JPH0464342A - Mri apparatus - Google Patents

Abstract

PURPOSE:To achieve a shorter photographing time eliminating possible overflow by arranging a maximum value detection means which picks up a plurality of MR data digitized sequentially to determine a maximum value and a normalization means which normalizes a plurality of MR data values to optimize a reproduction processing within a sampling capacity having a processing circuit based on the maximum value information. CONSTITUTION:When a system controller 13 applies an RF pulse to an organism with a transmitting/receiving coil 9, a magnetic resonance phenomenon occurs in the organism to generate an MR signal. The MR signal is converted into a digital MR data M with an A/D converter within a circuit 20 and the MR data M is taken into a conversion processing section 21 and subjected to a Fourier transform in a reading direction R to be transmitted to a detecting section 22. With the detecting section 22, maximum value information and phase correction information of all MR data are determined to be transmitted and stored into a waveform memory 23, an image reconstruction section 24 performs a normalization processing of the MR data based on the maximum value information of the MR data. Then a reconstruction processing by Fourier transform is performed in a phase encode direction E and a display section 25 shows an MR image subjected to the image reconstruction processing. This achieves a shorter photographing time eliminating possible overflow.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Field of Application) The present invention uses magnetic resonance phenomena to perform MR (Magnetic Resonance) of living organisms.
The present invention relates to an MRr apparatus that obtains magnetic resonance tomographic images (hereinafter referred to as "rMR images") by collecting RMR (abbreviation for tic resonance) signals.

(Prior art) An MRI apparatus uses a phase encoding method to obtain MR information from a living body.
This method collects a double signal and obtains a tomographic image based on the MR double signal. That is, a living body is placed in a static magnetic field, and a gradient magnetic field is superimposed on the static magnetic field under a plurality of different phase encode magnetic field conditions, and an RF pulse is transmitted to generate M from the living body.
Receive multiple R times signals. Next, the plurality of MR multiplied signals are converted into digital MR data. The MR data thus converted is subjected to reconstruction processing by two-dimensional Fourier transformation in the readout direction and the phase encoding direction to obtain a tomographic image of the living body.

Furthermore, the calculation methods used in the processing circuits that perform each of the above processes include a floating point calculation method, a fixed point calculation method, or a combination of both, but the fixed point calculation method is generally adopted because it is inexpensive, although there is a risk of overflow. ing.

Therefore, each processing circuit has a predetermined processing capacity, such as 16 bits, and in order to prevent the occurrence of an overflow exceeding this processing capacity, trial shooting (hereinafter referred to as "prescan") was performed, and the data collected by prescan. After finding the maximum value among all MR data, the normalization rate was determined, and the main imaging for image formation (hereinafter referred to as "main scan") was performed, and the MR data collected in this main imaging was obtained first. The MR data is normalized based on the normalization rate so that the predetermined ability of the processing circuit can be fully utilized.

Alternatively, a partial pre-scan was performed without collecting all the MR data in anticipation of some overflow.

(Problems to be Solved by the Invention) However, in order to completely prevent overflow, a pre-scan to collect all MR data must be performed, resulting in wasted imaging time.

Furthermore, in partial pre-scanning, overflow may occur during the main scan, resulting in the need to perform the main scan again, resulting in wasted imaging time.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an MRr device that is free from the risk of overflow and that shortens the imaging time.

[Structure of the Invention (Means for Solving the Problems)] In order to achieve the above object, the present invention digitizes a plurality of MR multiplied signals collected by a phase encoding method, and then performs reconstruction processing by a processing circuit. MRI to obtain tomographic images
In the apparatus, a maximum value detection means for sequentially capturing the plurality of digitized MR data to obtain a maximum value of the MR data, and a sampling capability of the processing circuit based on the maximum value information obtained by the maximum value detection means. and normalizing means for normalizing the plurality of MR data values so that the reconstruction processing can be performed optimally.

(for production) The operation of the device having the above configuration will be explained.

The maximum value detection means sequentially takes in a plurality of MR data and determines the maximum value of the MR data.

The processing circuit has a sampling capability of, for example, 16 bits, and when reconstruction processing is performed based on the values of the MR data normalized by the normalization means, this 16 bit sampling can be performed without overflow. Able to fully demonstrate their abilities.

(Example) Examples of the present invention will be described in detail below.

FIG. 1 shows a block diagram of a device 1 according to an embodiment of the present invention.

