Magnetic resonance imaging device

Abstract

An MRI apparatus having an ability of displaying images of flow in different directions in distinguishable manner. When this MRI apparatus performs multi-slice acquisition with a predetermined repetition time TR by selecting a plurality of slices approximately perpendicular to the flow direction of an object to be examined, it performs a first measurement of exciting the plurality of slices in a first order and a second measurement of exciting the same slices in the opposite order to obtain two kinds of data whose signal intensity differs depending on the flow direction. The two kinds of data obtained by two measurements are subjected to subtraction operation to obtain data with different signs depending on the flow direction. These signs combined with the signal intensity are made into images where flow in opposite directions are distinctively depicted. In the multi-slice acquisition, slices are selected so that adjacent slices partially overlap in the direction of the thickness of the slice. Thereby signals of a static part can be suppressed and contrast of flow images after substraction can be enhanced. EPI method of very short imaging time can be employed for the imaging sequence of MRA according to the present invention.

Description

technical field [0001] The present invention relates to a magnetic resonance imaging (hereinafter referred to as "MRI") device for obtaining a tomographic image of a desired part of a subject by using the phenomenon of nuclear magnetic resonance (hereinafter referred to as "NMR"), and particularly relates to a method for depicting the direction of the vascular system. , the MRI device whose directionality can be identified. Background technique [0002] The imaging function of the MRI apparatus includes MR angiography (hereinafter abbreviated as "MRA") that draws a blood flow map without using a contrast agent. Typical methods for drawing a blood flow map in an MRI apparatus include the time-of-flight method using the inflow effect of the tomographic plane, and the phase method using the principle that the spin of the blood flow is exerted in the direction of its movement. Under the action of the gradient magnetic field, it is subjected to phase diffusion. As the main meth...

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Problems solved by technology

For example, when using the 2D-TOF method in which RF irradiation (presaturration) is performed on a certain area with a short repetition time TR, and the blood flow signal flowing into the area is a strong signal, it is necessary to use a gradient Shorter TR procedures such as the echo method cannot use high-speed procedures such as EPI

In addition, since the spin of the blood flowing in from any direction also forms a strong signal in the area where pre-saturation treatment is performed, arteriovenous separation cannot be performed.

There is also a method of performing pre-saturation processing on an area adjacent to the imaging area, but in this case, blood flow in only one direction of the arteriovenous can be observed

[0004] Although the PC method also adopts the method of separating the arteries and veins by obtaining the phase difference of the flow encoding phase images with different polarities, it not only has the bending artifact in the high-speed flow where the phase shift of the blood flow spin exceeds π , but also has the following problem, that is, since the program is not of the Florey phase type, the turbulence or the change of the flow velocity is small, and it is easy to produce vascular defects or artifacts

In addition, the two-dimensional PC method for the quantitative measurement of blood flow velocity has the disadvantage that it cannot increase the thickness of a slice including blood vessels, and is not suitable for simultaneously observing the direction of the entire vascular system.

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