JPH038214B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to nuclear magnetic resonance (nuclear magnetic resonance).
Resonance (hereinafter abbreviated as NMR) phenomenon is used to obtain information about the distribution of specific nuclear nuclei within a subject from outside the subject, and in particular display data for displaying NMR images. This improves the format.

(Prior Art) In conventional NMR imaging devices, the obtained tomographic image of a subject is usually displayed on a linear scale and in gray scale.

However, the spin-lattice relaxation time (longitudinal relaxation time) T ₁ and the spin-spin relaxation time (transverse relaxation time) T ₂ change exponentially,
Therefore, the effects of T ₁ and T ₂ relaxation change exponentially on the image, which is an important parameter in NMR.
There was a problem that the effects of T ₁ and T ₂ could not be estimated intuitively on the image.

In view of these points, the purpose of the present invention is to provide an NMR imaging device in which the final image is displayed logarithmically and the influence of T ₁ and T ₂ , which are important parameters of NMR, can be intuitively estimated on the image. It is about providing.

(Means for solving the problem) In order to achieve such an object, the present invention provides an NMR mechanism that applies a magnetic field and an RF pulse to excite a measuring object to generate an echo signal, and an NMR mechanism that generates an echo signal by applying a magnetic field and an RF pulse. In an NMR imaging apparatus that includes means for processing signals to obtain an image related to the measurement object, and a display mechanism for displaying this image, the means for obtaining the image displays each image reconstructed using the echo signal. The NMR mechanism has a function of logarithmically converting each pixel, and the NMR mechanism is configured to scan to obtain multiple images with different relaxation states using a pulse casing that detects multiple different relaxation states in the process of a relaxation phenomenon. The display mechanism is characterized in that it has a function of simultaneously displaying a plurality of images having different relaxation states or rewriting and displaying them at high speed.

Further, in the present invention, the NMR mechanism is configured to be able to scan using the multi-echo method, and the means for obtaining images calculates a T ₂ relaxation time map from the difference of the same region in a plurality of images showing T ₂ relaxation using the multi-echo method. function, or the NMR mechanism is the spin echo method (SE method)
The means for obtaining images has the function of calculating a _T2 relaxation time map from multiple images taken at different TEs (echo times) using this SE method, or the NMR mechanism is configured to be able to scan using the anti-recovery method. (IR method), and the means to obtain images differs in TI (latency from inversion pulse) using this IR method.
The _NMR mechanism is configured to be able to scan using the saturation recovery method (SR method), and the means for obtaining images is the TR ( It has a function to calculate a _T1 relaxation time map from multiple images taken at different repetition times (repetition time), and a display mechanism has a function to simultaneously display multiple images obtained with the above configuration or rewrite and display them at high speed. It is characterized by having

(Example) The present invention will be explained in detail below using the drawings. FIG. 1 is a diagram showing the configuration of essential parts of an embodiment of an NMR imaging device according to the present invention. In the figure, 10 is an NMR mechanism that generates nuclear magnetic resonance by the spin warp method that applies a magnetic field to the subject, 11 is an RF phase detector that detects the phase of the NMR signal obtained from the NMR mechanism, and 12 is an RF phase detector. An AD converter samples the output at a predetermined timing and converts it into a digital signal, and 13 is a raw data memory. A processing device 14 reconstructs a tomographic image of the subject based on the data from the raw data memory, and performs logarithmic operations and other operations on each pixel data of the reconstructed original image. 15 is a buffer memory, 16 is an image memory for storing one frame of image data obtained by the arithmetic unit 14, and 17 is a display device for displaying the image in the image memory. 18 is a controller, so that each part operates properly.
NMR mechanism drive and AD conversion timing control,
It takes in data, controls the arithmetic unit, controls writing or reading from memory, controls the display device, etc.

