JPH05154133A - Mr image pickup method - Google Patents

Abstract

PURPOSE:To eliminate a useless scan and a useless image by executing a saturation sequence in both ends and an imaging sequence of one side of a desired area in one scan without executing the imaging sequence related to a slice deviated from the desired area in the end part of the desired area. CONSTITUTION:A scan by a sandwich saturation method is executed successively, while shifting a position in the vertical direction extending from the lower part to the upper part. In this case, in the case a slice of the upper side deviates from the upper end of desired area 2 by an (n-2)-th scan, an image on the other end side of the desired area 2 is also obtained simultaneously in the same scan. That is, in an (n-2)-th scan, the saturation sequence of an area 3' (n-2) in the vicinity of the upper end and an image sequence of a slice 5 (n-2) in the desired area 2 are executed, and also, a saturation sequence of an area 3 (n-2) in the vicinity of the lower end and an image sequence of a slice 4 (n-2) in the desired area 2 are executed.

Description

Detailed Description of the Invention

[0001]

This invention relates to nuclear magnetic resonance (NM).
The present invention relates to an MR imaging method for performing imaging using R), and particularly to an MR imaging method suitable for obtaining an image in which a fluid portion such as a blood vessel is emphasized.

[0002]

2. Description of the Related Art Conventionally, MR angiography for obtaining an image in which a portion of a blood vessel is emphasized by utilizing a blood flow in the blood vessel is known. In the case of ordinary two-dimensional MR angiography, since only one slice is imaged in one scan, only an arterial image, a venous image, or an image in which arteries and veins are mixed can be obtained.

On the other hand, in the sandwich saturation method, two slices sandwiching a saturated region can be simultaneously imaged by one scan, and an arterial image and a venous image can be separately obtained at the same time as in ordinary two-dimensional MR angiography. Can be obtained. Therefore, in an attempt to obtain an arterial image and a venous image at different positions in the slice thickness direction in a desired region having a large width in the slice thickness direction, a saturated region and two slices sandwiching the saturated region By repeating each scan by the sandwich saturation method while changing the position in the thickness direction, a normal two-dimensional MR can be obtained.
With the same number of scans as angiography, it is possible to obtain both a large number of arterial images and a large number of vein images in the above area.

That is, as shown in FIG. 4, when obtaining a large number of arterial images and a large number of vein images at each position from the lower end to the upper end of the desired region 2 of the subject 1, the lower end of the desired region 2 is obtained. The scan by the sandwich saturation method is repeated n times while moving the position from the to the upper end. Upper slices 41 and 4 sandwiching the saturated regions 31, 32, 33, ...
If the arterial image can be obtained at 2, 43, ... And the vein image can be obtained at the lower slices 51, 52, 53 ,. By gradually moving the position in the slice thickness direction (body axis direction of the subject 1) of one slice from the bottom to the top, n arterial images and n vein images are obtained, respectively.

[0005]

However, the n arterial images and the n vein images thus obtained have their slice positions vertically different by the width of the saturated region. The vein image obtained by several scans and the arterial image obtained by the last few scans are out of the desired region 2, and these are useless images. In other words,
Of the n scans, the first few scans and the last few scans are performed only for capturing an image in one slice, which is wasteful in terms of time.

In view of the above, the present invention obtains a large number of images in a short time only in the desired region with a lean number of scans when obtaining a large number of images at each position in the desired region by the sandwich saturation method. It is an object of the present invention to provide an MR imaging method improved so as to be capable.

[0007]

In order to achieve the above object, in the MR imaging method according to the present invention, one saturation sequence is set only when both slice positions of the saturation region in the sandwich saturation method are in the desired region. A scan with an imaging sequence in both the slices is performed, and when the slice position on one side deviates from one end of the desired region, one saturation sequence that saturates the region near the one end and the desired region The imaging sequence in one slice of this saturation region located and one saturation sequence that saturates the region near the opposite end of the region and one slice of this saturation region located in the desired region. It is characterized by performing a scan that includes an imaging sequence. By not performing the imaging sequence for the slices that deviate from the desired region at the end of the desired region and performing the saturation sequence at both ends of the desired region and the one-sided imaging sequence within one scan, it is wasteful. It is possible to obtain a large number of images in a desired area in a short time by reducing the number of scans by eliminating unnecessary scans.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. In this embodiment, as shown in FIG. 1, an artery image and a vein image in a desired region 2 of the subject 1 are repeatedly scanned by the sandwich saturation method to obtain a large number at each continuous position.
This sandwich saturation method will be described by taking the first scan as an example. First, as shown in FIG. 2A, the saturation pulse P31 is applied together with the slice selection gradient magnetic field shown in FIG. It is excited to saturate this region 31.

Thereafter, the imaging sequence by the field echo method is repeated twice to collect the data in the two slices 41 and 51 located on both sides of the saturated region 31. That is, the excitation pulse P41 is applied together with the slice selection gradient magnetic field (see B in FIG. 2) to obtain the slice 41.
After selective excitation, a gradient magnetic field for reading and frequency encoding (see C in FIG. 2) and a gradient magnetic field for phase encoding (see D in FIG. 2) are applied to generate an echo signal S41 from the slice 41. Next, an excitation pulse P51 is applied together with a gradient magnetic field for slice selection (see B in FIG. 2) to selectively excite the slice 51, and then a gradient magnetic field for reading and frequency encoding (FIG. 2).
C) and gradient magnetic field for phase encoding (Fig. 2).
Of the echo signal S from the slice 51.
51 is generated. In this way, data collection in the slices 41 and 51 is performed.

