JPH0622932A - Magnetic resonance diagnostic device - Google Patents

Abstract

PURPOSE:To obtain a magnetic resonance diagnosing device which can surely extract a blood flow image by measuring the signal intensity supplied from a same tissue part of each slice surface, multiplying the actually measured signal supplied from each slice surface by the inverted ratio of the signal intensity, and reconstituting the signal in multiplied state and generating an image. CONSTITUTION:When the blood flow image of a head part 6 is photographed by using a magnetic resonance diagnostic device, the slice thickness R is divided into slices S1, S2, S3,..., in order to correct the signal intensity variation according to the depth in the slice direction, and the signal value supplied from a prescribed region of each slice image is measured. Then, the function of the signal intensity I(z) for the slice depth Z is obtained. Accordingly, when the collected dats is multiplied by the value C/I(z) which is obtained by multiplying the inverted value of the signal intensity function I(z) by a proportional coefficient C, correction can be carried out so that the signal intensity which varies according to the slice depth is made constant. Accordingly, the signal intensity in the related region I is made nearly constant, and the blood flow signals 3 and 4 can be surely extracted on a photographed image 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance diagnostic apparatus, and more particularly to a technique for correcting a change in signal intensity due to slice depth.

[0002]

2. Description of the Related Art In recent years, a large number of magnetic resonance diagnostic apparatuses have been put to practical use for noninvasively diagnosing internal tissues.
MR angiography for capturing a blood flow image in the body is one of the methods for capturing an in-vivo image using such a magnetic resonance diagnostic apparatus, and the maximum intensity projection method is usually used.

The maximum intensity projection method obtains a three-dimensional original image by a pulse sequence that emphasizes a blood flow signal, projects this in the slice direction to obtain the maximum value on the projection line, and reconstructs this to obtain a blood image. It creates a flow image. The feature of this method is that the blood flow can be visualized if the blood flow signal is a little larger than the signal of the background portion on the projection line.

However, the selective excitation pulse for exciting the region of interest cannot slice the region of interest into a perfect rectangle. That is, as shown in FIG. 7, when the excitation pulse P1 is Fourier transformed, it becomes like a waveform P2,
It is not a perfect square wave. Therefore, the collected signal strength also changes when the depth in the slice direction changes.

This is schematically shown in FIG.
In the figure, the direction S indicates the slice direction and the direction K indicates the signal intensity, and the signal intensity of the region of interest 1 changes according to the depth in the slice direction. Now, for example, when the blood flow signals 3 and 4 are present in the region of interest 1, the blood flow signals are emphasized and thus become larger than other background signals.
As a result, the blood flow signal 3 at the position (mountain portion) where the signal intensity is strong appears on the projected image 2 as it is. However, the blood flow signal 4 at the position (valley portion) where the signal intensity is weak is buried in other background signals and does not appear on the projected image 2.

[0006]

As described above, in the MR angiography using the conventional magnetic resonance diagnostic apparatus, when the blood flow signal exists in the valley portion, the blood flow signal can be visualized. However, there is a drawback that an accurate blood flow image cannot be obtained.

The present invention has been made to solve such conventional problems, and an object of the present invention is to provide a magnetic resonance diagnostic apparatus capable of reliably drawing a blood flow image. .

[0008]

In order to achieve the above object, the present invention provides a magnetic resonance diagnostic apparatus for collecting and imaging magnetic resonance signals from a plurality of slice planes for use in diagnosis. Means for measuring the signal intensity from the same tissue part, means for multiplying the actual measurement signal from each slice plane by the inverse ratio of the measured signal intensity, and the signal multiplied by the inverse ratio of the signal intensity And a means for forming an image.

[0009]

With the above arrangement, a function indicating the relationship between the slice depth and the signal strength can be obtained in advance. Then, the actually measured signal is multiplied by the obtained function by the inverse ratio to correct the signal from the same tissue to be constant at each slice depth. As a result, the emphasized blood flow signal is not buried in the background signal, and the blood flow image can be reliably drawn.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing slice positions when a blood flow image of the head 6 is captured using a magnetic resonance diagnostic apparatus to which the present invention is applied. Then, three-dimensional data of the slice thickness R is collected and the maximum value projection is performed to obtain a blood flow image.

