JP2921078B2 - MRI equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MRI apparatus for obtaining an image using nuclear magnetic resonance (NMR).

[Prior art]

2. Description of the Related Art Conventionally, a technique called an arbitrary matrix (rectangular visual field) has been used in an MRI apparatus. This is usually
The matrix of the image is square and has the same number of vertical and horizontal matrices.The number of phase encodes must be the same as the number of vertical or horizontal matrices. Data collection is performed with the data reduced. This eliminates the waste of collecting data in an area where no human body exists, and reduces the number of phase encodings, thereby shortening the imaging time. Conventionally, when the user uses an arbitrary matrix, conventionally, the user determines the shape of the imaging target, and obtains the vertical / horizontal ratio of the rectangular visual field based on his or her experience.

[Problems to be solved by the invention]

However, if an arbitrary matrix is set based on the user's experience or the like as in the related art, imaging is performed without appropriate settings, and as a result, failure often occurs. In other words, if the setting of the arbitrary matrix is incorrect, a failure occurs such that an aliasing phenomenon occurs in an image or an image of a part to be diagnosed is cut off. In view of the above, it is an object of the present invention to provide an MRI apparatus improved so that an optimal arbitrary matrix ratio can be automatically set from a positioning image.

[Means for Solving the Problems]

In order to achieve the above object, in the MRI apparatus according to the present invention, a static magnetic field generating means, a means for generating a gradient magnetic field having a predetermined waveform, a means for exciting a subject with an RF signal having a predetermined waveform, and Means for receiving an NMR signal, means for forming an image by processing data obtained from the received NMR signal, and image display means for displaying an image,
Position input means for determining the position of the cursor on the screen of the image display means, means for obtaining the body surface position by extracting the contour of the positioning image, and means for automatically setting an arbitrary matrix from the position; Determine the number of phase encoding according to an arbitrary matrix, the above gradient magnetic field waveform and
Control means for controlling the RF signal waveform.

[Action]

By extracting the contour from the positioning image, the position of the body surface is obtained. If an arbitrary matrix is automatically set based on the position of the body surface, it is possible to avoid collecting data in a region outside the body surface where no human body exists. This prevents unnecessary data collection from occurring,
The imaging time can be reduced. In addition, since the arbitrary matrix is set based on the body surface position, the matrix size is too small and data collection inside the body surface will not be performed, and images will be missing or aliasing will occur. Is also gone.