At this time, in the desired region 2, the arteries flow from top to bottom, the veins flow from bottom to top, and the arterial flow saturated in the saturation region 31 reaches the slice 51 when excited by the excitation pulse P51. , The venous flow saturated in the saturation region 31 is sliced 41 when excited by the excitation pulse P41.
It has been reached. Then, a large signal does not occur from the already excited saturated blood, and a strong signal can be obtained from the unexcited unsaturated blood, so that the slice 41
In the signal S41 from, the signal from the blood (arterial flow) flowing in from above is large, and the signal from the blood (venous flow) flowing from below is weak, and the image of the artery in slice 41 is can get. Signal S5 from slice 51
In No. 1, the signal from the blood (venous flow) flowing in from the bottom is large, and the signal from the blood (arterial flow) flowing from the top is weak, so that an image of the vein is obtained for the slice 51.

From the first scan by such a sandwich saturation method, in which both of the slices on both sides of the saturation region fall within the desired region 2, the vertical position is gradually shifted from the bottom to the top ( n
-3) Repeat until the first time.

If the vertical positions are shifted at the same intervals,
In the (n−2) th scan, it is assumed that the upper slice deviates from the upper end of the desired region 2. In this way, when one of the slices on both sides of the saturated region deviates from one end of the desired region,
An image on the other end side of the desired area is also obtained at the same time within the same scan. That is, in the (n−2) th scan, the saturation sequence of the region 3 ′ (n−2) near the upper end and the slice 5 (n−2) on one side (lower side) located in the desired region 2 are detected. The imaging sequence is performed, and the saturation sequence of the region 3 (n−2) near the lower end and the imaging sequence of the slice 4 (n−2) on one side (lower side) located in the desired region 2 are performed. To do.

This will be described with reference to FIG.
2) In the second scan, first, the saturation pulse P3 (n-2) is applied together with the gradient magnetic field for slice selection shown in FIG. 8B to selectively excite the region 3 (n-2) to generate the region 3 (n-2). n-2) is saturated and then the excitation pulse P
4 (n-2) together with a gradient magnetic field for slice selection (see B of FIG. 3) to selectively excite slice 4 (n-2), and further a gradient magnetic field for readout and frequency encoding (see C of FIG. 3). ) And a gradient magnetic field for phase encoding (see D in FIG. 3) are applied to slice 4 (n−
The echo signal S4 (n-2) is generated from 2). Next, the saturation pulse P3 ′ (n−2) is applied together with the slice selection gradient magnetic field to apply the saturation pulse P3 ′ (n−2) to the region 3 ′ (n−2).
Are selectively excited to saturate this region 3 ′ (n−2), and then an excitation pulse P5 (n−2) is applied together with a slice selection gradient magnetic field to selectively excite slice 5 (n−2). Further, a gradient magnetic field for reading and frequency encoding and a gradient magnetic field for phase encoding are applied to generate an echo signal S5 (n-2) from the slice 5 (n-2).

Such scanning is repeated while shifting the position until the slice on one side included in the desired area 2 deviates from the area 2. In this scan, images of one side of the slice that enters the desired region 2 are obtained at both the upper end and the lower end of the desired region 2, so imaging of slices outside the desired region 2 is not performed, and the number of scans is reduced. Can be made The time required for each scan is the same as the time required for each scan when both slices are included in the desired region 2. That is, this (n
-2) Saturation pulses must be applied twice in the second and subsequent scans, whereas only one saturation pulse is required in scans when both slices are in the desired region 2. However, in each scan when both slices are in the desired region 2, the saturated region overlaps, so it is necessary to set a certain relaxation time. On the other hand, in the (n-2) th and subsequent scans, it is sufficient to saturate the saturated regions separated from the upper end and the lower end of the desired region 2, so that the two saturation pulses included in one scan may be saturated. There is no need for such relaxation time. Therefore, the time of each scan is the same when both slices are in the desired region 2 and at both ends.

As a result, if the width of the saturated region (width in the vertical direction) is 50 mm and the width of the slices on both sides is 5 mm, the number of scans can be reduced by 10 compared to the conventional method.

[0016]

As described in the above embodiments, according to the MR imaging method of the present invention, when obtaining a large number of images for each position of a desired region by the sandwich saturation method, slice positions outside the desired region are obtained. It is possible to obtain useless images in the above step and to avoid performing unnecessary scans, and it is possible to reduce the number of scans and obtain a large number of images in a desired area in a short time.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an MR imaging method according to an embodiment of the present invention.

FIG. 2 is a time chart showing a pulse sequence when both slices are included in a desired area in the embodiment.

FIG. 3 is a time chart showing a pulse sequence when a slice on one side deviates from a desired region in the embodiment.

FIG. 4 is a schematic diagram for explaining a conventional MR imaging method.

[Explanation of symbols]

 1 Subject 2 Desired Area 31, 32, ... Saturated Area 41, 42, ... Upper Slice 51, 52, ... Lower Slice

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location 9118-2J G01N 24/02 Y

Claims (1)

[Claims] 1. A scan having one saturation sequence and an imaging sequence in the slices on both sides of the saturated region in the sandwich saturation method only when the slice positions on both sides of the saturated region are in the desired region while shifting the positions. Repeatedly, when the slice position on one side deviates from one end of the desired region, one saturation sequence that saturates the region near that one end and imaging on one slice of this saturated region located in the desired region A staggered scan comprising a sequence and one saturation sequence that saturates a region near the opposite end of the region and an imaging sequence on a slice on one side of the saturated region located within the desired region MR characterized by repeating
Imaging method.