In such a configuration, the NMR mechanism 10 is operated to obtain an NMR signal for each view by, for example, the spin echo method (SE method). In the spin echo method, as shown in Fig. 2, a 90° pulse (RF pulse) is applied while a Z gradient magnetic field Gz ^- is applied to excite one side of the subject (turning the magnetization M by 90°). Next, the Z gradient magnetic field Gz ⁺ and the Y gradient magnetic field Gy (C in Figure 2)
is applied, and then the application of Gz and Gy is stopped, and the X gradient magnetic field Gx (FIG. 2B) is applied. When time τ has elapsed after the application of the 90° pulse, a 180° pulse is applied to rotate the relaxing spins by 180°. When this 180° pulse is applied (including a short time before and after), the application of Gx is stopped, and after that, Gx is applied again. Although the spin is still in the process of relaxation, the spin echo signal reaches its maximum τ time after the 180° pulse, and
The NMR signal obtained in this way (called an echo signal in this case) is then attenuated as shown in E of the figure.
The data is guided to the AD converter 12 through the A/D converter 12, where it is converted into digital data and then stored in the data memory 13.

Once the echo signals over all views are obtained by the same time sequence, the processing unit 14
Then, image reconstruction processing is performed using the image data to obtain one reconstructed image. The image data obtained in this way is temporarily stored in the buffer memory 15.

The arithmetic unit 14 logarithmically transforms the image data for each pixel as illustrated in FIG. 3, and the logarithmically transformed image data is stored in the image memory 16 and displayed on the display device 17 as appropriate. . More specifically, as shown in Figure 3,
The relative value of brightness (CT value) in the original image immediately after reconstruction (a so-called linear scale image expressed by an intensity that linearly corresponds to the intensity of the echo signal) is
The image portion represented by 100, 10, and 1 becomes an image converted into CT values of 40, 20, and 0 by performing logarithmic processing.

Now, in the sequence shown in FIG. 2, the intensity of the echo signal when the echo time TE (2τ time) is changed is as shown in FIG. 4A. That is, mutually different relaxation times T ₂ (5 msec,
10 msec, 20 msec) The signal intensity of each tissue a, b, c exhibits an exponential change (proton density is constant) with respect to the echo time.

When this is logarithmically transformed, the signal strength (expressed as a relative value) has a linear relationship with the echo time, as shown in FIG.

As is clear from Fig. 4, as the echo time changes (increases), the difference in the intensity of the echo signals from tissues a, b, and c increases, and the signal intensity of the tissue with a long _T2 relaxation time increases. emphasized. Therefore,
_T2 weighted images can be obtained by varying the echo time.

When multiple images are obtained at equal time intervals using the multi-echo method, displaying the first echo image I ₁ , the second echo image I ₂ , the third echo image I ₃ , etc. sequentially will reduce the brightness. The gray scale shown in stages (in this case the gray scale is also logarithmized) changes by a certain number of steps. for example,
If the gray scale changes by 2 steps between I ₁ and I ₂ , it will also change by 2 steps between I ₂ and I ₃ . FIG. 5 is a diagram showing an example of a display in such a case, and is an example in which phantoms (test samples) having three different T ₂ are imaged by the multi-echo method and displayed logarithmically. FIG. 6 is a graph showing the respective signal strengths. The upper left of Figure 5 is the echo time
Three _T2 images (#1, #2,
#3), when this echo time TE increases by 10 msec, the three images are sequentially upper right (I ₂ image),
Displayed in the lower left (I ₃ image) and lower right (I ₄ image).

This further simplifies image quantification.

In particular, T ₁ and T ₂ , which are important elements of NMR, are determined by spin echo method or inversion recovery method (IR method: IR is
It can be calculated by inter-image calculation of multiple images taken using Inversion Recovery (abbreviation for Inversion Recovery), and is usually approximated to an exponential function using the method of least squares, but if each pixel is expressed logarithmically, the 7th Just calculate the difference between T ₁ and T ₂ as shown in the calculation flow in the figure.
map can be visualized.