【Example】

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an MRI apparatus according to an embodiment of the present invention, in which a subject 1 is placed in a static magnetic field space created by a static magnetic field generating magnet 21. In this space, a gradient magnetic field generating coil 22 and a transmitting / receiving coil 23 are arranged. A current is supplied from the gradient magnetic field power supply 32 to the gradient magnetic field generating coil 22, and a slice selection gradient magnetic field, a readout (frequency encoding) gradient magnetic field, and a phase encoding gradient magnetic field are generated. The waveform generating circuit 31 determines the waveform of these gradient magnetic fields, and sends a signal representing the waveform to the gradient magnetic field power supply 32. On the other hand, an RF signal having an envelope corresponding to the waveform sent from the waveform generating circuit 33 is sent from the RF transmitting circuit 34 to the RF transmitting / receiving coil 23, and the subject 1 is irradiated with the RF signal. The NMR signal generated in the subject 1
After being received at 3 and detected by the reception / detection circuit 35, it is sampled by the A / D converter 36, converted into a digital signal, and taken into the computer 41. The computer 41 controls the gradient magnetic field waveform and the RF signal waveform, controls the gradient magnetic field and the RF signal generation timing, and controls the data sampling timing, and also processes the captured data to form an image. A CRT display device 42, a keyboard device 43, and a mouse 44 (or another position input device such as a trackball) are connected to the computer 41. The obtained image is displayed by the CRT display device 42. In this MRI apparatus, before performing the actual imaging, first, an imaging for positioning for determining a position of a slice of the actual imaging is performed. Here, four transverse images 51 of the body part of the subject 1 as shown in FIG. 2 are obtained as positioning images at four positions in the body axis direction. As the imaging sequence at this time,
A sequence that emphasizes fat near the body surface as much as possible is desirable. In addition, for a portion where the shape of the body surface changes drastically, imaging is performed not only at four locations but also as many slices as possible. After displaying the obtained transverse image 51 on the CRT display device 42 and activating the slice setting program in the computer 41, a planning cursor 52 as shown in FIG. 3 appears on the screen. Since the position indicated by the planning cursor 52 is the position of the imaging slice, the cursor 52 is moved using the keyboard device 43 or the mouse 44 to determine the position and direction of the imaging slice. Next, an arbitrary matrix automatic setting program is started in the computer 41, and contour extraction processing is first performed on the transverse image 51 for positioning. in this case,
In general, since fat near the body surface generates a high signal, an advanced contour extraction processing algorithm is not required, and a simple threshold processing for determining whether or not the MR value exceeds a threshold level as shown in FIG. Is enough. Then, it is not necessary to extract the contour over the entire body surface, and it is sufficient to extract the contour only at the intersection between the positioning image and the target slice. That is, when the image data of the portion of the planning cursor 52 of the transverse image 51 in FIG. 3 is taken out and arranged in the length direction of the cursor 52, the result becomes as shown in FIG. The end position exceeding a threshold level (for example, 1/2 of the maximum MR value) is detected in both end directions, and that position is determined as the position of the body surface. This is performed for the four transverse images 51, and the fifth
The distribution of the body surface position in the body axis direction as shown in # 1 to # 4 in the figure is obtained. The maximum length L can be obtained by selecting the most distant from the center of the image from the body surface position data for each of the slices # 1 to # 4. An arbitrary margin is added to the maximum length L to obtain L '. As shown in FIG. 6, what percentage of an arbitrary matrix is to be used is determined from the ratio between L 'and the field size l. The visual field size l indicates the same number of vertical and horizontal matrices in the square visual field and is specified in advance by the user using the keyboard device 43 or the like, and is set in accordance with the target slice corresponding to the planning cursor 52. When the setting of the arbitrary matrix for the target slice is completed in this way, the computer 41 obtains a gradient magnetic field waveform and an RF signal waveform corresponding to the set slice and the arbitrary matrix, and sets them in the waveform generating circuits 31 and 33. Thereafter, an imaging sequence is executed, data is collected for the target slice, and a sagittal image 61 as shown in FIG. 6 is obtained. At this time, the number of phase encodes corresponds to an arbitrary matrix,
It is possible to prevent data from being collected in a region where no human body exists at both ends (shaded portions) outside L '.

According to the MRI apparatus of the present invention, an optimal arbitrary matrix can be automatically set, unnecessary data is not collected, and imaging is performed by reducing the number of phase encodes. The time can be reduced and the burden on the patient can be reduced. In addition, since it is possible to prevent the setting of an arbitrary matrix from incorrectly reducing the matrix size, it is possible to prevent the image from being missing or the image from being folded back.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG.
FIG. 3 is a diagram showing a screen of a CRT display device at the time of planning,
FIG. 4 is a graph showing a signal distribution, FIG. 5 is a diagram showing a distribution of a body surface position, and FIG. 6 is a diagram showing a CRT display screen in which an image at a target slice appears. 1 ... subject, 21 ... magnet for generating static magnetic field, 22 ...
Gradient magnetic field generating coil, 23… Transceiver coil, 31… Gradient magnetic field waveform generating circuit, 32… Gradient magnetic field power supply, 33… RF
Signal waveform generation circuit, 34 RF transmission circuit, 35 reception
Detection circuit, 36 A / D converter, 41 Computer, 42 CRT display device, 43 Keyboard device, 44
... Mouse, 51 ... Transverse image, 52 ... Planning cursor, 61 ... Sagittal image.

Claims (1)

(57) [Claims] A means for generating a static magnetic field; a means for generating a gradient magnetic field having a predetermined waveform; a means for exciting a subject with an RF signal having a predetermined waveform; a means for receiving an NMR signal from the subject; Means for composing an image by processing data obtained from the NMR signal, and image display means for displaying the image,
Position input means for determining the position of the cursor on the screen of the image display means, means for obtaining the body surface position by extracting the contour of the positioning image, and means for automatically setting an arbitrary matrix from the position; Determine the number of phase encoding according to an arbitrary matrix, the above gradient magnetic field waveform and
An MRI apparatus comprising: control means for controlling an RF signal waveform.