This device 1 includes a static magnetic field coil 7 that forms a main magnetic field with a constant strength inside, a gradient magnetic field coil 8 that forms gradient magnetic fields in the X direction, the Y direction, and the Give a high frequency pulse (RF pulse) of
The magnet device 6 includes a transmitting/receiving coil 9 for receiving MR multiplied signals from within the body, a gradient magnetic field control circuit 14 that controls the gradient magnetic field by controlling current to the gradient magnetic field coil 8, and a static magnetic field. A static magnetic field control circuit 15 that controls the static magnetic field by controlling the current supplied to the coil 7, a high frequency oscillator 16 that oscillates a high frequency signal, and a timing signal for collecting the MR multiplied signal, which controls the operation of each part of the device 1. A system controller 13 that performs control, gradient magnetic field, and high-frequency pulse control to execute a predetermined pulse sequence based on a phase encoding method, and a system controller 13 that modulates a high-frequency signal oscillated from a high-frequency oscillator 16 using a timing signal from the system controller 13 to generate high-frequency pulses. a power amplifier 18 that amplifies the power of the high-frequency pulse outputted from the gate circuit 17 and supplies it to the transmitting/receiving coil 9 via the duplexer circuit 5; A preamplifier 19 that amplifies the captured MR multiplied signal, a phase detection circuit 20 equipped with an AD converter (not shown) that detects the phase of the amplified MR multiplied signal and converts it into a digital signal, and the MR data output from this circuit 20. A conversion processing unit 21 that performs one-dimensional Fourier transform in the readout direction and a conversion processing unit 21 that is connected to the subsequent stage of this conversion processing unit 21 and sequentially captures the MR data read out in the readout direction and converts maximum value information and phase of all MR data. A detection unit 22 that obtains correction information, and a waveform memory 23 that stores all MR data for one scan after each information is obtained by the detection unit 22.
and the MR connected to the subsequent stage of the waveform memory 23 and captured.
It has an image reconstruction unit 24 having a sampling capacity of, for example, 16 bits, which reconstructs an MR image based on the data, and a display unit 25 which visually displays the MR image reconstructed by the image reconstruction unit 24. There is.

The image reconstruction unit 24 obtains a normalization rate from the maximum value information of the MR data obtained by the detection unit 22, performs normalization processing on the MR data using this normalization rate, and converts the data into 16-bit data without overthrowing. We are making sure that our sampling ability is fully demonstrated. The image reconstruction unit 24 also performs phase correction on the MR data based on the phase correction information obtained by the detection unit 22, and finally performs 2DFT processing by Fourier transforming the MR data in the phase encoding direction.
It reconstructs the image.

Next, the operation of the present device 1 will be explained with reference to FIG. 2 as well.

First, under the control of the static magnetic field control circuit 15, the static magnetic field coil 7
A uniform static magnetic field is created in the Z direction by passing a current through. The living body is placed at the center of the magnet device 6.

Next, selective excitation is performed on a desired slice plane according to a predetermined pulse sequence, and as shown in FIG. 2, collection of, for example, 256 MR data M (M□ to M n ) is started from this slice plane. The gradient magnetic field control circuit 14 controls the current supplied to the gradient magnetic field coil 8 under the control of the system controller 13 to generate a predetermined gradient magnetic field (X, Y
or Z direction). System controller 13
applies an RF pulse to the living body from the transmitting/receiving coil 9.

A magnetic resonance phenomenon occurs in a living body and an MR multiplied signal is generated.

This MR multiplied signal is detected by the transmitting/receiving coil 9, taken into the phase detection circuit 20 via the preamplifier 19, phase detected, and converted into digital MR data M by the AD converter in this circuit 20. Next, this MR data M
is taken into the conversion processing section 21, subjected to Fourier transform in the readout direction R, and sent to the detection section 22. The detection unit 22 obtains maximum value information and phase correction information of all MR data and sends them to the waveform memory 23.

When all 256 MR data M are stored in the waveform memory 23 in this way, the image reconstruction unit 24 performs normalization processing on the MR data based on the maximum value information of the MR data, and performs Fourier processing in the phase encoding direction E. After performing reconstruction processing through conversion, the display unit 25 displays the MR image that has been subjected to image reconstruction processing.

Although one embodiment has been described above, the present invention is not limited thereto, and various modifications can be made without changing the gist thereof.

[Effects of the Invention] According to the present invention described in detail above, it is possible to provide an MHI device which is free from the risk of overflow and which aims to shorten the imaging time.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a device according to an embodiment of the present invention, and FIG. 2 is a diagram showing the operation of this device. ...MRI device, 13...system controller,
1... Conversion processing unit, 22... Maximum value detection unit, 3...
- Waveform memory, 4... Image reconstruction unit (normalization means). Agent Patent Attorney Nori Ken Yudo Konfuji Takeshi

Claims (1)

[Claims] After digitizing a plurality of MR signals collected using the phase encoding method, an MRI apparatus that performs reconstruction processing to obtain a tomographic image uses a processing circuit. a maximum value detection means for determining a value, and normalizing the plurality of MR data values so that the reconstruction processing can be performed optimally within the sampling capacity of the processing circuit based on the maximum value information obtained by the maximum value detection means. An MRI apparatus characterized by comprising: normalization means for normalizing.