JPS6012043A - Nmr imaging method - 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 (a) Field of Industrial Application ' This invention relates to NMR imaging that uses nuclear magnetic resonance to construct images of the inside of a patient's body, and in particular, to two-dimensional imaging using the spin warp method. Concerning improvements in Fourier transform methods.

(b) Prior art □ Various methods have been known in the past, such as the projection restoration method on the NMR image plane, but among these, the two-dimensional Fourier transform method using the spin warp method is It is known to have advantages such as less

However, the conventional two-dimensional Fourier transform method using the spin warp method has the disadvantage of poor patient diagnostic efficiency because image reconstruction calculations cannot be performed until all data has been collected.

(C) Purpose □ An object of the present invention is to provide a two-dimensional Fourier transform method using a spin warp method that enables image reproduction even during data collection and improves diagnostic efficiency.

(d) Configuration According to the present invention, in the spin warp method, the gradient magnetic field strength that determines the amount of phase encoding is gradually increased sequentially from zero, and data is collected for each of them, and data can be obtained up to that point in the middle of data collection. Image reconstruction is performed using the two-dimensional Fourier transform method from the low frequency components of the data.

(E) Example FIG. 1 shows a pulse sequence. As shown in this figure, first, in period TI, GZ is not applied in a gradient magnetic field in the X-axis direction, and then a 90' radio wave pulse is applied. Then, spins within a narrow slice close to the XY plane perpendicular to the Z axis are selectively excited. Next, during period T2, gradient magnetic fields GX, GY, and GZ are applied to three mutually orthogonal planes. The gradient magnetic field -GZ applied during this period is for re-aligning the phases of the spins in the slice that have been disturbed by the gradient magnetic field GZ applied during the period T1. The purpose of the gradient magnetic field -GX is to scatter the phase of the spins along the X direction as a preliminary step to signal reading, which is performed while applying the gradient magnetic field XX in the next period T3. Period T3
In the gradient magnetic field at , GX re-aligns the spin phase,
After a while, a spin echo signal is generated. The spin echo signal is read by being A/D converted at the timing shown in the figure. The Fourier transform of this spin echo signal becomes a one-dimensional projection of the spin density in the X-axis direction within the slice.

The purpose of the gradient magnetic field GY applied during the period T2 is to give a known amount of twist or warp to the spins in the longitudinal axis direction. This operation changes the phase before being projected in the X-axis direction. The above series of operations is repeated N times while changing the magnitude of the gradient magnetic field GY each time to obtain N spin echo signals. According to this invention, the absolute value of the integral value of this phase encoding gradient magnetic field GY is made to increase sequentially from zero as shown in FIG. In this way, as shown in FIG. 3, data of N spin echo signals are obtained one after another, the amount of phase encoding increasing sequentially each time. If the spin density in the X-axis direction obtained by Fourier transformation of these N spin echo signals is re-q-Fourier transformed in the N direction, the spin density distribution in the YM force direction can be obtained, and a two-dimensional distribution image of the spin density in the X-Y plane can be obtained. However, according to the present invention, even before all N pieces of data are collected, the amount of phase encoding increases sequentially as described above, even if only the data up to an arbitrary point in time are collected. By using the low frequency components of the data up to that point, image reproduction is possible, albeit with low resolution.

FIG. 4 shows a block diagram of the circuit configuration, and as shown in this figure, the spin echo signal is first read by the A/D converter 11 at the timing shown in FIG.
is memorized. Then, if a control signal is issued from the image reproduction instruction circuit 13 at any time before all data collection is completed by sequentially increasing the strength of the gradient magnetic field GY that determines the amount of phase encoding, the data will be The data stored in the storage device 12 is read out and subjected to two-dimensional Fourier transformation by the fast Fourier transform processing circuit 14, and the reproduced image is stored in the image storage device 15 and displayed on the display device 16.

(f) Effects According to the present invention, images can be reproduced even during data collection, although the resolution is lower than that of the final image, and a quick diagnosis can be made. Furthermore, since images are obtained midway through the process, it is possible to make a judgment at an early stage if a good image cannot be obtained due to patient movement. Furthermore, accurate images can be obtained from data taken before the patient moves. In this way, images can be obtained even during data collection, improving diagnostic processing efficiency.

[Brief explanation of drawings]

The drawings all represent an embodiment of the present invention, and FIG. 1 is a time chart showing a pulse sequence, FIG. 2 is a time chart of the integral value of the gradient magnetic field GY, FIG. 3 is a data map diagram, and FIG. 4 is a time chart showing the integral value of the gradient magnetic field GY. FIG. 2 is a block diagram showing a circuit. 11...A/D converter 12...Data storage device 1
3... Image reproduction instruction circuit 14... Fast Fourier transform processing circuit 15... Image storage device 16... Display device patent applicant Shimadzu Corporation

Claims (1)

[Claims] (1) Change the intensity of the gradient magnetic field whose intensity changes in the direction perpendicular to the straight line that projects the entire slice, and perform phase encoding of the phase in this direction using the spin warp method. Obtain data on spin echo signals for each strength of the gradient magnetic field, and reproduce the two-dimensional distribution image of the spin density in the slice by performing two-dimensional two-dimensional transformation on this data. Gradually increase the gradient magnetic field strength that determines the amount of encoding from zero and collect data in each step. NMR video image characterized by performing image reproduction by two-dimensional Fourier transform method