Note that the display of a plurality of images representing temporal changes in the relaxation phenomenon is not limited to simultaneous display, and may be rewritten and displayed at high speed. In addition, multiple images include multiple images captured using the multi-echo method, multiple images captured using the IR method at different TIs (latency from inversion pulse: see pulse sequence in Figure 8), and saturation recovery (SR) images. TR (repetition time:
It may be any one of a plurality of images captured by changing the pulse sequence (see pulse sequence in FIG. 9).

Further, the present invention is not limited to the above-mentioned embodiments; for example, it is also possible to handle data as logarithms at the raw data stage. in this case,
The main advantage is that multiplication in the reconstruction stage using fast Fourier transform can be done by addition. In addition, this method has the advantage of increasing the dynamic range even with the same number of bits.

(Effects of the Invention) As explained above, according to the present invention, the influence of T ₁ or T ₂ relaxation, which decays exponentially with time, is reflected on the image on a linear scale, so that the relaxation time of the region of interest is is easy to understand intuitively. It also has the advantage of easily increasing image contrast through T ₁ emphasis and T ₂ emphasis.

In addition, it is easy to quantify the relaxation time, and calculation time is short when calculating T ₁ and T ₂ by inter-image calculation.
This also has the advantage that simple interpolation can be applied.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of main parts showing an embodiment of the NMR imaging device according to the present invention, FIG. 2 is a diagram showing a pulse sequence, and FIG. 3 is an explanatory diagram for explaining the logarithmic transformation of an image. Fig. 4 is an explanatory diagram showing the relationship between echo time and signal intensity, Fig. 5 is an illustration showing the image display mode, Fig. 6 is an explanatory diagram showing the signal intensity corresponding to Fig. 5, and Fig. 7 is an explanatory diagram showing the relationship between echo time and signal intensity. 8 is a diagram showing the calculation flow of mapping, FIG. 8 is a diagram showing the pulse sequence of the IR method, and FIG. 9 is a diagram showing the pulse sequence of the SR method. 10...NMR mechanism, 11...RF phase detector, 1
2...AD converter, 13...raw data memory, 14...
Arithmetic device, 15... buffer memory, 16... image memory, 17... display device, 18... controller.

Claims (1)

[Claims] 1. NMR in which an echo signal is generated by applying a magnetic field and an RF pulse to excite the object to be measured.
In the NMR imaging apparatus, the NMR imaging apparatus includes a mechanism, a means for processing the echo signal to obtain an image related to the measurement object, and a display mechanism for displaying the image, wherein the means for obtaining the image reproduces the image using the echo signal. The NMR mechanism has a function of logarithmically exchanging the composed images for each pixel, and the NMR mechanism performs a scan to obtain multiple images with different relaxation states by a pulse sequence that detects multiple different relaxation states in the process of a relaxation phenomenon. What is claimed is: 1. An NMR imaging device configured to be able to perform the following: wherein the display mechanism has a function of simultaneously displaying a plurality of images having different relaxation states or rewriting and displaying them at high speed. 2. In the apparatus according to claim 1, the NMR mechanism detects a plurality of different relaxation states in the process of a relaxation phenomenon by a multi-echo method, and scans to obtain a plurality of images of different relaxation states. It is characterized by being configured so that it can
NMR imaging device. 3. In the apparatus according to claim 1, the NMR mechanism uses a spin echo method to change an echo time TE that determines which relaxation state to detect in the process of a relaxation phenomenon, and detects a plurality of different relaxation states. An NMR imaging device characterized in that it is configured to perform a scan to obtain an image of. 4. In the apparatus according to claim 1, the NMR mechanism uses an inversion recovery method to change the waiting time SI from the inversion pulse that determines which relaxation state to detect in the process of the relaxation phenomenon, and NMR characterized in that it is configured to enable scanning to obtain multiple images in different states.
Imaging device. 5. In the apparatus according to claim 1, the NMR mechanism changes a repetition time SR that determines which relaxation state to detect in the process of a relaxation phenomenon by a saturation recovery method, and detects a plurality of different relaxation states. An NMR imaging device characterized in that it is configured to perform a scan to obtain an image of.