations of current values to be passed through the three sets of coils for generating magnetic field gradients are obtained.

By the way, FIG. 4 is a block diagram showing the configuration of the above embodiment, but the device portion for applying a static magnetic field and the device portion related to image display are omitted. The configuration is similar to a normal NMR imaging apparatus, in which NMR excitation signals and detection signals are exchanged between an NMR signal excitation/detection antenna 21 and a signal transmission/reception section 22, while a magnetic field gradient generation coil group 23 is supplied with current by a current power source 24 for magnetic field gradient.

Both the signal transmitting/receiving section 22 and the current power source 24 are controlled by a computer 25. RO of computer 25
M contains a program for NMR signal excitation/detection operation according to the normal NMR signal excitation/detection sequence shown in Fig. 3;
Further, programs related to the calculation of the phase offset value described above and calculations related to normal NMR imaging are stored. Also, the RAM is NM shown in Figure 1.
The spins obtained by the R signal excitation/detection sequence
The echo signal 8 and the spin echo signal 8a obtained by the NMR signal excitation/detection sequence of FIG. 2 are stored.

<Effects of the Invention> As is clear from the above description, according to the present invention, in addition to the coordinate axes based on the external shape of the subject, the imaging cross section is You can choose the layer.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a tomographic plane in a subject that can be imaged according to an embodiment of the present invention. FIG. 2 shows a cross-sectional layer image perpendicular to the z-axis in FIG. 1. FIG. 3 shows an NMR signal excitation/detection sequence when imaging the cross-sectional layer shown in FIG. 2 in the embodiment of the present invention. FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention. 1.2-・Faith using spin echo method! Excitation pulse 3.4.5, 6.7-・Magnetic field gradient 8-Echo signal

Claims (1)

[Claims] The spin echo method is used to excite and detect NMR signals using a main static magnetic field for NMR on the specimen, and a magnetic field gradient as a tensor quantity is added to this main static magnetic field in a predetermined sequence. - In an apparatus that converts an echo signal into an image signal through two-dimensional Fourier transformation processing and displays an image of a predetermined cross-sectional layer in the subject on a CRT based on this image signal, the apparatus that generates the magnetic field gradient comprises three It consists of a set of coils and a power source that supplies pulsed currents to these three sets of coils, and by changing the combination of the values of the pulsed currents supplied from this power supply to the three sets of coils, the magnetic field as the tensor quantity can be adjusted. A variable imaging surface type MR device, characterized in that it is configured to arbitrarily change the principal axis direction of the gradient.