Here, in order to correct the change in signal intensity due to the depth in the slice direction, the slice thickness R is set to the slice S1,
The signal value from a predetermined area of each slice image is measured by dividing into S2, S3, .... That is, as shown in FIG. 2, the signal from the measurement region 5 of each slice image is acquired. At this time, it is necessary to prevent the measurement region 5 from having different tissues in each slice. Normally, in the case of the head, if the brain parenchyma is used as the measurement region 5, the tissue from which signals are acquired can be the same in all slices.

Then, if the acquired signal intensity is plotted with the horizontal axis as the slice depth as shown in FIG. 3, the signal intensity I (z) with respect to the slice depth Z can be obtained as a function. Therefore, if the collected data is multiplied by the numerical value C / I (z) obtained by multiplying the reciprocal of the signal strength function I (z) by the proportional constant C, the signal strength changing depending on the slice depth should be corrected. You can This is shown in a schematic diagram corresponding to FIG. 8 as shown in FIG. 4, and the signal intensity in the region of interest 1 is substantially constant. As a result, the blood flow signals 3 and 4 are reliably drawn on the projected image 2.

As described above, in this embodiment, the signal strength change due to the slice depth is corrected to keep the signal strength constant. Therefore, it becomes possible to reliably draw the blood flow signal in the region of interest.

FIG. 5 is a diagram showing a modification of this embodiment,
In this example, the region for measuring the signal strength is the phantom 8 provided outside the subject 9. Then, the tomographic image becomes as shown in FIG. 6, and the cross section of the phantom 8 is projected as the measurement region 7. Then, the signal intensity from the measurement region 7 is measured with a plurality of slices in the same manner as in the above-mentioned embodiment,
Based on this, the change in signal intensity due to the depth of the slice is corrected. With this, the same effect as that of the above-described embodiment can be obtained. The vertical relaxation time T ₁ and the lateral relaxation time T ₂ of the phantom are preferably the same as those of the tissue.

Further, as another embodiment, as shown in FIG. 7, even if the waveform P2 obtained by Fourier transforming the excitation pulse waveform P1 is used as the function I (z) of the signal intensity, Changes can be corrected.

Although MR angiography has been described in this embodiment, the present invention is not limited to this, and it goes without saying that general three-dimensional data can be corrected.

[0017]

As described above, in the present invention, the change in the signal strength in the slice depth direction is corrected to be constant by multiplying the inverse ratio of the signal strength.
Therefore, when the maximum value projection of the blood flow image is performed, there is an effect that the blood flow image can be reliably drawn without being buried in the background.

[Brief description of drawings]

FIG. 1 is a diagram showing an imaging region of a head according to the present embodiment.

FIG. 2 is a diagram showing a tomographic image at each slice position in a head imaging region.

FIG. 3 is a characteristic diagram showing a relationship between signal strength and slice depth.

FIG. 4 is a schematic diagram showing a blood flow signal intensity and a background signal intensity in the present embodiment, and a state when the maximum value projection thereof is performed.

FIG. 5 is an explanatory diagram showing an example in which a phantom is used for measuring signal strength.

FIG. 6 is a tomographic image showing a measurement region of a phantom.

FIG. 7 is an explanatory diagram showing an excitation pulse waveform and a rectangular wave obtained by Fourier transforming the excitation pulse waveform.

FIG. 8 is a schematic diagram showing a conventional blood flow signal intensity, background signal intensity, and a state when the maximum value is projected.

[Explanation of symbols]

 2 Photographed image 3, 4 Blood flow signal 5 Measurement area 8 Phantom

Claims (2)

[Claims] 1. A magnetic resonance diagnostic apparatus for collecting and imaging magnetic resonance signals from a plurality of slice planes for diagnosis, and means for measuring in advance the signal intensity from the same tissue portion of each slice plane, Means for multiplying the inverse ratio of the measured signal strength by the actual measurement signal from each slice plane, and means for reconstructing and imaging the signal multiplied by the inverse ratio of the signal strength,
A magnetic resonance diagnostic apparatus comprising: 2. The magnetic resonance diagnostic apparatus according to claim 1, wherein the same tissue part is a phantom placed near an imaging part.